Caracterización de poblaciones de especies endémicas en bosque tropical seco semideciduo. Parque Nacional Machalilla, Manabí, Ecuador

Seasonally dry tropical forests are ecosystems of high endemism and floristic diversity, but they have been relatively not well-studied ecosystems and are very much threatened by anthropic pressures. This study aimed to evaluate the dendrometric and horizontal structure characteristics of the population of 12 endemic plant species in the semideciduous forest of the Equatorial Pacific Coastal Cordillera of the Machalilla National Park, Manabí, Ecuador. This is one of the most extensive protected areas on the Ecuadorian coast, located in the Tumbes-Chocó-Magdalena biogeographic region. It is considered one of the 25 hotspots worldwide. We selected 12 species that hypothetically co-exist in this semideciduous forest (Bursera graveolens, Eriotheca ruizii, Handroanthus chrysanthus, Ziziphus thyrsiflora, Geoffroea spinosa, Myroxylon balsamum, Priogymnanthus apertus, Melicoccus bijugatus, Nectandra reticulata, Simira ecuadorensis, Coccoloba ruiziana, Klarobelia lucida). We studied five 2500 m2 transects, where dendrometric variables (tree height, diameter at breast height-DBH, basal area, altimetric and diameter classes) were evaluated. We evaluated the horizontal structure variables of populations like absolute/relative abundance, dominance and frequency, and the importance value index (IVI and IVN). In 12,500 m2, the results identified 331 individuals. M. balsamum was the highest species (9.41 m), while E. ruizii had the highest DBH (21.03 cm) and the biggest basal area (0.05 m2). The species with the highest absolute/relative abundance and frequency were S. ecuadorensis and H. chrysanthus, and the latter had the highest absolute dominance (1.23 m2•ha−1). S. ecuadorensis presented the highest importance value index based on 100 and 300, followed by H. chrysanthus and Z. thyrsiflora. P. apertus, M. balsamum, E. ruizii and C. ruiziana obtained intermediate values. The least ecological weight was for N. reticulata, K. lucida, M. bijugatus and G. spinosa. No B. graveolens individuals were observed in the studied transects in this forest because this species was found at altitudes < 240 m a.s.l. The results of the altimetric and diameter classes indicated that the studied sector corresponds to a relatively young secondary forest affected by natural and anthropic factors.