Epsilon Open Archive

Abstract

Tropical dry forests are one of the most degraded and threatened forest ecosystems in Central America. The thesis summarises results from four separate studies in the dry forests of Nicaragua with the aim to gain knowledge that will support future restoration endeavours. In the first study, aspects of stand dynamics in dry deciduous and gallery forests were investigated over a 7-year period. The result shows that stem density and basal area decreased by 13% and 8%, respectively for the dry deciduous forest. The changes in stem density and basal area for the gallery forest were negligibly low. The mortality and recruitment rates for the deciduous forest were 4.5 and 2.5 % year, respectively, and the corresponding values were 4.2 and 4.0% yearfor the gallery forest. The causes of mortality could be anthropogenic and natural disturbances. In the second study, the natural regeneration of three dry forest species (Lonchocarpus minimiflorus, Tabebuia ochracea and Lysiloma divaricatum) in relation to slope of the terrain and crown exposure to direct sunlight was investigated over three years. The density of recruits varied significantly among species and over time. L. minimiflorus and T. ochracea had the highest densities compared with L. divaricatum, and the net change in population density was slightly positive for T. ochracea only.-1-1 Regeneration was more abundant in the gentle and steep slopes under partial exposure of the crown to sunlight, thus resulting in aggregated pattern of distribution, especially for L. minimiflorus and T. ochracea. The third study dealt with recovery of woody vegetation after 4, 9 and 14 years of abandonment of agriculture. The floristic, structural and diversity measures increased with age of abandoned fields. In the fourth study, seed germination responses of four dry forest species: Bombacopsis quinata, L. divaricatum, Cordia alliodora and Tabebuia rosea, to different constant and alternating temperature regimes under continuous light or darkness in the laboratory, and the effect of canopy cover on seedling survival of B. quinata, C. alliodora and T. rosea in the field were investigated. The optimal temperature for germination was between 20 and 25°C for all species. The alternating temperature regimes tested in the present study did not bring beneficial effect on germination compared with the constant temperature regimes, although its effect was modulated by light condition for some of the species. Survival of C. alliodora seedlings was higher in open and partially-open sites than in the understory. B. quinata had the lowest survival, and survival of T. rosea was higher on open site. It can be concluded that restoration of degraded forests in the future should involve local people, natural regeneration alone is not sufficient, management plans for secondary forests derived from abandoned fields should be prepared and further screening of candidate framework species should be carried out.