Different temporal trends in vascular plant and bryophyte communities along elevational gradients over four decades

Despite many studies showing biodiversity responses to warming, the generality of such responses across taxonomic groups remains unclear. Very few studies have tested for evidence of bryophyte community responses to warming, even though bryophytes are major contributors to diversity and functioning in many ecosystems. Here, we report an empirical study comparing long-term change in bryophyte and vascular plant communities in two sites with contrasting long-term warming trends, using "legacy" botanical records as a baseline for comparison with contemporary resurveys. We hypothesized that ecological changes would be greater in sites with a stronger warming trend and that vascular plant communities, with narrower climatic niches, would be more sensitive than bryophyte communities to climate warming. For each taxonomic group in each site, we quantified the magnitude of changes in species' distributions along the elevation gradient, species richness, and community composition. We found contrasted temporal changes in bryophyte vs. vascular plant communities, which only partially supported the warming hypothesis. In the area with a stronger warming trend, we found a significant increase in local diversity and dissimilarity (beta-diversity) for vascular plants, but not for bryophytes. Presence-absence data did not provide sufficient power to detect elevational shifts in species distributions. The patterns observed for bryophytes are in accordance with recent literature showing that local diversity can remain unchanged despite strong changes in composition. Regardless of whether one taxon is systematically more or less sensitive to environmental change than another, our results suggest that vascular plants cannot be used as a surrogate for bryophytes in terms of predicting the nature and magnitude of responses to warming. Thus, to assess overall biodiversity responses to global change, abundance data from different taxonomic groups and different community properties need to be synthesized.Peer reviewe

Current knowledge on overall post-logging biomass dynamics in Northern Amazonian forests

This article presents the effects of logging on the dynamics of above-ground biomass from the results of the post-logging study within two forests: Cikel in Eastern Para, Brazil and Paracou in French Guiana. The main objective is to compare the impact of commercial logging on the regeneration of the above-ground biomass in these forests whose characteristics differ in terms of structure and growth. In both sites, the intensity of exploitation is a key factor in determining the loss of biomass and the time required for its regeneration. In Paracou, the regeneration of biomass lost during conventional logging of 10 trees per hectare takes 45 years and more than 100 years when operating with higher intensity (21 trees/ha). In Cikei the forest biomass regenerates after 49 years harvesting 6 trees/ha and that takes 87 years after removal of 8 trees/ha. This regeneration needs similar time on both sites but with lower logging intensity at Cikel, in which felled trees are larger with a greater biomass than those of Paracou. This post-logging study has established a direct correlation of the dynamics of the biomass with the initial structure of the forest, as well as with the parameters of forest dynamics: mortality, growth and recruitment. The accumulation of biomass by the tree growth of the two remaining stands is a key parameter for the net carbon storage, while the contribution of recruitment in Paracou becomes significant only after 10 years after felling. Therefore in view to improve the growth of residual trees, it is compulsory to apply adequate silvicultural treatments such as selective thinning or removal of vines. While the two forests are geographically close enough, their regenerative abilities differ and because of the significant difference in size of the trees, the forest could tolerate more intensive harvesting in French Guian

Segmentation 3D des arbres d'un peuplement forestier par fusion de données lidar aériennes et hyperspectrales.

International audienceAccess to data with high spatial and spectral resolution is becoming more widespread and makes it possible to consider new applications for monitoring forest ecosystems. In particular, it is possible to consider studies of an entire stand but at the tree level. However, this raises questions about the joint use of data from different sensors such as LiDAR and hyperspectral imagers. This study presents a fusion methodology between high-density LiDAR data (45 pts/m² minimum) and VNIR hyperspectral images (HI) - (80 cm spatial resolution) acquired on french Alpine forests along an altitude gradient. The objective is to extract the main architectural characteristics of each individual tree and in particular the dimensions of crowns knowing the species. The methodology is based on the integration of HI and LiDAR data at different levels of fusion. First species are identified using the reflectance attributes contained in HI and the LiDAR canopy model, and then the 3D point cloud is segmented based on the allometric characteristics of the species. The integration of this additional information together with the segmentation algorithm provides an essential association strategy for LiDAR points located in the lower part of the canopy. Finally, the main dimensions of the crowns and associated trees are extracted from the 3D segmentation

Projet PROTEST : vers une méthodologie pluridisciplinaire d'analyse territoriale forestière

