m United States

Department of ,-&iP Agriculture

Forest Service I\uaGuI bB I IAWbG

Southern Research SO-382

Station December 1995

Long-Term Responses of Understory Vegetation on a

Highly Erosive Louisiana Soil to Fertilization

James D. Haywood and Ronald E. Thill

SUMMARY

Responses of vegetation on highly eroded Kisatchie

soils to a broadcast application of 600 lb/acre of 16-30-l 3

granular fertilizer were monitored for 12 years. Understory woody and herbaceous vegetation responded to

fertilization immediately, and thus the soil surface was

protected from erosion sooner in the fertilized area than

in the two unfertilized areas. After 1 year, herbage on

the fertilized area increased to 4,712 lb/acre, and woody

plants shaded about 13 percent of the soil surface. Herbage and shade cover increased more slowly on the two

unfertilized areas. After 12 years, herbaceous plant yield

was 964 lb/acre in the fertilized area and averaged 614

lb/acre in the unfertilized areas, and understory woody

plants shaded 19 percent of the soil surface in the fertilized area and an average of 27 percent of the soil surface in the unfertilized areas. The frequencies of

occurrence of many plant species increased or remained

almost constant, but low panicums, Dicanthelium spp.,

disappeared from all areas over the 12-year period.

INTRODUCTION

The Kisatchie soil series (fine, montmorillonitic, thermic, Typic Hapludalfs) has the highest erosion potential

of any soil on the 600,000-acre USDA Forest Service,

Kisatchie National Forest (Thill and Bellemore 1986).The

Kisatchie series occurs on approximately 28,200 acres

of National Forest land in Louisiana, with about 12 percent on slopes less than 5 percent, 65 percent on slopes

of 5 to 40 percent, and 23 percent in gullies. This series

usually has thin surface horizons, high acidity, low natural fertility, relatively sparse vegetation, and longleaf pine,

Pinus palustris Mill., as the dominant forest type.

Prescribed burning is restricted on Kisatchie soils because of reported increases in soil erosion after winter

burns (Thill and Bellemore 1986). One way to increase

vegetative cover to reduce soil erosion is the application

of fertilizers. In May 1982, five sites totaling 220 acres

were fertilized to determine understory vegetation responses to nutrient amendment on sites where burning

was not practiced. Thill and Bellemore (1986) reported

vegetation responses through the third year after treatment. Vegetation responses on two of the sites through

12 growing seasons after fertilization are summarized in

this report.

STUDY SITES AND METHODS

The field work was done in west-central Louisiana on

the Kisatchie National Forest’s Kisatchie Ranger District.

Site 1 (47 acres) supported a 44-year-old sparsely

stocked pole-timber stand consisting mostly of longleaf

pine but including some loblolly pine, P. taeda L. Site 2

(49 acres) was logged and then planted with seedling

loblolly pine in February 1982. Longleaf pine had dominated Site 2 prior to logging. The 50-year site index for

longleaf pine was 40 feet for Site 1 and 60 feet for Site 2,

which are below the average 50-year site index of 80

feet for longleaf pine on the Kisatchie National Forest.

The 50-year site index for loblolly pine averages 65 feet

on Kisatchie soils and 90 feet on the Kisatchie National

Forest.

Samples of pine foliage and soil were analyzed for nitrogen, phosphorus, and potassium concentrations. On

the basis of these analyses (table 1 ), 16-30-l 3 granular

fertilizer was applied by helicopter at the rate of 600 lb/

acre to parts of Sites 1 and 2 in May 1982. Untreated

g-acre strips along the edges of the fertilized areas served

as controls.

