Restoration of degraded transitional (pinon-juniper) woodland sites improves ecohydrologic condition and primes understory resilience to subsequent disturbance

An overstory thinning and slash mulch treatment designed to improve ecohydrologic condition of degraded transitional (pinon-juniper) woodland sites was evaluated at four sites over a cumulative 16-year period beginning in 1994. Study sites were located within Bandelier National Monument and Santa Fe National Forest on the east-facing Pajarito Plateau of the Jemez Mountains in North-Central New Mexico. Across all sites, total understory cover increased several-fold at 3 to 5years post-treatment relative to both pre-treatment condition and control, whereas measures of runoff and sediment production were reduced by an order of magnitude. During the course of post-treatment monitoring, several coincident disturbances (multi-year drought beginning in fall 1999, wildfire in spring 2000 and pinon ips beetle outbreak in 2002) caused widespread vegetation mortality and allowed differential recovery patterns to be documented across treatment and control areas. Response to these unplanned disturbances suggested prior restoration to improve ecohydrologic function of denuded intercanopy locations also primed understory resilience as measured by the relative capacity of restored areas to regain levels of effective cover. Treatment areas affected by drought-beetle tree mortality exceeded pre-drought levels of understory cover within two growing seasons while retaining improved hydrologic function; by contrast, control areas continued to exhibit accelerated runoff and erosion despite temporary improvements in understory cover post-disturbance. Post-fire outcomes suggest that prior restoration also enhanced levels of understory cover post-burn relative to control, despite negative-soil-heating effects from consumed slash. Copyright (c) 2014 John Wiley & Sons, Ltd.