STRUCTURE AND SPATIAL DISTRIBUTION OF REPOPULATION AND UNDERSTORY DIVERSITY OF Hesperocyparis guadalupensis S. WATSON

Abstract

Hesperocyparis guadalupensis S. Watson is an endemic species of Guadalupe Island in the process of recovery after the feral goat (Capra hircus) eradication. In 2019, five sampling sites (400 m2) were established on three different categories of canopy cover: low (LC, ≤ 5 %), medium (MC, 6-23 %) and high (HC, ≥ 24 %) with the aim of evaluating the effect of canopy cover on the dynamics of regeneration and on the understory plant diversity. Information on tree height (H) and diameter at breast height (DBH) was obtainded from juvenile individuals (minimum heights of 1.5 and maximum of 10 m) and plant diversity of the understory was recorded; in addition, four sub-sites of 1 m2 were established per sampling site, where the number of seedlings with height less than 1.5 m was recorded. The canopy cover level did not influence the number of juveniles, but the number of seedlings was higher in HC (p = 0.003). Three categories of H (2.5, 4.5 and 6.5 m) and three of DBH (2.5, 7.5 and 12.5 cm) were identified in the population; the highest frequency of individuals was registered in the smallest categories (2.5 and 4.5 m in height, 2.5 and 7.5 cm in diameter), especially in MC and HC. At LC a uniform spatial distribution was found [L(t) < 0)], while at MM and HC the spatial distribution was grouped [(L(t) > 0]. In the understory, 24 species of 21 genera and 12 families were recorded, with no significant statistical differences between canopy covers in richness and alpha diversity of the understory. At least 60 % of the understory species were shared among the three canopy conditions (beta diversity). The vertical and horizontal structure of juveniles and seedlings confirms the recovery of the forest by showing an increase of individuals in low categories, with a spatial distribution associated with the opening of small clearings that promote the germination and recruitment of new individuals to the population.