Southern Research Station, U.S. Department of Agriculture, Forest Service,

P.O. Box 2680, Asheville, NC 28802.
Table 1. - Preliminary foliar and soil analyses for Sites 1 and 2

Foliage Soil

Site Plant Type N P K P

------________---_-_______ s/ks __-____________-______ --ppm--

Site 1 Longleaf pine 9.1* 0.63* 3.2 0.8

Loblolly pine 10.3* 0.71’ 2.9 0.8”

Site 2 Loblolly seedlings+ - - - 0.7*

*Nutrient concentration is below the critical level for optimum plant development; fertilization was

recommended.

Beedlings were in first growing season, and no foliar samples were taken.

Vegetation on six 100~ft-long permanent transects in

each fertilized and control area was measured. The six

transects in each fertilized area were located randomly.

The transects in the adjacent control area were then

selected to match the vegetation along the fertilized

transects.Transects were confined to slopes of less than

10 percent. Vegetation within gullies was not measured,

but some general observations were made.

A marked line was stretched tightly along each 1 00-ft

transect, and a 3/4-inch-diameter circular loop was used

at 100 equally spaced points along the marked line to

make ocular vegetation measurements (Parker and Harris 1959). The vegetation measurements (ground cover,

herbaceous plant composition, and absolute frequency)

were made in May 1982 just before treatment and again

in May 1983, May 1985, and November 1993. Ground

cover was reported as percentage bare ground, rock,

and vegetative cover (defined as litter plus live vegetation). The percentage of ground cover in each category

was to the nearest 5-percent increment; i.e., 0,5, 10, . . . .

100 percent. Herbaceous plants rooted within the loop

were tallied, and plant composition by absolute frequency

was calculated from these tallies. Line intercept methods (Canfield 1941) were used to estimate woody plant

cover to a height of 5 feet over the transects each time

the other vegetation measurements were made.

The herbaceous standing crop (ovendried weight) was

estimated in late August 1982, August 1983, August

1985, and November 1993. The herbaceous material in

seven 1 .5-ft2 subplots within 6.6 feet of each transect

was clipped, dried, and weighed. There were 168 subplots (2 sites x 2 treatments [fertilized and control] x 6

transects per site/treatment combination x 7 subplots per

transect).

Before the November 1993 plant survey, the understory vegetation on half of the fertilized transects in Site

2 was removed to improve habitat conditions within a

red-cockaded woodpecker, Picoides borealis, (FEW)

colony. Disturbance by animals caused extensive gully

erosion in another third of the transects. Since only two

of the fertilized transects at Site 2 were left undisturbed,

data from the fertilized transects at Site 2 were not used.

RESULTS

Ground Cover

Fire was excluded from the study sites over the 12-

year period to allow vegetation to develop and litter to

accumulate so that soil loss would be reduced. Before

treatment, vegetative cover (litter and live vegetation) was

64 percent in fertilized transects at Site 1 and 68 percent

in the control transects at that site (table 2). One year

after fertilization, vegetative cover averaged 96 percent

in the fertilized transects. On the control transects, cover

increased from 68 percent in May 1982 to 97 percent in

November 1993. Vegetative cover on fertilized transects

was 91 percent in November 1993.

On Site 2, there was little change in vegetative cover

for the first four growing seasons (table 2). However, logging debris was present in 1982, and vegetation and litter covered 86 percent of the soil surface at the beginning

of the study. Litter accumulated over the 12-year period;

therefore, vegetative cover averaged 97 percent in 1993.

Because the percentage of ground cover classed as

rock changed little from May 1982 to November 1993,

erosion, which would expose more rock at places already

James D. Haywood is a silviculturist in Pineville, LA, and Ronald E. Thill is a supervisory research wildlife biologist in Nacogdoches, TX, both with

the U.S. Department of Agriculture, Forest Service, Southern Research Station.

