Global patterns of vascular plant alpha diversity

Global patterns of regional (gamma) plant diversity are relatively well known, but whether these patterns hold for local communities, and the dependence on spatial grain, remain controversial. Using data on 170,272 georeferenced local plant assemblages, we created global maps of alpha diversity (local species richness) for vascular plants at three different spatial grains, for forests and non-forests. We show that alpha diversity is consistently high across grains in some regions (for example, Andean-Amazonian foothills), but regional 'scaling anomalies' (deviations from the positive correlation) exist elsewhere, particularly in Eurasian temperate forests with disproportionally higher fine-grained richness and many African tropical forests with disproportionally higher coarse-grained richness. The influence of different climatic, topographic and biogeographical variables on alpha diversity also varies across grains. Our multi-grain maps return a nuanced understanding of vascular plant biodiversity patterns that complements classic maps of biodiversity hotspots and will improve predictions of global change effects on biodiversity.

Environmental drivers of forest biodiversity in temperate mixed forests - A multi-taxon approach

Harmonization of timber production and forest conservation is a major challenge of modern silviculture. For the establishment of ecologically sustainable forest management, the management-related environmental drivers of multi-taxon biodiversity should be explored. Our study reveals those environmental variables related to tree species diversity and composition, stand structure, litter and soil conditions, microclimate, landscape, and land-use history that determine species richness and composition of 11 forest-dwelling organism groups. Herbs, woody regeneration, ground-floor and epiphytic bryophytes, epiphytic lichens, terricolous saprotrophic, ectomycorrhizal, and wood-inhabiting macrofungi, spiders, carabid beetles, and birds were sampled in West Hungarian mature mixed forests. The correlations among the diversities and compositions of different organism groups were also evaluated. Drivers of organism groups were principally related to stand structure, tree species diversity and composition, and microclimate, while litter, soil, landscape, and land-use historical variables were less influential. The complex roles of the shrub layer, deadwood, and the size of the trees in determining the diversity and composition of various taxa were revealed. Stands with more tree species sustained higher stand-level species richness of several taxa. Besides, stands with different dominant tree species harbored various species communities of organism groups. Therefore, landscape-scale diversity of dominant tree species may enhance the diversity of forest-dwelling communities at landscape level. The effects of the overstory layer on forest biodiversity manifested in many cases via microclimate conditions. Diversity of organism groups showed weaker relationship with the diversity of other taxa than with environmental variables. According to our results, the most influential drivers of forest biodiversity are under the direct control of the actual silvicultural management. Heterogeneous stand structure and tree species composition promote the different organism groups in various ways. Therefore, the long-term maintenance of the structural and compositional heterogeneity both at stand and landscape scale is an important aspect of ecologically sustainable forest management.

Old forests and old carbon: A case study on the stand dynamics and longevity of aboveground carbon

Most information on the ecology of oak-dominated forests in Europe comes from forests altered for centuries because remnants of old-growth forests are rare. Disturbance and recruitment regimes in old-growth forests provide information on forest dynamics and their effects on long-term carbon storage. In an old-growth Quercus petraea forest in northwestern Spain, we inventoried three plots and extracted cores from 166 live and dead trees across canopy classes (DBH ≥ 5 cm). We reconstructed disturbance dynamics for the last 500 years from tree-ring widths. We also reconstructed past dynamics of above ground biomass (AGB) and recent AGB accumulation rates at stand level using allometric equations. From these data, we present a new tree-ring-based approach to estimate the age of carbon stored in AGB. The oldest tree was at least 568 years, making it the oldest known precisely-dated oak to date and one of the oldest broadleaved trees in the Northern Hemisphere. All plots contained trees over 400 years old. The disturbance regime was dominated by small, frequent releases with just a few more intense disturbances that affected ≤20% of trees. Oak recruitment was variable but rather continuous for 500 years. Carbon turnover times ranged between 153 and 229 years and mean carbon ages between 108 and 167 years. Over 50% of AGB (150 Mg·ha^-1) persisted ≥100 years and up to 21% of AGB (77 Mg·ha^-1) ≥300 years. Low disturbance rates and low productivity maintained current canopy oak dominance. Absence of management or stand-replacing disturbances over the last 500 years resulted in high forest stability, long carbon turnover times and long mean carbon ages. Observed dynamics and the absence of shade-tolerant species suggest that oak dominance could continue in the future. Our estimations of long-term carbon storage at centennial scales in unmanaged old-growth forests highlights the importance of management and natural disturbances for the global carbon cycle.

