INDICATORS OF CONDITION

AND TREND ON fflGH

RANGE-WATERSHEDS

of the

INTERMOUNTAm REGION

Agriculture Handbook No. 19

UNITED STATES DEPARTMENT OF AGRICULTURE

Forest Service
INDICATORS OF CONDITION AND TREND

ON HIGH RANGE-WATERSHEDS

OF THE

INTERMOUNTAIN REGION

By

LINCOLN ELLISON, Forest Ecologist, A. R. CROFT, Forester

and REED W. BAILEY, Director, Intermountain Forest

and Range Experiment Station, Forest Service

Agriculture Handbook No. 19

U. S. Department of Agriculture August 1951

For sale by the Superintendent of Documents, U. S. Government Printing Office

Washington 25, D. C.-Price 30 cents
CONTENTS

Paée

The problem of judging condition and trend 1

The range-watershed complex ', 2

Components of the range-watershed complex 3

Animals 3

Vegetation 4

Soil 6

Climate 10

Topography 12

Interrelations between components of the range-watershed complex 13

How the range-watershed complex changes 14

Primary succession 14

Balance in the complex 16

Secondary succession 18

Destructive change 20

Change and management 21

Fundamentals for judging condition and trend 22

Condition 22

The normal a basis for judgment of range condition 24

Trend 25

Trend when soil is stable 25

Trend when soil is eroding 26

Relation between condition, trend, and utilization 25

Objectives 27

The primary objective 27

Secondary objectives 28

Indicators 28

Cover 29

Bare soil surface 31

Observed movement of soil 34

Trampling displacement 35

Soil remnants 36

Erosion pavement 39

Lichen lines 41

Active gullies 42

Wind-scoured depressions 44

Aeolian deposits 45

Alluvial deposits 47

Vegetal composition 48

Age classes 50

Annual weeds 51

Invasion of bared surfaces 53

Vegetation in gullies 55

Rill-channel ridges 56

Accessibility of palatable species 59

Relics 60

Hedged shrubs 62

Current utilization 63
811391

;^.> M\

THE PROBLEM OF JUDGING CONDITION AND

TREND

High mountain lands o£ the Intermountain West have great significance and importance to its people, even though they make up

only a small fraction of its total area. From these highlands the accumulation of winter snow yields yearlong stream flow, the lifeblood

of the Intermountain country. They provide summer grazing for

domestic herds and for wild game. They furnish timber for local sawmills. And finally, their forests, streams, and rugged landscape provide

an opportunity for enjoyment and inspiration to all.

The vegetation of these high mountain lands plays a particularly

important role in regulating stream flow. Grasslands, brush fields, and

forests hold the soil in place and keep it open and porous, so that even

the most violent summer rains are safely absorbed. When the vegetal

cover is intact, overland flow is virtually unknown. On the other hand,

if the vegetal cover is greatly reduced, dashing rains wear away the

soil, etching rills and gullies into the watershed slopes. In many years

this deterioration of the upper slopes is reflected only in the sediment

that collects in canals and reservoirs. But in those years when the most

intense storms occur, the eroded slopes discharge the flood waters almost

as fast as they fall. These pour down the gullies, uniting to gut the

larger channels and finally, spewing mud and boulders out of the

canyon mouth, wreak havoc on whatever—farm, dwelling, or townmay lie in their way.

Thus the condition of the plant cover on these range-watershed

lands, through its influence on soils and stream flow, is vital to the

welfare of people of the Intermountain region (fig. 1). This "condition" is the character of the vegetal cover and the soil, under man's

use, in relation to what it ought to be. Change in condition is referred

to as "trend."

Condition and trend are recognizable by certain signs, or "indicators," that can be seen in the soil and vegetation. These indicators tell

much about changes that have taken place in the past or that are taking

place at present. Often they suggest what may be expected in the way of

trend and condition in the future.

Judgment of condition and trend depends upon ability to recognize

indicators and understand their significance. By proper interpretation

of indicators constructive changes in management may be planned, and

on the same basis the effectiveness of management may be evaluated

later. On the other hand, unless indicators of downward trend are

recognized accurately and unless management is geared to correct the

causes of downward trend, costly and even irreparable damage may be

done to the range-watershed resource.

This publication is intended to help the range manager judge

condition and trend accurately in the course of range inspection. In

order to make best use of the evidence on the ground, he has three

major needs: First, a technical foundation of ecological principles
HANDBOOK 19^ U. S. DEPARTMENT OF AGRICULTURE

m

F-323029

FIGURE 1.—The welfare o£ all people dwelling in the Intermountain valleys is ultimately dependent on the condition of their mountain watersheds.

underlying the concepts of condition and trend; second, an understanding of condition and trend as they relate to the normal and to objectives

in management; and third, a knowledge of indicators of condition and

trend, their meanings and their limitations. The three major divisions

of this publication are intended to serve these needs, in the order given.

In preparing this publication many well-known ecological facts

and principles have been drawn upon, but no attempt is made to cite

the many references that would be necessary to review the ecological

literature. These facts and principles are presented in the light of the

authors' own experience with indicators on range-watersheds of the

Intermountain region.

THE RANGE-WATERSHED COMPLEX

A complex, by definition, is "a whole made up of interrelated parts."

The range ^ is such a complex, or whole, or system. It is made up of

1 The term "range-watershed" is frequently shortened to "range" in this publication. It will be understood when "range" is used alone that watershed as well as

forage aspects of the land are implied.
INDICATORS ON HIGH RANGE-WATERSHEDS 3

parts so closely interrelated, and normally so well integrated or adjusted to one another, that what affects one affects all. This principle

is of basic importance to judgment of range condition and trend, and

indeed to all range management.

The range-watershed complex is not necessarily considered as a

large area or even a single watershed. For purposes of judging condition and trend, the term will refer to a smaller area of essentially

homogeneous character—a flat, a single hillside within narrow elevational limits, or that part of a hillside upon which slope steepness and

exposure are essentially uniform.

COMPONENTS OF THE RANGE-WATERSHED COMPLEX

The ultimate parts of the range-watershed complex are numberless.

For convenience they are grouped into five classes—animals, vegetation,

soil, climate, and topography—and these classes are spoken of as ''components*' of the complex.

Animals

Animals as components of the range-watershed complex include not

only domestic livestock and game, but the entire fauna above and below

ground, varying from large animals down to forms of microscopic size.

Doubtless the greatest single influence on western range lands in

historic times has been the introduction of large numbers of domestic

animals. These have utilized vegetation more closely and consistently

than the original native animals, and in many places have so reduced

the cover as to cause rapid soil erosion. Moreover, the presence of

domestic animals and occupancy by man has often forced native wild

animals to change their habits. It is reasonably certain, for example,

that deer and elk have been forced to graze some ranges much more

heavily than they did naturally, especially in winter and spring.

Grazing animals exert three important influences on the range that

are relevant here. These influences are removal of herbage, trampling

of soil, and dissemination of seed.

Although any grazing is sometimes thought of as being injurious,

it is not necessarily so. Under certain conditions grazing has a stimulating effect on growth, and as a general rule, if the grazed plants are given

sufficient opportunity to make substantial r^growth, foliage removal

is not injurious. Injury done the individual plant by close or repeated

cropping is mainly in reducing its photosynthetic area and draining its

food reserves. Heavy grazing affects the vegetation as a whole by

handicapping preferred species, thus favoring less palatable species,

and by reducing the amount of foliage cover and litter, thus creating

a drier microclimate at the ground surface and inducing soil erosion.

Certain palatable species are better adapted than others, by growth

form, rapidity of development, or otherwise, to grazing. Other species

escape grazing at a time unfavorable to them because they are palatable

only late in the season after their growth cycle is complete. Species

so adapted tend to increase in the plant cover as the more palatable

plants decrease.
4 HANDBOOK 19^ U. S. DEPARTMENT OF AGRICULTURE

Heavy trampling not only damages plants but it may damage the

soil as well. Its effects are especially marked in the compaction o£ finetextured soils when wet. Rain water is then likely to flow off the surface, carrying topsoil with it, instead of soaking into the ground and

replenishing the soil moisture supply. Soil displacement by heavy

trampling, too, may be an important iorm of accelerated erosion, particularly on steep slopes when the soil is very dry or very wet.

The influence of animals in disseminating seed, while probably

universal, is most evident where the range has been heavily grazed

and trampled. Common dandelion and annuals like tarweed, lambsquarters, and knotweed are plants that have followed the white man's

flocks and herds, first becoming established along trails and on bedgrounds where the native cover had been most reduced. On the other

hand, through their dissemination and perhaps burial of seed, grazing

animals have been a constructive factor in the invasion and spread

of perennial herbs and grasses which have helped check erosion on

lands denuded by earlier overgrazing.

The relations of other components of the range-watershed complex

to animals are so well known that they need only be suggested here.

Vegetation, either as forage or cover, is often the reason for the presence

of animals on a particular part of a range. Slope and exposure determine distribution of animal life markedly, so that various intensities

of grazing and trampling—and ultimately of range condition—are

directly related to topography. Climate and soil, through their effects

on vegetation and topography, influence all animal life.

The relation of one kind of animal to another deserves special

mention. On many ranges there is question of competition between

livestock and game. Animals other than domestic livestock may be

responsible for unsatisfactory condition, or, on the other hand, they

may be blamed for a condition for which they are not responsible. The

better one understands interrelations among animals, therefore, and

the interrelations of animals and the rest of the range-watershed complex, the sounder his judgment of range condition or trend is likely to

be.

Vegetation

Vegetation is the total aggregate of plants. The term properly includes all kinds of plants: Minute bacteria, lowly molds and fungi,

lichens, algae, mosses, herbs, grasses, shrubs, and forest trees. The

smaller forms are known to be of great importance to the larger and

more familiar ones, chiefly through their action on soil or as parasites.

The range manager's most direct concern, of course, is with herbaceous

and woody plants which, as they grow together, form the basic units of

vegetation, commonly called '^stands," "communities," or "associations."

Three characteristics of high-mountain vegetation are particularly

noteworthy from the standpoint of judging range condition and trend.

First, on range in good condition, is the tendency of vegetation, with

the litter it produces, to form an effective protecting cover against soil

erosion. Partly this effectiveness results from an amount of cover that

tends to be greater on high-mountain range than on lowland range,

and partly it results from a high degree of vegetal dispersion Even on

dry uplands where crownspread cover and herbaceous litter are less

than—for example—on wet meadows, bare spaces are neither large nor
INDICATORS ON HIGH RANGE-WATERSHEDS 5

permanent if the range is in good condition. Whatever bare ground

may be present is dispersed irregularly in small spots throughout the

stand; likewise vegetation and litter are thoroughly dispersed, with the

result that their influence usually extends over the bare spots, shading

them part of the day and tending to shelter them from direct impact

of wind and rain. Although a well-dispersed cover may not be complete,

it can be completely effective. Even where bare spaces are not entirely

sheltered and tend to give rise to runoff and erosion on a small scale,

they are isolated from one another, held apart in a mesh of vegetation

that prevents the runoff from combining and increasing to cause erosion

of seriously destructive proportions.

A second characteristic of vegetation on high-mountain range in

good condition is that it usually consists of many kinds of plants. Even

so small an area as a square rod may contain 20 or 30 different forage

species (fig. 2). This diversity in kinds of forage plants is of special

significance in management. It means that many different degrees of

palatability are represented in the stand, many different patterns of

seasonal development, many variations in growth form. Hence, the

better the plants are known—not only their naiiies but their habits

of growth, flowering, and reproduction, their palatabilities, and the

time and intensity of their utilization—the better for management.

While a large number of species may seem to make judgment of trend

FIGURE 2.—A dense cover of vegetation, consisting nt a mixture of perennial species,

characterizes herbaceous mountain range in reasonably good condition. Such

vegetation provides effective protection to the soil as well as palatable forage.
6 HANDBOOK 19^ U. S. DEPARTMENT OF AGRICULTURE

difficult, this very complexity of vegetation suggests that a rather high

degree of precision in judgment of trend may be expected as the ecology

of mountain plant communities becomes better understood.

A third characteristic of high-mountain vegetation in good condition

is dominance by plant species of perennial life form. Annuals, if present

at all, make up only a small part of the stand. Where annuals are conspicuous in high-mountain vegetation, the range is not in good condition.

Vegetation is influenced by other elements of the range-watershed

complex than grazing animals. These influences may affect vegetal

composition, or changes in composition, in such a way as to be confused with the influence of grazing. A slight difference in exposure,

elevation, or degree of slope, may make a material difference. Some

species may be abundant or scarce, or may be reproducing aggressively

or hardly reproducing at all, because of weather. Certain species are

naturally restricted to certain types of soil; the character of soil surface,

as a result of past erosion, may prevent invasion of desirable species;

or the soil may be so thin that only certain species can survive in it.

And finally, different species of plants interact upon one another in

marked degree, partly in competitive, partly in commensal relations,

to produce trends. These facts emphasize the necessity to consider the

range-watershed complex as a whole rather than as vegetation alone.

Soil

Soil has been defined as a natural body on the surface of the earth

in which plants grow, composed of organic and mineral materials. The

phrase a natural body should be taken to mean that soil is something

with a definite form that is the result of a process of development, not

just an amorphous mass of dirt. The distinction is important to an

understanding of the range-watershed complex and to interpretation

of condition and trend.

Soil has two features of particular significance in range-watershed

management. One is that the soil itself, and the substratum upon w^hich

it rests, constitute a reservoir for water storage. This reservoir makes

possible development of all higher vegetation, including forest trees

and range forage plants, and prolongs discharge of water into streams.

The second feature of particular significance is that the normal soil

surface is highly permeable to water. Because of this fact large volumes

of snow melt and sudden dashing rains are readily absorbed by

mountain soils with normal protective cover. Where protective cover

has been reduced, as it has in most of the Intermountain region, the

urgent task of management is to restore it. Rehabilitation has the

multiple objective of stopping accelerated soil erosion and of increasing

the impaired soil's permeability to water, thereby augmenting water

storage (which in turn permits growth of more luxuriant vegetation)

and improving the character of stream flow.

The typical soil profile of well-drained high-mountain grassland,

as revealed in a trench or fresh road cut, is rather simple (fig. 3). At

the surface is a layer of litter made up of recognizable stems and leaves.

Beneath the surficial layer, processes of decay are active, and plant parts
INDICATORS ON HIGH RANGE-WATERSHEDS

.'•::: 'mLjjf.x^.

FIGURE 3.—Profile of a deep, mountain grassland soil that has developed on gently

sloping terrain. Dark soil with high organic content and crumh structure near

surface changes gradually downward, becoming lighter in color and more blocky.

The most marked profile change is between soil mantle and parent material about

halfway between surface and pick. Pick handle is 15 inches long.

936025»-51-2
8 HANDBOOK 19^ U. S. DEPARTMENT OF AGRICULTURE

are less recognizable in a brief transition to mixed organic and mineral

matter. In the profile below the litter layer, for a depth of perhaps

6 to 12 inches, are concentrated innumerable roots and rootlets. Here

the soil is darker and of better tilth than that into which it grades

beneath. Lower down, roots are fewer, the proportion of organic matter

is less, soil is lighter in color and more compact, and rocks are larger

and more numerous. The lowest part of the profile is, as a rule, essentially all rock or rock fragments. This is the ''parent material,*' socalled because the soil above it—the "soil mantle"—has been developed

from material of this sort. Although clear-cut horizons are seldom

distinguishable within the soil mantle, the contrast between mantle and

parent material is commonly fairly sharp (fig. 4).

The character of a mountain soil profile is often greatly modified

by normal soil movement, and compared with some lowland soils,

mountain soils are "young." In terms of human life, however, even a

soil as shallow as the one shown in figure 4, is really very old, probably

representing development over many centuries. Normal soil movement is accomplished mainly by two very slow, persistent processescreep, in which the whole soil mass moves downward, and surficial

erosion. Normally, on sites where a soil mantle has been developed,

these processes are much too slow to be extensively perceptible. This

last fact is basic to judgment of condition and trend whenever the

question arises of differentiating normal from accelerated erosion.

