is to be used, careful consideration should be given to the
background of the planting material selected.

Sources of Plant Data and Planting Guidelines

While a wide variety of data that deal specifically with
revegetation is available, information is scattered and
sometimes difficult to acquire. Schiechtl's (1980) Bioen-
gineering for Land Reclamation and Conservation is an
excellent source of information on planting techniques
and the range of microenvironments that can be stabi-
lized by revegetation. Much of the background data
Schiechtl uses is from Europe, and many of the species
that he recommends are not indigenous to North Amer-
ica. Similar species do occur in the United States, how-
ever, and substitutions can be easily identified.

The most readily available source of revegetation data has
been developed by the Soil Conservation Service (SCS) of
the U.S. Department of Agriculture. Some information is
available from the regional SCS Plant Materials Centers.
These organizations are responsible for the testing and
development of species that are suited for stabilization in
their respective regions. Prior to 1969, SCS prepared
several handbooks on stabilization issues that provide
regionally specific data.

Other sources of revegetation and stabilization data are
the U.S. Forest Service and the U.S. Army Corps of Engi-

neers (COE) laboratories, particularly the COE Water-
ways Experiment Station. The COE reference works gen-
erally deal with streambank and lakeshore erosion, in
contrast to the work of the SCS, which deals with both
wet and dry environments. Maritime erosion problems
are dealt with by the COE and the Shore Protection
Manual (1984), which is a highly technical source of
stabilization data. SCS publications are also available for
coastal areas.

Local and regional SCS offices can provide support in
making planting selections as well as determining fertil-
izer and lime requirements for revegetation projects. Soil
pH requirements for maximum growth will vary by spe-
cies, and soil testing should be completed after the plants
have been selected. In this manner, a fertilization and
liming plan can be devised that will be suited to the
selected cover plantings. At the same time, a maintenance
schedule for fertilization can be developed. From that
schedule future maintenance costs can be projected.

Installation Costs

Stabilization projects that employ revegetation as the
primary technique can provide one of the most
cost-effective means of site protection available. This is
true not only for initial installation but for long-term
maintenance as well.

Figure 4, Willow cuttings 12 months after sprigging, Lake Britton, Shasta County, CA.



Vogel, Willis
1981

Plant materials were assembled, propagated, and established along California State highways. Grasses, legumes, and the
California poppy were evaluated for erosion control, fire control, and aesthetic purposes. Shrubby species were evaluated
for revegetation and general landscaping. Emphasis was placed upon drought-tolerant, low-growing plants that would
require a minimum of maintenance. A herbaceous seeding guide and a list of native shrubs and trees were prepared for
California, classified by major land resource areas. Special and supplementary studies relevant to plant propagation and
establishment were conducted. Whenever possible, the plants were evaluated on representative highway sites using
common methods applied by contractors. Most data were collected by visual observation; no statistical analyses were
made beyond simple arithmetic averages. Some continued monitoring of plantings is recommended to assess anticipated
future changes.

G.
A Guide for Revegetating Coal Mine Soils. General Technical Report NE-68. U.S. Forest Service, Northeastern Forest
Experiment Station, Berea, KY.

This report provides information, recommendations, and guidelines for revegetating land in the Eastern United States that
has been disturbed by coal mining. Included are brief descriptions of major coal mining regions in the East, a discussion
of mine soil properties, and procedures for sampling, testing, and amending mine soils. Plant species that have been used
for revegetating surface-mined lands are identified and described. Selection criteria for plant species and methods and
requirements for seeding and planting are explained. Some of the data on tree species used in reforestation were obtained
from recent surveys of 30-year-old experimental plantings in several Easter States. Included are maps showing the Eastern
coal regions or portions of them where a plant species has been used successfully or its use is recommended.

Young, W. C.

1973,

Plants for Shoreline Erosion Control in Southern Areas of the United States, modified by W. C. Ackerman, G. F. White, E.
B. Worthington. In, Man-Made Lakes: Their Problems and Environmental Effects. Geophysical Monograph Series No.
17. American Geophysical Union.

