Home/Ecosystems/ Northern Rockies Western Larch Savanna

Northern Rockies Western Larch Savanna

EVT 7010Northern Rocky Mountain Western Larch Savanna

CES306.837GNRTreeConifer

Summary

This ecological system is restricted to the interior montane zone of the Pacific Northwest in northern Idaho and adjacent Montana, Washington, Oregon, and in southeastern interior British Columbia. It also appears in the east Cascades of Washington. Winter snowpacks typically melt off in early spring at lower elevations. Elevations range from 680 to 2195 m (2230-7200 feet), and sites include drier, lower montane settings of toeslopes and ash deposits. This system is composed of open-canopied "savannas" of the deciduous conifer Larix occidentalis, which may have been initiated following stand-replacing crownfires of other conifer systems, but are maintained by a higher frequency, surface-fire regime. These savannas are found in settings where low-intensity, high-frequency fires create open larch woodlands, often with the undergrowth dominated by low-growing Arctostaphylos uva-ursi, Calamagrostis rubescens, Linnaea borealis, Spiraea betulifolia, Vaccinium cespitosum, or Xerophyllum tenax. Less frequent or absence of fire creates mixed-dominance stands with often shrubby undergrowth; Vaccinium cespitosum is common, and taller shrubs can include Acer glabrum, Ceanothus velutinus, Shepherdia canadensis, Physocarpus malvaceus, Rubus parviflorus, or Vaccinium membranaceum. Fire suppression has led to invasion of the more shade-tolerant tree species Abies grandis, Abies lasiocarpa, Picea engelmannii, or Tsuga spp. and loss of much of the single-story canopy woodlands.

Source: NatureServe Explorer

Dynamics

Larix occidentalis is a long-lived species (in excess of 700 years in the northern Rocky Mountains), and thus stands fitting this concept are themselves long-persisting; the life of Larix-dominated stands probably does not much exceed 250 years due to various mortality sources and the ingrowth of shade-tolerant species. Occurrences of this ecological system are generated by stand-replacing fire, the fire-return interval for which is speculated to be on the order of 80 to 200 years. These sites may be maintained in a seral status for hundreds of years due to the fact that Larix occidentalis is a long-lived species and the understory is often dominated by Pseudotsuga, which will grow into the upper canopy. The potential dominants Abies lasiocarpa, Picea engelmannii, or Abies grandis are slow to establish on these sites and grow slowly presenting the distinct probability, given the fire-return intervals for this type, that the "climax" (long-term stable) condition is never realized.

It has been noted in northern Idaho that, following disturbance (particularly logging) in some mesic-site occurrences, Larix occidentalis does not necessarily succeed itself, the first tree-dominated successional stages being dominated by Pseudotsuga menziesii, Pinus contorta, or less frequently by more shade-tolerant species (Cooper et al. 1987); this response is a consequence of the episodic nature of favorable cone crop years in Larix occidentalis.

Landfire VDDT models: #RMCONm and #RMCONdy classes B, C, & D.

Source: NatureServe Explorer

Distribution

Source: NatureServe Explorer

Ecologically Associated Plant Species

Plant species that characterize this ecosystem type, organized by vegetation stratum. These are species ecologically associated with the ecosystem, not confirmed present in any specific area.

Tree canopy

Abies grandis, Abies lasiocarpa, Larix occidentalis, Picea engelmannii

Shrub/sapling (tall & short)

Acer glabrum, Ceanothus velutinus, Physocarpus malvaceus, Rubus parviflorus, Shepherdia canadensis, Spiraea betulifolia, Vaccinium caespitosum, Vaccinium membranaceum

Short shrub/sapling

Arctostaphylos uva-ursi, Linnaea borealis

Herb (field)

Calamagrostis rubescens, Chaenactis thompsonii, Silene seelyi, Valeriana columbiana, Xerophyllum tenax

Source: NatureServe Ecological System assessment

Ecologically Associated Animals (2)

Animal species ecologically associated with this ecosystem type based on NatureServe assessment. These are species whose habitat requirements overlap with this ecosystem, not confirmed present in any specific roadless area.