Soil is not something that has always existed as we now see it: it

is the result of an age-long development that might almost be called

a process of growth. Beginning with a parent material of mineral

matter, the combined action of all environmental factors produces the

soil mantle.

Climate is responsible for the earliest disintegration of rock, for

the physical weathering that results from freezing and thawing. The

action of climate is responsible for chemical changes also, dissolution

of certain minerals, their transportation through the soil in solution,

and their deposition at new levels in new combinations. These influences, both physical and chemical, are greatly modified by topographic situation and by the reactions of plants and animals.

Vegetation has an exceedingly important influence on soil, from

assisting disintegration of the original rock by means of the expansion

of roots to supplying organic reagents that take part in chemical

changes. Furthermore, a stand of vegetation, by furnishing dead parts

of plants as food materials and by modifying climate near the soil

surface, encourages a rich flora of microscopic plants-algae, fungi, and

bacteria. These are minute individually, but they teem in millions to

the cubic inch in a fertile topsoil, and are among the most potent

agents of the biotic community in developing soil and in maintaining

its fertility and tilth.

Organisms other than plants should be mentioned as mfluencing

soil formation. Burrowing mammals like pocket gophers play an

obvious role in mixing and aerating the soil, bringing subsoil to the

surface and carrying topsoil and organic matter below. Less conspicuous, but possibly even more important in transforming organic matter,

turning over the soil, and riddling it with tunnels that permit aeration

and promote percolation of water, are the myriads of smaller formsinsects, mites, mollusks, millipedes, worms, etc.-that are constantly at
INDICATORS ON HIGH RANGE-WATERSHEDS

P-319188

FIGURE 4.—Profile of shallow soil underlain by rock parent material on a steep

mountain slope. Gravel on surface has recently been washed down from an area of

accelerated erosion above, as indicated by partly buried vegetation. Pick handle

is 15 inches long.

work. Some evaluation of these organisms has been made in agricultural and forest soils, and though little is yet known about them on

high mountain range land, their importance there is probably also

very great.

Besides the part it plays in formation of soil, vegetation augments

the efficiency of soil and its rocky substratum as a reservoir for water.

While plants themselves use up a portion of the soil moisture, they make

soil receptive to infiltration of water so that, as compared with bare

ground, relatively little water is lost as overland flow. Effective precipi-
10 HANDBOOK 19^ U. S. DEPARTMENT OF AGRICULTURE

tation is thereby increased. The accumulation of organic matter from

dead plant parts in the soil, furthermore, increases the soil's capacity to

retain water and to support vegetation.

Vegetation has a protective function that is especially important

to mountain soils because of the continual tendency for soil displacement on sloping ground. Climatic forces may be considered destructive

to soil as well as constructive: frost loosens, rain washes, and wind blows

the soil. Vegetation tends to modify climatic influences and prevent

loss. The litter of dead plant parts on the soil surface and the cover

provided by branches and foliage hinder freezing and check blowing

and washing. At the same time, a fibrous interlocking system of roots

and other underground parts binds the soil firmly so that displacement

is held to a minimum. All these influences of vegetation constitute

what is referred to in this publication as "vegetal control" over soil

surface and microclimate.

The influence of topography upon soil formation is readily perceived in difl;erences in depth of soil mantle on slopes of varying steepness. Mountain topography induces wide variation in rate of both

normal and accelerated erosion. Part of this influence is exerted through

the influence of topography upon local climate and vegetation.

A characteristic of high-mountain lands having topography gentle

enough to be accessible to domestic livestock is, normally, the almost

universal presence of a soil mantle. On the other hand, most terrain

that is so rough and rocky as to be nongrazable—e.g., steep rock slopes

or talus—does not possess a true soil mantle. The loose rocks and rock

waste present on such sites form a mineral mantle, whether its components be coarse or fine—rock, sand or clay—that has not been stabilized

sufficiently long to be modified into soil under the influence of climate

and organisms. When the term **soil" is used in this publication, it

applies only to the former kind of substratum, where the mineral

mantle has been modified, by the combined action of climate and

organisms, into a well-defined body markedly different in character

from purely mineral materials.

The normal existence of a soil mantle on practically all grazable

terrain is the basis for all indicators of range condition and trend that

relate to soil. The soil mantle itself is an indicator of a long period

of essential stability. In view of this stability, signs of recent disturbance

such as active gullies, wind-scoured depressions, and topsoil remnants

indicate that the slow, constructive process of soil development has

been superseded by rapid, destructive processes of accelerated erosion.

Conversely, healing of erosion scars indicates that the erosive process

is being halted and soil development may again take place.

Climate

Under "climate" are included all the atmospheric factors of radiation, precipitation, wind, evaporation, etc., that exist in the rangewatershed complex.

A distinction must be made between climate and weather because

the two bear differently upon range condition and trend. The climate

of a given locality is a persistent feature continuing for hundreds, and

probably thousands, of years at about the same level. Weather, on the

other hand, changes from day to day and year to year. Variations in
INDICATORS ON HIGH RANGE-WATERSHEDS 11

temperature, rainfall, wind, sunshine, and so on, make different kinds

of weather, but it should be emphasized that these variations are themselves part of one climate. They are as much a part of that climate as

the characteristic maximum and minimum temperature or the average

annual rainfall; and like other features of climate, they influence development of vegetation and animals, evolution of topography, and

formation of soil.

The climate of high range lands is alpine or subalpine. Average

precipitation is adequate for luxuriant plant growth. An important

characteristic of precipitation at high elevations is its winterlong accumulation in the form of snow, which is the source of most of the

yearlong stream flow. For a period in early spring the moisture supply

of the soil mantle is invariably replenished to maximum capacity.

Thus, even though winter precipitation may be greatly below normal,

the vegetation begins growth each spring with about the same amount

of soil moisture. However, dry summers occur in which plant growth

is markedly curtailed. On sunny or windy sites, too, the advantages

of high average precipitation tend to be offset by high rates of evaporation.

A second important characteristic of mountain precipitation of the

Intermountain region is the occurrence of high-intensity summer storms.

Although these storms contribute only a minor part of total precipitation, they are responsible for most of the soil erosion and for summer

floods.

Low temperatures prevail in the mountains, and the growing season is short. This season nearly coincides with the period of grazing,

and the disadvantage of a short growing season is thereby intensified.

A double burden is laid upon vegetation, for plants that maintain

themselves under grazing must recover their food reserves and still

complete their seasonal growth cycle, all in a few weeks. Although

temperatures are low, freezing of the soil is slight because of insulation

by the deep snow cover. Shallow frost heaving is common in spring

and fall, with resulting injury or death to seedlings.

Three climatic levels may be distinguished, of which the first and

most extensive is an over-all climate characteristic of the region. It is

this climatic level with which human beings are most concerned, but

for plants of a particular site, rooted as they are in one place, the overall climate is modified by local topographic factors. This local climate,

induced by topography, is at a second, less extensive level. Examples of

differences in local climate are the contrasts to be found on a south

slope as compared with a north slope, or on a ridgetop as compared

with a vaUey. .

Finally, at the third and least extensive level, is a microclimate.

Microclimate is that climate at the surface of the ground and most

immediately under the influence of vegetation. It is a modification of

the local climate by vegetation as local climate is a modification of

over-all climate by topography. Microclimate includes all the atmospheric conditions beneath a vegetal canopy. In a timber stand

the microclimate may extend for more than 100 feet above the ground

surface; in an herbaceous stand it may be only a few inches in depth.

Living plants and the litter that accumulates on the soil surface

alter the microclimate by casting shade and obstructing movement of

wind. These influences result in lowered light intensity, more equable
12 HANDBOOK 19^ U. S. DEPARTMENT OF AGRICULTURE

temperature, higher atmospheric humidity, and reduced evaporational

loss from the soil, as compared with open spaces free of vegetation.

The difference in an herbaceous stand can be appreciated on almost

any clear day by placing one hand under vegetation and the other,

at the same time, on exposed bare ground.

In combination with the influences of vegetation on soil and soil

moisture previously described, the altered climate under vegetation

favors a different and more luxuriant population of animals and plants

than could endure if the protecting vegetation were not there. The

site can be occupied by species of plants that are too demanding in

their requirements to withstand the rigors of climate in the open.

Successful reproduction of desirable herbaceous species may not occur

where the sheltering influence of vegetation is lacking. The process

and rate of soil development also are influenced by the altered climate

under vegetation and the organisms that flourish in it. Near the

ground level even lowly herbaceous vegetation may do an important

job of air conditioning.

Microclimate is of more practical significance than either local

climate or over-all climate, because it is the one climatic level that can

be influenced through manipulation of grazing. If the vegetation is

allowed to grow tall, casting plenty of shade and litter, the establishment

of seedlings of the more moisture-demanding species in the stand is

encouraged.

Topography

Topography, or configuration of the land surface, includes degree

of slope, direction of slope, and position of any part of the land surface

in relation to adjacent parts.

The effect of topography upon climate is perhaps its most obvious

influence, for everyone has experienced the difference in temperature

and humidity of different exposures on a hot summer day. Topography

has much to do with air movement, distribution of rainfall, and accumulation of snow, as well as with temperature and humidity, from

place to place. Its effect upon season is manifest not only by a progressively later season with increase in altitude, but by variations in season

at the same altitude. Thus at a time when midsummer has arrived on

south-facing slopes, as attested by vegetation already brown and dried

the local season may be early spring on nearby snowbank areas. Thes^

variations may give rise to abrupt differences in range condition, for

the attractiveness of small spots of lush, early-season forage often results

in heavier and more continuous grazing, and more severe compaction

of the soil by trampling, than prevail over the range generally.

Topography also modifies the character of vegetation of mountain

range watersheds through the kind of local climate it creates and

through the relation of land surface to the water table. The natural

instability of surface on some very steep slopes, too, favors dominance

by plants adapted to such sites.

Distribution of animals, variations in the intensity of grazing and

trampling, and resulting changes in range condition, are closely related to character of topography.

The influence of topography upon soil formation is partly a result

of its influence upon local climate and upon the type of vegetation the
INDICATORS ON HIGH RANGE-WATERSHEDS 13

site supports, and in places upon drainage. At any one spot, normal

rates of soil accumulation and of soil loss are materially affected by the

topographic situation of that spot, and thus depth of soil mantle is

very closely correlated with character of topography.

In these ways and others, topography influences climate, vegetation,

and soil; but these also influence topography. The influence of vegetation on topography is subtly manifest by the even, rounded contours of

slopes that have been densely vegetated for centuries. These surfaces,

comparatively gentle elevations and depressions, are made possible by

vegetal stabilization and chemical weathering of irregular rock materials, and they reflect the age-long concurrent development of vegetation and soil. They reflect, in fact, the concurrent development of slope

surface with vegetation and soil. This influence of vegetation on topography is more dramatically apparent on such slopes after its vegetal

cover has been destroyed: the once-smooth surface is quickly cut up into

a miniature badland by gully systems.

As another example of interrelation, the contrasting climates and

corresponding contrasts in vegetation and soil of north and south

exposures produce marked differences in length and steepness of slope:

south-facing slopes tend to be long and gentle, north-facing slopes

short and steep. This difference results from differences in rate of

normal geologic erosion on the constrasting exposures. The erosion

rates relate to character of vegetation and soil, and these in turn to

local climate. There is thus an interlocking organization of cause and

effect, with many reciprocal relations, between these components of

the range-watershed complex.

While most indicators of range condition and trend relate directly

to vegetation or soil, certain indicators are topographic. The rounded

surfaces of vegetated slopes have indicator significance. So also have

the gullies that dissect them. A flood plain or an alluvial fan is a

topographic phenomenon indicating an area of deposition. If either

is incised by a gully, the indication is clear that a process of deposition

has been superseded by a process of erosion. Where this has happened

it is well to look to the condition of the cover in the drainage basin as

a possible cause of abnormal runoff.

Topographic factors must be taken into account in judging condition and trend, as well as in other phases of range management. *'Key

areas," for example, are often determined by the influence of topography on the distribution of animals, or by its influence on erosion

potential. Again, in making comparisons between ranges under differing management, judgment must be weighted by considering to what

degree the sites are comparable. For comparability, sites should be

essentially similar in topography.

INTERRELATIONS BETWEEN COMPONENTS OF THE

RANGE-WATERSHED COMPLEX

The fact that management practices modify not only forage but

set in motion an array of interrelated forces, gives rise to the term rangewatershed complex. The term complex is used to emphasize the significant interrelations that exist on the range and to mark a difference

from the oversimplified concept of range condition as being essentially
14 HANDBOOK 19^ U. S. DEPARTMENT OF AGRICULTURE

only forage production. Emphasis on the range-watershed complex as

a whole does not depreciate the products of management—forage and

water—with which the range manager is most directly concerned, but

serves to put these products in true relation to the environment that

produces them.

The concept of the range as a complex or system made up of interrelated parts aids an understanding of how invasion of an aggressive

species of plant may result in alterations of soil and microclimate so

far-reaching as to affect the entire population of plants and animals.

The wholesale invasion of a new species of animal might result eventually in just as complete a total change. In the closely integrated complex

any change may be almost automatically transmitted through a chain

of action and interaction to produce far-reaching changes in the complex as a whole. This, in general terms, is the essence of ecological

succession.

How THE RANGE-WATERSHED COMPLEX CHANGES

The range-watershed complex is never static, but constantly undergoes change. Normally the change is very slow and is marked by the

progressive invasion of certain species and elimination of others. Such

orderly change is called "succession." It is necessary in consideration

of condition and trend to distinguish two kinds of succession, primary

and secondary.

Primary succession begins by the invasion of vegetation on bare

areas not formerly occupied by plants and continues by normal development of vegetation and soil toward a climax determined predominantly

by over-all and local climate. Examples are successions on talus slopes,

on bare rock surfaces such as might be produced by glacial scouring, on

glacial moraines, or in lakes.

Secondary succession begins by the invasion of vegetation on bared

areas formerly occupied by plants, and hence possessing a soil, or it

may consist of successive changes resulting from some disturbance, like

the replacement of brush fields (that have followed fire) by coniferous

forest. Secondary succession may be favorable or unfavorable to grazing; and grazing itself may set a secondary succession in motion (fig. 5).

Succession involves more than a sequence of changes in dominant

vegetation. Parallel successional changes also take place in the understory vegetation, in the population of other organisms—of small mammals and insects, for example—and in microflora of the soil. Moreover,

the physical environment itself undergoes change—soil, microclimate,

and even microtopography. Thus succession is change in the complex

as a whole, and change in dominant vegetation is but the mark of this

total succession.

Primary succession

The range-watershed complex is rooted in the past. The complex

as a whole, and each of its component parts, is the product of slow

successional change over a long period of time—change that is still

going on, except as it may be disrupted by secondary succession or

destructive change. Various stages in successions of several different

types may be observed readily in the mountains. Perhaps the type most
INDICAIORS ON HIGH RANGE-WATERSHEDS 15

F-443895

FIGURE 5.—Small bushes in grassland near edge o£ dense stand o£ Rothrock sagel)riish

(Artemisia rothrockii, right) indicate succession from grassland to sagebrush. Most

bushes in the dense stand are 30 years old or more, while most in the grassland

are 10 years old or less. Invasion of sagebrush into this once fairly moist swale

was caused by overgrazing which exposed the soil and made the site abnormally

dry.

characteristic of mountain slopes is that which begins on loose rock.

The initial stage may be a cliff disintegrating into fragments of

rock that accumulate in all sizes at its base, forming a long talus slope.

At this stage the complex is relatively simple. It has little or no soil;

its vegetation is represented only by pioneer lichens and mosses; and

its animal life is represented only by a few insects that feed or breed on

these plants, and an even fewer number that prey in turn upon them.

In time a little soil, formed by pioneer plants or blown or washed

in from elsewhere, accumulates between the rock fragments, and larger

plants—forbs, grasses, shrubs, and trees—become established in the

interspaces. As centuries pass, the spaces between fragments of rock

fill up with an accumulation of finer materials, rock fragments disintegrate into smaller pieces, and a more luxuriant vegetation and a

more varied fauna develop. Spreading foliage shelters rock surfaces

that were formerly exposed, litter accumulates on them, and the cover

of soil and vegetation gradually becomes more and more complete

(fig. 6).

