Species-specific branching architecture influences sapling resilience to ungulate browsing pressure in temperate forests

Abstract

Abstract This study explores the role of branching patterns in determining sapling resilience to ungulate browsing, shedding light on the architectural traits that might shape regeneration dynamics in temperate forests. With ungulate populations rising and forest ecosystems increasingly impacted by browsing, understanding how architectural traits influence survival is vital for understanding how to maintain biodiversity and forest sustainability. We hypothesized that (1) browsing pressure varies significantly across tree architectural types and (2) these variations are most pronounced in the upper crown regions, critical for vertical growth. Data from over 2800 saplings growing in varied forest environments—ranging from dense canopies to open gaps—enabled us to classify six tree species into three functional groups: evergreen monopodial (EM), deciduous monopodial (DM), and deciduous sympodial (DS). Our findings reveal that trees with fewer lateral branches and lower shade tolerance, especially in the DM group, face the highest browsing impact in upper crown areas, which might severely hamper their vertical growth and prolong their vulnerability to browsing. In contrast, EM and DS groups displayed greater resilience due to the ability to develop lateral shoots, allowing them to withstand browsing while continuing to increase in height. Importantly, intense browsing pressure disproportionately affects DM species, which could limit the recruitment of ecologically important tree species into the forest canopy—especially in unmanaged stands. This limitation is likely to be exacerbated by climate change, as species such as Sycamore maple, anticipated to thrive in warming climates, may fail to establish due to increased browsing pressure. This study’s architectural approach offers a new perspective on browsing effects, challenging traditional classifications, and emphasizing the need for adaptive forest management strategies that consider tree structural traits. Our work supports more nuanced predictions of how browsing pressure influences forest dynamics, aiming to safeguard ecosystem resilience amidst rising ungulate densities and climate change.