Optimising seedling management: Pouteria sapota, Diospyros digyna, and Cedrela odorata in a Mexican rainforest

Abstract

Seedlings of three commercial native tree species were planted under heterogeneous light and nutrient conditions in primary rainforest, secondary forest, and open pasture in Los Tuxtlas (Veracruz, Mexico). Management consisted of weeding around seedlings, and watering during the dry period. The objective was to find those natural growth conditions that maximize height growth in the first 2 years after transplantation from a nursery. Using stepwise multiple linear regression, the combined effect of varying canopy openness, leaf nutrients, initial seedling height, and seed mass on the plant height at the end of the study were analysed. The effect of the light environment differed clearly between species: the fruit species Pouteria sapota (Jacquin) H.E. Moore & Stearn (Mamey) and Diospyros digyna Jacquin (Black Sapote) revealed an optimal canopy openness of 60 and 55%, respectively, while the timber species Cedrela odorata Linnaeus (Spanish Cedar) grew best under maximum openness. Consequently, P. sapota and D. digyna are recommendable for an enrichment or shelterwood system in the forest, while C. odorata is recommendable as a reforestation species in the open. For P. sapota and D. digyna, plant height variation at the end of the study was also explained by the leaf zinc concentration, initial plant height, and in P. sapota by the seed mass and leaf calcium/magnesium ratio (for C. odorata, seed mass and nutrients had not been measured). The regression model indicated that considerable height increases are possible by optimizing these growth parameters within the encountered ranges. For P. sapota, average height growth after 24 months in the field could be increased 2.5-fold, from 111 cm with average values to 280 cm with optimal values. For D. digyna, average height growth after 17 months could be increased 1.8-fold, from 78 to 138 cm. For C. odorata, the possible increase after 16 months was 2.7-fold, from 55 to 147 cm.