Longevity and Diversity – findings

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STAND LONGEVITY AND LIFE-FORM DIVERSITY AS CONTROLS OF ECOSYSTEM FUNCTIONING 

Five examples of findings from the project at La Selva are listed below. More detail on these and other results are found in PUBLICATIONS.

1. Did the systems containing three life forms exhibit complementary use of resources? Yes. But complementarity (as inferred from primary productivity) proved to be a transient phenomenon. As the stands developed, complementarity relationships among species (i.e., no species suffers because of the presence of others) often turned into compensatory growth (a decline in one species is offset by a positive response in another) and eventually into competition (one species prevails). (See papers with Haggar, Hiremath, Mazzarino, others.)

2. The efficiency with which nitrogen and phosphorus were used by plants differed at the scale of measurement: leaf level, plant level, or ecosystem level. It also differed among species. (See papers by and with Hiremath.)

3. Fast-turnover stands hemorrhaged nutrients, especially nitrogen and calcium. Little wonder that annual cropping schemes lead to soil and water degradation. (See papers with Bigelow, Mazzarino, Silver, Russell, others.)

4. Deciduous tree species were out-competed by shorter stature palms. Must be nutrient or water limitations? No. The evergreen palms grew upward, occupying what would have been crown space for tree leaves, thereby reducing tree leaf area. In a sense, the trees were out-competed for light from below. (See competition paper with Mazzarino.)

5. Soil fertility is sustained somewhat better by systems having three life forms than by equal-aged monocultures. More striking, however, was the effect of intermediate rates of stand turnover. Quadrennial deposition of large amounts of organic matter on the soil surface led to greater amounts of soil carbon, phosphorus, calcium, and potassium.