ponderosa pine forest

File:Pinus ponderosa range map 2.gif

Ponderosa pine forest is the largest western forest type in the United States. Ponderosa pine is the principal species on over {{convert|110000|km2|acre|abbr=on}} and is present on an additional {{convert|55000|km2|acre|abbr=on}}. Within the western United States, California alone contains the greatest concentrations of ponderosa pine ({{convert|20700|km2|acres|abbr=on|disp=or}}) closely followed by Oregon with {{convert|19000|km2|acres|abbr=on}} and, when combined, Arizona and New Mexico contain an additional {{convert|25000|km2|acres|abbr=on}} of ponderosa pine.{{cite conference|last1=Van Hooser|first1=Dwane|last2=Keegan|first2=Charles E III|year=1988|title=Distributions and volumes of ponderosa pine forests|editor1-last=Baumgartner|editor1-first=DM|editor2-last=Lotan|editor2-first=JE|conference=Proceedings of the symposium on ponderosa pine: the species and its management|location=Pullman, WA|publisher=Washington State University|pages=1–6}}{{USDA|source={{cite conference|url=https://www.fs.usda.gov/psw/publications/documents/psw_gtr198/|title=Ponderosa Pine Ecosystems|first1=Russell T|last1=Graham|first2=Theresa B|last2=Jain|publisher=US Forest Service|conference=Proceedings of the Symposium on Ponderosa Pine: Issues, Trends, and Management|id=USDA Forest Service Gen. Tech. Rep. PSW-GTR-198|year=2005}}}}{{rp|2}}

Since ponderosa pine has a rather wide range of adaptability and can dominate some of the less mesic true forest sites, it occupies low mountains and foothills in many places; yet in mixtures with other species, it is found at moderate elevations.

Local topography can be gentle, as on plateau tops and low mountains, or it can be steep, as on canyon walls and faces. Semiarid, low mountain sites are common, but it is difficult to characterize the physiography of the ecosystem because it varies greatly.{{USDA|source={{cite web|url=https://www.fs.fed.us/psw/publications/documents/misc/ah475.pdf|archive-url=https://web.archive.org/web/20170606152704/https://www.fs.fed.us/psw/publications/documents/misc/ah475.pdf|archive-date=2017-06-06|url-status=dead|last1=Garrison|first1=George A|display-authors=et al|year=1977|title=Vegetation and environmental features of forest and range ecosystems|publisher=US Forest Service|id=Agriculture Handbook No. 475|location=Washington D.C.|pages=21–22}}}}

Ponderosa pine forest occurs when the average mean temperature is between {{convert|42|and|50|F|C}} and the July/August mean temperature is {{convert|62|to|70|F|C}}.

The length of the frost-free season at any location in the ecosystem depends largely upon the latitude and elevation. In general, in much of the northern area the frost-free period is 120 days, whereas in many foothill areas and in parts of the Sierra Nevada and the Gila Wilderness in Arizona, it can be 240 days. Annual precipitation is about {{convert|15|to|20|in|mm}} in the more pure pine areas, but where there are combinations of pine and other conifers at moderate elevations, the precipitation can total {{convert|30|in|mm}}. In the far western sector, only 25 percent of this moisture falls in the warmest months. In the Northern Rocky Mountains, 40-50 percent of the precipitation occurs in the warmest months. In the middle to southern Rockies, 66 to 75 percent occurs in the warmest months. In the southern areas and those at low elevations, precipitation during the frost-free season is only 20 percent of the evaporation potential. In northern areas precipitation during the growing season may be as high as 40 percent of the evaporation potential.

File:Calamagrostis rubescens 3.jpg can aggressively compete with ponderosa pine seedlings]]

Ponderosa pine forest can occur in different types of ecological site. Each of these sites can be characterized by its potential vegetation type (PVT) after succession reaches equilibrium or climax community.

