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Recovery Strategy for the Buffalograss (Buchloë dactyloides) in Canada [Final Version]


1. Background

1.1 Species Assessment Information from COSEWIC

Date of Assessment. November 2001

Common Name: Buffalograss

Scientific Name: Buchloë dactyloides

COSEWICStatus: Threatened

Reason for Designation: A perennial clonal grass with male and female unisexual plants, with very restricted occurrences in two small areas of Saskatchewan and Manitoba and disjunction from the core range of the species to the south.

Canadian Occurrence: SK, MB

COSEWICStatus History: Designated Special Concern in April 1998. Status re-examined and designated Threatened in November 2001. Last assessment based on an existing status report.

1.2 Description

Figure 1. A buffalograss stolon.

Figure 1. A buffalograss stolon. © Enviornment Canada, Photo: Candace Neufeld.

Buffalograss (Buchloë dactyloides [Nutt.] Engelm.) is a member of the grass family (Poaceae). This perennial, late-developing (C4) shortgrass is unusual because it reproduces asexually by stolons1, and sexually by male and female flowers which almost always occur on separate plants (dioecious) (Quinn and Engel 1986, Huff and Wu 1992). Vegetative dispersal occurs along stolons (Figure 1), which root at the nodes, resulting in clonal patches as large as 3 m or more in diameter. Under ideal conditions, stolons can grow as much as 5.72 cm per day (Mueller 1941, Quinn 1991, Harms in press). Buffalograss can also reproduce vegetatively by rhizomes, but at a slower rate (Mueller 1941). Leaves are grayish-green and curly, about 2-10 cm long and 1-2 mm wide, with fine hairs on the upper and lower surfaces, including a fringe of hair where the leaf meets the stem. Flowering times vary among plants (Quinn 1991), but in Canada most flowering is complete by mid-July with ripened seed shattering by late July or early August (Harms in press, C. Neufeld, pers. obs.).

Figure 2. Male buffalograss plant (left) and female buffalograss plant (right).

Figure 2. Male buffalograss plant (left) and female buffalograss plant (right). ©USDA-NRCS PLANTS Database, Photo. Robert Soreng

Figure 3. Burs from female buffalograss plant.

Figure 3. Burs from female buffalograss plant. © Environment Canada, Photo: Candace Neufeld.

Buffalograss has separate male and female plants (Figure 2), with only an occasional report of monoecious plants containing both female and male parts (Quinn and Engel 1986, Shaw et al. 1987, Huff and Wu 1992). Male plants have 2 or 3 spikes, about 5 to 15 mm long, at the end of stalks up to 20 cm tall (Figure 2). Each spike is made up of spikelets, each of which contains two pollen-bearing grass flowers between papery bracts. Spikelets are arranged in two rows on one side of the spike. Pollen is wind dispersed, although dispersal distance is limited because the pollen is released close to the ground (Jones and Newell 1946, Beetle 1950, Quinn 1998). Male spikes superficially resemble flowering spikes of blue grama (Bouteloua gracilis), and because both species occur in the same habitat buffalograss is often overlooked. Tight clusters of two or three female flowers are hidden among the leaves, and enclosed in a bur-like structure on a short stalk (Figure 2). Upon maturing, these structures harden into globular, toothed burs containing 1-5 seeds (Figure 3; Looman and Best 1979, Boivin 1981, Quinn and Engel 1986, Harms in press). At least 50% of burs contain seeds producing both male and female plants (Quinn and Engel 1986, Quinn 1987). Burs become the dispersal units and remain intact to protect seeds from fire or heat damage, desiccation, or animal consumption. Burs also aid in dispersal, anchor seedlings to the ground, enhance seed longevity and inhibit germination until sufficient moisture is available (Ahring and Todd 1977, Quinn 1987). Dispersal of the bur by wind is limited because of its weight and location lower down in the foliage; thus, seeds tend to end up clumped in the soil near parent plants (Coffin and Lauenroth 1989, Quinn 1998). Long distance dispersal of burs is achieved through ingestion and passage through the intestinal tract of grazers (e.g., cattle or bison), and to a lesser extent by attachment to animal fur, mud on animal hooves, or in runoff water after a storm (Quinn 1987, Quinn 1991, Quinn et al. 1994, Quinn 1998). Buffalograss seeds, even within a single bur, have varying germination and dormancy periods, which may allow multiple chances to colonize a single microsite under varying climatic and competitive conditions (Quinn 1987).

