Neotropical epiphytic orchids, rare Hawaiian trees, and experimental translocation: A plant conservation florilegium

Abstract

Plant conservation is the science and practice of perpetuating species and the ecosystems in which they are embedded through sustainable management. In the Anthropocene, plant extinction rates have escalated due to climate change and habitat loss, and effective human stewardship of plant species is vital. Translocation (syn. reintroduction) is the planting of propagules to augment populations in decline, re-establish extirpated populations, or mobilize species to novel habitat. Translocation efforts have increased worldwide, yet without a priori experimental design, environmental determinants of success remain unknown. Furthermore, ~32% of terrestrial ecosystems are governed by Indigenous people and local communities (IPLC), yet the intersections between translocation science and IPCL management are largely unacknowledged. To develop translocation methods in collaboration with local communities and elucidate focal species’ habitat niche, I conducted two experimental translocations: ʻohe mauka (Polyscias bisattenuata), a rare endemic Hawaiian tree, and ye’ nagatx (Prosthechea karwinskii), a Mexican epiphytic orchid used in biocultural celebrations. I monitored the translocated populations for 4 years (P. bisattenuata) and 2 years (P. karwinskii) respectively and constructed mixed effects regression models to assess the relationship of abiotic and biotic habitat factors with translocation outcomes. ‘Ohe mauka four-year survival was 11.5% and growth had a positive relationship with site temperature; successful translocation sites were lower in elevation than the extant range, suggesting that remnant populations may not fully represent optimum habitat. Ye’ nagatx two-year survival was 28%, and initial propagule biomass and bryophyte cover had positive relationships with survival and growth; translocation holds potential to recover orchid material after traditional use and increase abundance of bioculturally-important epiphytic species. To further explore the microhabitat factors that influence epiphyte distributions, I conducted a survey of orchids in the canopy of the Osa Peninsula (Costa Rica). I found evidence of niche partitioning across canopy habitat quality gradients; variables that influenced epiphytic orchid density and richness included location within tree crown, host tree taxonomic identity, canopy openness, and surrounding cover of ferns. Together, this florilegium of studies demonstrates how knowledge of species-specific habitat requirements and biotic interactions are imperative to inform effective translocation methods. While human plant harvest is criticized as a threat to in situ populations, I demonstrate how sustainable use, celebration, translocation, and stewardship of species can form a holistic continuum of conservation practice.