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

Seedlings of three commercial native tree species were planted under hetero geneous light and nutrient conditions in primary rainforest, secondary fore st, and open pasture in Los Tuxtlas (Veracruz, Mexico). Management consiste d of weeding around seedlings, and watering during the dry period. The obje ctive was to find those natural growth conditions that maximize height grow th in the first 2 years after transplantation from a nursery. Using stepwis e multiple linear regression, the combined effect of varying canopy opennes s, leaf nutrients, initial seedling height, and seed mass on the plant heig ht at the end of the study were analysed. The effect of the light environme nt differed clearly between species: the fruit species Pouteria sapota (Jac quin) H.E. Moore & Steam (Mamey) and Diospyros digyna Jacquin (Black Sapote ) revealed an optimal canopy openness of 60 and 55%, respectively, while th e timber species Cedrela odorata Linnaeus (Spanish Cedar) grew best under m aximum openness. Consequently, P. sapota and D. digyna are recommendable fo r an enrichment or shelterwood system in the forest, while C. odorata is re commendable as a reforestation species in the open. For P. sapota and D. di gyna, 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 n utrients had not been measured). The regression model indicated that consid erable height increases are possible by optimizing these growth parameters within the encountered ranges. For P. sapota, average height growth after 2 4 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. odo rata, the possible increase after 16 months was 2.7-fold, from 55 to 147 cm . (C) 2000 Elsevier Science B.V. All rights reserved.