Soil Resource Heterogeneity Research Articles

Soil resource heterogeneity promotes species richness only at a fine scale at the early restoration of karst abandoned farmland

Soil resource heterogeneity promotes species richness only at a fine scale at the early restoration of karst abandoned farmland

Soil cover heterogeneity associated with biocrusts predicts patch-level plant diversity patterns

ContextSoil resource heterogeneity drives plant species diversity patterns at local and landscape scales. In drylands, biocrusts are patchily distributed and contribute to soil resource heterogeneity important for plant establishment and growth. Yet, we have a limited understanding of how such heterogeneity may relate to patterns of plant diversity and community structure.ObjectivesWe explored relationships between biocrust-associated soil cover heterogeneity and plant diversity patterns in a cool desert ecosystem. We asked: (1) does biocrust-associated soil cover heterogeneity predict plant diversity and community composition? and (2) can we use high-resolution remote sensing data to calculate soil cover heterogeneity metrics that could be used to extrapolate these patterns across landscapes?MethodsWe tested associations among field-based measures of plant diversity and soil cover heterogeneity. We then used a Support Vector Machine classification to map soil, plant and biocrust cover from sub-centimeter resolution Unoccupied Aerial System (UAS) imagery and compared the mapped results to field-based measures.ResultsField-based soil cover heterogeneity and biocrust cover were positively associated with plant diversity and predicted community composition. The accuracy of UAS-mapped soil cover classes varied across sites due to variation in timing and quality of image collections, but the overall results suggest that UAS are a promising data source for generating detailed, spatially explicit soil cover heterogeneity metrics.ConclusionsResults improve understanding of relationships between biocrust-associated soil cover heterogeneity and plant diversity and highlight the promise of high-resolution UAS data to extrapolate these patterns over larger landscapes which could improve conservation planning and predictions of dryland responses to soil degradation under global change.

Light heterogeneity affects understory plant species richness in temperate forests supporting the heterogeneity-diversity hypothesis.

One of the most important drivers for the coexistence of plant species is the resource heterogeneity of a certain environment, and several studies in different ecosystems have supported this resource heterogeneity–diversity hypothesis. However, to date, only a few studies have measured heterogeneity of light and soil resources below forest canopies to investigate their influence on understory plant species richness. Here, we aim to determine (1) the influence of forest stand structural complexity on the heterogeneity of light and soil resources below the forest canopy and (2) whether heterogeneity of resources increases understory plant species richness. Measures of stand structural complexity were obtained through inventories and remote sensing techniques in 135 1‐ha study plots of temperate forests, established along a gradient of forest structural complexity. We measured light intensity and soil chemical properties on six 25 m² subplots on each of these 135 plots and surveyed understory vegetation. We calculated the coefficient of variation of light and soil parameters to obtain measures of resource heterogeneity and determined understory plant species richness at plot level. Spatial heterogeneity of light and of soil pH increased with higher stand structural complexity, although heterogeneity of soil pH did not increase in conditions of generally high levels of light availability. Increasing light heterogeneity was also associated with increasing understory plant species richness. However, light heterogeneity had no such effects in conditions where soil resource heterogeneity (variation in soil C:N ratios) was low. Our results support the resource heterogeneity–diversity hypothesis for temperate forest understory at the stand scale. Our results also highlight the importance of interaction effects between the heterogeneity of both light and soil resources in determining plant species richness.

Soil resource availability is much more important than soil resource heterogeneity in determining the species diversity and abundance of karst plant communities.