This paper discusses various species of plants that have been tested for their adequacy in stabilizing eroding shorelines.
Maiden cane is specifically identified as a good choice for protection objectives that extent across waterlines.

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archeological component is concerned, these are minor
changes since they are largely confined to the humic zone
and will have little impact on the soils that lie below.
Principal changes occur in soil pH and in the organic
matter content. Plant health, and ultimately the success
of a revegetation effort, is dependent on the presence of
nitrogen, phosphorus, and potassium and appropriate
Hion concentrations.

The extent to which amounts of nitrogen, phosphorus,
and potassium adequate for successful plant growth can
alter artifacts seems to be largely unknown. One must
suspect that the presence of these chemicals has little
effect, given the excellent state of preservation of arti-
facts in heavily vegetated sites. It is worth noting, how-
ever, that when levels of decaying organic matter become
sufficiently high, carbonic and nitric acids are produced
in quantities that are sufficient to release phosphorus that
is present in parent soils (Longsdon 1975:58). Carbonic
and nitric acids are thus present in most decomposing
leaf and stem litter and may account for alterations in
soil/site matrix pH.

Higher concentrations of the H-ion, which are dependent
on the decomposition of plant litter, occur in the very top
layer of the O horizon, from 1 centimeter to 2 centimeter.
As the depth below this zone increases, H-ion concentra-
tion decreases and the pH of the soil remains stable
Graun-Blanquet 1932:173). At varying depths below the
A-l horizon, depending on the depth of soil develop-
ment, pH is controlled by moisture and the charac-
teristics of the underlying bedrock, and not on the
decomposition of plant litter.

While Mathewson (1989:230) addresses the issue of site
burial specifically, his archeological component/preser-
vation matrix provides some insight on the effects of
acidic versus basic environments with regard to artifact
Joss. If soil conditions are altered from basic to acidic, an
acceleration of the rate of loss of certain kinds of archeo-
logical remains will occur. Since changes in soil pH occur
in the humic zone (O horizon) and in the upper portions
of the A horizon when cover species are added or
changed, ieaching is likely to dissipate any significant acid
accumulation. Artifactual materials in and beneath the
A horizon are not likely to be altered at an increasing rate
as a result of decomposing organic debris on the surface.

Climate and topographic characteristics affect the pro-
duction of organic matter in soils while various soil types
also affect the accumulation of organic matter. Generally,
forest soils derive their organic matter content from leaf
fall, since tree roots usually live for many years and
decompose slowly. The upper 6 inches of a soil will
contain the highest concentrations of organic matter,
largely as a result of movement by insects, worms, and
small animals that live in the A horizon. Below the first
foot of depth, soil organic matter content is about 1
percent by volume, and organic matter is virtually absent
at a depth of 4 feet.

The relationship between organic matter content and soil
depth for grassed areas is similar to that of forested areas.
At the O horizon level organic matter is about 5 percent
by volume, at a depth of 1 foot it is about 1 percent, and
ata depth of 4 feet itis only about 0.1 percent (Thompson
and Troch 1957:126-130).

The introduction of vegetation or the revegetation of an
archeological site will have little effect on its organic
matter content, assuming that the site has had an existing
floral cover. On completely denuded surfaces, it will take
several years for organic matter to accumulate, and this
will be related to the presence of quantities of nitrogen
sufficient to allow plant growth (Thompson and Troch
1957:131). The addition of chemical nitrogen may prove
to be necessary to ensure successful revegetation.

Given the low levels of soil organic matter below the
A horizon, the loss of artifactual materials should not be
accelerated.

Project Planning

Even though revegetation projects can be put into place
in relatively short periods of time, project development
and implementation sometimes require a relatively long
preparation time. Plant selection, acquisition, and place-
ment must occur during periods of plant dormancy to
insure maximum survival once the growing season be-
gins. Freeze/thaw cycles, periods of dry weather, and
disease can lead to plant loss. Notice should be taken of
potential plant toxicity for the crews who will make an
installation. Commonly seen plants such as English ivy
cause allergic reactions in some people.

