Establishment, growth and biomass production of 10 tree woody species introduced for reforestation and ecological restoration in northeastern Mexico.
The coast of the Gulf of Mexico is characterized as a region with high variation in climatic conditions and rich in drought-tolerant or subhumid species. The species that are potentially useful for reforestation, regreening, agroforestry activities and the production of timber and fuelwood have been overexploited, resulting in a gradual decrease and degradation of their populations. In order to restore the soil and rehabilitate the disturbed areas inhabited by matorral vegetation, we tested the adaptability, development and establishment of 10 introduced tree species in northeastern Mexico. The species were: Albizia caribaea [A. niopoides], A. guachapele [Pseudosamanea guachapele], Caesalpinia velutina, Caesalpinia eriostachys, Crescentia alata, Enterolobium cyclocarpum, Gliricidia sepium, Haematoxylum brasiletto, Myrospermum frutescens and Pithecellobium dulce. The seeds of each species received different pretreatments. Seedlings were grown in plastic bags and planted out after 6 months by hand in August 1985 in a monoculture in four randomized blocks in a cleared area with deep loamy-clay soil, slightly alkaline. Measurements of different growth parameters and leaf/twig biomass over 15 years were evaluated. Crescentia alata, E. cyclocarpum, G. sepium and H. brasiletto tended to have better characteristics in terms of annual growth rate (33-62 cm in height and 1.7-2.6 cm in basal diameter during 1985-90), while A. caribaea, A. guachapele, Caesalpinia velutina and Caesalpinia eriostachys (20-30 cm in height and 1.2-1.7 cm in basal diameter) did not establish well due to susceptibility to frost. M. frutescens and Pithecellobium dulce had intermediate yields of great interest due to their multipurpose potential. The linear models gave a better estimate of tree biomass than the logarithmic functions. The species with the highest determination coefficient (r2) and the lowest mean square error (MSE), were E. cyclocarpum (r2=0.96; MSE=19.8), G. sepium (r2=0.99; MSE=15.3), H. brasiletto (r2=0.95; MSE=19.6) and M. frutescens (r2=0.98; MSE=18.1). The regression equations showed the close relationship between stem diameter (dn2), stem length (h) and number of stems above ground level. The low mortality shown by the majority of the introduced species coupled with their high reproductive capacities suggests that these species may serve to enrich the matorral of the region, especially for silvicultural purposes.