Critical importance of large native trees for conservation of a rare Neotropical epiphyte

The distribution of rare plants may be limited by environmental or density-dependent factors that reduce population growth and persistence. The relative importance of environmental limitations vs. the degree to which conspecifics influence recruitment may determine optimal management strategies for plants of conservation concern. We sowed seeds of a rare epiphytic orchid in trees from agricultural Costa Rican landscapes to ask how recruitment is influenced by established conspecific plants and the environment. We hypothesized that recruitment is positively influenced by conspecific plants. Conspecific adults were expected to be associated with favourable microhabitats and mycorrhizal fungi for germinating seeds, without creating unfavourably competitive conditions. Alternatively, we hypothesized that recruitment varies due to environmental differences among study sites or host trees, irrespective of adult proximity. We experimentally added 240 packets of seeds from 2 source populations into four naturally established populations. Germination was evaluated after fivemonths. We used mixed models and conditional inference trees to evaluate results. Proximity to conspecific adults neither increased nor decreased germination. Instead, large native trees and microsites with more closed canopies supported significantly greater germination than smaller cultivated trees and microsites with more open canopies.Synthesis. Landscape changes that replace large native trees with a more homogenous array of cultivated species may not only reduce rare epiphyte populations directly, but also limit their ability to colonize disturbed secondary habitats. Because the habitat is the prime determinant of recruitment, large and often isolated native trees that act as refuges for rare epiphytes in disturbed landscapes should be a top priority for local conservation efforts.