How do we find the balance between having healthy woodland caribou herds and human activity and development in southern Yukon?

This question is one of many tackled by Yukon biologists who are looking for ways to ensure that the territory's woodland caribou herds remain stable as their ranges come under increasing pressure from residential development, industrial development, roads and other human activities.

A new study looking at thresholds is providing some of the tools needed to help evaluate how much is too much activity in caribou herd ranges.

The Environment departments of both the federal and territorial governments contributed funds and data to a series of studies conducted by a local environmental consulting firm.

"We're trying to come up with an approach that would work in the Yukon for setting thresholds for human activity," says Robert Anderson, a researcher with Gartner Lee Ltd./Applied Ecosystem Management.

"We've looked at other jurisdictions in western Canada where different approaches have been used. In the past, most haven't dealt well with cumulative effects of industrial activity in woodland caribou range. As a result, a lot of caribou herds in southern Canada are threatened and they're having to deal with recovery programs."

In the Yukon there are two main herds where most research has been conducted, Little Rancheria and Southern Lakes. Working with Yukon biologists like Jan Adamczewksi and Rob Florkiewicz, and using the data from those herds and several in southern Canada, Anderson and his colleagues looked at whether approaches from other areas like Alberta and B.C. will be valid here, and how to adapt approaches where there are differences.

One of the theoretical approaches that make this study unique in Yukon is a concept known as a dose response curve.

"It's like applying pressure to something and then trying to figure out where the breaking point is," says Shawn Francis, a Yukon ecologist who has been involved in the studies.

Like a doctor applies different quantities of medicine to achieve certain results, biologists are looking at various doses or levels of human activity in caribou ranges and what effect the different levels of activity have on caribou populations.

"While we want to be able to provide for economic development, we need to also realize the inherent limits of the land base," says Francis. Determining caribou thresholds before large amounts of development takes place would help mitigate impacts to the herds while still optimizing economic opportunities within known constraints.

"The key to this approach is understanding the caribou's altered behaviour or avoidance of human activities and features, and how much of their range can be impacted before you start to measure population-level declines."

Marie Gallagher, another researcher with Gartner Lee/AEM, has been developing a land use map, based on empirical evidence from other jurisdictions plus whatever local data is available, that represents the 'zones of influence' surrounding different types of human features and activities.

Within a certain distance of human activities or features, the behaviour of caribou is being modified. Francis points out it could be positively modified, or perhaps negatively as avoidance or displacement.

"Zones of influence are a more accurate and effective way to represent the true impacts of human features," he says. "For example, the direct footprint of the Alaska Highway vastly understates its influence on the immediate surroundings. It appears as a small 50m linear corridor, but you need to understand that the highway influences a much larger adjacent area through traffic noise and increased activity levels".

"Caribou may use an area within 500 metres of a road less frequently compared to what you would expect at random, so you're potentially taking away a one kilometre swath of habitat with that single 50-metre road corridor," explains Francis.

Francis, Gallagher, and a number of colleagues have worked on a study of the Carcross herd winter range (a subset of the Southern Lakes herd) that has taken a mapping approach to quantifying the amount of disturbed habitat using the zone of influence approach in the area.

"Habitat effectiveness is the key," he adds. "What is the habitat quality, and how useful or available is it to caribou? You could have excellent caribou habitat, but it's right next to the highway or surrounded by human development. In addition to quality, you have to look at the ability of the habitat to be utilized."

Ultimately, the tools that are being created may provide a way to set a certain target or threshold for a herd as development is planned for an area.

"The purpose at this time is not to set thresholds, but to create planning tools that take a snapshot of what's out there, develop human influence zones and calculate what percent of an area might be affected under different scenarios," says Anderson. "Down the road, this type of tool might be used to help establish thresholds, which would be used in planning to allow for a certain level of economic and population growth, while limiting our overall impact on woodland caribou."