White spruce (Sw; Picea glauca) and Engelmann spruce (Se; Picea engelmannii) are economically important tree species in British Columbia. The complex of these two species and their hybrids (Sxw) (Picea glauca x engelmannii) are collectively managed as ‘interior spruce’ (abbreviated as Sx). The CCISS model predicts a decline or loss of suitability throughout much of the historic range of Sx under future climate warming. There is some opportunity for the expansion of Sx’s suitable range at higher elevation and further north.
While the CCISS tool offers valuable insights into broad-scale trends, summarized here by species, suitability projections must be interpreted with caution. Many areas of projected change are also areas with high uncertainty in climate predictions. Furthermore, factors such as soil texture, drainage, land-use history, forest health pressures, and biotic interactions (e.g., competition or browsing) can strongly influence actual outcomes on the ground. These nuances emphasize the importance of pairing climate tools with on-the-ground knowledge and site-specific judgement when planning future management.
Interior spruce (abbreviated as Sx) refers to white spruce (Sw), Engelmann spruce (Se) and their hybrids (Sxw; Picea glauca x engelmannii), which are very common throughout the interior of BC. These analyses and figures include Sw, Se and Sxw. Sx is found throughout BC, excluding the coast. White spruce and Engelmann spruce occupy different ecological niches separated primarily by elevation (De La Torre et al., 2014).
Se is most abundant in the subalpine region, in the Engelmann Spruce–Subalpine Fir (ESSF) zone. Se has relatively low tolerance of high temperatures and drought, but can withstand short growing seasons and high snowfall (Alexander & Shepperd, 1990). Whereas, Sw is primarily a boreal species, found most commonly in the Spruce–Willow–Birch (SWB), Boreal Black and White Spruce (BWBS), and Sub-Boreal Spruce (SBS) zones. Sw grows under highly variable conditions and can tolerate both low winter temperatures and summer drought, but is restricted to low elevations. The ranges of Se and Sw overlap in BC, hybrids are common and cannot be easily distinguished from the parent species. Hybrids occupy ecological and elevational niches intermediate to those of the parental species (De La Torre et al., 2014). Se is most abundant in the southern half of the province and Sw is most abundant in the northern half, with the highest frequency of hybrids in the central latitudes (Nocchi et al., 2025).
Sx is adapted to a wide range of edaphic and climatic conditions. The climatic amplitude of Sx spans cool temperate to subarctic, with Se frequently forming part of the alpine treeline and Sw forming part of the arctic treeline (Engelmann Spruce, 2025; White Spruce, 2025). Sx grows best on slightly dry to very moist and poor to very rich sites, with Sw preferring richer sites than Se (Engelmann Spruce, 2025; White Spruce, 2025).
In BC, Sx is most commonly found in mixed-species stands (Engelmann Spruce, 2025; White Spruce, 2025). Se is most frequently found alongside subalpine fir and lodgepole pine (Engelmann Spruce, 2025). Sw is found alongside trembling aspen, lodgepole pine, black spruce, subalpine fir, balsam poplar, black cottonwood, and paper birch (White Spruce, 2025). In the boreal forest (BWBS zone) wildfires are a major disturbance factor in re-establishing a Sw stand. Without fire, black spruce, which is more shade tolerant, would become the dominant species (White Spruce, 2025).
Species environmental suitability during the reference period (1961–1990)In the maps below, each colour represents the species environmental suitability during the historical reference period* of 1961–90 as determined by expert ratings. Green represents a high suitability (E1 rating), blue represents moderate suitability (E2), yellow represents low suitability (E3), and white indicates areas that are unsuitable for the species. See CCISS Documentation tab > Methods > Environmental Suitability Ratings for more detailed definitions and information on the expert rating process.
*Notes on terminology: 1) The historical reference period is sometimes referred to as the “baseline” or simply “historical” or “reference” period. 2) Edatope refers to the combination of relative soil nutrient regime and soil moisture regime at a given site which align with distinct site series in a given biogeoclimatic unit. Here we provide three of the possible edatopes as examples: the B2 edatope representing nutrient-poor and relatively dry (subxeric) sites; the C4 edatope representing nutrient-medium and moisture-average (mesic) sites; and the D6 edatope representing nutrient-rich and relatively moist (hygric) sites.
The pie chart to the right depicts the distribution of the total environmentally suitable area for Sx in BC by biogeoclimatic (BGC) zone, based on the climate of the historical reference period (1961–1990).
Sx is most abundant in the Boreal White and Black Spruce (BWBS) zone in the northeast of the province, where Sw and aspen forests are common. Sw and balsam popular stands are also found on richer well-drained sites along rivers (Forest Conservation Genetics, n.d.).
Sx is abundant in the Engelmann Spruce–Subalpine Fir (ESSF) zone, dominated by Se (Sw and Sx are also present). In old growth stands at low to mid-elevations, Se usually dominates the canopy and subalpine fir the understory (Forest Conservation Genetics, n.d.).
Hyrbid spruce (Sxw) is a major species in the Sub-Boreal Spruce (SBS) zone, common in old-growth stands alongside subalpine fir (Forest Conservation Genetics, n.d.).
In the Spruce–Willow–Birch (SWB) zone, Sw is the most common species, alongside subalpine fir.
Sx makes up a smaller component of the Interior Cedar–Hemlock (ICH) zone (including Se, Sw and Sxw).
In the Montane Spruce (MS) zone Sx occurs as a minor component of the canopy of older stands on wetter sites or wetter subzones, more prevalent on cool-aspect or seepage sites (Forest Conservation Genetics, n.d.).
Sx is also found on wetter cooler sites of the Interior Douglas-fir (IDF) zone and upper elevation subzones, on wetter sites of the Sub-Boreal Pine–Spruce (SBPS) zone, in northern and upper submaritime subzones of the Coastal Western Hemlock (CWH) zone, and Sx is a minor component of the Mountain Hemlock (MH) zone.