In the southern and extreme eastern portion of the range, ponderosa pine grows primarily on ponderosa pine PVTs. On these settings, quaking aspen is the most frequent early-seral tree species.{{cite report|last1=Hoffman|first1=GR|last2=Alexander|first2=RR|year=1987|title=Forest vegetation of the Black Hills National Forest of South Dakota and Wyoming: a habitat type classification|id=Research Paper RM-276|location=Fort Collins, CO|publisher=Rocky Mountain Forest and Range Experiment Station, US Forest Service|url=https://www.fs.usda.gov/treesearch/pubs/48215}}{{cite report|last1=Youngblood|first1=AP|last2=Mauk|first2=RL|year=1985|title=Coniferous forest habitat types of central and southern Utah|id=General Technical Report GTR-INT-187| location=Ogden, UT|publisher=Intermountain Forest and Range Experiment Station, US Forest Service|url=https://www.fs.usda.gov/treesearch/pubs/34457}}{{rp|6}} Ground-level vegetation includes oaks (Quercus spp.), grasses (Festuca and Andropogon spp.), and low shrubs (e.g., snowberry (Symphoricarpos spp.) and spirea (Spirea spp.)). Russet buffaloberry (Shepherdia canadensis), a frequent shrub in these forests, stands out for its nitrogen fixing properties which is the process of making elemental nitrogen in the atmosphere available to plants.{{cite conference|last1=Jurgensen|first1=Martin F|last2=Tonn|first2=Jonalea T|last3=Graham|first3=Russell T|last4=Harvey|first4=Alan E|last5=Geier-Hayes|first5=Kathleen|year=1991|title=Nitrogen fixation in forest soils of the inland northwest|editor-last=Harvey|editor-first=AE|conference=Proceedings of the symposium management and productivity of western Montana forest soils|id=General Technical Report INT-280|location=Ogden, UT: Intermountain Research Station|publisher=US Forest Service|pages=101–109|url=https://www.fs.usda.gov/rmrs/documents-and-media/nitrogen-fixation-forest-soils-inland-northwest}}{{rp|6}}

With increasing moisture, ponderosa pine occurs as a mid-seral species and Douglas-fir becomes the late-seral species (Douglas-fir PVT). Quaking aspen and lodgepole pine are early-seral associates of ponderosa pine on these sites.{{cite report|last1=Mauk|first1=RL|last2=Henderson|first2=JA|year=1984|title=Coniferous forest habitat types of northern Utah|id=General Technical Report GTR-INT-170|location=Ogden, UT|publisher=Intermountain Forest and Range Experiment Station, US Forest Service}}{{rp|6}} These ponderosa pine forests occur in the Rocky Mountains along the Front Range of Colorado, in Utah, and in southern Idaho. They also occur along the western slopes of the Sierra Nevadas in California and the eastern slopes of the

Cascades in Oregon.{{cite report|last1=Franklin|first1=Jerry F|last2=Fites-Kaufman|first2=Jo Ann|year=1996|title=Assessment of late successional forests of the Sierra Nevada|work=Sierra Nevada ecosystem project, final report to Congress|volume=II, assessments and scientific basis for management options|location=Davis, CA|publisher=University of California, Centers for Water and Wildland Resources|pages=627–662|url=https://pubs.usgs.gov/dds/dds-43/VOL_II/VII_C21.PDF}}{{cite book|last1=Hann|first1=Wendel J|last2=Jones|first2=Jeffrey L.|last3=Karl|first4=Michael G.|last4=Sherm|display-authors=et al|year=1997|chapter=Landscape dynamics of the Basin|editor1-last=Quigley|editor1-first=Thomas M|editor2-last=Arbelbide|editor2-first=Sylvia J|title=An assessment of ecosystem components in the interior Columbia Basin and portions of the Klamath and Great Basins|volume=II|id=General Technical Report PNW-GTR-405|location=Portland, OR|publisher=Pacific Northwest Research Station, US Forest Service|pages=338–1055|doi=10.2737/PNW-GTR-405 |chapter-url=https://www.fs.usda.gov/treesearch/pubs/24921}}{{cite report|last1=Steele|first1=R|last2=Cooper|first2=SV|last3=Ondov|first3=DM|last4=Roberts|first4=DW|last5=Pfister|first5=RD|year=1983|title=Forest habitat types of eastern Idaho-western Wyoming|id=General Technical Report INT-144|location=Ogden, UT|publisher=Intermountain Forest and Range Experiment Station, US Forest Service|url=https://www.fs.usda.gov/treesearch/pubs/32907}}{{rp|6}} Ground-level vegetation includes ninebark (Physocarpus spp.), elk sedge (Carex geyeri), and pine grass (Calamagrostis rubescens). These species, in particular, exemplify aggressive survivors after disturbance (e.g., fire, mechanical site preparation) and are strong competitors for light and nutrients which compete with ponderosa pine seedlings.{{cite book|last1=Baumgartner|first1=DM|last2=Boyd|first2=RJ|last3=Breuer|first3=DW|last4=Miller|first4=DL|year=1986|title=Weed control for forest productivity in the Interior West|location=Pullman, WA|publisher=Cooperative Extension, Washington State University}}{{rp|6}}

