Climate seasonality limits leaf carbon assimilation and wood productivity in tropical forests

The seasonal climate drivers of the carbon cycle in tropical forests remain poorly known, although these forests account for more carbon assimilation and storage than any other terrestrial ecosystem. Based on a unique combination of seasonal pan-tropical data sets from 89 experimental sites (68 include aboveground wood productivity measurements and 35 litter productivity measurements), their associate canopy photosynthetic capacity (enhanced vegetation index, EVI) and climate, we ask how carbon assimilation and aboveground allocation are related to climate seasonality in tropical forests and how they interact in the seasonal carbon cycle. We found that canopy photosynthetic capacity seasonality responds positively to precipitation when rainfall is < 2000 mm.yr−1 (water-limited forests) and to radiation otherwise (light-limited forests); on the other hand, independent of climate limitations, wood productivity and litterfall are driven by seasonal variation in precipitation and evapotranspiration respectively. Consequently, light-limited forests present an asynchronism between canopy photosynthetic capacity and wood productivity. Precipitation first-order control indicates an overall decrease in tropical forest productivity in a drier climate.Peer reviewe

Climate seasonality limits leaf carbon assimilation and wood productivity in tropical forests

The seasonal climate drivers of the carbon cycle in tropical forests remain poorly known, although these forests account for more carbon assimilation and storage than any other terrestrial ecosystem. Based on a unique combination of seasonal pan-tropical data sets from 89 experimental sites (68 include aboveground wood productivity measurements and 35 litter productivity measurements), their associated canopy photosynthetic capacity (enhanced vegetation index, EVI) and climate, we ask how carbon assimilation and aboveground allocation are related to climate seasonality in tropical forests and how they interact in the seasonal carbon cycle. We found that canopy photosynthetic capacity seasonality responds positively to precipitation when rainfall is  < 2000 mm yr⁻¹ (water-limited forests) and to radiation otherwise (light-limited forests). On the other hand, independent of climate limitations, wood productivity and litterfall are driven by seasonal variation in precipitation and evapotranspiration, respectively. Consequently, light-limited forests present an asynchronism between canopy photosynthetic capacity and wood productivity. First-order control by precipitation likely indicates a decrease in tropical forest productivity in a drier climate in water-limited forest, and in current light-limited forest with future rainfall  < 2000 mm yr⁻¹

Surviving winter: Food, but not habitat structure, prevents crashes in cyclic vole populations

Vole population cycles are a major force driving boreal ecosystem dynamics in north - western Eurasia. However, our understanding of the impact of winter on these cycles is increasingly uncertain, especially because climate change is affecting snow predict - ability, quality, and abundance. We examined the role of winter weather and snow conditions, the lack of suitable habitat structure during freeze- thaw periods, and the lack of sufficient food as potential causes for winter population crashes. We live- trapped bank voles Myodes glareolus on 26 plots (0.36 ha each) at two different eleva - tions (representing different winter conditions) in southeast Norway in the winters 2013/2014 and 2014/2015. We carried out two manipulations: supplementing six plots with food to eliminate food limitation and six plots with straw to improve habitat structure and limit the effect of icing in the subnivean space. In the first winter, all bank voles survived well on all plots, whereas in the second winter voles on almost all plots went extinct except for those receiving supplemental food. Survival was highest on the feeding treatment in both winters, whereas improving habitat structure had no effect. We conclude that food limitation was a key factor in causing winter population crashes

Surviving winter: Food, but not habitat structure, prevents crashes in cyclic vole populations

Vole population cycles are a major force driving boreal ecosystem dynamics in north - western Eurasia. However, our understanding of the impact of winter on these cycles is increasingly uncertain, especially because climate change is affecting snow predict - ability, quality, and abundance. We examined the role of winter weather and snow conditions, the lack of suitable habitat structure during freeze- thaw periods, and the lack of sufficient food as potential causes for winter population crashes. We live- trapped bank voles Myodes glareolus on 26 plots (0.36 ha each) at two different eleva - tions (representing different winter conditions) in southeast Norway in the winters 2013/2014 and 2014/2015. We carried out two manipulations: supplementing six plots with food to eliminate food limitation and six plots with straw to improve habitat structure and limit the effect of icing in the subnivean space. In the first winter, all bank voles survived well on all plots, whereas in the second winter voles on almost all plots went extinct except for those receiving supplemental food. Survival was highest on the feeding treatment in both winters, whereas improving habitat structure had no effect. We conclude that food limitation was a key factor in causing winter population crashes

Surviving winter: Food, but not habitat structure, prevents crashes in cyclic vole populations

Vole population cycles are a major force driving boreal ecosystem dynamics in north - western Eurasia. However, our understanding of the impact of winter on these cycles is increasingly uncertain, especially because climate change is affecting snow predict - ability, quality, and abundance. We examined the role of winter weather and snow conditions, the lack of suitable habitat structure during freeze- thaw periods, and the lack of sufficient food as potential causes for winter population crashes. We live- trapped bank voles Myodes glareolus on 26 plots (0.36 ha each) at two different eleva - tions (representing different winter conditions) in southeast Norway in the winters 2013/2014 and 2014/2015. We carried out two manipulations: supplementing six plots with food to eliminate food limitation and six plots with straw to improve habitat structure and limit the effect of icing in the subnivean space. In the first winter, all bank voles survived well on all plots, whereas in the second winter voles on almost all plots went extinct except for those receiving supplemental food. Survival was highest on the feeding treatment in both winters, whereas improving habitat structure had no effect. We conclude that food limitation was a key factor in causing winter population crashes

What is the spatial unit for a wintering teal Anas crecca? Weekly day roost fidelity inferred from nasal saddles in the Camargue, southern France

Dabbling ducks generally use distinct day roost and nocturnal habitats, the set of which constitute their ’functional unit’. The rate at which these birds may switch between day roosts has never been quantified. Using resightings of nasal- saddled birds and capture-recapture modelling in the Camargue, southern France, we estimated the weekly probability that a teal Anas crecca switches from one day roost to another one nearby (transition probabilities). We also estimated the probability that a teal survives and remains in our study area, consisting of four neighbouring roosts (apparent survival). Birds were highly faithful to one specific water body if they remained in our study area (i.e. weekly rate of switching between roosts was only about 2-6%), but the probability that an individual remained within one of the four roosts from one week to the next (local weekly apparent survival rate) was only 60-70%. Intensive search efforts led to a 60% detection probability. Low local apparent survival coupled with very high site fidelity within the system suggests that two distinct strategies may coexist, i.e. frequent movement between distant winter quarters vs very high fidelity to the very same local wetland. Such strategies may be used successively by the same individuals, or may alternatively represent distinct bird categories (i.e. transients vs residents). In any case, these different strategies suggest that habitat management procedures need to be considered at both local and flyway scales simultaneously. The former may ensure that sites repeatedly used by the same individuals can provide adequate conditions to birds when they remain in a given winter quarter, while the latter will ensure transient birds find appropriate sites within the network of distant wetlands they may use as successive wintering quarters during a seasonPeer reviewe