Conifer Establishment and Encroachment on Subalpine Meadows around Mt. Baker, WA, USA

The subalpine ecotone is experiencing significant changes in habitat availability and connectivity as a result of climate change. The conversion of meadow habitats to forests has been observed in many mountainous regions. Rates of conifer encroachment into meadows appears to have increased in the 20th century, but the patterns of conifer establishment seem highly variable over both space and time. To understand how and why these changes vary temporally and spatially in the Pacific Northwest, we collected cross-sections and whorl counts from conifers along four transects in subalpine meadows around Mt. Baker, Washington. We quantified the relationships between temporal patterns of conifer establishment and a suite of climate variables, and between spatial patterns of conifer density and microsite characteristics. Our results show that establishment occurred in pulses throughout the 20th century, with greater establishment on drier sites during periods of greater precipitation, and greater establishment on wetter sites during periods of higher temperatures. We found that April precipitation and September temperature are particularly strongly correlated with establishment rates, suggesting that the best conditions for conifer seedling establishment occur in years with the warmth and soil moisture needed for the growing season to start earlier or last longer. Within individual meadows, conifer seedling establishment was greater on convex surfaces and in areas with a higher percentage of Vaccinium cover. Our findings at Mt. Baker show that periods of conifer establishment occurred somewhat synchronously across multiple mountains in the region, but we also identified distinct spatial and temporal differences linked to local site conditions.

Fire Exclusion Destroys Habitats for At-Risk Species in a British Columbia Protected Area

Fire exclusion and suppression has altered the composition and structure of Garry oak and associated ecosystems in British Columbia. The absence of frequent low severity ground fires has been one of the main contributors to dense patches of non-native grasses, shrubs, and encroaching Douglas-fir trees in historical Garry oak dominated meadows. This case study uses remote sensing and dendrochronology to reconstruct the stand dynamics and long-term fire history of a Garry oak meadow situated within Helliwell Provincial Park located on Hornby Island, British Columbia. The Garry oak habitat in Helliwell Park has decreased by 50% since 1950 due to conifer encroachment. Lower densities and mortalities of Garry oak trees were associated with the presence of overstory Douglas-fir trees. To slow conifer encroachment into the remaining Garry oak meadows, we recommend that mechanical thinning of Douglas-fir be followed by a prescribed burning program. Reintroducing fire to Garry oak ecosystems can restore and maintain populations of plants, mammals, and insects that rely on these fire resilient habitats.

Is fire exclusion in mountain big sagebrush communities prudent? Soil nutrient, plant diversity and arthropod response to burning

Fire has largely been excluded from many mountain big sagebrush communities. Managers are reluctant to reintroduce fire, especially in communities without significant conifer encroachment, because of the decline in sagebrush-associated wildlife. Given this management direction, a better understanding of fire exclusion and burning effects is needed. We compared burned to unburned plots at six sites in Oregon. Soil nutrient availability generally increased with burning. Plant diversity increased with burning in the first post-burn year, but decreased by the third post-burn year. Burning altered the arthropod community, which included doubling the density of arthropods in the first post-burn year. Some arthropod Orders increased and others decreased with burning. For example, Araneae were 1.7- and 1.8-fold less and Hemiptera were 6.6- and 2.1-fold greater in the burn compared with the control in 2008 and 2009. Our results provide evidence that burning can create spatial and temporal heterogeneity in sagebrush communities and thus, it is an important component of the ecosystem. We suggest that management plans for many mountain big sagebrush communities may need to include infrequent burning. At the very least managers should be aware that fire exclusion has some potentially negative effects other than the encroachment of conifers in these communities.