Early ecological outcomes of natural regeneration and tree plantations for restoring agricultural landscapes

Abstract

Mixed tree plantings and natural regeneration are the main restoration approaches for recovering tropical forests worldwide. Despite substantial differences in implementation costs between these methods, little is known regarding how they differ in terms of ecological outcomes, which is key information for guiding decision making and cost-effective restoration planning. Here, we compared the early ecological outcomes of natural regeneration and tree plantations for restoring the Brazilian Atlantic Forest in agricultural landscapes. We assessed and compared vegetation structure and composition in young (7-20 yr old) mixed tree plantings (PL), second-growth tropical forests established on former pastures (SGp), on former Eucalyptus spp. plantations (SGe), and in old-growth reference forests (Ref). We sampled trees with diameter at breast height (DBH) 1-5 cm (saplings) and trees at DBH > 5 cm (trees) in a total of 32 20 × 45 m plots established in these landscapes. Overall, the ecological outcomes of natural regeneration and restoration plantations were markedly different. SGe forests showed higher abundance of large (DBH > 20 cm) nonnative species, of which 98% were resprouting Eucalyptus trees, than SGp and PL, and higher total aboveground biomass; however, aboveground biomass of native species was higher in PL than in SGe. PL forests had lower abundance of native saplings and lianas than both naturally established second-growth forests, and lower proportion of animal dispersed saplings than SGe, probably due to higher isolation from native forest remnants. Rarefied species richness of trees was lower in SGp, intermediate in SGe and Ref and higher in PL, whereas rarefied species richness of saplings was higher in SG than in Ref. Species composition differed considerably among regeneration types. Although these forests are inevitably bound to specific landscape contexts and may present varying outcomes as they develop through longer time frames, the ecological particularities of forests established through different restoration approaches indicate that naturally established forests may not show similar outcomes to mixed tree plantings. The results of this study underscore the importance that restoration decisions need to be based on more robust expectations of outcomes that allow for a better analysis of the cost-effectiveness of different restoration approaches before scaling-up forest restoration in the tropics.

Bird Functional Traits Respond to Forest Structure in Riparian Areas Undergoing Active Restoration

“…Therefore, there were very few tree and shrub saplings in R1, resulting in the absence of these lower layers below the canopy. César et al [60] found a similar pattern when monitoring mixed-species tree plantings, second-growth forests, and reference forests in nearby regions; they found that tree plantings that were between 7 and 20 years old had significantly less small trees (1-5 cm dbh) than second-growth forests of the same age, with limited recolonization of native trees and lianas. Therefore, when restored forests grow enough to close the canopies, these conditions may limit the growth of lower vegetation layers, simplifying forest complexity and resulting in low bird abundances.…”

Challenges in Engaging Birdwatchers in Bird Monitoring in a Forest Patch: Lessons for Future Citizen Science Projects in Agricultural Landscapes

“…Small amounts of semi-deciduous seasonal forest (Atlantic Forest biome) and savannah woodland (Cerrado biome) are confined to the native forest remnants found in the agricultural landscape (i.e., approximately 12% of the river basin, see Valente and Vettorazzi 2003). In the last few years, six focal landscapes covering 16 km 2 and representative of the river basin agricultural landscape in terms of land use composition (>70% agricultural matrix -sugarcane or cattle pasture -and >10% native forest) have been the focus of research on land use change, forest restoration, ecology, and ornithology (Cassiano et al 2013;Ferraz et al 2014;Alexandrino et al 2016Alexandrino et al , 2017César et al 2018) (Figure 2b). Many forest patches in the region have increased their area by passive restoration (Ferraz et al 2014;Alexandrino et al 2016).…”

Intensive silviculture enhances biomass accumulation and tree diversity recovery in tropical forest restoration

“…, César et al. ). Most of the regenerating tree species were medium‐seeded, bird‐dispersed species, a common feature in a degraded tropical habitat context (Lindell et al.…”

“…, César et al. ). Carbon‐centered restoration is indeed considered to be a risk for biodiversity conservation in many region of the world, notably through the use of exotic species, afforestation of native grasslands, alteration of natural disturbance regimes, and clearing of native vegetation to establish tree plantations (Lindenmayer et al.…”