Spatial patterns of woody plant encroachment in a temperate grassland

Abstract

Context: Woody encroachment is the process whereby grasslands transition to a woody-dominated state. This process is a global driver of grassland decline and is ultimately the outcome of increased woody plant recruitment in grasslands. Yet, little is known about how recruitment distances structure spatial patterns of encroachment. Objectives: Here, we develop a recruitment curve to describe the scatter of woody plant recruitment around seed sources and examine how this structures spatial patterns of encroachment. Methods: We developed a recruitment curve for Juniperus virginiana using an encroachment dataset that captures spread from tree plantings into treeless grassland sites in the Nebraska Sandhills (USA). In addition, we used height classes of encroaching J. virginiana as subsequent time steps of an encroachment process to examine how the leading edge of encroachment expanded over time. Results: The recruitment curve was characterized by a fat-tailed distribution. Most recruitment occurred locally, within 157 m of seed sources (95th percentile distance), while, sparse long-distance recruitment characterized the curve’s tail.