Carlton site in the Experimental Network for Assisted Migration and Establishment Silviculture (ENAMES)

Carlton site 3D map showing experimental plots color-coded by the climate scenario each seed source is adapted to. Map by Laura Gonzalez Mantecon.

Land manager: USDA Forest Service.

Location: Okanogan-Wenatchee National Forest, Methow Valley Ranger District.

Nearest town: Twisp, WA.

Species: Ponderosa pine (Pinus ponderosa.)

Site history: The site, near the Loup Loup Summit in central Washington, burned as part of the Carlton Complex Fire in the summer of 2014. The Carlton Complex burned across more than 250,000 acres and included a substantial component of high severity burned area. The planting site represented one such high severity area on the Methow Valley Ranger District of the Okanogan-Wenatchee National Forest. Prior to burning in 2014, the stand was dominated by ponderosa pine (Pinus ponderosa), with likely minor components of of Douglas-fir (Pseudotsuga menziesii), western larch (Larix occidentalis), and Engelmann spruce (Picea engelmannii).

Site characteristics: The site is at an elevation of 1100 ft and faces south-southeast, with a gentle slope of about 1 percent. The soil is very deep and well drained ashy sandy loam derived from outwash mixed with minor amounts of volcanic ash and loess. The mean annual temperature is 42 °F (coldest month: 21 °F, warmest month: 62 °F) and mean annual precipitation is 444 mm (166 mm as snow).

Planting date: Fall 2021.

Contact person:

Eireann Pederson, District Silviculturist, USDA Forest Service, Okanogan-Wenatchee National Forest - Chelan Ranger District.

Robert Slesak, Research Forester, USDA Forest Service, Pacific Northwest Research Station.

Site conditions at the Carlton site at the time of planting. Photo by Andrew Bower.

Management objectives and other considerations: Although the pre-fire stand likely contained minor components of other species, ponderosa pine was the only species targeted for this planting because it has relatively high drought tolerance and resistance to high-severity fire, perhaps favoring it for future climate conditions. Ponderosa pine is an important species for maintaining forest productivity, carbon storage and wildlife habitat east of the Cascade Range.

Site preparation: The site was salvage logged prior to planting.

Pre-planting site conditions: Given the high severity burn and salvage harvest, the site had virtually no remaining canopy and very minimal vegetation at the time of planting. Scattered shrubs, graminoids, and naturally regenerating pine seedlings were present at the site.

This site was planted as a research site to compare the performance of four ponderosa pine seed sources adapted to different source climates. Additionally, it was planted to reflect operational planting in all respects except seed source choice.

Experimental design: The experimental design in this site is a randomized complete block with four replications per treatment applied to 0.5-acre plots.

Assisted migration treatments: The team used the Seedlot Selection Tool to choose four planted seed sources (see table below.)

Seed source locations matching historical and predicted future climates for the Carlton site. Map by Laura Gonzalez Mantecon.

Silvicultural treatment/s: Shade cards were installed next to each seedling to protect them from intense afternoon sun.

Planting density: Operational contract crews planted 150 trees per acre.

Seedling stock type: 1-year-old bare root seedlings. Seed was sourced from the U.S. Forest Service Pacific Northwest Region 6 existing inventory at the Bend Seed Extractory and grown at J. Herbert Stone Nursery in Medford, OR.

Monitoring: A demonstration plot was set up for managers conducting site visits to visually compare performance of different seed sources during site visits. Detailed site measurements were collected in fall 2022, 1 year after planting. More measurements will be collected at least every 5 years well into the maturity of the stand.

A seedling with a shade card at the Carlton site right after planting. Photo by Andrew Bower.

Germination rates of the available seed from the selected seed lots were lower than expected. With fewer seedlings available, fewer acres were planted than originally planned. Depleted and aging seed inventories have been a reoccurring challenge within the Forest Service in recent years. As timber harvest levels decreased, fewer seeds were collected for reforestation. As seed required for post-fire reforestation has increased, efforts to increase seed collection capacity have begun, but still lag behind current needs.

A further challenge for this site was that, compared to operational planting without a research component, the contractors required additional oversight by the project team to ensure that the correct seedlings were allocated to each plot.

Survival 1 year after planting was high – between 80 and 90 percent – for all seed sources (Figure 1). However, first year growth was greatest for the seed source that reflected the local historical climate (Figure 2). Additional measurements are needed to understand how these trends will play out on longer time scales.

Year 3 Results

Figure 1. Seedling survival by seed source three years post-planting at the Carlton.

Figure 2. Seedling diameter by seed source three years post-planting at the Carlton.

Figure 3. Seedling growth by seed source three years post-planting at the Carlton site.