About the Northeastern Plateau
The Northeastern Plateau extends east of the Southern Cascade range and south along the east slopes of the Sierra Nevada. The topography is extremely abrupt and elevations, which range from 3,950 ft to 9,892 ft, can change quickly. The most prominent feature is the Modoc Plateau, which is high flat terrain characterized by basalt plains and volcanic shields.
The climate of the Northeastern Plateau is Mediterranean, with warm, wet winters and hot, dry summers. Most precipitation falls as snow at higher elevations between November and April. The Northeastern Plateau is in the rain shadow of the Cascade Range and the Sierra Nevada. The summer months are mostly rainless except for thunderstorms, which can cause lightning ignitions.
Most wildfires occur from June to September and certain weather conditions can affect fire ignitions and fire behavior during those months. Generally, years that are drier and warmer than normal have larger and more widespread fires.
Fire History of the Northeastern Plateau
Indigenous burning
Historically, intentional ignitions from Indigenous people contributed to the frequent presence of fire in these landscapes. The Northeastern Plateau region is the ancestral lands of many Indigenous tribes that still steward these lands today including the Modoc, Mountain Maidu, Northern Paiute, Pit River, and Washoe tribes to name a few. Tribes burn for many reasons, including the production of food and basketry materials, to aid in hunting efforts, and for cultural and ceremonial purposes. To learn more about other Indigenous tribes in the Northeastern Plateau region, visit https://native-land.ca/.
Historic Fire Occurrence
The Mediterranean climate, common occurrence of lightning ignitions, and widespread use of fire by Indigenous people historically promoted frequent surface fires of low- to moderate-intensity. This fire regime encouraged and maintained plant species with fire-adaptive traits across ecosystems in the Northeastern Plateau region. Generally, pine-dominated forests were less dense and consisted of larger-diameter trees; this was likely attributed to frequent fires in the region. However, after Euro-American settlement, some areas, especially forested areas, saw a decline in fire activity due to fire suppression. Additionally, the introduction of intensive, largely unmanaged grazing altered fire regimes by reducing perennial bunch grasses and smaller shrubs while also promoting the growth of annual grasses and unpalatable trees and shrubs.
Today, fire regimes in the region have changed – mostly due to the reduction of fine fuels through livestock grazing, fire suppression, the introduction of highly flammable, exotic annual herbs, and climate change. Since the 1870s some plant communities burn more frequently and others less frequently than in historic periods. Where fires were historically more frequent, less intense and less severe, they are now more infrequent but with increased intensity and severity. Warmer temperatures, reduced precipitation, and longer fire seasons have led to contemporary fires burning larger proportions of the landscape at greater proportions of higher severity.
Fire Ecology of the Northeastern Plateau by Ecoregion
Fire in the Sagebrush Steppe
Historically, fire regimes in this ecosystem type were characterized as fires of moderate to high intensity and severity with varying frequencies. Most fires burned between mid-summer and early fall with likely ignition sources being from lightning and Indigenous peoples. The fuel quantity is limited in most plant communities and fuel continuity is often broken up by patches of bare soil. Areas in the zone with shorter fire return intervals are likely dominated by grass. Generally, there is limited information about the fire frequencies of the area due to the lack of research.
Over the last 100 years, things like fire suppression, grazing, and introduction of exotic weeds have significantly altered fire frequency, intensity, and severity in these ecosystems. Fires in these areas have generally decreased, resulting in an increase in shrub cover and density, a decline in herbaceous understory plants, and a shift from shrub steppe communities to western juniper woodlands. On the other hand, some portions of the zone are burning more frequently due to cheatgrass (Bromus tectorum) invasion. Cheatgrass can outcompete native grasses, forbs, and shrubs by reducing moisture and nutrients in surface soils. Once established, cheatgrass can alter fire regimes by creating continuous beds of fine fuels that promote frequent, high- severity fires.
