Soil biodiversity under different land uses in New York State

Masha Minor

The background
There are strong indications that changes in land use and our appropriation of plant biomass in the form of agricultural production result in massive alterations of natural ecosystems and.could be a major cause of anthropogenic species extinction. Although subject to debate, a body of literature suggests that diverse ecosystems are more stable, more resistant to changes in the environment. If the relationship between diversity and stability holds, then it is in the interests of the long-term viability of a region to encourage diverse human and natural systems. One of the factors in future landscape diversity is the development of short-rotation forestry, a new land use for New York State. The SUNY College of Environmental Science and Forestry in Syracuse, NY is a center for research and development of willow biomass crops (see project home page at http://www.esf.edu/willow/). In the near future, 15,000 acres of willow biomass crop is to be established in Central and Western New York, on Conservation Reserve Program land. The goal is to produce biomass as a source of fuel and fiber, while keeping soil erosion potential low and providing wildlife benefits. If short-rotation forestry is to cover a part of agricultural land in New York, possible impacts and benefits should be known. One of important considerations is the effect on structure and biological activity of soil.

Soil is a unique natural body. It supports the growth of higher plants and therefore the agricultural production of the world, often indirectly determining the number of animals and humans that the land can support. The soil also provides habitat for hundreds of species of invertebrates, many barely visible to the naked eye. Many soil animals belong to so?called microarthropods, arthropods with a body size of 0.1?5.0 mm. These animals are unable to dig their own way in soil; they inhabit soil crevices, pores, and hollows created by larger animals and plant roots. By eating plant and animal residues, eating each other, grazing on soil fungi and bacteria and producing fecal pellets, soil animals promote the formation of humus in the soil and aid in maintaining soil structure and fertility (Coleman and Crossley, 1996). Free-living soil mites (Acari) comprise a large part of microarthropods, and by altering soil conditions, agricultural practices often reduce their number and decrease their diversity. Production of willow is similar to any agricultural cropping system in many respects. However, unlike other agroecosystems, willow plantations are maintained without additional tillage for 17-21 years of plantation life. The soil is minimally disturbed and plant residues are allowed to accumulate.

Willow plantings in Fall. Notice the thick layer of dead leaves on the ground.

The recovery of abundant and diverse communities of free-living soil mites would indicate that willow crop promotes a stable soil environment.

The research question
The objective of my research was to compare soil mite communities in willow plantings with those in agricultural and natural ecosystems in New York State. My goals were to assess the effect of the new land use - short-rotation forestry - on biodiversity in soil using a representative group of soil organisms. My research focused on two taxonomic and functional groups of free-living soil mites - Oribatida and Gamasida.

The research subjects
Mites of the suborder Oribatida, also called "beetle" or "moss" mites, are the world's most numerous arthropods living in soil.

Oribatid mites (immatures) feeding on a dead leaf tissue
( Photo courtesy of Roy A. Norton).

In the forest, their density can reach many thousands of individuals per square foot. There are several thousand described species, yet many are still unknown. These slow moving mites are 0.2 ? 1.0 mm in length. They occur in the top layer of soil, in mosses, lichens, and in litter debris. Oribatida have a low metabolic rate, slow development and low fecundity. These animals are incapable of fast population growth and are usually restricted to relatively stable environments. Oribatid mites graze on fungi, algae and decomposing organic matter; some oribatids feed on nematodes. For many groups feeding habits are still unknown. The soft?bodied immatures are attacked by many soil predators. Oribatida are regulators of the decomposition rate in soil, and through interactions with microflora they affect nutrient cycling, an important factor in soil fertility (Coleman and Crossley, 1996). Their abundance, species composition and diversity in a particular habitat serve as good indicators of soil "health".

The gamasid mites (Acari: Gamasida) are important predators in soil ecosystems. Similar to spiders, they inject digestive liquid into their and then suck up dissolved tissues. The larger surface?dwelling gamasid mites attack other soil arthropods.

Predatory gamasid mite Pergamasus crassipes L. (fam. Parasitidae).

Smaller deep-litter and soil forms are predominantly nematophagous and are the most important predators of nematodes in many habitats. Gamasid mites are universally present in soil, though not as numerous or diverse as oribatid mites. The abundance and community structure of these mites reflect the availability of their prey. Several genera are considered good bioindicators of habitat and soil condition.

Study design, sampling and data analysis
Soil samples from corn fields, old abandoned fields, fields overgrown with shrubs, hardwood forests, and 3-4 year old willow plantations in New York State were collected in Summer'99 and '01 by me and by Jennifer Cianciolo. There were three replications of each land use. Fifteen to twenty-five random soil samples were taken within each plot, using a stainless steel corer.

A soil core (5 cubic cm) can be a home to hundreds individuals of soil mites.

