Long-term monitoring of aspen forest regeneration and ungulate use shows successful recruitment amid landscape-scale forest restoration

Human-induced changes in forest disturbance patterns have altered the successional patterns of aspen-conifer forests. These changes can lead to failure in aspen forest recruitment due to altered disturbance and ungulate herbivory regimes. Our objective was to characterize the temporal trends of aspen regeneration, recruitment, and ungulate browsing in stable aspen stands and to evaluate the impact of ungulate browsing on aspen, within the context of a large-scale aspen restoration program. From 2015–2022, mountain-wide restoration through prescribed burns and mechanical thinning of late-successional aspen-conifer stands treated 14,400 ha of the 28,700 ha of forest. During these broader restoration efforts, we monitored aspen stands and herbivory pressure at 60 nearby untreated sites. During the initial five-year survey period, chronically high levels of ungulate herbivory resulted in aspen recruitment failure. However, by 2023, native ungulate fecal counts had decreased by 66 % for elk and 50 % for deer, and ungulate meristem removal had dropped by more than 50 %. Aspen regeneration height and recruitment density increased by 20 cm and 88 %, reaching restoration targets. Secondly, we showed that topographic features and weather patterns mediated restoration success. Aspen increased at sites with greater snowpack and summer precipitation. Recruitment was more prevalent in southern locations, where elk fecal counts were lowest. Our findings suggest that ungulate herbivory can suppress aspen recruitment success and that weather, topography, and disturbance can mediate regeneration success. However, landscape-scale restoration through prescribed disturbance likely promoted aspen regeneration indirectly by reducing ungulate herbivory in untreated stands. • Forest restoration efforts can indirectly promote aspen regeneration in untreated stands. • Our long-term monitoring revealed that restoration indirectly reduced ungulate browsing. • Stable aspen stands saw dramatic declines in browsing and increases in recruitment. • These improvements were further influenced by local topography and weather patterns. • Long-term and large-scale monitoring is crucial for measuring restoration success.