Spatial distribution and regeneration strategies of the main forest species on Robinson Crusoe Island
We describe the structure of the endemic Robinson Crusoe Island forest. We analyse the regeneration strategies of the trees: Myrceugenia fernandeziana, Fagara mayu, and Drimys confertifolia. Inventories were taken on nearly intact montane forest remnants with emphasis on spatial patterns by using Ripley's K (t) function. We hypothesized that i) ornithochorous and barochorous species should show a clumped regeneration, as a consequence of seed rain; ii) nurse effect, if present, should also contribute to a clustered pattern; iii) clustering should disappear at more developed life-stages due to self-thinning; iv) if gaps influence tree mortality and regeneration, these will present grouped patterns. Myrceugenia fernandeziana was the most abundant tree species, followed by F. mayu and D. confertifolia. The diameter distribution of M. fernandeziana suggested a continuous regeneration. The diameter distribution of F. mayu was typical of species that require disturbances to regenerate, whereas the diametric pattern of D. confertifolia was intermediate compared with the previous species. M. fernandeziana demonstrated a spatially clumped regeneration given its dispersal mode (hypothesis i), but did not show association with the large tree individuals, discarding a possible nurse effect (hypothesis ii). The large specimens of M.fernandeziana were randomly distributed, likely due to self-thinning (hypothesis iii). Mortality of M. fernandeziana trees did not seem to be a consequence of local disturbances, rejecting hypothesis iv). Fagara mayu distributed randomly showing in cases some aggregation. Drimys confertifolia presented a clustered pattern. Regeneration of F. mayu and D. confertifolia occurred mainly in gaps, but also under canopy for the latter species. D. confertifolia tended to regenerate near larger trees of the same species (hypothesis ii). M. fernandeziana seems to exhibit shade tolerance, although it showed plasticity to use different regeneration environments. F. mayu showed characteristics of a shade intolerant species, possibly requiring gaps, or larger disturbances to regenerate. D. confertifolia seems to be a shade semi-tolerant species, requiring areas with low canopy cover to establish.