Continuous and discontinuous variation in ecosystem carbon stocks with elevation across a treeline ecotone
Speed, James David Mervyn; Martinsen, Vegard; Hester, Alison J.; Holand, Øystein; Mulder, Jan; Mysterud, Atle; Austrheim, Gunnar
Journal article, Peer reviewed

View/ Open
Date
2015Metadata
Show full item recordCollections
- Institutt for naturhistorie [1177]
- Publikasjoner fra CRIStin - NTNU [34929]
Abstract
Treelines differentiate vastly contrasting ecosystems:
open tundra from closed forest. Treeline advance has
implications for the climate system due to the impact of the
transition from tundra to forest ecosystem on carbon (C) storage
and albedo. Treeline advance has been seen to increase
above-ground C stocks as low vegetation is replaced with
trees but decrease organic soil C stocks as old carbon is decomposed.
However, studies comparing across the treeline
typically do not account for elevational variation within the
ecotone. Here we sample ecosystem C stocks along an elevational
gradient (970 to 1300 m), incorporating a large-scale
and long-term livestock grazing experiment, in the southern
Norwegian mountains. We investigate whether there are
continuous or discontinuous changes in C storage across the
treeline ecotone, and whether these are modulated by grazing.
We find that vegetation C stock decreases with elevation,
with a clear breakpoint between the forest line and treeline
above which the vegetation C stock is constant. C stocks in
organic surface horizons of the soil were higher above the
treeline than in the forest, whereas C stocks in mineral soil
horizons are unrelated to elevation. Total ecosystem C stocks
also showed a discontinuous elevational pattern, increasing
with elevation above the treeline (8 gm-2 per metre increase
in elevation), but decreasing with elevation below the forest
line (-15 gm-2 per metre increase in elevation), such that
ecosystem C storage reaches a minimum between the forest
line and treeline. We did not find any effect of short-term
(12 years) grazing on the elevational patterns. Our findings demonstrate that patterns of C storage across the treeline are
complex, and should be taken account of when estimating
ecosystem C storage with shifting treelines.