Pinus strobiformis, southwestern white pine
Abrahamson, Ilana L., compiler. 2026. Species Brief: Pinus strobiformis, southwestern white pine. In: Fire Effects Information System, Online. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Missoula Fire Sciences Laboratory (Producer). Available: https://research.fs.usda.gov/feis/species-briefs/pinsto
This Species Brief is a concise summary of the biological, ecological, and fire‑related characteristics of an individual species derived from a Fire Effects Information System (FEIS) Species Review.
| Attribute | Characteristic | Justification | Source |
|---|---|---|---|
| Biological characteristics | |||
| Life form | Tree | Southwestern white pine is a native, five-needle conifer. Mature trees have an open, irregular crown with heights of 15 to 30 m and trunk diameters of 0.5 to 1.0 m. | FEIS: Botanical Description [1] |
| Typical lifespan | 201+ years* | Information about the typical lifespan of southwestern white pine is lacking, but one study reported a maximum age of 295 years in mixed-conifer stands throughout Arizona and portions of New Mexico. | FEIS [1]; Looney and Waring [3] |
| Life cycle | Perennial | Southwestern white pine is a native coniferous tree. | FEIS: Botanical Description [1] |
| Drought tolerance | Moderate* | Southwestern white pine appears moderately resilient to drought, although it is likely less tolerant than limber pine. MoreIt has genetic traits that confer drought tolerance and has the flexibility to adapt to hot and dry environments, enhancing its water use efficiency and chances of survival. | FEIS: Other Management Considerations; Site Characteristics [1] |
| Rooting depth | Deep* | Information about mature tree roots is lacking. However, seedlings develop a large taproot. | FEIS: Seedling Establishment and Mortality [1] |
| Bark thickness at maturity | Thick | Mature southwestern white pines have deeply furrowed bark with scaly ridges, enabling them to survive low-severity surface fire. MoreWhen trees are young, the bark is gray and smooth to shallowly fissured. | FEIS: Fire Adaptations; Botanical Description; Immediate Fire Effects [1] |
| Sheds low branches | Often* | Lower branches of southwestern white pine are horizontal to hanging, but lowest branches may get higher over time as a fire-resistance trait. MoreOver 65 stands, mean height of lowest live branches was 4.3 m. | FEIS: Botanical Description; Plant Response to Fire [1]; Leal-Saenz et al. [2] |
| Reproduction and Regeneration | |||
| Adventitious buds | None | Southwestern white pine does not reproduce or regenerate vegetatively. | FEIS: Vegetative Reproduction and Regeneration [1] |
| Time to reproductive maturity | 11-20 years | Southwestern white pine begins producing seed cones at about 15 years old. | FEIS: Seed Production and Predation [1] |
| Soil seed bank longevity | Transient (<1 year) | Evidence of soil seed banking in southwestern white pine was not found and is considered unlikely, given its large seed size and low seed production. MoreSeeds germinate the spring or summer after autumn dispersal, so they are not expected to persist in the soil. | FEIS: Seed Banking; Seasonal Development [1] |
| Month(s) when seeds typically ripen | September | Cones mature in September, and seeds are dispersed from September to October. | FEIS: Seasonal Development [1] |
| Serotinous cones | No | Southwestern white pine lacks serotinous cones. Its seed cones have thick, reflexed scales that open when mature to release seeds. | FEIS: Botanical Description; Fire Adaptations [1] |
| Seed dispersal mechanism | Animal; Wind; Gravity | Southwestern white pine seeds are dispersed by birds, rodents, gravity, and wind. MoreCones and seeds tend to decrease in size and weight from north to south, and southern populations have increasingly larger wings suggesting a greater reliance on wind dispersal in southern populations. | FEIS: Seed Dispersal [1] |