The more luxuriant the vegetation becomes, the more completely

it controls the microclimate and deepens the soil; new species of plants

and animals enter the complex, and old ones give way. On some sites

an aspen forest may invade and be succeeded by a conifer forest. Or,

on other sites, succession may proceed from scattered trees and brush,

with an herbaceous understory, to a dense stand of grasses and forbs

(broadleaved herbs) as a soil profile characteristic of grassland is

developed.

936025 "-SI-3
16 HANDBOOK 19_, U. S. DEPARTMENT OF AGRICULTURE

,^.

F-453956

Fir.uRE 6.—Talus slope on which soil is being formed and vegetation, consisting of

several species of £orl)S, grasses, and shrubs, is developing. This succession

has proceeded so far in middle distance that a complete cover of soil and vegetation has dexeloped there. Trees in Ijackground are part of another succession on a

different site.

If the succession can continue sufficiently long under constant external conditions, a status is reached in which comparatively little

further change takes place. The character of soil, of microclimate, and

of plants and animals—in a word, the character of the complex—remains

about the same indefinitely. This is the climax. Even the climax,

however, is not static. Like the stages that lead up to it, a certain

turnover in biota and soil is constantly going on; the slow, continual

loss of soil is made up by the continual formation of new soil; plants

and animals die and are replaced; fluctuations in external influences

occur, and the complex adjusts itself to them.

Balance in the complex

In all stages of primary succession the many elements making up

the range-watershed complex are in essential equilibrium with one

another. From the time talus reaches its angle of repose and soil begins

to accumulate between the rock fragments, until the climax is attained,

each element of the complex is in essential balance—or adjustment,

or harmony—with every other element. Changes are exceedingly slow.

As one element changes the others also change, and they change in

such a way that harmony within the whole is preserved.

Nowhere is successful balance within the complex more clearly

manifest than on steep slopes (fig. 7). Here, under the influence of a

particular climate, parent material, and topography, a soil has de-
INDICATORS ON HIGH RANGE-WATERSHEDS 17

F-3I982S

FiiiURE 7.—Grass-covered slopes of 90 percent, 20 percent steeper than the angle of

repose of the loose parent material. Salmon River, Idaho.

veloped and deepened over hundreds of years, while vegetation and

animal lite have undergone parallel successional development. The

steeper the slope the more certain it is that soil and vegetation must

have developed interdependently. Lacking soil, vegetation could not

have clothed the slope; lacking vegetation, soil could not have been

formed and retained in place. They must have grown up together;

for at any stage in development either would have been impossible

without the other. Proof, is provided by the fact that if present vegetation is removed the soil erodes rapidly, and in time the smooth surface

of the slope becomes gashed with gullies.

The sigHificance of balance to range condition, particularly on

range with steep slopes, is intensified by considering fluctuations in

weather. The fact that development of soil and vegetation requires a

span of time to be reckoned in thousands of years, a period long enough

to include all extremes of weather, not only the most violent storms

but prolonged dry spells, indicates in itself that an essential balance

has persisted through many environmental ciianges.

Figure 8, derived from records at a valley station, illustrates the recurrence of periods of dry and wet years as a normal feature of climate.

Note that although a cyclic tendency is suggested, there seems to be no

permanent trend, no true climatic shift during the half-century.

Persistence of a soil and plant cover on steep slopes through the

centuries during which similar fluctuations undoubtedly occurred is

proof that the complex is resilient enough to absorb these natural

impacts rather than be destroyed by them. During these many centuries the various components of the complex have undoubtedly had

to adjust themselves to changes other than those in weather—fire, and

changes in grazing use by wildlife, for example. That a soil mantle and
18 HANDBOOK 19^ U. S. DEPARTMENT OF AGRICULTURE

FIGURE 8.—Deviations from average annual precipitation at Manti, Utah, elevation

5,575 ft., 1894-1948 (U. S. Weather Bureau records).

vegetal cover have persisted is the best possible evidence that the adjustments have been made successfully and hence that balance between

the various components has been maintained throughout.

Thus an intact soil mantle is a record of a long period of balance.

This fact has a basic value in judgment of range condition, even where

the soil mantle may no longer be intact. Areas of partly eroded soil

or subsoil are evidence that a complete soil mantle once existed (fig. 9).

Evidence that the soil mantle has been recently destroyed is proof that

some powerful stress, of greater magnitude than normal stresses of the

environment, has been placed upon it.

Secondary succession

Examples of secondary succession—orderly change in which a soil

mantle, or at least part of the mantle, is present—may be seen wherever

vegetation has been disturbed. The most familiar example, perhaps,

is the reinvasion of abandoned cropland by shrubs or trees. Fire, as

well as the plow, prepares the way for secondary successions: sagebrush

or other shrubs may come in on burns, and be succeeded in time by

conifers. The sequential changes in plant composition that take place,

either as a direct result of disturbance or as release from disturbance,

along highways, railroad rights-of-way, or from flooding, draining,

mowing, or heavy grazing, are all examples of secondary succession.

If one were able to reconstruct the past, he would find an example

of secondary succession on practically every area of high mountain

range in the Intermountain region. Vegetation has improved general-
INDICATORS ON HIGH RANGE-WATERSHEDS 19

UP"

m. F-434366

FicURE 9.—An eroding slope with erosion pavement and soil remnants in background,

and exposed subsoil in foreground. These indicators suggest that the soil

: originally extended over the entire slope, even where no soil is now evident.

gullies

mantle <

ly, both in kind and in amount, where management has replaced the

exploitative grazing practices of early days. Although permanent plot

and photographic records attest the improvement that has occurred in

many places, there are no records on most of the range. These changes

are recognizable today only in the indicator aspects of vegetation and

soil—healed gullies, former wind-scoured depressions now clothed with

vegetation, etc.

Many secondary successions under grazing are undesirable trends,

usually resulting from differences in palatability of different species to

a given kind of grazing animal. The most palatable species are grazed

closest and are handicapped; the least palatable species are passed by

and, in relation to the others, are encouraged. The result is a trend

toward a stand containing a smaller proportion of palatable plants

and a larger proportion of unpalatable plants. Other factors than

palatability may play a part in secondary succession due to grazing—

growth form, physiological requirements, and season of development in

relation to time of grazing, may be just as important. As a result, some

fairly palatable species—e.g., dandelion, which happens to. be undesirable for other reasons—may actually increase on overgrazed range.

There are two important differences between primary and secondary

succession. First is a matter of time. A complete primary succession

on high mountain range land involves development of a soil mantle

and requires a very long time, probably thousands of years. Any substantial segment, such as development from one well-marked stage to

another, is probably to be leckoned in centuries at least. Secondary

succession, on the other hand, taking place where soil is already in

existence, is relatively rapid, and recognizable changes may take place

in a very few years or decades. Hence, to achieve short-term objectives.
20 HANDBOOK 19, U. S. DEPARTMENT OF AGRICULTURE

such a betterment of range condition within a Hfetime, management

must depend upon secondary successional processes, and not upon the

slow changes of primary succession.

A second important difference between primary and secondary

succession is that, whereas primary succession follows a relatively set

course determined by all the natural factors of a given site, secondary

succession may take many courses, depending on the kind of disturbance

or pressure applied. Vegetal composition may be changed by grazing,

first in one direction and then another in a great variety of ways,

depending on the kind of animals and the season and intensity of

grazing.

These differences ßhould not obscure an essential similarity between

primary and secondary succession, however, which is that in both,

change is orderly. In secondary succession, as well as in primary succession, vegetal control of the soil surface is maintained. If some soil

loss does occur, increase in vegetation is so rapid that the loss is soon

checked.

Destructive change

When vegetal control is lost and erosion sets in at a rate that is

accelerated rather than normal, the principal changes are no longer

evolutionary, but revolutionary in character. The constructive development of soil, vegetation, and animal life that took place under prevailing topography and climate, is overwhelmed by destructive processes,

and the orderly connotations of the term "succession" no longer apply.

Instead, the term "destructive change" is used in this publication to

describe changes that occur when accelerated erosion is involved.

Destructive change from overgrazing comes about in several ways.

One is the effect of decrease in cover through excessive cropping of

foliage. Besides the loss of established vegetation, the soil is abnormally

exposed to the influence of sun, wind, and water, with corresponding

chances for intensified erosion. The new, drier microclimate handicaps

seedlings of most species. Another way that damage is done is by impairing the tilth of surface soil. Surface soil is normally porous in

spring as a result of frost action and of alternate wetting and drying.

In this condition water is readily absorbed. However, if its tilth is

destroyed by trampling, the soil fails to absorb water quickly, and, in

event of a violent storm, overland flow and erosion are almost certain

to occur. Still another way that damage is done is by actual displacement of soil in trampling.

Accelerated erosion is conspicuous where gullies have been cut into

the soil, or where the soil has been stripped down to a heavy erosion

pavement (fig. 9). But erosion may be very rapid and still not be

recognized, particularly on slopes where replacement from above makes

up the quantity displaced below. On some soils, too, rills and even

small gullies cut during storms are soon obliterated as the soil dries

and sloughs down. Finally, erosion may be accelerated well above the

normal rate and still be scarcely perceptible because the individual

displacements are so slight.

These facts indicate the need for close observation of the soil surface,

particularly during and immediately after storms. Accelerated erosion

ought to be recognized early, not only so that damage can be prevented.
INDICATORS ON HIGH RANGE-WATERSHEDS 21

but so that the most economical remedial measures may be applied.

It is known that accelerated erosion, when well advanced, may continue

under its own momentum until all the soil is lost, even though grazing

is eliminated. The range area shown in figure 10 has not been grazed

for 20 years, yet the cover-effectiveness of vegetation had been so completely reduced by the time protection was given that soil losses have

continued. Thus, although simple management practices may suffice

to check accelerated erosion in its early stages, in advanced stages costly

artificial procedures are the only ones likely to be effective.

F-453951

FifiURu 10.—Deterioration on this area had gone so £ar 20 years ago when livestock

were reinoved that vegetation has not yet increased to the point where it can

staljilize the soil. Present vegetation (e.g., the low, tufted mint, Monardella

odoralissiina) is characteristic of sites naturally much drier than this, and indicates

a radical alteration in microclimate here.

Change and management

The foregoing ecological concepts have important bearing on judgment of condition and trend. The concept of balance, a normal state

of integration between components of the range-watershed complex

in which orderly successional change may take place, is basic to an

understanding of range condition. Equally basic to an understanding

of trend is the distinction between succession and destructive change.

Appraisal of trend is simply the recognition of the nature, rapidity,

and direction of ecological change.
22 HANDBOOK 19^ U. S. DEPARTMENT OF AGRICULTURE

The three kinds of change that have been distinguished relate

differently to range-watershed management. Primary succession, a

knowledge of which is fundamental to an understanding of the complex

and its ultimate potentialities, ordinarily has little direct application

to management. The changes involved in primary succession are too

slow to be manipulated readily.

Secondary succession is utilized in management, for most management problems at the present time consist, essentially, in changing

undesired to desired trends. A knowledge of the forage preferences

of different animals, of seasonal changes in palatability, and of growth

requirements of both desirable and undesirable species in the stand

provides an important basis for using particular methods of grazing

to solve particular problems.

Destructive change is also a matter of great concern in management.

Unlike secondary succession, destructive change has no positive application: the problem in management is everywhere the same, to stabilize

the eroding soil as quickly as possible so that constructive trends can

take over.

FUNDAMENTALS FOR JUDGING

CONDITION AND TREND

Judgment of range condition in any one place depends, first and

foremost, upon whether all components of the range complex are in

essential balance. When these components are well integrated, orderly

change or succession is possible; balance, therefore, does not rule out

change.

CONDITION

Range condition has been called "range health." The parallel is

apt. Like health, condition is relative, and when a particular piece of

range is described as being in "good condition*' or "poor condition"

the description is always relative to a standard or ideal for that kind of

range—its full potentiality in soil stability and in amount and quality

of forage.

An essential of satisfactory condition is successful balance within

the range-watershed complex. Normal soil stability or, put another

way, an amount of vegetal cover adequate to protect the soil from accelerated erosion, is a practicable index of such balance. Figure 2 (p. 5)

illustrates this aspect of satisfactory condition. Foliage, together with

litter on the ground, protects the soil and assures stability necessary

for continuing normal development.

But stability alone is not enough to define satisfactory condition.

A second requirement is that the vegetation include a large proportion

of desirable forage species. In figure 2, for example, the mixture of

several forbs and grasses of varying degrees of palatability meets this

second requirement for that particular area.

Unsatisfactory condition results when any one of the requirements

for satisfactory condition is lacking. Most important is lack of normal

soil stability. The elements of unsatisfactory condition—in fact, of
INDICATORS ON HIGH RANGE-WATERSHEDS 23

extremely unsatisfactory condition—may be illustrated with another

picture taken in the same type as figure 2, and on the same hillside, but

on an area that has been overgrazed for many years (fig. 11). Here, in

the first place, balance between soil and vegetation has long been upset.

Vegetal cover and litter are scanty. Sizable bare spaces have developed

and coalesced, and as a result of exposure fine soil particles have been

lost, leaving an erosion pavement. Rapid movement of surface soil is

indicated by the accumulation of fine materials and even gravel against

the uphill side of grass tufts. Another indication that balance has been

lost lies in the absence of grasses in young and intermediate age classes;

microclimate at the unshaded surface of the ground is probably inhospitable to seedlings. Finally, there is a contrast in species composition—against a mixture of many species, some of high forage value,

the almost exclusive presence on the overgrazed range of a single coarse,

rather unpalatable grass.

F-453964

FIGURE 11.—A stand reduced by selective grazing almost entirely to one rather unpalatable grass. Absence of young and middle-aged plants emphasizes the very

unsatisfactory condition indicated by bare soil and trampling displacement.

For purposes of this publication range condition may be divided

into four broad classes, as follows:

1. Soil stable under a normal or near-normal amount of vegetal

cover; a high proportion of desirable forage plants: satisfactory

condition.

2. Soil stable under a normal or subnormal amount of vegetal cover;

a low proportion of desirable forage plants: unsatisfactory condition.

3. Soil unstable under a subnormal amount of vegetal cover; a high

proportion of desirable forage plants: unsatisfactory condition.

9360250-51-4
24 HANDBOOK 19, U. S. DEPARTMENT OF AGRICULTURE

4. Soil unstable under a subnormal amount of vegetal cover; a low

proportion of desirable forage plants: very unsatisfactory condition.

The first of these classes does not occur widely on high rangewatershed lands of the Intermountain region today. The second may

be encountered in meadows and level uplands where the erosion potential is not great; it is also rather common in forest types, particularly

aspen, where the overstory provides litter for soil protection. The third

is almost never met with now, although after the first impact of excessive use it may have been fairly common on sloping lands. The

fourth is very common, especially in herbaceous types on well-drained,

sloping lands in the alpine and subalpine zones.

Within each of these broad classes further division may some day

be made within major vegetal types. For example, under the first

broad class, all degrees of desirability in species composition can be

conceived, depending on the combinations of species that are possible

and the relative abundance of each in the stand. Similarly, within

the last many rates of soil loss are possible, ranging from slow to fast,

but all in excess of the normal rate. Such refined classification, both in

regard to vegetal composition and soil erosion, will probably be found

feasible when specific complexes have been carefully studied.

The normal a basis for judgment of range condition

In deciding on the condition of a particular piece of range, judgment must spring from an understanding of the normal for such a

situation—not normal in the sense of usual or prevailing, but in the

sense of natural, undisturbed, or pristine. For most practical purposes

the best available approximation to this undisturbed state is given

by relic areas that have never been grazed by domestic livestock, excessively grazed by game, or otherwise disturbed.