Ponderosa pine forests in the north can occur in dry forests where the grand fir or white fir are the climax species.{{rp|7}} Additional trees that can occur in such forests include juniper (Juniperus spp.), pinyon pine (Pinus edulis), sugar pine (Pinus lambertiana), incense-cedar (Calocedrus decurrens), western larch, Jeffrey pine (Pinus jeffreyi), and lodgepole pine. Pinegrass and ninebark are frequent associates, but tall shrubs such as Rocky Mountain maple (Acer glabrum) often occur.{{rp|7}}

File:Ceanothus sanguineus 1.jpg grows in the understory of some ponderosa pine forests]]

The wettest forests where ponderosa pine occurs are the wet grand fir and/or white fir PVTs and the driest western redcedar PVTs. Such forests occur in the interior northwestern United States and in southern British Columbia.{{cite report|last1=Cooper|first1=SV|last2=Neiman|first2=KE|last3=Roberts|first3=DW|year=1991|title=Forest habitat types of northern Idaho: a second approximation|id=General Technical Report INT-236|location=Ogden, UT|publisher=Intermountain Research Station, US Forest Service|url=https://www.fs.usda.gov/treesearch/pubs/24623}}{{cite book|last1=Daubenmire|first1=R|last2=Daubenmire|first2=JB|year=1968|title=Forest vegetation of eastern Washington and northern Idaho|id=Technical Bulletin 60|location=Pullman, WA|publisher=Washington Agricultural Experiment Station}}{{rp|7}} The western redcedar PVT is by far the most productive type on which ponderosa pine occurs, and lush and complex vegetation mixes may develop. Western white pine is a frequent associate of ponderosa pine with an occasional paper birch (Betula papyrifera). A rich understory of shrubs, grasses, and forbs occur in these forests. Early seral-species such as redstem ceanothus (Ceanothus sanguineus), snowbrush ceanothus (Ceanothus velutinus) and Sitka alder (Alnus viridis ssp. sinuata) rapidly colonize sites after disturbance and are also active nitrogen fixers.{{cite report|last1=Smith|first1=Jane Kapler|last2=Fischer|first2=William C|year=1997|title=Fire ecology of the forest habitat types of northern Idaho|id=General Technical Report INT-GTR-363|location=Ogden, UT|publisher=Intermountain Research Station, US Forest Service|url=https://www.srs.fs.usda.gov/pubs/34304}}{{rp|7}} Mid-seral shrubs include Rocky Mountain maple which readily

survives disturbances and is joined by late-seral species such as huckleberry (Vaccinium spp.) and false huckleberry (Menziesia ferruginea). The latter readily survives disturbances but is an aggressive colonizer. Probably one of the greatest competitors and survivors after disturbance of any ground-level species occurring with ponderosa pine is pinegrass. This ground-level vegetation can play critical roles in forests such as providing wildlife habitat, stabilizing soil, and capturing nutrients after disturbance. For example, fireweed (Chamerion angustifolium) rapidly regenerates after fire and captures and recycles nitrogen.{{rp|7}} Because of

the range of species that can occur with ponderosa pine and their wide range of tolerance (e.g., shade, competition, fire) along with how they interact with

disturbances a plethora of vegetative compositions and structures can occur within ponderosa pine forests arranged and interspersed in a variety of mosaics.{{rp|7}}

The impact of logging and ecological dynamics can cause some problems in maintaining good delineation of the ponderosa pine ecosystem. This ecosystem is idealized as open and parklike with an excellent ground cover of grasses, sedges, and forbs or with an understory of shrubs of low to medium height. In perhaps 60 percent of the area, the idealized open character of the ponderosa pine ecosystem has changed to that of a dense and growth-retarded stand, particularly in the Pacific Northwest.

