Can’t See the Forest for the Climate Change
“Human activities are profoundly affecting the world climate, and mountains are sensitive indicators of that effect. Mountains are an important source of water, energy, biological diversity and areas of recreation and are a major ecosystem representing the complex and interrelated ecology of our planet and are essential for the survival of the global ecosystem” (Gosh & Kimothi, 2009).
According to the Millennium Ecosystem Assessment (Reid et al., 2005), 20% (or 1.2 billion) of the world’s people live in mountains or at their edges, and half of humankind depends, directly or indirectly, on mountain resources. The figure (Ibid) below reveals the distribution of the world’s mountain systems.
Mountains provide the following goods and services (IPCC, 2007):
- Support many different ecosystems and have among the highest species richness globally.
- Play a significant role in carbon storage and sequestration (28% of forests are in mountains. See: Global Warming Impact on Forests & Woodlands)
- Provide water purification and climate regulation that affects all continental mainlands.
- Increasingly offer refuge from direct human impacts for many native species.
- Provide many goods for subsistence livelihoods, are home to many indigenous peoples, and are attractive for recreational activities and tourism.
As climate warms, species will migrate to higher altitudes if possible. Temperature cools with height quite quickly so short distance migrations can counter the warming climate as long as there is room to move upward. Mountain tops are much smaller than their bases so there is less room for species that do move up the slopes. Species near mountain tops will have nowhere to go. The IPCC (2007) concludes that this will result in reduced genetic diversity and extinctions. Research has already shown gene drift effects from past climate changes. Tree species may be unable to migrate and keep pace with changing temperature zones (Ibid).
Where warmer and drier conditions are expected, forest die-back is expected in continental climate zones, in particular interior mountain ranges and Mediterranean areas (Ibid). Even in humid tropical regions, plants and animals have been shown to be sensitive to water stress on mountains and there is very high confidence that warming is a driver of amphibian mass extinctions at many highland localities, by creating increasingly favorable conditions for the pathogenic Batrachochytrium fungus (Ibid).
Due to warming at lower levels of mountain areas there will be a lack of snow cover which exposes plants and animals to frost and influences water supply in spring. Where animal movements have been disrupted by changing snow patterns, as has been found in Colorado, increased wildlife mortality has resulted. At higher altitudes, the increased winter precipitation likely to accompany warming leads to greater snowfall, so that earlier arriving species are confronted with delayed snowmelt (Ibid).
According to Barrera (2010) the Rockies feature three distinct ecosystems: montane, subalpine, and alpine. The range extends from Alberta and British Columbia in the north through Montana, Wyoming, Utah, Idaho, Colorado, and New Mexico in the south.
The montane is characterized by Ponderosa and Lodgepole pine, Douglas fir, golden-leafed quaking aspen, and is the winter home for mule deer, elk, moose, mountain lions (cougars), great horned owls, and black bears, among many others. The subalpine is characterized by a mix of Engleman spruce and subalpine fir which provides habitat for species such as the yellow-bellied marmot and the snowshoe hare. The transition between subalpine and the alpine is characterized by a dense growth of trees no taller than the rocks and snow that protect them from the wind. Above the last of these stunted trees is the open expanse of the alpine tundra (starting between 2,200 and 3,350 meters), home primarily to hardy flowering plants, such as the dwarf clover and low-lying mosses. Most plants here have adapted by growing long taproots for water and dense hair for wind protection (Ibid).
