Time matters: Temporally changing effects of planting schemes and insecticide treatment on native timber tree performance on former pasture

Reforestation of former pastures with native timber trees holds potential to improve small-scale farmers livelihoods while supporting ecosystem functioning and biological diversity. To promote successful reforestation with native tree species, more knowledge is needed, particularly on effects of species identity, tree diversity, and insecticide application on tree survival and growth at different time periods after plantation establishment. We assessed these effects for three native Central American timber species and compared results gained 2 and 5 years after tree establishment. Survival, stem diameter, and tree height were quantified for Tabebuia rosea, Anacardium excelsum, and Cedrela odorata, planted in (1) monocultures, (2) three-species mixtures, and (3) three-species mixtures treated with insecticides during the first 2 years of seedling establishment. We further tested how survival and growth performance were affected by the individual tree position within reforestation tree stands to account for border effects in small-scale tree patches in pasture-afforestations. Survival was significantly affected by tree species identity with the highest survival in T. rosea and the lowest survival in C. odorata. Tree growth was affected by tree species identity, tree diversity, insecticide treatment, environmental heterogeneity, and border effects, but these effects varied across the individual tree species. Interspecific analyses revealed significant differences between species. A. excelsum trees attained the largest and C. odorata the smallest size after 5 years of growth. Across species, tree growth in years 3–5 after tree planting was highest in mixtures treated with insecticides during tree establishment, followed by monocultures and then unprotected mixtures. Enhanced growth in monocultures compared to unprotected mixtures was particularly found in T. rosea during early establishment, and in A. excelsum at a later stage of tree stand development. Growth-enhancing effects of planting schemes may be related to differential responses to herbivore damage and to tree-tree competition. Positive border effects, i.e. a significantly enhanced growth at the border of a tree stand, were found for T. rosea in all three planting schemes and for A. excelsum in protected mixtures. Our results suggest that besides early, restricted insecticide application, tree diversity within stands should be considered as management measure to enhance timber tree growth on former pasture. The finding of enhanced growth of native timber trees at the border of small tree stands suggests small patches of native timber trees planted on former pasture as a promising reforestation strategy in Latin America.

► Effects of stand diversification on tree growth differ between tree species.
► Insecticide effects on tree size outlived duration of insecticide application.
► Positive border effects suggest small tree patches for pasture reforestation.
► Patterns of initial and later growth performance of timber trees differed.
► Tabebuia rosea and Anacardium excelsum established well on former tropical pastures.