Changes in soil and litter arthropod abundance following tree

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Forest Ecology and Management 202 (2004) 195–208

Changes in soil and litter arthropod abundance following

tree harvesting and site preparation in a loblolly pine

(Pinus taeda L.) plantation

Simon B. Birda,*, Robert N. Coulsonb, Richard F. Fisherc

aCentre for Ecology and Hydrology Bangor, School of Agriculture and Forestry Sciences, University of Wales Bangor,

Deiniol Road, Bangor, Gwynedd LL57 5UP, UKbKnowledge Engineering Laboratory, Department of Entomology, Texas A&M University, College Station, TX 77843, USA

cTemple Inland, PO Drawer N, 303 South Temple Drive, Diboll, TX 75941-0814, USA

Received 16 June 2003; received in revised form 5 May 2004; accepted 8 July 2004

Abstract

Soil and litter arthropods are important in many forest ecosystem processes where they help to regulate nutrient dynamics

and soil quality, and are useful bioindicators of ecosystem condition and change. This study was initiated in response to

concerns about possible decline in site productivity due to intensive forestry practices. We investigated the effects of tree

harvesting and site preparation treatments on soil and litter arthropod abundance in a loblolly pine plantation in eastern

Texas, USA. Using soil and litter cores, we sampled abundance of selected arthropods over two years following tree

harvesting. Response to treatments varied somewhat among arthropod taxa. Acari (mites) and Collembola (springtails), the

numerically dominant taxa in core samples, were initially higher in abundance in less intensive harvesting and site

preparation treatments. However, after 2 years, abundance of these arthropods was comparable in all harvesting and site

preparation treatments. Fertilization with nitrogen and phosphorus had a strong positive effect on abundance of most

arthropod groups in the second year of the study. The recovery of arthropod abundance through time suggests that the

silvicultural practices used did not jeopardize the ecological integrity of the site. The results reported here contrast with

other similar studies which suggests that soil and litter arthropod communities respond differently in different geographic

locations and forest types. Further comparative and extensive studies of this nature are needed therefore for a deeper

understanding of the impacts of forest management practices.

# 2004 Elsevier B.V. All rights reserved.

Keywords: Soil and litter arthropods; Effects of forest management; Soil ecology; Silvicultural practices; Mites; Springtails

* Corresponding author. USDA-ARS Jornada Experimental

Range, New Mexico State University, MSC 3JER, Las Cruces,

NM 88003, USA. Tel.: +1 505 646 4152; fax: +1 505 646.

E-mail address: [email protected] (S.B. Bird).

0378-1127/$ – see front matter # 2004 Elsevier B.V. All rights reserved

doi:10.1016/j.foreco.2004.07.023

1. Introduction

Soil and litter arthropods are important components

of forest ecosystems, and they play a particularly

.

S.B. Bird et al. / Forest Ecology and Management 202 (2004) 195–208196

significant role in the process of decomposition. In

addition, these organisms affect porosity, aeration,

infiltration, and the distribution of organic matter

within the soil. Soil and litter arthropods can,

therefore, be useful bioindicators of the effects of

land management on nutrient dynamics and site

productivity.

There has been recent concern regarding the

possibility of detrimental ecological effects caused

by forest management practices in the United States.

Silvicultural practices have been placed under

increased scrutiny in respect to their environmental

impacts and effects upon site productivity and

biodiversity (Burger and Zedaker, 1993; Gupta and

Malik, 1996). Tree harvesting and site preparation

practices, as part of intensive management regimes in

North American forests, can lead to significant loss of

nutrients and organic matter from forest ecosystems,

alteration of soil physical properties, significant

disturbance to trophic systems, and overall decrease

in site productivity (Likens et al., 1970; Pritchett and

Wells, 1978, Pritchett and Fisher, 1987; Bormann and

Likens, 1994).

Studies investigating the decline of site productiv-

ity following harvesting and site preparation in

southern US pine (Pinus spp.) plantations have

demonstrated mixed results. In their review, Powers

et al. (1990) found that the reports of productivity

decline due to intensive forest management were

inconclusive. However, they suggested that site

preparation treatments causing soil compaction and

organic matter removal pose the greatest risk to site

productivity over successive rotations. The study of

the responses of soil organic matter, trophic system

dynamics, and decomposer communities to forest

management has not been comprehensive across

geographic areas and the wide variety of management

techniques employed in North American forest

plantations. This may in part explain the lack of

agreement among results. Field studies designed to

analyze the effects of disturbance and management

practices on soil organic matter, and the biological

processes that regulate soil fertility and nutrient

conservation, are essential for defining sustainable

production systems (Gupta and Malik, 1996).

