• FIRE ECOLOGY OR ADAPTATIONS
• POSTFIRE REGENERATION STRATEGY

FIRE ECOLOGY OR ADAPTATIONS:

Black cottonwood sprouts from stumps, charred boles, root crowns, or lateral roots following fire [24,28,58,97,109] and because of this has been referred to as a fire "endurer" rather than "resister" [3]. Fire-induced sprouting is more common in the Tacamahaca section than in the Aigeiros section. Rates of sprouting are highest if fire occurs when cottonwoods are dormant [49]; this time also has the highest probability of fire, with late summer and fall, or late winter (in low snow years) most common [58]. In general older trees sprout less than young trees [49], and sprout survival is highest when the water table is close to the surface [58]. In 1986, Coates and Haeussler [28] stated that there was little information regarding black cottonwood sprout vigor after fire, or impact of fire severity on sprouting potential. Though this is still at least partially true, a study of clonal reproduction after fire in Alberta by Gom and Rood [49] provides much useful data that is summarized in the "Fire Effects" section of this species summary.

Black cottonwood is not only a fire "endurer" but also a fire "invader." Fire can improve seedling establishment by increasing light penetration and exposing mineral soil to allow seedling establishment if moisture is available [3,24]. Increases in light penetration following fire also aid establishment [24]. Black cottonwood seedlings have been observed 1 year after stand-replacing fire in upland ponderosa pine/ Rocky Mountain Douglas-fir habitat on the Bitterroot National Forest, Montana. The seedlings grew in cavities in mineral soil after the root systems of large trees had burned [131]. A study of seedling establishment (artificially seeded) of balsam poplar after experimental fires in a black spruce habitat demonstrated the dependency of the species on mineral soil exposure for germination and survival. Fire was prescribed on 1 m² plots. On moderately burned plots 17 black cottonwood germinated, 1 survived 1 year, and 0 survived 3 years. On heavily burned plots 71 germinated, 39 survived 1 year, and 39 survived 3 years [158].

Fire is infrequent on recently formed gravel bars, but when it does occur, damage to cottonwoods is greatest because their root systems have not developed [58].

Fire Regimes: Historic fire regimes have not been explicitly studied in black cottonwood communities [10]. It has been speculated that because of high moisture content and rapid decomposition of litter in riparian forests, frequency of fire is less than it is in adjacent areas [132]. These factors could protect forested riparian sites when severe fires occur on adjacent uplands. Conversely, wind-driven fires beginning in adjacent upland communities may spread to riparian forests, particularly when fuel accumulation on upland sites has increased as a result of fire suppression [132]. Arno [10] states that black cottonwood forests along major rivers of the Pacific Northwest likely burned frequently, as they were historically surrounded by communities characterized by high fire frequency, such as ponderosa pine savannas or sagebrush steppes. Fires could have easily spread from adjacent communities; prior to widespread livestock grazing and irrigation, dry grassy fuels were more continuous than they are currently [10]. When fires do occur, they are most severe in older cottonwood stands where fuel accumulation is highest [49,132].

Fire regimes for plant communities and ecosystems in which black cottonwood is dominant are summarized below. For further information regarding fire regimes and fire ecology of communities and ecosystems where black cottonwood is found, see the "Fire Ecology and Adaptations" section of the FEIS species summary for the plant community or ecosystem dominants listed below.

POSTFIRE REGENERATION STRATEGY [140]:

Related categories for SPECIES: Populus balsamifera ssp. trichocarpa | Black Cottonwood