Resource availability and heterogeneity are recognized as two essential environmental aspects to determine species diversity and community abundance. However, how soil resource availability and heterogeneity determine species diversity and community abundance in highly heterogeneous and most fragile karst landscapes is largely unknown. We examined the effects of soil resource availability and heterogeneity on plant community composition and quantified their relative contribution by variation partitioning. Then, a structural equation model (SEM) was used to further disentangle the multiple direct and indirect effects of soil resource availability on plant community composition. Species diversity was significantly influenced by the soil resource availability in shrubland and woodland but not by the heterogeneity in woodland. Abundance was significantly affected by both soil resource availability and heterogeneity, whereas variation partitioning results showed that soil resource availability explained the majority of the variance in abundance, and the contribution of soil resource heterogeneity was marginal. These results indicated that soil resource availability plays a more important role in determining karst plant community composition than soil resource heterogeneity. Our SEMs further found that the multiple direct and indirect processes of soil resource availability in determining karst species diversity and abundance were different in different vegetation types. Soil resource availability and heterogeneity both played a certain role in determining karst plant community composition, while the importance of soil resource availability far exceeded soil resource heterogeneity. We propose that steering community restoration and reconstruction should be highly dependent on soil resource availability, and multiple direct and indirect pathways of soil resource availability for structuring karst plant communities need to be taken into account.

Biological invasions and climate change amplify each other’s effects on dryland degradation

Climate models predict that, in the coming decades, many arid regions will experience increasingly hot conditions and will be affected more frequently by drought. These regions are also experiencing rapid vegetation change, notably invasion by exotic grasses. Invasive grasses spread rapidly into native desert ecosystems due, in particular, to interannual variability in precipitation and periodic fires. The resultant destruction of non-fire-adapted native shrub and grass communities and of the inherent soil resource heterogeneity can yield invader-dominated grasslands. Moreover, recurrent droughts are expected to cause widespread physiological stress and mortality of both invasive and native plants, as well as the loss of soil resources. However, the magnitude of these effects may differ between invasive and native grasses, especially under warmer conditions, rendering the trajectory of vegetated communities uncertain. Using the Biosphere 2 facility in the Sonoran Desert, we evaluated the viability of these hypothesized relationships by simulating combinations of drought and elevated temperature (+5°C) and assessing the ecophysiological and mortality responses of both a dominant invasive grass (Pennisetum ciliare or buffelgrass) and a dominant native grass (Heteropogan contortus or tanglehead). While both grasses survived protracted drought at ambient temperatures by inducing dormancy, drought under warmed conditions exceeded the tolerance limits of the native species, resulting in greater and more rapid mortality than exhibited by the invasive. Thus, two major drivers of global environmental change, biological invasion and climate change, can be expected to synergistically accelerate ecosystem degradation unless large-scale interventions are enacted.

Rapid redistribution and long-term aggregation of mulch residues by earthworms (Lumbricus terrestris)

There has been minimal study of how ecosystem engineering anecic earthworms such as Lumbricus terrestris L. may influence the distribution of mulch amendments across the soil surface by collecting residues into middens. The two primary research objectives of this study were: (1) to determine how rapidly earthworms change the surface distribution of mulch following amendment, and (2) to produce a more spatially explicit map of earthworm aggregation of mulch. This study used a microcosm experiment to assess the immediate, short-term impacts of earthworms on recently added mulch at a small scale, and an opportunistic field study of the longer-term impacts of earthworms on the distribution of corn ‘stubble’ mulch in a former agricultural field. In the microcosm experiment, earthworms rapidly redistributed mulch within the first week post amendment, decreasing initial ground cover (15-29% decrease). Over the subsequent five weeks, initial cover continued to decrease (20-45% decrease) as mulch was spread thinly onto adjacent, initially bare soil (49-69% increase). Higher mulch amendment mitigated losses in initial cover. In the field study, earthworms aggregated mulch across the soil surface, collecting 40% of the woody corn residues into 17% of the total area in regularly distributed middens. These results demonstrate the potential for L. terrestris to alter the distribution of mulch rapidly in the first several days and weeks following application and in the longer term over several years, increasing the spatial heterogeneity of soil resources. This physical redistribution has only been minimally investigated and may help inform models of earthworm impacts on various ecological processes and improve soil amendment and residue management in earthworm-occupied soils.

