Ecological Restoration of Southwestern Ponderosa Pine Ecosystems: A Broad Perspective

Abstract

The purpose of this paper is to promote a broad and flexible perspective on ecological restoration of Southwestern (U.S.) ponderosa pine forests. Ponderosa pine forests in the region have been radically altered by Euro‐American land uses, including livestock grazing, fire suppression, and logging. Dense thickets of young trees now abound, old‐growth and biodiversity have declined, and human and ecological communities are increasingly vulnerable to destructive crown fires. A consensus has emerged that it is urgent to restore more natural conditions to these forests. Efforts to restore Southwestern forests will require extensive projects employing varying combinations of young‐tree thinning and reintroduction of low‐intensity fires. Treatments must be flexible enough to recognize and accommodate: high levels of natural heterogeneity; dynamic ecosystems; wildlife and other biodiversity considerations; scientific uncertainty; and the challenges of on‐the‐ground implementation. Ecological restoration should reset ecosystem trends toward an envelope of “natural variability,” including the reestablishment of natural processes. Reconstructed historic reference conditions are best used as general guides rather than rigid restoration prescriptions. In the long term, the best way to align forest conditions to track ongoing climate changes is to restore fire, which naturally correlates with current climate. Some stands need substantial structural manipulation (thinning) before fire can safely be reintroduced. In other areas, such as large wilderness and roadless areas, fire alone may suffice as the main tool of ecological restoration, recreating the natural interaction of structure and process. Impatience, overreaction to crown fire risks, extractive economics, or hubris could lead to widespread application of highly intrusive treatments that may further damage forest ecosystems. Investments in research and monitoring of restoration treatments are essential to refine restoration methods. We support the development and implementation of a diverse range of scientifically viable restoration approaches in these forests, suggest principles for ecologically sound restoration that immediately reduce crown fire risk and incrementally return natural variability and resilience to Southwestern forests, and present ecological perspectives on several forest restoration approaches.

Can Land Management Buffer Impacts of Climate Changes and Altered Fire Regimes on Ecosystems of the Southwestern United States?

“…A hundred-plus years of livestock grazing, logging, and fire exclusion have altered pre-European era fire frequencies, creating increased surface fuel loads, dense, fuel-rich forests, and reduced structural and spatial heterogeneity of vegetation, especially in dry conifer forests with frequent-fire regimes (typically, those with fire return intervals <35 years) [16][17][18]. Fires in these forests are likely to be more intense with larger patches of high-severity fire than occurred historically [19][20][21][22][23], reducing biodiversity, ecological function, and resilience [12,17].…”

“…A hundred-plus years of livestock grazing, logging, and fire exclusion have altered pre-European era fire frequencies, creating increased surface fuel loads, dense, fuel-rich forests, and reduced structural and spatial heterogeneity of vegetation, especially in dry conifer forests with frequent-fire regimes (typically, those with fire return intervals <35 years) [16][17][18]. Fires in these forests are likely to be more intense with larger patches of high-severity fire than occurred historically [19][20][21][22][23], reducing biodiversity, ecological function, and resilience [12,17]. Observed 20th and 21st century anthropogenic climate changes of warming temperatures and an earlier onset of snowmelt have increased the length of fire seasons and lowered fuel moistures, making large portions of the landscape flammable for longer periods of time [21,24], and widespread, regional fire years have been associated with prolonged droughts [13,25,26].…”

Ponderosa Pine Forest Restoration Treatment Longevity: Implications of Regeneration on Fire Hazard

“…The ecological consequences of wildfires within ponderosa pine (Pinus ponderosa P. and C. Lawson) and dry-mixed conifer forests of the Rocky Mountains have arguably been exacerbated by what is thought to be uncharacteristically high uniformity and continuity of forest vegetation [5]. The high continuity of forest vegetation currently seen across the landscape is attributed to a combination of early 1900s livestock grazing and timber management practices and a century of fire exclusion causing changes in forest structure from spatially heterogeneous pre-Euro-American settlement conditions [6][7][8].…”

Overstory Structure and Surface Cover Dynamics in the Decade Following the Hayman Fire, Colorado

“…Restoration treatments in these forests primarily aim to increase their resilience to future burning (sensu [56]) by creating open and heterogeneous overstory conditions that are unlikely to carry large-scale high-severity crown fire [34,57,58]. Restoration objectives for a given area are usually informed by the range of conditions that occurred there historically (i.e., the historical range of variability (HRV)), as they represent the fire-resilient conditions that existed prior to post-settlement land-use practices like fire suppression, logging, and grazing [34,57,58]. Regarding live overstory structure, Battaglia et al [7] estimated that historical density in dry conifer forests of the Front Range ranged from about 62 to 214 stems ha −1 and that historical basal area ranged from about 5 to 11 m 2 ha −1 .…”