Milk and Lower Marias River Watersheds: Assessing and Maintaining the Health of Wetland Communities
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Milk and Lower Marias River Watersheds: Assessing and Maintaining the Health of Wetland Communities Prepared for: The Bureau of Reclamation By: W. Marc Jones Montana Natural Heritage Program Natural Resource Information System Montana State Library June 2003 Milk and Lower Marias River Watersheds: Assessing and Maintaining the Health of Wetland Communities Prepared for: The Bureau of Reclamation Agreement Number: 01 FG 601 522 By: W. Marc Jones 2003 Montana Natural Heritage Program P.O. Box 201800 • 1515 East Sixth Avenue • Helena, MT 59620-1800 • 406-444-3009 This prefered citation for this document is: Jones, W. M. 2003. Milk and Lower Marias River Watersheds: Assessing and Maintaining the Health of Wetland Communities. Report to the Bureau of Reclamation. Montana Natural Heritage Program, Helena. 17 pp. plus appendices. Table of Contents Introduction..................................................................................................................................... 1 Study Area ...................................................................................................................................... 1 Physical Setting ........................................................................................................................... 1 Vegetation and Ecological Processes .......................................................................................... 3 Methods........................................................................................................................................... 6 Data Collection............................................................................................................................ 6 Data Management........................................................................................................................ 7 Site and Community Ranking......................................................................................................7 Community Rarity Ranks (State and Global Ranks) ............................................................... 7 Community Viability Ranks..................................................................................................... 8 Site Ranks................................................................................................................................. 8 Plant Community Classification..................................................................................................9 Nomenclature.............................................................................................................................. 10 Results and Discussion .................................................................................................................. 10 Status of Wetland Resources...................................................................................................... 10 Riparian Wetlands................................................................................................................... 10 Depressional Wetlands........................................................................................................... 13 Conservation Implications......................................................................................................... 13 Acknowlegments........................................................................................................................... 14 Literature Cited............................................................................................................................. 14 Appendix A. Global/State Rank Definitions Appendix B. Site Descriptions Appendix C. Site Rank Criteria for Wetlands and Riparian Areas Appendix D. Plant Community Descriptions INTRODUCTION quality wetlands within the study area. Un- derstanding the diversity, location, and con- Historically, wetlands have been considered dition of wetland and riparian areas will help unproductive lands with little value to soci- to minimize potential impacts to these re- ety (Mitsch and Gosselink 1993). Conse- sources. quently, wetlands have long been drained, filled, or otherwise manipulated to produce STUDY AREA goods and services valued by society. This has resulted in significant wetland destruc- Physical Setting tion and degradation in the United States. Dahl (1990) estimated that over half of the The study area is in north central Montana in wetlands acres in the conterminous United Liberty, Choteau, Hill, Blaine, Phillips, and States have been lost since 1780, and that Valley Counties. It is within the Montana approximately 25% of Montana’s wetland Glaciated Plains subsection of the Great acres have been lost in the same period. Plains ecological unit and includes the lower Milk and Marias River watersheds below In the last 20 years, as awareness of the cu- Fresno and Tiber Dams, respectively (Figure mulative loss and damage to wetlands in the 1). Milk River tributaries, such as Battle, United States has grown, so too has soci- Assiniboine, and Whitewater Creeks, are ety’s appreciation of the ecological impor- within the study location. This region is tance and economic benefits of wetlands. characterized by plains, terraces, and flood- This recognition has increased the regula- plains that formed in glacial till, gravel de- tory oversight on wetland-disturbing activi- posits, and alluvium over clay shale, sand- ties and expanded opportunities for wetland stone, and siltstone (Nesser et al. 1997). conservation. The prairie landscape of the study area has In the semi-arid northern Great Plains, modest vertical relief. Elevations along the where water demand may exceed supply, Milk River range from 600 m at Glasgow to water resource management has a direct 750 m near Fresno Dam. Elevations along bearing on the condition and persistence of the Marias River range from 750 m at its remaining wetlands. The Bureau of Recla- confluence with the Missouri River to 900 m mation is one of the main government agen- at Tiber Dam. The gently rolling nature of cies charged with managing water flows and today’s landscape was created by episodes availability in the region. The Bureau is in- of past glaciation when this area was volved with settling a dispute between Na- scoured by the Keewatin ice sheet. Glacial tive American tribes and the government till, outwash, and drift up to 100 feet thick over availability of water in the Milk River mantle the rolling terrain (Nesser et al. drainage. Settlement of these water rights 1997). In areas lacking surface drainage, may change water diversions and distribu- small wetlands are sporadically distributed tions in the area, consequently affecting the and may have formed in partially filled ket- functional and ecological integrity of wet- tle holes created when stranded ice blocks lands and riparian areas. melted following glaciation. These small wetlands, termed prairie potholes, are espe- The purpose of this study is to provide the cially prevalent in the northern portion of Bureau information on riparian and wetland the study area. resources and to document remaining high 1 The most extensive geologic substrate in the at any time. However, wind redistributes study area, extending from Canada to the snow to lee positions (usually northeast- to Missouri River, is marine-origin clay shale east-facing exposures) and swales, where and shale of the Bearpaw and Claggett for- subsequent compaction results in considera- mations. Sandstone and sandy shale is lo- bly higher moisture content than on flats. cally common in the study area and is most Snow redistribution may play an under- abundant in the breaks along the Marias and appreciated role in the distribution of plant Milk Rivers. Quaternary age alluvium fills communities in plains environments. The most of the valley bottom of the Milk River. heaviest snowfalls consistently occur in late winter to early spring and are often accom- This part of Montana is considered semi-arid panied by high winds causing blizzard con- with a precipitation average from 10 to 12 ditions and massive drifting. inches annually. The climate is continental and temperate with frigid winters and warm Vegetation and Ecological Processes to hot summers. Average temperatures at Havre range from a minimum of 3.6ºF in Riparian habitats along the Milk and Marias January to a maximum of 84.7ºF in July Rivers are characterized by oxbow marshes, (Western Regional Climate Center 2003). shrub-dominated terraces, and cottonwood The precipitation regime peaks in late gallery forests. In the semi-arid Great spring-early summer with steady, soaking Plains, these riparian areas provide critically frontal system rains. Summer rainfall comes important wildlife habitat as well as eco- mainly from convection thunderstorms that nomic and recreational benefits (Finch and typically deliver bursts of intense rain in Ruggiero 1993). They also provide habitat scattered locations. These storms are often for several plant and animal species of con- accompanied by large-diameter hail and cern (Table 1). Cottonwood forests and flashfloods. Where rainfall exceeds evapo- woodlands are the most characteristic ripar- transpiration, conditions are suitable for ag- ian vegetation and are one of the few native riculture, particularly cereal grains. The habitats dominated by trees. Three species growing season is typically 110-130 days of cottonwood occur in the study area: with approximately 70-80% of annual pre- plains cottonwood (Populus deltoides), nar- cipitation falling within that