Validation of a simplified point frame method to detect change in tundra vegetation

Abstract

The point frame method is ideal for vegetation monitoring because exact locations may be precisely resampled over time. Many researchers, including those associated with the International Tundra Experiment (ITEX), have used a modified point frame method to document vegetation change in response to climate change and experimental warming. To save, time only the uppermost and lowermost encounter (TB method) of a plant below each grid point is recorded as opposed to all contacts (AC method). Here, we investigate the ability of this shortcut to accurately assess the community change and estimate the aboveground plant biomass at four long-term sites in northern Alaska. We found that the TB method underrepresented the species cover (by omitting intermediate contacts) between 35 and 50 % of the taxa at a site; however, the magnitude was less than 2 % cover for all but 17 of the 109 taxa and site combinations, and despite the smaller number of contacts in the TB method, it was nearly equal in its ability to detect a change in cover in response to warming as the AC method (only 1 of the 109 cases showed differences in the significance of the response). Linear regressions showed the accuracy of the TB, and AC methods were also similar in estimating aboveground plant biomass (same cases were significant, and all but 2 were within r 2 of 0.1). Thus, we conclude that TB method outlined in the ITEX manual is an efficient and accurate way of assessing vegetation changes in tundra plant communities.