La compréhension des impacts du réchauffement climatique anthropique sur la végétation terrestre nécessite une compréhension de base de la façon dont les voies directes et indirectes – médiées par la biodiversité – du changement climatique impactent le fonctionnement des écosystèmes. La décomposition et la minéralisation de la litière végétale sont des éléments clés du cycle mondial du carbone et représentent des incertitudes majeures dans la relation climat-biodiversité.
Abstract Question How does plant species richness respond to simulated area loss based on the realistic geometry of area loss in subalpine moorland ecosystems? Location Hakkoda mountain range, Aomori, Japan. Methods We constructed species distribution models based on relationships between species distributions and environmental conditions in subalpine moorland ecosystems. We then simulated moorland area loss based on the realistic geometry of area loss from the past (1967) to the present (2019) to predict future changes in plant diversity. Here, we defined the realistic geometry of area loss as the plausible spatial pattern of future habitat loss. Finally, we analyzed how the rate of species loss in response to the realistic area loss can be explained by a range of factors including spatial patterns in species distributions, total number of species present, and environmental variables for the focal moorland. Results Within each moorland site, areas prone or those less prone to be lost were distributed non‐randomly at a local scale. In general, the patterns of species loss caused by the realistic area loss differed from those caused by random area loss. At most sites, realistic area loss caused a relatively small decline in species richness up to a certain threshold of area loss, and accelerating decline thereafter. None of the factors can explain the rate of decrease in species richness caused by the realistic area loss. At the species level, however, species with lower occurrence rates at a given site can be lost earlier than those with higher occurrence rates by the realistic area loss. Conclusions Patterns of habitat loss and species distributions are not spatially random, and the classical approach based on the species–area relationship assuming random area loss can thus either under‐ or overestimate the risk of species loss.
Communities in isolated habitat patches surrounded by inhospitable matrices often form a nested subset pattern. However, the underlying causal mechanisms and conservation implications of nestedness in regional communities remain controversial. The nested ranks of species in a nested species‐by‐site matrix may reflect a gradient of species vulnerability to extinction or of colonization ability. However, nestedness analysis has rarely been used to explore determinants of species rank; consequently, little is known of underpinning mechanisms. In this study, we examined nestedness in moorland plant communities widely interspersed within the subalpine zone of northern Japan. Moorland sites differed in area (1000–160 000 m 2 ) and were naturally isolated from one another to various extents within an inhospitable forest matrix. We also determined whether site characteristics (physical and morphometric measures) and species characteristics (niche position and breadth, based on species’ traits) are related to nestedness. Moorland plant communities in the study area were significantly nested. The pH and moorland kernel density (proxy for spatial clustering of moorlands around the focal site) were the most important predictors of moorland site nested rank in a nestedness matrix. Niche breadths of species (measured as variation in leaf mass area and height) predicted species’ nested ranks. Selective environmental tolerances imposed by environmental harshness and selective extinction caused by declines in site carrying capacities probably account for the nested subset pattern in moorland plant communities. The nested rank of species in the nestedness matrix can therefore be translated into the potential order of species loss explainable by species niche breadths (based on variation in functional traits). Complementary understanding of the determinants of site ranking and species ranking in the nestedness matrix provides powerful insight into ecological processes underlying nestedness and into the ways by which communities are assembled or disassembled by such processes.
The performance of the three multi-trait metrics for convergence against the problems of scaling relationships, the sufficiency of traits, and local species richness.
