Wild rice has received considerable recent attention in the St. Louis River watershed due to concerns over the environmental effects of mining on Minnesota's Iron Range, on the northern border of the watershed. Of particular interest is the effect of higher than historical concentrations of sulfate leached into waterways from piles of waste rock and taconite tailings, and potentially from future non-ferrous mining operations.
Wild rice typically grows in shallow water - 1 to 3 feet in depth on soft organic (mucky) sediments, and prefers flowing water. Unlike many aquatic plants, wild rice is an annual, reproducing from seed each year. The seeds of wild rice require a winter dormancy of about three months, with immersion in water at freezing, or near freezing, temperatures needed to break down the waxy coating that covers the seed. Seeds germinate when water temperatures reach 45 oF (Oelke et al.). After germination, the plant develops a system of spongy white roots that grow horizontally 9-12 inches. Like other grasses, wild rice also produces tillers - underground stems that give rise to other shoots. The number of tillers depends on stem density - sparser stands of wild rice produce more tillers on individual plants. Tillers are important in that they can also produce grain, but they tend to flower later than the source plant, which affects both the length of the harvest season and total yield of grain.
Seedlings have 3-4 leaves that remain underwater, with subsequent leaves reaching to and floating on the surface (Marcum 2007). Wild rice forms characteristic floating mats of ribbon-like leaves during mid-June. At this time, the plant is sensitive to water depth - rising waters will uproot the plants and lower water levels will damage the weak hollow stems. Wind and wave action can also uproot plants, and wakes from recreational watercraft are a persistent management issue on wild rice lakes and rivers.
Aerial shoots emerge from the water in late June and early July. The emergent plants grow 3-6 feet tall, with a central stalk supporting 5-6 elongated ribbon-like leaves ½ to 1 ½ inch in width. Flowers are produced in terminal clusters, with staminate (male) flowers on the lower stalk and upright pistillate (female flowers) on the upper branches. The female flowers emerge before the males, so plants are typically cross pollinated. Wind is the primary means of pollination. The seeds are surrounded by a papery hull with a long terminal awn, both of which are removed when rice is processed as a food source.
Wild rice flower close up image - photo credit UMN Extension. Click to zoom.
Wild rice flower close up image - photo credit UMN Extension.
Seeds of wild rice mature in late August. Like other grasses, an important phase of the life history is the “shattering” of the mature seed, which refers to the seeds dropping off the plant as they ripen. In natural systems, shattering occurs over a period of days to weeks, allowing multiple harvests of the wild rice beds. In cultivated rice paddies, shatter-resistant varieties are used to allow for a single mechanized harvest.
The productivity of wild rice beds varies from year to year. A rule-of-thumb provided by the Great Lakes Fisheries and Wildlife Commission is “a typical four year period will include a bumper year, two fair years and a bust”. Walker et al (2010) have attributed this pattern to the nutrient dynamics of decomposition of wild rice straw - the remains of the parent plants. Following a productive year, microbes in the bottom sediments are thought to take up much of the nitrogen as they begin the initial decomposition of plant litter, making it less available to wild rice plants. After a year or two, the final stages of decomposition occur and nitrogen again becomes available for plant growth. Understanding litter dynamics is important, in that it can lead to more informed decisions on the optimal times for seeding wild rice beds.
The distribution of wild rice has been greatly reduced from its historic range prior to European settlement (Meeker 2000, Vennum 1988). Pillsbury and McGuire (2009) reviewed numerous studies on wild rice decline, which are variously attributed to changes in pH and the presence of heavy metals and acids from copper-zinc smelting, [reduced] sediment nitrogen, [increasing] water level changes, and competition from other plants (i.e. invasives). In their study, Pillsbury and McGuire evaluated 60 wetlands which had historically dense wild rice populations but now vary in wild rice productivity, from high, to moderate to degraded. The study included two sites in the St. Louis River Estuary - Boy Scout landing, which now has low wild rice density, and Skibo Mills, which retains a healthy population. They assessed a range of environmental factors, from water chemistry to sediment type to watershed land use, and found that the strongest declines were associated with increased residential development and increased levels of ammonia-N (NH4+-N). Residential development is a predominant environmental stressor, indirectly resulting in increased stream temperature, sedimentation, and ‘flashiness’ of streams that feed the St. Louis River Estuary. The inverse relationship with NH4+-N is less straightforward, as wild rice is often limited by nitrogen availability, but may be related to increased competition from other plants stimulated by increased nutrient levels.
