Tundra Vegetation 101

Tundra Vegetation

Table of Contents

Tundra Vegetation: A Tundra, is a major zone of treeless level or rolling ground found in cold regions, mostly north of the Arctic Circle (Arctic tundra) or above the timberline on high mountains (alpine tundra). Tundra is known for large stretches of bare ground and rock and for patchy mantles of low vegetation such as mosses, lichens, herbs, and small shrubs. This surface supports a meagre but unique variety of animals. The Finns called their treeless northern reaches the tunturi, but the concept of a vast frozen plain as a special ecological realm called tundra was developed by the Russians.

According to NASA, the tundra vegetation is the coldest of the biomes. It also receives low amounts of precipitation, making the tundra similar to a desert. Tundra is found in the regions just below the ice caps of the Arctic, extending across North America, to Europe, and Siberia in Asia. Much of Alaska and about half of Canada are in the tundra biome. Tundra is also found at the tops of very high mountains elsewhere in the world. Temperatures are frequently extremely cold, but can get warm in the summers.

Tundra winters are long, dark, and cold, with mean temperatures below 0°C for six to 10 months of the year. The temperatures are so cold that there is a layer of permanently frozen ground below the surface, called permafrost. This permafrost is a defining characteristic of the tundra biome. In the tundra summers, the top layer of soil thaws only a few inches down, providing a growing surface for the roots of vegetation.

Precipitation in the tundra totals 150 to 250 mm a year, including melted snow. That’s less than most of the world’s greatest deserts! Still, the tundra is usually a wet place because the low temperatures cause evaporation of water to be slow. Much of the arctic has rain and fog in the summers, and water gathers in bogs and ponds.

Vegetation in the tundra has adapted to the cold and the short growing season. Mosses, sedges, and lichens are common, while few trees grow in the tundra. The trees that do manage to grow stay close to the ground so they are insulated by snow during the cold winters.

Growthforms: typical are ground-hugging and other warmth-preserving forms including:

  • tussock-forming graminoids
  • mats or cushion plants, often evergreen members of the heath family
  • rosettes
  • dwarf shrubs, some of which are deciduous in habit

Climate: The high latitude conditions of Koeppen’s ET climate type that impact life in this biome include

  • extremely short growing season (6 to 10 weeks)
  • long, cold, dark winters (6 to 10 months with mean monthly temperatures below 32° F or
    0° C.)
  • low precipitation (less than five inches/year) coupled with strong, drying winds. Snowfall is actually advantageous to plant and animal life as it provides an insulating layer on the ground surface.

Edaphic controls: Permafrost, not cold temperatures per se, is generally believed to be what prevents tree growth. Furthermore, freeze-thaw activity, a thin active layer, and solifluction during the warmer months contribute to strong controls on vegetation patterns and create a mosaic of microhabitats and plant communities.

Soil: No true soil is developed in this biome due to the edaphic factors mentioned above.

Fauna: Strategies evolved to withstand the harsh conditions of the tundra can be divided among those species that are resident and those that are migratory.

According to Wikipedia, tundra (/ˈtʌndrə, ˈtʊn-/) is a type of biome where the tree growth is hindered by low temperatures and short growing seasons. The term tundra comes through Russian тундра (tundra) from the Kildin Sámi word тӯндар (tūndâr) meaning “uplands”, “treeless mountain tract”. Tundra vegetation is composed of dwarf shrubs, sedges and grasses, mosses, and lichens. Scattered trees grow in some tundra regions. The ecotone (or ecological boundary region) between the tundra and the forest is known as the tree line or timberline. The tundra soil is rich in nitrogen and phosphorus.

There are three regions and associated types of tundra: Arctic tundra, alpine tundra, and Antarctic tundra.