Mites were extracted from soil samples,

Berlese-Tullgren apparatus is a great tool for separating microscopic animals from the litter and soil they inhabit. Free of soil debris, they can be counted and identified. A soil sample is placed on the sieve at the top of a funnel. A small lamp with a low?power light bulb heats and dries the soil from above, which stimulates the soil animals to move downward (positive geotaxis in response to dryness). This downward movement eventually causes the soil animals to fall through the sieve into a container with preservative. This large funnel is for qualitative sampling. For quantitative sampling I use smaller funnels of similar construction.

counted and identified to the species level.

Free-living mites from a soil sample. The dark-brown and yellow-brown round mites are Oribatida; the lighter mites with long legs are Gamasida.

I use descriptors of diversity based on species density, species richness, and diversity indices such as Shannon's diversity index.

I used canonical discriminant and correspondence analyses to investigate the relationships between mite diversity and land use. The hypothesis of no significant effect of land use was tested with assumption that only the effect of land use is of interest; the possible differences in abundance and species diversity due to different sampling locations were considered to be random effect. Chi-square test was used to test the hypothesis of independence between mite community structure and land use. All statistical tests were conducted at the level of significance a = 0.05 using SAS (Statistical Analysis System, SAS Institute).

Results and conclusions
A total of 117 species of Oribatida and 105 species of Gamasida were represented in the samples. Many species were not previously known to occur in New York. The highest diversity of Oribatida was in the forests, decreasing dramatically in agroecosystems (Fig.1, Fig. 2).

Figure 1. Mean number of species found in studied habitats.

Figure 2. Diversity of oribatid mites under different land uses.

A similar situation was observed for population density of these mites. The number of species of predatory Gamasida found in any particular sampling site was less variable across land uses.

Figure 3 illustrates the overall relationship between the diversity of oribatid and gamasid mites in soil and the land use.

Figure 3. Scatterplot of two discriminant functions representing
diversity of Oribatida and diversity of Gamasida in individual
soil samples from all sampling locations.

The data points are individual soil samples. It is obvious that the diversity of oribatid mites contributes to the separation of observations, increasing in the order "corn fields - willow plantations - abandoned fields/shrubby old fields - forests", while the diversity of predatory Gamasida is random. The effect of land use, separated from the effect of location, was statistically significant for oribatid mites and not significant for gamasid mites.

Table 1 confirms the separation observed in Figure 3, suggesting that communities of oribatid mites in willow plantations are transitional between conventional agriculture (corn) and the communities at the beginning of forest successional series (old fields).

The density and diversity of predatory gamasid mites proved to be largely insensitive to land use factors and more related to local conditions of individual sampling sites. However, the analysis of community structure revealed correspondence between land use and the abundance of individual families of gamasid mites (Fig. 4),

Figure 4. Correspondence between land use and occurrence
of Gamasida families (correspondence analysis).

proving that this group has value as indicators of soil conditions. Many Gamasida species found in agricultural soils are those common in heavily disturbed or early successional habitats. The members of Zerconidae, Trachytidae and Parholaspidae are characteristic of the forest.

Agricultural cropping techniques, such as tillage and herbicide applications, are potentially crucial factors affecting soil biological activity and biodiversity. The diversity of free-living soil mites in 3-4 year old willow plantings approaches that of the early stages of forest succession, suggesting that soil communities are recovering from the initial stress of site preparation. I conclude that, unlike conventional agroecosystems, periannal willow crop creates a relatively more stable soil environment and therefore encourages the development of more diverse decomposer communities and slower nutrient turnover (Bear et al., 1992; Bardgett and Cook, 1998). In the long term, short-rotation forestry on agricultural land can be expected to have a positive effect on general stability and sustainability of soil ecosystems in New York.

Acknowledgements
This study is supported by the Roosevelt Wild Life Station and by the Biomass for Rural Development Project (Niagara Mohawk Power Corporation and the U.S. Department of Energy National Renewable Energy Laboratory). My many thanks go to Jennifer Cianciolo for providing data for comparative analysis.

Literature

Bardgett, R.D., and R. Cook. 1998. Functional aspects of soil animal diversity in agricultural grasslands. Applied Soil Ecology 10, p. 263-276.

Beare, M.H., R.W. Parmelee, P.F. Hendrix, and W. Cheng. 1992. Microbial and faunal interactions and effects on litter nitrogen and decomposition in agroecosystems. Ecological Monographs 62, p. 569-591.

Coleman, D.C., and D.A. Crossley, Jr. 1996. Fundamentals of Soil Ecology. Academic Press, New York. 205pp.

Crossley, D. A. Jr., Coleman, D. C., and P.F. Hendrix. 1989. The importance of the fauna in agricultural soils: research approaches and perspectives. Agriculture, Ecosystems and Environment 27, p. 47-55.

Contact information: e-mail me (Masha Minor, SUNY-ESF) at maminor@mailbox.syr.edu. More information on soil microarthropods is available at http://web.syr.edu/~maminor/mites.html.

Personal information:

Moscow State University, currently Ph.D. student at SUNY-ESF. My research interests include taxonomy and population biology of soil mites; effects of disturbance on the behavior of ecosystems at different spatiotemporal scales; influences of land use on landscape structure and processes; landscape patterns and the role they play in shaping biotic communities.