Conserving dominant trees in human-modified landscapes at the Lacandon tropical rainforest

Abstract

Deforestation of old-growth forests (OGF) is a significant driver of biodiversity loss, particularly impacting rare species. However, the threat to dominant species is usually overlooked, given their relatively high abundance. Therefore, assessing the impact of forest loss on dominant species is imperative, mainly because they play critical roles in the structure, functioning, and ecosystem services. In particular, identifying the amount of OGF required to avoid local extinction and conserve dominant species in human modified landscapes is critically needed. Furthermore, as dominant species may regenerate in secondary forests (SF), growing in abandoned fields, assessing whether SF may buffer species' local extinction is also needed. We addressed these issues by analyzing demographic changes of four canopy dominant tree species across twenty 1-km2 landscapes encompassing the whole deforestation gradient (0 to ~100% OGF and SF cover) in the Lacandon rainforest, Mexico. Non-linear modeling identified local extinction thresholds at 25–35% OGF cover, below which tree density (DBH ≥ 5 cm) and regeneration potential (juvenile/adult ratio) of all species sharply declined. Deforestation also increased the spacing of remaining trees and reduced tree size. Thus, we propose that ≥40% OGF cover be retained in the landscape to be conservative. SF were too young (<30 years fallow age) and perishable to sustain viable populations of our dominant species. Because the remaining OGF in the study region is within the estimated extinction thresholds, we urge the adoption of land uses promoting high-quality landscape matrices suitable for the conservation of dominant species and associated biodiversity.