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Rewilding is a flexible conservation approach that may be applicable to a wide variety of ecological, historical and socio-cultural contexts. We believe that comparative socio-ecological research on woodland habitat trajectories among contexts is an excellent opportunity to consider possible rewilding approaches. Here, we draw on a comparison between arid and seasonally dry woodlands of the Sahel region of Africa and the Southern Cone of South America. The two regions, while sharing a common Gondwanan floral origin, differ in terms of subsequent biogeographical processes and have different climatic gradients. Historically, both regions were colonised, although along different models, and the Southern Cone has experienced greater land-use change and agricultural modernisation. Culturally, both regions have indigenous populations with traditional management techniques and local ecological knowledge, although attention to these topics in research and conservation has had different emphases in each region. Rewilding, focusing on charismatic animals, has been proposed and implemented in some parts of the Southern Cone, but has hardly been mentioned for the Sahel. We discuss the applicability of potential rewilding models involving key plants for each region, and what a plant-focused rewilding practice could gain from a comparative approach in the two regions. [ABSTRACT FROM AUTHOR]

Meteorological extreme events such as El Niño events are expected to affect tropical forest net primary production (NPP) and woody growth, but there has been no large-scale empirical validation of this expectation. We collected a large high-temporal resolution dataset (for 1-13 years depending upon location) of more than 172 000 stem growth measurements using dendrometer bands from across 14 regions spanning Amazonia, Africa and Borneo in order to test how much month-to-month variation in stand-level woody growth of adult tree stems (NPPstem) can be explained by seasonal variation and interannual meteorological anomalies. A key finding is that woody growth responds differently to meteorological variation between tropical forests with a dry season (where monthly rainfall is less than 100 mm), and aseasonal wet forests lacking a consistent dry season. In seasonal tropical forests, a high degree of variation in woody growth can be predicted from seasonal variation in temperature, vapour pressure deficit, in addition to anomalies of soil water deficit and shortwave radiation. The variation of aseasonal wet forest woody growth is best predicted by the anomalies of vapour pressure deficit, water deficit and shortwave radiation. In total, we predict the total live woody production of the global tropical forest biome to be 2.16 Pg C yr-1, with an interannual range 1.96-2.26 Pg C yr-1 between 1996-2016, and with the sharpest declines during the strong El Niño events of 1997/8 and 2015/6. There is high geographical variation in hotspots of El Niño-associated impacts, with weak impacts in Africa, and strongly negative impacts in parts of Southeast Asia and extensive regions across central and eastern Amazonia. Overall, there is high correlation (r = -0.75) between the annual anomaly of tropical forest woody growth and the annual mean of the El Niño 3.4 index, driven mainly by strong correlations with anomalies of soil water deficit, vapour pressure deficit and shortwave radiation.This article is part of the discussion meeting issue 'The impact of the 2015/2016 El Niño on the terrestrial tropical carbon cycle: patterns, mechanisms and implications'.

Tropical ecosystems face escalating global change. These shifts can disrupt tropical forests' carbon (C) balance and impact root dynamics. Since roots perform essential functions such as resource acquisition and tissue protection, root responses can inform about the strategies and vulnerabilities of ecosystems facing present and future global changes. However, root trait dynamics are poorly understood, especially in tropical ecosystems. We analyzed existing research on tropical root responses to key global change drivers: warming, drought, flooding, cyclones, nitrogen (N) deposition, elevated (e) CO2, and fires. Based on tree species‐ and community‐level literature, we obtained 266 root trait observations from 93 studies across 24 tropical countries. We found differences in the proportion of root responsiveness to global change among different global change drivers but not among root categories. In particular, we observed that tropical root systems responded to warming and eCO2 by increasing root biomass in species‐scale studies. Drought increased the root: shoot ratio with no change in root biomass, indicating a decline in aboveground biomass. Despite N deposition being the most studied global change driver, it had some of the most variable effects on root characteristics, with few predictable responses. Episodic disturbances such as cyclones, fires, and flooding consistently resulted in a change in root trait expressions, with cyclones and fires increasing root production, potentially due to shifts in plant community and nutrient inputs, while flooding changed plant regulatory metabolisms due to low oxygen conditions. The data available to date clearly show that tropical forest root characteristics and dynamics are responding to global change, although in ways that are not always predictable. This synthesis indicates the need for replicated studies across root characteristics at species and community scales under different global change factors. [ABSTRACT FROM AUTHOR]

