Alpine Areas in the Colorado Front Range as Monitors of Climate Change and Ecosystem Response

Williams, Mark W.; Losleben, M. V.; Hamann, Hillary B.

doi:10.2307/4140969

Cited by 42 publications

(29 citation statements)

References 7 publications

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“…Plants from high‐latitude and high‐altitude sites are especially sensitive to climate warming [ Aerts et al , 2005]. Because of the harsh climate conditions characteristic of cold environments, alpine organisms are on the edge of environmental tolerances [ Williams et al , 1998]; consequently, these organisms and biogeochemical processes mediated by them may be sensitive to small environmental changes in climate and other parameters [ Williams et al , 2002].…”

Section: Discussionmentioning

confidence: 99%

Topographic controls on snow distribution, soil moisture, and species diversity of herbaceous alpine vegetation, Niwot Ridge, Colorado

2008

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[1] The nature of the snowpack has the potential to strongly influence the patterns of alpine plant productivity and composition by governing soil moisture levels, growing season duration and the thermal regime of alpine soils. This study evaluates these relationships by modeling the interrelationships of snow depth, snow water equivalent (SWE), snow disappearance rate, soil moisture, attributes of the alpine plant community and selected terrain factors using decision-tree techniques at Niwot Ridge, Colorado Front Range. The modeling results showed a strong correlation (r 2 > 0.9, P < 0.001) between the snow disappearance rate and SWE and terrain factors that control the degree of shelter and exposure of a given local and elevation. The model was sufficiently robust to predict the spatial distribution of the snowpack for 12 years that exhibited average snow fall (r 2 = 0.8, P < 0.001), but yielded lower correlation (r 2 = 0.2, P < 0.001) in drought years. Soil moisture was significantly correlated (r 2 = 0.7, P < 0.001) with snow-fall amounts and terrain factors; however, meltwater and summer rain offset the potential soil moisture deficit in windward sites. Annual plant biomass did not correlate well with snow attributes and soil moisture because the cascading impact of topography on snowpack and soil moisture was not well captured by measurements of aboveground biomass. In contrast, the species richness index was significantly correlated with snow depth and soil moisture (r 2 = 0.7, P < 0.001), thereby demonstrating the importance of snow on some attributes of the alpine plant community.Citation: Litaor, M. I., M. Williams, and T. R. Seastedt (2008), Topographic controls on snow distribution, soil moisture, and species diversity of herbaceous alpine vegetation, Niwot Ridge, Colorado,

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Section: Discussionmentioning

confidence: 99%

Topographic controls on snow distribution, soil moisture, and species diversity of herbaceous alpine vegetation, Niwot Ridge, Colorado

2008

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“…Recently, alpine tundra has also received increased attention given its role as an early warning indicator system of climate change, and its importance as a source area for nutrients and water (Williams et al 2002;Seastedt et al 2004;Knowles et al 2012). Alpine ecosystems are predicted to be among the most vulnerable to climate change because air temperatures are rapidly increasing, and the flora and fauna of highelevation ecosystems already exist near the edge of their environmental tolerance (Pepin et al 2015;Körner 1999;Settele et al 2014).…”

Section: Introductionmentioning

confidence: 95%

Soil respiration variability across a soil moisture and vegetation community gradient within a snow-scoured alpine meadow

