Brush Control, Livestock Grazing, Wildlife Habitat and Natural Ecosystems:

Integrated Land Management on Canadian Parkland Community Pastures

G.M. Luciuk, G. Bowes, B. Kirychuk, T. Weins, and R. Gaube

The Prairie Farm Rehabilitation Administration (PFRA) Community Pasture Program began in 1935 with dual economic and environmental objectives. The objectives of the program are to provide economical grazing for prairie farmers while conserving the ecosystems that the pastures are part of. PFRA currently manages 929,000 hectares in 87 pastures in the prairie and boreal plain ecozones of the Canadian prairies. Native rangeland comprises 782,000 ha (84%), while 147,000 ha (16%) is tame forage. Some 4,000 patrons use the grazing and breeding services provided by PFRA for 124,000 cows and 3,100 horses. Full care, on a cost recovery basis, is provided for the livestock during the May to October grazing season.

Brush encroachment, particularly by trembling aspen (Populus tremuloides), is a major management concern on 32 of the 87 pastures. Other species of concern are: Populus balsamifera, Symphoricarpos occidentalis, Rosa sp., Elaeagnus commutata, Salix sp., and Quercus macrocarpa. These pastures are located in the parkland and boreal transition ecoregions. This is a transition area between the prairie grassland and the boreal forest. Current estimates place native vegetation at less than 20% in this area. Historically this area was 10 - 30% aspen groves with the remaining area being grassland (Bailey and Wroe, 1974). Control of wildfire and loss of the large roaming bison herds which browsed and trampled the woody vegetation has eliminated natural vegetation controls (Nelson and England, 1971) resulting in more rapid woody plant expansion.

Brush Expansion

Brush cover was estimated using a combination of satellite imagery and pasture manager estimates on 28 of the 32 pastures affected by brush expansion (Bowes, 1998). Woody species currently cover 109,506 hectares of the 270,976 total hectares or 40% of the 28 pastures studied. Woody species expansion rate was estimated using regressions from measurement of brush expansion over a number of years (Figure 1) (Bowes, 1996a). As total area covered with aspen increases, the expansion rate increases. Applying these regressions to PFRA pastures revealed that brush is expanding at a rate of 5,881 ha (2.2% of studied area) per year. Areas with the greatest rate of expansion were previously cleared areas, with the uncleared areas having the lowest rate of expansion and the greatest amount of open grassland. It was concluded that rate of aspen expansion is associated with previous treatment method and current land coverage by brush.

Brush encroachment on pastures hinders PFRA's ability to meet both primary objectives of the community pasture program: 1) provision of economical grazing for producers; 2) conservation of the unique landscapes that the pastures represent.

Economic Costs

Forested rangelands produce less forage for cattle and horses than open grassland, thus reducing the amount of livestock grazing allocated to producers. A comparison of recommended stocking rates for the Canadian parklands shows that carrying capacity reductions can be significant. Wooded rangeland provides 70% less carrying capacity than open native grassland (1.25 AUM/ha on native grassland versus 0.38 AUM/ha under closed canopy mature aspen). Long term Good condition seeded pasture has 85% more carrying capacity (2.5 AUM/ha on Good condition seeded pasture versus 0.38 AUM/ha under closed canopy mature aspen). Analysis of the fields in parkland pastures demonstrates that as brush cover increases carrying capacity proportionally decreases (Figure 2). Closing of the aspen canopy does not immediately result in carrying capacity equal to that of an aspen forest (Garry Bowes, personal comm.). Even when the canopy closes, a number of years are required before the understory evolves to that of an aspen forest. Thus, in the transition period stocking rates are intermediate between open grassland and aspen forest.

Cost of operations are also increased as expenses increase for building, maintaining, and keeping fence lines cleared. Livestock health treatment costs increase as do labor requirements to check and treat livestock. Staff injury rates are also higher.

Conservation Concerns

Recent governmental agreements reflect emerging societal pressures for an expanded role of community pastures in the conservation of natural landscapes. In 1998 PFRA community pastures became part of the Saskatchewan Representative Areas Network, which is a system of areas legally designated to conserve landscapes that are representative of natural ecosystems. At the same time, proposed Federal and Provincial legislation will require public land managers to conserve habitat used by species at risk. Recent surveys show that more than 70% of the community pasture units in Alberta and Saskatchewan have endangered species present (Luciuk et al, 1997). Nineteen different species at risk have been found on PFRA pastures. These species are concentrated on community pastures because of the large contiguous blocks of good condition native rangeland. Since the parkland was historically 10-30% brush any further cover increases would represent a degradation of the natural ecosystem.

