Ecology of a steppe‐tundra gradient in interior Alaska

Abstract

Abstract. Subarctic steppe is currently restricted in interior Alaska and the Yukon Territory to steep, south‐facing river bluffs. Paleoecological and biogeographic evidence suggests that some steppe taxa may have been more widespread during the Full‐Glacial. We examined factors controlling the distribution of steppe taxa on an elevation gradient across a steppetundra ecotone; such analyses may help define potential Full‐Glacial distributions of these taxa. Multivariate analyses suggest that species can be divided into four spatially distinct groups, but individualistic species distributions create considerable overlap among these groups. The steppe‐tundra ecotone comprises a broad zone of mixing between steppe taxa and drought‐tolerant alpine tundra taxa, followed by an abrupt shift to alpine shrub tundra. The transition from low steppe to tundra vegetation is primarily associated with a gradient of decreasing soil temperature. The more abrupt transition from mixed steppe‐tundra to alpine shrub tundra vegetation is primarily associated with changes in soil depth and soil moisture. Variation in vegetation within steppe is associated with gradients in soil phosphorus and moisture. Greenhouse experiments on drought tolerance of two steppe and two tundra taxa suggest that the individualistic distribution of species along the ecotone is partly a function of physiological differences among species. Our analyses of vegetation‐environment relationships support the hypothesis that some components of the steppe community could have been more widespread during the colder Full‐Glacial.

Remote Sensing of Arctic Vegetation: Relations between the NDVI, Spatial Resolution and Vegetation Cover on Boothia Peninsula, Nunavut

“…Therefore, results presented for plot percent cover estimates (Fig. 3) follow expected trends in vegetation community composition and functional type dominance described in other tundra vegetation research (e.g., Bliss and Matveyeva, 1992;Lloyd et al, 1994;Walker et al, 1994;Murray, 1997;Henry, 1998;Young et al, 1999). The spatial heterogeneity of the study area, regarded as the irregularity of the physical environment that translates into different kinds of plant habitats, demonstrates the importance of local influences on creating a diversity of habitats that can maintain a diversity of species cover (Murray, 1997).…”

A Discriminant Analysis Model of Alaskan Biomes Based on Spatial Climatic and Environmental Data

“…A well-doc u ment ed example is the steppe-tundra ecotone found in interior Alaska around Kathul Mountain (Lloyd et al, 1994). This ecotone consists of a broad region of intermingling be tween steppe taxa and more drought-resistant alpine tun dra taxa, with an abrupt shift from the mixed steppe-tundra to wood land, shrub-dominated alpine tundra at the ridge line of Kathul Mountain.…”

Biogeographical Evidence for the Grass (Poaceae) Species of Pleistocene Beringian Lowlands

“…South-facing slopes in today's taiga zone are weaker analogs for the more mesic, loessal, nutrientrich soils of the Pleistocene Beringian plains, which, as discussed in the introduction, we have reason to believe were widespread. The greater overall heat supply (as shown by their lack of permafrost) on south-facing slopes with steppe vegetation in the taiga zone also creates niches for more warmth-demanding, southern species such as P. spicata (Lloyd et al, 1994), E. jacutorum, and H. krylovii, for which the Pleistocene Beringian lowlands apparently presented a barrier to migration. Grass-rich communities on pingos in northern Alaska often occur on fine-grained soils over permafrost, an environment that is probably closer to what prevailed on the Pleistocene Beringian plains.…”

“…Today's steppes on south-facing slopes share two significant environmental constraints with dry, windswept Pleistocene sites: summer drought and the occurrence of very low winter temperatures with little snow cover. Communities from the colder, high-elevation steppe-tundra transitional sites on south-facing slopes (Edwards and Armbruster, 1989;Lloyd et al, 1994) are especially promising as analogs of Pleistocene communities on droughty or shallow soils. South-facing slopes in today's taiga zone are weaker analogs for the more mesic, loessal, nutrientrich soils of the Pleistocene Beringian plains, which, as discussed in the introduction, we have reason to believe were widespread.…”

“…Islands of steppe habitat rich in grasses, found on dry, steep, south-facing slopes within the taiga of Alaska, the Yukon, and northeastern Asia, have attracted attention as possible analogs of the Pleistocene Beringian landscape (Hanson, 1951;Yurtsev, 1982;Murray et al, 1983;Edwards and Armbruster, 1989;Lloyd et al, 1994;Roland, 1996;Vetter, 2000). Four grasses common in steppes on south slopes in the taiga of the North American part of the study area are on the list of probable Pleistocene lowland grasses (Table 2): Calamagrostis purpurascens, Bromus pumpellianus, Festuca altaica, and Poa glauca.…”