APPLICATIONS OF SHRUB DENDROCHRONOLOGY IN TRACKING DECADAL CHANGES IN POND MARGIN DYNAMICS

Abstract

Decadal changes in the surface area of small ponds in the Kluane region, Yukon were quantified from remote sensing and dendrochronological techniques. Both dead and live shrubs from the genus Salix were sampled and cross-dated from a total of 28 pond ecotones in two different study areas. The rate of ecotone shrub colonization was calculated for each pond by determining the minimum age of Salix spp. in ten zones extending from forest edge to shoreline. Changes in the surface area of 20 ponds in each study area, for a total of 40 ponds, since 1948 were measured using multi-temporal remote sensing analysis. Measured changes were then validated using colonization rates derived from the dendrochronological analysis. Results were compared with meteorological records to elucidate the connection between climate change and shoreline dynamics. Ponds experiencing similar rates of ecotone colonization exhibited similar changes in shoreline position over the last 60 years. Ponds measured with remote sensing showed an overall decline in surface area since 1948; however, direction and extent of change varied within and between the two study areas. Colonization rates also varied within and between study areas. This corresponded to differences in pond ecotone population structure as well as relative extent and direction of changes in surface area, and supported the changes observed in the low-resolution remote sensing time series data. Changes in ponds tended to correspond to increases in annual temperatures which, when combined with a longer growing season and stable precipitation, may have accelerated evaporation potential causing ponds to decrease. The negative consequences of surface area decline are exacerbated by the potential increases in evapotranspiration and the much less extensive wetland system in southwest Yukon relative to other regions in the North. The successful implementation of remote sensing and dendrochronological techniques has value for remote areas that are sensitive to climate change, yet lack direct measurement of changing environmental conditions.