Fine-scale environmental heterogeneity and spatial niche partitioning among spring-flowering forest herbs

PREMISE

Environmental heterogeneity influences plant distributions and diversity at several spatial scales. In temperate forests, fine-scale environmental variation may promote local coexistence among herbaceous species by allowing plants to spatially partition microsites within forest stands. Here we argue that shallow soils, low soil water-holding capacity and fertility, and reduced light near tree boles should favor short, shallow-rooted, evergreen species like Anemone acutiloba with low moisture, nutrient, and light requirements. Farther from trees, richer, deeper soils should favor taller, deeper-rooted herbs with greater moisture and nutrient demands, such as Sanguinaria canadensis and Trillium flexipes.

METHODS

We tested these hypotheses by mapping the fine-scale distributions of Anemone, Sanguinaria, and Trillium individuals within a 50 × 50 m plot, comparing local species' distributions with respect to soil depth and proximity to neighboring trees, and characterizing intraspecific and interspecific spatial associations.

RESULTS

Local plant distributions were consistent with our predictions based on leaf height, physiology, and phenology. Anemone was found in microsites on shallower soils and closer to trees than either Sanguinaria or Trillium. In all three species, individual plants were spatially aggregated within 2 m, but spatially segregated from individuals of the other species beyond 2 m.

CONCLUSIONS

Differential plant responses to fine-scale environmental heterogeneity and observed spatial associations suggest that local species-environment associations could facilitate coexistence. These findings illustrate how fine-scale environmental heterogeneity coupled with phenological and physiological differences likely contribute to spatial niche partitioning among spring-flowering forest herbs and maintain high local plant diversity within temperate forests.

Trade-offs between carbon stocks and biodiversity in European temperate forests

Policies to mitigate climate change and biodiversity loss often assume that protecting carbon-rich forests provides co-benefits in terms of biodiversity, due to the spatial congruence of carbon stocks and biodiversity at biogeographic scales. However, it remains unclear whether this holds at the scales relevant for management, and particularly large knowledge gaps exist for temperate forests and for taxa other than trees. We built a comprehensive dataset of Central European temperate forest structure and multi-taxonomic diversity (beetles, birds, bryophytes, fungi, lichens, and plants) across 352 plots. We used Boosted Regression Trees (BRTs) to assess the relationship between above-ground live carbon stocks and (a) taxon-specific richness, (b) a unified multidiversity index. We used Threshold Indicator Taxa ANalysis to explore individual species' responses to changing above-ground carbon stocks and to detect change-points in species composition along the carbon-stock gradient. Our results reveal an overall weak and highly variable relationship between richness and carbon stock at the stand scale, both for individual taxonomic groups and for multidiversity. Similarly, the proportion of win-win and trade-off species (i.e., species favored or disadvantaged by increasing carbon stock, respectively) varied substantially across taxa. Win-win species gradually replaced trade-off species with increasing carbon, without clear thresholds along the above-ground carbon gradient, suggesting that community-level surrogates (e.g., richness) might fail to detect critical changes in biodiversity. Collectively, our analyses highlight that leveraging co-benefits between carbon and biodiversity in temperate forest may require stand-scale management that prioritizes either biodiversity or carbon in order to maximize co-benefits at broader scales. Importantly, this contrasts with tropical forests, where climate and biodiversity objectives can be integrated at the stand scale, thus highlighting the need for context-specificity when managing for multiple objectives. Accounting for critical change-points of target taxa can help to deal with this specificity, by defining a safe operating space to manipulate carbon while avoiding biodiversity losses.