Bad Tidings for Sage Grouse

The problem with sagebrush is that it has no resistance to fire disturbance. Even reasonably low intensity fires can kill a mature sagebrush during the right season with the right fuel priming. Sage is well adapted to dry conditions with its small, hairy, silvery leaves adept at holding onto what moisture it can against the negative pressure gradient of an arid western summer. Two, three, four months without rain can stress even the hardiest sage so that desiccation, scorch, and burn are inevitable when the wildfires come. Sage do not resprout. They rely on what seeds to survive in the insulating soil to recruit the new generation. However, climate change can throw a wrench into the historic cycle of wildfires burning through sagebrush steppe, clearing patches of decadent shrubs, and initiating new stand regeneration. 

Sagebrush seedlings (Top) beside skeletal mother plant (Center right). Photo by: K. Allen

Climatologists predict that the future weather will be hotter, wetter, less reliable, and with substantially more extreme events like wildfires. Ecosystems like sagebrush steppe could benefit from the reintroduction of fire after a century of suppression, but with some caveats. Sagebrush steppe benefits from a fire return interval of about ten years, enough time to allow the sage overstory to regenerate before it is knocked down by another fire. Were fires to become more frequent, there would not be enough time for the new sageling recruits to mature and disperse seed for the next generation. Fires returning every few years will suppress woody vegetation enough that it may disappear entirely from the landscape. Increased precipitation could also benefit sagebrush, but only if it falls during the critical window for seedling establishment. An extra inch of rain in July does no good to the seedling that withered and died last April. Also, an increase in average temperatures can wreak havoc on tender, young sagelings whose root systems have yet to reach toward the water table and thus have no buffer between themselves and the scouring heat. 

This is all troubling news if you are a sage grouse. Sage grouse are obligate sagebrush steppe species, who rely on a robust and heterogeneous sagebrush community for their entire life history.  Both sage grouse hens and cocks seek sand flats or sparse sage stands to lek – the annual mating ritual which brings sage grouse to the same spots year after year. Sage grouse hens require small sagebrush – between one and three feet tall – as cover for their nests. Sage grouse chicks require a diverse community of sagebrush, grasses, and forbs to support their herbivorous and insectivorous diet. And last, sage grouse of every stripe rely entirely on sage brush as their sole source of winter forage. Normally a population might respond to fire in sagebrush habitat by migrating to an unburned refuge. If fire frequency, scope, and intensity increase with changing climate, however, these refugia could shrink or disappear altogether. 

Cheat grass carpets the open spaces between the bunch grasses, even in unburned stands of sagebrush. Photo by: K. Allen

Another troubling detail is the impressive spread of the invasive annual cheat grass. Even if land managers were to mitigate damage to sagebrush communities, there is the ever-present threat of cheat grass invasion. Cheat grass is so named because it spreads easily, germinates early, develops and seeds before other grasses have begun to burgeon. Cheat grass is able to take advantage of early, sparse water resources as yet unused by native plants to reproduce and fill the interspaces so characteristic of western rangelands. 

Cheat grass moving in between the bunch grasses, post-burn. Photo by: K. Allen

Cheat grass also favors disturbed soil, such as bare soils following wildfires, and has been known to cover scorched landscapes before native plants have the opportunity to resprout or reseed.  This is also bad for sage grouse who alternately depend on bare ground and diverse communities throughout their lifecycle. Cheat grass broadcasts itself in the interspaces, competes for water, and chokes native seedlings as they emerge. What’s more, cheat grass sprouts early and cheat grass dies early, leaving thick purpleish carpets of fine dry fuels, boosting fuel continuity and sending invitation to yet more rangeland wildfires. Thus, the extirpation of sagebrush from western rangelands means the extirpation of sage grouse as well.