Fires in Lower-Montane Forests
Historically, fire regimes in this ecosystem type were characterized by frequent (5-20 years) fires of low to moderate intensity and severity. Most fires burned between mid-summer and early fall with likely ignition sources being from lightning and Indigenous peoples. Over the last 100 years, things like fire suppression, historic logging and grazing practices, and climate change have altered forest structure and composition, fuel loads, and fire regimes in the region. Where historic, frequent fires removed litter and fine fuels and created conditions suitable for conifer regeneration, contemporary forests are composed of denser stands of smaller-diameter trees with higher fuel loads. Contemporary forest stand and fuel conditions have lead to greater proportions of this region burning at moderate- to high-intensity and severity.
Fires in Mid-Montane Forests
Historically, fire return intervals were short and intensity and severity were low to moderate. The dominant conifer species in this zone all evolved with these fire regimes; which allowed them to develop various fire-adaptive traits. Mixed-conifer forests have changed since the onset of fire suppression, historic logging practices, and climate change. Forest density has increased along with a shift in species composition toward increasing density overall, particularly of fire-sensitive white fir and incense cedar. Contemporary forest stands with increased stand densities and fuel accumulation are more likely to burn severely. I addition, these dense forests are more susceptible to mortality from drought and insects.
As a result of these increased woody fuels and tree densities, there has been a significant increase in the proportion of area that burns at high severity in this zone. Historically, high severity fire was present in this system, just at smaller scales – likely a few acres to a few hundred acres. In recent years, we have seen high severity patches that are thousands of contiguous acres, which can affect postfire succession and the associated trajectory of the ecosystem. Succession in such fires usually begins with forests initially replaced with a combination of snags, herbaceous plants, and shrubs.
Generally, the larger the high-severity burn patch, the fewer the available seed trees, with increasingly less conifer regeneration except along edges of the patches. Most dominant conifer species in this zone rely on wind-driven seed dispersal for regeneration, with seeds generally travelling only ~200 feet from the parent tree. This means that in very large high severity patches, significant area is likely outside of the dispersal range of surviving mature trees. As a result, forest managers are increasingly working to actively reforest these areas. Where natural regeneration is lacking and no reforestation is undertaken, shrubs tend to come to dominate. In addition, all of the fire-killed trees in these areas will eventually fall and create heavy surface fuel loads. Taken together, these characteristics tend to result in high severity re-burns, which could result in a persistent type conversion to shrubland.
Fire in Upper Montane Forests
Historically, fire regimes in this ecosystem were characterized by infrequent, small, low-intensity fires due to lack and discontinuity of fuels. Fuel accumulation rates, not ignitions, are the limiting factor for fire occurrence in this zone. The dry climate and cold winters lead to slow fuel accumulation. The predominance of short needle conifers and snow compact the fuel bed, so fires that do start by lightning are often slow spreading, patchy, low-intensity surface fires. Fires generally only become more intense where there are concentrations of fuels from dead trees or small thickets (typically white fir regeneration).
Fire in Subalpine Forests
Historically, fire regimes in this ecosystem were characterized by infrequent, small, low-intensity fires due to lack and discontinuity of fuels. Fire return intervals varied due to topography, vegetation, and fuel availability, but generally, these high elevation sites had longer fire return intervals. Lightning is frequent in this zone, but fire does not play a significant role in these ecosystems. Because of late melting snowpack and fuel scarcity, the few fires that do ignite do not spread beyond individual or small clusters of trees. Trees in this zone are sensitive to even low-intensity fires.
Additional Resources
Check out these resources below to learn more about fire ecology and history in the Northeastern Plateau!
- Riegel, G. M., R. F. Miller, C. N. Skinner, S. E. Smith, C. A. Farris, K. E. Merriam. 2018. Northeastern Plateau Bioregion. In van Wagtendonk, J. W., N. G. Sugihara, S. L. Stephens, A. E. Thode, K. E. Shaffer, J. A. Fites-Kaufman (Eds.), Fire in California’s Ecosystems. 363-397.
- van Wagtendonk, J. W., N. G. Sugihara, S. L. Stephens, A. E. Thode, K. E. Shaffer, J. A. Fites-Kaufman. 2018. Fire in California’s Ecosystems (2nd ed.). University of California Press. https://www.ucpress.edu/books/fire-in-californias-ecosystems/hardcover.