RENR690 - Introduction

Introduction

Background and Rationale

Vegetation Management in Alberta

The transition to a sustainable management framework in Alberta’s forestry sector is reflected in shifting policies to address the complex intersection of economic, ecological, and social factors (Government of Alberta 2006). Following timber harvest, cutblocks (Fig 1) are typically planted with white spruce (Picea glauca (Moench) Voss) and lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) to achieve desired stocking levels to meet management objectives efficiently (Dempster 2022; Gärtner et al. 2011). Species well adapted to colonizing post-disturbance landscapes, like fireweed (Chamaenerion angustifolium L.) (Fig 2), bluejoint grass (Calamagrostis canadensis (Michx.) P. Beauv.), and aspen (Populus tremuloides Michx.), can establish rapidly in cutblocks and may inhibit the success of planted seedlings by competing for critical resources, like water, nutrients, and light (Dempster 2022; Gärtner et al. 2011; Cortini & Comeau 2008). To mitigate this, vegetation management is used to reduce the amount of competitive vegetation, in turn increasing coniferous tree growth and survival (Cortini & Comeau 2008; Balandier et al. 2006), and promoting the development of mature coniferous stands.

Fig 1. Aerial view of a harvested cutblock selected for grazing in the Weyerhaeuser Pembina Timberlands Forest Management Agreement area (FMA).

Fig 2. Fireweed flowers. Fireweed reproduces via wind dispersal, establishing rapidly on disturbed sites.

Current Practices and Public Perceptions

Glyphosate-based herbicides are widely used for vegetation management in Alberta, with thousands of hectares receiving aerial application of herbicides each year; it is also extensively used around the world in both agricultural and forestry contexts (Duke & Powles 2008; Comeau & Fraser 2018). The use of glyphosate-based herbicides can be credited to their success in controlling bluejoint grass and aspen in Alberta’s forest plantations while having relatively low negative environmental impact (Comeau & Fraser 2018). While Glyphosate-based herbicides have proven effective, they are not widely accepted by the public. In Ontario, a study of public perceptions of vegetation management revealed that aerially-applied herbicides were viewed as least acceptable, while manual cutting and grazing animals were ranked as most acceptable (Wagner et al. 1998). Additionally, the use of herbicides is particularly concerning amongst Indigenous peoples, with some First Nations community members expressing concerns about the impact of glyphosate-based herbicides on the environment and human health, and the movement and persistence of herbicides in the forest landscape (Patterson et al. 2023).

Growing public concern has motivated interest in alternative vegetation management methods that align with sustainable forest management values. Grazing sheep are more costly than aerial herbicides (averaging $465/ha compared to $248/ha), but less expensive than manual removal ($740/ha) (Newsome et al. 1995).

As forest policy and management decision-making become more complex, having a range of vegetation management options is essential to meeting reforestation and timber growth objectives. Current knowledge of sheep vegetation management in coniferous forests in British Columbia is promising, with one study finding increased internodal length in trees on sheep-grazed sites, while another observed a reduction in vegetation cover and a slight improvement in seedling growth (Serra et al. 2014; Newsome 1996). However, success is dependent on several factors, including palatability of vegetation, the timing of grazing, frequency, and stocking levels, so the need to further understand and refine this vegetation management alternative remains.

Fig 3. Ewe (female sheep) grazing in overnight pen.

Fig 4. Livestock guardian and herding dogs work with shepherds to protect and move the flock through cutblocks.

Fig 5. Flock of sheep resting in cutblock. The ewes cycle between grazing and resting.

Research Objectives

This project aims to determine if sheep grazing is a viable vegetation management tool in response to public scrutiny over current practices and shifting management paradigms. As stakeholder values are increasingly brought to the forefront of decision-making, the need for diverse tools to manage forests effectively grows. With this research, we hope to not only explore the connection between grazing and tree competition but also expand the silvicultural toolkit available to foresters with a potentially beneficial and sustainable option for managing vegetation aligned with management objectives and stakeholder values. With this in mind, the objectives of this project are as follows:

Evaluate the effect of sheep grazing on spruce and pine seedling competition, by assessing overall vegetation competition and competition from specific vegetation groups (deciduous trees, shrubs, forbs, and grasses).
Assess the impact of sheep grazing treatment by evaluating vegetation biomass and crop tree condition in grazed and fenced plots.

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