This should not be interpreted to mean that an undisturbed, pristine

range is the objective in management. The pristine serves only as a

guide to indicate what species and what volume of herbage the site is

capable of supporting, the normal character of litter cover, and the

normal appearance of surface soil. It gives the essential characteristics

of the range likely to be achieved under successful management, but

not necessarily details such as a desired species composition.

For any piece of range there are certain limits within which condition must be judged. These limits are imposed primarily by site factors of climate and topography and by status in primary succession.

Stages in secondary succession resulting from grazing are sometimes

used as degrees of condition. Stages in primary succession cannot be

used in this way, however, for the reason that well-marked stages in

primary succession are separated by immense spans of time—hundreds

or thousands of years rather than decades as in secondary succession.

Each particular stage of primary succession itself determines a potential

that may be achieved within a reasonable time, and it is with respect to

this potential that condition should be evaluated. Comparison can

justly and practicably be made only between ranges of similar potentiality. Condition of a wet meadow, for example, should be judged by

the soil stability, herbage production, and species composition of such

a meadow, not by those characteristic of a dry upland site. Similarly,
INDICATORS ON HIGH RANGE-WATERSHEDS 25

north slopes should not be compared with south slopes, aspen forest

with open grassland, nor conifer forest with aspen.

An important feature of the normal is that fluctuations in weather

are part of normal climate. Fluctuations in weather must be accepted

as normal events, and effort must be made to distinguish the effects of

grazing from them in judging range condition. Variations in amount

of rainfall and in the monthly pattern of distribution of rainfall cause

natural variations in volume of vegetal production and response of

different plants. Probably they also cause variations in the normal

rate of erosion. On high mountain range-watershed lands these variations are of a minor order compared with the changes that take place

in the long process of soil development and primary plant succession.

This long process has included many of the same extremes of weather

we experience today, and probably even greater ones.

It follows that variations in weather alone cannot account for such

indicators of accelerated erosion as incision of a soil mantle by an

active gully system. Soil mantle and gully system cannot both be

normal; the two are irreconcilable. The same may be said for occurrence of bare soil surfaces unsheltered by vegetation, wind-scoured

depressions, observed movement of soil, soil displacement by trampling,

pedestaling of plants by sheet erosion, and widespread accumulation

of gravel at the soil surface to form erosion pavement. On high

mountain range land none of these indicators is compatible with development of a soil mantle.

TREND

Trend is change in condition. When a trend takes place, some kind

of change in every component of the complex may be expected to

occur. For the purpose of using the indicators of trend described in

this publication, however, it will be necessary only to consider changes

in soil and vegetation.

In speaking of trend, one must distinguish between those cumulative

changes that produce a real difference in condition and changes that

are mere fluctuations. A large crop of seedlings of certain desirable

perennial species,-for example, may reflect only a temporarily favorable

combination of circumstances. One would be surer of an upward trend

if he found, in addition to the seedlings, plants of successively older

age classes.

Trend when soil is stable

On most sites in the mountains a prerequisite for stable soil is

a fairly dense cover of vegetation and litter. On some sites, however,

particularly where slope is slight and soil is not greatly exposed to

drying and blowing, a sparse cover may suffice to hold it. These two

circumstances present two rather different problems in judging trend

by means of indicators.

With normal or near-normal cover there are no known indicators

with which, merely by inspection, change in amount of vegetation can

be detected. Records on permanent plots over a period of years are

especially needed to detect such trends. Changes in proportion of

species in the stand are mor« easily detected, both by permanent plot
26 HANDBOOK 19^ U. S. DEPARTMENT OF AGRICULTURE

records and by indicators. Evidence of increase in desirable species is

evidence of improvement, while increase of undesirable species is of

course the reverse.

When amount of cover is abnormally low, evidence of change in

amount of vegetation is usually easier to detect. Scanty cover usually

means either that fairly large bare surfaces exist or that annuals and

early-season perennials predominate. In either case, the extent to which

perennials have recently invaded bespeaks an increase in amount of

protective cover. Rate of invasion is indicated by age classes, and with

this the residue of litter from past years and extent of current utilization are likely to be correlated. A circumstance that indicates increase

in vegetal cover is evidence of a formerly unstable surface that has

become stabilized, e. g., healed gullies or other types of erosion surface

that have been reclaimed by perennial vegetation. Perhaps it is too

much to infer that this increase in vegetation is continuing currently,

but the indication is at least one of upward trend in the recent past.

Trend when soil is eroding

While soil is eroding the amount of vegetation does not necessarily

decrease, though it may. Ultimately, of course, very little vegetation

will remain if the soil is destroyed, but for long periods while erosion

is going on the amount of vegetation may appear essentially constant,

or it may even increase. Similarly vegetal composition may or may not

improve. Far from being rare, such paradoxical combinations of trends

are common on herbaceous subalpine slopes in the Intermountain

region.

There can be no question but that net trend is downward when

soil is eroding and either amount or quality of vegetation is decreasing.

There may be a question, however, when the two trends are in different

directions. In such a case, since one cannot add unlike things, a precise

judgment is not possible.

It is possible, of course, to describe the trends rather precisely in

separate terms and suspend judgment as to net trend. Such a description may be cumbersome and difficult for some people to understand,

but it is capable of giving a better picture of what is happening than

any single term. In reaching a decision about net trend, however, it

it not so necessary to be precise as it is to weigh the facts realistically.

Whether loss of soil be fast or slow, so long as the rate is greater than

normal, the basic resource is being destroyed. This is a fact of tremendous weight. Any increase in vegetation is important in cutting

down the rate of loss, but no increase in vegetation can compensate for

soil that is gone. In the authors* opinion, therefore, the prudent judgment is that trend is downward unless evidence to the contrary is very

strong.

RELATION BETWEEN CONDITION, TREND, AND UTILIZATION

It is necessary to distinguish sharply between condition and trend.

Condition is the status of the range. Trend is the way in which that

status is changing. Utilization is one of the most important causes of

trend, and hence ultimately of condition. The relations between these
INDICATORS ON HIGH RANGE-WATERSHEDS 27

three are, very simply, that utilization (together with other influences

of the animals besides cropping) may set an upward or downward trend

in motion, and if it does a different condition, or status of the range,

will result.

OBJECTIVES

THE PRIMARY OBJECTIVE

Mountain range-watersheds are multiple-use lands, yielding a variety

of products and services. Since a stable soil is basic to them all, the

primary objective in management is to maintain and improve those

soils that are stable and to stabilize those that are now eroding. An

axiom of sound management is that stable soil is prerequisite to satisfactory condition on any area where a soil mantle has been developed.

This principle is applicable to range anywhere and relates to any

normal vegetal cover; it does not change with site or with type of

vegetation. If the cover is lost, the soil is lost; and with the soil gone

there will no longer be a resource. If the soil is partly lost and then

stabilized, which is the best that can be done now with many high

range-watershed slopes, the resource will be but partly restored. Full

restoration of soil will probably require centuries. The practical objective, therefore, is to develop and maintain a cover adequate to assure

soil stability as quickly as possible.

Flow is one to know what adequate protective cover is on any particular site? Comparable natural areas, if any can be found, may tell

him. The grazed range itself provides valuable opportunities to develop guides. If one makes it a point to be out on the range during

i»nd immediately after torrential storms (and during is better than

after), he can see which kinds and amounts of cover appear adequate

to protect the soil, and which plainly are not.

Criteria of inadequate cover are surface washing during storms

or evidences of runoff afterward—at the least rill marks, pedestaled

pebbles, and tiny alluvial deposits. If water does not run over the

surface, the cover may be presumed adequate to protect the soil against

storms of that particular intensity and duration. A satisfactory cover

for that kind of site, in other words, must be at least similarly dense

and well dispersed. Further observation during still more intense storms

may cause upward revision of these preliminary standards of cover adequacy. Improvement in range-watershed management is greatly dependent on standards built up from widespread observation of this

kind.

If the soil is stable, maintenance of that stability and improvement

of soil and vegetation often may be achieved simply by manipulating

the grazing. Even when the soil is eroding, simple management practices may increase the amount of vegetation so as to bring about stabilization, if certain requirements can be met. These requirements are

that most of the topsoil is intact, that slopes are not particularly steep,

and that a sufficient stand of erosion-preventing perennials remains to

provide a seed source. When these requirements cannot be met, artificial planting will be necessary. Where much soil has been lost and

erosion is rapid, still more costly measures must be taken—not only

reseeding, but artificial mulching or contour trenching.
28 HANDBOOK 19, U. S. DEPARTMENT OF AGRICULTURE

SECONDARY OBJECTIVES

Secondary objectives are products of the land. So far as rangewatershed management is concerned these objectives are a full, continuing supply of desirable forage and well-regulated stream flow.

The vegetal types most desirable from the standpoint of water yield

are those that use up least water in transpiration. Nevertheless, irrespective of the water it consumes, a certain minimum cover must be

maintained to protect the soil and hold it firmly in place. Although

it appears probable that shallow-rooted species consume less soil water

than deep-rooted species, too little is yet known about water consumption and soil protection requirements to permit recommending one

type over another.

With forage the situation is different: certain types and subtypes

are known to be more desirable than others. The secondary objective

in management is therefore to develop that combination of species

which, within the productive potential of the site, is most desirable as

forage. As part of this objective, management will naturally attempt

to reduce the undesirable species.

In general, a mixture of many species is better than predominance

by one or two. And, as a matter of practical necessity, until nutritive

values of more forage plants are known, the most palatable species are

regarded as being highest in forage value. In making this approximation to forage value one is not concerned with pleasing the palates of

the animals, but simply with providing a large volume of herbage they

will eat readily with a minimum of travel and trampling.

INDICATORS

An indicator is a sign in the vegetation, soil, or topography, which

may be used to interpret condition or trend in the complex. Stated

another way, an indicator is a clue to events that have happened, are

happening, or will happen on the range-watershed. This publication

emphasizes indicators associated with soil and vegetation on rangewatershed slopes where grazing use is taking place. Indicators that

do not exist on the range itself, like downstream channel cutting and

flood deposits, will not be considered here, even though they are valid

evidence of events that have happened on the watershed.

The indicators described here are mostly of wide application and

are not restricted to any single plant community, type, or subtype.

They apply particularly to herbaceous vegetation in the subalpine zone,

but most of them are applicable in greater or less degree in other zones.

Naturally they must be employed with caution on range at a distance

from the subalpine zone, for with increasing distance the basic premises

about the character of the normal complex become increasingly different.

Absence of an indicator may, in itself, have indicator value. The

absence of rill marks and recent cutting in gullies, for example, may

indicate that accelerated erosion has been checked. As a rule, however,

absence of an indicator is very weak evidence and depends for its

validity upon the support of independent, positive evidence. For this

reason one cannot give the same weight to the positive and negative

aspects of an indicator. Thus, absence of rill marks or fresh gully
INDICATORS ON HIGH RANGE-WATERSHEDS 29

cutting may mean, not that accelerated erosion has been checked, but

only that storms of sufficient intensity to produce these effects have not

occurred for some time.

As a matter of fact, few indicators have absolute value which permits them to be used mechanically. To interpret a single indicator

correctly it is usually necessary to have additional evidence. Several

indicators are usually observable on any range, and each may have a

bearing on condition or trend. For the sake of brevity it is necessary

to treat the indicators as if they occurred alone rather than in combination with other indicators as they naturally occur. This treatment

may seem to give each indicator an arbitrary and absolute significance.

In application, however, no one indicator should be accepted at the

full value ascribed to it here without due consideration, from evidence

of associated indicators, of the extent to which that value actually applies.

Consideration of each indicator in the following pages will, so far

as possible, cover four points in the following order: (1) Definition of

the indicator; (2) how to recognize it in the field; (3) what it indicates

as to range condition; and (4) what it indicates as to range trend.

COVER

Cover includes both vegetation and litter as they overlie the surface

of the ground. It is made up of the spreading crowns of living plants

and the dead organic matter that accumulates on the ground surface.

That litter lying in openings rather than under foliage, and thus complementing crownspread cover, is the part of the litter cover that is

most important from the standpoint of condition and trend.

Amount and character of cover naturally vary greatly according to

kind of vegetation. In a closed coniferous forest, cover may really be

complete, even though the understory vegetation is sparse, because

litter forms a continuous carpet an inch or more deep. It differs from

the litter of dry grassland in being formed primarily from the coniferous overstory, and owes little to the foliage of herbs, grasses, and shrubs,

which are usually sparse. Grassland other than wet meadow, in contrast, seldom forms a complete cover. The volume of herbage may be

great in a normal stand, but if one looks vertically downward, he will

usually find many openings among the leafage. In some of these litter

is thin and broken, with a certain amount of bare soil exposed. It is

necessary to pay particular attention to these openings in evaluating

cover, in order to give proper weight both to litter and to bare ground.

The eye tends to be unduly impressed by foliage, which is high lighted,

and to ignore the many small openings between leaves and between

plants, which are overshadowed. When quantitative estimates of cover

are made, as a proportion of the total ground surface, the same consideration should be given to bare surface and to litter as to leafage.

A characteristic of normal cover is a high degree of dispersion, which,

for effective soil protection is as important as a large amount of cover.

Figure 12, ^ shows a thin cover of poor-quality vegetation, but it happens to be fairly well dispersed and holds the soil much more efficiently

than the patchy vegetation in figure 12, B, which gives only localized

protection.
30 HANDBOOK 19^ U. S. DEPARTMENT OF AGRICULTURE

F.329I39, F-27069J

FIGURE Í2.—A, Well-dispersed vegetation and litter, with small, scattered openings,

tend to provide better soil protection than B, poorly dispersed vegetation. Although growing in dense patches, this cannot protect adjacent bare surfaces against

Condition.—On mountain range-watersheds in satisfactory condition

cover of perennial plants is essentially complete, even though small

openings are a normal feature of many herbaceous types on slopes and

other fairly dry situations. On many subalpine slopes of moderate

steepness, a cover of well-dispersed vegetation and litter together should

amount to between 50 and 75 percent. To the casual eye either of these
INDICATORS ON HIGH RANGE-WATERSHEDS 31

amounts of cover appears practically complete. While obviously only

approximate for general application, these figures may serve as a useful

rule of thumb for moderate slopes until more specific values are determined. On wet meadows in satisfactory condition, on the other hand,

under the most critical inspection leafage cover is often 100 percent,

particularly when the growing season is well advanced. If openings

between the leaves exist, these are covered by litter so that total cover

is still 100 percent; no bare ground can be seen.

When cover of perennial plants is less than that normal for the site,

even though it may not permit accelerated erosion, unsatisfactory condition is indicated on two counts. First, reduced cover reflects reduced

volume of forage, and second, it is associated with a microclimate that

is drier than normal. A drier microclimate will lead to, if it has not

already brought about, a change toward dominance by more xeric

(drought-resistant) species than are normal for the site. In other words,

a material reduction both in quantity and quality of forage commonly

accompanies a material reduction in cover.

On most range-watershed lands of the Intermountain region any

material reduction in cover of herbaceous types is accompanied by

accelerated erosion. Condition in this case is still more unsatisfactory

than that described in the last paragraph. Many degrees of unsatisfactoriness are possible. The incipient stages of accelerated erosion

on slopes, when cover is just beginning to break, are detectable only

during infrequent torrential storms of very great intensity—perhaps

once in 20 years or more. At the other extreme, when little cover is

left, accelerated erosion may be seen after every storm of moderate

intensity; the signs are freshly made several times each summer in

most years. For such an extreme in unsatisfactory condition the indicator ''bare soil surface" is more appropriate than ''cover."

Tr^nd.—Changes in amount of cover are a very important element

in range trend, whatever the condition may be. A desirable change

usually involves increasing cover; an undesirable change, decreasing

cover. Increase or decrease of cover may be inferred from several other

indicators—"soil remnants," "vegetal composition," "age classes," "invasion of bared surfaces," and "vegetation in gullies," presented later.

Amount of cover by itself is not an indicator of change, but of

condition. Where the amount of cover is slight, and consequently the

soil is abnormally exposed, trend is almost certainly downward (see

"bare soil surface").

