Tree Growth in the Swedish Sub-Arctic: Setting New Records
Hedenas, H., Olsson, H., Jonasson, C., Bergstedt, J., Dahlberg, U. and Callaghan, T.V. 2011. Changes in tree growth, biomass and vegetation over a 13-year period in the Swedish Sub-Arctic. Ambio 40: 672-682.
In a continuation of these types of studies, Hedenas et al. say that in 2010 they re-surveyed shrub, tree and vegetation data at 549 plots grouped into 61 clusters that were originally surveyed in 1997 in two areas close to the Abisko village, which is located approximately 200 km north of the Arctic Circle at 68°20'N, 18°50'E. According to the six Swedish scientists, results indicated that "tree basal area and biomass increased by 19% between 1997 and 2010 with the main increase occurring in established birch forest," noting that this result "concurs with the results of other studies which suggest that there has been a general increase in cover and biomass of trees and shrubs in sub-Arctic and Arctic areas," additionally citing in this regard, the studies of Sturm et al. (2001), Tape et al. (2006), Danby and Hik (2007), Forbes et al. (2010), Hallinger et al. (2010) and Van Bogaert et al. (2011).
Hedenas et al. write that in spite of the increased browsing pressure provided by an increasing reindeer population over the period of their study, as well as periodic outbursts of geometrid moths - which severely defoliated the birch trees in their study area in 2004 (Babst et al., 2010) - "there has been a net increase in biomass - and carbon drawdown - of 19%." As for the cause of this welcome phenomenon, they say "it has been suggested that increased nutrient availability associated with higher soil temperatures, and a longer growing season could underpin increased tree and shrub abundance and biomass in the Arctic (e.g., Chapin, 1983; Weih and Karlsson, 1997; Hartley et al., 1999)," as a result of "a delayed re-expansion of shrubs and trees following the 'Little Ice Age'," as suggested by Grubb (2008). And, of course, we have the ongoing and ever-increasing aerial fertilization and transpiration-reducing effects of the concomitant rise in the atmosphere's CO2 concentration, which must be playing significant roles as well, as the remarkable Greening of the Earth continues.
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