Epsilon Open Archive

Abstract

The thesis summarises results from four studies in dry forests of Nicaragua aiming to gain knowledge supporting conservation and rehabilitation efforts in these highly threatened forests. In the first study, tree species composition, structure and diversity of dry deciduous and gallery forests was carried out in Chacocente National Wildlife Refuge during 1994 and 2000. A total of 29 families, 49 genera and 59 species were represented in 2 ha permanent plots in dry deciduous forest during 1994 and 2000 assessments. In the gallery forest, the number of families, genera and species recorded in 2000 inventory was 33, 48 and 58, respectively, and slightly higher than the 1994 inventory. The number of stems ≥ 10 cm dbh varied from 451 (1994) to 489 (2000) per ha in the deciduous forest, and from 283 (2000) to 298 (1994) per ha in the gallery forest. The gallery forest was found to be more diverse than the deciduous forest using Fisher’s diversity index. In the second study, the temporal and spatial variation in seedling and sapling population densities of Gyroscarpus americanus, Calycophyllum candidissimum, Haematoxylon brasiletto and Cedrela odorata were investigated in the dry forest in Chacocente National Wildlife Refuge for three consecutive years. The density of seedlings and saplings varied significantly over time and among species. The overall density of recruits was higher for G. americanus and C. candidissimum compared with H. brasiletto and C. odorata. The net change in population density of seedlings and saplings was positive for C. candidissimum only, indicating a continuous and advanced regeneration. For the two most abundant species, G. americanus and C. candidissimum, the population density of recruits varied with respect to slope of the terrain and crown exposure to direct sunlight, thus resulted in clumped pattern of regeneration. The third study dealt with soil seed bank assembly following secondary succession on abandoned agricultural fields in a chronosequence of 4 to 14 years. The species composition of the seed bank and seed density varied significantly with increasing age of abandonment. A total of 3, 5 and 9 species were found on sites abandoned 4, 9 and 14 years ago, respectively. The total number of seeds ranged from 327 in the 4-year old site to 146 in the 14-year old site, and the density of viable seeds ranged from 141 seeds m-2 in the 4-year old site to 22 seeds m-2 in the 14-year old site. In the fourth study, seed germination responses of C. candidissimum, C. odorata and Guaiacum sanctum, 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 C. odorata and G. sanctum in the field were investigated. Among the species tested, germination of C. candidissimum seeds was positively photoblastic, and for all species the optimal temperature for germination was 20-25ºC. Survival of G. sanctum seedlings was higher in all three sites, but the relative growth rate in collar diameter was higher in open sites. Survival was poor for C. odorata.