Biology subjects

Aandahl, Z.

Publications and source records attributed to Aandahl, Z..

3 recordsLinked to original sources

bioRxiv2023

Tree species richness and evenness affect forest biomass differently across biogeographic regions

The relationship between tree species diversity, measures of forest structure, and forest biomass has long been debated, with local- or continental-scale studies often finding contrasting results. Given the importance of forests as global carbon sinks, understanding the characteristics that underpin biomass accumulation is thus a critical component of mitigating climate change. Here we present a global analysis of 11,400 forest plots, sourced from scientific publications and forest inventories, to investigate the association of forest basal area (used as a proxy for biomass) with stem density and measures of tree species diversity (richness and evenness). We used generalised additive models to account for the confounding effects of climate and spatial signal and we modelled the density, climate, and diversity effects both globally and for each biogeographic region. Stem density showed a strong positive association with basal area across all biogeographic regions, while the effect of species richness varied. In the Palearctic, Nearctic, and Neotropical biogeographic regions, basal area was positively associated with species richness, although this was only detectable for lower values of basal area. In the Ethiopian and Oriental biogeographic regions there was no relationship between richness and basal area, while in the Australian biogeographic regions it was negative. The weak-to-no association between species evenness and basal area in all bioregions other than Australia suggests that the overall correlation emerges from processes operating at more local scales. Our results highlight the importance of accounting for biogeographic processes when evaluating strategies to mitigate climate change and support nature conservation.

ecology↗

bioRxiv2023

Land use change drives major loss of Southeast Asian biodiversity

Southeast Asia is highly biodiverse and currently experiences among the highest rates of tropical deforestation globally, but impacts on biodiversity are not well synthesized. We use Bayesian multi-level modeling to meta-analyse 831 pairwise comparisons of biodiversity in sites subject to human land use change and anthropogenic forest disturbance (for example in plantations or logged forest) versus undisturbed sites. After controlling for hierarchical dependences, we show that biodiversity is a fifth lower in sites with these land-use changes (95% credible interval= 16-28%, mean = 22%). This reduction was greater when land use change/anthropogenic forest disturbances were high-intensity (34% reduction in biodiversity) compared to low-intensity (18% reduction), and effects were consistent across biogeographic regions and taxa. Oil-palm plantations lead to the greatest reduction in biodiversity (39%, CI 27-48%), and agroforests the least (24%, CI 10-37%). We also find that biodiversity is reduced in young secondary forest by 26% (CI 4-42%) compared to undisturbed forest, but there is no reduction in biodiversity for intermediate or mature-aged secondary forest (although species composition is potentially altered). Overall, our study provides the clearest evidence yet of the substantial detrimental impact of land-use change and anthropogenic forest disturbance on the biodiversity of Southeast Asia.

ecology↗

bioRxiv2022

Continuing decline of the eastern quoll in Tasmania

Like many other Australian mammals, the eastern quoll (Dasyurus viverrinus) was widespread on the Australian mainland but went extinct there during the 20th century. The species remained abundant in Tasmania until a rapid decline occurred from 2001 to 2003, coinciding with a period of unsuitable weather. We provide an updated analysis of eastern quoll population trends in Tasmania by analysing a Tasmania-wide time series of annual spotlight counts (1985-2019). Eastern quolls were widespread and abundant in Tasmania until the early 2000s. A distinct change occurred in the early 2000s in the east and northeast, which led to severe population reductions. However, we present new evidence of an earlier decline in the north (mid-1990s) and a more recent decline around 2009 in the south. Range-wide declines have continued unabated during the last decade, resulting in a [~]67% decline (since the late 1990s) in the area with high quoll abundance. Although the timing of the major decline in the early 2000s coincided with unfavourable weather, the continuing decline and more recent change points suggest other causes are also involved. We can no longer assume that the existence of eastern quolls in Tasmania ensures the species long-term survival, highlighting the urgent need to increase efforts to conserve the remaining populations in Tasmania.

ecology↗