The goal of this study was to investigate the effects

of silvicultural practices of varying intensity on the

abundance of soil and leaf litter arthropod taxa in an

east Texas loblolly pine (Pinus taeda L.) plantation.

The objectives were (1) to measure the quantitative

response of this arthropod community to treatments of

different intensities and (2) to monitor the changes in

this arthropod community over a 2-year period

following tree harvesting and site preparation.

2. Methods and materials

2.1. Study site

The study site was located on land owned by

Temple-Inland Forest Products Corporation in Tyler

County, TX, USA. The site was located approximately

10 km south of Spurger, and just north of Fred, at

30.68N and 94.48W. Annual mean temperature is

19.4 8C and annual mean precipitation is 136 cm

(Griffiths and Bryan, 1987). Elevation ranges from 17

to 19 m above sea level.

The soil of the area is a Bowie–Caddo–Rains

association. This varies from an acid fine sandy loam

to an acid sandy clay loam, with variable drainage, and

a topsoil varying in depth from 12 to 45 cm. The

vegetation in the surrounding geographic area is

dominated by loblolly pine, longleaf pine (P. palustris

Mill.), shortleaf pine (P. echinata Mill.), and oaks

(Quercus spp.).

Prior to harvesting, the site was a 30 ha, 27-year-

old loblolly pine stand established by direct seeding

and thinned in corridors at age 15 years. At least three

harvests of pine have occurred in the past from this site

and there is no history of cultivation. The stand was

partitioned into 28 plots. Each plot was approximately

28 m � 42 m (0.12 ha) in size: large enough to allow a

14 � 14 grid of new seedlings to be planted on a 2 m �3 m spacing following tree harvesting and site

preparation. Four plots were allocated as a contiguous

undisturbed reference area and situated approximately

200 m from the rest of the site.

2.2. Treatments

Two harvesting, two site preparation, and two

fertilization treatments were arranged in a 2 � 2 � 2

factorial to give eight different treatment combina-

tions in a randomized block design with three blocks

based on generalized soil texture and drainage. Hence,

S.B. Bird et al. / Forest Ecology and Management 202 (2004) 195–208 197

3 of the 24 plots were randomly allocated to each one

of these 8 combinations.

Trees were harvested either with a hand-fell, bole-

only-removal method or with a whole-tree mechanical

harvesting procedure. Hand-felling employed hand-

held chainsaws to harvest trees, the tree boles were

removed with cranes to minimize physical distur-

bance, and the foliage and branch material was left at

the site. The mechanical treatment involved harvesting

trees with a feller-buncher with rotary cutter and

skidders, and all foliage, branch, and bark material

was removed along with the tree bole. Harvesting was

conducted between July and August 1994, and a total

area of approximately 10 ha was harvested.

In September 1994, the harvested area of the site

was treated aerially with broadleaf herbicides (ima-

zapyr and triclopyr at 0.5 and 1.12 kg/ha, respec-

tively). In October 1994, half of the 24 harvested plots

were subjected to a bedding procedure in which

topsoil was arranged into elevated rows for seedling

planting. Rows were approximately 50 cm high and

50 cm wide separated by 50 cm wide furrows, and

coarse woody felling debris was removed from the

elevated surface. All beds appeared to be in good

condition for the duration of the study. Bedding was

applied in October 1994. Loblolly pine seedlings were

planted in March 1995, but due to pales weevil

(Hylobius pales L.) damage, trees were pulled up, the

site re-treated with herbicide in September 1995, and

re-planted in February 1996. Harvested plots were

either left unfertilized or fertilizer was broadcast by

hand at a rate of 250 kg/ha with diammonium

phosphate (DAP) in May 1996. All treatments were

performed by Temple Inland Forest Products Corpora-

tion staff under supervision of R.N. Coulson.