While not directly a concern for stabilization projects,
care must be exercised to protect against the introduc-
tion of species that might ultimately become weeds. The
best approach to a revegetation program is to try to select
species that are native to the vicinity of the stabilization
project. If a non-native or commercially supplied species

Figure 3. Willow cuttings immediately after sprigging, Lake
Britton, Shasta County, CA.



Cost projections for a program of revegetation should Request for Assistance
include plant purchase costs if the species to be installed

cannot be collected. If collection is possible, projected Information exchange about site stabilization is available
labor costs must include not only the time needed to from and should be reported to: Dr. Robert M. Thorne,
install the materials but collection time as well. Neither National Clearinghouse for Archaeological Site
of these tasks requires skilled labor, so costs can be Stabilization, Center for Archaeological Research,

minimized. If purchasing of materials is required and the University of Mississippi, University, MS 38677.
materials must come from some distance, shipping

charges may add significant cost.

References Cited

Andropogon Associates, Ltd.
1988 Earthworks Landscape Management Action Plan for the Petersburg National Battlefield. Report prepared for the
Mid-Atlantic Regional Office, National Park Service, Philadelphia, PA.

1989 Earthworks Landscape Management Manual; Section I. Prepared for the Mid-Atlantic Regional Office, National Park
Service, Philadelphia, PA.

Braun-Blanquet, J
1932 Plant Sociology: The Study of Plant Communities. First Edition, McGraw-Hill, New York.

Brown, Margaret K.
1983 Mothballing Albany Mounds, American Archaeology (formerly Contract Abstracts and CRM Archaeology) 3G).

Gray, Donald H. and Andrew T. Leiser
1989 Biotechnical Slope Protection and Erosion Control. Robert E. Krieger, Malabar, FL.

Haffenrichter, A.L., John L. Schwendiman, Harold R. Harris, Robert . McLauchlan, and Harold W. Miller
1968 Grasses and Legumes for Soil Conservation in the Pacific Northwest and Great Basin States. Agricultural Handbook
339, Soil Conservation Service, U.S. Department of Agriculture, Washington, DC.

Keown, M. P., N. R. Oswalt, B. B. Perry, and B. A. Dardean, Jr.
1977 Literature Survey and Preliminary Evaluation of Streambank Protection Methods. Technical Report H-77-9. U.S. Army
Corps of Engineers Waterways Experiment Station, Vicksburg, MS.

Knutson, Paul L.
1977 Planting Guidelines for Dune Creation and Stabilization. Coastal Engineering Technical Aid 77-4, Coastal Enginecring
Research Center, Ft. Belvoir, VA.

Longsdon, Gene
1975 The Gardener's Guide to Better Soil. Rodale Press, Emmaus, PA.

Mathewson, Christopher C.
1989 Interdisciplinary Workshop on the Physical-Chemical Biological Processes Affecting Archeological Sites, Contract
Report EL-89-1, U.S. Army Corps of Engincers Waterways Experiment Station, Vicksburg, MS.

Meyer, Bernard S. and Donald B. Anderson
1939 Plant Physiology. D. Van Nostrand, New York.

Laycock, William A.
1967 Distribution of Roots and Rhizomes in Different Soil Types in the Pine Barrens of New Jersey. Geological Survey
Professional Paper 563-C, U.S. Geological Survey, Washington, DC.

Schiechtl, Hugo
1980 Bioengineering for Land Reclamation and Conservation. University of Alberta Press, Edmonton, AB.

Thompson, Louis M. and Frederick R. Troch
1957 Soils and Soil Fertility. Third Edition, McGraw-Hill, New York.

Thorne, Robert M., Patricia M. Fay, and James J. Hester
1987 Archaeological Site Preservation Techniques: A Preliminary Review. Technical Report EL87-3, U.S. Army Corps of
Engineers Waterways Experiment Station, Vicksburg, MS.



OY

U.S. Department of the Interior
National Park Service
Cultural Resources

Technical Brief No. 8
September 1990 (Revised March 1992)
ISSN 1057-1574

Introduction

This Technical Brief is the third in a series that addresses
the issues of archeological site stabilization and protec-
tion, Each Technical Brief in the series describes a poten-
tially useful technique for maintaining the integrity of an
archeological deposit. This series, and the complemen-
tary Technical Notes assembled by the U.S. Army Corps
of Engineers Waterways Experiment Station in its Archeo-
Jogical Sites Protection and Preservation Notebook, are
designed to provide baseline data for the initiation of site
stabilization projects. The use of vegetation always
should be considered a viable means of site protection
when developing a set of stabilization alternatives.

