Early growth performance of native and introduced fast growing tree species in wet to sub-humid climates of the Southern region of Costa Rica

Abstract

Early growth performance of six native and two introduced tree species was studied for seven years at 16 sites in the Southern region of Costa Rica. Selected study sites represent a wide environmental gradient that ranges from acid low fertility soils such as Ustic Haplohumults and Typic Haplustults to fertile soils such as Typic Hapludand and Fluventic Eutropepts. Mean annual precipitation ranges from 2600 to 4500 mm and length of dry season from none to more than three months each year. The experimental layout was a randomized complete block design nested within four eco-regions, with all plots on private farms. The size of the experimental plot was 11 × 11 trees planted at a spacing of 3 × 3 m with a sampling plot of 7 × 7 trees. The species included in the initial trials were: Pinus caribaea Morelet var hondurensis (Barret y Golfari) and Gmelina arborea Roxb as the introduced species (from Honduras and southeast Asian regions, both of which benefit from genetic selection), and Terminalia amazonia (J. F. Gmelin) Exell, Vochysia ferruginea Mart., Vochysia guatemalensis Donn. Sm., Hieronyma alchorneoides Fr. Allemao, Calophyllum brasiliense Cambess and Schizolobium parahyba (Vell.) S. F. Blake (collected extensively in this project from indigenous populations from across the Southern region of Costa Rica). All plots were measured annually and data collected for tree height, DBH and mortality. Composited soil samples were taken at three depths in each site to characterize chemical and physical soil properties. In general, the native species were highly responsive to eco-regions, the introduced species much less so. The yield and dominant stand height of the introduced species were higher in acid soils with well defined dry season than the selected native species. As soil nutrient and water supply improved, the differences between introduced and native species decreased in mean stand height and yield. Two species ( Calophyllum brasiliense and Schizolobium parabyba) had more than 80% mortality in almost all plots during the first two years of establishment. The results of this study contrasts with findings obtained in the Northern region of Costa Rica on acid Ultisols (Typic Tropohumult), where at least Vochysia guatemalensis and Vochysia ferruginea out-competed the best introduced species, Gmelina arborea and Pinus spp. Results are mainly attributed to the pronounced ustic moisture regime in the Southern region of Costa Rica that is able to be tolerated by Gmelina arborea and Pinus spp. but not by the selected native tree seedlings.