Methods

Changes in caribou habitat are tracked by quantifying the amount of disturbed area within caribou range, which is a key component of the federal definition of critical habitat for woodland caribou (ECCC 2020; Environment Canada 2011, 2014). For each caribou range, the amount of disturbed area is estimated annually from 1960 to the most current year of data. Caribou range boundaries are delineated by provincial jurisdictions.

Disturbance data

Disturbances within caribou range are modelled using Geographic Information System (GIS) data representing various disturbance types, including: burns (i.e., wildfire), timber harvest, roads, geophysical exploration lines (e.g., seismic lines), clearings related to oil and gas resource development (e.g., pipelines and well pads), forests killed from mountain pine beetle, and other anthropogenic disturbances such as mines, agriculture, railways, and urban areas. 

The data sets used represent the best available data for the given jurisdiction (i.e., Alberta or BC) and disturbance type. Note that each data set will vary in the degree to which they accurately and precisely represent the true disturbance footprint, and thus outputs from all analyses should be viewed as best estimates of disturbance impacts within caribou range. See Data Sources for more information on each data set used to quantify disturbance.

Most data sets contain information on the date of disturbance creation (i.e., timestamped data), which is necessary to track annual changes in disturbed area. However, data sets do differ in their timespans. For example, in British Columbia, the timespan for burns and timber harvest data extends to 2024 whereas all other disturbance types have data sets that extend only to 2021. Similarly, in Alberta burns and timber harvest data extends to 2024, but the timespan of other disturbance data extends only to 2022.

All data sets are clipped to caribou range boundaries. For each caribou range, three metrics are tracked: the Current State of Disturbance, the Cumulative Rate of Disturbance, and the Net Rate of Disturbance.

Calculating the cumulative rate of disturbance

The Cumulative Rate of Disturbance estimates the cumulative amount of disturbance annually within a given caribou range from 1960 to the most current year of data. Because this metric is cumulative and does not consider recovery from disturbance, the rate will always be greater than zero (i.e., never decreasing). Estimates are presented both as the percentage of the range area disturbed and the actual area of disturbance (in hectares). Estimates are also provided for each disturbance type (i.e., burns, forest harvest, and linear features). 

Plots of annual estimates through time provide an evaluation of trends in the rate of disturbance accumulation within a given caribou range since 1960. In addition, histograms depicting the amount of disturbance created within caribou range during a given year or decade are also provided for each disturbance type to further evaluate trends in the rate of disturbance accumulation.

Estimating the annual disturbance footprint

To estimate the amount of disturbed area per range annually from 1960 to the most current year of data, all disturbances known to occur during or before 1960 are placed in each range. In each subsequent year, disturbances occurring in that year are added in the following order: seismic lines, pipelines, mountain pine beetle, timber harvest, agriculture / cultivation, abandoned well sites, residential areas, transmission lines, recreational areas, other vegetated surfaces, landfills, active well sites, industrial sites, mines, verges, canals, railways, roads, BPSDL (borrow pits, sumps, dugouts, and lagoons), hydroelectric dams and reservoirs, then burns. Added disturbances superseded existing disturbances where overlaps occurred (e.g., an area of timber harvest that was burned  was subsequently tracked as a burn). After this process, the amount of disturbed area annually was calculated as the total area (in hectares) of the disturbance footprint.

To derive the various metrics outlined above, the structure of the disturbance footprint varied depending on the metric. Specifically, the annual area of cumulative disturbance is derived by summing the area of all disturbances occurring within a caribou range up to a given year with no consideration of recovery. To estimate the area of net disturbance, disturbances considered to be recovered are removed and only the areas of unrecovered disturbances are summed. For buffered analyses, all unrecovered human-caused disturbances are first buffered by 500 m, then any overlapping buffers are dissolved.  This buffered area is then added to the area of unrecovered natural disturbance (e.g., wildfire burns and forested areas affected by pest outbreaks). 

The estimates of disturbed area are also expressed as a percentage of the range that is disturbed, using the following equation

% undisturbed = (area of disturbances / range area

where the structure of the numerator is changed to derive the various metrics outlined above. For example, to estimate the percentage of net disturbance, the numerator consists of the summed  areas of unrecovered disturbances. 

Estimates of the various metrics are also provided at the population level (Boreal, Northern Mountain, and Southern Mountain) and, for Southern Mountain caribou, at the group level (Central, Northern and Southern). For these estimates, the numerator in the above formula comprises the amount of disturbed area per range annually summed across all ranges within the population or group and the denominator is the area of each range summed across all ranges within the population or group.