Golder Associates
December 2015
Executive Summary
To meet habitat targets within boreal caribou ranges, the federal Recovery Strategy for the Woodland Caribou, Boreal Population in Canada (Environment Canada 2012) identifies coordinated actions to reclaim woodland caribou habitat as a mitigation step to meeting current and future caribou population objectives. Actions include restoring industrial landscape features such as roads, seismic lines, pipelines, cut-lines, and cleared areas in an effort to reduce landscape fragmentation and the changes in caribou population dynamics associated with changing predator-prey dynamics in highly fragmented landscapes. Based on the federal recovery strategy habitat targets and current range conditions, it is expected that boreal caribou range plans in Alberta will have a requirement to restore significant amounts of habitat along linear disturbance features. Habitat restoration (i.e., mechanical site preparation, planting and/or seeding of tree species) as well as implementing access control measures are considered the primary mechanisms to enhance the rate of recovery of linear disturbance features to naturally occurring vegetation.
As caribou habitat restoration initiatives have become more widespread across Alberta in the last decade, key uncertainties have been recognized regarding what treatment types are appropriate for habitat restoration, how to measure success, and timelines to reach functional habitat. To that end, a collaborative research initiative was initiated by Golder Associates with support from the Foothills Landscape Management Forum (FLMF), the Petroleum Technology Alliance of Canada (PTAC) and the Government of Alberta to monitor the vegetation attributes on restoration treatment sites implemented from 2001 to 2007, as part of the Caribou Range Restoration Project in the Little Smoky caribou range.
The study approach for this project attempted to understand how planted and naturally ingressing tree seedling species (black spruce and lodgepole pine) responded to site treatments in order to answer the following questions: 1) Are planted seedlings significantly taller compared to naturally ingressing seedlings on treated sites?; 2) Is the average current year’s leader growth significantly greater for planted seedlings compared to naturally ingressing seedlings on treated sites?; and 3) Are planted seedlings or naturally ingressing seedlings on treated sites significantly taller than seedlings on untreated naturally recovering lines? Growth patterns (i.e., individual tree height-age trajectories) were also modelled for both planted and naturally ingressing tree species on treated sites using mean leader growth, mean height and age to determine their respective trajectories within both lowland and upland sites.
A field program was conducted during the summer of 2015 to collect regeneration data on treated seismic lines (68 plots) and naturally revegetating seismic lines (3 plots). Data collected in 2015 was supplemented by 2008 data collected on naturally regenerating seismic lines (13 plots). Survey locations were selected from seismic lines treated under the Caribou Range Restoration Project. Various ecological and tree regeneration data were collected at each site, as well as cursory soil information, and documentation of any wildlife or human usage. Treatment site details from the Caribou Range Restoration Project files including the time since treatment, type of treatment and a photographic inventory of all visited sites were captured together with the field data. Wooden fences installed through the Caribou Range Restoration Project for access control purposes were documented photographically as encountered during travel between survey sites.
For the purpose of analysis, treatment types were not separated out as the majority of sites were mounded and planted. The primary response variables were mean black spruce height and mean black spruce leader growth (current year) of planted and naturally ingressing seedlings. Mean lodgepole pine height and leader growth (current year) were also analyzed, though only for naturally ingressing seedlings, as lodgepole pine was generally not included in the original planting regime. Mean maximum age and height of lodgepole pine and black spruce were calculated to provide a relative comparison that could be plotted on respective height – age growth trajectories. Height – age trajectory models were developed for planted and natural ingress black spruce seedlings, on upland and lowland site types, as well as natural ingress of lodgepole pine seedlings on upland sites.
Overall, treated lines had little to no recent signs of ATV/UTV use and more than half of the wooden fences installed for access control in this area were found to be in relatively good condition. Mounding was the primary site treatment applied (69% of upland sites and 85% of lowland sites) and black spruce was the primary species planted on the mounds. Mounds degraded over time and were more obvious in upland sites compared to lowland sites. Mounding provided suitable microsites for natural ingress and both planted and natural ingress species were present on mounds.
Planted black spruces on treated sites were significantly taller and had significantly greater leader growth compared to natural ingress black spruce. Additionally, black spruce on treated lowland sites were found to be significantly taller and had significantly greater leader growth than upland sites. Overall, lowland sites on average had taller seedlings, with planted individuals being taller than naturally ingressing individuals. Treatment age, shrub cover and depth to water did not have a significant effect on the height of all black spruce seedlings (planted and natural ingress) measured on seismic lines.
The results from the height-age trajectory models showed that the predicted height of black spruce and lodgepole pine on upland or lowland sites, respectively, tended to be at the lower end of the provincial site index curves for the Upper Foothills Subregion, indicating a conservative model. Treating seismic lines on wetter sites through mounding and planting of black spruce indicated an acceleration of recovery times by a minimum of 4 to 5 years compared to natural ingress on treated lines and 10 years compared to naturally recovery on untreated lines. Planted black spruce on treated lowland sites reached 1.4 m by age 14 and 2.7 m by age 22, compared to natural ingress black spruce which reached 1.4 m by age 18 and 2.7 m by age 29.
In contrast, treating upland sites with mounding and planting of black spruce did not appear to accelerate the rate of recovery over natural vegetation recovery for either lodgepole pine (natural ingress) or black spruce. Although growth rates were similar or inconclusive for upland planted or natural ingress black spruce seedlings, it should be noted that the CRRP used mounding with the planting of black spruce on the top of the mounds within these treatment sites. These results suggest that treatment needs to be more targeted to natural regenerative systems and applied based on an understanding of site limiting factors (moisture, nutrients, shade) and conditions to achieve the most optimal results.
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