Wild Rice Conservation
Because of the degradation to natural populations, there are strong interests, particularly among the Fond du Lac Band of Lake Superior Ojibway (FDL), which directly and indirectly manages the wild rice resource in the St. Louis River watershed. The dominant method for managing wild rice is by control of water levels, through water control structures, ditch maintenance and beaver dam maintenance. FDL also has a strong program for removing competing vegetation, particularly the widespread pickerelweed (Pontederia cordata), an invasive species which has extensively colonized Perch and Jaskari Lakes on the reservation (Forbes 2005). The band uses a “Cookie Cutter” - a large platform based aquatic plant harvester that severs the mat of vegetation, which is then removed from the lake. This is often followed by wild rice re- seeding.
Photo courtesy of Fond du Lac Natural Resources Department.
At the landscape scale, wild rice conservation involves a complex interplay among social values, economy and ecology, all of which have underlying spatial dynamics (Drewes and Silbernagel 2012). Not only are populations and the yield of wild rice reduced from historic numbers, but the number of people participating in wild rice harvest is declining, and the average age of active harvesters is increasing. Moreover, management occurs at the level of individual lakes or individual communities - there are few active regional statewide or broader entities that look at the collective effects of local decisions. Given the current social and ecological trends, a regional perspective that allows for broader conversation and planning is essential to ensure the sustainability of this important species (Drewes and Silbernagel 2012).
Drewes, A. and J. Silbernagel. 2012. Uncovering the spatial dynamics of wild rice lakes, harvesters and management across Great Lakes landscapes for shared regional conservation. Ecological Modelling 229: 97-107.
Forbes, M. E. 2005. Assessing competitive interactions between wild rice (Zizania aquatica) and pickerel week (Pontedaria cordata) in a disturbed northern Minnesota wild rice lake. M.S. Thesis, University of Minnesota Duluth, Duluth, MN 99p.
Marcum, D.B. 2007. Cultivate wild rice production in California. University of California Agriculture and Natural Resources Publication 21622. 25 p.
Meeker, J. 2000. Ecology of ‘wild’ wild rice (Zizania palustris var palustris) in the Sakagon Sloughs, a riverine wetland on Lake Superior. p 68-84 In L. S. Williamson, L. A. Dlotkowski, and A. P. McCommon-Soltis (eds) Wild rice research and management. Great Lakes Fish and Wildlife Commission publication, Odanah, Wi, USA.
Oelke, E. A., T.M. Teynor, P.R. Carter, J.A. Percich, D.M. Noetzel, P.R. Bloom, R.A. Porter, C.E. Schertz, J.J. Boedicker, and E.I. Fuller. Alternative Field Crops Manual: Wild Rice. http://corn.agronomy.wisc.edu/Crops/WildRice.aspx Accessed 6.6.2013
Orcajada, P. 2012. Harvesting Wild Rice. Dept. of Crop Science, U. of Saskatchewan. http://www.agriculture.gov.sk.ca
Vennum, T. 1988. Wild Rice and the Ojibway People. Minn Historical society Press St. Paul.
Walker, R,. J. Pastor, and B. Dewey. 2010. Litter quantity and nitrogen immobilization cause oscillations in productivity of wild rice (Zizania palustris) in Northerm Minnesota. Ecosystems 13:485-498.
Wild Rice Information Resources
GLFWIC Wild Rice Brochure
Minnesota Wild Rice Management
Wisconsin Wild Rice Harvest Data
1854 Treaty Authority