1.3 Populations and Distribution

Buffalograss is native to North America, ranging from the Chihuahuan desert of central Mexico, through the west interior basin, and south-central and west-central semi-arid prairies of the United States, to the temperate semi-arid prairies of Canada (Figure 4; Commission for Environmental Cooperation 1997). In Canada, buffalograss is only found along the Souris River and its tributaries in south-east Saskatchewan, and south-west Manitoba. In both provinces, buffalograss is ranked as S1, or critically imperiled. Similarly, its national ranking in Canada is also critically imperiled, or N1 (NatureServe 2006). In 2001, the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) reassessed buffalograss as threatened instead of special concern based on an existing status report (COSEWIC in press). In the United States, buffalograss has a national status of N4N5, or demonstrably widespread, abundant and apparently secure (NatureServe 2006). Within its core in the United States, a status ranking has not been assigned for most of the states including Texas, Colorado, New Mexico, Oklahoma, Kansas, Nebraska, South Dakota, North Dakota, and Montana (NatureServe 2006). Disjunct or peripheral populations occur in Arkansas, Louisiana, Wisconsin, Georgia and Nevada where the status is not ranked. Peripheral populations of buffalograss in Arizona, Missouri, Iowa, and Utah have a status of critically imperiled (S1), and in Illinois buffalograss is imperiled (S2). An introduced population occurs in Virginia (NatureServe 2006). Globally, buffalograss is ranked as G4G5, or secure (NatureServe 2006).

Figure 4. Known range of buffalograss in North America (modified from Harms in press, USDA2006).

Figure 4. Known range of buffalograss in North America (modified from Harms in press, USDA 2006).

Buffalograss is a common grass species in much of the core of its range in the United States. It is likely that only one percent or less of the species' global distribution and abundance is found in Canada (Figure 4). According to the United States Department of Agriculture (USDA) Natural Resources Conservation Service's plant database (USDA 2006), the nearest locations in the United States are likely in North Dakota in the counties of Ward, Pierce and Walsh. Exact information on locations of buffalograss within these counties is not available; however, these sites are over 50-100 kilometers from locations in Manitoba and Saskatchewan.

1.3.1 Canada

In Canada, buffalograss is very restricted to localized areas of Manitoba and Saskatchewan (Figure 5). In Manitoba, 5 populations2 have been identified to date along a 17 km length of the Souris River valley, and an 8 km length of the Blind River valley (Foster and Hamel 2006, Manitoba Conservation Data Centre, unpubl. data). At the time the COSEWIC status report was prepared, Buffalograss was only known from 6 quarter-sections and was estimated to occupy 1.01 hectares in Manitoba (Harms in press). Subsequent search efforts have been more intensive, and as of 2006 Buffalograss is known to have an area of occupancy3 greater than 407 hectares distributed over 49 quarter-sections (Manitoba Conservation Data Centre, unpubl. data). Area of occupancy has not been measured for all known locations of buffalograss; only presence data has been collected for large portions of some populations. For example, mixed grass prairie surveys around the Souris River have found buffalograss present in 1,992 hectares; this value represents the total area surveyed rather than the specific areas where buffalograss is located, and may be considered the potential area of occupancy. Future surveying and mapping efforts will likely increase the known area of occupancy, and potentially the extent of occurrence (C. Foster, pers. comm.); currently disjunct populations may be amalgamated into fewer and larger populations.

In Saskatchewan, one population has been identified along the Souris River valley southwest to west of Estevan (Figure 5). At the time the COSEWIC status report was prepared, Buffalograss was only known from 10 quarter-sections and was estimated to occupy 0.02 hectares (234.5 ) in Saskatchewan (Harms in press). Following surveys completed in 2005 and 2006, Buffalograss is known to have an area of occupancy at least 1.27 ha distributed across at least 17 quarter-sections (C. Neufeld, unpubl. data). However, as with Manitoba, area of occupancy has not been measured for all known locations of Buffalograss; only presence data has been collected for some quarter-sections. Future surveying and mapping efforts will likely increase the known area of occupancy, and additional populations may be discovered in native grasslands south and east of Estevan.

Although it is likely that some buffalograss sites have been lost, there is insufficient historical and long-term data collected for this species, and a lack of standardized methodology, to determine a trend for area of occupancy.

Figure 5. Known range of buffalograss in Canada.

Figure 5. Known range of buffalograss in Canada.

