The ecology of Swietenia macrophylla and three associated tree species in seasonal tropical forests in Quintana Roo, Mexico were studied to improve the design of sustainable forest management methods. Seed production of 82 Swietenia trees from 15 to >100 cm diameter at breast height (DBH) was estimated by counting fruit pericarp segments beneath the tree crowns. The number of fruits/tree increased with DBH size and was related to increasing tree crown. Trees >75 cm DBH had significantly greater fruit production than smaller trees, and had a larger median seed dispersal distance (38 m) that was skewed to the west of the trees. Fruit production varied among the six-years, but did not reach the population variability or tree synchronicity that is found in masting species. The effect of 7%, 22%, and 45% sunlight and two soil moisture types on seedlings of Swietenia, Cedrela odorata, Cordia dodecandra, and Manilkara zapota were studied in shade houses in Quintana Roo, in order to examine plasticity of physiology, morphology, and biomass allocation as a background to understanding growth and competition in forest conditions. Some expected trends occurred in all species: leaf area ratio (LAR), specific leaf area (SLA), and foliar biomass allocation all increased with decreasing light. Good soil moisture increased height, diameter and biomass, therefore greater photosynthesis rates may be explained by more water availability. However, comparisons among species did not always show trends expected to be associated with different levels of shade tolerance. Shade tolerant Manilkara had the lowest total biomass, and the highest foliar biomass allocation, but did not have the expected high SLA because of its thick evergreen leaves. Shade intolerant Cedrela had the lowest foliar allocation, but compensated with the highest SLA, foliar nitrogen content, and photosynthetic rate. Intermediate/intolerant Swietenia had the highest biomass production of all species; it had high plasticity in foliar allocation such that there was little difference in total biomass among light levels. Intermediate/intolerant Cordia had lower plasticity in foliar allocation than Swietenia , so a lower LAR and substantially less total biomass in low light. It had thicker leaves and higher foliar nitrogen-area in high light.

By studying crown structure, leaf area index (LAI), and light interception during the first 3.5 years of development, I assessed the patterns of above-ground space partitioning and stand dynamics in monocultures and mixtures of three tree species (Cedrela odorata, Cordia alliodora, and Hyeronima alchorneoides). Plantations were established in the tropical rain forest of Costa Rica. To understand species differences during the period of free growth, I measured leaf distribution, crown shape, and biomass allocation strategies of each species at age one year. To compare stands dynamics among monocultures and mixtures I obtained the size, crown shape, and relative position of plants at regular time intervals between age 1.5 and 3.5 years. Stand-level measurements of LAI, and canopy light transmission complemented these individual-tree measurements. Before the onset of competition, there was a statistically significant multivariate difference in crown architecture among the three species. The mean dry biomass (grams/tree)was 990.0 in Cedrela, 665.3 in Cordia, and 1281.4 in Hyeronima. Proportionally Cedrela allocated more biomass into roots than the other two species. Biomass allocation within crowns was correlated with specific above-ground architecture. Differences in stand composition caused major modification in several morphological traits. On average, the performance of Cordia and Hyeronima individuals growing in mixtures exceeded that observed in monocultures. Cedrela showed an opposite trend with larger trees in monocultures than in mixtures showing the effect of suppression in mixtures. At age 2.0 years monocultures had almost reached their maximum LAI values. Approximate LAI values were 4.5 for Hyeronima and 2.0 for the other two monocultures. LAI of the mixtures increased from 2.0 at age 1.5 years to 4.0 at age 3.5. At the end of this study a two-stratum canopy had developed in mixed-species stands with the shade-intolerant Cordia above both the gap-dependent Hyeronima and the suppressed Cerela. Thus, Cordia and Hyeronima showed compatible height growth and crown structural characteristics in mixtures. The growth patterns of mixed stands suggests that both inter-specific competition with neighboring trees and infections by shoot-boring larvae of a lepidopteran species are responsible for the suppression of Cedrela.