Common (Translated Scientific) Name: Boreal Forest & Woodland Formation
Colloquial Name: Boreal Forest & Woodland
Hierarchy Level: Formation
Type Concept: Boreal Forest & Woodland (or taiga) extends across the northern regions of North America and Eurasia, with extended cold winters and short mild summers. It is bounded on the north by tundra and on the south by either the northern limit of temperate lowland and subalpine forests or grasslands (steppes). A number of ecological factors, including topography, climate and edaphic conditions, control Boreal Forest & Woodland distribution. It is dominated by needle-leaved (usually evergreen, conical-shaped) conifers, and broad-leaved deciduous hardwoods. Lichens and mosses often dominate the ground layer. The structure of Boreal Forest & Woodland varies from closed forest to lichen woodland and forest-tundra. Closed forests dominate the southern boreal zone; lichen woodlands dominate the northern regions; and isolated forest-tundra patches occur in the tundra zone near or just above treeline. Boreal forests are disturbance-based, with fires the primary disturbance.
Diagnostic Characteristics: Boreal Forest & Woodland is dominated by needle-leaved (usually evergreen, conical-shaped) conifers, and broad-leaved deciduous hardwoods, with extended cold winters and short mild summers. Tree height rarely exceeds 15 m, and may be as low as 2 m in subarctic conditions. Lichens and mosses frequently dominate the ground layer.
Rationale for Nominal Species or Physiognomic Features:
Classification Comments: The Braun-Blanquet approach generally recognizes the Vaccinio-Piceetea class of vegetation as synonymous with Eurasian and North American boreal and sub-boreal coniferous forests, including both upland boreal forests and forested swamps (Peinado et al. 1998, Spribille and Chytrý 2002, Kolbek et al. 2003); however, Rivas-Martinez et al. (1999b) separated the North American Boreal Forest & Woodland into a separate class, distinct from both European boreal forests and western temperate forests.
Various ecoregional treatments recognize the distinct vegetation and climate of the boreal region, compared to the temperate region. Brown et al. (1998) separates arctic-boreal from both cool-temperate and warm-temperate vegetation. Walter (1985) recognizes the boreal biome "Zonobiome of the Cold-temperate Boreal Climate" (Zone VIII), distinct from the cool-temperate biome "Zonobiome of the Temperate-Nemoral Climate" (Zone VI) and two warm-temperate biomes, the "Zonobiome of the Winter-Rain Region with an Arid-Humid Climate and Sclerophyllic Woodlands" (Zone IV) and the "Zonobiome of the Warm-Temperate Humid Climate" (Zone V).
Some authors extend the North American Boreal Forest & Woodland southward into the southern Rocky Mountains and/or Appalachian Mountains (e.g., Whittaker 1975, Brown et al. 1998, Kuennecke 2008), primarily because of the spruce-fir zones that occur in those ranges. But the more temperate climate, increasingly diverse conifer and hardwood growth forms, biogeographic patterns and distinctive species suggest that they can satisfactorily be placed in a temperate formation, where they extend up to the treeline in the subalpine regions [see also Rivas-Martinez et al. (1999b)]. However, biogeographic comparisons across larger regions, including biome or formation scales, and which can be done at the genus level and above (e.g., McLaughlin 2007), suggest a greater similarity of high-elevation Engelmann spruce-fir in the Rocky Mountains with that of the boreal. But similarities are less strong in the eastern deciduous region, where red spruce-fir forests share more species with the eastern temperate region. Chris Lea (pers. comm. 2012) notes that there are a number of subdominant species common to North American high montane/subalpine forests, North American boreal forests, and Eurasian boreal forests (a number of Vaccinium spp., Linnaea borealis, Carex aquatilis, Carex utriculata, etc.), and at least one dominant tree species (Populus tremuloides) that is common to North American high montane/subalpine and North American boreal forests. Additionally, many fauna species (lynx, pine marten, pine grosbeak, golden-crowned kinglet, crossbills, etc.) show similar species distribution patterns. But many of these species also have considerable overlap in the temperate zone. We will continue to review this issue with North American and Eurasian colleagues.
Similar NVC Types:
F036 Boreal Flooded & Swamp Forest, note:
F008 Cool Temperate Forest & Woodland, note:
CFO02 Forest Plantation & Agroforestry, note: Long-rotation plantations or woody restoration plantings of 1.B.4 ~Boreal Forest & Woodland Formation (F001)$$ with an irregular structure and a largely spontaneous ground layer may initially be similar in their early stages of development, especially if planted in rows and the understory is strongly manipulated.
Physiognomy and Structure: Boreal Forest & Woodland is dominated by needle-leaved (usually evergreen, conical-shaped) conifers, and broad-leaved deciduous hardwoods. Lichens and mosses often dominate the ground layer. The structure of Boreal Forest & Woodland varies from closed forest to lichen woodland and forest-tundra. Closed forests dominate the southern boreal zone; lichen woodlands dominate the northern regions; and isolated forest-tundra patches occur in the tundra zone near or just above treeline (Elliott-Fisk 2000). Boreal forests are a disturbance-based forest, with fires and insect outbreaks as primary disturbances. Tree species diversity is very low. Evergreen spruce (Picea), fir (Abies), and deciduous larch (Larix) are common, distinctive genera, as are broad-leaved deciduous aspen (Populus) and birch (Betula) (Whittaker 1975).
