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Narrow-ranging species are usually omitted from Species distribution models (SDMs) due to statistical constraints, while they are predicted to be particularly vulnerable to climate change. The recently available high-resolution environmental predictors, along with recently developed methods enable to increase the eligibility of narrow-ranging species for SDMs, provided their distribution is well known. We fill a gap of knowledge on the effect of predicted climate change on narrow-ranging species. We modelled the distribution of the golden mantella frog Mantella aurantiaca and the Manapany day gecko Phelsuma inexpectata, for which the distribution of their occurrence records is well documented. Our modelling scheme included a range of processes susceptible to address statistical issues related to narrow-ranging species. We predict an alarming decline in climate suitability in the whole current distribution area of both species by 2070, potentially leading to a complete extinction in most scenarios. We identified the areas with the best climate suitability in the future, but these remain largely suboptimal regarding species climatic niche. The high level of habitat fragmentation suggests that both species likely need to be at least partly translocated. Climate change may not only drive range contractions or distribution shifts in narrow-ranging species, but may lead to the complete extirpation of suitable environments across their entire region. This study suggests that the level of threats of narrow-ranging species already identified as threatened may be underestimated, especially in heterogeneous tropical areas. We stress the need to develop sampling campaigns and implement proactive actions for narrow-ranging species in the tropics.

International audience

Narrow-ranging species are usually omitted from Species distribution models (SDMs) due to statistical constraints, while they are predicted to be particularly vulnerable to climate change. The recently available high-resolution environmental predictors, along with recently developed methods enable to increase the eligibility of narrow-ranging species for SDMs, provided their distribution is well known. We fill a gap of knowledge on the effect of predicted climate change on narrow-ranging species. We modelled the distribution of the golden mantella frog Mantella aurantiaca and the Manapany day gecko Phelsuma inexpectata, for which the distribution of their occurrence records is well documented. Our modelling scheme included a range of processes susceptible to address statistical issues related to narrow-ranging species. We predict an alarming decline in climate suitability in the whole current distribution area of both species by 2070, potentially leading to a complete extinction in most scenarios. We identified the areas with the best climate suitability in the future, but these remain largely suboptimal regarding species climatic niche. The high level of habitat fragmentation suggests that both species likely need to be at least partly translocated. Climate change may not only drive range contractions or distribution shifts in narrow-ranging species, but may lead to the complete extirpation of suitable environments across their entire region. This study suggests that the level of threats of narrow-ranging species already identified as threatened may be underestimated, especially in heterogeneous tropical areas. We stress the need to develop sampling campaigns and implement proactive actions for narrow-ranging species in the tropics.

Miombo woodland is the dominant tropical dry forest formation in Africa. Its importance for local populations’ livelihoods and increased pressure has turned the spotlight on this ecosystem, now considered one of the five global wilderness areas prioritized for conservation and restoration. Forest regeneration is a key to restoring ecosystem services, but the characteristics, conditions and dynamics of this specific biome remain largely understudied. The aim of this study was to analyze the current status and evolution of woody species biodiversity, stand structure and soil properties of regrowth plots after slash-and-burn farming in Mozambique. Our survey focused on the area surrounding Gile National Park in Mozambique, which is dominated by a mosaic of vegetation including mature Miombo woodland, grassland, cropland, and land abandoned after slash-and-burn cycles. We sampled 20 plots in mature woodland and 36 plots in a chronosequence of Miombo regrowth from 1 to 35 years old, grouped in four age classes: 4–6, 8–12; 20–25 and 30–35 years. We observed that woody species richness and diversity increased with time after abandonment until similar values to those in mature woodlands were reached between 20 and 25 years later. Despite the presence of the dominant Miombo tree species belonging to the genera Julbernardia and Brachystegia, after 20–35 years of regeneration species composition remained different from that of mature woodlands. Mean DBH, tree height, and carbon stock increased while tree density decreased along the chronosequence. Tree density and tree carbon stocks in 30–35-year-old Miombo regrowth exceeded those of mature woodland. Soil C stock increased during vegetation regeneration after abandonment. Results suggest that two or three decades are necessary to reach values similar to those of mature woodland. Overall, these findings show that the region has a high regeneration capacity in terms of woody species diversity and soil properties but that disturbances have a long term effect on species composition and stand structure, underlining the importance of integrated landscape management to enhance the provision of ecosystem goods and services.

Madagascar is recognized both for its unparalleled biodiversity and the high level of threat suffered by this biodiversity, associated in particular with anthropogenic deforestation. Despite sustained efforts to fight poverty and curb deforestation, forest cover in Madagascar is rapidly decreasing. To try to explain why it is so difficult to stop deforestation in Madagascar, we analyzed the recent deforestation process in Western Madagascar through satellite image analysis and field surveys. We show that deforestation has increased from less than 0.9%/yr on 2000-2010 to more than 2%/yr on 2010-2017. We identified two major causes of deforestation, which were not associated with subsistence agriculture: slash-and-burn agriculture for the cultivation of cash crops (maize and peanut), and uncontrolled fires to create open pasture. Maize production is mainly at the destination of the domestic market and is used in particular for livestock feeding. Peanut production has boomed since 2013 and more than half of it is now exported towards Asiatic countries. The money earned by farmers is principally invested into zebu herd acquisition. Trade of agricultural commodities benefits several intermediaries, some of whom have political responsibilities thus creating conflicts of interest. On the other hand, agents from institutions in charge of the management of the protected areas have no means to enforce laws against deforestation. In the absence of an efficient strategy to stop deforestation, we predicted that 38-93% of the forest present in 2000 will have disappeared in 2050. Forest loss, apart from biodiversity loss and climate-change global issues, will be at the expense of local population. In order to stop deforestation, international aid should be used to improve local governance to enforce environmental laws and pressure should be put on trading companies to buy certified agricultural commodities that are not derived from deforestation.

