Controls on Arctic NDVI Patterns: a Zonal Analysis
Abstract
Summer temperatures are thought to be the primary control of circumpolar-scale phytomass patterns. The Normalized Difference Vegetation Index (NDVI) is often used as an index of vegetation greenness, and consequently the amount of green phytomass. Understanding the variation in NDVI and phytomass along present-day climate gradients provides key information for predicting responses to global climate change. The Arctic Zone (the tundra region north of the arctic treeline) has been subdivided into five bioclimate subzones, with boundaries at approximately 2oC intervals between 12oC mean July temperature (MJT) at continental treeline areas to 0oC at the ice margin. We estimated total-aboveground-phytomass density (TAPD) within the five arctic bioclimatic subzones using a regression of phytomass against NDVI that was developed along the arctic climate gradient in arctic Alaska with supplementary data from the Canadian High Arctic. Total aboveground phytomass for the Arctic is estimated at 2.42 Gg. TAPD in subzones 1 through 5 was: 51 g m-2, 116 g m-2, 169 g m-2, 454 g m-2, and 796 g m-2 respectively. Circumpolarly, Subzone 3 has anomalously low TAPD values. We investigated three possible causes of this anomaly: (1) greater elevation in Subzone 3 causing relatively lower biomass on average, (2) relatively large areas of low phytomass on limestone substrates in Subzone 3, (3) a greater percentage of barren areas and lakes in Subzone 3 due to late-Pleistocene glaciation. When the NDVI data are broken down according to region, Eurasia has much higher NDVI values than Canada. The lower NDVI values in Canada are the result of a combination of factors. The primary cause is the late-Pleistocene glaciers that covered nearly all of Arctic Canada, and left large areas of barren rock, and lake-covered landscapes . Both rock and water have low NDVI values that lower the mean NDVI values within each subzone. Canada also has large areas of limestone and relatively high elevations, particularly in Subzone 3. Circumpolarly, higher elevation corresponded with lower NDVI values. For areas in both Alaska and Canada, where substrate pH data are currently available, nonacidic substrates had lower NDVI values than acidic substrates.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2001
- Bibcode:
- 2001AGUFM.B22C0176W
- Keywords:
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- 1620 Climate dynamics (3309);
- 1640 Remote sensing;
- 4806 Carbon cycling;
- 9315 Arctic region