Restoring forbs for sage grouse habitat: fire, microsites, and establishment methods

Summary

In North America, the decline and range reduction of sage grouse Centrocercus urophasianus is primarily due to loss and degradation of sagebrush Artemesia–grassland habitat. Sage grouse productivity may be limited by availability of nutritious forbs that have also declined. This study determined the suitability of three forb species (Modoc hawk’s-beard Crepis modocensis, occidental hawk's-beard C.occidentalis and woolly pod milkvetch Astragalus purshii) for revegetation purposes, one objective being to improve sage grouse habitat. Their emergence, survival and seeding in response to establishment method (seeding or transplanting), site preparation (burned or unburned) and microsite was evaluated in Wyoming big sagebrush Artemisia tridentata wyomingensis habitat in the Hart Mountain National Antelope Refuge, Oregon, western USA.

Study sites: Eight similar 400 ha areas were selected. Before prescribed burning in 1997, dominant plants were big sagebrush and the perennial grasses, Sandberg's bluegrass Poa secunda, bottlebrush squirreltail Elymus elymoides, with Thurber's needlegrass Achnatherum thurberianum and P.spicata.

Prescribed fires and plant response: In autumn 1997, four of the areas were randomly selected and burned. Within 25 randomly located 20 × 50 cm plots. Fire consumption was calculated and ranged from 60 to 93%. Fire behavior data were collected (flame height, depth, angle and length, and rate of spread). Fires produced a mosaic of burned and unburned areas. Sagebrush cover generally decreased in burned areas. Grass cover stayed the same or increased slightly in burned areas, remaining the same in unburned areas. Forbs increased in burned areas and remained similar in unburned areas.

Forb restoration experiments: In late June 1997, seed of C.modocensis, C.occidentalis and A.purshii was collected locally. Viable seeds (based on appearance) were selected for planting using a randomized block split-plot design. After burning (four of the eight areas), a 1-ha plot was randomly located within each site (i.e. four burned and four unburned replicates). In October, 250 seeds of each species was sown per site along 10, 80-m long, randomly located transects. One seed was planted 1 cm deep within alternating microsites (mounds and interspaces) as they occurred naturally along each transect, randomizing species order. Monitoring for seedling emergence and survival began on 21 March 1998. Survival status was recorded during censuses (8 and 28 April, 19 May, 17 June, 7 and 28 July in 1998 and 17 April, 15 May, 15 June and 20 July in 1999).

Plants were also raised at Oregon State University in winter 1997 and 1998. Seedlings were grown for 10 weeks in the greenhouse and then placed in a cold frame for three weeks to harden. They were transplanted into the field (random locations along new transects in the plots) on 28 April 1998. Limited numbers of Crepis transplants allowed only three burned and three unburned sites to be planted (50 per microsite). All sites received 50 A.purshii transplants per microsite. Survival was recorded.

Seedling survival: Seed viability was high for all three species (>93%) but emergence of A. purshii was only 8% and that of the two Crepis 38%. Significantly more Crepis seedlings emerged from mounds in unburned areas (50%) than in any other sites (33 to 36%). A.purshii emergence was higher in the burned interspaces (c.11%) compared with the burned mounds (c.4%). No other comparisons differed statistically. Crepis seedling survival (both species) was higher in burned (c.58%) compared with unburned sites (c.32%) and higher on mounds (c.47%) than interspaces (c.38%). Burning was the only treatment that affected A. purshii survival with nearly twice as many emerging in burned locations surviving (42%) compared to unburned (c.22%).

Transplant survival:  Overall survival of C. occidentalis was 13.7% and that of C.modocensis 7.2%. Regardless of species, survival of Crepis transplants was higher in burned (c.16%) than unburned treatments (c.5%) and higher in mound (c.12%) than interspace (c.5%) microsites. A.purshii transplants had similar survival to those emerging from seed. Transplant survival was higher in burned (c.50%) than unburned (c.18%) treatments but did not differ significantly between microsites (c.35-37%). Burning enhanced A. purshii flowering, with 97 of 99 transplants that flowered occurring in burned areas. Also, the seven Crepis plants that flowered all did so in burned areas. No significant difference in seed production was found between burned mound (45.4/plant) and burned interspace microsites (29.6/plant).

Conclusions: The higher survival of Crepis seedlings over transplants, yielded 3-10 times more established plants of both species. Nearly twice as many emerging Crepis seedlings survived in the burned areas resulting in more plant establishment on burned mounds despite higher emergence on unburned mounds. A. purshii transplant establishment was similar to or slightly greater than those from seeds in all treatments except on unburned mounds. A.purshii seedlings survived better in burned areas regardless of microsite. For transplants, fire enhanced survival of all three species. The authors conclude that seeding the two Crepis species is a viable option for improving sage grouse habitat. Better techniques are required to establish A.purshii.


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