File:Abert’s squirrel (11740399534).jpg is only found in mature ponderosa pine forest.{{cite journal|doi=10.2307/1935266|jstor=1935266|title=The Abert Squirrel and Its Dependence on Ponderosa Pine|journal=Ecology|volume=46|pages=150–163|year=1965|last1=Keith|first1=James O.|issue=1/2|bibcode=1965Ecol...46..150K }}]]

The large mammals that inhabit the ponderosa pine ecosystem are the Rocky Mountain elk, mule deer, mountain lion, and coyote. Smaller animals include the bushy-tailed woodrat, white-footed mouse, bobcat, rock squirrel, cottontail rabbit, porcupine, and golden-mantled ground squirrel. The Kaibab squirrel is rare and endemic to this ecosystem on Arizona's Kaibab Plateau on the north rim of the Grand Canyon.

Bird species that live in the ponderosa pine ecosystem include the pygmy nuthatch, Steller's jay, sharp-shinned hawk, Rocky Mountain nuthatch, mountain chickadee, Cassin's finch, redshafted flicker, red-backed junco, northern goshawk, and western red-tailed hawk. Birds that are common during the summer include the western bluebird, Audubon's warbler, Williamson's sapsucker, western chipping sparrow, horned owl, and band-tailed pigeon.

Ponderosa pine grows on a variety of soils ranging from volcanic to sedimentary origin. The physical properties of the soil, and thus its moisture-retaining capacity, play an important role in the tree's development, possibly more than the chemistry of the soil. Studies have shown strong relationships between the vertical growth of ponderosa pine and soil depth. In the Black Hills of South Dakota, soil depth had more influence on tree height than soil parent material. In Montana, pine growth response has been related to soil type, effective soil depth, landform, and moisture availability. Increased water at a site increased plant growth regardless of the soil type and landform. The high water tables associated with springs tend to increase site productivity regardless of the soil type and landform.

Along the western edge of the Columbia Plateau and the east slope of the Cascade Mountains, common soil types are mollisols, inceptisols, entisols, and aridisols. In northern and eastern California, ponderosa pine stands are associated with ultisols. In the Okanogan Highlands at the northern edge of the Columbia Plateau and in much of the Northern Rocky Mountains, pine and the related forest types occur on inceptisols; the soils of the rest of these areas are largely alfisols and entisols. In the Blue and Wallowa Mountains of eastern Oregon, pine stands occupy mollisols. In the Middle and Southern Rocky Mountains, pines and associates are on mollisols, aridisols, entisols, and alfisols. Pine stands in the Gila Mountains are largely on mollisols. The small stands

of pine in the Great Basin are on aridisols.

File:Ponderosa pine prescribed burn.jpg, Arizona]]

Before successful fire exclusion, temperature and precipitation patterns combined with natural and human ignitions allowed fires to burn the dry ponderosa pine forests at relatively frequent (e.g., < 40 years) intervals,{{cite book|last=Agee|first=James K|year=1993|title=Fire ecology of Pacific Northwest forests|location=Washington, DC|publisher=Island Press}}{{rp|7}} even as frequent as every 6.5 years in Arizona.{{cite journal|journal=Ecological Applications|volume=7|issue=3|year=1997|pages=895–908|title=Determining reference conditions for ecosystem management of southwestern ponderosa pine forests|first1=PZ|last1=Fulé|first2=WW|last2=Covington|first3=MM|last3=Moore|doi=10.1890/1051-0761(1997)007[0895:DRCFEM]2.0.CO;2|url=http://openknowledge.nau.edu/id/eprint/1408/7/Fule_PZ_etal_1997_Reference_conditions_ecosystem_SW_ponderosa(1).pdf}} Cultural burning by Native Americans augmented and even dominated burning in several locations.{{cite journal|last1=Barrett|first1=SW|last2=Arno|first2=SF|year=1982|title=Indian fires as an ecological influence in the Northern Rockies|journal=Journal of Forestry|volume=80|issue=10|pages=647–651}}{{cite journal|last=Stewart|first=OC|year=1951|title=Burning and natural vegetation in the United States|journal=Geographical Review|volume=41|issue=2 |pages=317–320|doi=10.2307/211026 |jstor=211026 |bibcode=1951GeoRv..41..317S }}{{rp|7}} In the northern Rocky Mountains of Idaho and western Montana, dry settings of ponderosa pine forests historically burned by low severity surface fires that did not kill overstory trees at 15 to 23 year mean return intervals.{{rp|7}}

