Primary Productivity and Resource Partitioning in Model Tropical Ecosystems

The diversity of plant life forms in tropical forests affords the opportunity for assembly of plant combinations, both natural and managed, that make full use of resources and sustain high productivity. The influence of combining life forms on productivity and resource use was evaluated using three fast-growing tree species (Hyeronima alchorneoides, Cedrela odorata, and Cordia alliodora); each species was grown alone and with two perennial, large-stature, self-supporting monocots (Euterpe oleracea and Heliconia imbricata). Aboveground net primary productivity was extremely high in all stands. The monocots did not contribute significantly to the productivity of the Hyeronima polycultures, which was 4.5–8.4 g·m22·d21 between 18 and 36 mo. In contrast, the monocots accounted for 57% of the productivity (9.7 g·m22·d21) of Cedrela polycultures and 67% of the productivity (6.8 g·m22·d21) of the Cordia polycultures, by age 3 yr. The leaf area and density of fine roots in the Cedrela and Cordia polycultures were also significantly increased by the presence of the monocots, reaching or surpassing the levels found in the Hyeronima stands. The high productivity of Hyeronima, coupled with poor growth of its interplanted monocots, indicated that Hyeronima was able to achieve nearly complete use of resources. Ecosystem productivity and resource capture were increased when the monocots were grown with the other two tree species, and this occurred because of the inability of the tree species to completely utilize available resources, which provided an opportunity for the monocots to flourish in the understory. Monocot productivity in the Cedrela stands was additive to that of the trees, indicating complementary resource use between the monocots and this tree species. In the case of Cordia, tree productivity was slowed by the monocots, but this decline was more than compensated for by the high productivity of the associated monocots. Whether in natural forests or human-constructed agroforestry systems, the presence of dominant species that do not fully exploit all available resources allows the coexistence of other species and creates the potential for complementary resource use. The resource use characteristics of such species should be a key consideration in forest restoration efforts and in the design of sustainable land use systems.