2.3. Sampling

Core samples were taken using 10-cm deep, 5-cm

diameter plastic corers at random positions within

randomly selected plots. Individual sample points

were selected using random numbers. In bedded plots,

all samples were taken on the ridges of the elevated

beds and the depressions between beds were not

sampled. Cores were wrapped in aluminum foil and

packed in ice in the field to immobilize arthropods and

to equilibrate litter and soil temperature (Mitchell,

1974). Sampling was done at approximately the same

time of day (between 11 a.m. and 3 p.m.) during each

visit to the site to minimize the effects of diurnal

fluctuations in abiotic conditions and the resulting

vertical movement of the arthropod fauna (Seastedt

and Crossley, 1981). Cores were transported to a

laboratory and arthropods extracted using modified

Tullgren funnels. Arthropod samples were stored in

80% isopropyl alcohol. The fauna were identified to

suborder or family level, and abundance recorded to

generate an index of abundance for major taxonomic

groups.

Samples were removed from the site on a total of 24

dates between February 1994 and December 1996.

Five of those dates occurred before tree harvesting

occurred and 19 afterwards. Samples were taken at

approximately monthly intervals within this time

period. During the pre-harvest period, one core sample

was taken from four randomly selected plots of each

treatment block and two samples were taken from the

unharvested area. On each post-harvesting sampling

visit, two core samples were randomly taken from

plots of each of the eight treatment combinations and

two taken from the undisturbed plots.

2.4. Data analysis

Abundance data for numerically dominant arthro-

pod taxa (Mesostigmata, Prostigmata, Oribatida, and

Collembola) were normalized with a log (x + 1)

transformation (Macfayden, 1962) and analyzed by

analysis of variance using StatViewTM software

(Abacus Concepts Inc., 1996). The DAP fertilization

treatment was not applied until May 1996, so data

were split into pre- and post-fertilization time periods

for analysis. Data from between February 1995 and

May 1996 (pre-fertilization) were analyzed with a

two-way ANOVA based on a randomized block with

three blocks and a 2 � 2 factorial assignment of

harvesting and site preparation treatments (Zar, 1996).

Data from between May to December 1996 (post-

fertilization) were analyzed with a three-way ANOVA

as a 2 � 2 � 2 factorial. A critical level of a = 0.05 was

used in all cases. Abundance data from the undis-

turbed plots were not included in the ANOVA due to

the lack of randomization and spatial independence of

these plots. Pre-harvest data also were omitted from

ANOVA due to imbalanced sampling effort across

treated plots.


Fig. 1. Post-harvest mean abundance of Mesostigmata per core

sample for pre-fertilization (February 1995–April 1996) treatment

combinations. Error bars represent standard errors. Different letters

above bars indicate significant difference between treatments as

detected by ANOVA and Tukey’s post-hoc testing.

Mean abundance for different treatment combina-

tions, as well as for individual treatments, was

calculated from both pre- and post-fertilization time

periods to investigate any interaction between the

three treatment types (harvesting, bedding, and

Fig. 2. Post-harvest mean abundance of Prostigmata per core sample for p

Error bars represent standard errors. Different letters above bars indicate si

Tukey’s post-hoc testing.

fertilization). Total mean abundance of all arthropods

per core sample was calculated for each sampling date

to investigate temporal trends and overall response to

treatments.

3. Results

A diverse group of arthropod taxa was collected

from core samples. Acari (mites) were the most

abundant group collected, Oribatida being the

numerically dominant suborder in all samples. Data

analysis was focused on the four most abundant

arthropod groups: Mesostigmata, Prostigmata, Oriba-

tida, and Collembola.

3.1. Effects of harvesting technique

A varied response to harvesting treatment was

observed among arthropod taxa. During pre-fertiliza-

tion sampling, mean abundance of Mesostigmata,

Prostigmata, and Collembola was slightly higher in

treatment combinations that included hand-felling

compared to those that included mechanical-felling

(Figs. 1–4). During post-fertilization sampling, no

re-fertilization (February 1995–April 1996) treatment combinations.

gnificant difference between treatments as detected by ANOVA and


Fig. 3. Post-harvest mean abundance of Oribatida per core sample

for pre-fertilization (February 1995–April 1996) treatment combi-

nations. Error bars represent standard errors. Different letters above

bars indicate significant difference between treatments as detected

by ANOVA and Tukey’s post-hoc testing.

consistent differences between the two harvesting

treatments were observed in Acari and Collembola

(Figs. 5–8). Mean abundance of Prostigmata, Astig-

mata, Oribatida, Protura, Collembola, Psocoptera, and

Fig. 4. Post-harvest mean abundance of Collembola per core sample for pr

Error bars represent standard errors. Different letters above bars indicate si


Isoptera per individual treatment (as opposed to

combinations of different treatment) was higher in the

hand-fell treatment (Tables 1 and 2). Araneae and

Pseudoscorpiones were not detected from mechani-

cally-felled plots and detected in low abundance in

hand-felled plots (Table 1). ANOVA suggested no

significant differences in abundance of numerically-

dominant taxa between harvesting treatments prior to

fertilization (Table 2). Following fertilization, only

Collembola were significantly higher in hand-

felled plots, albeit at relatively low mean abundance

(Table 3).

