2011 Assessing WBP Successional Dynamics & Regeneration Following Disturbance

Project: Assessing Whitebark Pine Successional Dynamics and Regeneration Following Disturbance by Blister Rust, Bark Beetles and Wildfire in the Eastern Cascade Mountains: Implications for Restoration

Center stake of one of the study plots

Center stake of one of the study plots

Agency/Forest or Park/District: Wenatchee‐Okanogan National Forest

Project coordinator: Dr. Cara Nelson

Contact:  Dr. Cara R. Nelson, Associate Professor of Restoration Ecology, College of Forestry and Conservation, University of Montana, 32 Campus Drive, Missoula, Montana 59812. Phone: 406‐243‐6066.  Email: cara.nelson@umontana.edu.

Collaborative effort between University of Montana, the Okanogan‐Wenatchee National Forest and the Missoula Fire Sciences Lab.

  • Jeremy Amberson: UM graduate student assigned to develop and lead project.
  • Dr. Robert E. Keane, Research Ecologist, USDA Forest Service Rocky Mountain Research Station, Fire Sciences Laboratory, Missoula, MT: served as a research advisor and was on the student’s Graduate Advising Committee.
  • Dr. Richy Harrod, Deputy Fire Management Officer, Okanogan‐Wenatchee National Forest, Wenatchee, WA: provided logistical support and access to sites.

Source of funding /amount

FHP: $15000

UM: In kind donation of sampling equipment and waived indirect costs ($6299).

Dates of restoration efforts

No treatments were implemented under this agreement.


The response of whitebark pine plant communities to changing climate and mortality agents such as wildfire, mountain pine beetle, and white pine blister rust are not well understood. Understanding the mechanisms that drive whitebark pine recruitment and growth, including environmental limitations, is critical for managing this species. We assessed successional development, interspecific plant interactions, and environmental limitations to natural recruitment by re‐sampling 19 whitebark pine stands in the Wenatchee‐Okanogan National Forest that that were originally sampled in the 1990s and 2000s as part of the USFS Region 6 Current Vegetation Survey (CVS) Program. Dynamics of whitebark pine stands have been understudied in general, but particularly so in the Eastern Cascades of Washington State. Taking advantage of a long‐term ecological dataset in this region, we asked questions about patterns of succession and tree recruitment over the last 25 years and in the face of climate change, wildfire, and beetle outbreaks. Specific research questions included:

1) Has tree community composition changed within whitebark pine stands over the last 20-25 years? If so, are changes related to mountain pine beetle, white pine blister rust, or wildfire incidence?Megan Keville recording data at one of the study CVS plots

2) Has basal area (m2 ha-1) of mature trees, poles, or saplings, or density (#/ha) of large seedlings changed over the last 20-25 years for common tree species (whitebark pine, subalpine fir, and Engelmann spruce)? If so, are changes related to mountain pine beetle, white pine blister rust or wildfire incidence?

3) Is current seedling density related to mountain pine beetle, white pine blister rust, or to other variables such as stand basal area?

4) Is current whitebark pine seedling density related to basal area of cone-producing whitebark pine trees?

5) Is seedling density higher than would be expected in particular microsite types (rocks, stumps, logs, herbs or shrubs, or beneath tree canopies) given the prevalence of that microsite type?

Acres/ha treated

No area was treated.  We sampled 19 untreated stands, with different disturbance histories.


This study was conducted on Current Vegetation Survey (CVS) research plots established by the USDA Forest Service on the Okanogan-Wenatchee National Forest in the early 1990s for the purpose of characterizing vegetation and assisting with landscape-level planning and monitoring. All CVS plots were established from a random point within the Forest and placed systematically across the landscape on a 2.74-km grid. Following the first re-measurement of these plots, the CVS program was subsumed by the USFS Forest Inventory and Analysis program.

All CVS plots used for this study were located outside of designated wilderness areas to reduce travel time and maximize the number of plots sampled. Study sites were located along the eastern crest of the Cascade Mountain Range in Washington State on a ca. 200-km. north-south transect between 47°01’06”N and 48°48’09”N. Sites were located in a variety of environmental and ecological conditions, from mesic closed-canopy stands to relatively open xeric stands where whitebark pine is the climax species. CVS plots chosen for this study were sampled once during 1991 – 1998 (hereafter, “Cycle I”) and again during 2001 – 2007 (hereafter, “Cycle II) by USFS personnel.

In 2012 (hereafter, “Cycle III”), we re-measured all CVS plots located on the Forest where: 1) whitebark pine was the dominant or co-dominant tree species at the time of establishment, 2) the site was sampled during both previous sample cycles, and 3) the site was located outside of designated wilderness areas. A total of 19 plots on the Forest met these criteria. Within each plot, all trees ≥ 2.54-cm DBH were re-measured according to size-classes as defined in original CVS protocol (Johnson 1995). Additional data on whitebark pine trees, seedlings, and microsites were collected according to protocol developed for this study (see Jeremy Amberson’s Masters Thesis, University of Montana, College of Forestry and Conservation; Spring 2014).

Planting? If so, source of seedlings? Resistance?  No


Study Results — We found that tree community composition changed significantly during the study period, primarily due to a significant decline in mature (≥20-cm DBH) whitebark pine. Despite loss of mature whitebark pine, we did not find evidence of successional replacement by other tree species. We also did not find a correlation between whitebark seedling density and basal area of mature whitebark pine. Seedling density was negatively correlated with wildfire and was positively correlated with herb and shrub cover. These observed regeneration dynamics appear to contradict the conventional view that seedling establishment is contingent on local seed production and microsites free of competing vegetation. Additional, long-term studies are needed to quantify the effects of novel disturbances on successional trajectories in whitebark pine ecosystems.

Products — Results of this study are summarized in Jeremy Amberson’s Masters Thesis, Effects of Disturbance on Tree Community Dynamics in Whitebark Pine Ecosystems (Submitted Spring 2014, University of Montana, College of Forestry and Conservation). A manuscript is in preparation for Canadian Journal of Forest Research (target submission date:  March 2014). Dr. Nelson and Mr. Amberson will also present results to managers on the Okanogan Wenatchee National Forest and at an upcoming Whitebark Pine Ecosystem Foundation Conference.

Monitoring since completion of the project                                        

This project did not involve treatment implementation.

Will outcome meet goals?

We successfully achieved all project goals.

Future actions/follow up?

These sites represent a long-term ecological database for whitebark pine.  We are interested in sampling all 19 sites again in 5-10 years.