Resource islands of Salix cupularis facilitating seedling emergence of the companion herbs in the restoration process of desertified alpine meadow, the Tibetan Plateau

Salix cupularis is a common shrub for ecological restoration of the desertified alpine meadow on the Tibetan Plateau. However, the effect of S. cupularis on spatial heterogeneity of soil resources (i.e., resource islands effect) has not been systematically evaluated, and the influence of shrub patches on the rehabilitation of understory herbs has also been unknown. In this study, we randomly selected S. cupularis individuals in the early restoration stage of desertified alpine meadow, where the three native forages (Elymus nutans, Elymus sibiricus and Festuca sinensis) were sown at different microsites around S. cupularis to explore the effects of S. cupularis on soil resources and emergence rates of the native forages. The results showed that S. cupularis significantly increased SWC (soil water content), C (carbon) and N (nitrogen) nutrients (p < 0.01) and enzyme activities (p < 0.05) under canopy compared with the bare land, and the improvement performed better in the topsoil (0–5 cm) than in the subtop-soil (5–15 cm). Moreover, the soil properties were affected significantly by microsites around S. cupularis, resulting in regular changes of SWC, nutrients and enzyme activities in different microsites (Shrub center > Middle of canopy radius > Bare land). In addition, there are significant regression relationships between emergence rates and enriching soil water, C and N nutrients, so the emergence rates of native forages under canopy may be improved significantly with the enriched soil resources, especially for E. nutans. As a result, S. cupularis is a suitable pioneer shrub for the vegetation restoration of desertified alpine meadow on the Tibetan Plateau, because it could not only shape the enrichment of soil resources under canopy, but also facilitate emergence of companion forages in the process of vegetation restoration.

Impacts of shrub introduction on soil properties and implications for dryland revegetation

The intensive introduction of shrubs to drylands can alter species composition and affect a series of biotic and abiotic processes. This topic has attracted increasing attention by researchers. To assess the response of soil properties to vegetation succession in arid regions of China, we measured the soil water content (SWC) to a depth of 5-m and determined soil properties of surface (0–5 cm) and subsurface (20–25 cm) layers in areas of natural grasses (NGs) and planted shrubs (PSs). The patch size of Caragana korshinskii shrubs resulted in different soil water storage losses (small shrub patch: 206.67 ± 35.58 mm; medium shrub patch: 416.88 ± 35.12 mm; large shrub patch: 588.63 ± 72.00 mm; degraded shrub patch: 740.54 ± 17.00 mm). Shrub cover showed an initial increase but then decreased as shrubs extracted soil water from the deep soil layers (>1 m). The species richness index in the PSs decreased with increasing shrub patch sizes. Surface soil organic carbon (SOC), extractable nitrogen (NH4+-N and NO3−-N), and available phosphorous contents and saturated soil hydraulic conductivity (Ks) in the PSs were all significantly (p < 0.05) lower than those in NGs. Soil particles in the range of 0.002–0.2 mm explained 28.0% and 47.3% of the total variability of these surface indices under NGs and PSs, respectively. The differences in SOC, NH4+-N, NO3−-N, Ks, and field capacity between the surface and subsurface layers declined significantly (p < 0.05). The introduction of shrubs affected the plant community by increasing the spatial heterogeneity of soil resources (e.g. water and nutrient contents). Therefore, the strong feedback between SWC and vegetation succession should be carefully considered when revegetating drylands. The evaluation of regional soil property responses to vegetation succession aids in a better understanding of soil water–vegetation feedback and provides important implications for future revegetation in arid regions.

Soil resource heterogeneity competitively favors an invasive clonal plant over a native one.

