Transformation of natural habitat disrupts biogeographical patterns of orchid diversity

Physical gradients are major natural drivers of global biodiversity. A key question is understanding how biogeographic patterns are impacted by transformation of natural habitats. We aim to elucidate the complex relationships between two core biogeographic drivers of biodiversity—elevation and precipitation—, local deforestation, and their additive and interactive effects on Andean orchid diversity in the Colombian Andes. We sampled understory orchids across 341 plots pairing natural and transformed habitats along a wide elevational (1163–3415 m) and precipitation range (879–3817 mm per year). We found 35,891 adult individuals in 341 species peaking at mid-elevations (∼2500 m) and mid-to-high precipitations (>1600 mm/yr). Conversion of natural to transformed habitats caused substantial orchid diversity loss, with ten-fold fewer species at the plot level equating to a 6-fold loss in overall species richness, and 23-times fewer individuals. The additive and interactive effects better explained the main patterns: conversion reconfigured the natural mid-elevation trends in orchid diversity and positive trend in diversity with precipitation to a quasi-linear trend in transformed habitats. This reflects the inherent dependency of orchid species to a host tree as well as lower resilience to transformed habitats. Our findings highlight the importance of halting deforestation across environmental gradients, but in particular at elevations and precipitations where reshaping of biogeographic patterns maximises the losses of biodiversity.