Woody plant encroachment and the sustainability of priority conservation areas

Woody encroachment is a global driver of grassland loss and management to counteract encroachment represents one of the most expensive conservation practices implemented in grasslands. Yet, outcomes of these practices are often unknown at large scales and this constrains practitioner’s ability to advance conservation. Here, we use new monitoring data to evaluate outcomes of grassland conservation on woody encroachment for Nebraska’s State Wildlife Action Plan, a statewide effort that targets management in Biologically Unique Landscapes (BULs) to conserve the state’s natural communities. We tracked woody cover trajectories for BULs and compared BUL trajectories with those in non-priority landscapes (non-BULs) to evaluate statewide and BUL-scale conservation outcomes more than a decade after BUL establishment. Statewide, woody cover increased by 256,653 ha (2.3%) from 2000–2017. Most BULs (71%) experienced unsustainable trends of grassland loss to woody encroachment; however, management appeared to significantly reduce BUL encroachment rates compared to non-BULs. Most BULs with early signs of encroachment lacked control strategies, while only one BUL with moderate levels of encroachment (Loess Canyons) showed evidence of a management-driven stabilization of encroachment. These results identify strategic opportunities for proactive management in grassland conservation and demonstrate how new monitoring technology can support large-scale adaptive management pursuits.