Patterns of snow, deposition, and soil nutrients at multiple spatial scales at a Rocky Mountain tree line ecotone

• Published in: Journal of Geophysical Research: Biogeosciences 2009-12, Vol.114 (G4), p.n/a
• Main Authors: Liptzin, Daniel, Seastedt, Timothy R.
• Format: Article
• Language: English
• Subjects: Colorado Front Range; dust deposition; Earth sciences; Earth, ocean, space; ecotone; Exact sciences and technology; nitrogen cycling; Niwot Ridge; tree line
• ISSN: 0148-0227; 2156-2202
• DOI: 10.1029/2009JG000941

The forest‐alpine tundra ecotone in the Front Range of Colorado typically occurs as a gradual transition from the treeless tundra to the closed canopy coniferous subalpine forest. We evaluated the patterns of snow, deposition inputs, and soil properties at three spatial scales: across the entire ecotone, with distance from tree limit in the transitional krummholz zone, and around individual trees. Snow depth was deepest in the krummholz zone and lowest in the alpine tundra and upwind of trees near tree limit, but was not predictive of most soil properties except for surface litter decomposition. Inorganic deposition ranged from 0.7 to 7.7 g m−2 yr−1 across the ecotone and tended to be higher downwind than upwind of trees. The exchangeable acid cation concentrations were significantly higher in the forest and increased gradually toward the tundra. The exchangeable base cations (Ca, Mg, and K) were only predictable at the scale of individual trees with greater concentrations downwind of trees. Resin bag available N was rarely predictable at any spatial scale, but was correlated among seasons. While the ecotone is in many ways a gradual transition from alpine tundra to subalpine forest, patterns observed across this vegetation gradient were often replicated on the scale of individual trees: downwind of trees was more similar to the forest, and upwind of trees was more similar to the tundra. No single spatial scale or gradient can provide uniform generalities about the amounts or fluxes of materials that determine the soil properties of this ecotone.