Faster growth is often assumed to be the basis of success, whether it is in economy, agronomy or ecology. However, comparative studies of plant species suggest that long-term achievement of positive net growth requires avoidance of tissue loss (i.e., reduction of risk for capitol loss) through a carbon allocation strategy emphasizing tissue toughness and energy storage. Species that employ this type of strategies persist in late successional communities, and are often known as K-strategists. The opposite allocation pattern of high leaf area ratio (= leaf area / total biomass) enables faster short-term net carbon gain rate. However, this strategy, common among disturbance specialists (r-strategists), is accompanied with a cost of high mortality. Here, I report key results from recent studies of seedlings at standardized ontogenetic stages, comparing 8-100 species of coexisting woody species on Barro Colorado Island, Panama, focusing on physical defense (tissue density and fracture toughness of stems and leaves), and storage of non-structural carbohydrates (NSC) in relation to vital rates (survival rates, growth rates).
Results/Conclusions
There were significant interspecific correlations such that seedlings of tropical woody species with high survival had greater tissue density, fracture toughness and higher carbohydrate storage in stems and roots, but grew more slowly. These results support a hypothesis that persistence in low-resource availability, such as deep shade in the understory, is not a mere function of short-term resource-use efficiency, but more likely a function of conservative carbon allocation to physical defense and storage. In all shade tolerant species, both concentration and pool size of NSC increase even in very deep shade with seedling age. This supports a hypothesis that maintenance of long-term positive net carbon gain requires energy storage to survive periods of negative carbon gain, imposed by attack by natural enemies, small-scale disturbance, and seasonal stress. These findings have parallels in life history strategies of many organisms, as well as in social and economical issues. This basic ecological research also illustrates importance in ecological educations of being assertive of underlying assumptions, such as equating success and competitiveness with faster growth rates at individual and population levels.
