Introduction

The vegetative cover of upland areas is vital to the existence of a wetland area. By trapping snow during the winter months, trees, shrubs and grasses contribute to the replenishing of the wetland water supply. Any possible changes in climate resulting from human activity will have an effect on both wetlands and uplands. Because of this close relationship, an investigation of the carbon-holding potential of wetlands must incorporate the associated upland areas.

The extent of the carbon reservoir represented by upland areas depends on the size, location and type of cover in the area. Size can range from a fringe of a few metres to an entire watershed, depending on topography, location and wetland type. Vegetative cover types can vary greatly, from grasslands to forests or some combination. The potential of each cover type to sequester more carbon will depend on the land base available for improvement or enhancement. Another variable is the inclusion (or not) of the below-ground portion of the trees and plants. Inclusion of the carbon held in the roots of plants could increase the size of the reservoir by 0.3 to seven times, depending on cover type.

An altered prairie climate could substantially reduce the number of prairie wetlands. Changes in the frequency and quantity of precipitation may increase the need for snow trapping by upland cover so that current wetland areas are maintained. A wide variety of drought-hardy tree, shrub and grassland species are available for planting in the prairie and parkland region. The availability of these species makes it possible to design upland landscapes that maximize the carbon-holding and snow-trapping potential of a given cover type, and therefore its benefit to the wetland.

This section describes some of the information available on the carbon-holding potential of certain cover types. It will illustrate the range of possible values, and indicate areas where information is lacking.

Grasslands

Grasslands are the most common cover type in the prairie and parkland region. The carbon-holding potential of native and tame grasslands varies greatly, depending on soil type, soil texture, condition and climate. Above-ground biomass (dry weight) values for native grasslands are available for most of the region from rangeland management information. Animal stocking rates can also be readily converted to carbon values per hectare. The results of such conversions will yield above-ground carbon values for native prairie grasslands in the range of 0.04 to 0.9 tonnes per hectare, depending on soil zone and range condition (Abouguendia, 1990). The wide range of soil types and conditions described above provides information for most of the prairie and parkland region. The amount of below-ground biomass and carbon for this cover type may be worth investigating further. Estimates have been suggested at four to seven times the above-ground portion (Coupland, 1970), which would greatly increase the size of this carbon reservoir.

For this discussion, tame or seeded grasslands will include alfalfa, a non-grass species. These types of grasslands are very important in the agricultural parts of the region, and can represent a significant short-term carbon reservoir. The size of the reservoir varies depending on species, soil zone, stand age and other factors (Kirychuk and Tremblay, 1995) . Above-ground carbon values from 0.4 tonnes of carbon per ha to 2.6 tonnes of carbon per ha are possible. The below-ground component of this reservoir may increase the amount of carbon by two to four times (Rochette and Jaques, 1995).

Trees and Shrubs

Native tree and shrub cover occurs to some extent in all parts of the prairie and parkland region. In some of the drier parts, this type of cover is found exclusively in riparian or wetland-related areas. In much of the prairie region, the typical woody cover type around sloughs and wetlands is a ring of willows or other shrub species such as alder and dogwood. Connolly and Grigal (1983) describe biomass equations developed for these shrub species. These equations are applicable to the entire region, and the results are easily converted to above-ground carbon values. What must be developed is a sampling program, using these equations, which will provide carbon values (tonnes per hectare) for these species. Biomass equations and carbon content have also been developed for 12 woody species including choke cherry and buffaloberry (Kort and Turnock, 1996).

In the dark grey and black soils of the parkland and northern plains, trembling aspen and balsam poplar are the dominant tree species associated with riparian and wetland areas. Freedman and Keith (1995) provide carbon content for these stands for the Manitoba aspen parkland region. Above-ground values of 25.6 tonnes of carbon per ha and total values of 34.5 are described for 60-year-old stands on medium sites. Kort and Turnock (1997) give total carbon values for the woody component of riparian areas in the agricultural soil zones of Saskatchewan. They use a carbon value of 34.0 tonnes of carbon per hectare for the black soil zone, 22.3 tonnes carbon per ha for the dark brown soil zone and 20.6 tonnes carbon per ha for the brown soil zone. The carbon content of other native tree species associated with riparian areas has also been determined (Freedman and Keith, 1995), and can be applied to similar sites throughout the region.

Extensive information exists on the carbon content of native tree cover. However, much of this information is based on timber harvest yields, expanded to whole-tree and stand values. While these numbers are useful, more accurate, whole-tree sampling may be necessary to derive more reliable biomass and carbon values. This type of information may soon be available as a result of actions by the National Forestry and/or Sinks tables on climate change.

Upland areas can be planted with non-native tree and shrub species. This practice has been common on the Canadian prairies, where a tree planting program has been in existence for almost 100 years. Planted species are often used for field and farmyard shelterbelts, wildlife enhancement plantings, snow traps, watershed stabilization, or to otherwise enhance the prairie environment. Trees and shrubs often thrive in low areas around wetlands and are capable of sequestering large amounts of atmospheric carbon in their biomass. The PFRA Shelterbelt Centre has developed biomass equations and has determined the carbon content of 12 tree and shrub species (Kort and Turnock, 1996; Kort and Turnock, 1999). Above-ground carbon content ranges from 32.2 tonnes of carbon per ha for sea-buckthorn, a small shrub, to 298.0 tonnes of carbon per ha for hybrid poplar, a large tree. This wide range in carbon contents and adaptability allow for the creation of site-specific tree plantings. These plantings can be designed to maximize their carbon-holding potential and still function as an integral component of the wetland-based landscape.

Summary

The upland areas associated with prairie and parkland wetlands exhibit a variety of vegetative cover types capable of sequestering carbon to varying degrees. The carbon reservoirs that these areas represent are not as long lasting (years to decades) as other carbon sinks, such as soil organic carbon. But they are easy to establish, fast growing, significant in size, measurable, and vital to the health and stability of the local environment. These plants represent the link between atmospheric carbon and the more permanently fixed carbon held in the soil.

These types of cover also play an important role in the nitrogen cycle. Where these types of covers are established, nitrogen emissions from agricultural soils are reduced and nitrogen fertilizer use can be dramatically minimized. Alfalfa, caragana and sea-buckthorn are nitrogen-fixing plants, so the ability of trees and plants in upland areas to mitigate nitrogen-based greenhouse gas levels may extend beyond the carbon held in their biomass. It is because of the complex relationships between the different components of the prairie landscape that the carbon-holding potential of any one area must be seen as only a part of the overall picture. To conserve wetlands and to maximize their greenhouse gas mitigative potential, wetlands must be seen as a vital and contributing component of a healthy prairie environment.