Revegetation History

Archeological sites throughout much of the United States
have been covered with some form of vegetation since
they were abandoned by their original inhabitants. Care-
fully planned revegetation of such a site will not consti-
tute a previously unknown intrusion into the cultural
deposit. Such major earthworks as those at Cahokia,
Emerald, the Pharr Mounds (Figure 1) on the Natchez
Trace, and the Great Serpent Mound have been main-
tained through the use of floral cover (Thorne, Fay, and
Hester 1987). More recently, the Albany Mound group in
Ilinois has been stabilized through a program of vegeta-
tion removal and replacement (Brown 1983), and the
Petersburg National Battlefield is being protected with a
carefully devised landscape management plan (Andropo-
gon Associates 1988, 1989). Part of the Newark Earth-
works has been protected through the upkeep of golf
course grasses, At the Winterville Mound group in Missis-
sippi (Figure 2), dense stands of tall grass have been used
for several years to stabilize the sides of the mounds as
well as to direct the movement of visitors around the
park.

Revegetation is currently being undertaken as a part of
the total site stabilization package at Lake Britton in
northern California, Willow (Salix negra) cuttings were
put into place on a sloping bank and beneath a midden
deposit (Figure 3). Figure 4 indicates the extent of cutting,
growth after 12 months.

Departmental Consulting Archeologist + Archeological Assistance

Revegetation: The Soft Approach to
Archeological Site Stabilization

By Robert M, Thorne

Center for Archaeological Research, University of Misstssippt

Willow was selected for use in this particular setting
because the rate of shoreline loss is very slow and imme-
diate protection was not deemed necessary. In this par-
ticular instance, as the willows mature and begin to drape
over the edge of the lake, mayflies will find a suitable
habitat. A secondary benefit of this site stabilization effort
will then be the improvement of the local fishery.

Revegetation Benefits

The reintroduction of plants on or around an archeologi-
cal site can be one of the least visually intrusive stabiliza-
tion techniques available. Careful species selection
produces a vegetative cover that blends well with the
surrounding environment, and places a site in a more
“natural” setting. Properiy seiected species can also en-
hance a habitat for the faunal community that frequents
the site. As a result, habitat enhancement carries the
additional advantage of letting the archeological commu-
nity develop a protectionist alliance with groups whose
primary interests lie outside the area of cultural resource
management.

The use of vegetation as a means of achieving site stability
can be viewed as a soft approach in comparison to the
more traditional engineering approaches such as riprap
or revetments. Floral systems have the advantage of being
elastic, and species easily can be found that are adapted
to a broad range of micro-topographic settings. Vegeta-
tion can also effectively dissipate wind and water energy
that can destroy a cultural deposit.

Depending on the setting of a specific site, both types of
force can come into play. The majority of soil movement
that is stimulated by wind action takes place ina zone that
extends from the surface of the ground to heights that are
below 3 feet. Wind velocities necessary to move soil
particles are less than 13 miles per hour at a height of 1
foot above the ground. Once wind-generated soil move-
ment starts, velocities less than 13 miles per hour are
likely to be sufficient to continue soil loss. Since 62
percent to 97 percent of soil loss activity occurs in the
3-foot vertical zone closest to the ground, vegetation that
exceeds 3 feet in height will serve to filter soil agitated by
a driving wind and at the same time lessen the force of
the wind (Gray and Leiser 1989:12-13).



US. Army Corps of Engineers Waterways Experiment Station
1984 Shore Protection Manual, Volumes I and II. Coastal Engincering Rescarch Center, U.S. Army Corps of Engineers
Waterways Experiment Station, Vicksburg, MS.

U.S. Department of Agriculture
1976 Plant Materials Study: A Search for Drought-Tolerant Plant Materials for Erosion Control, Revegetation, and Landscap-
ing along California Highways. Soil Conservation Service Research Project, USDA/SCS LPMC-1, Davis, CA.

