Decomposer functional breadth maintains litter decomposition patterns three decades after Eastern Hemlock decline

Soil microbial communities, key drivers of decomposition and carbon cycling, can retain historical legacies whereby past environmental conditions, such as litter inputs or climate, shape contemporary function. The decline of eastern hemlock (Tsuga canadensis) due to the invasive hemlock woolly adelgid (HWA) is shifting North American forests toward birch-dominated stands, potentially imprinting a functional legacy on soil carbon cycling. However, due to the gradual nature of hemlock decline, it remains unclear whether this legacy persists over time, and if so, for how long. To test for an HWA-induced legacy effect, we measured litter decomposition and soil carbon and nitrogen pools across a chronosequence of six sites within the CT River valley (Connecticut and Massachusetts, USA). The sites span the northward spread of HWA ranging from 1987 infection in Southern Connecticut to 2020 infection in northern Massachusetts. We found no significant differences in litter mass loss across sites or litter types, suggesting that the functional breadth of soil microbial communities in hemlock forests persists even after hemlock mortality. Latitude was a strong predictor of soil labile carbon and nitrogen cycling, with higher values observed at lower latitudes where tree species richness was also greater. These findings indicate that legacy hemlock soils maintain microbial functional breadth for at least three decades following HWA invasion, sustaining decomposition and nutrient cycling during stand transition. Our results highlight the role of fine-scale microbially driven processes in mediating forest ecosystem responses to invasive pests, and suggests that microbial functional legacies may buffer ecosystem shifts following tree mortality.