Seed dispersal and germination of the epiphyte Tillandsia brachycaulos (bromeliaceae) in a tropical dry forest, Mexico

A crucial need for population maintenance of epiphytic species is the location of suitable microsites on a host tree. Quantitative evaluation of epiphyte seed dispersal and germination is needed to more fully understand successful host colonization; this process is especially important in dry forests, where drought and oligotrophy diminish population growth rates. In a 3-year field experiment, we evaluated seed dispersal and germination of Tillandsia brachycaulos and explored some environmental factors affecting these life-cycle phases. There was significant variation in dispersal curves depending on year and height of seed release. Forty-one percent of seeds experimentally released were not dispersed and only ca. 0.5% of dispersed seeds were captured in seed traps. The number of trapped seeds decreased with distance; most seeds were captured within 1.5 m of the seed source. Seeds dispersed farther (15 m) when released from greater heights. Seed germination under controlled conditions (98%) was higher than in a field experiment (3%). Neither year nor tree height significantly affected germination of T. brachycaulos. Differences in seed dispersal and germination among years could result from variable precipitation. Establishment of new genets seems to be an important bottleneck for population growth in T. brachycaulos. Our results show that seed dispersal and germination are processes that determine such establishment.