M. D. Swaine

DISPERSAL PATTERNS AND SEED BANK DYNAMICS OF PIONEER TREES IN MOIST TROPICAL FOREST

Seed dispersal patterns and seed persistence in the soil should strongly influence the distribution of pioneer tree recruits in gaps. Nonetheless, seed distribution patterns for pioneers are poorly known, and processes controlling the fate of seeds in the soil have been little explored. We examined patterns of seed rain, seed abundance in the soil, and seed mortality of two common pioneer trees, Miconia argentea (Melastomataceae) and Cecropia insignis (Moraceae), on Barro Colorado Island, Panama. For each species, we selected four isolated, reproductive trees within a 50-ha forest dynamics plot. Seed rain and soil seed bank samples were collected, respectively, in mesh traps and from soil cores sampled along transects radiating away from the tree crowns. At below-crown sites, seed rain inputs far exceeded soil seed bank densities measured at the end of the fruiting season. For Miconia, the below-crown seed bank in the surface 3 cm of soil accounted for only 23% of seed rain, and for Cecropia, only 2%. How...

Use of hemispherical photographs in forest ecology: measurement of gap size and radiation totals in a Bornean tropical rain forest

Study of forest dynamics commonly requires measurement of canopy gap size. Hemi- spherical photographs can be analysed to provide various measures whereby gaps can be ranked in order of size. For ten artificial gaps in a Bornean tropical rain forest these measures were better correlated with gap microclimate than gap area measured physically on the ground. All these measures are however relative. For detailed (e.g. ecophysiological) studies the greater detail pro- vided by absolute measures of photosynthetically active radiation (PAR) are required. Long term PAR values can be computed from hemiphots so long as measurements in the open nearby are available. Correction for cloudy weather is essential. Computed and measured PAR are compared for the test gaps. Both have inherent limits which means that below c. 15% canopy openness, differences in PAR between gaps cannot be assessed accurately.

Effect of three species of climber on the performance of Ceiba pentandra seedlings in gaps in a tropical forest in Ghana

The proliferation of climbers can have deleterious effects on tree regeneration, especially in forest canopy gaps where climbers increase in abundance. In response to the colonization by climbers, the supporting tree can suffer a reduction in growth and its allometric relationships may be modified. We evaluated the effects of three species of climber on the performance of the pioneer tree Ceiba pentandra in a moist semi-deciduous tropical forest in Ghana. In each of three gaps, four plots were set up, each with eight Ceiba seedlings paired with a single plant of one of three climber species, planted within 5–10 cm of the tree seedling, plus a control (no climber). The climber species were: Centrosema pubescens , a nitrogen-fixing woody climber; Combretum racemosum , a woody climber and Dioscorea praehensilis , an herbaceous climber. After 12 mo, Centrosema and Combretum had about four to five times more biomass than Ceiba seedlings. There was no effect of climber competition on Ceiba biomass growth, and no relationship between climber biomass and Ceiba growth rate. Individual climber species, however, had other effects: Combretum caused a significant reduction in the height and diameter growth of Ceiba , whilst competition with Centrosema was associated with significant reduction in the crown area and increase in internode length in Ceiba . The results indicate that even very different climber species appear to cause negative effects on trees during regeneration.