BARE SOIL SURFACE

"Bare soil surface" means a soil surface that is not sufficiently covered

with vegetation and litter for protection against accelerated erosion.

The term has reference either to generally scanty cover (fig. 13) or to

abnormally large spaces devoid of a vegetal cover (fig. 14, B and C).

Since some bare spots may be found even on virgin range, and

larger bare spots, more conspicuous but of a temporary nature, may

occur as a result of burrowing by animals, one needs to have some

conception of the normal to use this indicator. In general, bare spots

that occur normally on mountain range land are small and well dispersed. At the other extreme, when plant cover is very greatly reduced

it is not difficult to detect that the soil is so bare that vegetal control

of the surface is lacking. Rill marks after every rainstorm, wind-scouring

936025°-51-5
32 HANDBOOK 19^ U. S. DEPARTMENT OF AGRICULTURE

F-416094

FIGURE 13.—Bare soil surface. Although plants are distributed fairly uniformly, the

stand is so thin that vegetal control is far below normal. Pedestaling of the older

plants indicates continuing loss of soil. The species present reflect harshness in

the site and soil instability: Yarrow (Achillea lanulosa), the plant with white

flowers, can spread in this eroding soil by vegetative means; dandelion (Taraxacum

officinale) and slender wheatgrass (Agrupyron trachycaulum) are aggressive seeders

capable of reproducing on a bared surface of this character.

after every dry spell, and almost complete mortality of seedlings, indicate that vegetal control is inadequate. But with range in less extreme degrees of deterioration, lack of control becomes increasingly hard

to detect. Even though plant cover may fall considerably short of

normal, its ineffectiveness may be apparent only for short periods after

occasional severe storms.

Condition.—No bare ground should be visible on wet-meadow

range in good condition, and that which may be present on drier uplands and slopes should not be evident upon casual inspection. Closely

examined, uplands and slopes in good condition may show small and

well-dispersed bare spots, aggregating no more than .SO to 50 percent

of the surface. If the proportion of bare soil is very much greater than

50 percent, there is cause for alarm.

For a given site the greater the proportion of a.rea in bare soil surface, the more unsatisfactory the condition. The process of enlargement of bare spaces on a level, turfy, subalpine range is illustrated

in figure 14. The turf in A is almost solid, forming an effective protective cover. The turfs in B and C are in progressively less satisfactory

condition because of smaller amounts of cover coupled with greater

exposure of bare soil. This change has resulted from elimination of

the more palatable broadleaved species present in A and even some of

the relatively unpalatable grass. A slight accumulation of gravel on

the surface of the bared soil in C indicates that erosion has taken place;

the closed character of the depression, that fine soil particles were carried away by wind. The hummocked appearance of the grass is due

to deposition of part of this fine material, as well as to erosion from

the bare spaces.
INDICATORS ON HIGH RANGE-WATERSHEDS 33

.¿i^ -mm

fe-.

F-453980, F-453994, F-453999

Fir.iiRE 14.—Stashes in the formation of bare spaces in subalpine meadow turf: A,

Almost solid co\cr; B, openings in the cover, some species eliminated.
34 HANDBOOK 19, U. S. DEPART^rE^•T OF AGRICULTURE

FIGURE 14 Continued.—C, Enlarged bare spaces and greatly reduced protective influence of \egetation.

Figure 13 illustrates bare soil surface on a moderate slope. The

species present are aggressive perennials that characteristically invade a

harsh, eroding surface. With so much bare soil, rapid erosion is to be

expected lierc during storms merely of moderate intensity. Pronounced

pedestaling, especially of the older grasses, shows that soil has been

eroding rapidly, and the evidence of drainage that this erosion has been

by water.

In short, on high range-watershed lands a soil surface unprotected

by vegetation and litter is unnatural in the highest degree. It is a

powerful indicator of unsatisfactory condition.

Trend.—As long as bare spots occur generally over a range, with

vegetation insufficient to protect the soil against accelerated erosion,

it is certain that wind or running water will eat away the soil and that

an unfavorable microclimate will continue to handicap plant establishment. Such bare soil surfaces are, therefore, almost conclusive

evidence of downward trend, and they set the stage for more positive

and extreme indicators of soil erosion such as wind-scoured depressions,

erosion pavement, and gullies. The larger the eroding bare areas, for

a given site, the more rapid the rate of downward trend.

OBSERVED MOVEMENT OF SOIL

This indicator is the visible displacement of part of the soil mantle.

The agent of displacement may be wind, running water, or hoofs of

animals. Soil movement may be observed during windy weather, heavy

rainstorms, or at times when animals are traversing slopes having loose

soil.
INDICATORS ON HIGH RANGE-WATERSHEDS ÓD'

In the extreme, visible displacement by wind takes the form of

dust clouds, but it is important to detect displacement by wind in early,

less obvious stages—the blowing of soil particles from bare spaces underfoot, undercutting on the windward side of grass tufts, and accumulation of particles in vegetation. Soil displacement by water is obvious

in the dramatic violence of muddy torrents and in discharging flood

deposits, but the displacement to be watched for is the cutting of tiny

rills and deposition of small alluvia on slope surfaces. In the early

stages of accelerated erosion few or none of these rills and alluvia even

reach main stream channels. As used here, observed'soil movement

refers to displacement on the watershed itself, where cause and effect

are nearest together. Mud that discolors the water of a main stream

channel may be misleading. It may not relate to range condition or

come from the watershed slopes at all. It may relate to improper road

drainage, to caving stream banks, or to stream cutting of a landslide

that has blocked the channel.

A small amount of soil displacement takes place normally: throughout the ages of successional change, many small, imperceptibly slow

movements of soil have occurred. For short periods in certain places

movement has been rapid or extensive—as, for example, after some fires

—when control of the surface by vegetation has been temporarily relaxed. But since soil development is extremely slow, and since a soil

mantle—the net excess of development over loss—is normal on mountain

range-watershed slopes, it follows that such obvious soil movement

must be rare. Hence, when the surface is disturbed so that widespread

soil movement may be detected, the probability is great that soil loss h

abnormal. When such loss continues year after year, the probability

becomes a certainty.

Condition.—OhseYYed soil movement on high range-watersheds is

accelerated erosion in process and indicates unsatisfactory condition.

Indeed, it is itself an unsatisfactory condition—soil instability. The

less wind, rain, or trampling with which it is associated, the more

serious the condition.

Tr^?íc¿.—Observed soil movement on disturbed surfaces means that

soil is being destroyed and indicates that soil trend is downward. As

with condition, the less force producing movement, the more rapid the

trend.

TRAMPLING DISPLACEMENT

By trampling displacement is meant evidence that surface soil has

been moved downslope under the hoofs of grazing animals. It is soil

displacement in a consistent direction. The displacement that occurs

on level ground as a result of trampling, a churning of the soil into

dust or mud, is not covered by this term.

Trampling displacement is a form of erosion similar to displacement by water, in that movement of soil is consistently downhill, but

it tends to be less definitely channeled. Like erosion by water, trampling

displacement becomes more and more clearly marked as steepness of

slope increases, other things being equal. It occurs most readily when

soil is very wet or very dry, and least readily when soil is merely moist.

Almost any grazing on slopes is bound to cause soil displacement,

if only as part of the normal process of mantle creep. Some slopes,

because of their steepness and character of soil, are particularly suscepti-
36 HANDBOOK 19^ U. S. DEPARTMENT OF AGRICULTURE

ble, and on certain ones a person cannot walk without displacing soil

markedly. It may well be doubted whether on slopes of such instability

there should be grazing by domestic livestock.

Condition.~Wiáespre3.d trampling displacement is evidence of soil

instability and therefore of unsatisfactory condition.

Evidence of trampling displacement takes two forms. In the case

of excessive trailing the surface is imprinted with nearly level terraces,

like contour lines (fig. 7, p. 17). The banks above these terraces are often

steep, exposing plant roots.

Displacement that is not concentrated in trails, but is more generally distributed over the slope, is marked by soil accumulations on

the upslope side of perennial plants (fig. 11, p. 23) and irregularities

in the form of mounds or ridges downslope from each hoofprint. Such

general displacement is less easily observed than terrace trails, but is

probably more serious. Terrace trails suggest a measure of stability,

by virtue of which the range has reached a compromise, if only a

temporary one, with an abnormal concentration of grazing animals.

With general displacement, however, no compromise is reached, not

even temporarily, except where surface soil may accumulate above an

obstruction.

Trend.—Terr3.ce trails may relate to excessive trampling many years

ago rather than to excessive trampling at the present time, and hence

may not bear strongly on current trend. lii contrast, evidence of general displacement over the slope by trampling relates directly to a

current cause, and is an indicator of downward trend. Like other

evidence of accelerated erosion, such trend is particularly important

because it is away from a balanced range-watershed complex.

SOIL REMNANTS

Soil remnants are relics of surface soil. They are miniature mesas

remaining in position after the soil which formerly lay between them

has been eroded away. They owe their persistence to the persistence

of protecting vegetation, and this is said to be "pedestaled" because of

its position atop the soil remnants (fig. 15).

A former continuity of surface from remnant to remnant is sometimes suggested by a similarity in level. Sometimes it is suggested by

the repeated appearance of similar parts of the soil profile in each

elevated section, alternating with its absence in the depressions.

^'Islands" of soil above a common level of erosion pavement, as in

figures 9 and 10, pages 19 and 21, suggest the former existence of a

continuous mantle. In the places pictured, erosion has proceeded so

far that the remnants are really remnants of subsoil. In some instances

plants are unable to protect the soil remnants fully, and when the

remnants are lost the plants remain for a time with elevated root crowns

and exposed roots.

Elevated islands and soil pedestals are often caused by joint erosion

and deposition. Erosion of the nearby soil surface lowers the general

level. At the same time, deposition of a portion of the disturbed soil

particles in the protecting vegetation, commonly by wind but sometimes

in other ways, builds up the level of the islands. A vertical section

made with knife or shovel through the island can often reveal this

fact, with the deposited soil lying above the root crown of the plants
INDICATORS ON HIGH RANGE-WATERSHEDS 37

B :

FIGURE 15.—Formation of soil remnants. A, Thinned stand of plants and scarcity of

litter permit erosion by sheet wash and raindrop splash; B, more soil has been

carried away, plants are left on pedestals, and small stones accumulate at surface;

C, plants are weakened and dying not only because of heavy grazing but because

of drying from root exposure and undercutting by erosion. Accumulation of

stones on surface shows development of an erosion pavement.

(fig. 21, p. 46). Having taken the precaution to make such a section,

one is not likely to overestimate the amount of erosional loss, as he

may if he simply measures the difference between the level of the

island and that of the eroded surface. On the other hand, the height

of pedestals, after making any necessary allowance for deposition,

usually provides an underestimate of total loss. For, on most range

where pedestaling is common, accelerated erosion is not new; soil has

been slipping away for several decades, and the height of pedestals

represents only the latest decrement in the process.

A special type of soil remnant is formed by the impact of raindrops

and sheet flow of water over bared surfaces. Small rocks and pebbles

lying on the surface protect the underlying soil, while that round about
38 HANDBOOK 19, U. S. DEPARTMENT OF AGRICULTURE

^ ¿VM

;.^v-:c>.o-í>V

FIGURE 16.—Where soil is bared, v4, raindrop splash and flow of water over the surface remove fine soil particles and leave small stones perched on pedestals, B,

a special type of soil remnant.

is carried away. The result is that the pebbles appear elevated on low

pedestals of soil above the surrounding surface (fig. 16). Close observation is usually necessary to discover these because, as one looks down

from above, the pedestal is concealed until the pebble is carefully

removed. This indicator is especially valuable in giving convincing

evidence of current accelerated erosion during storms that are of such

moderate intensity or duration as not to form gullies or alluvial deposits.

Condition—Soil remnants reflect a state of deterioration, and their

position in the soil profile indicates how serious the loss of soil has

been. Least serious loss is indicated when interspaces, as well as

remnants, are still essentially topsoil. When the remnants are still topsoil but subsoil is exposed in the interspaces, loss is much greater,

and likelihood of getting vegetation readily established to stabilize the

interspaces is less. When the remnants themselves are nothing but raw

subsoil, and the interspaces are reduced to erosion pavement, the job

of rehabilitation is likely to be very difficult indeed.

Soil remnants are a result of accelerated erosion. If the remnants

are abundant or conspicuous, or if pedestaled pebbles can be found,

erosion is undoubtedly current. Hence soil remnants indicate very

unsatisfactory condition, especially when sides of the remnants are

vertical and depressions between them are still not clothed with vegetation.

Trend.—Soil remnants with plant roots exposed or vertical sides

are a result of recent soil erosion. They indicate rapid downward trend.

If the remnants themselves are not adequately sheltered by vegetation,

downward trend is even more marked. Remnants with sloping sides,

or with sides vegetated by mosses and lichens or small seed plants,

indicate less recent soil erosion. To this extent they suggest that a

degree of stability is being reached. This may be misleading, however,

if torrential storms have not occurred for some time. The more com-
INDICATORS ON HIGH RANGE-WATERSHEDS 39

pletely sides of remnants are occupied by vegetation, the better the

evidence of a current trend toward restored stability. When the sides

are strongly sloped and well covered with perennials, and when successful colonization of the depressed interspaces has occurred, the indication is that stabilization has been taking place in recent years, and

improvement may be continuing.

Pedestaled pebbles indicate erosional loss during the current season,

and hence unqualified downward trend.

EROSION PAVEMENT

Erosion pavement is the name given a concentration of gravel and

rock at the soil surface as a result of blowing or washing away of finer

particles of soil (figs. 14, C, and 15). As used here the term means a

concentration caused by accelerated erosion, in distinction to one caused

by normal geologic erosion.

It is sometimes difficult to tell whether the erosion pavement has

been produced by accelerated or by normal processes. One criterion of

a pavement produced by accelerated erosion is that beneath it the lower

portion of a true soil profile, characteristic of normal soil development

for the site, remains. If there is no evidence of such a truncated profile,

and the material beneath the surface consists of slightly altered mineral

matter and fragmented rocks, the pavement is probably normal. Evidence of abnormal pavement is provided by associated signs of accelerated erosion, either on the area in question or on essentially similar

sites elsewhere. These signs include soil remnants and elevated root

crowns.

There are circumstances in which gravel may be spread over the

soil surface giving an appearance of erosion pavement. Figure 4 (p. 9)

provides an example. Here some disturbance of the slope above has

caused gravel to wash down, partly burying the plants. Soil loss, as it

would be revealed by formation of erosion pavement, is clearly not

indicated here.

Condition.—Erosion pavement—due to accelerated erosion—is an

indicator that soil has been lost, and hence that the site has deteriorated

from its original state. For a given soil, progressive deterioration is

marked by progressive increase of gravel at the surface (fig. 17, A).

Whether amount of loss has been great or little cannot be told solely

from amount of gravel, however. One needs also to know the proportion of gravel in the normal profile of that particular soil from the

surface downward. In soils that have little gravel in the profile, erosion

pavement means severe soil loss.

Microclimate on erosion pavement is hot and dry, and if the surface

is frequently disturbed by trampling, small, xeric pioneer seed plants

are the usual vegetation. When trampling disturbance is lessened,

species of increasingly mesic (moisture-demanding) character may become established and help in checking soil loss. Establishment of the

more mesic species gives some measure of improvement over the condition when they were absent and more active erosion was taking place.

Trend.—Erosion pavement provides some protection for the soil

surface, and as it is formed the rate of accelerated erosion is slowed.

Soil loss continues even after pronounced pavement has formed, however, because frost action and burrowing or trampling by animals bring
40 HANDBOOK 19_, U. S. DEPARTMENT OF AGRICULTURE

F-454060

FIGURE 17.—A, Erosion pavement far aihanced on steep slope in background and

in process of formation, foreground. Stones first appear in gully bottoms (lower

left). Other indicators of very unsatisfactory condition and downward trend are

bare soil surface and pedestaled grasses. B, Pebbles still showing from a partial

erosion pavement formed at some previous time. Present amount of vegetal cover

indicates that erosion has been greatly slowed, or perhaps stopped so that an

upward trend may Ije in progress.
INDICATORS ON HIGH RANGE-WATERSHEDS 41

soil particles to the surface between the stones, and some of this fine

material is later washed or blown away. Close inspection after rainstorms often reveals evidence of this removal of fine soil material in the

pedestaling of pebbles. For this reason most erosion pavement indicates

downward trend.