3.2. Effects of bedding

During pre-fertilization sampling, Acari and

Collembola were higher in abundance in treatment

combinations that included the non-bedding treatment

compared to those that included bedding (Figs. 1–4).

These differences did not persist during post-

fertilization sampling, however (Figs. 5–8). Overall

mean abundance of Acari, Diplopoda, Protura,

Collembola, Isoptera, and Pselaphidae per individual

treatment was higher in the non-bedding treatment

(Table 1). Mean abundance of Symphyla, Psocoptera,

e-fertilization (February 1995–April 1996) treatment combinations.

gnificant difference between treatments as detected by ANOVA and


Fig. 5. Post-harvest mean abundance of Mesostigmata per core sample for post-fertilization (May–December 1996) treatment combinations.

Error bars represent standard errors. Different letters above bars indicate significant difference between treatments as detected by ANOVA and


and Formicidae were higher in the bedding treatment

(Table 1). Mesostigmata and Collembola were

significantly higher in abundance in non-bedded plots

during pre-fertilization sampling (Table 2), but no

significant post-fertilization differences were sug-

gested by ANOVA (Table 3). While not statistically

significant, mean abundance of Oribatida was

observed to be higher in bedded plots following

fertilization (Table 3).

3.3. Effects of fertilization

Fertilization had the most dramatic effect on

arthropod abundance. Mean abundance in treatment

combinations that included fertilization was higher for

all numerically dominant taxa (Figs. 5–8). Fertiliza-

tion led to an increase in the numerical dominance of

Oribatida, primarily at the expense of Collembola.

Overall mean abundance of Acari, Diplopoda,

Collembola, Isoptera, Psocoptera, and Formicidae

was higher in fertilized plots (Table 1). A few of the

rarer taxa, such as Diplura, Pselaphidae, and Dipteran

larvae, were lower in abundance in non-fertilized plots

(Table 1). ANOVA suggested significantly higher

abundance of Mesostigmata, Prostigmata, and Oriba-

tida following fertilization (Table 3).

3.4. Unharvested reference area

Arthropod abundance in the unharvested plots was

for the most part comparable to fertilized harvested

plots. However, Prostigmata were less abundant in the


Fig. 6. Post-harvest mean abundance of Prostigmata per core sample for post-fertilization (May–December 1996) treatment combinations. Error

bars represent standard errors. Different letters above bars indicate significant difference between treatments as detected by ANOVA and Tukey’s

post-hoc testing.

harvested plots (Fig. 9) and Diplopoda, Isoptera, and

Staphylinidae were not detected from unharvested

plots (Table 4). Pauropoda was high in abundance and

Collembola and Psocoptera low in abundance

compared to treated plots (Fig. 9). Relative abundance

of Acari and Collembola was similar to treated plots

(Tables 2 and 4; Fig. 9).

3.5. Temporal trend

Mean total abundance of all arthropods showed a

temporal trend of lower abundance in the hottest

months of the year (June–September) (Fig. 10). Mean

abundance was highly variable from month-to-month,

particularly following tree harvesting and site pre-

paration (Fig. 10). Highest abundance occurred

between November 1995 and March 1996. Total

abundance tended to be vary greatly between

individual samples on any one sample date.

4. Discussion

4.1. Overall disturbance

The cumulative disturbances caused by tree

harvesting and site preparation have many potential

abiotic and biotic effects on a forest ecosystem. With

removal of the tree canopy higher levels of solar

radiation reach the forest floor, organic matter input

patterns are altered, and temperature and moisture

fluctuations increase in the top 10 cm of the soil


Fig. 7. Post-harvest mean abundance of Oribatida per core sample for post-fertilization (May–December 1996) treatment combinations. Error


post-hoc testing.