1.4 Needs of Buffalograss

1.4.1 Habitat and biological needs

Buffalograss occurs in the Moist Mixed Prairie Ecoregion of Saskatchewan and in the Aspen Parkland Ecoregion of Manitoba, within the Prairie Ecozone (Wiken 1986, Ecological Stratification Working Group 1995; for more detail on physiography see Harms in press). This area is dominated by a steppe climate (northern cool-temperate zone) characterized as having occasional water deficits resulting from low precipitation, high evaporation, and rapid surface run-off (Harms in press, Fung et al. 1999). There is a strong seasonal pattern in both precipitation and temperature. Mean annual precipitation ranges from 433 mm in Saskatchewan to 467 mm in Manitoba; most falls in summer with a peak in June and winters are relatively dry. Summers are warm with a mean July temperature of 19.5 ° C, while winters are cold with a mean January temperature ranges from -14.8 ° C in Saskatchewan to -15.5 ° C in Manitoba (Environment Canada 2006).

Buffalograss is co-dominant with blue grama over much of the shortgrass and mixed-grass prairie of the United States, and is also common there in numerous other ecosystems (e.g., semidesert grasslands, coastal prairie, tallgrass prairie, pinyon-juniper, ponderosa pine woodland). On a microsite level, buffalograss occurs mostly on clay soils with a relatively higher moisture and phosphorus availability (Schimel et. al. 1985, Bai 1989, Richard and Redente 1995), and is more prevalent on lower slope positions relative to upland summits (Richard and Redente 1995, Reimer et al. 2003, C. Neufeld, pers. obs.). In Canada, Buffalograss is at its northernmost extent and appears restricted to specific habitat along the Souris River valley and tributary coulees in Saskatchewan and Manitoba, including the Blind River valley in Manitoba. Buffalograss inhabits dry, shallow coulee bottoms, lower coulee slopes, mid-slope benches, and adjacent upland in slight depressions or adjacent to soil disturbances like cattle trails (Harms in press, Reimer et al. 2003, C. Neufeld, pers. obs.). Soil parent materials include glacial fluvial meltwater channels with marine sedimentary rock exposures, as well as more recent eroded and colluvial slopes, alluvial fans and channels surrounded by glacial moraine and lacustrine deposits. The varying stages of soil development result in a range of soil suborders from orthic dark-brown and black chernozems, solods and solonetzic to rego chernozems, orthic and cumulic regosols (Eilers et al. 1978, Manitoba Land Resource Unit 1997, Saskatchewan Soil Survey 1997). One apparently consistent soil characteristic where Buffalograss occurs is clay to loam texture (Eilers et al.1978, Harms in press, Saskatchewan Soil Survey 1997, Reimer et al. 2003, C. Foster, pers. comm.).

Buffalograss typically inhabits areas disturbed by grazing and dominated by blue grama (Bouteloua gracilis), needle-and-thread grass (Stipa comata) and western wheatgrass (Agropyron {Pascopyrum} smithii) (Harms in press, Reimer et al. 2003). As buffalograss typically forms dense circular clones which exclude most other species, it is often the dominant plant where it grows, comprising up to 80-90% of the ground cover (Reimer et al. 2003, C. Neufeld unpubl. data). Other commonly associated vegetation includes Kentucky bluegrass (Poa pratensis), June grass (Koeleria macrantha), gumweed (Grindelia squarrosa), pasture sage (Artemisia frigida), prairie sage (Artemisia ludoviciana), royal pennyweed (Hedeoma hispida), foxtail barley (Hordeum jubatum), yellow flax (Linum rigidum), prairie coneflower (Ratibida columnifera), yarrow (Achillea millefolium), sweet clover (Melilotus spp.), broomweed (Gutierrezia sarothrae) inland salt grass (Distichlis stricta), little club moss (Selaginella densa), tumblegrass (Schedonnardus paniculatus), prairie bird's-foot trefoil (Lotus purshianus), fragile pricklypear (Opuntia fragilis) and pincushion cactus (Coryphantha vivipara) (Harms in press, Reimer et al. 2003, Manitoba Conservation Data Centre, unpubl. data, C. Neufeld, unpubl. data).