In French mountain areas, the heterogeneity of forests, the fragmentation of ownership and accessibility constraints hamper inventory and management actions. To ensure the sustainability of ecosystem services provided by forests, it is necessary to evaluate them while taking into account the local and global socio-economic context. The PROTEST project aims to build a methodology for territorial analysis of forest resources, based on advances in remote sensing, GIS, forest dynamics modelling and territorial foresight. The study area of the project is the Geopark Massif des Bauges (France) that contains 50000 ha of forests. The first task is to produce a map of forest resources, based on airborne lidar remote sensing, and of its accessibility, based on the Sylvaccess model. The second task is to implement a territorial foresight work and define forest management scenarios that combine environmental and societal determinants. Societal factors and their possible evolutions will be defined on the basis of field surveys and expert opinions. Depending on these factors and on a typology of parcels, scenarios of forest management will be proposed to simulate the behavior of owners. In the third task, these scenarios will be integrated into a spatialized model of forest dynamics, in order to simulate the evolution of the forest mosaic at the parcel level. Linker functions will be integrated to evaluate ecosystem services (wood production, biodiversity, carbon stock...) from simulated forest characteristics. The results will be used to support participatory workshops that will aim to define a forest management strategy supporting the territorial development

Energy, water and carbon exchanges in managed forest ecosystems: description, sensitivity analysis and evaluation of the INRAE GO+ model, version 3.0

International audienceThe mechanistic model GO+ describes the functioning and growth of managed forests based upon biophysical and biogeochemical processes. The biophysical and biogeochemical processes included are modelled using standard formulations of radiative transfer, convective heat exchange, evapotranspiration, photosynthesis, respiration, plant phenology, growth and mortality, biomass nutrient content, and soil carbon dynamics. The forest ecosystem is modelled as three layers, namely the tree overstorey, understorey and soil. The vegetation layers include stems, branches and foliage and are partitioned dynamically between sunlit and shaded fractions. The soil carbon submodel is an adaption of the Roth-C model to simulate the impact of forest operations. The model runs at an hourly time step. It represents a forest stand covering typically 1 ha and can be straightforwardly upscaled across gridded data at regional, country or continental levels. GO+ accounts for both the immediate and long-term impacts of forest operations on energy, water and carbon exchanges within the soil–vegetation–atmosphere continuum. It includes exhaustive and versatile descriptions of management operations (soil preparation, regeneration, vegetation control, selective thinning, clear-cutting, coppicing, etc.), thus permitting the effects of a wide variety of forest management strategies to be estimated: from close to nature to intensive. This paper examines the sensitivity of the model to its main parameters and estimates how errors in parameter values are propagated into the predicted values of its main output variables.The sensitivity analysis demonstrates an interaction between the sensitivity of variables, with the climate and soil hydraulic properties being dominant under dry conditions but the leaf biochemical properties being most influential with wet soil. The sensitivity profile of the model changes from short to long timescales due to the cumulative effects of the fluxes of carbon, energy and water on the stand growth and canopy structure. Apart from a few specific cases, the model simulations are close to the values of the observations of atmospheric exchanges, tree growth, and soil carbon and water stock changes monitored over Douglas fir, European beech and pine forests of different ages. We also illustrate the capacity of the GO+ model to simulate the provision of key ecosystem services, such as the long-term storage of carbon in biomass and soil under various management and climate scenarios

Amplification of Diacylglycerol Activation of Protein Kinase C by Cholesterol

The combined effects of cholesterol, a major cell membrane component, and the lipid second messenger diacylglycerol on the activity of protein kinase C (PK-C) and the structure of phosphatidylcholine/phosphatidylserine bilayers were investigated using specific PK-C assays and 2H NMR. Whereas the classical activation of PK-C was observed as an effect of diacylglycerol, in the absence of this second messenger, cholesterol did not affect PK-C activity. A novel effect of amplified PK-C activation was observed in the presence of both cholesterol and diacylglycerol concentrations within the physiological range of each of these components. 2H NMR results suggest that this phenomenon is due to cholesterol- and diacylglycerol-induced increased propensity of the lipids to adopt nonbilayer phases, effectively destabilizing the bilayer structure. The magnitude of the effect was a function of cholesterol concentration, implying that laterally separated cell membrane domains with distinct cholesterol concentrations have the capacity to differ in their sensitivity to extracellular stimuli