Twentieth century temperature trends in the Western Cordilleras of the Americas broadly reflect the global signal of warming and decreasing diunal temperature range. Precipitation changes are more modest and vary strongly with region. Mountain glaciers have retreated considerably since the Little Ice Age in response particularly to the temperature rise and an upward shift in tropical freezing level over the last three decades. The changes are already affecting hydrologic regimes. Potential negative ecological consequences for the cloud forest ecosystem have also been suggested. Andean agriculture might benefit, however, from an upward shift in the zone of frequent frosts.

This paper presents examples of environmental changes in the Canadian Rockies in the context of a 1.5°C increase in mean annual temperatures over the last 100 years. During this period increases in winter temperatures have been more than twice as large as those during spring and summer. Glacier cover has decreased by at least 25% during the 20th century and glacier fronts have receded to positions last occupied ca. 3000 years ago. These two lines of evidence suggest that the climate of the late 20th century is exceptional in the context of the last 1000 to 3000 years. Detailed studies in three closely located upper treeline sites document variable responses of vegetation to climate change that reflect species differences as well as local differences in microclimate and site conditions. Treeline has advanced upslope in response to climate warming, but site and species differences control the rate and nature of the advance. Human impacts on the environment compound the changes due to climate warming. Historic photographs indicate significant changes in the type and density of forest cover due to the absence of significant forest fires within these National Parks during the last 70–80 years. The visual impact of these changes, which partially reflects a policy of fire suppression, is far greater than the impact of changes associated with more direct tourist-related impacts. It is therefore important that monitoring programs examine vegetation changes over the entire landscape rather than focussing exclusively on supposedly climate-sensitive sites.

Timber harvesting in British Columbia influences (a) forest hydrology; (b) fluvial geomorphology; (c) terrain stability; and (d) integrated watershed behavior. Impacts on forest hydrology are well understood and include increased average runoff, total water yield, increased storm runoff and advances in timing of floods. Stream channels and valley floors are impacted differently by fine sediment, coarse sediment and large woody debris transport. Terrain stability is influenced through gully and mass movement processes that are accelerated by timber harvesting. Impacts on integrated watershed behavior are assessed through disturbed sediment budgets and lake sediments. The Forest Practices Code (1995) is a significant step towards sustainable management of the land in so far as it attempts to minimize these geomorphic impacts of forest in B. C.

The factors and plant processes that have been proposed to control treeline location are evaluated for European and North American treelines. While often presented as alternative determinants of treeline, the ideas of the increased environmental hazard and the idea of tree material limitation are considered to be complementary. This is because plant damage, rather than outright death, coupled with difficult conditions for material acquisition and small available material pools, eventually makes accretion of biomass untenable. The location where this balance is achieved varies with climate, but catastrophic events and human activities make correlation with climate tenuous and future predictions difficult. Field manipulation of conditions for many tree species in many geographic locations at and below the treeline are needed to develop generalizations that are both explanatory and predictive.

Alpine tundra of the Rocky Mountains is subject to relatively little direct anthropogenic environmental change, and provides a good ecosystem for the detection of human effects associated with climate change and atmospheric pollution. The majority of the plants have patterns of vegetative development which limit the degree to which they can respond to variation in resource availability. Field experiments indicate that changes in the abundance of plant species is the predominant response of alpine tundra to simulated climate change (snow augmentation) and increased nitrogen deposition. This biotic change in turn influences ecosystem function, including the magnitude and variation in primary production, and nutrient cycling. These biotic responses may have a greater impact on changes in ecosystem function than the direct effects of environmental change.

Despite their protected status, aquatic ecosystems of Banff National Park have been subjected to a number of human stresses. Largely as the result of stocking programs earlier in the century, 10 species of nonnative fishes now occur in the Park, while one endemic subspecies of fish has been extirpated, and 2 other species are threatened. A number of rare invertebrates occur in hot springs and caves, including one mollusk that is endangered. Key invertebrates were extirpated from a number of fishless lakes by stocked fish, and in some cases have not returned, even though fishes did not survive. Restoration efforts in 2 small alpine lakes are described. Addition of nutrients and road salt have changed the chemical nature of the Bow River and its tributaries, and caused incidence of benthic algal mats to form in some sections. Impoundment and diversions affect over 40% of the Bow River catchment within the Park. Airborne organic contaminants concentrate in glaciers and high elevation snowpacks, yielding amounts high enough to contaminate fisheries to levels that in some cases approach guidelines for human consumption.

Although they may have been studied less extensively than those in developing nations, mature mountain tourism communities such as Banff, Canada, potentially have useful insights to offer the international community regarding principles and practices for developing sustainable, community-based mountain tourism. Toward that end, this paper focuses on the Banff Community Plan in order to highlight ‘made-in-Banff’ solutions to issues of governance in sustainable mountain tourism. Banff's approach to balancing tourism development and environmental protection may be unique, given its complex 115-year history of association with Banff National Park. Nevertheless, the town now employs innovative principles such as ‘no net negative environmental impact’ and ‘appropriate development and use’ in its efforts to become a balanced and sustainable national park community. Such principles may contribute to implementation of Chapter 13 (the Mountain Agenda) of Agenda 21 and to resolution of governance issues in achieving sustainable mountain communities.

