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 Eastside Ponderosa Pine Forests

Ponderosa PineOld-growth ponderosa pine in the Metolius Research Natural Area in central Oregon Effects of reintroducing fire in eastside ponderosa pine forests.

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 historic 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.


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

Research description:
  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?
Burn Unit LocationsLocation of the burn units and study plots within the Metolius Research Natural Area in central Oregon.

Study design: We are studying old-growth ponderosa pine (Pinus ponderosa)with understories dominated by antelope bitterbrush (Purshia tridentata) stands within the 581-hectare (1,436 acre) Metolius Research Natural Area on the Deschutes National Forest in central Oregon. 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 ponderosa pine. 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 1-hectare (2.47 acre) 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.


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









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





Initial findings:

    Age DiameterAge-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 and intermediate and overtopped trees in the lower canopy.


    Natural AreaSpatial point pattern of large live and dead trees in the upper canopy of old-growth plot 32 at the Metolius Research Natural Area in central Oregon.


    Ponderosa PineThe second burn of a 10-year return treatment (2002) in the Metolius Research Natural Area in central Oregon.
  1. Mean density of live ponderosa pine in the upper canopy was 54 trees ha-1 with range 34 to 94 trees ha-1 (22 trees per acre, range 14 to 38 trees per acre); mean density of dead trees (snags) was 10 trees ha-1 (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 60.5 cm with range 12.0 to 133.1 cm (mean 23.8 in, range 4.7 to 52.4 in), mean diameter of dead trees (snags) was 60.9 cm with range 36.4 to 110.8 cm (mean 24.0 in, range 14.3 to 43.6 in).
  3. Total ages of 215 trees were computed. These trees ranged from 37 to 618 years in age. Individual 1-ha 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 towards uniformity with increasing age, our ponderosa pine stands exhibit a high degree of spatial heterogeneity, with clustering of all stems within the 1-ha plots at distances > 2.8 m (9.2 ft). Clumps of large live and dead upper canopy trees were about 22.5 m (73.8 ft) in diameter. In addition, bivariate Ripley’s K (d) analysis between different tree strata indicated, in general, repulsion between large live and small live or small dead stems, but independence between large dead and small live stems and attraction between large dead and small dead stems.
  5. A total of 170 logs at Metolius Research Natural Area as measured; mean density was 40.5 logs ha-1 (16.4 logs per acre), the mean large end was 38.9 cm (15.3 in), and mean length was 4.0 m (13.1 ft). The majority of these logs as 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) 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.
  7. Fire decreased the cover of some mid- and late-seral fire sensitive plant species such asIdaho fescue (Festuca idahoensis), western fescue (F. occidentalis), and grand collomia (Collomia grandiflora). Cover of early-seral and fire-adapted species such as squirreltail (Elymus elymoides) and western brackenfern (Pteridium aquilinum) increased in burned units four to five times that of the controls. Bastard toadflax (Comandra umbellata),alternate host of the Comandra blister rust, also increased after the burns.

Published products:

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 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

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

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.







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