Ecological dynamics

The potential native plant community is dominated by buckwheat (Eriogonum spp.), Thurber’s needlegrass (Achnatherum thurberianum) and Sandberg bluegrass (Poa secunda). Bluebunch wheatgrass (Pseudoroegneria spicata), bottlebrush squirreltail (Elymus elymoides) and a variety of forbs are present. Scabland sagebrush (Artemisia rigida) is scattered. Vegetative composition of the community is approximately 75 percent grasses, 20 percent forbs, and 5 percent shrubs. Approximate ground cover is 40 to 60 percent (basal and crown). There is a weak diversified soil microbiotic crust between plant interspaces.

Range in Characteristics:
Plant composition and production is dependent on soil depth, precipitation and bedrock fracture. The soil typically tapers to a very thin layer adjacent to extensive areas of convex bedrock. Sandberg bluegrass increases as the soil depth decreases to less than 4 inches. Thurber’s needlegrass increases on deeper gravelly loams. Bluebunch wheatgrass increases over silt loams on southerly aspects. Idaho fescue (Festuca idahoensis) increases over deeper silt loams on northerly aspects. Soil microbiotic crust development is limited on gravelly surface textures. Western juniper (Juniperus occidentalis) is not prevalent due to the thin soil surface and unfractured bedrock. Junipers occur primarily on widely scattered small rock outcrops. Production increases with soil depth and precipitation.

Buckwheat species vary in their response to fire with some resprouting following low severity fire and others commonly experiencing mortality. Many species may be reduced immediately following fire yet in the absence of repeated fire will return to pre-burn levels or even increase in a few years following fire (Gucker and Shaw 2019, Monson et al. 2004, Landfire 2014). Thurber's needlegrass is considered to be the least fire-resistant needlegrass, Thurber's is often damaged by moderately severe fire. It recovers slowly following fire and regenerates primarily by seed rather than resprouting from crowns (Archer 2000). Bluebunch wheatgrass is considered to be a highly fire adapted grass species with low buds often protected from fire. Recovery following fire is rapid and it often increases relative to other plants post fire, especially after spring burning. While burning may improve the nutritional quality of bluebunch, defoliation during the regeneration period can be very detrimental to the stand and grazing should be avoided immediately after (Zlatnik 1999). Stiff sagebrush is killed by fire and does not sprout (Young 1983). Establishment after fire is from seed, generally blown in and not from the seed bank (Bradley et al. 1992).

Climate cycles would have been an important driver of ecological dynamics historically, with drought periods possibly leading to reductions in sagebrush cover and wet years increasing fire occurrence due to increased perennial grass production and fine fuels loads. Historically these communities would have likely encountered very infrequent fire due to patchy fuel, possibly on the order of 250 years between fires (Landfire 2014).

If the condition of the site deteriorates as a result of chronic improper grazing management, Thurber’s needlegrass, other bunchgrasses and Sandberg bluegrass decrease. Exotic annual grasses such as cheatgrass (Bromus tectorum), North African grass (Ventenata dubia), and medusahead (Taeniatherum caput-medusae) may invade and become problematic. Exotic annual grass invasion may increase the size and frequency of fires and extend the season when fires are likely by augmenting early season fine fuel loads and fuel continuity. Sites may be particularly fire prone following years of above average precipitation during which invasive annual grass production can increase dramatically (Pilliod et al. 2017). On very thin surfaces less than 2 to 4 inches bare soil increases. The very thin surfaces have insufficient water holding capacity to support high annual plant densities. Early spring grazing on saturated soils increases erosion by loosening the exposed thin surface and breaking up soil microbiotic crusts. Accelerated soil erosion on the bare soil interspaces increases and areas of exposed bedrock markedly increase. Soil erosion contributes to downstream sedimentation and potential site productivity is reduced. According to Johnson and Simon (1987) similar buckwheat dominated plant community types in near the Wallowa Mountains may be the result of soil loss due to wind and water erosion exacerbated by livestock grazing. Many of these buckwheat scabland sites are heavily invaded by invasive annual grasses and may be imperiled in the region (Natureserve 2020). Rehabilitation of native plant communities will be very difficult on this site due to thin soils, high potential for invasive annual grass encroachment, susceptibility of soils to erosion and damaging frost heaving, and mechanical limitations due to areas of rock outcrop.

An understanding of the site specific ecological dynamics for this site are incomplete. Little is known about the ecological dynamics of buckwheat dominated sites and how these plants may respond to disturbance. Current and anticipated effects of climate change are not included in this model, yet this site may experience significant impacts as climate continues to change. Ecological dynamics of this site are informed by disturbance response group 7 described in Stringham et al. 2016 yet are considerably different due to the dominance of buckwheat rather than scabland sagebrush on this site. This model is likely to undergo refinements and revisions as more data becomes available.