Advantages and limitations of tree mixtures in enhancing avian diversity in commercial timber plantations: Early insights from southern China

Abstract

Commercial timber plantations, particularly monocultures, have limited capacity to support biodiversity. A widely promoted approach to enhance this capacity is the diversification of monocultures into tree mixtures, by adding “secondary” timber species while retaining the production focus on the monoculture species. However, the presumed biodiversity benefits of tree mixtures are yet to be robustly tested, because current evidence predominantly comes from mixed plantations in the general sense, which are often not under active production or differ from monocultures in other important ways. To address this gap, we assess the effectiveness of earlystage tree mixtures in enhancing the avian diversity of Eucalyptus monocultures in southern China, which is the country’s most important timber production region and has been pioneering tree mixtures in large trials over the past decade. During the avian breeding and non-breeding seasons in 2021, we conducted rigorous surveys to compare the avian diversity of Eucalyptus monocultures and their tree mixtures involving slow-growing native species, against the reference baseline of mature native forests. We found that tree mixtures exhibited modest advantages over monocultures during the breeding season, and both plantation types had notable shortfalls relative to mature native forests. We additionally found that tree mixtures tended to benefit species that foraged in the medium–low strata, consumed diets of higher trophic levels, and depended more on mature forest habitat. We conclude that the biodiversity benefits of early-stage commercial tree mixtures were rather limited and more modest than typically assumed, highlighting the importance of studying tree mixtures in real-world production settings. Our study also underscores the conservation importance of protecting existing mature native forests Show more