Monitoring disturbance intervals in forests: a case study of increasing forest disturbance in Minnesota

Key Message: We develop analytical methods and explore trends in disturbance interval via systematic forest inventory observations at a bioregional scale. Context: Our study spans the dynamic ecotone at the intersection of southern boreal forest, mixed hardwood forest, and tall-grass prairie ecosystems in Minnesota, USA. Disturbance-related tree mortality is a major driver of demographic and successional change in this bioregion. Aims: We aim to provide reliable disturbance estimates for forest ecology and economic research. Methods: We develop methods applicable to any region with systematic forest inventory observations. We assess disturbances observed by the United States Department of Agriculture-Forest Service Forest Inventory and Analysis program on permanent sample plots in Minnesota, USA. Results: A roughly 50% reduction in disturbance interval is apparent across all forest cover types and for most disturbance categories. The largest changes are for insect damage, disease, wind events, drought, and fire. Conclusion: Publicly available forest inventory data captures the frequency of disturbance events across bioregional landscapes and over time. Our methods serve to highlight rapid changes in rates of damage to standing trees within the study area.