2
Table 2. - Percentages of vegetative cover, rock, and bare ground on control and fertilized areas in

May 1982 (before fertilization), May 1983, May 1985, and November 7993

Ground cover

Site Treatment Year Vegetation Rock Bare ground

----___________________ percent ----------__-__________

Site 1 Control 1982 88.2’ 1.5 30.3

1983 77.7 1.5 20.8

1985 84.4 1.9 13.7

1993 97.2 0.8 2.0

Fertilized 1982 84.0 0.0 36.0

1983 95.6 0.0 4.4

1985 96.0 0.0 4.0

1993 90.8 0.0 9.2

Site 2t Control 1982 85.7 1.8 12.5

1983 88.8 2.5 8.7

1985 85.8 2.8 11.4

1993 96.5 2.2 1.3

*Vegetative cover included both plant litter and live vegetation.

tFertilized transects on Site 2 were not used because prior to measurement either the understory

vegetation was removed to improve habitat conditions within a red-cockaded woodpecker colony or

disturbance by animals had caused extensive erosion across the transects.

bald, was counterbalanced by the accumulation of litter

on existing bald places (table 2). Little bare ground remained at either study site by 1993, and thus the exclusion of fire reduced exposed soil with or without

fertilization.

Woody Plants

Woody-plant cover in the understory was similar at all

sampling areas just before treatment in May 1982 (table

3). Carolina jessamine, Gelsemium sempervirens (L.) Ait.

f.; yaupon, llex vomitoria Ait.; southern bayberry or

waxmyrtle, Myrica cerifera L.; and blackjack oak, Quercus

marilandica Muenchh., were the principal species on Site

1. Yaupon; southern bayberry; tree sparkleberry,

Vaccinium arborem Marsh.; and blueberries; primarily

V: e//iotiiiChapm. and K virgatumchapm., were the principal species on Site 2.

At Site 1, woody cover in the understory of the fertilized transects increased from 6 percent in May 1982 to

13 percent in May 1983, and woody cover on the control

transects increased from 6 percent in May 1982 to 8

percent in May 1983 (table 3). At Site 2, understory woody

cover on the control transects was 5 percent in both May

1982 and May 1983. In November 1993, understory

woody cover averaged 19 percent on the fertilized

transects and 26 percent on the control transects at Site

1. At Site 2, understory woody cover averaged 28 percent on the control transects in November 1993. It is

known that fertilization increases the leaf area of pine

trees (Teskey and others 1994), and so the slower

long-term development of understory woody cover in the

fertilized transects may have resulted from increased

overstory shading.

By November 1993, yaupon, southern bayberry, and

loblolly pine contributed most to the increase in understory woody cover at Site 1 (table 3). The understory

woody species present at Site 2 in November 1993 were

yaupon, southern bayberry, loblolly pine, tree sparkleberry, and blueberries.

Herbaceous Plants

The herbaceous standing crop varied substantially

from year to year (table 4) with ovendried herbaceous

production on control areas averaging 1 ,011 lb/acre in

August 1982 and 614 lb/acre in November 1993. The

fertilized area produced an average of 4,712 lb/acre 3

months after treatment, but the amount of production

decreased to 594 lb/acre by November 1993. The decline in herbaceous production was associated with an

increase in woody plant cover in the understory (table 3)

and probably with greater leaf area in the overstory.

Herbage composition values summarized in table 5

were calculated as absolute frequencies; i.e., the number of rooted-plant occurrences/total number of sampling

points. In 1982, low panicums, Dicanthelium spp., and

pinehill bluestem, Schizachyrium scoparium var.

divergens (Hack.) Gould, were the most abundant

grasses on both study sites (table 5). Among the grass-
Table 3. - Line-intercept coverage (percent) of principal woody plants on control and fertilized transects in May 7982

