Vegetation type conversion in the US Southwest: frontline observations and management responses

Abstract

Background Forest and nonforest ecosystems of the western United States are experiencing major transformations in response to land-use change, climate warming, and their interactive effects with wildland fire. Some ecosystems are transitioning to persistent alternative types, hereafter called “vegetation type conversion” (VTC). VTC is one of the most pressing management issues in the southwestern US, yet current strategies to intervene and address change often use trial-and-error approaches devised after the fact. To better understand how to manage VTC, we gathered managers, scientists, and practitioners from across the southwestern US to collect their experiences with VTC challenges, management responses, and outcomes. Results Participants in two workshops provided 11 descriptive case studies and 61 examples of VTC from their own field observations. These experiences demonstrate the extent and complexity of ecological reorganization across the region. High-severity fire was the predominant driver of VTC in semi-arid coniferous forests. By a large margin, these forests converted to shrubland, with fewer conversions to native or non-native herbaceous communities. Chaparral and sagebrush areas nearly always converted to non-native grasses through interactions among land use, climate, and fire. Management interventions in VTC areas most often attempted to reverse changes, although we found that these efforts cover only a small portion of high-severity burn areas undergoing VTC. Some areas incurred long (>10 years) observational periods prior to initiating interventions. Efforts to facilitate VTC were rare, but could cover large spatial areas. Conclusions Our findings underscore that type conversion is a common outcome of high-severity wildland fire in the southwestern US. Ecosystem managers are frontline observers of these far-reaching and potentially persistent changes, making their experiences valuable in further developing intervention strategies and research agendas. As its drivers increase with climate change, VTC appears increasingly likely in many ecological contexts and may require management paradigms to transition as well. Approaches to VTC potentially include developing new models of desired conditions, the use of experimentation by managers, and broader implementation of adaptive management strategies. Continuing to support and develop science-manager partnerships and peer learning groups will help to shape our response to ongoing rapid ecological transformations.

Restoring bigcone Douglas-fir post-fire in drought-stricken Southern California: Assessing the effects of site choice and outplanting strategies

“…Importantly, the low survival in this study is higher than other known restoration efforts of the same species. Other studies have shown total die-off in censused seedlings (Guiterman et al, 2022) and personal communications with Forest Service employees reiterate these challenges. Literature describing dryland forest restoration is sparse, and we found low rates of survival (even below 10%) are not uncommon in studies with little to no seedling management post-planting (Höhl et al, 2020;Holl and Brancalion, 2020).…”

Where can managers effectively resist climate‐driven ecological transformation in pinyon–juniper woodlands of the US Southwest?

“…Meanwhile, a sizeable proportion of sites are classified as having vulnerable populations in worst-case scenarios. Managers could use a "wait and see" approach (Guiterman et al, 2022) or intentionally accept transformation here, supported by knowledge about plausible future ecological scenarios (Crausbay et al, 2022,). Alternatively, managers could direct ecological trajectories to more preferred conditions.…”

Evaluación post-incendio de un bosque mixto de Pinus-Quercus en Zaragoza, Nuevo León

“…En otro orden de ideas, las arbustivas se regeneraron rápidamente formando parches densos con gran diversidad, esto coincide con lo que encontraron ), Hammond et al (2019 quienes mencionan que el sotobosque no se vio afectado por el fuego, de lo contrario contribuyó en una mayor diversidad. Por su parte, Guiterman et al (2022) encontraron que los bosques de coníferas, generalmente se convierten en matorrales después de la alteración del régimen de incendio (principalmente la frecuencia y severidad). Aunque no se tienen antecedentes del régimen del fuego en el área de estudio, sucedió lo que mencionan estos autores.…”

“…Algunos estudios realizados en bosques templados de coníferas han constatado que el éxito de la regeneración está estrechamente influenciado por la distancia a la fuente de semillas, la elevación, la exposición, la pendiente, la competencia con especies rebrotadoras y el clima (Stevens y Morgan, 2019;Singleton et al, 2021). Además, los bosques de coníferas, generalmente se convierten en matorrales, después de la alteración de los regímenes de incendios (Guiterman et al, 2022). De esta manera, favoreciendo o restringiendo la dominancia de ciertas especies (Sáenz y Pérez, 2019).…”