(Weber and Methven, 1985; Bird and Chatarpaul,

1988). The mechanical tree felling and bedding

treatments used in this study have the potential to

alter nutrient dynamics and increase soil compaction,

soil erosion, and leaching losses (Tuttle et al., 1985).

Due to these effects, clear-cutting and other silvicul-

tural practices have been recognized to have

significant effects on the invertebrate fauna of the

forest floor (Heliovaara and Vaisanen, 1984; Hoekstra

et al., 1995). Despite these potential risks, in this study

the abundance of arthropods dwelling in the upper

10 cm of the forest floor was not observed to decrease

significantly over a 2-year period following clear-

cutting. It should be noted, however, that 2 years is a

relatively short time period and longer term changes to

this arthropod community are feasible (Blair and

Crossley, 1988).

4.2. Tree harvesting and site preparation

Although only minimal pre-harvest data was

available for comparison, it appeared that there were

no overall and significant declines in total arthropod

abundance throughout the study above and beyond

expected seasonal fluctuations. Over 2 years following

tree harvesting, Acari, the numerically dominant taxa

collected from core samples, recovered rapidly in the

more intensive harvesting and site preparation

treatments. These trends suggest that the microenvir-

onmental conditions these arthropods were exposed to


Fig. 8. Post-harvest mean abundance of Collembola per core sample for post-fertilization (May–December 1996) treatment combinations. Error


post-hoc testing.

stabilized during this time period, despite the removal

of tree canopy cover. The lack of significant

differences between harvesting and site preparation

treatments in 1996 suggests that the effects of

disturbance intensity caused by levels of each did

not persist during the course of the study. The lower

mean abundance of some taxa, particularly Collem-

bola, in the mechanical-fell treatment could have

resulted from the removal of harvesting debris and the

more severe soil compaction caused by this treatment.

In mechanically-felled plots, where all felling debris

was removed, the soil surface was likely to be more

exposed to moisture and temperature fluctuations and

available organic matter was likely reduced in

comparison to hand-felled plots. Collembola survival

and reproduction is strongly influenced by tempera-

ture and moisture and many species are detritivorous

(Christiansen, 1964; Huhta and Mikkonen, 1982),

which may explain the lower abundance observed in

the more intensively harvested plots.

The majority of similar studies have shown

significant reduction of Acari and Collembola

abundance over a number of years following tree

harvesting. Hence, the rapid recovery of Acari in this

study is surprising. Huhta et al. (1967, 1969) and

Huhta (1979) reported initial increases in mite and

springtail densities after clear-cutting followed by

significant declines. Other authors have reported

arthropod abundance decreases after tree harvesting

without initial increases (Vlug and Borden, 1973; Hill

et al., 1975; Lasebikan, 1975; Abbott et al., 1980;

Seastedt and Crossley, 1981; Bird and Chatarpaul,


Table 1

Mean abundance per core sample of selected arthropod taxa split by harvesting, site preparation, and fertilization treatments

Taxon Treatment

TH0 TH1 SP0 SP1 FE0 FE1

Araneae 0.08 0.00 0.05 0.03 0.00 0.11

Pseudoscorpiones 0.08 0.00 0.04 0.04 0.04 0.07

Acari 32.47 21.62 29.63 23.90 18.92 48.35

Chilopoda 0.05 0.07 0.08 0.04 0.04 0.04

Diplopoda 0.25 0.21 0.45 0.01 0.00 1.07

Pauropoda 0.01 0.04 0.03 0.03 0.04 0.07

Symphyla: Scolopendrellidae 0.32 0.33 0.25 0.40 0.50 0.32

Protura 2.36 1.03 2.07 1.33 1.39 1.82

Diplura: Japygidae 0.75 0.74 0.80 0.68 1.29 0.82

Collembola: Hypogastruridae 0.53 0.57 0.84 0.28 0.29 0.75

Isotomidae 7.11 4.24 5.82 4.16 3.21 3.86

Entomobryidae 1.79 1.13 2.16 0.76 0.46 1.29

Sminthuridae 1.18 0.86 1.33 0.72 0.25 0.29

Isoptera: Rhinotermitidae 0.21 0.05 0.24 0.03 0.07 0.61

Psocoptera 1.32 0.47 0.62 1.17 0.25 3.82

Thysanoptera: Phlaeothripidae 0.11 0.08 0.08 0.11 0.04 0.29

Coleoptera: Carabidae 0.00 0.11 0.07 0.04 0.00 0.04

Staphylinidae 0.04 0.09 0.07 0.07 0.04 0.04

Pselaphidae 1.17 1.00 1.37 0.79 1.21 0.82

Larvae 0.47 0.38 0.54 0.34 0.07 0.61

Diptera: Larvae 0.40 0.40 0.38 0.41 0.21 0.18

Hymenoptera: Formicidae 1.90 5.58 1.53 5.83 0.68 12.43

TH0, hand-fell, bole-only harvesting; TH1, mechanical-fell, whole-tree harvesting; SP0, non-bedding; SP1, bedding; FE0, non-fertilization;