Vogel, Willis G.
1981 A Guide for Revegetating Coal Mine Soils. General Technical Report NE-68. U.S. Forest Service, Northeastern Forest
Experiment Station, Berea, KY.

Young, W. C.
1973 Plants for Shoreline Erosion Control in Southern Areas of the United States. In, Man-Made Lakes: Their Problems and
Environmental Effects. Geophysical Monograph Series No. 17, American Geophysical Union.

Annotated Bibliography

Andropogon Associates, Ltd.
1989 Earthworks Landscape Management Manual; Section I. Prepared for the Mid-Atlantic Regional Office, National Park
Service, Philadelphia, PA.

This manual’s primary focus is to develop management strategies and interpretive guidelines that resolve current conflicts
between the requirements for preservation and the impacts of interpretation and visitor use at earthwork sites. The manual
is intended to serve as a guide for all earthworks in the National Park Service (NPS) system and for application to similar
environments within the NPS system with limited study. A major observation noted during the review of the sites evaluated
for the preparation of the manual was that earthwork sites stabilized by healthy, native plant communities are in the best
condition, while some current management practices have contributed directly to the degradation of the resources. The
manual is divided into two major sections. The first section is a review and evaluation of current management practices
and an assessment of present vegetative cover types. Recommendations are made for an overall management program
aimed at integrating preservation and interpretation objectives. The second section begins with procedures for evaluating
and monitoring a site with respect to the proposed guidelines. Since many of the management techniques focus on native
plant communities, the management of which is unfamiliar to many park employces, workshops at various levels of NPS
employees were held. Actual hands-on instruction sessions were used as a means of both teaching park employees how
to use the soil bioengineering techniques and to begin restabilization and revegetation on damaged ground surfaces that
needed immediate attention. Critical to the soil bioengineering techniques is the need to prioritize problem areas to include
both short term and long term management practices.

Brown, Margaret K.
1983 Mothballing Albany Mounds. American Archeology (formerly Contract Abstracts and CRM Archeology) 3G).

‘The Albany Mound site consists of some 40 to 50 mounds and 3 village areas and is owned by the Illinois Department of
Conservation. Preservation of the site, with a very limited budget, was a multidisciplinary effort. Invasion species were
removed from the site, and prairie grasses, brush, and trees that would have been a part of the original prairie community
‘were left to grow to maturity. Management of the prairie environment will be through controlled burns, and the expense
of maintenance will be minimized.

Hafenrichter, A. L., John L. Schwendiman, Harold L. Harris
1968 Grasses and Legumes for Soil Conservation in the Pacific Northwest and Great Basin States, Agricultural Handbook
339, Soil Conservation Service, U.S. Department of Agriculture, Washington, DC.

This handbook was revised in 1979 and is no tonger listed as a handbook. It identifies grasses and legumes that are suitable
for erosion control, categorizing them according to the projected life of each. Each species is discussed, and line drawings
as wellas Agricultural Zone maps are included. Planting directions are a part of each species description, and recommended
planting rates are listed in an appendix.

Knutson, Paul L.
1977 Planting Guidelines for Dune Creation and Stabilization. Coastal Engincering Technical Aid 77-4, Coastal Engineering
Research Center, Fort Belvoir, VA.

Beach grasses have been used to stabilize dune systems. Techniques are available to propagate beach grasses. Guidelines
for selecting plants and planting methods, obtaining plants, storing, planting and maintaining plants, and estimating labor
requirements for dune vegetation projects are included.

U.S. Department of Agriculture
1976 Plant Materials Study: A Search for Drought-Tolerant Plant Materials for Erosion Control, Revegetation, and Landscap-
ing Along California Highways. Soil Conservation Service Research Project, USDA/SCS LPMC-1, Davis, CA.



Figure 1. Pharr Mounds, Natchez Trace Parkway, MS, stabilized
with native grasses. (All photos courtesy of the University of
Mississippi.)

