Site characteristics of burned krummholz at alpine treeline in the Northern Rocky Mountains, USA

Background/Question/Methods

The alpine treeline ecotone supports a dynamic ecosystem that is juxtaposed between the alpine tundra and the subalpine forest. This study presents information from a multi-faceted perspective on the effects of fire on the alpine treeline ecotone. Very limited research has been performed on fire and treeline, and this study provides a baseline of data on the conditions present at alpine treeline several years after fire. The study site is located in the northern Rocky Mountains in Glacier National Park, Montana, at a site that experienced a high severity burn in 2006. Methods consisted of collecting diameters of 40 clonal trees and counting their number of stems, acquiring albedo values of four different ground covers and air temperatures associated with burned and unburned krummholz and unvegetated ground, and measuring soil compaction in the field during the summers of 2009 and 2010. Soil pedestal heights were also measured to estimate soil erosion.

Results/Conclusions

The site contained a mosaic of unvegetated ground, herbaceous vegetation, burned krummholz, and unburned vegetation. Albedo was lowest on the burned krummholz with an average value of 19.80±1.87% compared to unburned krummholz (29.93±0.84%), exposed rock (29.19±1.27%), and low vegetation (29.12±1.87%). Average temperature was 38.9±7.5 °C for burned trunks in the sun, 37.4±6.2 °C near unburned trunks, and 38.4±8.6 °C for unvegetated ground. An area that appeared to experience more erosion contained a covering of gravel and resulted in greater soil compaction (0.62±0.39 kg/cm²). Conversely, a nearby area contained a layer of ash and fine particles and experienced less compact soils (0.48±0.41 kg/cm²). Average stem diameter was 8.2±3.0 cm, and the 40 trees averaged 2.1 stems each. Several soil pedestals indicated that about 6 cm of soil had been lost and several gullies were present. The results provide preliminary data on the influence of fire on this ecosystem and an overall site assessment on select vegetation and soil conditions present after fire at treeline. The harsh growing environment found at treeline contributes to it being an area that is especially sensitive to disturbance such as fire and one that needs to be better understood.