and FE1, fertilization. Harvesting and bedding treatment means were calculated from a total of 228 samples taken from each treatment

between February 1995 and December 1996. Fertilization treatment means were calculated from 126 samples taken between May and December

1996.

1986; 1988; Cancela da Fonseca, 1990), including

impacts lasting up to 30 years (Blair and Crossley,

1988). Many Collembola are able to respond

numerically to disturbance with rapid reproduction

rates (Coleman and Crossley, 1996) so the lack of

significant recovery in this study could be seen as

surprising. Oribatida, however, tend to be slow

Table 2

Mean abundance of soil and litter arthropods per core sample for the pre

Treatment Mesostigmata

Harvesting

Hand-fell, bole-only harvesting 4.6 (0.8)a

Mechanical-fell, whole-tree harvesting 6.3 (2.2)a

Bedding

Non-bedding 7.0(1.9)a

Bedding 3.9(1.4)b

Significant differences for each pair of treatments from two-way ANOVA

parentheses. Data were transformed to log (x + 1) for all analyses. No si

reproducers that take longer to recover from dis-

turbance so the abundance increase observed in this

study could also be viewed as unusual. Differences

between the findings reported here and other similar

studies may reflect geographic variation, the suit-

ability of specific silvicultural practices to different

forest types and locations, the size of study plot used in

-fertilization sampling period (February, 1995 to May, 1996)

Prostigmata Oribatida Collembola

6.7 (1.6)a 44.5 (6.5)a 10.9 (1.7)a

5.6 (1.5)a 47.1 (10.4)a 9.0 (2.2)a

8.2 (2.0)a 50.4 (9.0)a 12.7 (1.9)a

4.0 (0.8)a 41.3 (8.3)a 7.3 (2.0)b

are designated by different letters (P < 0.05). Standard errors are in

gnificant interactions were detected between treatments.


Table 3

Mean abundance of soil and litter arthropods per soil sample for the post-fertilization sampling period (May, 1996 to December, 1996)

Treatment Mesostigmata Prostigmat Oribatida Collembola

Harvesting

Hand-fell, bole-only harvesting 5.3 (1.5)a 12.8 (3.2)a 48.5 (14.9)a 6.8 (1.2)a

Mechanical-fell, whole-tree harvesting 4.8 (1.1)a 6.2 (1.4)a 39.5 (8.8)a 3.7 (0.8)b

Bedding

Non-bedding 6.8 (1.6)a 10.4 (2.4)a 36.0 (8.2)a 6.7 (1.3)a

Bedding 3.3 (0.8)a 8.6 (2.6)a 52.0 (15.1)a 3.8 (0.8)a

Fertilization

Non-fertilization 2.9 (0.6)a 4.8 (1.0)a 19.8 (3.5)a 4.3 (0.9)a

Fertilization 7.1 (1.7)b 14.2 (3.2)b 68.2 (15.7)b 6.3 (1.2)a

Significant differences for each pair of treatments from three-way ANOVA are designated by different letters (P < 0.05). Standard errors are in

parentheses. Data were transformed to log (x + 1) for all analyses. No significant interactions were detected between treatments.

different studies, and the need for further research into

the responses of soil and litter arthropods to forest

management regimes.

The bedding treatment employed in this study

concentrates nutrients into upper soil layers for

utilization by newly planted tree seedlings. This

treatment also can increase the risk of wind and water

Fig. 9. Comparison of mean abundance of selected arthropod taxa in po

standard errors.

erosion and leaching losses. Nitrogen and phosphorus

levels have been shown to decrease following bedding

(Pye and Vitousek, 1985; Tew et al., 1986) and erosion

and soil compaction shown to increase (Tew et al.,

1986). The lower abundance of many arthropod taxa

observed prior to fertilization may have resulted from

these detrimental effects of bedding. The observation

st-harvest treated plots and unharvested plots. Error bars represent


Fig. 10. Temporal trend in mean abundance of all soil and litter arthropods per core sample showing timing of treatment applications. Error bars

represent standard errors.

that post-fertilization abundance was comparable in

the two site preparation treatments for most taxa

indicates that the arthropod community was suffi-

ciently intact to enable a recovery in bedded plots 2

years following tree harvesting.

