The long-term goal of the Niwot Ridge/Green Lakes Valley (NWT) LTER program is to build a comprehensive and predictive understanding of ecological processes in high-elevation mountain ecosystems, and – as much of these processes can be generalized across the globe  -- to contribute to broad synthetic and conceptual advances in ecology. We provide education and training (K-12 to postgraduate), public outreach, and knowledge to inform alpine resource management and conservation. The rich history of research and current template of long-term experiments at NWT allows us to advance ecological theory and address timely questions regarding high-elevation responses to climate change.

Mountain ecosystems have been identified as among the most vulnerable to climate change. Small changes in temperature can turn ice and snow to liquid water, and sharp physical gradients can lead to rapid shifts in habitat over small distances. Nitrogen pollution contributes to these changes, affecting nutrient limitation in the resource-poor environment.

In NWT VII we found that the predicted vulnerability of mountain systems needs to be viewed in the context of high spatial complexity and temporal variability. High topographic relief and variation in the physical soil environment forms the template for climate-related changes. Terrain modulates climate effects by dictating where the fierce alpine winds redistribute snow and when and how fast snow melts. The water from melting snow flows downhill to connect terrestrial habitats with one another, and ultimately links these habitats to alpine lakes and streams. Our work illuminated several ways that this landscape complexity can translate climatic drivers into ecological responsiveness and stability. We list several of our main findings below.

First, NWT has experienced a strong signal of warming over the past 70 years, with an annual maximum temperature increase of ~0.5 degrees C/decade in both subalpine and alpine environments. In contrast to the directional trends in air temperature, precipitation (75% of which falls as snow at NWT) shows high interannual variability with little to no overall trends through time. We expect further monitoring will soon begin documenting decreasing precipitation trends that are occurring in other areas of the Western United States.

Second, we have found that rising temperatures have substantially increased the length of the ice-free season in NWT lakes: since 1983, the ice-free period in the Green Lake Valley has increased more than two weeks.

Third, rising temperatures are having increasingly detectable effects on geophysical processes at Niwot Ridge and throughout the Green Lakes Valley. Higher temperatures are associated with increased weathering, permafrost and rock glaciers throughout the valley and across the ridge are thawing, and the glacier at the top of the valley is shrinking and projected to disappear within two decades. Thawing ice and snow create new flow paths in areas that may not often receive flushing from snowmelt water, enhancing sulfate and ammonium export in surface waters and possibly contributing to net ecosystem carbon loss by stimulating soil respiration.

Fourth, patterns of alpine plant community response to warming depends on landscape position. Changes in species composition has been fastest in the communities that experience the most extreme abiotic conditions: wet meadow and snowbeds (with persistent snowpack, short growing seasons, and high soil moisture) and fellfields (with the least snow and longest, driest growing season). Plant species whose geographic ranges extend to areas warmer than Niwot are becoming more abundant in moist meadow, wet meadow, and snowbed communities, while species whose ranges are cooler than NWT are becoming increasingly common in the dry meadow.

Fifth, in the subalpine forest, warmer climate conditions have been broadly associated with decreased seedling establishment and increased tree mortality. Moisture availability and stand age have influenced aboveground live tree biomass production in NWT permanent plots over a 35-year time period.

Lastly, shrubs (predominantly willows) have rapidly expanded into alpine tundra at NWT. This encroachment has been linked to warming by experimental work. Shrubs change fine-scale patterns of snow accumulation and microclimate, and may provide refugia to alpine plant communities under their canopy.

These and many other scientific results of our recent work on Niwot Ridge provide critical information about how mountain ecosystems are responding to the rapidly changing conditions that are under way on our planet. This research has been led by a collaborative team of interdisciplinary scientists that include the next generation of high-elevation scientists, and has been shared broadly with students, stakeholders, and the general public.

Last Modified: 02/08/2024
Modified by: Katharine N Suding