The importance of ecological stress factors for plant growth in a tropical forest and two grassland communities

The growth of plant species was examined in relation to ambient stress factors, both biotic and abiotic. The growth of Passiflora vitifolia was recorded by natural observations and by an experiment in Corcovado National Park, Costa Rica. The growth of Schizachyrium scoparium was measured in an experimental study in central Texas. The growth of both grasses and forbs was recorded in an experimental study in Wales.; Two sets of data were collected from P. vitifolia. The first was a set of "natural" observations and the second was a set of measurements made on plants of four different clonal origins that were transplanted into a forest gap and an adjacent understory habitat. In the "natural" observations, plant growth was positively correlated with the level of soil nutrients but negatively correlated with light level. Plants at the experimental study site grew better in the forest gap where both light and soil nutrient levels were enhanced. The clonal origin of P. vitifolia was important for plant growth.; Passiflora vitifolia is host plant to flea beetles (Alticinae spp.). Pathogens also cause foliar damage to P. vitifolia. I examined the connection between: plant growth and beetle herbivory, and plant growth and pathogen attack. Both beetle and pathogen damage were associated with reduced plant growth. Damage levels depended on clonal type.; This work also addresses questions about plant growth in two temperate plant communities. On one hand, I examined the importance of soil water supply and intraspecific competition among S. scoparium plants, native to semi-arid grassland. Competition among the plants increased under conditions of increased water supply. On the other hand, I recorded the colonization of experimental patches in mown grassland; the experiment simulates processes of natural disturbance and competition. Land management and formation of new gaps may explain species coexistence at this study site.