Soil resource heterogeneity can affect plant growth and competitive ability. However, little is known about how soil resource heterogeneity affects competitive interactions between invasive and native plants. We conducted an experiment with an invasive clonal plant Alternanthera philoxeroides and a coexisting native one Alternanthera sessilis. The experiment was a randomized design with three factors, i.e. two species (A. philoxeroides and A. sessilis), two interspecific competition treatments (with and without) and five soil treatments (three homogeneous treatments and two small-scale heterogeneous treatments consisting of two patches of 10cm × 15cm and with different initial planting positions). Irrespective of competition, increasing soil resource availability increased the growth of A. philoxeroides. Increasing soil resource availability alsoincreased the growth of A. sessilis without competition, but had no impact with competition. Irrespective of competition, soil resource heterogeneity increased biomass and ramet production of A. philoxeroides, andsuch effects were independent of initial planting position. For A. sessilis, however, soil resource heterogeneity only increased ramet production when the initial plant was grown in the low-resource patch without competition. Our results suggest that both high soil resource availability and small-scale soil resource heterogeneity can increase the relative competitive ability of the invasive plant A. philoxeroides when grown with its native congener A. sessilis. These findings may partly explain the invasion success of this clonal species in area with high soil resource availability and heterogeneity caused by e.g. nitrogen deposition, fertilization and disturbance.

Soil heterogeneity increases plant diversity after 20 years of manipulation during grassland restoration.

The "environmental heterogeneity hypothesis" predicts that variability in resources promotes species coexistence, but few experiments support this hypothesis in plant communities. A previous 15-yr test of this hypothesis in a prairie restoration experiment demonstrated a weak effect of manipulated soil resource heterogeneity on plant diversity. This response was attributed to a transient increase in richness following a post-restoration supplemental propagule addition, occasionally higher diversity under nutrient enrichment, and reduced cover of a dominant species in a subset of soil treatments. Here, we report community dynamics under continuous propagule addition in the same experiment, corresponding to 16-20yr of restoration, in response to altered availability and heterogeneity of soil resources. We also quantified traits of newly added species to determine if heterogeneity increases the amount and variety of niches available for new species to exploit. The heterogeneous treatment contained a factorial combination of altered nutrient availability and soil depth; control plots had no manipulations. Total diversity and richness were higher in the heterogeneous treatment during this 5-yr study due to higher cover, diversity, and richness of previously established forbs, particularly in the N-enriched subplots. All new species added to the experiment exhibited unique trait spaces, but there was no evidence that heterogeneous plots contained a greater variety of new species representing a wider range of trait spaces relative to the control treatment. The richness and cover of new species was higher in N-enriched soil, but the magnitude of this response was small. Communities assembling under long-term N addition were dominated by different species among subplots receiving added N, leading to greater dispersion of communities among the heterogeneous relative to control plots. Contrary to the deterministic mechanism by which heterogeneity was expected to increase diversity (greater variability in resources for new species to exploit), higher diversity in the heterogeneous plots resulted from destabilization of formerly grass-dominated communities in N-enriched subplots. While we do not advocate increasing available soil N at large scales, we conclude that the positive effect ofenvironmental heterogeneity on diversity can take decades to materialize and depend on development of stochastic processes in communities with strong establishment limitation.

Comparing Spatial Heterogeneity of Bioavailable Nutrients and Soil Respiration in Boreal Sites Recovering From Natural and Anthropogenic Disturbance

The mining of oil sands in Alberta, Canada is a large-scale disturbance that requires land reclamation to equivalent land capability. Cover soils used for upland forest reclamation are forest floor mineral-mix (FFM) sourced from upland forest ecosystems and peat mineral-mix (PM) sourced from lowland ecosystems. Spatial heterogeneity and quantity of soil resources, especially nutrient bioavailability, is important because it affects the establishment of native vegetation in forest ecosystems and soil respiration is an indicator for overall soil biologic activity. We studied spatial heterogeneity of soil nutrients as well as seasonal and spatial patterns of soil respiration in two sites reclaimed either with FFM or PM and two reference sites recovering either from harvest or fire. Contrary to our initial hypothesis, we identified spatial heterogeneity in some bioavailable nutrients in FFM and PM cover soil, indicating that standard placement processes can recreate spatial heterogeneity. However, some nutrients such as P, K and S showed no heterogeneity in PM at all. P and K availability was significantly lower and S was significantly higher in PM than in FFM and reference sites. Seasonal pattern of respiration showed variability on natural reference sites and on FFM, indicating that disturbance had not removed belowground function completely. PM reclaimed sites showed no strong seasonal respiration patterns indicating homogeneous belowground function. Surprisingly PM treatments were not characterized by highest rates of soil respiration while having highest amounts of total organic carbon. We conclude that FFM reclaimed sites may be more successfully reclaimed than PM sites because they are more similar to reference sites in terms of nutrient status and seasonal respiration patterns.