Ponderosa pine forests appear to have evolved with fire and many authors have suggested that their composition and structure are dependent on the vegetation's relations with fire.{{cite book|last1=Covington|first1=WW|last2=Moore|first2=MM|year=1994|chapter=Postsettlement changes in natural fire regimes and forest structure: Ecological restoration of old-growth ponderosa pine forests|editor1-last=Sampson|editor1-first=R. Neil|editor2-last=Adams|editor2-first=David L|title=Assessing forest ecosystem health in the Inland West|location=New York|publisher=The Haworth Press Inc|pages=153–181}}{{cite journal|last1=Everett|first1=RL|last2=Schellhaas|first2=R|last3=Keenum|first3=D|last4=Spurbeck|first4=D|last5=Olson|first5=P|year=2000|title=Fire history in the ponderosa pine/Douglas-fir forests on the east slope of the Washington Cascades|journal=Forest Ecology and Management|volume=129|issue=1–3 |pages=207–225|doi=10.1016/S0378-1127(99)00168-1 }}{{cite conference|last1=Harvey|first1=Alan E|last2=Graham|first2=Russell T|last3=McDonald|first3=Gerald I|year=1999|title=Tree species composition change: forest soil organism interaction: potential effects of nutrient cycling and conservation processes in interior forests|editor1-last=Meurisse|editor1-first=Robert T|editor2-last=Ypsllantis|editor2-first=William G|editor3-last=Seybold|editor3-first=Cathy|conference=Pacific Northwest forest and rangeland soil organism symposium|id = General Technical Report PNW-GTR-461|location=Portland, OR|publisher=Pacific Northwest Research Station, US Forest Service|pages=137–145|url=https://www.fs.fed.us/pnw/pubs/pnw_gtr461.pdf}}{{rp|21}} However, when wildfires burn altered ponderosa pine forests, the extent or area burned is similar to historical times but they tend to burn more severely.{{cite report|last=Graham|first=Russell T|year=2003|title=Hayman Fire case study|id=General Technical Report RMRS-GTR-114|location=Ogden, UT|publisher=Rocky Mountain Research Station, US Forest Service|url=https://www.srs.fs.usda.gov/pubs/5588}}{{cite report|last1=Graham|first1=Russell T|last2=McCaffrey|first2=Sarah|last3=Jain|first3=Theresa B|year=2004|title=Science basis for changing forest structure to modify wildfire behavior and severity|id=General Technical Report RMRS-GTR-120|location=Fort Collins, CO|publisher=Rocky Mountain Research Station; US Forest Service}}{{cite report|last1=Kaufmann|first1=MR|last2=Fornwalt|first2=PJ|last3=Huckaby|first3=LS|last4=Stoker|first4=JM|year=2001|chapter=Cheesman Lake a historical ponderosa pine landscape guiding restoration in the South Platte watershed of the Colorado Front Range|editor1-last=Vance|editor1-first=RK|editor2-last=Edminster|editor2-first=CB|editor3-last=Covington|editor3-first=WW|editor4-last=Blake|editor4-first=J|title=Ponderosa pine ecosystems restoration and conservation: steps toward stewardship|id=RMRS-P-22|location=Fort Collins, CO|publisher=Rocky Mountain Research Station, US Forest Service|pages=9–18|chapter-url=https://www.fs.usda.gov/treesearch/pubs/6266}}{{rp|21}} They often kill large continuous expanses of vegetation, consume the forest floor, volatilize nutrients, provide for exotic species introductions, increase soil erosion, and, in general, create forest conditions that may not be favorable to society. The long-term consequences are not well understood for issues such as water quality and wildlife habitat. Nor will the sense of place that forests often provide which, in some cases, will not be replaced for many generations.{{cite report|last1=Galliano|first1=Steven J|last2=Loeffler|first2=Gary M|year=1999|title=Place assessment: how people define ecosystems|id=General Technical Report PNW-GTR-462|location=Portland, OR|publisher=Pacific NorthwestResearch Station, US Forest Service|url=https://www.fs.fed.us/pnw/pubs/pnw_gtr462.pdf}}{{cite journal|last=Schroeder|first=Herbert|year=2002|title=Experiencing nature in special places: surveys in the north central region|journal=Journal of Forestry|volume=100|issue=5|pages=8–14}}{{rp|21}}

