Woody cover increases linked to forest infilling and land conversion in the eastern United States
Abstract
Woody cover increases in historically open ecosystems are occurring across the globe, leading to ecosystem degradation and increased wildfire risk. Tree and shrub cover is increasing in the eastern United States, which historically was dominated by open forest ecosystems; however, it is still unclear whether recent woody cover increases are due to infilling, linked to ecosystem degradation due to fire suppression, or to land use changes such as conversion of croplands to commercial pine plantations. Understanding the nature of recent woody cover increases is essential for identifying and addressing potential risks to ecosystem function and human activities. Using remotely sensed data, we quantified woody cover changes from 2001 to 2021 across land use types and compared the relative contribution of infilling and land-use conversion to increasing woody cover trends. We found that although overall forest cover had decreased, remaining forests became denser, especially deciduous forests. This infilling contributed the majority of increasing woody cover on the landscape. However, the conversion of non-forested land-cover types to evergreen forests was also a significant contributor to increasing woody cover on the landscape, especially in the southern half of the region. Our findings suggest that forest infilling is the greatest contributor to increasing woody cover in the eastern U.S., suggesting the continued degradation of fire-dependent open forests in the eastern U.S.