1.4.2 Ecological role

Buffalograss is an important forage grass for livestock grazing in the United States, due to its resilience to grazing, tolerance to semi-arid and drought conditions, and its palatability with high protein and nutrient content year-round (Dittberner and Olson 1983, Howard 1995). It is also important forage for a variety of wildlife, including elk (Cervus elaphus), deer (Odocoileus spp.), and pronghorn antelope (Antilocapra americana). Buffalograss is increasingly becoming important in the United States as a turfgrass for golf courses and landscaping projects, including ditches, airport runways, athletic fields, and recreational areas because of its low maintenance, sod-forming nature, short stature, drought tolerance, trampling tolerance, and good competitive abilities (Pozarnsky 1983, Quinn 1998, Mintenko et al. 2002); cultivars have been developed which are easier to establish from seed rather than from plugs or sod (Mintenko et al. 2002). Buffalograss is also being used in revegetation projects to decrease erosion and rehabilitate surface-mined lands, bentonite/ coal-mine spoil piles, and drilling fluid burial sites (Vogel 1981, Thornburg 1982, Sieg et al. 1983, McFarland et al. 1994). In the United States, studies have found buffalograss to be an important recolonizer of cultivated fields and old roads 5-10 years after abandonment because of its ability to rapidly spread vegetatively (Judd 1974, Coffin et al. 1996). This recolonization reduces wind and water erosion, and returns these areas back to native species. These abandoned fields can become dominated by buffalograss and blue grama 25-50 years after abandonment (Coffin et al. 1996).

Historically, buffalograss served numerous functions. Buffalograss sod was used by settlers to build sod houses in the west-central Great Plains, and likely was used for grazing cattle and horses (Lowe 1940, Harms in press). Acoma and Laguna tribes in the southern United States crushed buffalograss stolons with yucca root or soaked it in water for use as a dermatological aid to make hair grow (Swank 1932). The Blackfoot tribe used buffalograss as forage for horses during fall and winter (Johnston 1987).

1.4.3 Limiting factors

All plants require sunlight, heat, moisture, nutrients and space for establishment, growth, and reproduction. As a warm-season (C4) perennial grass at the extreme northern edge of its range, buffalograss is probably limited primarily by growing season length. C4 perennial grasses transplanted further north often develop slowly and fail to complete reproduction (Potvin 1986, Linhart and Grant 1996). Also, populations at the limits of a species' range often are more fragmented and less dense, and they occupy poorer habitat than populations at the core of the species' range (Vucetich and Waite 2003, Channell and Lomolino 2000). This may make them more susceptible to fragmentation effects, such as lower immigration rates and higher extinction rates. Habitat differences at the limits of its range may also affect a species persistence; as a short-statured perennial grass adapted to dry and relatively nutrient-poor ecosystems with a similarly low vegetation structure, habitats supporting taller plants that would otherwise form a canopy and limit sunlight availability would likely limit buffalograss.

The seed-containing burs of buffalograss are adapted to dispersal by animals. Small hairs on the awns of the burs aid in attachment to fur, and slow passage of the bur through the rumen, allowing greater dispersal distances. Retention time of burs within cattle digestive tracts is between 1-5 days during which cattle can move a substantial distance (Quinn and Hervey 1970, Quinn et al. 1994, Ortmann et al. 1998). Ingestion of burs, and their subsequent deposition on the ground in dung, results in higher germination rates than undigested burs (Quinn et al. 1994, Ortmann et al. 1998). The dung substrate initially kills or suppresses existing ground cover thereby reducing competition, and provides moisture and nutrients to the seedling (Quinn et al. 1994). In the absence of these grazing animals, or restriction of their movement by fenced areas, there may be an accumulation of seeds under the parent plants leading to a lack of germination, seedling death or eventual inbreeding depression (Quinn 1987, Coffin and Lauenroth 1989, Quinn 1991, Quinn et al. 1994). With a lack of reproductive dispersal, vegetative growth by stolons would be the main method of increasing distribution.

1.5 Protection

Buffalograss is protected under the Canadian Species at Risk Act (SARA) where it occurs on federal lands. It was recently declared as threatened under the Manitoba Endangered Species Act, but as of 2007, it was not listed under provincial legislation in Saskatchewan, although a small Buffalograss Provincial Ecological Reserve has been established in Saskatchewan where buffalograss is protected by the Ecological Reserves Act.  Conditions at this site are not optimal for buffalograss and require some management; however, grazing is not allowed under the current management plan.  In Saskatchewan, buffalograss also occurs on private and leased provincial crown land.  In Manitoba, buffalograss occurs primarily on private land, with one location within a park owned by a rural municipality.

1.6 Threats

The major threats to buffalograss relate to habitat loss and degradation, and invasion by exotic species. Because buffalograss has a small area of occupancy where it is localized into clumped patches or narrow bands, destruction to even small areas of existing sites would greatly decrease the known population in Canada. Threats are discussed in more detail below, with a categorization of the threats in Table 1.