Comparison of old and new vegetation maps is an effective way to detect vegetation dynamics. Recent developments in computer technology have made it possible to accurately compare old paper vegetation maps with current digitized vegetation maps to reveal long-term vegetation dynamics. Recently, a 1:50,000 scale vegetation map of the Hakkoda Mountains in northern Japan, located in the ecotone of cool temperate and subalpine forests in northern Japan under an East Asian monsoon climate, from 1930 was discovered. We compared the 1930s vegetation map with the most recent 2010 vegetation map to test the following hypotheses: 1) the occurrence of upward expansion of the upper limit of cool-temperate deciduous forests, and 2) whether designation as a national park in 1936 would have reduced forestry and land use, expanded beech forests, and cool-temperate deciduous forests. To compare vegetation changes, 67 types of vegetation legends for the 1930 and 2010 maps were unified to 21 based on plant species composition. Consequently, vegetation has changed substantially over the past 80 years. 1) In the subalpine zone above 1,000 m, the coniferous forest area decreased by half. In the cool temperate zone below 1,000 m, the area of beech forests increased 1.48 times, and some of them could be shifted upwards, replacing subalpine fir forests in the lower part of the subalpine zone. 2) In areas below 700 m, deciduous oak forests once used as thickets were almost halved. Instead, climax and beech forests expanded. However, we also found that even after the area was declared a national park, oak forests were cleared and converted to commercial forests such as cedar plantations, cattle ranches, and horse pastures in some areas. These results will be useful for future ecosystem and biodiversity research/conservation and will provide baseline information for climate change adaptation policies.
Abstract Aridity, edaphic variables related to aridity, and livestock grazing are major drivers of plant community composition across dryland grasslands. With accounting these factors, little is known about differences in determinants and changing patterns along aridity gradients with different average of aridity. Thus, the comparative investigations of communities without and with grazing in semi-arid and arid regions are suitable to clarify the difference in compositional responses along aridity gradients between potential vegetations and degraded ones with grazing. We investigated compositional changes of communities without/with grazing in semi-arid (north) /arid (south) regions across Mongolia. The compositional changes based on Bray-Curtis dissimilarity were investigated by generalized dissimilarity modeling, including geographic distance, aridity, soil pH, and sand and clay contents as independent variables. The determinants and changing patterns of community composition were compared among the four groups. Aridity had significant impacts on community composition regardless of the regions and the absence/presence of grazing. However, without the dependency on grazing, the difference in response patterns was observed between the regions. The compositional change was steeper especially at the upper edge of aridity rather than the lower edge in the arid region. This indicates the vulnerability of plant communities to aridity shifts due to future climate change in desert steppe of Mongolia. In addition, regardless of the regions, the effects of soil pH on community composition were eliminated by grazing. Because soil pH indirectly affected by aridity shifts can have impacts on community composition of potential vegetations without grazing, the long-term monitoring of vegetation dynamics needs observations of both of communities without and with grazing.
Abstract Understanding how ecosystem multifunctionality is maintained in naturally assembled communities is crucial, because human activities benefit from multiple functions and services of various ecosystems. However, the effects of above‐ and below‐ground biodiversity on ecosystem multifunctionality in alpine and boreal moorland ecosystems remain unclear despite their potential as global carbon sinks. Here we evaluated how ecosystem multifunctionality related to primary production and carbon sequestration, which are crucial for global climate regulation, is maintained in natural systems. We disentangled the relationships between diversity and composition of plants and soil microbes (fungi and bacteria) and ecosystem multifunctionality in subalpine moorlands in northern Japan. We found that microbial composition primarily regulated carbon sequestration, whereas plant taxonomic and functional composition were related to all functions considered. Plant and microbial α diversity (diversity within local communities) were not generally related to any single function, highlighting the important roles of specific plant and microbial taxa in determining ecosystem functioning. When single functions were aggregated to ecosystem multifunctionality within local communities, plant and microbial community composition rather than diversity regulated ecosystem multifunctionality. We further found that plant and bacterial taxonomic β diversity (taxonomic turnover between local communities) primarily regulated the dissimilarity of ecosystem multifunctionality between local communities. Synthesis. We provide observational evidence that plant and microbial community composition rather than diversity are essential for sustaining subalpine moorland multifunctionality. Furthermore, plant and bacterial β diversity enhance the dissimilarity of moorland multifunctionality. Our study provides novel insights into biodiversity–ecosystem multifunctionality relationships occurring in nature, and helps to sustain desirable ecosystem functioning to human society.