(before fertilization), May 1983, May 1985, and November 1993

Site 1 Site 2*

Control Fertilized Control

Taxa 1982 1983 1985 1993 1982 1983 1985 1993 1982 1983 1985 1993

________________________________________------------- percent ________________________________________------------

Gelsemium sempervirens

Carolina jessamine 0.6 1.0 1.6 0.0

9.0

4.7

0.7

9.7

0.7

0.0

0.0

0.7

0.0

25.5

0.6 1.7 1.9

2.8 6.7 6.9

0.0 0.3 0.4 1.3 0.0

5.3 1.8 1.8 2.4 15.0

3.5 0.5 0.2 0.9 1.5

1.2 0.1 0.0 0.0 0.0

7.5 0.1 0.1 1.0 2.3

hex vomitoria

Yaupon

Myrica cerifera

Southern bayberry

Pinus palustris

Longleaf pine

Pinus taeda

Loblolly pine

Quercus marilandica

Blackjack oak

&bus spp.

Blackberries

Vaccinium arboreum

Tree sparkleberry

Vaccinium spp.

Blueberries

Others

Totals

2.9 3.4 3.6

0.7 1.3 1.0

0.5 0.5 0.4

0.1 co.1 0.1

1.4 1.3 1.4

0.0 0.0 0.0

0.0 0.0 co.1

<O.l 0.0 0.0

<O.l 0.2 0.1

6.3 7.7 8.2

1.0 2.3 3.2

0.1 0.0 <O.l

0.1 0.3 0.8

0.6 0.9 0.5 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0

0.1 0.3 0.2

0.0 <O.l 0.1 <O.l 0.0

0.0 0.8 0.8 1.1 3.3

0.1 0.2 0.4 1.3 1.1 1.6 1.4 6.2

0.2 0.2 0.5 0.0 0.4 0.3 0.2 0.0

5.6 12.6 14.4 18.8 5.2 5.3 8.3 28.3

‘Fertilized transects on Site 2 were not used because prior to measurement either the understory vegetation was

removed to improve habitat conditions within a red-cockaded woodpecker colony or disturbance by animals had caused

extensive erosion across the transects.

like and forb plants, the beakrushes, Rhynchospora spp.;

fringe razorsedge, Scleria data Michx.; and rayless goldenrod, Bigelowia nutfallii L.C. Anderson, were the most

abundant.

The low panicum grasses began declining in absolute

frequency of occurrence after the initial inventory and

were not found on any of the transects in 1993 (table 5).

Other taxa also declined in frequency on certain transects

during the 12-year period: threeawns, Aristida spp.;

cutover muhly, Muhlenbergia expansa (DC.) Trin.; fringe

rasorsedge (on the fertilized transects only); stargrasses,

A/et& spp.; and gayfeathers, Liafris spp.

However, the absolute frequency of pinehill bluestem

increased during the study, and following fertilizer treatment, pinehill bluestem formed dense stands 3 to 5 feet

tall over much of the fertilized area and accounted for

most of the increase in herbage by August 1982 (Thill

Table 4. - Herbaceous standing crop (ovendried weights) on control

and fertilized areas during August of the treatment year

(1982), August 1983, August 1985, and November 1993*

Site 1 Site 2+

Year Control Fertilized Control

____________________________ Lb/acre __________________________

1982 770 4,712 1,252

1983 849 2,239 1,872

1985 1,971 1,120 891

1993 751 964 476

*The fertilizer was applied in May 1982.

+Fertilized transects on Site 2 were not used because prior to measurement either the understory vegetation was removed to improve

habitat conditions within a red-cockaded woodpecker colony or disturbance by animals had caused extensive erosion across the

transects.

4
Table 5. - Herbaceous composition values (frequency of occurrence) on control and fertilized transects in May 7982

(before fertilization), May 1983, May 1985, and November 1993

Taxa

Site 1 Site 2

Control Fertilized Control

1982 1983 1985 1993 1982 1983 1985 1993 1982 1983 1985 1993

________________________________________------------- percent ____________.___________________________------------

Grasses

Aristida purpurascens

Arrowfeather threeawn 0.0

Aristida spp.

Threeawns 0.2

Dicanthelium spp.