1.6.1 Threat classification

Table 1. Threat Classification Table
Type of ThreatThreat Information
1. Coal strip mining
Threat CategoryHabitat loss and degradationExtentLocalized
 LocalRange-wide
General ThreatCoal strip (open-pit) miningOccurrenceCurrent/ Anticipated 
FrequencyOne-time 
Specific ThreatsHabitat conversion, habitat fragmentation, removal of substrate/plants/seed bed, introduction of invasive exotic speciesCausal CertaintyHigh 
SeverityUnknow. (High) 
StressMortality of plants and seeds, reduced population sizeLevel of ConcernHigh
2. Invasive Exotic Species
Threat CategoryExotic speciesExtentWidespreada
 LocalRange-wide
General ThreatInvasive exotic speciesOccurrenceCurrentAnticipated
FrequencyContinuous 
Specific ThreatResource and plant competition, alteration of habitat characteristics (e.g., litter, vegetation height and composition), changes in species communityCausal CertaintyUnknown 
SeverityHighModerate
StressReduced population size, increased seed dormancy, increased plant mortality, reduced germinationLevel of ConcernHigh
3. Lack of grazing and/or alteration to fire regime
Threat CategoryChanges in ecological dynamics or natural processesExtentLocal (Grazing)/Range-wide (Fire)
 LocalRange-wide
General ThreatLack of, grazing and/or alteration to fire regimesOccurrenceCurrentCurrent
FrequencyContinuousContinuous (?)
Specific ThreatPlant competition, alteration of habitat characteristics (e.g. litter, bare ground, vegetation height), changes in species communityCausal CertaintyMediumMedium
SeverityLow-ModerateHigh
StressReduced population size/viability, increased mortality, increased seed dormancy, reduced seed germinationLevel of ConcernMedium
4. Flooding by Reservoirs and Dams
Threat CategoryChanges in ecological dynamics or natural processes/ Habitat loss or degradationExtentLocal
 LocalRange-wide
General ThreatFlooding by small catchment dams and dugouts in valleys and coulees; Flooding by existing large-scale dams/reservoirs.OccurrenceHistoric/Current/ Anticipated 
FrequencySeasonal 
Specific ThreatReduced microhabitat, alteration of habitat characteristics, possible change in species communityCausal CertaintyMedium 
SeverityMedium 
StressReduced population size, increased mortalityLevel of ConcernMedium
5. Cultivation
Threat CategoryHabitat loss and degradationExtentRange-wide
 LocalRange-wide
General ThreatCultivation, crop production. conversion to tame foragesOccurrenceMostly Historic/ Unknown
FrequencyOne-time/Recurrent
Specific ThreatHabitat conversion, fragmentation, isolation, disturbance/removal of substrate and/or seed bedCausal CertaintyHigh
SeverityHigh
StressMortality of plants and seeds, reduced population size, local extinctions, reduced genetic exchangeLevel of ConcernMedium
6. Road Construction or Upgrades
Threat CategoryHabitat loss or degradationExtentLocal
 LocalRange-wide
General ThreatConstruction or upgrading of roadsOccurrenceHistoric/
Anticipated
 
FrequencyOne-time/ recurrent 
Specific ThreatHabitat fragmentation, isolation, habitat conversion, direct mortality, exotic species invasionCausal CertaintyHigh 
SeverityLow 
StressReduced population size, increased mortality, reduced genetic exchangeLevel of ConcernLow-Medium
7. Urban expansion
Threat CategoryHabitat loss or degradationExtentLocalized
 LocalRange-wide
General ThreatUrban expansion/ acreage or housing developmentOccurrenceAnticipated 
FrequencyOne-time 
Specific ThreatHabitat conversion, fragmentation, isolation, disturbance/removal of substrate and/or seed bedCausal CertaintyHigh 
SeverityLow 
StressMortality of plants and seeds, reduced population size, local extinctionsLevel of ConcernLow-Medium
8. Clay pit mining
Threat CategoryHabitat loss and degradationExtentLocalized
 LocalRange-wide
General ThreatClay pit miningOccurrenceHistoric/ Anticipated 
FrequencyOne-time 
Specific ThreatHabitat conversion, removal of substrate/ plants/ seed bed, introduction of invasive exotic speciesCausal CertaintyHigh 
SeverityLow 
StressMortality of plants and seeds, reduced population sizeLevel of ConcernLow

aThe presence of particular invasive exotic species, and their extent or degree of threat differs between occurrences.

