Tree species that ‘live slow, die older’ enhance tropical peat swamp restoration: Evidence from a systematic review

Abstract

Degraded tropical peatlands lack tree cover and are often subject to seasonal flooding and repeated burning. These harsh environments for tree seedlings to survive and grow are therefore challenging to revegetate. Knowledge on species performance from previous plantings represents an important evidence base to help guide future tropical peat swamp forest (TPSF) restoration efforts. We conducted a systematic review of the survival and growth of tree species planted in degraded peatlands across Southeast Asia to examine (1) species differences, (2) the impact of seedling and site treatments on survival and growth and (3) the potential use of plant functional traits to predict seedling survival and growth rates. Planted seedling monitoring data were compiled through a systematic review of journal articles, conference proceedings, reports, theses and unpublished datasets. In total, 94 study‐sites were included, spanning three decades from 1988 to 2019, and including 141 indigenous peatland tree and palm species. Accounting for variable planting numbers and monitoring durations, we analysed three measures of survival and growth: (1) final survival weighted by the number of seedlings planted, (2) half‐life, that is, duration until 50% mortality and (3) relative growth rates (RGR) corrected for initial planting height of seedlings. Average final survival was 62% and half‐life was 33 months across all species, sites and treatments. Species differed significantly in survival and half‐life. Seedling and site treatments had small effects with the strongest being higher survival of mycorrhizal fungi inoculated seedlings; lower survival, half‐life and RGR when shading seedlings; and lower RGR and higher survival when fertilising seedlings. Leaf nutrient and wood density traits predicted TPSF species survival, but not half‐life and RGR. RGR and half‐life were negatively correlated, meaning that slower growing species survived for longer. Synthesis and applications. To advance tropical peat swamp reforestation requires expanding the number and replication of species planted and testing treatments by adopting control vs. treatment experimental designs. Species selection should involve slower growing species (e.g. Lophopetalum rigidum, Alstonia spatulata, Madhuca motleyana) that survive for longer and explore screening species based on functional traits associated with nutrient acquisition, flooding tolerance and recovery from fire.

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

“…Marginal R 2 , conditional R 2 and intra-class correlations (ICC) showing variation explained by fixed and random effects terms. studies showed no significant effect of prior drainage on seedling mortality, but found species choices to be important-slower growing tree species survived for longer [47].…”

“…Our datasets were compiled from online literature searches following the protocols outlined below (see electronic supplementary material, appendix S1 for further details), supplemented by additional published studies compiled by co-authors S.W.S. and N.E.B.R from peat swamp forest sites [47], and unpublished data and royalsocietypublishing.org/journal/rstb Phil. Trans.…”

“…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 ].…”

“…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 ]. The most widely available functional trait information is wood density [ 50 ] which presents a preliminary opportunity to explore relationships between species-level vital rates and traits.…”

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

“…Mycorrhizal inoculations can thus be incorporated with plantings to facilitate establishment, growth and canopy closure [ 89 , 90 ], with outcomes depending upon plant functional type, restoration context and time [ 91 ]. However, the role of belowground diversity can be complex, and data are lacking to identify levels of degradation that would necessitate the use of soil treatments [ 92 , 93 ]. There is also still substantial uncertainty and inter-site variability in soil carbon accumulation rates under forest recovery [ 94 ].…”