Low panicum grasses 6.4

Muhlenbergia expansa

Cutover muhly 1.8

Schizachyrium

scoparium var. divergens

Pinehill bluestem 3.8

S. tenerum

Slender bluestem 0.0

Others: mostly Panicurn,

Andropogon, and

Sporobolus junceus 0.2

Subtotal 12.4

Grasslike plants

Rhynchospora spp.

Beakrushes 5.5

Scleria cilia ta

Fringe razorsedge 1 .O

Others: mostly Juncus 0.4

Subtotal 6.9

Other herbs

Aletris spp.

Stargrasses 0.4

Aster dumosa

Bushy aster 0.8

Bigelowia nuttallii

Rayless goldenrod 9.0

Helianthus angustifolius

Swamp sunflower 0.9

Liatris spp.

Gayfeathers 0.1

Cladonia dimorphoclada

A lichen 1.9

Selaginella spp.

Spikemosses 0.9

Others: mostly

Heterotheca graminifolia

and Solidago nitida 1.7

Subtotal 15.7

Total 35.0

0.1 0.0 0.0 0.0 1.9 0.0 0.2 0.0 0.1 0.0 0.7

0.9 0.8 0.0 0.2 0.1 0.0 0.0 0.8 1.0 0.0 0.8

5.4 6.1 0.0 3.1 4.3 1.1 0.0 11.0 10.2 6.1 0.0

1.1 1.9 0.8 0.8 1.2 1.6 0.7 0.0 0.1 0.0 0.0

6.4 7.6 27.8 7.4 23.0 22.8 24.2 7.2 6.6 7.7 21.8

0.3 0.6 3.2 0.0 0.1 0.5 1 .o 0.4 0.4 1.6 2.2

0.1 0.0 9.2 0.0 0.5 0:6 7.5 0.0 0.0 0.0 8.9

14.3 17.0 41.0 11.5 31.1 26.6 33.6 19.4 18.4 15.4 34.4

6.8 5.8 3.2 3.8 2.3 1.3 3.7

1.6 1.6 0.8 1.4 2.1 1.2 0.2

0.2 0.0 0.0 1.0 0.2 0.0 0.7

8.6 7.4 4.0 6.2 4.6 2.5 4.6

0.4 0.2 0.0 0.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.4 0.1 0.7 0.2 0.0 0.8 1.0 0.0 0.1 0.1 0.0

10.3 10.9 6.7 12.6 7.3 4.0 14.3 4.0 4.2 4.5 7.0

1.1 0.4 1.2 0.5 0.9 0.9 1.2 0.9 1.8 3.1 0.5

1.4 1.8 0.0 0.1 0.5 0.1 0.0 1.4 0.8 2.6 0.2

2.8 3.6 2.8 2.8 0.4 0.1 8.7 1.8 2.1 1.6 4.7

0.4 1.2 21.5 0.6 0.6 1.8 3.9 0.8 1.9 2.9 4.2

1.4 1.6 3.8 1.3 1.3 1.4 2.3 1.4 1.7 1.7 1.3

18.2 19.8 36.7 18.2 11.0 9.1 31.4 10.3 12.6 16.5 17.4

41.1 44.2 81.7 35.9 46.7 38.2 69.6 32.6 33.8 33.9 55.0

1.3 0.8 1.5 1.0

1.4 1.4 0.5 1.7

0.2 0.6 0.0 0.0

2.9 2.8 2.0 2.7

‘Fertilized transects on Site 2 were not used because prior to measurement either the understory vegetation was

removed to improve habitat conditions within a red-cockaded woodpecker colony or disturbance by animals had caused

extensive erosion across the transects.

5
and Bellemore 1988). A thick mat of litter accumulated

as this herbage died over winter, and this mat smothered subsequent herbage production. Weight of the

standing crop in the fertilized area decreased by 52 percent between August 1982 and 1983 and decreased by

76 percent between August 1982 and 1985 (table 4).