Tropical forests cover large areas of equatorial Africa and play a substantial role in the global carbon cycle. However, there has been a lack of biometric measurements to understand the forests’ gross and net primary productivity (GPP, NPP) and their allocation. Here we present a detailed field assessment of the carbon budget of multiple forest sites in Africa, by monitoring 14 onehectare plots along an aridity gradient in Ghana, West Africa. When compared with an equivalent aridity gradient in Amazonia, the studied West African forests generally had higher productivity and lower carbon use efficiency (CUE). The West African aridity gradient consistently shows the highest NPP, CUE, GPP, and autotrophic respiration at a medium-aridity site, Bobiri. Notably, NPP and GPP of the site are the highest yet reported anywhere for intact forests. Widely used data products substantially underestimate productivity when compared to biometric measurements in Amazonia and Africa. Our analysis suggests that the high productivity of the African forests is linked to their large GPP allocation to canopy and semi-deciduous characteristics. [ABSTRACT FROM AUTHOR]

Estimates of decomposition rates of coarse woody debris (CWD) and fluxes of nutrients therein are essential components of carbon (C) and nutrient budget models. In a 30-year field experiment, we periodically measured mass remaining and nutrient concentrations in log segments of pine, spruce, and fir in natural, mature coniferous forests in Alberta, Canada. The predicted turnover times ([t.sub.95]; years) were 43-44 years for pine, 42-60 years for spruce, and 38-46 years for fir. Extrapolating from best-fit models, we predict that decomposition of these logs would be complete within 50-60 years. The ratio of carbon to nitrogen (C:N) declined for most of the decomposition period, and ratios of the three species converged at Key words: coarse woody debris, decomposition, mass loss, nutrient, turnover. Les estimations du taux de decomposition des debris ligneux grossiers (DLG) et des flux de nutriments qui y sont associes sont des composantes essentielles des modeles de bilan de C et des nutriments. Dans le cadre d'une experience sur le terrain vieille de 30 ans, nous avons periodiquement mesure la masse residuelle et la concentration des nutriments dans des segments de billes de pin, d'epinette et de sapin dans des forets naturelles de coniferes matures en Alberta, au Canada. Le temps de renouvellement anticipe ([t.sub.95]; annees) etait de 43-44 ans pour le pin, 42-60 ans pour l'epinette et 38-46 pour le sapin. En extrapolant a partir des modeles les mieux ajustes, nous predisons que ces billes seront completement decomposees d'ici 50 a 60 ans. Le rapport C:N a diminue pendant presque toute la periode de decomposition et les rapports des trois especes ont converge vers une valeur Mots-cles: debris ligneux grossiers, decomposition, perte de masse, nutriments, renouvellement., Introduction Measurements of decomposition rates of coarse woody debris (CWD) are necessary to estimate carbon (C) stores and rates of C[O.sub.2] release in forests and are components of most C [...]

Abstract: Net Primary Productivity (NPP) is one of the most important parameters in describing the functioning of any ecosystem and yet it arguably remains a poorly quantified and understood component of carbon cycling in tropical forests, especially outside of the Americas. We provide the first comprehensive analysis of NPP and its carbon allocation to woody, canopy and root growth components at contrasting lowland West African forests spanning a rainfall gradient. Using a standardized methodology to study evergreen (EF), semi‐deciduous (SDF), dry forests (DF) and woody savanna (WS), we find that (i) climate is more closely related with above and belowground C stocks than with NPP (ii) total NPP is highest in the SDF site, then the EF followed by the DF and WS and that (iii) different forest types have distinct carbon allocation patterns whereby SDF allocate in excess of 50% to canopy production and the DF and WS sites allocate 40%–50% to woody production. Furthermore, we find that (iv) compared with canopy and root growth rates the woody growth rate of these forests is a poor proxy for their overall productivity and that (v) residence time is the primary driver in the productivity‐allocation‐turnover chain for the observed spatial differences in woody, leaf and root biomass across the rainfall gradient. Through a systematic assessment of forest productivity we demonstrate the importance of directly measuring the main components of above and belowground NPP and encourage the establishment of more permanent carbon intensive monitoring plots across the tropics. [ABSTRACT FROM AUTHOR]