Mammals (2)

Common Name	Scientific Name	G-Rank
Snowshoe Hare	Lepus americanus	G5
Yellow-bellied Marmot	Marmota flaviventris	G5

Source: NatureServe Ecological System assessment

At-Risk Species Associated with this Ecosystem (3)

Species with conservation concern that are ecologically associated with this ecosystem type. G-Rank indicates global conservation status: G1 (critically imperiled) through G5 (secure). ESA status indicates U.S. Endangered Species Act listing.

Common Name	Scientific Name	G-Rank	ESA Status
Thompson's Pincushion	Chaenactis thompsonii	G3	--
Seely's Silene	Silene seelyi	G3	--
Wenatchee Valerian	Valeriana columbiana	G2G3	--

Source: NatureServe Ecological System assessment

Component Associations (4)

Plant community associations that occur within this ecological system. Associations are the finest level of the U.S. National Vegetation Classification (USNVC) and describe specific, repeating assemblages of plant species. Each association represents a distinct community type that may be found where this ecosystem occurs.

Name	G-Rank
Larix occidentalis / Clintonia uniflora Forest	GNR	NatureServe
Larix occidentalis / Clintonia uniflora - Xerophyllum tenax Forest	GNR	NatureServe
Larix occidentalis / Vaccinium cespitosum / Clintonia uniflora Forest	GNR	NatureServe
Larix occidentalis / Vaccinium cespitosum Forest	GNR	NatureServe

State Conservation Ranks (4)

Subnational conservation status ranks (S-ranks) assigned by Natural Heritage Programs in each state where this ecosystem occurs. S1 indicates critically imperiled at the state level, S2 imperiled, S3 vulnerable, S4 apparently secure, and S5 secure. An ecosystem may be globally secure but imperiled in specific states at the edge of its range.

State	S-Rank
ID	SNR
MT	SNR
OR	SNR
WA	SNR

Roadless Areas (15)

Inventoried Roadless Areas where this ecosystem is present, identified from LANDFIRE 2024 Existing Vegetation Type spatial analysis. Coverage indicates the proportion of each area occupied by this ecosystem type.

Montana (9)

Area	Forest	Coverage	Hectares
North Siegel	Lolo National Forest	1.5%	56.61
Patricks Knob - North Cutoff	Lolo National Forest	1.1%	76.14
Gold Hill #668	Kootenai National Forest	1.1%	28.35
Mt. Hefty Ra 1481	Flathead National Forest	1.0%	51.93
Galena #677	Kootenai National Forest	0.7%	53.01
Roderick #684	Kootenai National Forest	0.6%	75.15
Bmss Ra 1485	Flathead National Forest	0.6%	751.59
Trout Creek	Kootenai National Forest	0.5%	65.79
Bear - Marshall - Scapegoat - Swan	Lewis and Clark National Forest	0.2%	286.38

Washington (6)

Area	Forest	Coverage	Hectares
South Ridge	Okanogan National Forest	8.0%	198.27
Tiffany	Okanogan National Forest	4.8%	430.11
Granite Mountain	Okanogan National Forest	3.8%	425.7
Hungry Ridge	Okanogan National Forest	1.4%	49.23
Abercrombie - Hooknose	Colville National Forest	0.7%	94.23
Profanity	Colville National Forest	0.6%	68.76

Methodology and Data Sources

Ecosystem classification: Ecosystems are classified using the LANDFIRE 2024 Existing Vegetation Type (EVT) layer, mapped to NatureServe Terrestrial Ecological Systems via a curated crosswalk. Each EVT is linked to the USNVC (U.S. National Vegetation Classification) hierarchy through pixel-level co-occurrence analysis of LANDFIRE EVT and NatureServe IVC Group rasters across all roadless areas.

Vegetation coverage: Coverage percentages and hectares are derived from zonal statistics of the LANDFIRE 2024 EVT raster intersected with roadless area boundaries.

Ecosystem narratives and community species: Sourced from the NatureServe Explorer API, representing professional ecological assessments of vegetation composition, environmental setting, dynamics, threats, and characteristic species assemblages.

IVC hierarchy: The International Vegetation Classification hierarchy is sourced from the USNVC v3.0 Catalog, providing the full classification from Biome through Association levels.

Component associations: Plant community associations listed as components of each NatureServe Ecological System. Association data from the NatureServe Explorer API.

State ranks: Conservation status ranks assigned by NatureServe member programs in each state where the ecosystem occurs.