COS 56-3 - Evaluating drivers of revegetation following agricultural disturbance

Abstract: Agricultural lands continue to be abandoned globally due to a variety of environmental and social factors such as reduced water availability and rural to urban migration. Recent studies have characterized patterns of revegetation on abandoned agricultural land, finding that secondary vegetation can recover the structure and composition of nearby undisturbed ecosystems over several decades. However, some abandoned fields have low vegetation cover for decades after agricultural disturbance ceases. We still lack an understanding of when and where vegetation succession on abandoned fields tends toward ecosystems resembling their pre-agricultural conditions or degraded alternative vegetated states. Here we use the rich empirical opportunity of sugarcane fields in Hawaiʻi that were abandoned between 4 and 117 years ago to study the effects of environmental conditions on unassisted vegetation succession. We leverage fixed and random effects models to assess how environmental variables influence the structure and composition of recovering vegetation. The relevance of environmental drivers varies with the structure of secondary vegetation. For example, preliminary results indicate that the recovery of shrubs was primarily driven by precipitation, soil pH, and soil cation exchange capacity; the recoveries of trees and grasses were affected by those same environmental conditions as well as elevation, slope, and the age of the volcanic substrate. Both native and invasive vegetation cover increased with more basic soil pH. While increased age of volcanic substrates hindered native vegetation growth, it enhanced invasive vegetation cover. This ongoing research effort seeks to distill relationships between environmental conditions and vegetation outcomes to guide future management of abandoned fields globally for a variety of goals such as conservation of biodiversity or carbon storage.