Shrub and tree expansion reduce grassland habitat for wildlife species requiring this type of landscape. Many species require a diversity of cover, for various life functions (thermal cover, protection, food, breeding). A recent study of on farm wildlife habitat and biodiversity found the largest variety of plant and animal species in the transition area between aspen groves and open grassland (Godwin, et. al, 1998). Thus, conservation objectives necessitate land management strategies that maintain historical levels of open grassland.

The Action Plan

PFRA has set a goal of maintaining the current level of brush cover, thus brush expansion must be arrested. Management plans will be implemented to stop brush expansion on most cleared fields, and uncleared fields with large areas of grassland. The focus will be on juvenile woody species which are easier to control. An integrated approach will be used as any single treatment will not be effective (Bailey, 1990). Available field scale aspen control measures result in dense suckering (Kirychuk, 1994). Thus, follow up treatments must focus on sucker control. A combination of fire, controlled grazing, herbicide and mechanical treatments will be used.

Fire is a natural method of controlling tree invasion, and is very inexpensive on large areas, but also very dangerous. Fire will be used on juvenile and some mature aspen to prevent large blocks of over mature or decadent aspen.

Various mechanical treatments will address specific field management needs. Rotary mowers will be used primarily to keep fence lines clear. Relatively inexpensive bark scrapers, will be used in limited areas, to lay down and scrape the bark of 2 to 7 metre tall trees. While scrapers reduce suckering compared to mowers and fire, dead trees must be cleaned up to allow livestock access. The primary implement used will be a roller-chopper which rolls over and cuts trees into small pieces. The level of suckering following the roller-chopper remains unstudied.

Herbicide has also proven very effective in controlling 1-2 year old aspen suckers (Bowes, 1996a). Reduced reliance on aerial application of herbicides and increased precise ground application methods are being examined. Global positioning systems, will enhance the capability to precisely locate areas for ground spraying or wiping. Wipers are effective but only on trees up to 1-2 metres in height. However, wipers are target selective and allow the flexibility of cheaper non-selective herbicides. Boom buster and cluster nozzles are more effective on taller brush, but less selective. Non-target damage will be minimized by applying herbicide only to areas with controllable sized trees.

Controlled grazing will be used in conjunction with the above treatments and is the key to overall effectiveness. Cattle concentrated in high densities will reduce grazing selectivity and increase browsing, thus reducing the density of 1 year old suckers (Bailey, 1990). Two pass grazing systems (June and August) will enhance winter killing of suckers which are repeatedly browsed.

In order to meet the dual goals of economic livestock grazing and ecosystem conservation, brush expansion must be managed. Current research will give PFRA the technology to achieve multiple resource management goals.

References

Bailey, A.W., B.D. Irving, and R.D. Fitzgerald. 1990. Regeneration of woody species following burning and grazing in aspen parkland. J. Range Manage. 43: 212-215.

Bailey, A.W. and R.A. Wroe. 1974. Aspen invasion in a portion of the Alberta parklands. J. Range Manage. 27: 263-266.

Bowes, G.G. 1996a. Aspen sucker control with herbicides. Saskatoon Research Centre. 4pp.

Bowes, G.G. 1998. Brush on PFRA Pastures: The best approach to maintaining pasture productivity and wildlife habitat is an integrated brush management and control program. PFRA, Regina. 22pp.

Godwin, B., J. Thorpe, K. Pivnick, and J. Bantle. 1998. Conservation and enhancement of on-farm wildlife habitat and biodiversity. Saskatchewan Research Council Pub. No. R-1540-5-E98. 136pp.

Kirychuk, B.D. 1994. The effects of fire and grazing on herbaceous and woody plant species on seeded grazing land in east-central Saskatchewan. M.Ag Thesis, University of Alberta. 52pp.

Luciuk, G.M., B. Bristol, T.W. Weins, and D.M. Boyle. 1997. The potential impact of endangered species legislation on federal grazing lands and the livestock industry. Proc. XVIII Int. Grassland Congr. Winnipeg and Saskatoon.

Nelson, J.G. and R.E. England. 1971. Some comments on the causes and effects of fire in the northern grassland area of Canada and the nearby United States. CA. 1750-1900. Can. Geogr. 15: 295-306.