Biomass harvesting alters pollen deposition in Patagonian forests: Strong effects on herbs, weak or absent in woody species

Abstract

Woody biomass harvesting is increasingly promoted as a sustainable management strategy in temperate forests. However, its potential impacts on ecological processes essential for forest regeneration, such as pollination, remain poorly understood. We experimentally assessed how biomass harvesting affects floral abundance and pollen deposition in Nothofagus antarctica forests of Patagonia, Argentina. Using a gradient of harvesting intensities (0 %, 30 %, 50 %, 70 % cover removal), we evaluated three plant species representing different growth forms: an herb (Phacelia secunda), a shrub (Diostea juncea), and a tree (Embothrium coccineum). Our results show that harvesting strongly increased floral density and conspecific pollen deposition in the herbaceous species, with more modest or absent effects in shrubs and trees. Total pollen deposition followed a similar pattern, while heterospecific pollen deposition remained unchanged across all growth forms. In P. secunda, floral density partially explained the observed increase in conspecific pollen, suggesting that both floral resources and environmental conditions contribute to pollination responses. Site influenced floral density, while both site and time affected pollen deposition, with no interaction with harvesting intensity, indicating spatio-temporal heterogeneity. These findings highlight a growth-form dependent response of pollination to biomass removal, with herbaceous species benefiting most from increased canopy openness and floral abundance. In contrast, woody species exhibited limited or no response. Our study demonstrates that the ecological consequences of biomass harvesting are not uniform across plant communities and emphasizes the need to consider species traits, such as growth form, when designing sustainable forest management practices that aim to maintain pollination services and ecosystem functioning.