**1. Introduction**

The linkage between caribou and the aboriginal people in the North America has existed for thousands of years. Caribou have played a critical role in the economy, culture, and way of life of the aboriginal people (Hall, 1989; Madsen, 2001). Currently, there are 60 major migratary tundra caribou herds circum-arctic, of which 30 are located in North America, including the Porcupine caribou herd in northern Yukon, Canada and northern Alaska, USA (Russell et al., 1992; Russell et al., 1993; Russell & McNeil, 2002; Russell et al., 2002; Griffith et al., 2002). The Porcupine caribou herd has been at the centre of debate between wildlife habitat conservation and industrial development in the Arctic because of the potential oil drilling in the Arctic National Wildlife Refuge (ANWR) 1002 area, which happens to largely overlap with the calving ground of the Porcupine caribou herd (Griffith et al., 2002; Kaiser, 2002; National Research Council, 2003; Heuer, 2006).

One of the objectives of the Canadian International Polar Year (IPY) project entitled "Climate Change Impacts on Canadian Arctic Tundra Ecosystems (CiCAT): Interdisciplinary and Multi-scale Assessments" was to assess the impact of climate change on caribou habitats over Canada's north, in close collaboration with the CircumArctic Ranfiger Monitoring and Assessment network (CARMA) (http://www.rangifer.net /carma/). Because of the vastness and remoteness of the arctic landmass, inherent logistic difficulty, and high cost of conducting field measurements, an approach that is solely based on field inventory is clearly impractical for monitoring and assessing the impact of climate on caribou habitats. Satellite remote sensing can monitor land surfaces from space repeatedly and consistently over large areas. Therefore, remote sensing provides a powerful tool for monitoring and assessing the impact of climate on caribou habitats, when calibrated and validated against the field measurements and other independent data.

In this study, we report the development of baseline maps of aboveground and foliage biomass over the Porcupine caribou habitat in northern Yukon and Alaska, using Landsat and JERS-1/SAR data. Specifically, we will (1) describe aboveground and foliage biomass measurement, (2) establish and validate relationships between measurements and remote sensing indices, and (3) map aboveground and foliage biomass for the Porcupine caribou habitat.

Mapping Aboveground and Foliage Biomass Over the Porcupine Caribou

of the trees were then calculated on basis of allometric equations.

weight.

laboratory.

Habitat in Northern Yukon and Alaska Using Landsat and JERS-1/SAR Data 233

with *DBH* is in centimeters and plot radius is in meters, *PRF* is in m cm-1. A tree is included or "in" if *DBHi* > *ri/PRF*, and excluded or "out" otherwise. A difficulty may arise as whether to include or exclude a tree if it's at the edge, namely, *DBHi* ≈ *ri/PRF*. If this is the case, the distance from the plot centre to the tree is measured. Using the tree's *DBH* and the appropriate PRF, this distance can then be compared to the radius of the plot as calculated by equation 1, and the tree place "in" or "out" of the plot after-the-fact. The measurements included tree height, diameter at breast height (*DBH*), and stand density. The heights of trees are recorded using a laser height measurement instrument (Impulse Forest Pro, Lasertech, Clarkston, MI, USA). Trees for height measurement are selected on basis of the point plot scheme. The value of *DBH* was measured using a tape. The stocking and biomass

If tree regeneration was present, we measured the biomass of the seedlings using a fixed circular plot of radius of 3.99 m. The measurements included counting the number of stems per tree species, selecting an average-sized seedling to estimate its ground stem diameter, height, and sampling one or two average-sized seedling to measure its fresh and oven-dry

For the understory layers, namely, high shrub, low shrub, herbs/graminoids, moss, and lichen, we harvested samples at five 1 m × 1 m plots to measure the total aboveground biomass: four at four directions and one random (Fig. 2). All the aboveground biomass within the plots were cut and collected into plastic bags and their green biomass weighed. Out of the five plots, we selected one representative plot to conduct an intensive sampling. For this plot, we measured the average height, visually estimate the ground cover percentage, and then cut and weighed the fresh biomass, sequentially, for tall shrub, low shrubs, herbs/graminoids, moss, and lichen. The ratio of green to oven-dry biomass was measured by bringing a sample of the aboveground biomass from the plot back to

If a site had no trees, then we applied the aforementioned understory procedure. Note that the plot number and design of a specific site were determined on basis of site conditions: the more heterogeneous and sparse the vegetation is at a site, the more plots are needed (Chen et al., 2009b; Chen et al., 2010b). The procedure was modified for tall shrubs if the tall shrubs (higher than 50 cm) were clustered instead of homogeneous distribution. Our field experience indicated that it was often the case for tall shrubs. In this case, we measured the biomass of tall shrubs using a fixed circular plot of radius = 3.99 m. The measurements included identifying shrub species, counting number of clusters of shrub in the plot, and selecting two average-sized clusters of shrub for more extensive sampling. All aboveground biomass of the two clusters of shrub were cut and weighed for total green biomass. A fraction of the biomass was brought back to measure the ratio of oven-dry to fresh weight. If there are more than one tall shrub species, we repeated the measurements for each of them.

The procedure for low shrub, herbs/graminoids, moss, and lichen remain the same.

For foliage biomass measurement during the summers of 2006 and 2008, we selected only non-treed sites. At each sites, five 1 m × 1 m plots were sampled (Fig. 3). Fig. 3 shows a photograph of the field sampling at a coastal plain site in the Ivvavik National Park during the summer of 2008. At each plot, all plants were harvested, sorted into dead and live, different species, and leaves and stem, and recorded for their fresh weights. A fraction of the harvested biomass for all components were brought back to the laboratory, oven-dried, and

*PRF r / DBH or r PRF DBH i ii i* (1)
