University Northern Arizona, USFS Southwestern Region
Richard T. Reynolds
Many forests in the southwestern U.S. are adapted to frequent, low-intensity fires. These forests are currently experiencing uncharacteristicly severe wildfire, insect, and disease episodes resulting in altered plant and animal demographics, reduced productivity and biodiversity, and impaired ecosystem functions. These disturbances are predicted to increase as future climates in the Southwest become warmer and dryer. This research aimed to develop a restoration framework for frequent-fire forests based on restoring the historical composition, structure, and spatial patterns of vegetation. Implementing the restoration framework is expected to improve the resiliency of frequent-fire forests by allowing natural ecosystem processes such as low-intenisty fire to resume. Restoring key elements may position frequent-fire forests throughout the western U.S. to better resist, respond, and adapt to future climates and disturbances.
Ponderosa pine and dry mixed-conifer forests in the Southwest United States are experiencing, or have become increasingly susceptible to large-scale severe wildfire, insect, and disease episodes resulting in altered plant and animal demographics, reduced productivity and biodiversity, and impaired ecosystem processes and functions. We present a management framework based on a synthesis of science on forest ecology and management, reference conditions, and lessons learned during implementations of our restoration framework. The framework focuses on the restoration of key elements similar to the historical composition and structure of vegetation in these forests: (1) species composition; (2) groups of trees; (3) scattered individual trees; (4) grass-forb-shrub interspaces; (5) snags, logs, and woody debris; and (6) variation in the arrangements of these elements in space and time. Our framework informs management strategies that can improve the resiliency of frequent-fire forests and facilitate the resumption of characteristic ecosystem processes and functions by restoring the composition, structure, and spatial patterns of vegetation. Restoration of key compositional and structural elements on a per-site basis will restore resiliency of frequent-fire forests in the Southwest, thereby position them to better adapt to future disturbances and climates.
Numerous implementations of the framework have been completed in the past 20 years in New Mexico and Arizona. Currently, the framework's key elements are being evaluated via LiDAR regarding their effects on biodiversity, food webs, and the long-term demographic performance of an apex predator (northern goshawk) on the Kaibab Plateau.
One implementation, Eager South on the Apache-Sitgreaves National Forest, was hit by the 2011 Wallow Fire. The Eagar South WUI Fuel Reduction Project environmental assessment was finalized in 2006. The project area was chosen to be used as a demonstration to provide the framework for understanding historical conditions, ecological processes, and the natural range of forest conditions. These concepts form the basis for ecological strategies in restoring the integrity of ponderosa pine ecosystems within and outside the wildland-urban interface. A collaborative approach was used to develop thinning prescriptions that had no diameter cap and created leave tree groups (RMRS-GTR-217, RMRS-GTR-310). Tree groups were based on current conditions and not on a forestry standard spacing between individual trees, but between the collective group of trees. This approach created or maintained uneven-aged forest conditions (groups of trees each composed of different ages), valuable wildlife habitat, and met fuel reduction objectives.
The Eagar south landscape is variable with the elevation on the south end at 8,600’ dropping to the north to 7,100’. The vegetation is primarily ponderosa pine with mixed conifer on the north aspects and drainages and piñon/juniper woodland at the lower elevations.
On June 7th the 2011 Wallow Fire made a push from the southwest into the Eagar South WUI first burning an untreated mixed conifer slope. The running crown fire hit the treatment full force, the blast of hot air caused mortality at the edge and into the treated area for a distance of up to 300’. However, the crown fire did not penetrate the treatment area. The subsequent ground fire that followed in the treatment area had variable flame lengths with moderate intensity. The fire spread was greatly reduced by the treatment area and the fire was stalled for several hours as it slowly progressed down slope (before and after treatment aerial photos, and before and after Wallow Fire photos are available).
This synthesis integrates recent research concerning socioecological resilience in the Sierra Nevada, southern Cascade Range, and Modoc Plateau. Among the focal topics are forest and fire ecology; soils; aquatic ecosystems; forest carnivores; air quality; and the social, economic, and cultural components of socioecological systems. A central theme is the importance of restoring key ecological processes to mitigate impacts of widespread stressors, including changes in climate, fire deficit and fuel accumulations, air pollution, and pathogens and invasive species.
Water stress represents a common mechanism for many of the primary disturbances affecting forests, and forest management needs to explicitly address the very large physiological demands that vegetation has for water. This study demonstrates how state-of-science ecohydrologic models can be used to explore how different management strategies might improve forest health.
Widespread threats to forests due to drought stress prompt re-thinking of priorities for water management on forest lands. In contrast to the widely held view that forest management should emphasize providing water for downstream uses, we argue that maintaining forest health in the face of environmental change may require focusing on the forests themselves and strategies to reduce their vulnerability to increasing water stress in the context of a changing climate. Management strategies would need to be tailored to specific landscapes but could include: a) thinning; 2) encouraging drought-tolerant species; 3) irrigation; and 4) strategies that make more water available to plants for transpiration. Hydrologic modeling reveals that specific management actions could reduce tree mortality due to drought stress. Adopting water conservation for vegetation as a priority for managing water on forest lands would represent a fundamental change in perspective and potentially involve tradeoffs with other downstream uses of water.
The Water Erosion Prediction Project (WEPP), is a physically-based soil erosion prediction technology. WEPP has a number of customized interfaces developed for common applications such as roads, managed forests, forests following wildfire, and rangelands. It also has a large database of cropland soils and vegetation scenarios. The WEPP model is a distributed parameter, continuous simulation model, and is able to describe a given erosion concern in great detail for an experienced user.
The WEPP model consists of multiple applications that can estimate erosion and sediment processes on hillslopes and small watersheds, taking into account climate, land use, site disturbances, vegetation, and soil properties.