Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols Used xiii 1. The Importance of Islands 3 2. Area and Number of Speicies 8 3. Further Explanations of the Area-Diversity Pattern 19 4. The Strategy of Colonization 68 5. Invasibility and the Variable Niche 94 6. Stepping Stones and Biotic Exchange 123 7. Evolutionary Changes Following Colonization 145 8. Prospect 181 Glossary 185 References 193 Index 201

The Theory of Island Biogeography

Defining and Assessing Soil Quality

▪ Abstract We explore empirical and theoretical evidence for the functional significance of plant-litter diversity and the extraordinary high diversity of decomposer organisms in the process of litter decomposition and the consequences for biogeochemical cycles. Potential mechanisms for the frequently observed litter-diversity effects on mass loss and nitrogen dynamics include fungi-driven nutrient transfer among litter species, inhibition or stimulation of microorganisms by specific litter compounds, and positive feedback of soil fauna due to greater habitat and food diversity. Theory predicts positive effects of microbial diversity that result from functional niche complementarity, but the few existing experiments provide conflicting results. Microbial succession with shifting enzymatic capabilities enhances decomposition, whereas antagonistic interactions among fungi that compete for similar resources slow litter decay. Soil-fauna diversity manipulations indicate that the number of trophic levels, spec...

Biodiversity and Litter Decomposition in Terrestrial Ecosystems

Sampling and analysis or visual examination of soil to assess its status and use potential is widely practiced from plot to national scales. However, the choice of relevant soil attributes and interpretation of measurements are not straightforward, because of the complexity and site-specificity of soils, legacy effects of previous land use, and trade-offs between ecosystem services. Here we review soil quality and related concepts, in terms of definition, assessment approaches, and indicator selection and interpretation. We identify the most frequently used soil quality indicators under agricultural land use. We find that explicit evaluation of soil quality with respect to specific soil threats, soil functions and ecosystem services has rarely been implemented, and few approaches provide clear interpretation schemes of measured indicator values. This limits their adoption by land managers as well as policy. We also consider novel indicators that address currently neglected though important soil properties and processes, and we list the crucial steps in the development of a soil quality assessment procedure that is scientifically sound and supports management and policy decisions that account for the multi-functionality of soil. This requires the involvement of the pertinent actors, stakeholders and end-users to a much larger degree than practiced to date.

Soil quality – A critical review

Maintenance and improvement of soil quality in continuous cropping systems is critical to sustaining agricultural productivity and environmental quality for future generations. This review focuses on lessons learned from long-term continuous cropping experiments. Soil organic carbon (SOC) is the most often reported attribute from long-term studies and is chosen as the most important indicator of soil quality and agronomic sustainability because of its impact on other physical, chemical and biological indicators of soil quality. Long-term studies have consistently shown the benefit of manures, adequate fertilization, and crop rotation on maintaining agronomic productivity by increasing C inputs into the soil. However, even with crop rotation and manure additions, continuous cropping results in a decline in SOC, although the rate and magnitude of the decline is affected by cropping and tillage system, climate and soil. In the oldest of these studies, the influence of tillage on SOC and dependent soil quality indicators can only be inferred from rotation treatments which included ley rotations (with their reduced frequency of tillage). The impact of tillage per se on SOC and soil quality has only been tested in the ‘long-term’ for about 30 yrs, since the advent of conservation tillage techniques, and only in developed countries in temperate regions. Long-term conservation tillage studies have shown that, within climatic limits: Conservation tillage can sustain or actually increase SOC when coupled with intensive cropping systems; and the need for sound rotation practices in order to maintain agronomic productivity and economic sustainability is more critical in conservation tillage systems than conventional tillage systems. Long-term tillage studies are in their infancy. Preserving and improving these valuable resources is critical to our development of soil management practices for sustaining soil quality in continuous cropping systems.

The role of soil organic matter in maintaining soil quality in continuous cropping systems