| Seed dispersal distance | Mostly under parent plant; <100 m*; 101 m-1 km*; >1 km* | Southwestern white pine seeds, being large and mostly wingless, do not typically disperse far by wind or gravity. MoreBirds and rodents disperse seeds farther. In northern populations, Clark's nutcracker caches seeds over considerable distances (>20 km), but nutcrackers are absent from much of the southern range. | FEIS: Seed Dispersal [1] |
| Optimal conditions for seedling establishment | Litter and/or duff; Shade | Shaded duff and litter layers significantly enhance survival and growth of southwestern white pine seedlings. MoreRegeneration is positively linked to abundant litter and log cover and negatively associated with bare mineral soil. | FEIS: Regeneration Processes; Seedling Establishment and Mortality [1] |
| Successional Status | |||
| Shade tolerance | Moderately shade tolerant | Southwestern white pine exhibits a moderate level of shade tolerance, allowing it to regenerate and grow in undisturbed environments. MoreIts shade tolerance is intermediate compared to its associated tree species. It is often the most shade-tolerant of the pines it grows with, but generally less shade-tolerant than firs and spruces. | FEIS: Plant Growth and Mortality; Successional Status [1] |
| Successional status | Mid; Late* | Depending on its associates, southwestern white pine can occupy lower strata, the mid-canopy, or dominate the overstory. MoreAs a canopy dominant in mixed-species stands, southwestern white pine is likely to be replaced by more shade-tolerant species such as Douglas-fir and white fir. However, it dominates the overstory in some old-growth forests. | FEIS: Stand Structure; Successional Status [1] |
| Fire | |||
| Primary fire response(s) or adaptation(s) | Resist | Mature southwestern white pine trees survive low-severity surface fires, aided by deeply furrowed bark, as shown by widespread fire scarring. | FEIS: Immediate Fire Effects; Fire Adaptations [1] |
| Germination is fire stimulated | Rarely/No | Southwestern white pine seeds germinate in spring or summer after rain and require 2 weeks to 4 months of stratification before germinating. No fire-related germination cue is described. | FEIS: Seasonal Development; Germination [1] |
| Flowering/fruiting is fire stimulated | Rarely/No* | Southwestern white pine flowers in June and produces seed crops every 3 to 4 years. The source does not provide explicit information about fire-stimulated flowering or fruiting. | FEIS: Seasonal Development; Seed Production and Predation [1] |
| Season when it is most sensitive to fire | Insufficient information | The source does not provide explicit information about the season in which southwestern white pine is most sensitive to fire. MoreIn communities where southwestern white pine is most common, fires primarily occurred in the spring (as indicated by earlywood fire scars), suggesting that mature trees survive spring fires under historical conditions. | FEIS: Fire Regimes [1] |
| Plant flammability | Insufficient information | The source does not provide explicit information about southwestern white pine's own flammability. | FEIS [1] |
| Early colonizer/recolonizer of burned or disturbed sites | Rarely/No* | Southwestern white pine is a secondary colonizer from off-site seed. MoreEstablishment may increase with the time between historical fires. Its large, mostly wingless seeds do not disperse far by gravity or wind, so where Clark's nutcrackers are absent, colonization into large burns is limited. | FEIS: Fire Adaptations; Plant Response to Fire [1] |
| Effect of fire exclusion on population | Possible decrease* | With fire exclusion, southwestern white pine populations could decrease in areas where it is replaced by more shade-tolerant competitors such as Douglas-fir and white fir. MoreHowever, southwestern white pine is moderately shade tolerant, so it may continue to persist with fire exclusion. | FEIS: Stand Structure [1] |
| Is this species typically managed with prescribed fire? | Rarely/No | Published literature on the use of prescribed burning in southwestern white pine stands was not found. | FEIS: Fire Management Considerations [1] |
