Climate Change and the Rocky Mountains - Impact of Global Changes on Mountains: Responses and Adaptation - page 437

identifi ed as distinct communities from alpine tundra plants (Malanson and
Fagre 2013), will have few, if any, options since they already occupy the
highest elevations. In Europe, where there are summit vegetation records
going back a century, some plant species have disappeared from some
mountain ranges and others are now found much higher in elevation than
before (Parolo and Rossi 2008, Pauli et al. 2007). It is reasonable to expect
the same trend in the Rocky Mountains of North America.
The interface between alpine tundra and high-elevation forests, the
Alpine Treeline Ecotone (ATE), is another area where reduced snow
persistence and rising temperatures have started to profoundly change
the dynamics of mountain ecosystems. Although the position and form of
the ATE is thought to be climatically controlled, and therefore changes in
it are an indication of climate warming, as much as half of the treelines are
affected by geomorphology (e.g., debris fl ows, rockfall, landslides), snow
avalanches, and occasional fi res in the northern Rocky Mountains (Butler
et al. 2007). Nonetheless, ATEs have increased in biomass, canopies have
become denser, and the mean position of trees have moved upward in North
America and the Rocky Mountains and this has been attributed to climate
change (Malanson et al. 2007, Holtmeier and Broll 2007, Klasner and Fagre
2002). One consequence is that more snow is now retained at the ATE with
taller and more complex canopy architecture, potentially affecting alpine
hydrology and seedling establishment. Another, however, is that there is
more fuel continuity and fi res from downslope can now be carried into the
alpine when dry conditions exist. Westerling et al. (2006) indicated that
the largest increases in fi re frequency for the past six decades have been in
mid-elevation forests above 2,100 m. As trees become established further
upslope there is a corresponding reduction in the area of alpine tundra that
is also host to many of the Rocky Mountains' charismatic wildlife species,
such as mountain goats ( Oreamnos americanus ) and bighorn sheep ( Ovis
canadensis ). In addition to loss of habitat area, in the future when trees may
cover passes, there could be reduced migration between sub-ranges due to
predator avoidance, and consequent genetic isolation.
Another consequence of enhanced montane tree growth related to
changes in snow is the in-fi lling of subalpine meadows. Deep snow that
accumulates in meadows and persists to mid-summer or later can suppress
tree seedling establishment but has less effect on establishment and vitality
of meadow forbs and grasses. These forbs and grasses provide valuable
food resources and high quality habitat for insects, birds, many burrowing
mammals, ungulates and bears. Some of the forest/meadow patterns in
upper elevation basins are alternating ribbons of trees and open meadow
that are largely controlled by underlying bedrock topography with snow
accumulating in the depressions between ridges (Butler et al. 2003). This
pattern provides a large edge effect, which maximizes the value to wildlife.