Academic journal article The American Midland Naturalist

Effects of Weather and Land Management on the Western Prairie Fringed-Orchid (Platanthera Praeclara) at the Northern Limit of Its Range in Manitoba, Canada

Academic journal article The American Midland Naturalist

Effects of Weather and Land Management on the Western Prairie Fringed-Orchid (Platanthera Praeclara) at the Northern Limit of Its Range in Manitoba, Canada

Article excerpt

Introduction

The western prairie fringed-orchid (Platanthera praeclara Sheviak and Bowles) is a rare North American orchid restricted to a few remnants of wet to mesic tallgrass prairie in the American Midwest and southern Manitoba (Environment Canada, 2006). Populations have declined primarily because of loss and degradation of native tallgrass prairie habitat on which the species depends. Much of the North American tallgrass prairie was cultivated by early Europeans because of its high fertility, and sites unsuitable for ploughing were typically grazed by domestic livestock (Steinauer and Collins, 1996). Fire was suppressed where formerly wildfires and fires set by native tribes had burned portions of the landscape as regularly as every 2.6 y in some areas (Allen and Palmer, 2011), and periodic grazing by bison (Bison bison) was largely replaced by regular and often uniform grazing by cattle (Bos taurus:, Knapp et ai, 1999). These changes have had profound effects on the tallgrass prairie ecosystem. Less than 5% remains of the 68 million ha that are estimated to have existed prior to European arrival (Samson and Knopf, 1994). Fire suppression and unmanaged grazing have resulted in extensive woody encroachment and poor diversity in many remnant tallgrass prairie patches (Howe, 1994; Briggs et ai, 2002; Lett and Knapp, 2005). Many species that are dependent on native tallgrass prairie, such as the western prairie fringed-orchid, are now found only in small pockets of isolated prairie or in protected areas.

The western prairie fringed-orchid is federally listed as endangered in Canada and threatened in the United States. Two key management objectives identified in federal recovery plans are to monitor population trends and identify beneficial management practices to counter continued population declines of this species. Our objectives were to assess how weather and land management affect the western prairie fringed-orchid metapopulation in Manitoba. Specifically, we were interested to know; (1) if and how population fluctuations corresponded with weather patterns, and (2) which broad-scale management practices best supported the fringed-orchid metapopulation. Understanding the effects of weather on western prairie fringed-orchid populations can improve management by enabling managers to predict population fluctuations and adjust management activities accordingly.

METHODS

STUDY AREA

The 12,728 acre (5170 ha) Tall Grass Prairie Preserve (TGPP) near Tolstoi, Stuartbum, and Gardenton, Manitoba (49°04'45"N, 96°43'53"W) protects most of the known Canadian metapopulation of western prairie fringed-orchids (Environment Canada, 2006). Most of the TGPP lands (78%) are owned by the Nature Conservancy of Canada (NCC) with the balance being owned by Nature Manitoba and Manitoba Habitat Heritage Corporation. The lands are jointly managed through a Management Committee that includes NCC, Manitoba Conservation and Water Stewardship, Environment Canada, Nature Manitoba, and the Manitoba Habitat Heritage Corporation.

Management activities at the TGPP include prescribed burning and grazing. Long-term fire management plans call for each TGPP property to be burned through prescribed fire once every 5 y, typically in spring or fall. Properties are not grazed in the year prior to prescribed fire. Actual fire frequency often departs from prescription due to occasional wildfires and seasonal weather conditions not conducive to the use of prescribed fire (e.g., too wet, too dry). Since 1995 a twice-over rotational grazing system has been used with regularity (*.«., at least one site grazed each year, more typically 6-8 sites) for management at the TGPP. Prior to 1995 grazing was irregular with some sites grazed using a once-over rotational grazing system, and at one site season-long grazing was permitted.

DATA COLLECTION

Tall Grass Prairie Preserve biological staff (via the Critical Wildlife Habitat Program) has conducted annual surveys for flowering western prairie-fringed orchid at the TGPP and surrounding areas since 1992 (Fig. …

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