Mass balance has been continuously monitored on Chacaltaya Glacier (16°S, Cordillera Real, Bolivia) since 1991, and on the Antizana Glacier 15 (0°, Ecuador) since 1995. In ablation areas, mass balance has been surveyed on a monthly scale, providing interesting details about the seasonal pattern in 2 contrasting tropical environments. Intermittent information about ice recession exists in both regions for the last 4 decades. The data point to a clear acceleration in glacier decline during this decade; ablation rates have been 3–5 times higher than during the former decades. Fluctuations measured before on 3 glaciers in northern Peru, allow the assumption that the rate at which the glaciers retreated in the tropical Andes increased in the late 1970s. The present situation is particularly dramatic for the small-sized glaciers (< 1 km²) and many such as Chacaltaya, could disappear in the next 10 years. As evidenced by the data collected, ablation increases significantly during the warm phases of ENSO (El Niño) and decreases during the cold phases (La Niña). Warm events becoming more frequent and intense since the late 1970s, it can be assumed that they have played an important role in the recent glacier decline in the central Andes, together with the global warming.

The rate at which deforestation of montane cloud forests of the Tropical Andes is documented, and the extent of different productive land uses in those areas, make it difficult to forecast appropriate conservation scenarios for countries that occupy the crescent of the Northern Andes, abode of one of the richest biological and cultural diversity of the world. Because of ancient human impacts on soils and wildlife, as well as current intensive land-use practices, Tropandean landscapes are being depleted not only of nutrients and organic matter in cultivated soils, but also water catchment and other resources, including fisheries, forestry, mining, agriculture, and livestock that mountain peoples are producing as a result of the governmental policies of subsidized capital inputs. The exodus of young people to the cities in the Andean world exacerbates the deterioration of the rural quality of life and brings issues of marginality, poverty, and neglect into the cultural landscape. In view of this critical situation, novel conservation approaches are suggested, reflecting needed changes to contemporary paradigms of mountain studies; with the use of case examples from Andean countries, mainly Ecuador, are questioned axioms of tropical ecology. These are less clear in the field than in the scanty literature on tropical mountains, offering a holistic view of the Tropandean landscape. Hence, verticality, marginality, centrality, power and violence, expansion, religion and myth, ethnic pride and inspiration, are seen as conventional paradigms of montology that have to be re-examined in light of modern environmental thought in the Andes.

Since pre-Columbian times, Colombia has undergone transformation of large parts of its natural ecosystems, in particular in the Andean region. To date, little is known about the patterns and processes of this transformation and their relation with socioeconomic and biophysical aspects. Traditionally, the lack of integration of multidisciplinary data has hampered the possibility to understand complex phenomena like this. An integrated approach helps to bring into a relevant contextual analysis, data that are normally analyzed separately. This paper presents an approach to understanding ecosystem transformation by linking and integrating, spatially, data on ecosystem distribution and transformation, with demographic, land use, and settlement history data on a national scale. The transformation is analyzed and documented in order to explain the present situation and to make some general predictions about future tendencies. The results show that the demographic and transformation patterns follow clear historical trends that can be spatially differentiated, and are related to natural regions—plains and mountains, and altitude belts—and to general land uses. In particular, the patterns of the Andes and the lowlands show historically distinct tendencies. The Andean region has higher densities and transformation proportions than the lowlands. The older settlement areas show higher densities and more intensive land use, and tend to be strongly related to the Andean region.

Andean cloud forests play an important role in watershed hydrology and protection against erosion. Even though most cloud forests fall under officially protected areas, a good deal of the cloud forests are being deforested and replaced by pastures for grazing cattle, which is the most important land use in Venezuelan cloud forest environments. The water dynamics of the natural forest as well as the impact of replacement by pastures are poorly understood. We have been conducting a research project since 1996, in order to study some of the water fluxes of the forest and to evaluate the hydrological impact of replacement by pasture. The study site is located at La Mucuy (2300 m with 3124 mm rainfall), Merida State, in the Venezuelan Andes. The results show that, in the forest, 91% of total incoming water was from rainfall and 9% was from cloudwater. Total foliage interception was 51%, which is a high value for a tropical montane forest. About 49% of the total incoming water reaches the ground as throughfall, whereas litter intercepts 6% of the water and a final 1.4% was lost by surface runoff. Therefore, infiltration must be about 42%. Approximately 16% was lost by transpiration leaving about 26% for drainage. Results from pastureland studies show 7% interception, while surface runoff (2%) and transpiration (about 66%) were higher than in the forest. Our first results on soil water status suggest that the forest soil (upper horizon) has a significantly higher % moisture than the pasture soil.

The Upper Bermejo River Basin (UBRB) is the most bio-diverse region in Argentina. A rugged territory and a long history of human settlement, combined with social and political isolation, have resulted in large areas with well-preserved forests, a large number of wild plant and animal species, and indigenous crops. Several factors, including agriculture expansion, intense logging activities, and oil and gas prospecting, are posing a threat to biodiversity. Current national parks and reserves are not enough to secure the survival of functional populations, especially of the large mammals. Conservation of biodiversity in the UBRB requires a broader approach: e.g. protection of the most sensitive areas outside present reserves; maintaining the remaining forest matrix under sustainable management regimes, involving the local communities in the process; and encouraging uses synergetic with conservation. Recent purchases by private enterprises of new protected areas, the willingness of local administrations to establish a new legal conservation framework, and local communities considering sustainable management of their lands, represent encouraging opportunities for the region.

The village of La Morada on the northeastern slopes of the Andes, Peru, is a typical example of a recent settlement founded in the Ceja de Selva Alta by families of indigenous and mestizo descent, who originally came from the highlands. They have accumulated experiences of the impact of their resource-management practices, but with heavy emphasis on their highland background. Tremendous changes in the environment have been catalyzed by road construction, introduction of new settlements, crops, and most of all by the introduction of large numbers of cattle.