File:Evening colours on Ponderosa pine snags (bark beetle kill). (18343281801).jpg affected by bark beetles]]

In the western United States domestic livestock grazing and harvesting of ponderosa pine forests was occurring by the mid-1800s.{{cite journal|last=Cooper|first=CF|year=1960|title=Changes in vegetation, structure, and growth of southwest pine forests since white settlement|journal=Ecological Monographs|volume=30|issue=2 |pages=129–164|doi=10.2307/1948549 |jstor=1948549 |bibcode=1960EcoM...30..129C }}{{cite journal|last=Rasmussen|first=D Irvin|year=1941|title=Biotic communities of the Kaibab plateau, Arizona|journal=Ecological Monographs|volume=11|issue=3|pages=229–275|doi=10.2307/1943204 |jstor=1943204 |bibcode=1941EcoM...11..229R }}{{rp|8}} Ponderosa pine was extensively harvested, altering both forest composition and structure.{{cite report|last=Barrett|first=James W|year=1979|title=Silviculture of ponderosa pine in the Pacific Northwest: the state of our knowledge|id=General Technical Report PNW-97|location=Portland, OR|publisher=Pacific Northwest Forest and Range Experiment Station, Forest Service U.S. Department of Agriculture|url=https://archive.org/details/SilvicultureOfPonderosaPineInThePacificNorthwestTheStateOfOur}}{{cite book|last=Pearson|first=GA|year=1950|title=Management of ponderosa pine in the southwest as developed by research and experimental practices|id=Agriculture Monograph 6|location=Washington, DC|publisher=US Forest Service; 218}}{{rp|8}} In mesic forests, grand fir and/or white fir and Douglas-fir rapidly colonized these sites when ponderosa pine was harvested. Especially on the ponderosa pine PVT, grass cover tended to decrease ponderosa pine seedling establishment and survival.{{cite book|last1=Brawn|first1=JD|last2=Balda|first2=RP|year=1988|chapter=The influence of silvicultural activity on ponderosa pine forest bird communities in the southwestern United States|editor-last=Jackson|editor1-first=JA|title=Bird conservation|volume=3|location=Madison, WI|publisher=The International Council for Bird Preservation, United States Section|pages=3–21}}{{rp|8}} However, when heavy livestock grazing ceased in the early 1900s in the southwestern United States, dense stands of ponderosa pine seedlings became established. Because of fire exclusion, climate changes, and other factors these trees readily developed into dense stands.{{cite journal|last=Stein|first=SJ|year=1988|title=Explanations of imbalanced age structure and scattered distribution of ponderosa pine within a high-elevation mixed coniferous forest|journal=Forest Ecology and Management|volume=25|issue=2 |pages=139–153|doi=10.1016/0378-1127(88)90125-9 }}{{rp|8}}