Erosion pavement alone never indicates upward trend. A stand of

vegetation over erosion pavement, particularly vegetation of relatively

mesic character, may indicate upward trend (fig. 17, B). If the vegetation provides sufficient cover so that the pavement could not have been

formed under it, undoubtedly it has invaded since the original pavement was formed. Erosion is less rapid than it was before. When vegetation is so dense that soil loss no longer occurs, an upward trend is

clearly indicated.

LICHEN LINES

Lichens grow on the above-ground portion of fixed rocks, usually

most abundantly on the shaded side and near ground level where

moisture is greatest. They grow very slowly. If surface soil is eroded

its former level can sometimes be traced, often from one rock to another, by the abrupt break between the level of great lichen density

and the relative scarcity, usually absence, of lichens below. These

abrupt breaks are known as "lichen lines."

Very little is known about the process of lichen colonization on

rock surfaces of our western mountains, and it is therefore difficult to

estimate the time period that lichen lines represent. It is certain,

however, that lichen growth is sufficiently rapid to keep pace with

normal surficial erosion. Probably, too, lichens can establish themselves and grow rapidly enough to keep pace with slightly or even

moderately accelerated sheet erosion. Well-marked lichen lines therefore reflect a very rapid rate of accelerated erosion at some former

time.

The lichen pattern on the rock in the foreground of figure 18

suggests that: (1) Only an inch or two of the rock extended above the

original soil level; (2) lichen growth may have kept pace with the

F-443897

FK.URE 18.—Lichen lines on the northern and eastern faces of three large limestone

rocks on subalpine range. The lower edges of the lichen concentrations indicate

that the original soil surface was at least 3 inches (left) to 6 inclies (right) above

the present one.
42 HANDBOOK 19, U. S. DEPARTMENT OF AGRICULTURE

earliest accelerated soil loss; and (3) a very rapid loss of from 3 to 6

inches of topsoil followed. At present soil erosion, although from other

evidence probably still accelerated, has evidently slowed greatly from

this rapid rate because the soil surface is now partly protected by

vegetation and rock fragments.

Lichen lines are best defined on slightly elevated terrain, particularly

on ridgetops or the shoulders of ridges. They are seldom well defined

on slopes, even where erosion is obviously greatly accelerated, because

soil losses alongside any particular rock tend to be made up by deposition from farther upslope.

Condition,—Lichen lines provide a fairly accurate measure of the

amount of accelerated soil loss that has taken place at a particular spot,

and thus an estimate of range deterioration. The weakness of such an

estimate is that it tends to be highly localized, since lichen lines are

seldom widely evident.

The information that lichen lines give as to condition is only relative. Thus, in figure 18 it is reasonably certain, from the rather slight

evidence of current accelerated erosion, that vegetal cover at present is

greater than it was while the soil below the lichen lines was being lost.

This does not tell us, however, whether condition is satisfactory at

present. Indeed, from other evidence—rather scanty cover and poor

species composition—we know it is not.

Trend.—luichen lines give an indication of current range trend only

indirectly. That they exist above the present soil surface indicates

rapid soil loss at some time in the past. If signs of current accelerated

erosion are strong, continuing loss up to the present is suggested. If

they are not marked, however, the collective evidence indicates that

vegetation has increased on the formerly eroding surface since the soil

below the lichen lines was lost, and that more recent trend has been

toward stability.

ACTIVE GULLIES

Gullies are channels cut into the soil mantle by running water (fig.

19). They are said to be "active" when their sidewalls are unstable—

that is, when their sidewalls are clothed with insufficient vegetal cover

to protect the soil—or when there is evidence of recent cutting in the

bottom. Rill channels are active gullies so small as to be obliterated

easily by trampling or slight natural soil movement. "Gullies*' therefore include channels very much smaller than the one in figure 19. If

vegetation occurs only in its bottom, the gully is probably active. Only

when vegetation clothes the sidewalls may the gully be considered

healed. Vegetation in gullies will be treated in some detail later.

The term "gullies" as here used does not refer to main downstream

channels, but rather to channels on the range-watershed itself. Cutting

or deposition in downstream channels should call attention to the

possibility of unsatisfactory condition on the watershed above. On tlie

watershed itself gullies should lead the observer to see less obvious signs

he might otherwise miss. For a gully denotes a concentration of erosive

power, and is obvious when many of the tributary surfaces that feed

it may be difficult to see.

Gullies are caused by rapid surface drainage of water which, under

normal conditions, would enter and filter through the soil. Rills are

formed and gully cutting begins as the infiltration capacity of the soil
INDICATORS ON HIGH RANGE-WAIERSHEDS 43

F.386204

FIGURE 19.—A deep and active gully extending through the soil mantle and shaly

subsoil. The steep, active tributary gullies at the left indicate that the gully

system is being enlarged. Note the similarity in level of the land surface on each

side, suggesting former continuity and indicating that this gully is a topographic

abnormality.

is reduced by heavy forage utilization and trampling. Gullies are also

I'ormed by improper road drainage, breaking of diversion ditches, etc.

Like downstream channels, such gullies may give an erroneous impression of range condition unless they are shown to relate to the

soil-vegetation balance on the range-watershed proper.

Once formed, gullies intensify the rapidity with which moisture

drains out of the soil mantle. More rapid drainage promotes more

rapid soil erosion, excavation of plant roots, loss of moisture through

exposure of a larger soil area to evaporation, and, in turn, still more

rapid drainage. With each torrential storm a gully system becomes

entrenched more deeply and becomes more effective as a collector and

conductor of runoff. It is easy to understand, therefore, why an active

gully system, once established, tends to perpetuate itself and grow.

Even after vegetation on the watershed slopes has improved materially,

rainstorm runoff from the raw gully sidewalls, or snow melt in spring,

may continue to cut out the bottom and keep the gully open.

Rill marks are of special interest because they reflect current soil

loss and because they are among the signs by which soil erosion may be

detected before a system of large gullies has been formed. Rill marks

can be seen most easily right after a storm, for the smaller ones are

easily obliterated in a few days by trampling, frost heaving, or even

alternate wetting and drying of the soil. The next storm creates a new

set, and these in turn are obliterated. This unspectacular process can

go undetected, frequently on a wide scale and over a long period of

time, until much soil is lost. Much of what is referred to as "sheet ero-
44 HANDBOOK 19, U. S. DEPARTMENT OF AGRICULTURE

sion" is really rill erosion. An established gully system comes into existence when certain rills cut deeply and entrench themselves so that their

channels are not filled and blocked by ordinary movements of surface

soil.

The real significance of rill marks or of gullies on mountain range

land lies in the fact that they are incised into a soil mantle. They occur

naturally and normally on loose material where a soil mantle has never

developed, as on areas of rock waste in very rugged terrain—which is

why soil development has not occurred on such areas. But where a

soil mantle has been developed, rills and ,2^ullies are abnormal in the

highest degree. Here they indicate the sudden domination of one

process, soil development, by a wholly different process, accelerated

erosion.

Condition.~A gully, whether active or healed, represents range

deterioration-both because of the soil that has been lost and because

of accelerated drainage of soil water and drying of the soil mantle.

An active gully, which has resulted from range deterioration, indicates

very unsatisfactory condition on at least part of the area it drains.

Rill marks indicate very unsatisfactory condition of the site on which

they occur. The more gullies or rill marks per unit area, and the deeper

and more active they are, the more serious the unsatisfactory condition.

Trend.—Active gullies indicate downward trend. Whatever the

source of water that forms them, the soil mantle in which gullies arc

entrenched continues to deteriorate. Some gullies, originally excavated

by summer storms, are currently kept open by snow melt each spring;

these do not necessarily indicate downward trend on the slopes above.

If the water runs off these slopes, downward trend is indicated there.

Rill marks are of particular importance for, in contrast to many

indicators, they relate to current causes rather than to causes in the

indeterminate past. They testify to the inadequacy of present vegetal

cover in protecting the soil surface, and are therefore an unmistakable

indicator of downward trend.

WIND-SCOURED DEPRESSIONS

Wind-scoured depressions are shallow basins in bared surface soil

between patches of vegetation, from which wind has carried away the

finest soil particles.

The action of wind may be recognized by a residue of fine gravel

or sand particles, too large to be blown away, resting on the scoured

surface of depressions. Fresh evidences of wind-scouring are lines etched

in the surface, paralleled by tiny, streamlined ridges of fine soil material

in the lee of pebbles. The depressions usually have no outside drainage.

In extreme cases the soil surface is merely a series of such shallow depressions separated by low ridges of vegetation (fig. 20). The depressions

may be fairly symmetrical or they may be irregular, a few inches or a

few feet across.

Wind-scoured depressions develop when the soil is exposed to wind

as a result of thinning of the plant ccver. Figure 14 (p. 33) portrays

the process that leads to development of wind-scoured depressions like

those in figure 20. Such scouring is caused by winds of moderate intensity such as may occur on almost any day of the snow-free season, as well

as by stronger winds. A fine-textured soil in an exposed situation, and
INDICAIORS ON HIGH RANGE-WATERSHEDS 45

F-453927

EuaiRK 20.—Large and severely eroded wind-stoiired depressions, some of which are

surfaced with a light erosion pavement, on level motmtain range. Exposure of

roots hy wind erosion is killing the grass on the windward (left) side of the

hummocks. Deposition of hue soil particles is responsible for the gentler slope on

the leeward side.

one that is repeatedly pulverized by trampling, is most liable to this

kind ot erosion.

Condition.—Wind-scoured depressions indicate unsatisfactory range

condition, and the greater the extent of barrenness, and the fresher the

evidence of scouring, the more unsatisfactory the condition. Depending

on its natural abundance in the soil, the amount of gravel that has

accumulated on the surface indicates something as to the severity oí

erosion.

Trend.—IÏ the surface of wind-scoured depressions is exposed bare

soil, and especially if it is plainly scoured or etched, rapid and recent

downward trend is indicated and further soil loss is to be expected. If

the surface is covered with erosion pavement, soil loss is probably continuing, but its rate is less because the gravel affords some protection

to finer materials. In this case evidence of wind scouring may be difficult to detect, but past action of wind in excavating the depressions

may be inferred when aeolian deposits are close by and where there is

but little evidence of drainage between depressions. Checking of erosion

is chiefly to be judged by evidence of vegetal invasion. If vegetation

covers the surface of the depressions, soil loss may have been stopped

completely.

AEOLIAN DEPOSITS

Aeolian deposits are eroded soil materials laid down by wind. They

represent the depositional end of the process that begins with wind

erosion.
46 HANDBOOK 19^ U. S. DEPARTMENT OF AGRICULTURE

F-415490

FIGURE 21.—Wind-deposited soil built up in a currant bush. Original surface level is

indicated by white line. Vertical bar is one meter (39.4 inches) long.

Aeolian deposits are confined almost exclusively within, or to the

leeward of, patches of vegetation that catch moving soil particles and

protect accumulating material. Such deposits are composed of fine,

even-textured particles and usually contam no rocks. However, especially in large deposits that accumulate in shrubs (fig. 21), rodents

sometimes bring some rocks to the surface which become mixed with

the fine-textured, blown material. Aeolian deposits are very common

in grass clumps on deteriorated range. I'hcy consist of fine material

lying above the root crown. If the residual soil beneath the root crown

contains much gravel, the zone of contact may be clearly marked.

It is advisable to cut a vertical section in hunnnockcd grasses or

shrubs so as to see how much of the difference in soil level is due to

erosion of the adjacent surface and how much to de])osited soil in the

vegetation. In figure 21 the difference in level is a residt both of erosion

and of deposition.

Relative age of deposits may .sometimes be judged by the degree of

decomposition of buried plant parts. Thus the original soil level along

the white line in figure 21 is marked by an accunuilation of leaves ancl

twigs that are still recognizable. One may reasonably conclude that

the deposit is recent and reflects accelerated rather than normal erosion.

The age of the deposit might be estimated more exactly by counting

growth rings of buried living stem branches.

Condition.—Crowns and stems of plants buried by even-textured

material are evidence of deposition by wind, and indicate disturbance

of balance between vegetation and soil in the vicinity. They therefore

indicate range deterioration. When it appears from the character of
INDICATORS ON HIGH RANGE-WATERSHEDS 47

deposit that accelerated erosion is still in progress, unsatisfactory condition is indicated. Thus the occurrence of aeolian deposits in young

plants is more reliably indicative of current disturbance, and of unsatisfactory condition at the present time, than their occurrence in old

ones.

Trend.—Aeolian deposits indicate downward trend. If the deposits

are found in small, young plants of a stand, as well as in large, old

ones, downward trend is probably current. On the other hand, if they

are found only in large, old plants, and not in young ones, downward

trend has probably been checked. Small deposits close to the ground

surface are a more sensitive indicator of current soil instability than

deposits upon an already large accumulation well above the erosion

level, as in the currant bush shown in figure 21. If the duff that has

accumulated under shrubs is partly intermingled with fine soil, probably

deposition is still occurring, but if a deep and distinct layer of duff is

found, with no evidence of current deposition, downward trend has

probably been checked.

ALLUVIAL DEPOSITS

Alluvial deposits consist of soil material that has been dislodged,

transported over the watershed surface by running water, and laid

down again. They have the form of fans or cones at the end of small

gullies or rill channels, or of accumulations on the uphill side of clumps

of vegetation, logs, or litter.

The small alluvial deposits in figure 22, formed by ponding of

overland flow above and to the left of the two gopher mounds, were

produced by a rather low-intensity rain falling on a partly denuded

slope. The fine rill marks on this slope were nearly obliterated by the

time the picture was taken. The coarser the material of which an

F-443917

FícuRíí 22.—Small alluvial deposits of fine sediment where water running over the

surface from the upper left was ponded hy two crescent-shaped pocket gopher

mounds.
48 HANDBOOK 19, U. S. DEPARTMENT OF AGRICULTURE

alluvial deposit is composed, the more violent the overland flow that

produced it. The flow that deposited the fine mud in figure 22, for

example, was much gentler than the one that laid down the gravel in

figure 4 (p. 9).

As used here the term ''alluvial deposits" refers to deposits on the

surface of the range watershed rather than at the remote mouths of

major stream channels. These large downstream flood deposits may

or may not relate to unsatisfactory range condition; they do indicate

disturbance of some sort on the watershed. Only a small part of these

deposits is topsoil, even when they are caused by unsatisfactory range

condition. The great bulk of it is canyon fill, usually containing a high

proportion of rock and gravel.

Condition.—AlluYÍ3.l deposits, since they result from soil erosion

associated with inadequate cover, indicate soil deterioration on the

watershed above.

Like gullies, erosion pavement, and aeolian deposits, alluvial deposits may relate to unsatisfactory condition in the past rather than

the present. Their bearing on current condition is directly proportional to their recency. If an alluvial deposit is fresh, without a vegetal

cover, it points unmistakably to unsatisfactory condition on the tributary slopes. If it is vegetated with annuals, short-lived perennials, or

young woody plants, the probability of unsatisfactory condition still

is great. But if the deposit has long-lived vegetation well established

upon it, one may conclude either that the erosion which made it possible has been checked or that intense rainstorms have been lacking.

Trend.^Kecent alluvial deposits indicate downward trend. As with

condition, old well-vegetated deposits may or may not indicate a trend

toward stabilization.

VEGETAL COMPOSITION

Vegetal composition is the relative abundance of the various species

that make up a stand.

Vegetal composition on high range-watershed land with cover adequate to protect the soil is evaluated primarily in terms of the palatabilities of the component species. Where accelerated erosion is taking

place, however, vegetal composition is evaluated primarily by the effectiveness of the component species in protecting the soil.

