Understanding and predicting the likely response of ecosystems to climate change are crucial challenges for ecology and for conservation biology. Nowhere is this challenge greater than in the tropics as these forests store more than half the total atmospheric carbon stock in their biomass. Biomass is determined by the balance between biomass inputs (i.e., growth) and outputs (mortality). We can expect therefore that conditions that favor high growth rates, such as abundant water supply, warmth, and nutrient-rich soils will tend to correlate with high biomass stocks. Our main objective is to describe the patterns of above ground biomass (AGB) stocks across major tropical forests across climatic gradients in Northwestern South America. We gathered data from 200 plots across the region, at elevations ranging between 0 to 3400 m. We estimated AGB based on allometric equations and values for stem density, basal area, and wood density weighted by basal area at the plot-level. We used two groups of climatic variables, namely mean annual temperature and actual evapotranspiration as surrogates of environmental energy, and annual precipitation, precipitation seasonality, and water availability as surrogates of water availability. We found that AGB is more closely related to water availability variables than to energy variables. In northwest South America, water availability influences carbon stocks principally by determining stand structure, i.e. basal area. When water deficits increase in tropical forests we can expect negative impact on biomass and hence carbon storage.

Rewilding is emerging as a promising restoration strategy to enhance the conservation status of biodiversity and promote self-regulating ecosystems while re-engaging people with nature. Overcoming the challenges in monitoring and reporting rewilding projects would improve its practical implementation and maximize its conservation and restoration outcomes. Here, we present a novel approach for measuring and monitoring progress in rewilding that focuses on the ecological attributes of rewilding. We devised a bi-dimensional framework for assessing the recovery of processes and their natural dynamics through (i) decreasing human forcing on ecological processes and (ii) increasing ecological integrity of ecosystems. The rewilding assessment framework incorporates the reduction of material inputs and outputs associated with human management, as well as the restoration of natural stochasticity and disturbance regimes, landscape connectivity and trophic complexity. Furthermore, we provide a list of potential activities for increasing the ecological integrity after reviewing the evidence for the effectiveness of common restoration actions. For illustration purposes, we apply the framework to three flagship restoration projects in the Netherlands, Switzerland and Argentina. This approach has the potential to broaden the scope of rewilding projects, facilitate sound decision-making and connect the science and practice of rewilding.This article is part of the theme issue ‘Trophic rewilding: consequences for ecosystems under global change’.

Physical factors that may account for regional patterns of plant species diversity remain controversial. We aim to determine the relationship of tree species diversity to environmental factors identifiable at regional scale in the northern Neotropics. We use a high-resolution data set based on herbarium collections of all native tree species known to occur in the highly diverse and physiographically heterogeneous Mexican state of Chiapas. We analyzed 114 grid cells (5 min latitude)/5 min longitude each) with 40 or more vouchers. We obtained from maps (scale 1:250 000) data on temperature, rainfall, elevation, and soils, and calculated for each grid cell mean actual evapotranspiration (AET), its ratio during the rainy and dry seasons (RET), average fertility/quality of soils (SFQ), and elevation (coarse-scale topography) variance (SDE). These variables were largely independent of each other, and were entered in multiple regression models to predict species diversity assessed with Simpson's index of concentration. A model that accounted for 41.4% of the total variance in tree diversity showed positive effects of AET and seasonality (RET), whereas SFQ had a negative effect. A curvilinear model described well the relationship between tree diversity and AET (R 2 0/0.45), and an intermediate maximum was detected. The data pattern suggested an asymptotic relationship as well, which was confirmed with a two-part regression. Regression quantiles provided better estimates of the effect of SFQ with the upper envelope of the data (0.85 Á/0.90 quantiles). Minimum diversity at intermediate rainfall values hints at a bimodal model of tree diversity along a rainfall gradient, in opposition to the frequent contention of a positive linear relationship. We suggest that broad-scale climatic gradients interact with intraregional landscape-level influences, thus leading to the observed nonlinear responses of tree diversity to environmental predictors. M. González-Espinosa

1. Forest area is increasing in temperate biomes through active and passive restoration of old fields. Despite the large extension of restored forests, the success of contrasting restoration strategies (active -planted forests -vs. passive -secondary forests -) over time has never been evaluated in Mediterranean forests.2. We studied how restoration strategy determined forest restoration success. We evaluated which restoration strategy resulted in forests more like references (i.e. forests with continuous canopy cover since at least the 1940s) in terms of structure, diversity, functional composition, and dynamics. We then assessed whether active restoration accelerated forest recovery compared to passive restoration.3. We studied a chronosequence of recovery in four forest types (mountain and Mediterranean pine forests and mesic and Mediterranean oak forests) using the data of the Spanish Forest Inventory in central Spain. Each plot was classified as planted, secondary or reference forest. We modelled the response ratios of 11 forest attributes and a multifunctionality index as a function of restoration strategy, forest age, and abiotic and biotic constraints. 4. Secondary forests showed a greater likeness to references than planted forests in oak forests while minor differences between secondary and planted forests were found in pine forests. The recovery speed of most forest attributes in secondary and planted forests was similar. Multifunctionality was higher, and increased more rapidly, in planted than in secondary forests in Mediterranean oak forests. However, multifunctionality was similar for both restoration strategies in the other forest types. Synthesis and applications. The long-term assessment of forest recovery inMediterranean abandoned fields indicated that both planted forests and natural forest succession are successful restoration strategies, depending on the aim and the forest type. In our research, restoration strategy did not influence the magnitude and speed of forest recovery in pine forests. However, in oak forests, natural forest succession led to forests more alike to references, but planted forests can maximize and accelerate recovery of forest multifunctionality. K E Y W O R D Sabandoned fields, forest age, forest inventory, forest recovery, forest succession, Mediterranean, multifunctionality, restoration strategy | 747Journal of Applied Ecology CRUZ-ALONSO et AL.

Scatter-hoarding animals such as corvids play a crucial role in the dispersal of nut-producing tree species. This interaction is well known for some corvids, but remains elusive for other species such as the magpie (Pica pica), an abundant corvid in agroecosystems and open landscapes of the Palearctic region. In addition, the establishment of the individual dispersed seeds-a prerequisite for determining seed-dispersal effectiveness-has never before been documented for the interaction between corvids and nut-producing trees. We analyzed walnut dispersal by magpies in an agroecosystem in southern Spain. We used several complementary approaches, including video recording nut removal from feeders, measuring dispersal distance using radio tracking (with radio transmitters placed inside nuts), and monitoring the fate of dispersed nuts to the time of seedling emergence. Magpies were shown to be highly active nut dispersers. The dispersal distance averaged 39.6 ± 4.5 m and ranged from 4.1 to 158.5 m. Some 90% of the removed walnuts were cached later, and most of these (98%) were buried in the soil or hidden under plant material. By the time of seedling emergence, ca. 33% of nuts remained at the caching location. Finally, 12% of the cached nuts germinated and 4% yielded an emerged seedling, facilitating the transition to the next regeneration stage. The results demonstrate for the first time that magpies can be an effective scatter-hoarding disperser of a nut-producing tree species, suggesting that this bird species may play a key role in the regeneration and expansion of broadleaf forests in Eurasia.