The spread of Kalmia angustifolia on black spruce forest cutovers contributes to the spatial heterogeneity of soil resources.

Kalmia angustifolia is a boreal ericaceous shrub that can rapidly spread on black spruce forest cutovers in eastern Canada, where CPRS (i.e. Cutting with Protection of Regeneration and Soils”) is practiced. The proliferation of Kalmia often coincides with a reduction in the growth rate of regenerating black spruce seedlings. We report on a study where we compared the local effects of Kalmia and black spruce seedling patches (i.e. two types of “Vegetation”) on chemical and biochemical soil properties in CPRS cutovers within mesic spruce-moss and xeric spruce-lichen ecosystems, as well as in four mature spruce-moss forests (i.e. three “Site Types”). Results from 13C-CPMAS-NMR revealed lower O-alkyl C (i.e. carbohydrates), higher aromatic C (i.e. lignin and other phenolics) and higher carbonyl-C (i.e. amide-C and carboxyl groups) in spruce-moss than in spruce-lichen forest floors (F-horizon). In spite of these distinctions, we observed only a small number of Site Type x Vegetation interactions controlling soil properties. Vegetation had a significant effect on ten forest floor properties. Most notably, Kalmia patches had higher concentrations of condensed tannins and lower mineral N cycling. On the other hand, Site Type had a relatively greater effect on the deeper podzolic-B horizons, where mineral N and microbial activity were higher in mature spruce-moss forests than in the cutovers. Green and senescent Kalmia leaves collected at these sites had higher N, tannin and phenolic concentrations than green and senescent spruce needles. A 25 month litter bag study found lower decomposition of Kalmia leaf litter in spruce patches on spruce-lichen cutovers compared to spruce patches on spruce-moss cutovers, or to Kalmia patches on spruce-lichen cutovers. Given that black spruce seedlings obtain most of their nutrients from the forest floor, our results suggest that CPRS may have long-term negative effects on black spruce forest productivity if the spread of Kalmia is left unchecked.

Post-fire Redistribution of Soil Carbon and Nitrogen at a Grassland–Shrubland Ecotone

The rapid conversion of grasslands into shrublands has been observed in many arid and semiarid regions worldwide. Studies have shown that fire can negatively affect shrub communities and promote resource homogenization, thereby providing some reversibility to the resource heterogeneity induced by shrub encroachment, especially in the early stages of encroachment. Here, we used prescribed fire in a grassland–shrubland transition zone in the northern Chihuahuan Desert to test the hypothesis that fire facilitates the remobilization of nutrient-enriched soil from shrub microsites to grass and bare microsites and thereby reduces the spatial heterogeneity of soil resources. Results show that the shrub microsites had the lowest water content compared to grass and bare microsites after fire, even when rain events occurred. Significant differences of total soil carbon (TC) and total soil nitrogen (TN) among the three microsites were not detected 1 year after the fire. The spatial autocorrelation distance increased from 1 to 2 m, approximately the mean diameter of an individual shrub canopy, to over 5 m 1 year after the fire for TC and TN. Patches of high soil C and N decomposed 1 year after the prescribed fire. Overall, fire stimulates the redistribution of soil C and N from shrub microsites to nutrient-depleted grass and bare microsites, leading to a decrease in spatial heterogeneity of these elements. The redistribution of soil C and N from shrub to grass and bare microsites, coupled with the reduced soil water content under the shrub canopies but not in grass and bare microsites, suggests that fire might influence the competition between shrubs and grasses, leading to a higher grass, compared to shrub, coverage in this ecotone.

