We have two transects running straight through the summer ranges of two different caribou herds: the Central Arctic Herd and the Teshekpuk Lake Herd. We are lucky in that one of these transects (the Central Arctic Herd) has a convenient road running right through the herd’s range, which makes sampling easy. We go on sampling trips quite frequently throughout the growing season in order to assess how much biomass is growing along the range of the herds and to collect forage quality samples of a few preferred forage species to bring back to the lab for analysis.
Why measure biomass?
Forage quality isn’t the only thing that determines the amount of protein an animal is able to take in over the summer – the quantity of forage available plays a large role as well. Total protein available for a specific location can be calculated by multiplying how much forage is at each location by how much protein is available in forages collected from that same spot. Even though protein content in forages is highest early in the season, it’s entirely possible for total protein available across a landscape to occur midway, or even at the end, of the growing season. This is because plants will continue growing through the spring and summer, and there will be much more forage available later on – compared to early on, when there is hardly anything growing at all. This is comparable to getting a steady paycheck from constant work, versus working only sporadically but getting a large paycheck each time.
We can’t measure exactly how much biomass is on the tundra (this would involve picking and weighing every single plant on the tundra!), but we can take small multiple small samples and extrapolate to a larger area. Biomass plots take a long time to complete and are very tedious, which is why they aren’t completed as often as they should be.