Moderate responses of early tree growth to herbivore exclusion following fire in Alaskan boreal forests

Fire is a key driver of secondary succession in northern boreal forests, influencing tree species dominance through variations in fire severity. Mammalian herbivores may modify these successional pathways by selectively browsing regenerating trees. Here, we established paired exclosure and control plots to test effects of native moose (Alces alces) and hare (Lepus americanus) on postfire tree growth at five sites in interior Alaska across a gradient of fire severity. Browsing and growth were monitored on tagged individuals of black spruce (Picea mariana), trembling aspen (Populus tremuloides), and Alaskan paper birch (Betula neoalaskana) over four years, one decade after a stand-replacing fire. Birch and aspen exhibited increased height growth inside exclosures, while spruce growth was greater outside, indicating species-specific responses linked to herbivore preferences and canopy position. Despite these differences, overall herbivore exclusion had modest effects on tree growth, suggesting that mammalian browsing is unlikely to alter post-fire canopy succession in these boreal forests. These findings enhance understanding of biotic interactions shaping forest recovery under changing fire regimes.