1.6.2 Description of threats

Coal strip (open pit) mining

Lignite coal occurs in horizontal beds within the Ravenscrag Formation, which extends over the Estevan area. Coal is surface mined from large open pits about 35 mdeep, created by draglines removing topsoil, subsoil, and overlying rock covering the coal seams. There are four actively producing coal mines in the Estevan area (Saskatchewan Industry and Resources 2006), some of which are operating immediately adjacent to existing buffalograss sites (Harms in press, C. Neufeld, pers. obs.). Expansion of strip mining in the direction of existing sites would destroy large portions of the Saskatchewan population. It is unknown whether any sites have already been impacted by strip mining. Fragmentation and destruction of potential habitat, however, is evident despite attempts at post-mining land reclamation. Surveys of proposed mining areas are important to ensure occurrences are not impacted.    

Invasive exotic species

Invasive exotic species, through deliberate and accidental introduction, are often associated with displacement of native species and decreases in species diversity or richness through their increased competitive ability and effects on ecosystem functioning (Wilson 1989, Wilson and Belcher 1989, Reader et al. 1994, Christian and Wilson 1999, Bakker and Wilson 2001, Henderson 2005, Henderson and Naeth 2005). Because buffalograss appears to be limited to areas with little shade and reduced competition from taller species, invasion by taller exotics, such as crested wheatgrass (Agropyron cristatum), Kentucky bluegrass (Poa pratensis) and smooth brome (Bromus inermis), would pose a threat (Wu and Harivandi 1995, Harms in press). Stoloniferous and less productive plants, like buffalograss, tend not to persist in areas with more productive dense grass (Richard and Redente 1995). The encroachment of crested wheatgrass, smooth brome and Kentucky bluegrass is a threat to buffalograss in Saskatchewan; Kentucky bluegrass is a dominant species within the Buffalograss Ecological Reserve in Saskatchewan likely due to the lack of grazing and management. Leafy spurge, an invasive exotic Eurasian species, is thought to be a major threat to buffalograss in Manitoba. Leafy spurge reduces the abundance of native species in areas where it occurs through direct competition (Wilson and Belcher 1989), and has been rapidly expanding through the Souris and Blind River valleys in recent years (Foster and Hamel 2006). Crested wheatgrass, smooth brome, and Kentucky bluegrass have been recorded at some buffalograss sites in Manitoba (Reimer et al. 2003, Manitoba Conservation Data Centre, unpubl. data). Controlling the abundance and further spread of these invasive exotic species is critical for the survival of buffalograss; however, care must be taken that buffalograss is not harmed, or its habitat negatively altered, by indiscriminate use of any herbicides used to control invasive species.

Lack of Grazing and/or Alteration to Fire Regime

Prairie plants evolved with the ecological processes of fire and grazing which were important for maintaining ecosystem function. Post-European settlement reduced both the frequency and extent of prairie fires, and variability in grazing patterns, which has collectively changed the structure and composition of many plant communities (Higgins et al. 1989, Frank et al. 1998, Brockway et al. 2002). Historically, buffalograss adapted to fire and grazing by evolving structures, such as hardened burs, which protect the enclosed seeds from heat damage and aid in endozootic dispersal (Ahring and Todd 1977, Wright and Bailey 1982, Quinn et al. 1994, Ford 1999).

The impact of fire on buffalograss appears largely dependent on precipitation, seasonality, and the time since the last fire (Higgins et al. 1989, Ford 1999). Because buffalograss is a late-developing, warm season grass (C4), a fire during the growing season kills actively growing leaves. Buffalograss cannot reallocate its energy reserves to produce more leaves before the end of the season, significantly reducing its cover for up to two years post-fire (Brockway et al. 2002, Ford 2003, Ford and Johnson 2006). Fire during the dormant season (e.g., fall, winter) has been found to have little effect on buffalograss cover because aboveground tissues are already dead (Ford 1999, Ford 2003, Ford and Johnson 2006).. Fires that occur during dry years also appear to elicit at least an initial negative response by buffalograss as the plants may already be under physiological stress. It can take over three years for buffalograss to recover after a dry-season fire (Brockway et al. 2002, Ford 2003). A review of studies on buffalograss and fire found that, overall, buffalograss shows a positive to neutral response to fire (Ford 1999). More long-term investigations are needed on the interactions of factors such as drought, season, and fire history, and the mechanisms driving responses. For example, Ford (2003) found greater buffalograss cover in an area that had a growing-season fire than an unburned control area and an area with a dormant-season fire during a drought year five years after the experiment. Studies are also needed on long-term effects of fire on buffalograss and its ecosystem in Canada.