The role of tamarisk in the spatial heterogeneity of soil resources in the northern Tarim Basin, Xinjiang, China

The encroachment of halophytic shrubs including tamarisk into saline meadows is accelerating with global warming in the northern Tarim Basin, Xinjiang, China. However, the role of tamarisk in the spatial heterogeneity of soil resources in different desertification stages remains unclear. The influences of tamarisk on soil resources were assessed via soil salinity and soil organic matter (SOM) measurements under tamarisk canopies and in interspaces. Geostatistical methods were applied to compare the spatial heterogeneity of these soil properties in three regions representing different desertification stages: 1) a meadow with shrubs, 2) a shrubland and 3) shrub duneland. The highest coefficient of variation (CVs) of the soil analytes and most developed “resource islands” were observed in the shrubland. The overall variation of most of the soil variables was lower in the shrub duneland than in the shrubland and similar to that in the meadow with shrubs. The distribution of SOM and most soil salinity ions were moderately spatially dependent in the meadow with shrubs but highly spatially dependent in the shrubland and shrub duneland. The autocorrelation distances of the most of soil salinity ions were approximately 6- to 15- fold and 2- to 4-fold highest than the tamarisk shrub size in the meadow with shrubs and shrubland, respectively. In contrast, the distribution range of total soil salinity (TSS) and soil K+, Na+ and Cl− in the shrub duneland were 1/5 ~ 2/3 of the tamarisk size. 1) Compared with the effect of tamarisk on soil resource heterogeneity in the meadow with shrubs, that in the shrubland was enhanced due to the larger shrub size and more open and scattered canopy in the latter.2) Although the largest shrub size were observed in the shrub duneland, the role of tamarisk in redistributing soil resources was overriden by those of physical processes due to the loose canopy. 3) The spatial heterogeneity of soil resources is determined by not only tamarisk but also environmental factors, such as the connectivity of bare areas and topography.

Functional responses of Mediterranean plant communities to soil resource heterogeneity: a mycorrhizal trait‐based approach

AbstractQuestionsHow are ectomycorrhizal (ECM) and arbuscular mycorrhizal (AM) traits related to other plant traits at the community level? Which abiotic factors drive the variability of these ECM and AM traits? What is the relative importance of plant species turnover and plant intraspecific differences on mycorrhizal trait variability among communities?LocationNine Mediterranean woody communities, Sierra Morena Mountains, Córdoba, south Spain.MethodsMycorrhizal and plant traits were weighted by the abundance of constitutive plant species to calculate community‐weighted means (CWM). Maximum likelihood techniques were used to analyse how variation in these functional community traits was driven by soil abiotic factors.ResultsThe degree of ECM colonization was positively related to the abundance of evergreen species and to tissue dry matter content (in leaves and roots), but negatively to specific root length and specific leaf area. The best abiotic predictor of ECM colonization was soil moisture, with higher ECM colonization in drier sites. However, AM colonization was not related to any of the plant traits studied, and was positively related to soil Cu and other physico‐chemical soil properties. Changes in community mycorrhization of both types were primarily due to plant species turnover (mainly species occurrence), with a remarkable importance of plant intraspecific variability in the case of AM colonization (especially in the percentage of vesicles).ConclusionsThe degrees of colonization by ECM and AM at the community level exhibited different patterns, influenced by both biotic factors (plant functional structure) and abiotic conditions (soil moisture and chemical composition). The proposed mycorrhizal trait‐based approach can help to better understand the role of these symbioses on plant community functioning.