| Predominant historical fire frequency where it most commonly occurs | Frequent | Where southwestern white pine is most common, the presettlement fire regime was characterized by frequent fires with estimated mean intervals under 20 years. MoreIn Arizona, New Mexico, and Texas, estimated mean fire intervals ranged from 3 to 35 years. Intervals are longer on mesic, higher elevation sites. | FEIS: Fire Regimes [1] |
| Predominant historical fire severity where it most commonly occurs | Low; Mixed | Where southwestern white pine is most common, historical fires were mostly low-severity, with some component of mixed-severity fire and patches of high-severity within larger fires. | FEIS: Fire Regimes [1] |
| Predominant historical fire regime group where it most commonly occurs | 1 | Southwestern white pine is most common in forests with historically frequent, mostly low-severity fire, corresponding to fire regime group 1. | FEIS: Fire Regimes [1] |
| Alters historical fuel characteristics of ecosystems where it occurs | Rarely/No | Southwestern white pine is a native species and is typically a component of complex, mixed-species forests, rarely dominating stand composition. MoreAltered fuels where southwestern white pine occurs are attributed to grazing and fire exclusion over more than 100 years, not to southwestern white pine. | FEIS: Fuel Characteristics [1] |
| Biophysical Setting | Mean Fire Interval (years) | Fire Severity Percent (%) | ||||||
|---|---|---|---|---|---|---|---|---|
| Code | Fire Regime Group | Low | Mixed | Replacement | All | Low | Mixed | Replacement |
| Series 10240 - Madrean Lower Montane Pine-Oak Forest and Woodland | ||||||||
| 10240_25_27 | I-B | 11 | 30 | 60 | 7 | 65 | 23 | 12 |
| 10240_26 | I-A | 10 | 24 | 16 | 5 | 50 | 20 | 30 |
| Series 10520 - Southern Rocky Mountain Mesic Montane Mixed Conifer Forest and Woodland | ||||||||
| 10520_27 | III-A | 77 | 98 | 253 | 37 | 48 | 37 | 15 |
| 10520_28 | III-A | 153 | 144 | 202 | 54 | 35 | 38 | 27 |
| Series 10540 - Southern Rocky Mountain Ponderosa Pine Woodland | ||||||||
| 10540_26 | I-B | 11 | 105 | 76 | 9 | 79 | 9 | 12 |
| Series 10610 - Inter-Mountain Basins Aspen-Mixed Conifer Forest and Woodland | ||||||||
| 10610_15_25 | I-B | 110 | 20 | 43 | 12 | 11 | 61 | 28 |
| Series 10510 - Southern Rocky Mountain Dry-Mesic Montane Mixed Conifer Forest and Woodland | ||||||||
| 10510_28 | I-C | 32 | 54 | 325 | 19 | 59 | 35 | 6 |
| Summary | ||||||||
| Minimum | 10 | 20 | 16 | 5 | 11 | 9 | 6 | |
| Maximum | 153 | 144 | 325 | 54 | 79 | 61 | 30 | |
| Mean | 58 | 68 | 139 | 20 | 50 | 32 | 19 | |
| Median | 32 | 54 | 76 | 12 | 50 | 35 | 15 | |
| Percentage of fires in 3 fire severity classes, derived from LANDFIRE succession modeling. Replacement-severity fires cause >75% kill or top-kill of the upper canopy layer; mixed-severity fires cause 26%-75%; low-severity fires cause <26%. | ||||||||
| LANDFIRE. 2020. Biophysical settings models and descriptions, [Online]. Washington, DC: U.S. Department of Agriculture, Forest Service; U.S. Department of the Interior; U.S. Geological Survey; Arlington, VA: The Nature Conservancy, (Producers). Available: https://www.landfirereview.org/search.php [96496] | ||||||||
Fire Effects Information System
1. McKinney, Shawn T. 2025. Pinus strobiformis, southwestern white pine. In: Fire Effects Information System, Online. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Missoula Fire Sciences Laboratory (Producer). Available: https://research.fs.usda.gov/feis/species-reviews/pinsto
Other References
2. Leal-Saenz, Alejandro; Waring, Kristen; Menon, Mitra; Cushman, Samuel; Eckert, Andrew; Flores-Renteria, Lluvia; Hernandez-Diaz, Jose; Lopez-Sanchez, Carlos; Martinez-Guerrero, Jose; Wehenkel, Christian. 2020. Morphological differences in Pinus strobiformis across latitudinal and elevational gradients. Frontiers in Plant Science. 11: 559697. [100083]
3. Looney, Christopher E.; Waring, Kristen M. 2012. Patterns of forest structure, competition and regeneration in southwestern white pine (Pinus strobiformis) forests. Forest Ecology and Management. 286: 159-170. [86898]