The types of water-generated erosion that are most fre-
quently mentioned as impacting archeological deposits
are sheet erosion and stream channel erosion. In many
areas, lacustrine erosion of sites has a greater impact on
archeological materials than channel erosion, but a one-
to-one comparison is not possible since two very different
kinds of forces are operating to remove the cultural
deposit.

Cultural resources managers, including archeologists, sel-
dom recognize the impact that rainfall has on unvege-
tated and unprotected surfaces. Raindrop impact can
cause soil particles to move as much as 2 feet vertically
and 5 feet laterally on level surfaces and, if a sufficiently
steep gradient is present, slope movement of soil can
occur (Gray and Leiser 1989:12-13). From the perspec-
tive of energy, raindrop impact generates greater kinetic
forces than water that causes sheet erosion. Soil move-
ment results from both rain and sheeting water with
raindrops serving to dislodge individual soil particles that
are then moved farther by the sheet erosion process.

The volume of soil removed through sheet erosion is
increased also as a result of frost heave, since this heaving
action will uniformly loosen the soil. Some counter-ero-
sion compaction occurs as rain falls on unprotected soil,
but the rate of compaction is not sufficient to prevent
sheet erosion from occurring.

The destructive force of various forms of erosion can be
lessened, if not completely stopped, in many situations
through the use of carefully selected vegetation. As the
lateral roots of vegetation spread and intermingle, the soil
becomes bound together and acts like a composite mate-
rial. Stresses in the soil are transferred to the root fibers,
which have relatively high tensile strength, and in this
manner the soil is reinforced and strengthened (Gray and
Leiser 1989:39).

In aquatic environments where moving water pressures
are fairly constant on the vegetation, a well established
stand of grass will react accordingly and can reduce
stream velocity and wave forces by as much as 90 percent
(Keown, Oswalt, Perry, and Dardean 1977:59). Mitiga-

tion of lateral shear force is accomplished by a variety of
plants through the development of special stabilizing
tissue and root stiffening and strengthening (Schiechtl
1980:208). Mechanical stabilization techniques do not
exhibit this self-regulating capability, nor are they pliable.

Budgetary constraints make the use of vegetation an
especially attractive choice because of the low cost of
initial installation and post-placement maintenance. In
addition, plantings can be used in combination with a
number of mechanical stabilization techniques and fur-
ther strengthen the mechanical installations. In most
cases, no special labor expertise is required to put plant-
ings in place, and labor costs can be held at a minimum.
Plant installation is, however, a labor intensive operation.

When necessary, vegetation can be reestablished without
disrupting a cultural deposit by using seed-bearing spray
mulches or by seeding beneath biodegradable mats. The
use of mulches and matting can add appreciably to the
cost of a revegetation effort. As a cost cutting measure,
used carpeting can sometimes be substituted for matting
at no cost. Frequently, planting materials such as willows
can be obtained locally, which can further reduce instal-
lation costs.

Plant materials have the additional advantage of adapting
toa wide variety of environmental conditions and topog-
raphical features. Maiden cane (Panicum hemitomon
Schult.), which has been tested for its capabilities as a
mechanism for erosion control, will grow in shallow
water, across a shoreline, and up a bank for a short
distance (Young 1973). Similarly, species can be obtained
that will grow on dry soils (Haffenrichter, et al. 1968; U.S.
Department of Agriculture 1976), on sand dunes (Knut-
son 1977), and in rocky or badly disturbed terrains (Vogel
1981). Some degree of control of ultimate plant height
can be exercised during the plant selection process, and
important anti-looting protection can also be obtained
through careful plant selection.

Once established, a protective live vegetative cover re-
quires little or no maintenance. Grasses can be managed
through hay-cutting. In addition to maintaining an attrac-
tive appearance, haying has the potential of being a
no-cost operation that could generate a portion of the
site’s maintenance funds.

Revegetation Limitations and
Liabilities

Revegetation, like other stabilization techniques, is not
without its own set of liabilities, and these must be
carefully considered and weighed against its advantages.
An assumption that must be accepted as a part of most
stabilization projects is that, since a significant resource
is being lost, some negative effects resulting from the
stabilization effort are acceptable and preferable to the
continuing loss of the site. In a revegetation effort a small



Figure 2, Winterville Mounds in Mississippi with a dense growth
of Johnson grass (Shorghum halepense) used for stabilization and
traffic routing.

amount of additional site loss can be predicted before the
plantings reach their maximum protection potential.