The dense stands that developed increased the abundance of insect and disease epidemics, and when combined with fire exclusion, significantly altered the composition and structure of these forests.{{cite conference|last1=Harvey|first1=Alan E|last2=Graham|first2=Russell T|last3=McDonald|first3=Gerald I|last4=Larsen|first4=Michael J|year=2000|title=Fire/decay: managing codependent processes across the landscape|editor1-last=Neuenschwander|editor1-first=Leon F|editor2-last=Ryan|editor2-first=Kevin C|conference=Crossing the Millennium: Integrating spatial technologies and ecological principles for a new age in fire management|location=Spokane, WA|publisher=International Association of Wildland Fire|pages=179–189}}{{rp|8}} Historically, western pine beetle (Dendroctonus brevicomis), pine engraver (Ips spp.), fir engraver (Scolytus ventralis), Douglas-fir tussock moth (Orgyia pseudotsugata) were insects associated with regularly burned areas.{{cite report|last1=Hessburg|first1=Paul F|last2=Mitchell|first2=Russel G|last3=Filip|first3=Gregory M|year=1994|title=Historical and current roles of insects and pathogens in eastern Oregon and Washington forested landscapes|id=General Technical Report PNW-GTR-327|location=Portland, OR|publisher=Pacific Northwest Research Station, US Forest Service|url=https://www.fs.fed.us/pnw/pubs/pnw_gtr327.pdf}}{{rp|8}} In most years bark beetles occurred at endemic levels in ponderosa pine, Douglas-fir, and grand fir killing large and weakened trees that were struck by lightning, infected by root disease (Armillaria spp.), or too old to resist attack.{{cite book|last1=Williams|first1=RE|last2=Shaw|first2=CG III|last3=Wargo|first3=PM|last4=Sites|first4=WH|year=1986|title=Forest insect and disease|id=leaflet 78|location=Washington, DC|publisher=US Forest Service}}{{cite report|last1=Wu|first1=Y|last2=Johnson|first2=DW|last3=Angwin|first3=PA|year=1996|title=Identification of Armillaria species in Rocky Mountain Region|id=Report R2-58| location=Golden, CO|publisher=Rocky Mountain Region, US Forest Service}}{{rp|8}} Pine engraver and fir engraver beetles attacked young, densely stocked ponderosa pine or removed trees scorched by low-intensity surface fires and/or trees severely infected with disease. Sometimes disease and insect infestations increased during droughts when trees were stressed.{{rp|8}}

After a century of fire suppression, these same insects have occurred at epidemic levels in some locations.{{cite report|last1=Hedden|first1=R|last2=Barras|first2=S|last3=Coster|first3=J|year=1981|title=Hazard-rating system in forest insect pest management|id=General Technical Repport GTR-WO-27|location=Washington, DC|publisher=US Forest Service}}{{cite book|last1=Gardner|first1=B|last2=Mocettini|first2=P|last3=Halsey|first3=D|year=1997|title=Forest, insect, and disease conditions|location=Ogden, UT|publisher=Intermountain Region, US Forest Service}}{{cite report|last1=Schmid|first1=JM|last2=Mata|first2=SA|year=1992|title=Stand density and mountain pine beetle-caused tree mortality in ponderosa stands|id=Research Note RM-515|url=https://archive.org/details/IND92022689|location=Fort Collins, CO|publisher=Rocky Mountain Forest and Range Experimental Station, US Forest Service}}{{rp|8–9}} Ponderosa pine continues to be susceptible to the western pine beetle and mountain pine beetle. These beetles often kill ponderosa pine on Douglas-fir and grand fir/white fir PVTs. The pine engraver beetle is more abundant and destructive with some of the severest outbreaks occurring on low-elevation ponderosa pine PVTs.{{cite report|last1=Hessburg|first1=Paul F|last2=Mitchell|first2=Russel G|last3=Filip|first3=Gregory M|year=1994|title=Historical and current roles of insects and pathogens in eastern Oregon and Washington forested landscapes|id=General Technical Report PNW-GTR-327|url=https://www.srs.fs.usda.gov/pubs/6390|location=Portland, OR|publisher=Pacific Northwest Research Station, US Forest Service}}{{rp|8–9}} Pandora moth (Coloradia pandora) defoliates ponderosa pine and scattered outbreaks have occurred in Arizona, California, Colorado, and Oregon during the 20th century. The larvae prefer loose soils created by weathered granites or pumice where they burrow and pupate.{{cite journal|last1=Speer|first1=James H|last2=Swetnam|first2=Thomas W|last3=Wickman|first3=Boyd E|last4=Youngblood|first4=Andrew|year=2001|title=Changes in pandora moth outbreak dynamics during the past 622 years|journal=Ecology|volume=82|issue=3|pages=679–697|doi=10.1890/0012-9658(2001)082[0679:CIPMOD]2.0.CO;2 }}{{rp|8–9}} In addition to ponderosa pine being damaged by insects, dense stands of Douglas-fir and grand fir or white fir that developed on many settings arevery susceptible to both defoliators and root diseases.{{rp|8–9}}

• Maritime Coast Range Ponderosa Pine forests
• Rocky Mountain ponderosa pine forest
• California Floristic Province

{{reflist}}

Category:Temperate coniferous forests of the United States

Category:Plant communities of the Western United States

Category:Natural history of the California Coast Ranges

Category:Forests of California

Category:Forests of the Rocky Mountains

Category:Forests of the Sierra Nevada (United States)