According to The Royal Society, Herbivores are known to be important components of Arctic ecosystems, and many species like the large reindeer and caribou herds, and high densities of voles and lemmings during peak years, are well known to exert large effects on the ecosystems when they feed on the plants and serve as food for predators. Despite their importance, the diversity of herbivores is low in the Arctic. About 50 species of mammalian herbivores are found in the Arctic as a whole, and most regions have a local species richness of mammalian herbivores below 10. Most of these herbivores are small- or medium-sized rodents, and only six large mammalian herbivores occur in the Arctic. Four of these six herbivores have narrow distributional ranges and are only found in marginally Arctic habitats (moose, Dall’s sheep, Siberian bighorn sheep and American bison). This means that the only two large herbivores with wide distributional ranges are caribou/reindeer (Rangifer tarandus; hereafter ‘caribou’, unless used in reference to the domestic or semi-domestic sub-species) and muskoxen (Ovibos moschatus). The species richness of large herbivores in the Arctic thus varies between 0 and 2 species in most Arctic regions. The most widespread of the two herbivores, caribou, are also domesticated in many of these regions. We will here explore how this low species richness of large herbivores influences the vulnerability of arctic ecosystems to climate change, especially warming. We also discuss implications of the fact that only domesticated herbivores exist in many parts of the Arctic.

Tundra Vegetation: Selected Excerpts from Scientific Articles

Tundra ecosystems are found in the arctic and on alpine zones of mountains. Arctic tundra is relatively homogeneous and with low biodiversity due to its recent glacial history, while alpine tundra is much more diverse and with higher biodiversity mostly because of its fragmentation on isolated mountains. Tundra is part of the periglacial environment, affected by past ice ages, permafrost and current freeze–thaw cycles. This has a major effect on the ecology of the tundra. Both plants and animals show adaptations to extreme cold, short-growing seasons, and other aspects of the tundra climate and geomorphology. The lemming cycles are the dominant biological phenomenon, affecting all other species, the vegetation, and other aspects of the tundra ecology. Some special cases of high levels of adaptation are presented. The history of the tundra shows frequent changes, and more change can confidently be predicted for the future, to a large degree, as the result of anthropogenic effects. (R. Harmsen, 2008)

Tundra ecosystems are dominated by perennial grasses, forbs, shrubs, and biological soil crusts consisting of cyanobacteria, lichens, and mosses (Figure 1). These species can tolerate the climatic conditions of high latitudes or altitudes. Tundra ecosystems are generally set apart from forested ecosystems by a climatic tree line defined by the 10 °C isotherm for the mean temperature of the warmest month. Tundra plants are low in stature with growth buds near the soil surface, where temperature is less variable. The morphology of herbaceous plants are often cushion or rosette growth forms and lichens are usually a foliose form. Shrubs are low-growing with short internodes between leaves. Temperate alpine tundra communities have short growing seasons similar to those in arctic tundra. In contrast, tropical alpine tundra communities of Africa, South America, and Oceania exist in conditions of freezing or near-freezing temperatures each night, with daytime temperatures allowing for active plant growth throughout the year.

The important herbivores of the Arctic are rodents and ungulates. Lemmings (Dicrostonyx spp. and Lemmus spp.) can have great impacts on arctic ecosystems during years of high population densities. Lemmings exhibit different seasonal patterns of use within various parts of their habitats. During the winter, they use wetlands and graze the soil-level parts of plants while discarding the upper portions of the plants. This grazing pattern results in piles of graminoid litter known as lemming hay. During spring, lemmings move to south-facing slopes, where solar insolation results in the earliest available green biomass. During peak population cycles when densities are high, lemmings can consume between 20 and 70% of the available plant mass.

The dominant native ungulates in the Arctic include caribou or reindeer (Rangifer tarandus) and musk ox (Ovibos moschatos). Domestication of reindeer and musk ox has led to their introduction throughout the arctic tundra and to reindeer introduction into northern Antarctica. Alpine tundra provides seasonal habitat for wild ungulates, including elk, deer, red deer, mountain sheep, and mountain goats. Domestic livestock breeds adapted to cooler environments are also present in various arctic or alpine tundra communities of the world (e.g., cattle, sheep, goats, horses, llamas, and yak). (J. Boone Kauffman, David A. Pyke, 2001)