Root Disturbance

The most frequently voiced objections to site revegeta-
tion center around the intrusion of roots into the cultural
deposit. Beyond doubt, root growth can disrupt and
contaminate what may appear to be an otherwise undis-
turbed deposit. With the exception of historic and late
prehistoric sites, forests and grasslands have covered
many of the sites in North America, and such site con-
tamination and disruption has already taken place.

‘The potentially negative impacts from a revegetation
program can be recognized, and ways to deal with those
impacts can be identified during the project design proc-
ess. Perhaps the best approach to problem solving in
planning for revegetation stabilization is to recognize two
broadly defined kinds of disruptions. One may be of a
physical nature while the other may be biochemical.

Within the context of an archeological deposit, physical
disruption includes the lateral and vertical displacement
of artifacts and biofacts and the interruption of the gen-
eral contimuity of the archeological deposit. Bio-chemical
disruption stems from changes in soil pH, changes in the
hydrological characteristics of the cultural deposit, and
changes in the microfaunal community, which could in
turn alter the chemical constituency of the deposit.

The majority of the physical disruptions that a site expe-
riences from revegetation derives from the root systems
of the cover species. The depth and lateral spread of
various plants is species-specific, as some species are
more deeply rooted than others, while some species have
a greater lateral distribution of the supporting roots
(Meyer and Anderson 1939:266-267). However, knowl
edge of the variability of root system development for
specific species is not sufficient to allow prediction of
root growth and the concomitant potential for site distur-
bance. Other factors, many of which are specific to site

location, must be taken into account. Among these are
depth of the water table, the presence of a subsurface
hardpan, buried sand strata, and gravel deposits.

Primary root systems, such as taproots and the laterals
that radiate from them, are likely to cause the most site
disruption since these are the largest roots in a complex.
The secondary root system of most species is threadlike
or fibrous and generally too small to pose any displace-
ment problems. These smaller roots do have the potential
of invading small spaces in artifacts, bone, and charcoal,
and in sufficient numbers or size can wedge these mate-
rials apart. This kind of potential destruction is likely to
be minimized since the nature of these roots is such that
impenetrable, non-nutrient bearing substances will cause
the roots to grow in another direction (Laycock
1967:C21-C22). By the same token, if archeological ma-
terial is not cracked or broken, the potential wedging
action of secondary roots is not likely to pose a problem.
Primary roots are generally of sufficient size that artifacts
will be displaced rather than broken or destroyed by
them.

Perhaps the most destructive physical impact that floral
cover can have on an archeological deposit comes from
overtumed trees. Since the majority of the primary root
system of most trees is within the first few fect below the
surface of the ground (Meyer and Anderson 1939:267),
blowdowns are likely to pull large chunks of soil and
artifacts from a cultural deposit. Tree throws can produce
large holes that are subject to being refilled by accumu-
lated leaves and the materials that were pulled up by the
falling tree. This material must be accounted for in sub-
sequent scientific excavations.

‘This points out the care that should be exercised in the
selection of species to be used in revegetation projects.
Species of larger vegetation such as trees that have heavy
crowns with broad lateral root systems should generally
be avoided. Similarly, species that have massive and deep
root systems should be avoided to insure that deep dis-
turbance is minimized.

Bio-Chemical Disruptions

Biochemical destruction of archeological materials that
may result from revegetation seems to be much less of a
problem than site destruction from physical forces. The
chemical composition of the leaf fall of different plant
communities varies according to the predominant spe-
cies of the community and will vary somewhat within a
community depending on the volume of litter produced
and the age of the dominant species. Soil pH is controlled
by plant litter to a relatively shallow depth, being princi-
pally confined to the humic zone, while the pH of soils
beneath the humic layer reflects the petrographic nature
of the substrata (Braun-Blanquet 1932:245).

When a plant community changes as a result of increasing
numbers of an invasion species, soil pH may change to
reflect the character of the invaders. In so far as the