Rainfall, microhabitat, and small mammals influence the abundance and distribution of soil microorganisms in a Chilean semi-arid shrubland

Patterns in rainfall and soil water availability are considered to be the main drivers governing arid and semiarid ecosystems. While the mechanisms by which water limits aboveground net primary production has been widely explored, few long-term studies have examined interactions between precipitation, soil resources, plant communities, and soil microbial communities; these may be critical to understanding soil biogeochemical cycles and above- and belowground interactions. We capitalized on a long-term biotic manipulation (exclusion of small mammal herbivores from replicate plots) and long-term variation in rainfall to assess how precipitation, small mammals, and shrub cover act directly and interactively to influence the spatial and temporal distribution of soil microorganisms, a key first step to understanding soil biogeochemical cycles. We measured the abundance of arbuscular mycorrhiza (AM), soil fungi, soil bacteria, and soil physicochemical characteristics over 10 consecutive years in a semiarid thorn scrub community in north–central Chile; we sampled two microhabitats (under shrub cover, and in open spaces between shrubs colonized by ephemeral plants), and in plots with or without the presence of native small mammals, the main herbivores in this environment. Annual rainfall ranged widely (11–356 mm) in this period and was the primary factor affecting abundance of AM root colonization and soil microbes. While the percentage of root length with AM was higher in dry compared to wet years, free-living soil bacteria and fungi were more abundant during wet years. All microorganisms were more abundant in the resource islands beneath the shrubs compared to open microhabitat between shrubs, although the relation between soil biota and the concentration of some particular nutrients was negative. These patterns were modulated by the presence of small mammals, which enhanced root colonization by AM fungi, particularly for ephemeral plants, but which were negatively associated with soil fungi abundance. The abundance of soil bacteria showed a more complex response to the presence of small mammals and was dependent on microhabitat and year. The spatial and temporal heterogeneity of soil resources and the activity of small mammals are important modulators of subterranean biotic responses to rainfall, the primary factor affecting soil microbiota abundance in this semiarid ecosystem.

Linkage of plant trait space to successional age and species richness in boreal forest understorey vegetation

Summary Determining the changes in within‐ and between‐species functional diversity in plant communities, and their contribution to overall species trait overlap, can enhance efforts at understanding mechanisms of species coexistence. However, little is known about how variation in species functional diversity influences variation in species trait overlap among contrasting environments. Here, we studied the understorey vegetation in a well‐characterized 5000‐year‐old chronosequence involving 30 forested islands that differ greatly in size, soil fertility and species diversity. Across this chronosequence, we expected consistent changes in both within‐ and between‐species functional diversity that would lead to decreasing overall species trait overlap with increasing successional age, species richness, understorey vegetation density and spatial heterogeneity of soil resources. For each island, we measured specific leaf area (SLA) of each of ten individuals of each plant species present. Using a variance decomposition method, we partitioned the total community functional diversity of SLA on each island into within‐ and between‐species functional diversity. Further, we estimated overall species trait overlap as the ratio of within‐species functional diversity to total functional diversity. Using regression analyses, we then explored relationships of within‐ and between‐species functional diversity, and of overall species trait overlap, with several environmental variables across the 30 islands. Consistent with our hypotheses, overall species trait overlap decreased with successional age due to a statistically significant decrease in within‐species functional diversity, and decreased with species richness due to a simultaneous decrease in within‐species functional diversity and increase in between‐species functional diversity. Against our predictions, overall species trait overlap increased in more competitive environments and did not change with increasing spatial heterogeneity of soil N or P. Synthesis. Our study suggests niche packing as a key mechanism for species coexistence in plant communities. Using SLA as an integrator of plant ecological strategy, we show that community successional age and species richness are significantly linked to trait space distribution of plant individuals of boreal forest understorey vegetation and therefore to local species coexistence. Our results also suggest that the trait space of dominant and subordinate species may respond differently to local environmental variables.

