North America's Northern Research Articles

Fire controls annual bromes in northern great plains grasslands—Up to a point

Concern about the impacts of two invasive annual brome grasses (cheatgrass and Japanese brome, Bromus tectorum L. and B. japonicus Thunb. ex Murray) on the mixed-grass prairie of North America's northern Great Plains (NGP) is growing. Cheatgrass is well known west of the NGP, where replacement of fire-intolerant, native sagebrush steppe by fire-prone, exotic annual grasslands is widespread. Consequently, fire is often not considered as a tool for controlling annual bromes. This should not be the case in the NGP, where mixed-grass prairie is adapted to frequent fires. Fire's efficacy may vary with the degree of invasion, though; suppressing postfire annual brome populations or enhancing the native plant community may improve postfire annual brome control in highly invaded areas. To test this, we performed an experiment at two sites to evaluate the relative effectiveness of prescribed fire alone, fire followed by imazapic application and fire followed by native seeding across a pretreatment invasion gradient of annual brome-to-native species cover ranging from 0.05 to 2.35. Fall-prescribed fire alone greatly reduced annual bromes, but by the second yr after treatment the effect was significant only at invasion ratios < 1.2. Postfire imazapic application reduced annual bromes even further than fire alone, but only for 1 yr at the less invaded site and only at invasion ratios > 1.2 in yr 2 at the other site. Native species cover and total species richness responded positively to all treatments, but the degree of their response varied along the invasion gradient, between sites, with time since treatment and among treatments. Also, at one site, fire yielded a lagged stimulation of short-lived, exotic forbs. Seeding had little effect. Fire is an effective tool for reducing annual bromes in the NGP at lower invasion levels, but more tools are needed for long-term, effective control at highly invaded sites.

Patch-Burning Buffers Forage Resources and Livestock Performance to Mitigate Drought in the Northern Great Plains

Summer droughts in North America's northern Great Plains are expected to increase in frequency and duration as precipitation shifts toward spring and fall. Two rangeland experimental stations in North Dakota experienced drought in 2017 relative to 25-year averages. The southwest location had a 170-mm deficit from the 360-mm normal rainfall and was grazed by cattle (Bos taurus L.) and sheep (Ovis aries L.); the south-central location had 109 mm below the 403-mm normal rainfall and was grazed by cattle. We evaluated patch-burn grazing as a drought resilient land management strategy in the northern Great Plains by comparing average daily gains, fecal density, available forage biomass, and forage crude protein content. At the southwest location, livestock performed better during the drought season compared with animals on the same pastures in the previous year, which had near-normal rainfall but no fire. At the central location, cows on patch-burned pastures performed better than cows on continuously-grazed, unburned pastures in the same year under drought conditions; all cows were nursing calves and calf gains did not vary between treatments. In both locations, the burned patches had higher fecal density and lower available forage biomass than patches not yet burned throughout the grazing season, indicating grazer attraction to burned areas. Despite drought, burned patches maintained grazer attraction and animal performance was maintained or even improved, which contrasts with the expected relationship between animal performance and precipitation. This study indicated that prescribed patch-burning might mitigate drought by buffering forage resources (crude protein content and availability) and maintaining animal performance (average daily gains).

Chloride inputs to the North Saskatchewan River watershed: the role of road salts as a potential driver of salinization downstream of North America's northern most major city (Edmonton, Canada)

