BACKGROUND:
Fig. 1 Composition of neighboring vegetation can vary drastically in plantations. One goal of this study is to determine whether differing weed compositions have an impact on tree growth
As global demand for fiber increases the ability of western Canada to help meet the demand is largely restricted without a suitable alternative method of production. Fortunately, plantations of fast-growing hybrid poplar trees show good promise as a stable wood fiber source to help increase the supply and stimulate local economies throughout the region. Hybrid poplar trees are particularly well suited for the task due to their ability to survive cold annual temperatures while capable of producing on average 3-29 t ha-1yr-1 when grown in a plantation setting (Park and Wilson 2007, Christersson 2010).
Hybrid poplar plantations are often less than successful because competitive pressures from weeds prevent many trees from surviving or reaching their full potential. This is especially evident during the early establishment years (1-3) when the seedlings are at their most vulnerable to competition for sunlight as well as water and nutrients due to their roots occupying the same soil horizons as most forms of herbaceous vegetation (Balandier et al. 2002; Zutter et al. 1999), see Fig 1.
The consequences of competition are an overall reduction in fiber production and thus the loss of profitability for the forest industry. Most commercial operations at the present manage weed competition by adopting standard silvicultural practices consisting of frequent cultivation during the early establishment years coupled with the application of non-selective herbicides in the springtime prior to leaf-out. Selective herbicides and pesticides may be applied as needed during the growing season. When the trees are older it may also be necessary to use directed applications of a non-selective herbicide to the understory.
Such measures, though effective in reducing weed cover, are also extreme in terms of costs to the operators (equipment, fuel, supplies) and the local environment (erosion, pesticide accumulation, loss of soil carbon). Moreover, the efficacy of these methods for increasing tree growth is unknown because of the lack of knowledge concerning the quantifiable impacts of weeds to the well-being of nearby poplar trees. Little is known about how the composition and abundance of weed communities and their spatial relationships to nearby poplar trees will affect the trees’ growth. The ability to enumerate this relationship will be essential for the development of an integrated weed management plan in the future that will operate on a strategy of economic thresholds to maximize income for the industry while minimizing negative environmental impacts.
Hybrid poplar plantations are often less than successful because competitive pressures from weeds prevent many trees from surviving or reaching their full potential. This is especially evident during the early establishment years (1-3) when the seedlings are at their most vulnerable to competition for sunlight as well as water and nutrients due to their roots occupying the same soil horizons as most forms of herbaceous vegetation (Balandier et al. 2002; Zutter et al. 1999), see Fig 1.
The consequences of competition are an overall reduction in fiber production and thus the loss of profitability for the forest industry. Most commercial operations at the present manage weed competition by adopting standard silvicultural practices consisting of frequent cultivation during the early establishment years coupled with the application of non-selective herbicides in the springtime prior to leaf-out. Selective herbicides and pesticides may be applied as needed during the growing season. When the trees are older it may also be necessary to use directed applications of a non-selective herbicide to the understory.
Such measures, though effective in reducing weed cover, are also extreme in terms of costs to the operators (equipment, fuel, supplies) and the local environment (erosion, pesticide accumulation, loss of soil carbon). Moreover, the efficacy of these methods for increasing tree growth is unknown because of the lack of knowledge concerning the quantifiable impacts of weeds to the well-being of nearby poplar trees. Little is known about how the composition and abundance of weed communities and their spatial relationships to nearby poplar trees will affect the trees’ growth. The ability to enumerate this relationship will be essential for the development of an integrated weed management plan in the future that will operate on a strategy of economic thresholds to maximize income for the industry while minimizing negative environmental impacts.
OBJECTIVES:
To order to obtain the knowledge of weed-tree dynamics which is required to make an effective integrated weed management plan a two part study was carried out on operational plantations in central Alberta with the following objectives:
- Quantify the impact of weed composition, abundance, and proximity on growth and survival of hybrid poplar in plantations during the early establishment period (years 1-2).
- Test the effectiveness of different vegetation control methods employing a combination of cultivation and herbicide regimes varying in intensity in both space and time