Gradient (elevation) vs. disturbance (agriculture) effects on primary Cloud forest in Ecuador: seed predation, seed pathogens, germination

Abstract

Background: Gradients and disturbances affect plant communities. Cloud forests exist on elevational gradients and are often disturbed by being cleared for agriculture, so they present a unique opportunity for the investigation of how gradients and disturbances affect their structure, function and dynamics. The focus of the current study was on seed predation, seed pathogens and seed germination: all key factors in tree recruitment and regeneration. Methods: Three hundred seeds of three species—Solanum stenophyllum Bitter (Solanaceae: bird-dispersed), Palicourea amethystina (Ruiz & Pav.) DC. (Rubiaceae: bird-dispersed) and Clusia flaviflora Engl. (Clusiaceae: mammal-dispersed)—were studied at primary (1°) cloud forest at Guandera Reserve. After 2 weeks in the field, losses due to seed predation or pathogens were counted and the remaining seeds were tested for germination. These results were then compared with similar data collected and published previously from a 1° cloud forest and a secondary (2°) cloud forest, both at Maquipucuna Reserve, Ecuador. Results: In both closed-canopy forest and tree-fall gaps at Guandera Reserve, S. stenophyllum Dunal seeds suffered the greatest losses to predators, P. amethystina seeds had the greatest germination and C. flaviflora seeds had the greatest losses to pathogens. Comparison with data from Maquipucuna Reserve showed the following: (1) Solanum sp. suffered the greatest losses for seeds lost to seed predators in general but Cecropia sp. and Ficus sp. also had high losses in Maquipucuna 1° cloud forest; (2) for seeds lost to pathogens, species that lost the most seeds were unique to each study site: Clusia flaviflora seeds at Guandera 1° cloud forest, Cecropia sp. seeds at Maquipucuna 1° cloud forest and Piper aduncum L. seeds at Maquipucuna 2° cloud forest; (3) for seeds that germinated the most, species were again unique to the study site: Palicourea amethystina seeds at Guandera 1° cloud forest, Otoba gordoniifolia (A. DC.) A.H. Gentry seeds at Maquipucuna 1° cloud forest and Solanum ovalifolium Dunal seeds at Maquipucuna 2° cloud forest; and (4) in general, forest types differed significantly for both seed predation and seed pathogens. Within the 1° cloud forest at Maquipucuna, there was a significant difference among tree seed species for pathogens and a significant difference among the tree seed species for germination, and within the 2° cloud forest at Maquipucuna, there was a significant difference among tree seed species for pathogens. Conclusions: As elevation increases in 1° cloud forests, the proportion of seed that germinates remain largely constant, but the major seed loss shifts from being due to predators to being due to pathogens. Conversion to agriculture also leads to seeds mainly lost to predators, but individual species loss levels depended on what crop had been planted previously.