USDA Forest Service

Pacific Northwest Research Station

Pacific Northwest Research Station
1220 SW 3rd Ave.
Portland, OR 97204

(503) 808-2100

US Forest Service

Land and Ecosystem Management


Effects of reintroducing fire in east-side ponderosa pine forests

Low elevation ponderosa pine forests east of the crest of the Cascade Range in Oregon and northern California have changed substantially in the last 100 years. There is a critical need to understand ecosystem processes in these forests and the effect of management activities designed to mimic natural disturbances. The degree to which burning mimics historic fires in frequency and severity is not known, nor is the attempt by managers to manipulate stand structure always successful. A long term study in the Metolius Research Natural Area addresses stand dynamics, changes in understory vegetation, and soil properties when fire is reintroduced in old-growth ponderosa pine at different burn frequencies. (Read more)

Old-growth ponderosa pine
Old-growth ponderosa pine in Metolius Research Natural Area in central Oregon

Study goal

Dry forests throughout the West have changed substantially in the last 100 years. Much of the change is expressed as accumulated litter and dead and dying trees, increased stand densities, new species compositions, and disruption of historical insect populations. Many forest managers are prescribing a series of repeated burns to return fire to more natural frequencies and to maintain and protect old-growth structural characteristics that are important for wildlife. Yet there is little information available on the effects of repeated fires. This study will help fill that void.

Matt Busse, Research Soil Scientist, Pacific Southwest Research Station
Gregg Riegel, Area Ecologist, Deschutes National Forest

Study design
We are studying old-growth ponderosa pine (Pinus ponderosa)with understories dominated by antelope bitterbrush (Purshia tridentata) stands within the 1,436 acre Metolius Research Natural Area on the Deschutes National Forest in central Oregon. The Metolius Research Natural Area was established in 1931 to protect and exemplify old-growth ponderosa pine and shrub communities on the east slopes of the Cascade Range. This area currently exhibits symptoms of fire exclusion including reduced rates of tree growth, accumulated litter and ladder fuels, senescent shrubs, and dense regeneration of Pinus ponderosa.

Location of the burn units
Location of the burn units and study plots within the Metolius Research Natural Area in central Oregon

We are pursuing five questions: (1) How are creation and retention of snags in late-successional/old-growth forests related to periodic fire? (2) What are the horizontal and vertical structure components of trees in late-successional/old-growth forests and how are these components related to periodic fire? (3) How is understory plant species diversity in late-successional/old-growth forests affected by periodic fire? (4) What is the relation between overstory canopy cover and understory species composition, cover, and biomass production in late-successional/old-growth forest? (5) How are soil processes and characteristics in late successional/old-growth forests affected by periodic fire? Repeated burns are being applied at 0-, 5-, 10- and 20-year intervals in 12 burn units, These burn intervals were chosen to resemble a mean fire return interval of 11 years and a range of 4 to 20 years reported for this portion of the Cascade Range. Initial burns were conducted in a randomized block design beginning in the spring of 1992, 1993, and 1994, with blocking based on year of initial burn. Beginning in 1997, all burns were conducted as late-season burns. In each unit, we established a 2.47-acr square plot on which changes in overstory stand structure, spatial arrangement, tree mortality, understory species composition and productivity, and soil carbon and productivity will be characterized.

Initial findings

Age-diameter distribution Age-diameter distribution for two sets of sample trees at the Metolius Research Natural Area in central Oregon: dominant and codominant trees in the upper canopy (O) and intermediate and overtopped trees in the lower canopy (▲)
  1. Mean density of live ponderosa pine in the upper canopy was 22 trees per acre (range 14 to 38 trees per acre); mean density of dead trees (snags) was 4 snags per acre. These densities are nearly identical to old-growth ponderosa pine stands at Pringle Falls Experimental Forest south of Bend, Oregon and Blacks Mountain Experimental Forest in northern California.
  2. Mean diameter of live upper canopy ponderosa pine was 23.8 in (range 4.7 to 52.4 in), mean diameter of dead trees (snags) was 24.0 in (range 14.3 to 43.6 in).
  3. Total ages of 215 trees as computed. These trees ranged from 37 to 618 years in age. Individual plots were highly heterogeneous with respect to age, and contained as many as 16 age classes. .
  4. While studies of some western conifer forests have shown a tendency for the spatial point pattern of tree stems to move toward uniformity with increasing age, our ponderosa pine stands exhibit a high degree of spatial heterogeneity, with clustering of all stems within the a plots at distances > 9.2 ft.
  5. A total of 170 logs at Metolius Research natural Area are measured; mean density was 16.4 logs per acre, the mean large end was 15.3 in, and mean length was 13.1 ft. The majority of these logs were classified as decomposition class 5, characterized by the absence of bark and twigs, soft, blocky pieces of wood that have faded to light yellow or gray, overall log shape round to oval, and the log resting fully on the ground. This suggested that most of the logs have been in place for a considerable time.
  6. Nearly 100 percent of the preexisting antelope bitterbrush (Purshia tridentate)Spatial point pattern
    Spatial point pattern of large live (●) and dead (o) trees in the upper canopy
    of old-growth plot 32 at the Metolius Research Natural Area in central Oregon.
    cover was consumed during the initial spring burns. Although fire patterns produced a mosaic of understory mortality, shrub and herbaceous cover was significantly reduced. Cover of antelope bitterbrush increased the first and second years and then declined in the third and fourth years from sprout and seedling mortality. By the fifth year, cover had increased to nearly four times that of the first year. Continued monitoring of antelope bitterbrush seedling recruitment and sprout mortality will aid in developing models of shrub dynamics for wildlife biologists and fire managers.

Additional reading

Youngblood, A.; Riegel, G. 1999. Reintroducing fire in eastside ponderosa pine forests: a long-term test of silvicultural practices. In: Proceedings of the Society of American Foresters 1999 national convention. Bethesda, MD: Society of American Foresters: 291-298.

Youngblood, A.; Riegel, G. 2000. Reintroducing fire in eastside ponderosa pine forests: a long-term test of fuel treatments. In: Neuenschwander, L.F.; Ryan, K.C., tech. eds. Proceedings of the Joint Fire Science conference and workshop: crossing the millennium: integrating spatial technologies and ecological principles for a new age in fire management. Moscow, ID: The University of Idaho and the International Association of Wildland Fire: 142-150 Vol II.

Youngblood, A. 2001. Old-growth forest structure in eastern Oregon and Washington. Northwest Science. 75: 110-118.

second burn The second burn of a 10-year return treatment (2002) in the Metolius Research Natural Area in central Oregon.

Youngblood, A.; Max, T.; Coe, K. 2004. Stand structure in eastside old-growth ponderosa pine forests of Oregon and northern California. Forest Ecology and Management 199: 191-217.

Spies, T.A.; Hemstrom, M.A.; Youngblood, A.; Hummel, S. 2006. Conserving old-growth forest diversity in disturbance-prone landscapes. Conservation Biology. 20: 351-362.

Table 1—Timing of burn treatments by unit at the Metolius Research Natural Area in central Oregon



Size (ha)


Treatment years









1992, 2002, 2012




1992, 2012




1992, 1997, 2002, 2007, 2012









1993, 2013




1993, 2003, 2013




1993, 1998, 2003, 2008, 2013





1994, 2014




1994, 1999, 2004, 2009, 2014




1994, 2004, 2014






Andrew Youngblood
PNW Research Station
LaGrande Forestry Sciences Lab
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US Forest Service - Pacific Northwest Research Station
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