SUMMARY A study was conducted to determine if ectomycorrhizal fungi in an age sequence of jack pine (Pinus banksiana Lamb.) stands which had regenerated following wildfire disturbance followed a successional pattern. Ectomycorrhizal development and number of symbionts were assessed in the forest floor and 0-20 cm deep mineral soil in 6, 41, 65 and 122-yr-old stands by conducting a macrofungal fruit body survey and examining pine root tips microscopically for mycorrhizal status and types of fungi forming the symbiosis. The majority of roots were located in the mineral soil with no substantial invasion of the forest floor except in the 122-yr-old stand. Over 90 % of the jack pine root tips were mycorrhizal and the majority of fruit bodies were produced by ectomycorrhizal species, regardless of stand age. There was no decrease in ectomycorrhizal colonization of roots with stand age. Both fruit body and root assessments revealed a distinct sequence of mycorrhizal fungi with stand age consisting of early-stage fungi [Coltricia perennis (L: Fr.) Murr., Thelephora spp., E-strain]; multi-stage fungi [Suillus brevipes (Pk.) Kuntze, Inocybe spp., Cenococcum geophilum Fr., Mycelium radicis atrovirens Melin] and late-stage fungi [Cortinarius spp., Lactarius spp., Russula spp., Tricholoma spp., Hygrophorus spp., Hydnellum peckii Banker, Suillus tomentosus (Kauff.) Sing., Snell & Dick, Piloderma byssinum (Karst.) Jul. and Sarcodon scabrosus (Fr.) Karst.]. Many of the basidiomycete species fruiting above ground were detected also on the roots below ground. Fruit bodies of 50 species of ectomycorrhizal fungi were recorded while 39 distinct mycorrhizal types were identified on the roots. There was a significant increase in mycorrhizal species richness between the 6 and 41-yr-old stands and this was primarily the result of partial replacement of Suillus brevipes on the 6-yr-old trees by late-stage fungi in the older stands. Very few species present in the 6-yr-old stand were completely replaced in the older stands; rather, the multi-stage species present in the young stand were joined by late-stage species in the mature stands. The species abundance distribution of fungi on the roots in the 6-yr-old stand was best described by a geometric series which is typical of an early successional community while the distributions in the three oldest stands conformed to a lognormal series which is indicative of a stable, species rich community. Both the composition and structure of the ectomycorrhizal community had stabilized 41 yr after wildfire.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-8137.1995.tb04309.x

Ectomycorrhizal fungal succession in jack pine stands following wildfire

Diverse soil microbiological studies have attempted to assess deterioration or improvement in soil quality. These studies have been done on three levels: population level studies of the dynamics of species that are presumed to be important or sensitive; community level studies of microbial community structure, such as species diversity and frequency of occurence of species; and ecosystem level studies of a range of soil processes. We suggest that ecosystem level approaches offer the best possibilities for rapidly assessing changes in soil quality. Data from such studies will allow researchers to decide whether to proceed with population or community level studies.

Soil biological criteria as indicators of soil quality: Soil microorganisms

Using simple laboratory systems, an attempt was made to assess the importance of selective collembolan (Onychiurus subtenuis Folsom) grazing on the colonization of L layer leaf litter from a cool temperate deciduous forest by two common litter fungi (a Sterile dark form and a Basidiomycete). The results indicate that relatively low selective grazing rates could have potentially important effects on the growth and competitive colonizing ability of individual fungi. The relation of such a laboratory study to actual field events is only feasible when there is a thorough knowledge of the organisms being used. Preamble In common with numerous other forest systems, detailed data have been accumulated over the last decade on various groups of organisms active in the litter layers of a cool temperate deciduous forest (Kananaskis, Alberta, Canada) where the major tree species is Populus tremuloides Michx. Detailed studies on fungi in the litter layers of this forest (Visser & Parkinson, 1975 a, b) indicate that the time of spring thaw is one of considerable and rapid change in the populations of these organisms. This change was particularly well seen when concurrent (April) replicate samples of L layer leaf litter were taken from the melting edge of snow patches and from areas where complete snow melt had occurred and fungal biomass and species complement were determined. The data obtained from this study are summarized in Table 1.

Effects of collembolan grazing on fungal colonization of leaf litter

Oribatid mites enhance the recovery of the microbial community after a strong disturbance

SUMMARY
Seedlings of Pinus contorta Dougl. and Phleum pratense L. were grown in the greenhouse in forest floor (F/H horizons) and mineral soil from a P. contorla stand which had been acidified (pH 1.6 5.2) with S° dust over a 5-year period. Although S° dust was the primary treatment it was assumed that acidification accounted for the major effects on the plants and mycorrhizas. Pinus contorla failed to grow below pH 2.8 and ectomycorrhizas were absent below pH 3.3. Pheleum pratense ceased growth at pH 3.3 and no vesicular-arbuscular (VA) mycorrhizas were formd below pH 4.0. There did not appear to be any relationship between the relative abundance of coarse and fine VA mycorrhizal endophytes and soil acidity. Cenococcum geophilum L. was a common ectomycorrhizal associate of pine seedlings grown in the F/H soil, and E-strain fungi (Complexipes), Mycelium radicis atrovirens Melin, Tomentella sp. and Suillus sp. were all more common in the mineral soi than in the F/H soil. Piloderma bicolor (Peck) Julich was observed to occur in large, discrete patches in the undisturbed natural stand but did not form ectomycorrhizas in the greenhouse. Both P. pratense and P. contorla were capable of good growth in extremely acid soils in a non-mycorrhizal state.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1469-8137.1989.tb00306.x

Suzanne Visser

Papers

Ectomycorrhizal fungal succession in jack pine stands following wildfire

Soil biological criteria as indicators of soil quality: Soil microorganisms

Effects of collembolan grazing on fungal colonization of leaf litter

Oribatid mites enhance the recovery of the microbial community after a strong disturbance

Effects of forest soil acidification on ectomycorrhizal and vesicular—arbuscular mycorrhizal development