Land cover change on the Seward Peninsula: The use of remote sensing to evaluate the potential influences of climate warming on historical vegetation dynamics
Vegetation on the Seward Peninsula, Alaska, which is characterized by transitions from tundra to boreal forest, may be sensitive to the influences of climate change on disturbance and species composition. To determine the ability to detect decadal-scale structural changes in vegetation. Change Vector Analysis (CVA) techniques were evaluated for Landsat Thematic Mapper (TM) imagery of the Seward Peninsula from 1986 to 1999. Scenes were geographically corrected to sub-pixel accuracy and then radiometrically rectified. Between the 1986 and 1992 satellite scenes, the CVA detected changes in direction and magnitude of the two indices (TM Band 4/TM Band 3. TM Band 5). For Row 14, change was detected for 135,518 ha and for Row 15, change was detected for 111,831 ha. Between the 1992 and 1999 scenes, change was detected by CVA for 93,278 ha. CVA results and photo interpretation together show that shrub advance is approximately 100 metres in valleys north of the Bendeleben Mountains and that shrubs have increased along riverbed bottoms. Across Path 78 Row 14 and 15, the unsupervised classification detected that 55% of the pixels changed between 1986 and 1992. Overall, approximately 759,610 ha changed to a class with a more developed canopy and only 268,132 ha changed to a class with a less developed canopy. Thus, the change detection analysis based on the unsupervised classification indicates that land-cover change on the Seward Peninsula was predominantly in the direction of increased shrubbiness. Taken together, our comparison of CVA results, unsupervised classification results, and visual interpretation of aerial photographs suggests that shrub cover may be increasing on the Seward Peninsula, which is consistent with results from experimental warming in tundra. The use of both CVA and unsupervised classification together provided a more powerful interpretation of change than either method alone in transitional regions between tundra and boreal forest.