Dynamics: Ecologically, the boreal landscape is relatively young. For example, in North America, as recently as 21,400 calendar years ago at the peak of the Wisconsin glaciation, the entire boreal zone was covered with ice, excluding parts of the Yukon Territory, the Northwest Territories, and Alaska. With the melting of the glaciers over the next 15,000-16,000 years, the current tree species migrated northward from refugia south of the ice margin (Brandt 2009).
Environmental Description: According to Brandt (2009), the boreal zone's northern boundary in both North America and Eurasia is generally the southern limit of the tundra; its southern boundary generally coincides with the northern limit of temperate forests, or grasslands (steppes).
Climate: There are lengthy periods of freezing temperatures with the coldest month isotherm of -3°C, and the growing season generally averaging less than 100 days, occasionally interrupted by nights of below-freezing temperatures. Snow may be present for extended periods (7-10 months) and soils are typically frozen in winter. Annual precipitation is 38-50 cm (15-20 inches). In North America, the northern boundary of the forest corresponds to the July isotherm of 13°C, with departures due to montane or maritime influences (Elliott-Fisk 2000). The southern boundary in central and eastern Canada corresponds approximately with the 18°C July isotherm, but in the west the forest border shifts to slightly cooler regions with higher precipitation (Elliott-Fisk 2000). These broad-scale climatic factors are modified by local and regional topography, climates and soils.
Brandt (2009, and Table 2 therein) characterizes the limits of boreal forests based on their dominance by "cold-tolerant" trees species, i.e., tolerant of temperatures of -80°C or lower (primarily within Abies, Larix, Picea, or Pinus but also Populus and Betula). Temperate forests are characterized by "cold-intolerant" species, i.e., they require temperatures above -45°C to survive. A number of temperate species have "intermediate cold-tolerance," common to the cool-temperate forest. Regions of the landscape where both species co-occur is sometimes referred to as the "hemiboreal subzone," that is, the northern parts of the cool-temperate zone where cold-intolerant tree species, cold-tolerant tree species, and species with intermediate cold-tolerance co-occur, and with the cold-tolerant species contributing substantially to the forest cover. Brandt's information provides the cold-tolerance limits of these species, but equally valuable in understanding the temperate versus boreal distinction would be the warm-tolerance limits. For example, in North America, Picea mariana appears to be less warm-tolerant than Pinus banksiana, but both have the same cold tolerance.
Soil/substrate/hydrology: Most boreal soils were subject to extensive glaciations (excluding parts of the Yukon Territory, the Northwest Territories, and Alaska). Soils are somewhat poorly to excessively drained. They are the result of podzolization, which is a consequence of low temperatures and excess precipitation above that of evapotranspiration. Soils often contain a sandy ash-colored A horizon, with an accumulation of iron and aluminum with organic matter in the B horizon. Soils are generally of low fertility, as nutrients are also removed from the upper horizons. With the low temperatures, organic matter decomposes slowly, resulting in acidic soil conditions and low nitrogen and mineral levels (Elliott-Fisk 2000, Kuennecke 2008). Permafrost is absent or typically occurs <100 cm below the surface in the Boreal Forest & Woodland zone. Spodosols are most common; Inceptisols, Histosols, and Entisols occasional (Soil Survey Staff 1999) [see Brady and Weil (2002) for a comparison of U.S. soil orders with Canadian and FAO systems].
Geographic Range: Boreal Forest & Woodland is found in North America from Greenland to Newfoundland and across northern Canada into Alaska, and in Eurasia, throughout most of Scandinavia and Russia, and parts of China, Kazakhstan, and Mongolia (Brandt 2009). It is absent from the Southern Hemisphere.
Nations: CA, US
Confidence Level: Moderate
Confidence Level Comments:
Synonomy: = Linnaeo americanae-Piceetea marianae (Rivas-Martínez et al. 1999b) [The concept of Boreal Forest & Woodland as applied within North America closely corresponds to the concept here. The authors also appear to be the first in the Braun-Blanquet tradition to recognize a distinct North American Boreal Forest & Woodland class.]
< Vaccinio-Piceetea (Peinado et al. 1998) [The authors discuss the full diagnostic floristic composition of boreal forests across the Northern Hemisphere, and then focus on North America. They extend the Boreal Forest & Woodland further south (into the temperate-montane and cool-temperate regions of western and eastern North America) than the concept provided here.]
< Boreal Forest & Woodland Biome (Kuennecke 2008) [The author provides a general introduction to the entire boreal forest, but in North America extends the concept into the Southern Rockies and Appalachian Mountains.]
= Taiga and Boreal Forest & Woodland (Elliott-Fisk 2000) [The treatment is restricted to North America.]
< Taiga or Subarctic - Subalpine needle-leaved forests: biome-type 6 (Whittaker 1975) [Whittaker combines the subalpine forests of the temperate region with boreal forests.]
Concept Author(s): Hierarchy Revisions Working Group, Federal Geographic Data Committee (Faber-Langendoen et al. 2014)
Author of Description: D. Faber-Langendoen
Acknowledgements: Ken Baldwin, Chris Lea
Version Date: 17Oct2014
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