Although Buffalograss still dominates areas where fire or grazing have been excluded (Hulett et al. 1972, Howard 1995), a lack of these disturbances can increase litter levels and vegetation height (Hayes and Holl 2003), which can result in reduced growth of short growing and shade intolerant species like buffalograss. Perhaps more importantly, removal of grazing and fire can also increase the susceptibility of rangeland to invasion by weedy species, or less fire-tolerant exotic invasive species (Higgins et al. 1989, Milchunas et al. 1989, Milchunas et al. 1992). Grazing is present on all existing buffalograss sites in Saskatchewan and Manitoba with the exception of the Sourisford Park in Manitoba (but mowing occurs) and the Buffalograss Ecological Reserve in Saskatchewan. Both sites have problems with weedy species, and the ecological reserve is dominated by taller invasive exotic species such as Kentucky bluegrass. Prescribed burns are not a regular practice on any of the sites and wildfires are typically suppressed.

The impact of grazing on buffalograss appears to be positive, as increased grazing intensity has been found to increase buffalograss cover and/or frequency (Herbel and Anderson 1959, Anderson et al. 1970, Bonham and Lerwick 1976, Klatt and Hein 1978, Ring et al. 1985, Hart and Ashby 1998). A wide range of animals, in addition to cattle, horses and bison, are known to eat buffalograss, including deer, elk, pronghorn antelope, white-tailed jackrabbit (Lepus townsendii), black-tailed prairie dog (Cynomys ludovicianus), upland game birds and various small mammals (see Howard 1995). Buffalograss appears tolerant of moderate to heavy grazing, and may have an advantage by rapidly spreading vegetatively once grazing has reduced competitors, particularly taller grasses. As with fire effects, buffalograss can withstand more defoliation during periods of dormancy than periods of active growth (Vallantine 1990). Nevertheless, its deepset root crowns seem resistant to trampling by ungulates, making buffalograss quite hardy even during active growing periods (Young 1956).

Small Catchment Dams and Dugouts

Small catchment dams and associated dugouts have been placed in the bottoms of coulees to retain runoff water for consumption by cattle. Harms (1997) estimated that these have eliminated a 300 m extent of buffalograss habitat in coulee bottoms. Buffalograss has been observed growing in a ring surrounding a dugout; however, it is not known whether the buffalograss grew here prior to dugout construction, or if it was transported here by cattle using the dugout, and then became established due to the favourable microsite conditions created by high cattle traffic (i.e., trampled, bare clay with high moisture and high nutrient availability, low competition, warm temperature) (C. Neufeld, unpubl. data). 

Flooding by Exising Large-scale Reservoirs/Dams

Changes to the moisture regime at a site could adversely affect buffalograss growth and survival. As most of the buffalograss sites occur on lower slopes of valley and coulee walls, any prolonged inundation of these areas resulting from developments or disturbances that cause unnatural flooding, inhibit channel migration, or divert water could alter the disturbance regime beyond the range of natural variability, negatively impacting the creation and maintenance of buffalograss habitat. The creation of the Rafferty and Boundary Dams and Reservoirs in Saskatchewan flooded a considerable area of habitat along the Souris River Valley, where populations of buffalograss likely occurred. Sites that currently exist adjacent to the Rafferty reservoir may be at risk in years when water levels rise (Harms in press). To date, no dams have been built in Manitoba that affect populations of buffalograss, although dam 357 on the Souris River in North Dakota, downstream of Buffalograss sites in Manitoba may have been a seed source before that area was flooded (Reimer et al. 2003).

Cultivation

Less than 20% of the mixed grass prairie in Manitoba, and 31.3 % of that in Saskatchewan is estimated to remain uncultivated (Gauthier et. al. 2002, Nernberg and Ingstrup 2005). The remaining native prairie is fragmented, and most remnant patches are small and isolated from other patches by cropland (James et al. 1999), which threatens natural patterns of seed dispersal and gene flow within former populations and between extant populations. The threat of cultivation is more historic than current, with most of the damage already having occurred. Remaining uncultivated prairie where buffalograss occurs will likely not be broken for agriculture as the soils are generally unsuitable for cultivation. In Manitoba, buffalograss grows on soils that have severe limitations for crops due to soil structure, low permeability and presence of soluble salts (Eilers et al.1978). In Saskatchewan, soils with buffalograss are suited only for grazing due to their shallow nature, bedrock exposures, and dissected terrain. A few buffalograss sites have suitable agricultural soils, but they occur in irregular bands in valleys which is less feasible tillage (Saskatchewan Soil Survey 1997). Additionally, the topography of sites located on valley walls or dissected coulee bottoms is not conducive to cultivation. The use of some chemicals (e.g., herbicides, fertilizer, pesticides) on adjacent cultivated areas has the potential to alter habitat on the native prairie as well (e.g., change species composition, canopy cover, hydrology, and soil stability, degrade pollinator populations). Cultivation has likely reduced overall habitat availability, population size, and genetic diversity of this species to the point where parts of its historical range may have been destroyed, and larger expansion of its current range is no longer possible.

