Hernández, Vidal P.

Fires are ecological disturbances that change the structure of populations, and accordingly demographic response is determined by the particular attributes of each species. The present study evaluates the effect of fire on a population of Hypericum styphelioides subsp. styphelioides through its population structure. The structure of the population in unburned and burned areas was characterized. In the burned area, medium reproductive adult occurs in larger numbers and its density is higher in comparison to the unburned area, this pattern could have been determined by a post-fire population explosion. On the other hand, the classes below the medium reproductive adult were less represented in the burned area, probably as a consequence of the continue decline on the recruitment of younger individuals of each generation due to the reduction of nutrient levels after the fire. This pattern matches the similarity of the densities of these performance classes and the overall density between both areas. Furthermore, the smaller dimensions found in medium and small breeding adults in the burned area of the pine forest also indicates the nutrient deficiency that affected the growth of the individuals after the fire. However, similar dimensions found among vegetative adults of both areas may indicate the recovery of the levels of nutrients in the burned area of the pine forest to the pre-fire levels, by the accumulation of organic matter.

The areas characterized by soils derived from quartz rocks are among those that have contributed the most to the endemism of the Cuban flora. In western Cuba sandy-quartzite soils are restricted to few outcrops that support pine forests. Tabebuia lepidophylla is an endemic species of this vegetation, both in plains and heights slate. Particularly in the first, the conditions imposed by the nutrient-poor substrate are critical in the development of populations. In the present study, the population structure of T. lepidophylla in the pine forest on quartzite sands of the Ecological Reserve Los Pretiles is characterized. Twenty plots of 25 m2 were established, 10 parallel to the coastline and 10 were set into the pine forest, to assess the influence of the gradient in the structure of the population. The population is stable with a predominance of individuals in the first two height classes, with lower frequencies to the higher. This structure is an indicator of the optimal condition of the population and of its capacity to sustain itself. The density values varied between areas, with higher values far to the coast. The spatial distribution pattern of the population was clustered both at the population level and between areas. The distance to shore conditions and influences the structure of the individuals of the population.