Soil properties and neighbouring forest cover affect above‐ground biomass and functional composition during tropical forest restoration

Abstract

Questions:We studied the importance of soil properties and neighbouring forest cover in affecting plant community biomass and assembly during the tropical forest restoration process. We also investigated how compositional responses depended on traits expected to influence individual success.Location: Forest restoration sites across anthropogenic grasslands in mixed use agricultural watersheds, eastern São Paulo state, Brazil. Methods:We identified and measured all woody individuals (DBH ≥ 5 cm) in four 200-m² plots per site. Then we translated these measurements into above-ground biomass (AGB), and related AGB variability to neighbouring forest cover, soil texture and chemical fertility using mixed effect models. We assessed the effect of these predictors on different species groups, arranged according to variation in wood density, tree height or habitat selectivity, through multivariate abundance models.Results: AGB ranged between 0 and 104.7 t/ha (median of 10.4 t/ha), with high variation within, as well as between, watersheds. Sand percentage, forest cover and the interaction between soil nutrient concentrations and sand percentage were good predictors of measured AGB. The most parsimonious model projected a seven growing seasons AGB recovery of 70.90 t/ha, when a site is on fertile soils with 10% sand and surrounded by forest cover of 50%. In contrast, only 5.24 t/ha is predicted on acidicpoor soils with 67% sand and 0% forest cover. Increasing forest cover favoured smaller trees and habitat generalists while increasing sand percentage inhibited taller species and forest specialists. Sand percentage constrained softwoods in fertile soils. Conclusion:Our results confirm that the likelihood of restoration to pre-disturbance conditions is constrained in contexts of higher degradation, such as when agricultural use adversely affects soil properties and/or motivates extreme deforestation. Lower AGB found on sandy soils suggests that forest recovery is sensitive to local drought intensification. Given regional projections for extended dry seasons, restoration approaches could consider targeting alternative reference states, rather than historical/ undisturbed ones, under highly altered environments, while aiming to improve soil and microclimate conditions to allow moist tropical forest recovery where feasible.

Atlantic Forest topsoil nutrients can be resistant to disturbance and forest clearing

“…In addition, the very low Al, P, Ca, and Mg backgrounds on lowland Atlantic forest soils suggest they are resistant and K resilient to human‐induced disturbances, in cases where sites were left to regenerate naturally and were not subsequently used or disturbed. Although some studies have shown that soil with very low nutrient availability can limit the absorption of nutrients and the regeneration of secondary forests (Pinho et al., ; Toledo et al., ; Wang & Houlton, ), we show that the deep‐weathered sandy soils of lowland Atlantic forests might not act as a filter for natural vegetation recovery (see Toledo et al., ). Therefore, our findings have potentially important implications for passive restoration projects (Mendes et al., ), as they reflect the ability of the lowland Atlantic forest to recover naturally over time, following disturbance or field abandonment, without requiring active regeneration or soil management (Chazdon et al., ; Crouzeilles et al., ; Poorter et al., ).…”

“…Depending on the intensity and frequency of the disturbance, soil properties can be negatively affected leading to soil degradation via increased erosion, compaction, sealing, leaching, salinization, acidification, and nutrient losses (Lal, ; Oldeman, ). In this case, forest productivity and ecosystem functions are also affected and, ultimately, the capacity of the ecosystem to recover after disturbance (Chazdon, ; Pinho et al., ; Toledo, Perring & Verheyen, ; Wall, ). For these reasons, deforestation and degradation of tropical forests are especially harmful to the environment and ecosystem functioning.…”

“…Aluminum (Al) is known to limit plant growth in acidic soils (Rout, Samantaray & Das, ). The soil properties mentioned above can drive net primary production (Vitousek & Sanford, ) and plant distribution, thus affecting forests natural regeneration capacity (Chazdon, ; Moran et al., ; Pinho et al., ; Powers & Marín‐Spiotta, ; Toledo et al., ).…”

Selection of shade trees in forest restoration plantings should not be based on crown tree architecture alone

“…Although we did not directly address the causes of species differences between sites, our results suggest that soil fertility and texture may play an essential role. In fact, other studies have documented that poor soils with a greater percentage of sand are not favorable to aboveground biomass accumulation (Toledo et al ) and that low nutrient availability is the dominant abiotic factor limiting the growth of young trees (Mayoral et al ).…”

Recovery of Soil Hydraulic Properties for Assisted Passive and Active Restoration: Assessing Historical Land Use and Forest Structure

“…For sampling vegetation and soil attributes, the size of each plot was 500 m 2 (50 m long and 10 m wide), a total area of 2000 m 2 for each site. The size and number of plots were chosen according to similar investigations aimed at evaluating vegetation structure and composition in tropical forest restoration projects [40][41][42].…”