Tree patch distribution drives spatial heterogeneity of soil traits in cork oak woodlands

Spatial heterogeneity of soil resources is linked to tree patch distribution in Mediterranean cork oak woodlands. Tree patch distribution modifies soil traits by varying litterfall inputs due to different tree covers. The spatial heterogeneity of soil resources affects the structure and functioning of the different plant communities on ecosystems. In Mediterranean oak woodlands, the scattered trees play a key role in this spatial heterogeneity and might strongly influence ecosystem functioning and its productivity. To assess the influence of the spatial pattern of trees and litter nutrient content on the spatial heterogeneity of soil properties. We used a combination of geostatistical techniques and a linear mixed model to evaluate the spatial heterogeneity of soil and the seasonal and spatial variability of litter nutrient content, respectively. Soil parameters showed a high spatial heterogeneity. Tree cover was positively related with soil pH, and the organic matter, N, K, and Ca soil content. The return of nutrients to the soil via leaf fall had a marked seasonality and a high spatial variability, but this spatial variability had no effect on the spatial pattern of soil resources. The spatial heterogeneity of soil in cork oak woodlands is mainly driven by tree patches distribution. The importance of the spatial heterogeneity of soil resources and the spatial pattern of trees on the functioning of the dehesa ecosystem makes it necessary to include them in plant nutrition studies and modeling approaches in these ecosystems.

Why is seed production so variable among individuals? A ten-year study with oaks reveals the importance of soil environment.

Mast-seeding species exhibit not only a large inter-annual variability in seed production but also considerable variability among individuals within the same year. However, very little is known about the causes and consequences for population dynamics of this potentially large between-individual variability. Here, we quantified seed production over ten consecutive years in two Mediterranean oak species – the deciduous Quercus canariensis and the evergreen Q. suber - that coexist in forests of southern Spain. First, we calibrated likelihood models to identify which abiotic and biotic variables best explain the magnitude (hereafter seed productivity) and temporal variation of seed production at the individual level (hereafter CVi), and infer whether reproductive effort results from the available soil resources for the plant or is primarily determined by selectively favoured strategies. Second, we explored the contribution of between-individual variability in seed production as a potential mechanism of satiation for predispersal seed predators. We found that Q. canariensis trees inhabiting moister and more fertile soils were more productive than those growing in more resource-limited sites. Regarding temporal variation, individuals of the two studied oak species inhabiting these resource-rich environments also exhibited larger values of CVi. Interestingly, we detected a satiating effect on granivorous insects at the tree level in Q. suber, which was evident in those years where between-individual variability in acorn production was higher. These findings suggest that individual seed production (both in terms of seed productivity and inter-annual variability) is strongly dependent on soil resource heterogeneity (at least for one of the two studied oak species) with potential repercussions for recruitment and population dynamics. However, other external factors (such as soil heterogeneity in pathogen abundance) or certain inherent characteristics of the tree might be also involved in this process.

Permissible Soil Loss Limits for Different Physiographic Regions of West Bengal

Land degradation due to water erosion is a major impediment for optimum land productivity in West Bengal (WB). Sustainable development of the state needs appropriate land-use planning taking into account the heterogeneity in soil and land resources. In this study, the maximum permissible soil loss rates ( T values) were computed for 115 mapping units of WB by integrating the most sensitive soil indicators such as infiltration rate, bulk density, water stable aggregates, organic carbon and fertility status to assess soil quality governing soil resistibility to erosion. For each mapping unit, indicator soil attribute values were quantitatively expressed in the 0 to 1 scale and an aggregate score was computed from the attribute scores and the corresponding weights. The results suggested a wide difference in the T values among the regions and mapping units, with values ranging from 2.5 to 12.5 Mg ha -1 yr -1 . In the state as a whole, about 88% of the area has 'T' value of 12.5 Mg ha -1 yr -1 . The relatively plain lands in the Indo-Gangetic plain, coastal and delta plain and the Bengal basin have a higher soil loss tolerance of about 4.0 Mg ha -1 yr -1 than the hilly and undulating regions in the Eastern Himalaya and Eastern plateau regions. The information generated will serve as a useful guide for devising differential conservation and resource use plans on the basis of soil resource potential.