Driving from Blackfoot to almost anywhere in southern Idaho, we’ll eventually travel through wide swaths of sagebrush, sometimes stretching as far as the eye can see. To most folks, this landscape appears as an uninteresting, dull, gray-green mass of shrubs. To animals dependent on sagebrush for survival, nothing could be further from the truth.
Scientists have documented everything from mule deer to sage-grouse using sagebrush. Indeed, some species like sage-grouse and pygmy rabbits are entirely dependent on sagebrush for their survival. Studies indicated some sagebrush plants or groups of plants were used more often than others by these animals, but until fairly recently there was little information to explain why this occurs. Just as important, scientists lacked tools to adequately identify types of sagebrush and predict their forage quality for wildlife. All that has recently changed.
About 14 years ago, scientists at Boise State University, cooperating with state and federal agencies, began examining the relationship between the chemical makeup of sagebrush and wildlife use. They found that chemistry differed among plants and groups of plants. In other words, not all sagebrush was created equal. These researchers discovered that sage-grouse selected relatively large stands of sagebrush based on lower amounts of plant secondary compounds (think toxins) but chose patches within stands and individual plants within patches largely based on protein content. These findings have management value but would be even more useful to habitat managers if there was a relatively quick and reliable way of characterizing sagebrush. Thanks to the efforts of BSU scientists Roger Rosentreter, Brecken Robb, and Jennifer Forbey, they now have that ability.
There are nearly two dozen species of sagebrush found across the Intermountain West and each species contains several subspecies and hybrids, as well as chemical and structural diversity within individual plants. BSU scientists tested different sagebrush species and subspecies from herbarium specimens and found three types of sagebrush that were often misidentified. This surprising discovery is worrisome because it suggests that resource managers don’t have a complete understanding of sagebrush habitats that provide critical wildlife habitat and are rapidly disappearing due to fire, invasive species, and energy development.
If there are problems correctly identifying types of sagebrush, how can resource managers possibly understand which ones are most valuable to wildlife? It turns out that sagebrush plants produce a variety of chemicals called coumarins that fluoresce a blue color under ultraviolet (UV) light. The BSU scientists found a UV light test can greatly improve identification of sagebrush species. Moreover, the UV light and chemicals that distinguish varieties of sagebrush are also an indirect biomarker of sagebrush palatability for some wildlife species. This means that a UV light test can be used to predict forage quality for species like sage-grouse and pygmy rabbits. Determining differences in coumarin concentrations among plants should now allow for a better understanding of habitat use by sagebrush obligates like sage-grouse and big-game species like mule deer. For example, the sagebrush species preferred by mule deer generally have higher coumarin concentrations than less preferred species do. Similarly, sagebrush species preferred by sage-grouse have higher coumarin concentrations than avoided plants do. How can animals differentiate among plants? Taste-testing may be one way, but sage-grouse have UV photoreceptors in their eyes that may allow them to see into the UV spectrum and use coumarins as a cue.
As sagebrush habitats continue to be altered, it becomes increasingly important to correctly identify sagebrush species to allow an understanding of consequences of climatic and human disturbances and restoration practices such as reseeding. Moreover, identification of palatable sagebrush species is critical for conserving animals like sage-grouse, pygmy rabbits, and mule deer that are selective toward sagebrush species and the chemistry of those species.