However, vegetation and litter still covered 91 percent of

the soil surface in the fertilized area in 1993 (table 2).

Slender bluestem, Schizachyrium tenerum Nees; Panicum spp.; Andropogon spp.; and pineywoods dropseed,

Sporobolusjunceus (Michx.) Kunth-as well as the dominant pinehill bluestem-were more frequent on both

study sites in November 1993 than they were in May

1982 (table 5). The beakrushes were still common on

both study sites in 1993. Rayless goldenrod was still

found frequently on areas where it was common in 1982,

as were the lichen Cladonia dimorphoclada (no common

name); spikemosses, Selaginella spp.; goldaster,

Heterotheca graminifolia (Michx.) Shinners; and shiny

goldenrod, Solidago nifida T.&G.

DISCUSSION

The fertilizer used in this study was a custom formulation designed to meet the nutrient deficiencies of the pine

trees rather than those of the native herbage (Thill and

Bellemore 1986). However, forest managers now prefer

to use diammonium phosphate, which increases pine

productivity on upland forest soils regardless of other

management practices (Haywood and Burton 1990,

Haywood and Tiarks 1990).

Nutrient amendment is largely unnecessary to protect

Kisatchie soils from erosion provided fire is excluded,

but the use of fertilizer speeds plant growth, and the soil

is protected sooner if fertilizers are used. Also, fertilizer

may have to be applied where gullies and balds are common. Thill and Bellemore (1986) observed that grass

became well established near the gullies and on the more

level, lower portions of several gullies in the fertilized area.

The presence of this ground cover may have reduced overland flow into the gully and thereby gully-bank cutting.

Protection from erosion is a management objective on

Kisatchie soils. Neither study site was burned during the

12-year study period, and the herbaceous standing crop

declined as the woody understory and forest floor litter

developed. Several herbaceous plant taxa declined in

frequency by the end of the study, and the accumulation

of litter was probably largely responsible for the decreases

in plant occurrence. However, other herbaceous plant

taxa increased in occurrence.

Management of the longleaf pine ecosystem to protect understory herbaceous plant communities is another

objective on Kisatchie soils. The need to use fire to reduce litter accumulation and help maintain herbaceous

vegetation in this ecosystem may outweigh the importance of maximizing erosion control.The exclusion of fire

no doubt contributed to the general decrease in herbaceous plant productivity over the 1 e-year period, especially on the fertilized area where a very productive cover

of pinehill bluestem developed after fertilizer application.

LITERATURE CITED

Canfield, R.H. 1941. Application of the line interception

method in sampling range vegetation. Journal of Forestry. 39(4): 388-394.

Haywood, J.D.; Burton, J.D. 1990. Phosphorus fertilizer,

soils, and site preparation influence loblolly pine productivity. New Forests. 3(4): 275-287.

Haywood, J.D.; Tiarks, A.E. 1990. Eleventh-year results

of fertilization, herbaceous, and woody plant control

in a loblolly pine plantation. Southern Journal of Applied Forestry. 14(4): 173-l 77.

Parker, K.W.; Harris, R.W. 1959. The 3-step method for

measuring condition and trend of forest ranges: a resume of its history, development, and use. In: Techniques and methods of measuring understory

vegetation: Proceedings of the symposium; 1958 October; Tifton, GA: U.S. Department of Agriculture, Forest Service, Southern and Southeastern Forest

Experiment Stations: 55-69.

Teskey, R.O.; Gholz, H.L.; Cropper, W.P., Jr. 1994. Influence of climate and fertilization on net photosynthesis

of mature slash pine. Tree Physiology. 14(11): 1215-

1227.

Thill, R.T.; Bellemore, J.C. 1986 Understory responses

to fertilization of eroded Kisatchie soil in Louisiana. Res.

Note SO-330 New Orleans, LA: U.S. Department of

Agriculture, Forest Service, Southern Forest Experiment Station. 6 p.

6