Bertrand, R. | bioRxiv Science

bioRxiv2017

Unequal contributions of species’ persistence and migration on plant communities’ response to climate warming throughout forests

Community reshuffling is lagging behind climate warming for many taxa, thereby generating a climatic debt. However, only few studies have attempted to assess the underlying factors that explain this debt, and none has gone further to explore this issue from a biogeographical perspective. Here I examine how effects of species migration and persistence on the current climatic debt vary spatially in forest herbaceous communities throughout the French territory. I show that Mediterranean communities are responding to climate warming through both high species migration and persistence effects, while alpine forest is the only ecosystem where species migration overtakes species persistence mechanisms. Such an approach seems promising in assessing the underlying mechanisms of the biodiversity response to climate change locally, and it can be applied for conservation issues to assess biodiversity sensitivity and optimize its management.

ecology↗

bioRxiv2017

Decreasing before increasing: Evolution of nitrogen availability conditions in French forest ecosystems over the last century according to forest herbs

O_LINitrogen (N) is a key nutrient elements for ecosystems which has been highly impacted by human development and activities since the early 20th century. Despite that changes in N-availability have been demonstrated to impact forests, we still miss evidence of its effect on species composition over the long-term.\nC_LIO_LIBased on a large number of floristic observations (n = 45 604), the French forest status related to soil N-availability was reconstructed from herb species assemblage between 1910 and 2010 using both a bioindication approach and a spatiotemporal sampling aiming to pair past and recent floristic observations.\nC_LIO_LIWe showed that soil N content bioindicated from forest herb communities was higher at the start of the 20th century than over the 2005-2010 period. It decreased more or less continuously until 1975 and 2005 in coniferous (mean {Delta}C:N=+0.79) and broadleaved (mean {Delta}C:N=+0.74) forests, respectively, and then was lower than the most recent bioindicated N level observed over the 2005-2010 period (mean {Delta}C:N=-0.10 and -0.16, respectively). Spatial analysis confirmed the temporal trends with a decrease and increase in forest surface areas where soil N impoverishment and enrichment have been bioindicated over the time, respectively.\nC_LIO_LIN bioindicated trends are opposite to changes in N atmospheric deposition compared the 2005-2010 period, while they follow temporal variation in mean N deposition until 1990.\nSynthesis. Our results showed that forest herb communities have been reshuffled in regards of their soil N requirements over the 20th century highlighting that temporal changes in soil N supply have impacted the understory species composition of forest. We evidenced changes in communities towards less nitrophilous plant assemblage followed by a recent eutrophication since 2005. We propose that the nitrogen forest vegetation status is likely related to N atmospheric deposition trend, but also to both acidification, climate change and forestry management which impacted organic matter decomposition and soil N mineralization through effects on soil microbial and fauna activities. The current eutrophication observed in forest herb communities is worrisome for temperate forest ecosystem and its functioning in regards of biodiversity homogenization which often accompanied such a community reshuffling.\nC_LI

ecology↗