Some autecological characteristics of early to late successional tree species in Venezuela

The breadth of the continuum concept of strategy with respect to succession was tested on 21 tree and shrub species common in either unlogged or logged stands, respectively, in the Forest Reserve of Caparo, Venezuela, by examining morphological, physiological and population characteristics. Based on a preliminary abundance analysis, `early', `mid' and `late' successional species as well as `generalists' were distinguished. Early successional species, i.e. Ochroma lagopus, Heliocarpus popayanensis and Cecropia peltata were similar in many autecological aspects, e.g. monolayered leaf arrangement, orthotropic architectural models, no adaptive reiteration, clumped distribution, but differed in gap association and distribution along a drainage gradient. Mid-successional species established themselves both in large and small gaps (> 300 msup2 ]; 80–300 msup2 ]) and showed a clumped to regular distribution pattern in logged areas; they exhibited more diverse crown and leaf characteristics than early successional species. Late successional species established themselves only in small gaps and understorey, and showed a regular spatial pattern in undisturbed areas. All late successional species displayed architectural models with plagiotropic lateral axes and showed a multilayered leaf arrangement. Adaptive reiteration was a common feature of late successional species which could be further subdivided into large, medium-sized and small trees, indicating different light requirements at maturity. Generalists were common treelet and shrub species in both disturbed and undisturbed sites where they are also capable of completing their life cycle. The light compensation point (LCP) of an individual plant was strongly influenced by its crown illuminance. Large late successional species showed the widest range of LCP values, reflecting the increasing light availability with increasing height in mature forest. On the basis of many autecological characteristics, it was found (i) that there is in fact a continuum of species strategies with respect to succession even among early and mid-successional species and (ii) that the latter group of species showed the widest breadth of autecological traits, reflecting the heterogeneous environment in which they establish and mature.