“The higher elevations of the Rockies in Montana, Wyoming, and Northern Idaho have experienced three times the global average temperature increase of 0.74 degrees Celsius (1.3 degrees Fahrenheit) in the last century. These areas not only host many species, but also provide most of the water for western cities and towns, as well as natural space for snow-based winter recreation and many summer activities that underpin key portions of Rocky Mountain state economies. Wolves and grizzly bears are among the animals that have found unfragmented habitat in the parks and wilderness areas of the Rockies, and they will be most at risk if those habitats disappear.” (Ibid)
Barrera also notes that low-elevation Douglas fir has already moved toward higher elevations and the upward movement of alpine trees has also been documented in the northern Rockies. “Eventually it may become warm enough that the uppermost ecosystem in the Rockies, the alpine tundra, could disappear, which would trigger the extinction of the well-known resident Bighorn sheep.” 30 populations of bighorn sheep in the southwest United States became extinct between 1900 and the early 1980s due to increased temperature and decreased precipitation leading to a loss of food sources (Ibid).
“The American pika (pronounced pie-ka), for example, is a small, furry relative of the rabbit that is at risk of extinction because of changes to the alpine tundra it calls home. Pika are unable to withstand even a few hours outside their dens in temperatures higher than about 27 degrees Celsius, and they usually nest above 2,400 meters in areas where the temperature rarely exceeds 25 degrees. At least one-third of pika colonies in Nevada and Utah have disappeared in the last century, with warming temperatures being considered a main reason, according to the U.S. Geological Survey. If this trend continues, pika will probably be extinct in 100 years.” (Ibid)
Drought and warmer temperatures has accelerated mountain pine beetle population growth. As the forests are decimated by the pine beetle, the species that depend on them will also decline. “The boreal owl, which likes to hunt largely in mature forests, will be scarce for 40-60 years following the end of the beetle epidemic. Populations of snowshoe hare, and therefore lynx and other predators, will also decline for at least 10 to 15 years until the Lodgepole pine forests become dense once more.” (Ibid)
Wildflower populations are projected to decrease along the slopes of the Rocky Mountains as global warming causes earlier spring snowmelt. Larkspur, aspen fleabane, and aspen sunflower grow at an altitude of about 9,500 feet where the winter snows are deep. After the snow melts, the flowers form buds and prepare to bloom. With earlier snow melt these buds are exposed to frost. The percentage of buds that were frosted has doubled over the past decade. Frost makes the flowers unable to seed and reproduce, meaning there will be no next generation. Insects and other animal species depend on the flowers for food, and other species depend on those species, so the loss is likely to propagate through the food chain (USGRP, 2009).
“The Greater Himalayas hold the largest mass of ice outside polar regions and are the source of the 10 largest rivers in Asia. Rapid reduction in the volume of Himalayan glaciers due to climate change is occurring. The cascading effects of rising temperatures and loss of ice and snow in the region are affecting, for example, water availability (amounts, seasonality), biodiversity (endemic species, predator–prey relations), ecosystem boundary shifts (tree-line movements, high-elevation ecosystem changes), and global feedbacks (monsoonal shifts, loss of soil carbon).” (Xu, et al., 2009)
Rising temperatures will strongly influence plant reproduction and the timing of leaves and flowering, thus impacting the activities of various flower-visiting species such as bees and butterflies For example, roughly two-thirds of all known species of Rhododendrons in the world are located in the Himalayas and several species of rhododendrons are now flowering a month earlier than normal. The flowering of most alpine species is also significantly influenced by the pace of snow melt. Alpine plants and flower-dependent species may be particularly vulnerable to climate change due to disruptions in pollinator relationships (Ibid).
The length of the dry season for much of the Himalayas is projected to become shorter. This is likely to have a direct impact on plants. In the low elevation tropical Himalayas, a shorter, less intense dry season may inhibit plant flowering. A shortened dry season may also disrupt herbivore populations during the main period of leaf expansion. Brown locust outbreaks, for example, are believed to be associated with climate variability. Historical plagues of the high-elevation Tibetan migratory locust are closely related to droughts. Grasshopper survival is associated with soil type and adequate topsoil moisture (Ibid).
Spiders also play important roles in limiting locust populations. Rising temperatures significantly decrease the effect of spider predation. At the same time rising temperatures increases the number of grasshopper adults by lengthening the period of reproduction of mature adults in late summer. This can lead to increases in grasshopper populations the following year if winter conditions are ideal for egg survival (Ibid).