Road Construction or Upgrades

Road construction has likely impacted buffalograss populations in the past. Highway 18 in Saskatchewan, heading west from Estevan, dissects buffalograss occurrences, which now exist adjacent to the highway ditches (Harms in press, C. Neufeld, pers. obs.). These fragmented occurrences were likely joined prior to the construction of that highway. Similarly, highway 251 and an abandoned railbed dissect buffalograss populations near Coulter, Manitoba (Harms in press). Buffalograss is occasionally found along vehicle track trails, where it seems to take advantage of decreased competition. Upgrades to these roads will destroy the buffalograss clones growing along them (Harms in press). Roads can also change the hydrology of habitat by modifying drainage patterns and water flow in an area.

Urban expansion

In Saskatchewan, locations of buffalograss have been found within one kilometer of the Estevan city limits. There also may be suitable habitat closer to the city, or undeveloped land within city limits which is already supporting buffalograss. Future growth of Estevan, particularly acreages on the outskirts of town, could threaten existing buffalograss sites, or further reduce remaining suitable habitat.

Clay-pit mining

Clay-pit mining historically occurred in the area, and at least two mines are in close proximity to existing buffalograss sites (Harms in press, C. Neufeld pers. obs.). Although these mines appear to be abandoned and should not pose a future threat, it is possible that some buffalograss was destroyed in the past by one of these mines, as evident by buffalograss currently occurring adjacent to the pit. There is revised interest in mining clay in southern Saskatchewan as an additive in specialized concrete mixes (S. McAdam, pers. comm.).

1.7 Knowledge Gaps

Knowledge gaps for buffalograss are identified in section 2.4 Recovery Objectives, section 2.5 Approaches Recommended to Meet Recovery Objectives, and Table 2, and include a need for:

  1. Standardized guidelines for buffalograss inventory and monitoring.
  2. Complete extent of occurrence, and more accurate and precise knowledge regarding the area of occupancy for buffalograss in Canada.
  3. Population trends, including reproduction and mortality rates, to better understand the population viability of buffalograss in Canada.
  4. Habitat associations and critical habitat identification for buffalograss in Canada.
  5. Genetic similarity and magnitude of isolation effects of Canadian buffalograss populations relative to each other, and to nearby populations in the U.S.A.

1 Stolons are elongated, horizontal above-ground stems that creep along the ground, rooting at nodes or tips resulting in new plants (Harrington 1977, Harris and Harris 2001). Rhizomes are elongated, horizontal underground stems which root at the nodes, producing new plants (Harrington 1977, Harris and Harris 2001).

2 Using the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) definition, populations are defined as geographically or otherwise distinct groups within a species that have little demographic or genetic exchange (typically one successful breeding immigrant individual or gamete per generation or less) (COSEWIC 2006). This is equivalent to the term “subpopulation” employed by the World Conservation Union (IUCN 2001). NatureServe considers sites within 1 km of each other, or within 2 km if there is appropriate habitat between the sites, to be from the same element occurrence (population) (NatureServe 2006). It should be noted that with genetic research, it may be found that genetic exchange occurs at distances further or less than 1 km, and therefore, our definition of a population may change; this may result in splitting or lumping of sites which will change the number of populations, but this itself should not be interpreted as an increasing or decreasing trend. The Canadian population, or total population, is the total number of mature individuals in Canada (equivalent to the term “population” employed by the World Conservation Union) (COSEWIC 2006).

3 As buffalograss is a clonal species, and often forms dense mats or turf when clones merge with neighbouring clones, it is impossible to count individual plants and difficult to accurately count clones. Therefore, its area of occupancy, or the size of the patches it forms, are often recorded and used as a way to monitor buffalograss. Area of occupancy as defined by COSEWIC is “the area within 'extent of occurrence' that is occupied by a taxon, excluding cases of vagrancy” (COSEWIC 2006). Extent of occurrence as defined by COSEWIC is “the area included in a polygon without concave angles that encompasses the geographic distribution of all known populations of a species” (COSEWIC 2006).