The boreal tundra woodland ecological zone (10 million km2), which is about one-half forested, spans a range of woody plant densities from shrub tundra to woodland. This GEZ has received much attention for SOC vulnerability to permafrost thaw due to warmer soil temperatures, longer mineralization seasons, and feedbacks involving wildfires and hydrology (Hobbie et al., 2000; O’Donnell et al., 2011; Wilmking et al., 2006). As forests expand into tundra during permafrost thaw, detrital inputs to soil may increase, but changes in SOC may occur in either direction (Hartley et al., 2012; Parker et al., 2015; Steltzer, 2004). In contrast to this ambiguity, it is clear that N inputs have positive effects on SOC. In northern Europe, where a larger fraction of boreal tundra woodlands are managed or subject to atmospheric N deposition, N inputs can improve tree growth for economic purposes, while increasing detritus inputs, slowing decomposition, and increasing C storage in O-horizons (Berg, 2000; Hyvonen et al., 2007; Makipaa, 1995; Prescott, 2010). If active management follows forest expansion into this GEZ, it is likely possible to increase SOC storage through N-fertilization. However, C accumulation in surface detritus and litter is not without risk; these materials are fuels and fire management will therefore be critical to realize the potential C gains associated with fertilization.

The most widespread soils in the boreal tundra woodland are Cambisols, Cryosols, and Histosols, where the SOC densities of these widely distributed soils are 10%–30% higher than boreal coniferous forests and 70%–130% than temperate continental forests (Table 11.2). Superficially, these three soils are quite distinct (Table 11.1), but in boreal landscapes they often inter-grade based on their depth to permafrost and amounts of organic versus mineral materials. The presence of mineral soil materials is a critical factor for SOC management in these soils because it can determine whether SOC that was previously frozen or saturated has secondary stability via clay minerals, Al and Fe hydroxides, or Ca bridging (Table 11.12; Tarnocai and Bockheim, 2011; Shaw et al., 2008). In many cases, physical changes due to warming and drying (e.g., drainage, subsidence) can be sufficient to shift soils currently classified as Cryosols or Histosols to Cambisols, the latter of which are frequent associates on warmer, drier, or higher topographic positions in Cryosol or Histosol-dominated landscapes. The extensive area of Cambisols in this GEZ indicates the very wide range of parent materials, landforms, vegetation types, and SOC stocks associated with these soils, highlighting the difficulty of generalizing at broad scales. In ecoregions, landscapes, or landforms where Cambisols are reasonably accessible, freely drained, and capable of supporting forest, they afford the widest latitude in SOC management options because of their physical characteristics. Because their limited degree of development in many places results from low vegetation productivity and short thaw seasons, practices that increase forest stocking and production rates (e.g., supplemental planting, fertilization) on climatically favorable sites may in the long run lead to SOC gains as detrital inputs accumulate and pedogenesis advances. The very high SOC densities of Histosols in the boreal tundra woodland (nearly double those of Cryosols) reflects the difficulty of constraining their distribution and depth (Hugelius et al., 2014), but suggests that thawing alone does not mean the release of all C held in Cryosols. (Luke Nave, … Chris Swanston, 2019)

Polar ecosystems, generally called tundra (tundra vegetation), occur across the northern coastal plain of Eurasia but also in both upland and high-mountain situations, such as the lower mountains of boreal northeastern Siberia and the high Tibetan Plateau. Upland tundra in the boreal zone represents the first upward vegetation belt and is thus commonly called montane tundra. In high mountains, tundra-like ecosystems occur above the alpine treeline and are generally called alpine tundra. In all three situations, these are treeless landscapes dominated by mosaics of the following basic associations:

1. Largely evergreen, microphyllous dwarf-scrub on locally somewhat higher, drier areas
2. Wet graminoid vegetation in the lowest areas, generally flat, marshy depressions
3. Mixes of evergreen and summergreen plants, herbaceous and dwarf-shrub, including minigeophytes, on the broad, slight slopes between the higher and lower areas
4. Mainly mosses and lichens on the most extreme areas, including the coldest but also the most exposed upland areas where little snow remains

In mountains, two additional types can be identified. One is the “snow valleys” (Schneetalchen), depressions with deep snow accumulations which have shorter snow-free seasons and specialized floras composed of plants which can complete their life cycles in periods as short as one month in summer. The other is the extensive alpine mats, often dominated by Kobresia, found in drier high-mountain areas such as the Tien Shan, Hindu Kush, and Tibetan highlands, generally above 3000 m.