Evaluation of vegetal composition, both as to condition and trend,

must always take into account the potentiality of the site, whether it

be north slope, south slope, ridgetop, or meadow. It must be based

on an understanding of the normal vegetal composition and amount

of cover of the particular site under consideration, gained through a

study of comparable natural areas or grazed range in satisfactory condition. Relic plants, too, give valuable clues as to normal vegetal composition.

Condition.—NsitursLl vegetation on high range-watersheds in good

condition consists of a mixture of many species, practically all of which

are perennials, and a considerable proportion of the plants are palatable.

Unsatisfactory condition with a stable soil, which is sometimes encountered in herbaceous types on level ground—particularly when

subirrigated—is characterized ordinarily by a sufficiently great volume

of herbage to create the needed protective cover, but usually a low
INDICATORS ON HIGH RANGE-WATERSHEDS 49

volume for the site, and always an abnormally high proportion of

inferior forage plants. A common characteristic of such range is dominance over extensive areas by one or a very few species that are not

very palatable to the kind of livestock that has been using the range.

While there are exceptions to the rule, cattle tend to favor grasses over

forbs, while sheep tend to favor forbs over grasses. The result is that

forbs of low value for cattle often characterize depleted cattle range

and grasses of low value for sheep characterize depleted sheep range.

These tend to be the more xeric species in the normal stand or introduced species, usually from a drier natural habitat. Such dominance

is usually referred to as a result of "class overgrazing."

An example of this kind of change in vegetal composition is given

in figure 14 (p. 33). Here, on level, dry alpine meadow, the native

forbs, sedges, and grasses have been reduced by heavy sheep grazing

until one relatively unpalatable grass predominates. A few forbs persist that are low in palatability and otherwise resistant to grazing.

Under continued heavy sheep grazing and trampling even these forbs

are eliminated.

When annual weeds form a very large proportion of the vegetation

unsatisfactory condition is indicated. If annuals are abundant and

conspicuous it is practically certain that perennials have been very

greatly reduced, and there is a strong likelihood of accelerated soil

erosion. .

A surface on which rhizomatous species are dominant may be one

that has been severely eroded. Rhizomatous species usually provide

better soil protection than annuals, and, because they spread underground, they are able to colonize harsh, eroding surfaces where seedlings fail. They may provide the soil stability and favorable microclimate needed for the establishment of other perennials. Some

rhizomatous species like yarrow (Achillea) become less effective as they

grow older because their crownspread becomes incomplete and produces little litter. There are exceptions, but generally speaking dominance by rhizomatous species represents an intermediate level of

condition, much better than dominance by annuals, and not so good

as dominance by a mixture of more mesic perennials.

Those mesic species that succeed in becoming established on areas

that have been stabilized or semistabilized by rhizomatous vegetation,

particularly if they are species that reproduce only from seed, usually

indicate a condition that is more nearly satisfactory. Species with large,

spreading crowns (e.g., lupine) obviously provide more shelter for the

soil surface, plant for plant, than species with small crowns (e. g., dandelion). Fibrous-rooted grasses are more effective, as a rule, than taprooted forbs, partly because their roots promote crumb structure of

the soil more efficiently, and partly because the litter they produce

tends to lie longer on the ground surface. Persistent, perennial forbs

and grasses are more effective in sheltering the surface and improving

quality of soil than either annuals or early-season perennials with their

limited root systems and usually small, early-withering tops.

Trend ~A mixture of desirable and undesirable species will occur

either when the stand is improving or declining in value. Whichever

trend is taking place can only be told by finding out which species are

increasing in the stand and which are decreasing. To do this, it is

necessary to ascertain their relative ages, or, if accelerated erosion has
50 HANDBOOK 19^ U. S. DEPARTMENT OF AGRICULTURE

occurred, to recognize old erosion surfaces and be able to infer invasion

ot characteristic species on them. The presence of more mesic and

more palatable species in rhizomatous patches that have stabilized the

soir indicates upward trend in those stabilized patches. Of more immediate concern is the trend of the less well-vegetated openings between

the patches, as revealed by evidence of plant colonization on the one

hand and of soil erosion on the other. The rapidity of the apparent

increase of invading species, as shown by their distribution of a^e

classes, and particularly the rapidity of invasion of the openings, provides a rough measure of the rate of upward trend or of trend toward

stability.

AGE CLASSES

Plants of a given species may be grouped into age classes-for example, seedling, young, middle-aged, and old plants. Members of a given

age class are thus of approximately the same age, and the different

classes represent broadly differing ages.

Abundance of individual plants in each of the various age classes

gives a clue to recent history of that species in the stand and indicates

whether the species is maintaining itself, or is increasing or decreasing.

The significance of age classes to condition and trend depends, therefore, on the value of the given species, either as protective cover or as

forage.

Woody plants may be grouped into age classes with relative ease by

counts of growth rings or less certainly by means of size differences.

Age classes of herbaceous plants are less easily defined. The size of an

herbaceous plant is not always a reliable criterion of its age, but

massiveness of root crown tends to be proportionate to age and is a

more reliable criterion than volume of foliage. Old grass clumps have

a tendency to break up into a number of smaller tufts that may be

mistaken for young plants; often excavation will reveal the former

continuity between tufts. Similarly, a little digging will often show

that small plants which are thought at first sight to be seedlings are

really attached to underground parts of old plants. Very young seed

lings can usually be told by the presence of attached seed coats or by

their cotyledons.

Species that reproduce vegetatively often defy estimates of age.

About all that can be done is to distinguish between plants that are

young and those that are much older. Young plants of rhizomatous

species like penstemon (Penstemon rydbergii),y2irrow (Achillea lanulosa),

and sweet sage (Artemisia discolor) are taller than average and form

a dense, compact growth in which other species are scarce or absent.

Older plants of this type extend over a greater surface area, lack sharply

defined margins, and have individual shoots that are scattered and

short; and plants of other species are commonly intermingled with them.

Often on eroding range the height of soil pedestals above the general

level may be still another clue to relative age of the plants upon them.

The pedestals are remains of a series of erosion levels upon which

plants have become established, and reflect the progressive sinking of

the general soil level as erosion has continued over a period of years.

Age is therefore correlated with height of pedestal (fig. 23, p. 53).

Reasoning in application of age-class indicators may be illustrated

as follows. Suppose for example that the age-class distribution of three
INDICATORS ON HIGH RANGE-WATERSHEDS 51

herbaceous species, in relative numbers o£ individuals, is as shown in

the tabulation:

species A Species B Species C

Age class: ^^^^^"^ ^^^^^^^ ^^^"^^^

Seedlings 50 0 85

Young 30 0 0

Middle-aged 15 20 0

Old . . . __5 _80 _15

Total 100 100 100

Species A has a fairly large proportion of individuals in all age classes,

which indicates that it is maintaining itself successfully. This is approximately what is believed to be normal age-class distribution, with

very high mortality of seedlings and young plants, progressively fewer

individuals in older age classes, and progressively less difference between

numbers of plants in older classes. Species B, on the other hand, is

represented almost entirely by old plants, which would suggest that no

new plants have become established for several years; and it may be

inferred, if the individuals are few, that the species is dying out. The

grass in figure 11 (p. 23) has an age-class distribution of this kind.

Species C is represented by only two age classes-plants that are manifestly old, and seedlings, with no plants of intermediate age. Such a

distribution is evidence that no successful establishment has occurred

for a number of years. The presence of seedlings may be interpreted

in two ways: either the species has begun to reproduce just this year,

or it is producing seedlings year after year which for some reason never

succeed in becoming established. Additional evidences is needed to

settle this question.

Condition—On a range in satisfactory condition, normal distributions of age classes of the desirable species would be expected, but

in a heavy cover of vegetation they may be difficult to recognize. Abnormal age-class distributions of desirable species, especially when the

stand is thin, indicate unsatisfactory condition. With reservations,

since some undesirable species may well occur in the ideal natural stand,

a normal distribution of age classes of undesirable species indicates

unsatisfactory condition.

Trend—In interpreting trend the question is: will future composition of the stand, as indicated by the tendency for some species to

increase and others to decrease, be more desirable or less desirable

than its present composition? Thus, returning to the tabulation of age

classes, if species B were of low palatability, the evidence of its passing

out of the stand would indicate a desirable trend in vegetal composition, whereas if it were a palatable species similar evidence would indicate an undesirable trend.

Heavy grazing tends to eliminate the more mesic species and to

encourage species that are better able to endure drought. On average

sites, therefore, evidence of increase among species characteristic of

moister sites indicates improvement while evidence of increase in species

characteristic of drier sites indicates depletion.

ANNUAL WEEDS

Certain annual forbs become abundant on high mountain ranges

where perennial species are greatly reduced and bare soil surface is
52 HANDBOOK 19, U. S. DEPARTMENT OF AGRICULTURE

exposed. The indicator "annual weeds" means an abundance of annuals, together with an abnormally low cover of perennials.

Among the most common annuals found on high mountain range

lands are pepperweed (Lepidium spp,), knotweeds (Polygonum aviculare

and P. douglasii), goosefoot (Chenopodium album), tarweed (Madia

glomerata), and tansymustard (Descurania incisa). Although these are

typically annuals at low elevations, completing their growth and maturing seed in a single season, some, particularly tansymustard, may become biennials at high elevations.

Annual weeds furnish little litter and have taproots rather than

fibrous roots.2 Their abundance and volume of growth vary greatly

from year to year, depending largely upon early-season precipitation.

In many years they complete growth, dry up, and virtually disappear

before the end of summer. For these reasons annual weeds furnish an

uncertain, and at best unsatisfactory, cover. Moreover some, particularly tarweed, may form heavy stands that provide severe competition

and greatly retard reinvasion of perennials.

Since one of the important characteristics of normal vegetation of

high range-watershed lands is that it is composed almost entirely of

perennials, abundance of annuals is evidence of abnormality. An

abundance of annuals reflects the fact that perennials, which in a stand

of anywhere near normal abundance would suppress the annuals, have

been reduced.

Condition.—Annmil weeds, when they occur abundantly on high

range-watershed land, indicate unsatisfactory condition because they

provide uncertain, often scanty cover, and usually inferior forage.

When the site dominated by annuals is one on which accelerated

erosion occurs readily, condition is very unsatisfactory. Tarweed, which

is a very strong competitor and almost completely unpalatable, is

considered to indicate a poorer condition than other annuals.

The mere presence of annuals as minor constituents of a perennial

stand does not necessarily indicate unsatisfactory condition. Having

once been introduced, some annual species seem able to remain on the

range indefinitely, perpetuating themselves by colonizing each year the

more or less temporary bare spots, like gopher mounds, that occur

naturally. Nor do annual weeds necessarily indicate an unproductive

soil, for they thrive on fertile soil. There is reason to think that some

of the annual weeds listed above are more demanding in their soil

requirements than many native perennials.

The presence of annual weeds in the shadow of perennial vegetation, together with their absence in nearby bare spaces, suggests that

microclimate of the bare spaces may be too severe for their survival.

This may be a clue as to why perennial seedlings have not been able

to colonize the bare spaces.

Tr^nd.—Although any plant cover is an improvement over none,

annual weeds give such inadequate protection against soil erosion

that continued soil loss is almost a foregone conclusion where they are

dominant. Annual weeds are therefore an indicator of downward trend.

The small contributions they make to soil quality in the way of struc2 These statements apply to annual forbs rather than annual grasses. Cheatgrass (Bromus tectorum), a very important annual grass of valleys and foothills in

the Intermountain region, is not included here because it is not common or abundant

on high mountain range-watersheds.
INDICATORS ON HIGH RANGE-WATERSHEDS 53

ture and organic-matter content are offset many times by the great

amount of erosion they permit.

INVASION OF BARED SURFACES

Invasion of bared surfaces means the successful establishment of

vegetation on soil surfaces from which most of the original vegetation

has been lost. Although this indicator includes initial invasion by

annuals, it relates primarily to invasion by perennials, either on bare

surfaces or on surfaces supporting annuals.

To use the indicator it is necessary to be able to recognize formerly

bared surfaces after they have been partly or completely covered with

vegetation. Such recognition is based on rather distinctive characteristics both of soil surface and of vegetation. Usually the two are related.

A formerly bared surface may be indicated by depressions alternating with hummocks, a result of accelerated erosion and perhaps deposition. Gullies and erosion pavement, when covered with vegetation,

are special kinds of formerly bared surfaces.

Where the soil surface is uneven as a result of accelerated erosion,

the vegetation is likely to be decidedly patchy. That of hummocks may

consist of shrubs or tenacious mat-forming species—plants which have

persisted while erosion has lowered the interspaces. The contrasting

vegetation of the depressed interspaces consists of plants that have invaded, and is often markedly different from that of the hummocks.

If succession is not well advanced, it consists of annuals and perennials

that flourish early in the season, withering in midsummer. If succession

is farther advanced, it consists of perennial grasses and herbs that grow

throughout the season.

In figure 23, for example, three erosion levels are shown: (1) That

upon which the larger and older Penstemon plant became established,

perhaps 20 years ago, as indicated by its root crown about 2 inches

above the white line; (2) that upon which the younger plant became

established, as indicated by its root crown at the level of the white line;

and (3) the present erosion surface between the two Penstemon patches

about 2 inches below the white line. This surface is vegetated chiefly

F-443920

FIGURE 23 —Patchy vegetation produced by invasion of a mat-forming Penstepion

into deteriorated subalpine range vegetated with annuals. Two widely separated

age classes of Penstemon and three erosion surfaces are indicated.
54 HANDBOOK 19^ U. S. DEPARTMENT OF AGRICULTURE

with annual and early-season species. A few persistent perennial grasses

have become established, of which two plants may be seen between the

Penstemon patches.

Often bare depressions, in which perennials that reproduce only by

seed cannot get established, are invaded by rapidly growing rhizomatous

species, like Kentucky bluegrass and yarrow. The young plants coming

up at the end of the rootstocks are able to draw on the parent plant

for moisture and food until they can exist independently. Figure 24

shows the invasion of a bare depression between masses of vegetation.

The cracked soil surface is obviously a harsh site for seedling establishment, but the rhizomatous aster has succeeded in colonizing it vegetatively.

F-443898

FIGURE 24.—Rhizomatous plants like this aster invade eroded depressions that are

inhospitable to seedlings. The rule is resting on the soil surface of the densely

vegetated hummocks.

Condition—ln\2iúon of bared surfaces represents progress in greater

or less degree toward restoration of balance between vegetation and

soil. If the vegetation that has occupied formerly bared surfaces provides effective soil protection, the first requisite of satisfactory condition

has been met. Condition can be considered satisfactory when the

vegetation on the range as a whole is desirable as forage.

Trend.—Invasion of bared spaces by perennial plants indicates increasing soil stability and an increasing volume of vegetation. Invasion

by palatable species is a more positive indication of upward trend than

invasion by unpalatable species, because it indicates that the palatable

species present on the range are capable of reproducing under current

management. However, perennials low in palatability, or even annual

weeds, are preferable to bare ground. Also, invasion of perennials by

seed is a more favorable indication than invasion by vegetative means

alone because it suggests the existence of a microclimate favorable for

seed germination and seedling establishment.
INDICATORS ON HIGH RANGE-WATERSHEDS 55

In arriving at a judgment of net trend where erosion may be continuing, the rapidity of establishment of new plants, together with

their value in furnishing soil protection, must be weighed against plant

mortality and evidence of continuing erosion. The evidence of rapid

erosion in figure 13 (p. —) is so strong, for example, and the evidence

of vegetal increase so weak, that stabilization of the surface in a reasonable time is highly improbable. Occupance of erosion surfaces by

annuals and early-season perennials, although preferable to bare

ground, is hardly an indication of improvement. Except in very wet

summers these species wither without producing much litter, and so

expose the soil.

VEGETATION IN GULLIES

Vegetation in gullies is a kind of invasion on bare erosion surfaces

in which either the gully bottoms, or the bottoms and sidewalls, become

clothed with plants and litter. It is given separate treatment because

it is a commonly observed type of invasion on erosion surfaces, and

because vegetation in a stabilized gully helps define not only condition

of the erosion surface on which it grows, but condition of all the watershed surface drained by the gully.