Land degradation and regeneration are complex processes that greatly impact climate regulation, ecosystem service provision, and population well-being and require an urgent and appropriate response through land use planning and interventions. Spatially explicit land change models can greatly help decision makers, but traditional regression approaches fail to capture the nonlinearity and complex interactions of the underlying drivers. Our objective was to use a machine learning algorithm combined with high-resolution data sets to provide simultaneous and spatial forecasts of deforestation, land degradation, and regeneration for the next two decades. A 17,000-km(2) region in the south of Madagascar was taken as the study area. First, an empirical analysis of drivers of change was conducted, and then, an ensemble model was calibrated to predict and map potential changes based on 12 potential explanatory variables. These potential change maps were used to draw three scenarios of land change while considering past trends in intensity of change and expert knowledge. Historical observations displayed clear patterns of land degradation and relatively low regeneration. Amongst the 12 potential explanatory variables, distance to forest edge and elevation were the most important for the three land transitions studied. Random forest showed slightly better prediction ability compared with maximum entropy and generalized linear model. Business-as-usual scenarios highlighted the large areas under deforestation and degradation threat, and an alternative scenario enabled the location of suitable areas for regeneration. The approach developed herein and the spatial outputs provided can help stakeholders target their interventions or develop large-scale sustainable land management strategies.

Context: In the Mediterranean area, numerous decline and mortality processes have been reported during recent decades, affecting forest dynamics. They are likely due to increases in summer drought severity and therefore especially affect drought-sensitive species, such as silver fir (Abies alba Mill.). [br/] [br/] Aims and methods: To understand the relationships between tree growth, crown condition and mortality probability, radial growth trends of healthy, declining (showing crown damages) and dead trees were compared using tree-ring analysis. Factors involved in determining this mortality were also examined at the plot and tree level using altitudinal gradients on three contrasted sites in southeastern France. [br/][br/] Results: Individuals with higher inter-annual variability in growth were more prone to dieback. At two sites, dead trees displayed lower growth rates over their entire lifetime, while, on the last site, their juvenile growth rate was higher. Trees with crown damage had higher growth rates than healthy trees on one site, and their radial growth trends over time always differed from those of dead trees.Mortality and crown damage were little related to altitude, but strongly differed between sites and among plots underlining the importance of local edaphic and topographic conditions.[br/] [br/] Conclusion: These results suggest that the relationships among mortality probability, crown condition and growth can differ among sites, and highlight the impact of soil conditions and the need to assess them in tree mortality studies.

Context: Silver fir is declining and dying at its southern margin on the Mediterranean area, where climate is expected to be warmer and drier. At a regional scale, silver fir seems to be vulnerable to drought, and at a forest stand scale, tree death seems to be distributed according to soil water availability.[br/] [br/] Aim: To understand the vulnerability of silver fir to drought, factors involved in the regulation of transpiration were assessed with respect to soil properties in order to document the spatial distribution of death rates.[br/] [br/] Methods: Soil properties were characterized by electric resistivity measurements. Sap flow density and predawn needle water potential were recorded on sampled trees during several years, and crown specific transpiration was estimated. In addition, the vulnerability of coarse roots and branches to cavitation was quantified.[br/] [br/] Results and conclusion: Trees growing on soils with a large water storage capacity were the most vulnerable to drought induced soil water deficits. Transpiration was down-regulated as soon as predawn water potential decreased. The vulnerability to cavitation was low, which protected the trees from run-away xylem embolism. Severe soil water deficits led to a rapid decrease of transpiration, which was still visible the following year. The drop-off in transpiration was mainly due to inner sap flow that almost ceased after the drought on all monitored trees. Our results suggest that root dynamic and the ability of roots to take up water were modified by soil water deficit over several years. Such a regulation scheme needs to be better documented and included in models to address silver fir forest responses to drought.

International audience; Context : The thermal dissipation method to measure sap flow in tree stems can be used with cyclic heating to reduce electricity consumption and/or to account for natural temperature gradients. Nevertheless, errors in sap flow estimation can be introduced because the thermal equilibrium has not been reached at the measurement time. Aim: We propose a method to assess this error and to estimate sap flow density. It is based on Granier’s (Ann For Sci, 42:193–200, 1985) non-species-specific calibration. Methods: This work was performed on silver fir trees (Abies alba Mill.) with low sap flux densities (maximum of 0.68 L dm−2 h−1). To estimate the error, we developed a calibration procedure using the experimental set-up in trees. This approach is based on a pair of sensors having similar temporal patterns in sap flux density, one being under cyclic heating while the other is continuously heated. Results: Applying Granier’s calibration without correction led to large errors (relative error reached 200%). After correction, the error was greatly diminished; it was lower than 0.042 L dm−2 h−1 when using short heating cycles (0.5 h). Conclusion: The correction was applicable to all silver fir trees monitored. However, this method can be easily repeated to investigate the validity domain of the correction