Below-ground traits mediate tree survival in a tropical dry forest restoration

Abstract

Reforestation is one of our most promising natural climate solutions, and one that addresses the looming biodiversity crisis. Tree planting can catalyse forest community reassembly in degraded landscapes where natural regeneration is slow, however, tree survival rates vary remarkably across projects. Building a trait-based framework for tree survival could streamline species selection in a way that generalizes across ecosystems, thereby increasing the effectiveness of the global restoration movement. We investigated how traits mediated seedling survival in a tropical dry forest restoration, and how traits were coordinated across plant structures. We examined growth and survival of 14 species for 2 years and measured six below-ground and 22 above-ground traits. Species-level survival ranged widely from 7.8% to 90.1%, and a model including growth rate, below-ground traits and their interaction explained more than 73% of this variation. A strong interaction between below-ground traits and growth rate indicated that selecting species with fast growth rates can promote establishment, but this effect was most apparent for species that invest in thick fine roots and deep root structures. Overall, results emphasize the prominent role of below-ground traits in determining early restoration outcomes, and highlight little above- and below-ground trait coordination, providing a path forward for tropical dry forest restoration efforts. This article is part of the theme issue ‘Understanding forest landscape restoration: reinforcing scientific foundations for the UN Decade on Ecosystem Restoration’.

Belowground foundations of tropical forest restoration

“…One of the reasons is the lack of connection with ecological theory and processes (e.g., competition, dispersal, succession), particularly with belowground processes. Belowground processes are relatively understudied (Averill et al., 2022; Seidl & Turner, 2022; Werden et al., 2022), yet the interactions of plant roots, soil microbes, and soil properties drive critical belowground ecosystem services such as erosion control, water and nutrient cycling, and soil carbon sequestration. Attention to these critical interactions has the potential to substantially increase the success of restoration efforts.…”

“…Increased carbon storage can be observed in less than a decade when aboveground carbon is measured in restored areas (Philipson et al., 2020), with changes in soil carbon stocks occurring up to 40 years (Holl & Zahawi, 2014; Jones et al., 2019; Zanini et al., 2021). However, the trajectories of soil stabilization (Ford et al., 2016), plant survival (Werden et al., 2022), and soil carbon storage (Craig et al., 2018) in regenerating forests are affected by the belowground plant growth strategies of the selected plant species (Figure 1c). For example, species with thick fine roots and deep root structures have been linked to slower growth rates and plant establishment, both of which increase the amount of carbon stored in the ecosystem (Werden et al., 2022).…”

Fifteen essential science advances needed for effective restoration of the world's forest landscapes

“…For example, and also in this theme issue, Werden et al . [ 97 ] demonstrate that root traits of planted trees can be used to predict species success in dry forests. Further new research in this theme issue shows how information on soils is necessary for tailoring restoration and remediation methods to local site conditions [ 70 , 98 ].…”

“…as nurse trees to encourage shade for natives [ 133 ] or to fix soil nitrogen [ 95 ], but further research in this theme issue suggests that exotic tree presence reduces overall biodiversity [ 134 ]. In order for tree-planting to be successful, other research in the theme issue highlights important decisions regarding correct selection of species (for drought tolerance; [ 97 ]) and planting location (for maximizing survival and natural succession; [ 70 ]).…”

The road to recovery: a synthesis of outcomes from ecosystem restoration in tropical and sub-tropical Asian forests

“…Higher community-average wood densities are typically found where dry seasons are more intense or in well-drained soil conditions, where high wood density may offer hydraulic safety [ 44 – 46 ]. Wood density was positively related to survival of trees planted into pasture in a restoration site in Australia and peat swamp forests in Asia [ 47 , 48 ] while greater allocation to rooting depth enhanced tree survival in a seasonally dry forest in Costa Rica [ 49 ]. The role of functional traits in explaining recovery and determining species-specific responses has not been widely explored in Asian forests and predictive site–species matching is hampered by a lack of trait data for most species [ 47 ].…”