Gully bottoms offer favorable conditions for quick plant establishment and luxuriant growth. They may, in fact, be the only sites on

badly deteriorated slopes where certain kinds of vegetation can grow

at all. Bottom vegetation may persist for several seasons in truly active

gullies if by chance there are no storms causing enough runoff to

destroy it. Hence its presence is not a reliable indicator of soil-plant stability in the drainage above. The grass shown in figure 25 is commonly

found in moist situations. It has become established in the gully bottom

because of an abundant seed source nearby, favorable moisture relations in the gully, and absence of much competition. This grass, around

which considerable soil has accumulated, is likely to be wiped out when

a high-intensity storm occurs, for the adjacent area is too poorly

vegetated to prevent surficial runoif.

Gully walls offer a less favorable environment for plants than gully

bottoms. Seeds are less likely to lodge on the walls, and because the

soil is drier and more unstable, seedlings have more difficulty in becoming established there. After a gully bottom has been vegetated and

the flows of water in the gully have been reduced by better vegetal

control on the watershed above, sloughing of the sidewalls tends to

build up the bottom and lessen the sidewall slope. Vegetation spreads

sideward, colonizing the moister and more stable surfaces first and the

drier, more unstable parts of the slopes progressively later (fig. 26, A).

Portions of the gully shoulders, their steepness temporarily maintained

by the binding roots of plants, are the last parts of the gully walls to

slough down and merge with the gentle contours of the stabilized gully

(fig. 26, B). Mantling of gully walls by vegetation therefore indicates

a much longer period of freedom from cutting than establishment

of vegetation in the bottom alone, and makes it safer to infer that the

trend toward stabilization is lasting.

Condition—Gullies caused by accelerated erosion, no matter how

well vegetated subsequently, represent deterioration in comparison with

the original, intact soil mantle. Those that have raw sidewalls, even
56 HANDBOOK 19^ U. S. DEPARTMENT OF AGRICULTURE

h-..,-

tr'^P

:J.

'/

F-366ei7

FIGURE 25.—Meadow barley, Hordeum nodosum, in a gully bottom contrasts strongly

with the bare soil surface at either side. Because of the likelihood of overland

flow from surfaces like these, the tenure of this grass in the gully bottom probably

is temporary.

though vegetation grows along their bottoms, indicate unsatisfactory

condition. If the walls are clothed with vegetation and the gully has

a rounded or flat-bottomed cross section, however, balance between

soil and vegetation has probably been restored on the area drained.

If other evidence supports this conclusion, further judgment of condition will depend upon forage value of the vegetation in relation to

what the site is capable of producing.

Trend.—While any vegetation is better than none, it is not safe

to infer material improvement from vegetation in the bottoms of gullies

with bare walls. Neither are scattered plants established on gully sides

an indicator of upward trend. A fairly complete cover of vegetation on

gully walls is, however, an indicator of genuine, continuing improvement, especially if the gully shoulders are well rounded, the bottom is

flat, and the walls slope gently.

RILL-CHANNEL RIDGES

Rill-channel ridges are low, narrow ridges that follow a former rill

pattern. They are formed by the establishment of vegetation in rill

channels and subsequent more rapid erosion of the soil on either side.

The mechanism by which these ridges form is shown diagrammatically in figure 27, in four stages. In A the raw channel, an inch or two

deep, iï cut into the soil. A few established plants are shown in surface

view. In B plants have become established along the channel. This
INDICATORS ON HIGH RANGE-WATERSHEDS 57

^^üHäia^^'f^

il"^^

i ._.. ..

F-434369, F-434370

FIGURE 26.—TWO stages in healing ot gullies on the same slope: A, An early stage,

with plants established in the bottom and on the lower parts of the sidewalls; B,

a much later stage in which the gully walls are practically healed, having become

vegetated except for a few sharp shoulders.

Strip of vegetation diverts later flows of water to either side, forming

two channels at a lower level, as in C, making a slight ridge of the

former channel bottom. As these channels are cut deeper, and the
58 HANDBOOK 19^ U. S. DEPARTMENT OF AGRICULTURE

adjacent bare surface is eroded, the little ridges of vegetation become

relatively higher. They tend, also, to become broken into smaller and

smaller segments by undercutting and by dying of the pedestaled plants

from drought, as in D. The lower channels may be invaded by strips

of vegetation paralleling the first, similar to the stand shown in B, and

the process may repeat itself indefinitely. Evidence of these rill-channel

ridges may consist at times only of a linear arrangement, up and down

the slope, of distantly spaced, pedestaled plants (fig. 28).

Condition.—R.i\\-ch2innt\ ridges indicate deteriorated range. Some

idea of the extent of erosion can be obtained by imagining the tops of

the ridges as former rill bottoms, and the height of the surrounding

soil surface as it must have been to be drained by these. This, however, usually provides a very incomplete estimate of total soil loss.

When levels of different age can be made out, it follows that this form

of erosion has been going on for many years. These levels record, in a

way, the sinking of the soil surface as persistent rill cutting has planed

it lower and lower.

A product of continuing accelerated erosion, rill-channel ridges

indicate very unsatisfactory condition.

Tr^n<i.—Rill-channel ridges indicate rapid downward trend. Although plants that become established in the process of ridge formation may represent some gain in total vegetal cover, this gain is trifling

compared with the losses of soil that result from continued rill cutting.

1.1 /f

I

i

1%

Y /

FIGURE 27.—Four stages in the formation and decadence of ridges formed by invasion

of vegetation in rill channels. A, Raw channel cut into soil; ¿, plants established

in channel; C, diversion of water forming new channels alongside vegetation; D,

undercutting and pedestaling of the plants.
INDICATORS ON HIGH RANGE-WATERSHEDS 59

F-4160II, 434343

FIGURE 28.—Continuous rill-channel ridges, A, in time may become so greatly broken

that they are represented only by a linear arrangement of plants up and down

slope, B.

ACCESSIBILITY OF PALATABLE SPECIES

Accessibility is the extent to which plants can be reached easily by

grazing animals. The premise for this indicator is the fact that, normally, palatable plants tend to occur on parts of the range where they are
60 HANDBOOK 19^ U. S. DEPARTMENT OF AGRICULTURE

accessible to grazing animals, as well as where they are inaccessible.

If palatable plants are found only where animals cannot easily reach

them, it is probable that they have been eliminated from accessible

places by grazing.

Difference in accessibility is sometimes caused by physical barriers

like rock ledges or crowns of some shrubs. On cattle range the upper

portions of steep slopes and areas that are distant from water may be

practically inaccessible. Sometimes the barrier is not entirely physical,

as when palatable forbs and grasses grow in close association with other

herbaceous species that are so highly unpalatable as to repel grazing

animals. On overgrazed cattle range, for example, palatable grasses

may tend to be confined to the shelter of orange sneezeweed (Helenium

hoopesii) plants.

Condition,—R.-3iUiç:r uniform distribution of palatable species in

both accessible and inaccessible places is a sign that composition of the

vegetation has not been materially altered by grazing, or, if it has been

altered, that palatable plants have succeeded in reestablishing themselves. If cover is about normal for the site, satisfactory condition is

indicated. When palatable species tend to be confined to inaccessible

places, on the other hand, range condition is unsatisfactory.

Trend,—SMh^rç: numbers of young palatable plants, well beyond

the seedling stage, are found in accessible places, whereas old plants

of the same species are confined to inaccessible places, the indication

is that this species is reinvading grazed portions of the range. This

suggests that trend is upward. Where a greater proportion of large

dead plants is found in accessible than in inaccessible places, without

much replacement by younger plants, downward trend is indicated.

RELICS

Relics are remnants of vegetation and provide a means of visualizing

its character after it has undergone modification. A relic may be a

remnant of a plant community or it may be a single persistent species.

A patch of virgin vegetation isolated from the grazed range by a

natural barrier, as by talus rock impassable to domestic livestock, is

an example of a relic. Provided the two sites are comparable, the relic

gives a picture of the grazed range in pristine condition.

A species of palatable plant found only in the shelter of shrubs is

very likely a relic, restricted to inaccessible places by heavy grazing.

Sometimes the palatable plant has a particularly large and decayresistant root crown. Finding such root crowns on accessible range,

and living plants confined to inaccessible places, is confirmation of the

species' being a relic resulting from overgrazing. The stumps of heavily

grazed shrubs provide another example of a relic (fig. 29, B), They indicate the existence of the shrub in a former vegetal community now

largely destroyed by overgrazing. Such relics, besides being species that

are infrequent on the grazed range and more abundant in protected

areas, may be recognized by one or more of the following characteristics:

On the grazed range they tend to be almost wholly old plants and remains of dead plants; they give little or no evidence, from survival of

young plants, of reproducing successfully; and their accessible parts

are grazed excessively closely.

Relics may also be a natural consequence of plant successions that

do not relate to grazing. An example is sometimes provided near the
INDICATORS ON HIGH RANGE-WATERSHEDS 61

»»*' ■■•V' :<>• í^;.

-iîSi.-^.

F-4S40I6, 4S4024

FIGURE 29.—A, Patches of shrubby cinquefoil (Potentilla fruticosa) in a meadow; B,

relics—heavily grazed, dead or dying stubs—o£ this shrub indicate its former

existence on a site made abnormally dry by severe grazing, trampling, and exposure and erosion of the soil.
62 HANDBOOK 19^ U. S. DEPARTMENT OF AGRICULTURE

boundary between an aspen and a sagebrush stand, by dead and dying

sagebrush bushes within the invading aspen. It is necessary, therefore,

by considering associated indicators, to know the process by which a

given species has become a rehc in order to understand its significance.

Condition.—Relics due to overgrazing, reflecting as they do a

depleted forage supply on the range, indicate unsatisfactory condition.

Relics of normally rather unpalatable or moderately palatable species

indicate a more depleted condition than relics of highly palatable

species. In figure 29, B, for example, very unsatisfactory condition is

indicated, not only by the exposure of bare soil and associated evidence

of accelerated erosion—pedestaled plants and erosion pavement—but

by the fact that this shrub is normally of low palatability.

Trend.—Rdics from overgrazing indicate downward trend. In

figure 29, B, downward trend is indicated not only by the continued

destruction of this shrub but by an obviously abnormal exposure of

bare soil. On the other hand, if a population of well-established young

plants is found when relics of the same species are present, improvement

from a more deteriorated condition is suggested. Another indicator

of improvement from a deteriorated condition would be relics of an

unpalatable species in a stand of relatively palatable species. The

relics in this case would, of course, not bear the marks of heavy grazing.

HEDGED SHRUBS

Shrubs or low trees that exhibit densely twiggy crowns, like clipped

ornamental plants, are said to be hedged.

Such hedged crowns result from repeated browsing, but under

certain conditions they may be caused by snow blast, that is, by windborne particles of ice carried at the level of snow accumulation in

winter. Effects of snow blast are most evident on ridgetops and other

situations greatly exposed to wind. If hedging occurs in relatively unexposed situations and only as high as animals can reach, it is probably

caused by overbrowsing. When overuse is extreme, all twigs and leaves

FIGURE 30.—Regrowth from hedged shrubs: A, Of a single season; B, of three or

four seasons. The former suggests that overbrowsing is Hkely to continue; the latter

that grazing pressure has been lessened.
INDICATORS ON HIGH RANGE-WATERSHEDS 63

being taken as high as animals can reach, a ''highline" or /'high-water

mark" is produced because of the regularity of pruning up to a common

level.

Severe hedging results in death of numerous branches and, if long

continued, may cause death of the entire plant. Hence many dead

shrubs or much dead wood in the crowns indicate that overbrowsing

of the species has continued for a long time. Dead branches or dead

crowns are sometimes caused otherwise than by overbrowsing, so that

severe overbrowsing should not be inferred without evidence of hedging

or utilization.

Condition.—Hedging indicates decreased productivity as compared

with normal range, and hence unsatisfactory condition. The normal

palatability of shrubs that are hedged by grazing suggests something of

the degree of unsatisfactoriness. The lower the normal palatability to

the kind of animal grazing the range, the more unsatisfactory range

condition is likely to be. On the other hand, absence of hedging, if

the shrub is positively known to be palatable, shows that use has not

been heavy enough to inhibit normal growth.

Tr^nd.—Hedging indicates downward trend. Shrubs that are hedged

from overbrowsing in fall or winter show a single year's regrowth during summer. If there is only this single year's growth above the hedged

surface, trend shoulc| be considered downward because these twigs

are likely to be completely utilized before the next growing season, just

as past years' twigs have been (fig. 30). Several years' growth above old

hedged surfaces, however, suggests that grazing pressure has recently

been lessened and that trend is upward.

CURRENT UTILIZATION

The extent to which current growth of a species is grazed constitutes

the utilization of that species for the season, and is designated as **current utilization" to distinguish it from utilization of past years.

The criterion for evaluating current utilization should be the

amount of vegetation left after grazing. The objective should be to

leave sufficient crownspread cover unutilized to protect the soil against

erosion and provide a microclimate favorable for reproduction. This

protective phase deserves the utmost consideration where an excessive

area of soil surface is exposed. Heavy grazing under such conditions

aggravates an already serious situation (fig. 31). Where protection is

less urgent, emphasis can be transferred to the desirable forage species,

which should be so utilized that they have ample opportunity to flower

and produce seed. Equally important is the effect of current utilization

on young plants. Sometimes utilization of young plants of desirable

species, which tends to be complete because of their small size, prevents

successful maintenance of those species in the stand.

Seasonlong familiarity with the range is essential so that vegetal

composition, developmental characteristics of plants, and preferences

of grazing animals can all be considered when judging utilization.

Careful and systematic study of current utilization provides first-hand

knowledge of forage preferences. Animals usually change their forage

preferences during a season, and these changes need to be understood

to interpret trends correctly. Observations made only near the end of

the grazing season may be misleading, particularly on heavily grazed
64 HANDBOOK 19, U. S. DEPARTMENT OF AGRICULTURE

range; moderately palatable plants are then often found to be cropped

about as closely as the most desirable species (fig. 32).

A knowledge of forage preferences of all species in the stand is

important in appraising condition, trend, and utilization. For most

purposes this knowledge need not be precise—perhaps no more than a

listing of the various species in approximate order of the use they receive—but it should be fitted to each particular range on the basis

of first-hand observation. This knowledge will indicate which species

are the important ones. It is on these species that more detailed observaF.454009

FIGURE 31.—Stubble of needlegrass that has been grazed excessively by sheep, in

front of ungrazed fescue. On range so badly deteriorated such removal of herbage

of weakened plants aggravates an already serious condition.

tions should be made as to time and intensity of utilization, opportunity

to flower and produce seed, and success or failure in establishment of

young plants.

CondihoM.—Current utilization is more an indicator of trend than

of condition.

Trend.—Current utilization is one of the most sensitive indicators

of trend, suggesting changes before they occur as well as while they are
INDICATORS ON HIGH RANGE-WATERSHEDS 65

F-453919, 454040

FIGURE 32—Marked change in appearance of range brought about by one season's

utilization: A, Before grazing; B, after grazing.
66 HANDBOOK 19, U. S. DEPARTMENT OF AGRICULTURE

in progress. Continued heavy use may result eitiier in preventing reproduction of desirable species or in outright death of established

plants, and is therefore an indicator of downward trend. If a heavily

grazed species is low in palatability, or if its most unpalatable parts,

(e.g., coarse stems) are grazed, the trend is more steeply downward.

Heavy utilization of all or most of the vegetation in the stand is an

even more definite indicator of downward trend. If the utilization is

so severe as to result in baring and disturbance of the soil, the rate of

downward trend is very rapid indeed.

On the other hand, if the most desirable species in a stand are

moderately or lightly utilized, and have the opportunity to flower and

scatter seed, there is reason to expect maintenance and increase of those

species. At least one necessity—a seed source—has been provided, and

upward trend will depend in large part upon the success with which

new plants become established.

"ÄrU. s. GOVERNMENT PRINTING OFFICE: 195! 93602S