2015

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The alpine tundra landscape is a patchwork of co-mingled ecosystems that vary due to mesotopographical (\100 m) landscape position, shallow subsurface heterogeneity, and subsequent soil moisture availability. This results in hotspots of biological activity, variable carbon cycling over short horizontal distances, and confounds predictions of the alpine tundra response to forecasted environmental change. To advance our understanding of carbon cycling within snow-scoured alpine meadows, we characterized the spatio-temporal variability of soil respiration (R S ) from 17 sites across a broadly representative soil moisture and vegetation gradient, within the footprint of ongoing eddy covariance measurements at Niwot Ridge, Colorado, USA. Chamber-based R S samples were collected on a weekly to bi-weekly basis over three complete growing seasons (2011)(2012)(2013), and a soil moisture threshold was used to integrate the data into dry, mesic, and wet tundra categories. In every year, measured R S was greatest from mesic tundra, followed by wet and then dry tundra locations. Increasing soil moisture invoked a bidirectional R S response from areas of dry and mesic tundra (directly proportional) compared to wet tundra (inversely proportional), and the optimum R S conditions were between 0.30 and 0.45 m 3 m -3 soil moisture, which mainly coincided with soil temperatures below 8°C. We also developed simple models to predict R S from concurrent measurements of soil moisture and temperature, and from nighttime eddy covariance measurements. Both models were significant predictors of R S in all years and for all ecosystem types (where applicable), but the models did not adequately capture the intra-seasonal R S variability. The median cumulative growing season R S flux ranged from 138.6 g C m -2 in the driest year (2013) to 221.4 g C m -2 in the wettest year (2011), but the cumulative growing season fluxes varied by a factor of five between sites. Our results suggest that increased or more intense precipitation in the future has the potential to increase alpine tundra R S , although this effect will be buffered to some degree by compensatory responses from dry, mesic, and wet alpine tundra.

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“…Additionally, mountain regions have recently been appreciated as sensitive ecosystems, thus observations in these regions over the last 20-50 years may serve as early warning indicators of global environmental changes (Williams et al 2002;Seastedt et al 2004). For example, observations of vegetation dynamics at the alpine tree line have indicated changes in species composition (e.g.…”

Section: Introductionmentioning

confidence: 99%

A comparison of water and carbon dioxide exchange at a windy alpine tundra and subalpine forest site near Niwot Ridge, Colorado

et al. 2009

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Eddy covariance measurements of the surface energy balance and carbon dioxide exchange above high-elevation (3,480 m above sea level) alpine tundra located near Niwot Ridge, Colorado, were compared to simultaneous measurements made over an adjacent subalpine forest over two summers and one winter, from June 9, 2007 to July 3, 2008. The surface energy balance closure at the alpine site averaged 71 and 91%, winter and summer, respectively, due to the high wind speeds, short turbulent flux footprint, and relatively flat ridgetop location of the measurement site. Throughout the year, the alpine site was cooler with higher relative humidity, and had a higher horizontal wind speed, especially in winter, compared to the forest site. Wind direction was persistently downslope at the alpine site (summer and winter, day and night), whereas upslope winds were common at the forest site during summer daytime periods. The latent and sensible heat fluxes were consistently larger in magnitude at the forest site, with the largest differences during summer. The horizontal advective flux of CO 2 at the alpine site averaged 6% of the net ecosystem exchange (NEE) during summer nights (5% during summer daytime), and was small in relation to the high wind speeds, relatively flat site, and weak sources of CO 2 upwind of the site. The magnitudes and diurnal behavior of the alpine NEE calculated using three methods; eddycovariance, friction velocity filter, and with advection and storage calculations, gave similar results. The period of net CO 2 uptake (negative NEE) was 100 days at the alpine site with a net uptake of 16 g C m -2 , compared to 208 days at the forest site with a net uptake of 108 g C m -2 , with initiation of net uptake coinciding with air temperatures reaching ?10°C. Winter respiration loss at the alpine site was 164 g C m -2 over 271 days, compared to 52 g C m -2 over 175 days at the forest site, with the initiation of net loss coinciding with air temperatures reaching -10°C at each site.

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Alpine Areas in the Colorado Front Range as Monitors of Climate Change and Ecosystem Response

Cited by 42 publications

References 7 publications

Topographic controls on snow distribution, soil moisture, and species diversity of herbaceous alpine vegetation, Niwot Ridge, Colorado

Topographic controls on snow distribution, soil moisture, and species diversity of herbaceous alpine vegetation, Niwot Ridge, Colorado

Soil respiration variability across a soil moisture and vegetation community gradient within a snow-scoured alpine meadow

A comparison of water and carbon dioxide exchange at a windy alpine tundra and subalpine forest site near Niwot Ridge, Colorado

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