Seed regeneration mechanisms over fine spatial scales on recovering Coffee plantation and pasture in Puerto Rico

Abstract

Researchers have long been interested in the scale-dependence of ecological processes and, more recently, in the precise scale at which a process operates. Plant regeneration studies have also been interested in scale questions, but have not studied either several regeneration mechanisms at once or the exact scales they work at. To address these issues, I set out 256 seeds for each of four species in each of two 16 × 16 cell plastic grids placed on a 1 year old Coffee plantation and on a 4 year old pasture, both in Puerto Rico. I found that seed predation was the dominant mechanism (50%–75% losses among species) of seed mortality compared to seed disease (20%–45% losses); while germination accounted for 15%–35% of the seed. In general, species responded individualistically with no clear trends within coffee or pasture. I next used Ripleys K-function to investigate spatial-dependency over spatial scales ranging from 2 cm to 20 cm for each seed mechanism, each species and within each field type. Again the most recurrent patterns came from taking the seed mechanisms separately, compared to species or field type trends. I found that (1) seed predation clumped at scales of 2 cm to 11 cm, (2) clumping for seed disease was rare and scattered among scales, and (3) seeds germinated in a clumped pattern at scales of 11 cm to 23 cm. These results reflect the behavior of seed predators, and may also mimic the size of sun flecks, in disturbed areas of Puerto Rico. Finally, I discuss their implications for old-field microsite preferences, safe sites and patch dynamics.