In the Tibetan Plateau, tree lines are expected to shift upward and northward. In northwest Yunnan a comparison of repeat photographs taken in 1923 and 2003 indicate tree lines rose by 67 m and tree limits rose by 45 m. In the eastern Himalayas researchers estimate tree-line movement was 110 m over the past century and predict that by 2100 the elevational range of Abies georgei forest will decrease between 4.6 and 25.9% and forest size will decrease between 5% and 38.6% under different emission scenarios. Studies in the western Himalayas have recorded an upward shift of tree line species of 19 and 14 m over 10 years on south and north slopes, respectively (Ibid).
Xu, et al. (2009) used a simplified Holdridge life zone system, and modeled the potential response of Greater Himalayan life zones to an increase in temperature of 5 ◦C along elevational gradients (without considering precipitation). Results indicated that elevational distribution of life zones would shift significantly: alpine vegetation shrank, evergreen forest decreased significantly, and tropical lowland forest increased (see figure below). The boundaries of farming and pastoral regions in western China also shifted, which increased grassland areas. Farming and agropastoral regions, however, also have a potential for increasing desertification.
High-elevation wetlands can be affected by very small changes in the water cycle. Shifts in Tibetan Plateau ecosystems due to climate change are projected to be significant. Today, alpine steppe and alpine desert cover 53.5% of the plateau; their combined area is projected to contract to 37.9%, a loss of 15.6%.
Forest areas are projected to increase in some regions and decrease in others across the Greater Himalaya through the 21st century. On the Tibetan Plateau, for example, forest ecosystems now cover <10% of land area and are projected to increase to 22.4% (Ibid). Himalayan forests have multiple functions: they harbor biodiversity, anchor soil and water, provide carbon sinks, regulate climate, and temper stream flow. They also supply forest products for local livelihoods and economies (Ibid).
The authors conclude that the response of natural vegetation to projected climate change will be complex; some species will decrease, some increase, and new ones may also appear. Invasions of weedy and exotic species from lower elevations are likely. More research is needed in this region.
Other Mountain Ecosystems:
Ruiz, et al. (2008) studied the impact of climate change on mountain ecosystems in the high mountain basin of the Claro River, on the west flank of the Colombian Andean Central mountain range. According to the authors:
“These striking changes might have contributed to the retreat of glacier icecaps and to the disappearance of high altitude water bodies, as well as to the occurrence and rapid spread of natural and man-induced forest fires. Significant reductions in water supply, important disruptions of the integrity of high mountain ecosystems, and dramatic losses of biodiversity are now a steady menu of the severe climatic conditions experienced by these fragile tropical environments.”
The two figures below illustrate these changes quite well:
The Australian Alps National Parks (2010) assessed the research related to climate change impacts on Australia and their study concluded that climate change will strongly impact ecosystems of the Australian Alps region. The Australian Alps span across New South Wales, Victoria and the Australian Capital Territory, and winter snow from their peaks is crucial to the water supply of the Snowy River and the Murray-Darling Basin, as well as the habitat of threatened species. Commonwealth Scientific and Industrial Research Organisation (CSIRO) scientists predict that inaction on climate change will cause the length of the average snow season to contract 85 to 96 per cent by 2050, and to disappear by the end of the century.
This region is home to many plants and animals not found anywhere else on earth, which rely on snow conditions. Many of these species face extinction. For example, the entire habitat of the mountain pygmy possum (pictured below) will be eliminated with a temperature rise of just one degree, which is expected to occur by the year 2030 (Ibid).
As snowpack diminishes, species that rely on downstream waters will face increasing hardship during the drier summer months when water is scarce. For example, Brown and Rainbow trout are likely to find that habitat is more restricted in some streams, due to increased water temperatures and reduced flows in summer. There are now only 38 southern corroboree frog males (pictured below) remaining in the wild, and without intervention this species will be extinct within the next five years (Ibid).