NON‐TIMBER FOREST PRODUCT EXTRACTION: EFFECTS OF HARVEST AND BROWSING ON AN UNDERSTORY PALM

Abstract

Despite the advocacy for non‐timber forest product (NTFP) extraction as a form of sustainable development, the population ecology of many NTFPs remains unstudied, making it difficult to assess the ecological impacts of extraction. We investigated the demography and population dynamics of the harvested, understory palm, Chamaedorea radicalis in the El Cielo Biosphere Reserve, Mexico. Our objectives were: (1) to describe patterns of C. radicalis abundance and population size structure, (2) to document C. radicalis demography, (3) to test experimentally how this demography was affected by different leaf harvest regimes and livestock browse intensities, and (4) to project their effects on transient and long‐term population dynamics.Data on palm abundance and population size structure were collected from belt‐transects along hillsides. We also exposed 100 adult palms to each of five leaf harvest treatments (N = 500): control, harvest once per year, harvest twice per year, harvest four times per year, and a modified four times per year harvest where only one leaf was removed each harvest. Browse experiments were conducted to assess the effect of burro browse on demography. Experiments were monitored over two years, and results were incorporated with other demographic data to parameterize stage‐based (Lefkovitch) matrices for each year × treatment combination.Topographic position influenced both population size structure and density, with a gradient from valleys (727 palms/ha) to upper slopes (5513 palms/ha). Palm demography was characterized by low mortality, low reproductive activity, and high seed germination rates. Leaf harvest increased adult mortality and reduced fecundity, and it was projected to reduce λ (finite rate of increase). However, λ for harvested populations did not differ significantly from 1. Browsing increased mortality of seedlings, juveniles, and small adults, resulting in populations projected to decline (λ < 1).These findings indicate that browsing by free‐range livestock impacts C. radicalis populations more than leaf harvest and could explain the low density and skewed size structure in valleys. The modest impact of leaf harvest treatments is due in part to the reduction in the availability of marketable leaves. Detection of such feedbacks exemplifies how the incorporation of human management practices enhances the insights that experiments bring to studies of the population ecology of NTFPs.