Lookout Mountain Forest Dynamics After Thinning and Fuel Reduction in Dry Forests

Project Description

More than 10 million hectares of western United States forests are classified as having moderate to high fire hazards. Such conditions are most notable at lower to mid elevations typified historically by short-interval, low- to moderate-intensity fire regimes, and characterized by the presence of ponderosa pine (Pinus ponderosa). Regional management initiatives and policies have identified the need for large-scale, strategically located restoration and fuel reduction treatments to manage these landscapes in the context of ecological processes and associated disturbance regimes. Thinning and prescribed burning to reduce environmental stresses and the risk for uncharacteristic fire or pest outbreaks are common practices on federal lands in these dry forests. Yet, the ecological consequences of these practices remains uncertain.

The Lookout Mountain study, a 1430-hectare management experiment, provides a unique venue for long-term investigation of a diverse array of silvicultural treatments that address the uncertainties and benefits associated with ecosystem responses to multiple, interacting stresses and disturbances. The experimental landscape serves as the platform for a core study of vegetation dynamics that is overlain with several complimentary studies addressing a broader array of ecosystem components and questions related to forest structure, tree vigor, bark beetles and other pests, soil ecology, microclimate, and wildlife habitat and use.

The operational, landscape scale of the study makes the findings readily transferable to management practice and policy. The treatments imposed are directly relevant to restoration practices being considered and implemented on Forest Service lands in central Oregon, and therefore the study can be used to assess and monitor the effectiveness of these practices now and into the future – providing a learning platform critically needed for effective learning and adaptation to the changing ecological and social conditions facing land managers, communities, and policymakers into the future.

Purpose and Scope

Researchers and managers of the U.S. Forest Service Pacific Northwest Research Station and the Deschutes National Forest jointly conceived the landscape management study in central Oregon to:

• Refine management options for restoring resiliency in ponderosa pine ecosystems
• Evaluate the effects of thinning and fuel reduction on long-term susceptibility to fire, insects, wind, climate change, and other forest disturbances
• Protect long-term experiments and enhance future research opportunities

Methods

The study comprises five alternative thinning and fuel reduction treatments implemented as 19 experimental units organized into five geographically delineated blocks:

1. Thin from below to the Upper Management Zone (UMZ, a density of trees that fully occupies the growing space and available light, water and nutrient resources without excessive loss of tree vigor or excessive vulnerability to fire or pests), then masticate and underburn
2. Thin from below to 75% of the UMZ, then masticate and underburn
3. Thin from below to 50% of the UMZ, then masticate and underburn
4. Regeneration cut to 75% of the UMZ with 0.1 ha gaps to begin transition to a multi-cohort stand structure, then masticate and underburn
5. Retain for near-term the current structure (untreated) Individual experimental units range in area from 20 ha to 107 ha. In total, approximately 1,190 ha are thinned, masticated and underburned with another 240 ha left as untreated reference stands. Treatments were implemented between 2011 and 2015.

A set of permanent sampling plots were established to monitor vegetation dynamics in the “core” vegetation dynamics study. Additional sampling designs have been implemented for monitoring various ecosystem responses in support of the multidisciplinary ancillary studies. Although microclimate data are collected continuously, the long-term studies over the next 30 years will be conducted through planned episodic data collections with the timing varying according to the particular ecosystem attributes being measured and the research questions being addressed.

Key Findings

Early findings from the study reveal different effects of burn intensity on soil community ecology. Soil burn intensity effects on nutrients and ectomycorrhizal communities were compared through three experimental treatments: high -intensity soil burn from large downed wood combustion (HB), low-intensity soil burn from dispersed, small surface fuels combustion (LB), and unburned reference (UB). Four months after treatment, planted ponderosa pine seedling root tips assayed for mycorrhizal fungal symbionts indicated that the combustion of large downed wood (high-intensity burn) can alter the soil environment directly beneath it. Although all burn intensities tended to result in an initial decrease in soil fungal species diversity, an ectomycorrhizal fungi community similar to low-intensity burn soils recolonized the high-intensity burn HB soils within one growing season, suggesting that quick initiation of mycorrhizal recolonization is possible depending on the size of high-intensity burn patches, proximity of low-intensity and unburned soil, and survival of nearby hosts. The importance of incorporating mixed fire effects in fuel management practices will help to provide mycorrhizal refugia for ponderosa pine forest regeneration. Spatial analysis of microclimate (soil and air temperatures) beneath the forest canopy has revealed that the amount of residual forest cover, ranging from completely open forest gaps to dense unharvested patches and an array of tree densities in between, results in surface climate conditions that are highly variable. These distinct microclimates resulting from the array of stand conditions will be monitored over time as a likely determinant of understory vegetation community development. The resultant landscape variability arising from thinning and fuels reduction treatments provides for development of complex habitat conditions and fuels loading important to understanding the effectiveness and persistence of forest restoration treatments targeting habitat and fire risk objectives.

Project Deliverables

• Restoration management options
• Characterization of mycorrhizae host compatibility
• Soil heating effects on soil communities and processes
• Microclimate surface models
• Canopy water use models
• Biomass equations for golden chinkapin
• Sapwood - leaf area equations for ponderosa pine
• Characterization of vegetation and stand structure dynamics
• Bark beetle dynamics in relation to tree vigor
• Landscape responses of northern spotted owl and its small mammal prey base