Autumn Watkinson PhD Graduate Defense Seminar

Restoration of Sagebrush Grassland For Greater Sage Grouse Habitat in Grasslands National Park, Saskatchewan

 

Student:  Autumn Watkinson

Degree:  PhD

Supervisors:  Dr. M. Anne Naeth and Dr. Shelley Pruss

Date:  June 24, 2020

Time:  11 a.m.

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Abstract:

Populations of Greater Sage-grouse (Centrocercus urophasianus Bonaparte [Phasianidae]; hereafter Sage-grouse) have been in decline in North America for the last 100 years; since 1988, the Canadian population has declined by 98 %. Initial declines of Sage-grouse populations were likely due to habitat loss, degradation, and fragmentation, which continue to be major contributors to ongoing declines. This research focused on developing methods to improve restoration of Sage-grouse habitat by increasing establishment, growth, and survival of Silver sagebrush (Artemisia cana Pursh), a critical component of Sage grouse habitat. Field research was conducted in Grasslands National Park (GNP), Saskatchewan, Canada.

Models that enable the calculation of seeding or planting densities to obtain desired sagebrush cover within specific time frames are essential for restoration. Cover and density of naturally occurring Artemisia cana stands were measured in 10 m x 10 m plots, with stem diameter, crown diameter, canopy cover, and age measured on individuals. Sagebrush mortality was estimated from stand age demographics, and seedling survival of other studies. Strong relationships between morphological characteristics and age were found. Age was significantly correlated with stem diameter (r² = 0.79) allowing non-destructive age estimations to be made for Artemisia cana. Age was also correlated to canopy cover (r² = 0.49 to 0.67) and allowed models of Artemisia cana landscape cover over time at different planting densities to be were constructed. Largest cover increases can occur in areas that are grazed by cattle. Cover is maximized after 11 years in heavy cattle grazed areas, and after 21 years in light cattle grazed areas.

Artemisia cana emergence under field conditions has been extremely low. Seed dormancy and low germination were identified as possible factors reducing seedling emergence and were investigated. Seeds were cleaned and after ripened in cold storage for 4 to 18 months. Before germination in light or dark, a physical scarification treatment was applied. Pericarp removal and after-ripening for 16 to 18 months marginally increased germination (approximately 10 %) of Artemisia cana under laboratory conditions. Even without treatment, Artemisia cana germination in a laboratory was very high. Results suggest that low success of Artemisia cana seeding in the field is not due to seed dormancy or poor germination but from limiting environmental factors.

Survival of outplanted Artemisia sp. seedlings has been low, with studies reporting 30 to 36 % survival after two years. Increasing nutrient availability during greenhouse growth via nutrient loading was investigated. Extending growth time in the greenhouse to 26 weeks and applying 175 and 245 mg nitrogen plant^‑1 on exponential or modified exponential dosing schedules facilitated nutrient loading Artemisia cana seedlings. Seedlings were outplanted into a field plot and monitored for two growing seasons. Nutrient loaded seedlings had greater survival (80 %) than unloaded seedlings (57 %) and increased second season canopy development (1040 cm² vs 680 cm²). Elimination of herbaceous competition likely contributed to greater survival and is recommended for the first two years after outplanting. Use of nutrient loaded seedlings in restoration planting increased outputs for sagebrush landscape cover in light cattle grazed areas to 24 % and to 12 % in bison grazed areas.

The intense anthropogenic disturbance and alteration of potential Sage-grouse habitat necessitate that effects of land management be considered in its restoration. Research plots investigating revegetation (fall seeding, spring seeding, outplanting, control) and herbicide use to control non-native species were established in cattle grazed, bison grazed, watered and ungrazed areas of GNP. Land management significantly altered soil properties and vegetation and invertebrate communities. Outplanting seedlings resulted in greater Artemisia cana cover than seeding. Very heavy grazing by cattle prevented adequate litter build up. Excess litter cover in bison grazed and ungrazed areas aided outplanted seedling survival but prevented broadcast seed from reaching the soil surface. Herbicide decreased non-native cover the first year after application but increased non-native cover thereafter. Herbicide did not negatively affect pre-existing Artemisia cana. All sites had key components of Sage-grouse habitat and showed high potential for restoration success given land management modification. To maximize sagebrush landscape cover, nutrient loaded seedlings should be planted into appropriate microsites within areas where land management has achieved litter cover of 15 to 30 %.