The polar tundra extends from extreme northern Fennoscandia across northern Russia to coastal northeastern Siberia in a narrow strip which is widest on the Taimyr peninsula. Due to continentality effects, however, the Taimyr is also the area where boreal forest extends farthest north, reaching about 72.5°N (as larch forest) north of Khatanga. On the flat coastal topography, herbaceous tundra is perhaps most extensive. The polar tundra can be represented zonally, however, in four subzones from south to north:

    1. The transitional forest-tundra of largely dwarf-shrub tundra with scattered but still tall individual conifers (mainly larches in the east and spruces in the west)2. Dwarf-shrub tundra, dominated largely by shrub forms from summergreen tree genera, mainly
    , and 
    3. Largely herbaceous tundra with few dwarf-shrubs but still a continuous vegetation cover including many mosses and lichens4. The discontinuous High Arctic cold-desert with vegetation restricted to more scattered individuals of a few vascular plants (especially 
     spp.) and various lichens and mosses

The forest-tundra vegetation and dwarf–shrub tundra zones of the lowlands are better represented in western Siberia, but montane analogs are fairly widespread in the lower mountain areas east of the Lena River in eastern Siberia. Cold-desert, on the other hand, is a bit more widespread in the east and on the Arctic islands.

Two other prominent features of the polar zone are the prevalence of permafrost and substrates divided into stone polygons by frost action. Permafrost occurs where mean annual temperatures are below 0°C, i.e., north of about 62°N continuously and discontinuously in uplands further south. Polygon substrates (and other features such as pingos) occur where seasonal freezing and thawing of “soil” which is largely water forces the larger solids (i.e., rocks) to the surface in a slow, bubble-like fashion that distributes them into polygons which become connected into polygon networks. The interiors of the polygons are lower, flat, and wetter, whereas the rocky borders, only 10–20 cm higher, represent drier biotopes.

Polar tundra in particular (including boreal montane tundra) involves many taxa with circumpolar distributions, including genera such as Carex, cotton grass (Eriophorum), and other sedges; many ericads (e.g., VacciniumArctostaphylos, and Cassiope); other forbs, such as Dryas; and both evergreen dwarf-shrubs (e.g., Empetrum) and sometimes taller deciduous dwarf-shrubs (e.g., BetulaSalix, and Alnus). For nonvascular plants, an even larger percentage of the taxa are circumpolar, including mosses such as SphagnumPolytrichum, and Hylocomnium, and lichens such as Cladonia and Cladina. As in the boreal zone, the flora of eastern polar Siberia is richer than that of western Siberia due to its lack of Pleistocene glaciation.

Most of the same genera, of vascular and nonvascular plants, also occur in the high-mountain tundra. Alpine treeline in mountains of northern Asia is commonly formed by Ppumila krummholz, whereas the alpine tundra typically involves familiar heath taxa such as EmpetrumPhyllodoceCassiope, and Dryas as well as dwarf Salix and sedges. In general, however, alpine tundra vegetation is more species rich than is corresponding polar tundra, perhaps due to the lack of permafrost and the greater number of microhabitats in the more heterogeneous terrain of high mountains. Many more localized species usually occur. Some important genera of Asian high mountains which are not important (if present at all) in polar tundra include GeumGentiana, and Leontopodium.

Despite its relatively low productivity, the polar tundra vegetation supports many animal species and in surprisingly large numbers, at least in summer. Caribou (reindeer) winter in the boreal zone and migrate to the tundra during the summer. Birds migrate from much greater distances away, some from as far as tropical Asia. Other birds, such as ptarmigan, overwinter near the polar zone. Mammals such as polar bears and some small rodents (e.g., lemmings) also live year-round in the polar zone. (Elgene O. Box, Kazue Fujiwara, 2001)

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