Several taxa were of higher abundance in the

bedded plots than in non-bedded plots. Formicidae

were noticeably higher in mean abundance in both

bedded and mechanically-felled treatments. Solenop-

sis was the dominant genus among collected speci-

mens. These ants are, in general, omnivorous, highly

competitive, and successful at exploiting disturbed

habitats. Due to the eusocial nature of these insects

however, spatial aggregation may cause these data to

be misleading when using the core sampling method.

4.3. Nitrogen and phosphorus fertilization

Varied responses of arthropod communities to

nitrogen and phosphorus fertilization have been

reported in other studies. For example, Kopeszki

(1993) concluded that the numerical response of Acari

and Collembola was determined by the mode of action

of the fertilizer used, while Hill et al. (1975) noted a

delayed effect of fertilization on arthropod abundance

due to a period of nutrient immobilization by

microorganisms. The immediate increase in arthropod

abundance following fertilization in this study

suggests that immobilization did not have a delaying

effect.

4.4. Arthropods, plant growth, and sustainable

timber production

Soil and litter arthropods have many interactions

with microorganisms in forest systems (e.g. see

Werner and Dindal, 1987) and positive feedbacks

exist between the activities of both. Considering these

relationships and the importance of many soil and

litter arthropods for decomposition and soil condition,

the increase in arthropod abundance following

fertilization has implications for future tree growth.

By regulating decomposition rates, organic matter and

soil aggregation dynamics, and soil aeration, the

recovery of the arthropod community observed here

could indicate a local environmental stabilization


Table 4

Mean abundance per core sample of selected arthropod taxa for the

unharvested reference area

Taxon Mean abundance

Araneae 0.03

Pseudoscorpiones 0.11

Acari: Mesostigmata 3.99

Prostigmata 6.39

Astigmata 1.92

Oribatida 36.06

Chilopoda 0.03

Diplopoda 0.00

Pauropoda 0.18

Symphyla: Scolopendrellidae 0.11

Protura 0.53

Diplura: Japygidae 0.42

Collembola: Hypogastruridae 0.87

Isotomidae 5.00

Entomobryidae 0.84

Sminthuridae 0.47

Isoptera: Rhinotermitidae 0.00

Psocoptera 0.21

Thysanoptera: Phlaeothripidae 0.05

Coleoptera: Carabidae 0.03

Staphylinidae 0.00

Pselaphidae 0.47

Larvae 0.16

Diptera: Larvae 0.32

Hymenoptera: Formicidae 2.55

Mean values represent overall averages calculated from 57 core

samples taken within the unharvested plots between February 1995

and December 1996.

leading to more optimal plant growth conditions.

These factors also have positive implications for

sustainability of timber production at this site when

using the combination of silvicultural practices

studied.

In conclusion, the overall rapid recovery of the

abundance of the soil and litter arthropod community

observed in this study indicates that the silvicultural

practices used at this site may not have jeopardized

long-term site productivity. Arthropod diversity, soil

respiration, and soil nutrient data from the same site

support this conclusion (Messina personal commu-

nication, 1997; Bird et al., 2000). More extensive and

comparative studies of this nature are needed to

investigate the differences observed between different

geographic locations, forest types, and specific tree

harvesting and site preparation treatments.

Acknowledgments

We would like to thank M.G. Messina, M.C. Carter,

D.A. Crossley Jr., P.D. Teel, T.R. Seastedt, E. Rebek,

M. Telfer, A. Gilogly, A. Bunting, J.E. Herrick, G.

Forbes, B. Sutter, A. Scott, and two anonymous

reviewers for manuscript review and helpful input. We

also thank P.E. Pulley and P.A. Dacin for statistical

advice. This study was made possible by a grant from

the Texas Research Enhancement Program and was

part of a collaborative study between the USDA Forest

Service, Temple Inland Forest Products Corp.,

Louisiana State University, and Texas A&M Uni-

versity.

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Changes in soil and litter arthropod abundance following tree