Initial establishment of commercial tree species under enrichment planting in a Central Amazon secondary forest: Effects of silvicultural treatments

Enrichment planting has the potential to conserve wide areas of secondary forest in the Amazon. Therefore, it is necessary to understand the effects of silvicultural treatments applied to secondary forest management on the initial establishment of planted species. Enrichment planting was performed in a Central Amazon secondary forest to test whether the growth, mortality and presence of shoot borer attacks of six commercial trees species - in the first two years after planting - depend on canopy trees refinement and understory slashing. Six commercial tree species were planted under a gradient of light transmittance that was created by canopy trees refinement applied in six levels of basal area reduction (0; 20; 40; 60; 80 and 100%) and combined with two understory slashing levels (control and understory slashed). The effects of silvicultural treatments on root collar diameter and height growth (realized and relative), mortality and shoot borer attack were evaluated during the first and second year after planting. The relationships between realized growth and light transmittance were different among the species, but maximum growth was observed at high light transmittance for all species. Understory slashing slightly increased the response of realized growth to light transmittance. Species relative growth was strongly affected by light transmittance, but there was a reduced response in the second year after planting, particularly in the light-demanding pioneer species (Cedrela fissilis, Tabebuia rosea and Swietenia macrophylla). Pioneer species mortality was higher in deep shade (lowest transmittance) and was related to fast growth at full sun (highest transmittance) during the first, but not the second, year after planting. Shade-tolerant species (Hymenaea courbaril, Carapa guianensis and Bertholletia excelsa) have slower growth in full sun than pioneers, but only during the first year. Shoot borer attacks in Meliaceae species (C. fissilis, S. macrophylla and C. guianensis) occurred more frequently in high light transmittance and understory slashed environments but were absent in intermediary to low light transmittance and untreated understory. Thus, silvicultural treatments improve the initial establishment of commercial tree species in secondary forest enrichment planting sites. However, such findings should be analyzed considering the effects on growth, mortality and pest attacks during the seedling to juvenile tree development stages after planting.