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Forest-savanna boundaries extend across large parts of the tropics but the variability of photosynthetic capacity in relation to soil and foliar nutrients across these transition zones is poorly understood. For this reason, we compared photosynthetic capacity (maximum rate of carboxylation of Rubisco at 25 C° (Vcmax25), leaf mass, nitrogen (N), phosphorus (P) and potassium (K) per unit leaf area (LMA, Narea, Parea and Karea, respectively), in relation to respective soil nutrients from 89 species at seven sites along forest-savanna ecotones in Ghana and Brazil. Contrary to our expectations, edaphic conditions were not reflected in foliar nutrient concentrations but LMA was slightly higher in lower fertility soils. Overall, each vegetation type within the ecotones demonstrated idiosyncratic and generally weak relationships between Vcmax25 and Narea, Parea and Karea. Species varied significantly in their Vcmax25 ↔ Narea relationship due to reduced investment of total Narea in photosynthetic machinery with increasing LMA. We suggest that studied species in the forest-savanna ecotones do not maximize Vcmax25 per given total Narea due to adaptation to intermittent water availability. Our findings have implications for global modeling of Vcmax25 and forest-savanna ecotone productivity.

The transition region between two major South American biomes, the Amazon forest and the Cerrado (Brazilian savanna), has been substantially converted into human-modified ecosystems. Nevertheless, the recovery dynamics of ecosystem functions in this important zone of (ecological) tension (ZOT) remain poorly understood. In this study, we compared two areas of cerradao (a forest-woodland of the Brazilian savanna; Portuguese augmentative of cerrado ), one in secondary succession (SC) and one adjacent and well preserved (PC), to test whether the ecosystem functions lost after conversion to pasture were restored after 22 years of regeneration. We tested the hypothesis that the increase in annual aboveground biomass in the SC would be greater than that in the PC because of anticipated successional gains. We also investigated soil CO 2 efflux, litter layer content, and fine root biomass in both the SC and PC. In terms of biomass recovery our hypothesis was not supported: the biomass did not increase in the successional area over the study period, which suggested limited capacity for recovery in this key ecosystem compartment. By contrast, the structure and function of the litter layer and root mat were largely reconstituted in the secondary vegetation. Overall, we provide evidence that 22 years of secondary succession were not sufficient for these short and open forests (e.g., cerradao ) in the ZOT to recover ecosystem functions to the levels observed in preserved vegetation of identical physiognomy.

The impact of agricultural and livestock activities on tropical forests often results in long-lasting damage to soil and vegetation. In undisturbed tropical forests, nutrient stocks tend to be larger in the aboveground biomass than in the soil profile; therefore, deforested sites may remain bare for decades due to nutrient limitation. In such circumstance, amelioration of edaphic conditions and planting of tree species adapted to open canopy conditions (pioneers) could help restore ecosystem functions while providing a sustainable source of timber and prompting natural succession. The aim of this study was to evaluate the use of biochar as a soil amendment that could accelerate the reforestation of degraded lands. We used a randomized block design with five treatments and four replications, comparing the performance of exotic eucalyptus (Eucalyptus urophylla × Eucalyptus grandis) and native Tachigali vulgaris trees. We monitored reforested plots for 49 months, evaluating tree survival and growth rates, litter production, canopy cover and density of invasive grasses. The addition of biochar in the soil did not result in significant differences in tree survival or productivity when compared to controls. Comparing the two species, native trees (T. vulgaris) performed better by all metrics, showing 52% survival and producing 241.7 Mg ha−1 of aboveground biomass after four years of growth. During that same period the survival rate of eucalyptus was 38% and the aboveground productivity was only 82.4 Mg ha−1. In contrast with eucalyptus plantations, T. vulgaris showed rapid canopy cover and completely suppressed invasive grasses, generating up to 11.7 Mg ha−1 more litter than eucalyptus trees. Although eucalyptus is one of the most commonly used species in reforestation for timber, charcoal, and pulp and paper production in Brazil, our results demonstrate that T. vulgaris has the potential to replace eucalyptus in commercial plantations with the added benefit of being a native species that can promote the establishment of a stable forest cover in degraded sites.

The present study analyzed the influence of edaphic variables on the floristic compositions and structures of the arboreal and shrub vegetation of typical cerrado (TC) and rocky outcrop cerrado (RC) communities in the Serra Negra mountain range in Piranhas Municipality, Goiás State, Brazil. Ten 20 × 50 m plots were established in each community, and all individuals with minimum diameters ≥ 5 cm measured at 30 cm above soil level were sampled. Composite soil samples were collected at 0-20 cm depths in each plot for physical and chemical analyses. The proportions of above-ground rock cover work also estimated in each RC plot. A total of 2,009 individuals (83 species, 69 genera, and 34 families) were recorded. Qualea parviflora was the only species consistently among the 10 most structurally important taxa in both communities, and was considered a generalist species. The observed and estimated species richnesses were greater in RC than in TC, although plant basal areas and heights did not differ between them. There were positive correlations between rock cover × plant density and rock cover × basal areas. TWINSPAN and PCA analysis separated the TC and RC plots, and three RC habitat specialist species (Wunderlichia mirabilis, Norantea guianensis, and Tibouchina papyrus) were identified. Soil variables were found to have greater effects on the species compositions of the TC and RC sites than the geographic distances between sampling plots. According to CCA analysis, the exclusive (or more abundant species) of each community were correlated with soil variables, and these variables therefore determined the selection of some species and influenced the differentiation of the vegetation structures of the communities studied.