Multiple anthropogenic activities are driving the salinization of freshwater environments threatening water resources worldwide. Accordingly, this research will first examine the spatial and temporal variability of major ions (i.e. Ca2+, Mg2+, Na+, K+, SO42−, CO32−, and HCO3−) upstream and downstream of the northernmost major city in North America (Edmonton, Canada). Second, this research will estimate the relative contributions of the major sources of chloride (Cl), the main constituent of road deicers, to the sub-basin around Edmonton. Monthly water quality data was for three sites on the North Saskatchewan River (NSR): Rocky Mountain House (RMH - downstream of the Rocky Mountain headwaters), Devon Bridge (upstream of Edmonton) and Pakan Bridge (downstream of Edmonton). Change ratios investigate the downstream alterations of major ions at Pakan and Devon, relative to RMH. Seasonal Kendall tests examine temporal trends (1987–2017). A mass-balance approach then quantifies the major sources of Cl in the sub-basin of the NSR between Devon and Pakan. Progressing from the Rocky Mountain headwaters (at RMH) to downstream of Edmonton (at Pakan), Cl− increased by >5.5 times, Na+ by 4.8 times and K by 2.7 times. No significant temporal trends for Cl−, Na+ and K+ were evident at Devon (upstream of Edmonton), whereas all three significantly increased at Pakan (downstream of Edmonton). Deicers (54%), agriculture (20%), along with waste water treatment plant and industrial effluent (15%) were the largest Cl sources in the NSR Devon-Pakan sub-basin. In total, 77 Gg yr−1 of Cl (or 6 t km2 yr−1) is added to the Devon-Pakan sub-basin, of which, 43 Gg yr−1 is retained. Understanding and managing the major drivers of freshwater salinization will be of increasing importance in the 21st century owing to the potential salinization of freshwater resources in the context of a changing climate.

Loss of genetic diversity and reduction of genetic distance among lake trout Salvelinus namaycush ecomorphs, Lake Superior 1959 to 2013

North America's northern lakes are undergoing major changes. Lake Superior is the coldest and northernmost of the Laurentian Great Lakes. Here, we present an extension of a long-term data set that monitors genetic and phenotypic diversity of lake trout Salvelinus namaycush in Lake Superior. Hypotheses were investigated pertaining to loss of genetic diversity and genetic homogenization among three lake trout ecomorphs in Lake Superior during their recovery several decades after a major fishery collapse in the early 1960s. Comparison of a contemporary (2004–2013) microsatellite DNA data set to a previously published, post-collapse recovery period data set (1995–1999) indicated substantive losses in genetic diversity. Allelic richness decreased by 5.7%, 12.3%, and 6.8% at Isle Royale, Stannard Rock, and Klondike Reef, respectively. A 60.7% reduction in genetic distance among ecomorphs since the 1990s was detected. Comparisons with a third data set of samples collected during the fishery collapse (1959) indicated an overall 18.2% loss in allelic richness at Isle Royale. The amount of introgression among ecomorphs has likely increased over time. Apparent losses in genetic diversity could be a consequence of historical fishery harvests (early 1900s) exacerbated by intensive stocking (1950s–1980s) and invasions of non-native species (1960s–1990s). Overlap in foraging and breeding areas may have contributed to increasing levels of hybridization among ecomorphs. Knowledge of these processes will help to identify impediments and strategies for the maintenance of lake trout biodiversity in northern Great Lakes, and their re-establishment in the Laurentian Great Lakes.

Conservation genetics of endangered flying squirrels (Glaucomys) from the Appalachian mountains of eastern North America

We assessed the genetic status of two endangered subspecies of the northern flying squirrel (Glaucomys sabrinus) that are restricted to isolated stands of high elevation spruce-fir and adjacent spruce-fir-hardwood ecotonal habitat in the Appalachian Mountains of eastern North America. We used mitochondrial DNA (mtDNA) and allozyme data to estimate levels of genetic variability in the two subspecies of interest and then evaluated this information in the context of large-scale phylogeographical structure and overall genetic variability for the entire species and for the closely related and partially sympatric southern flying squirrel (Glaucomys volans). This broader analysis involves much of North America's northern coniferous forest biome, together with the deciduous forest biome of eastern North America. Our results support the evolutionary distinctness of the endangered Appalachian populations of G. sabrinus. These populations possess several private alleles and have levels of genetic variability that are substantially lower than those observed in conspecific populations found elsewhere. However, the endangered Appalachian populations of G. sabrinus have higher levels of genetic variability than those observed in populations of G. volans from across eastern North America. These results highlight the utility of evaluating the conservation genetics of small and isolated populations within a broad-scale comparative evolutionary and biogeographical framework.