Although sagebrush is the quintessential plant of the Basin and Range physiographic province, quickly, the naturalist will take note of the Pinyon-Juniper or PJ Woodlands that give the mountain mid-slopes both color and contrast. The sagebrush gives home to greater sage-grouse, sagebrush sparrow, and sage thrasher, while a dozen or more bird species are critically dependent on the PJ woodland such as pinyon jay, juniper titmouse, Woodhouse’s scrub-jay, gray flycatcher, black-throated gray warbler, etc. Dozens more take advantage of what the PJ offers but are not strictly dependent, such as chipping sparrow, ferruginous hawk, common raven, and ash-throated flycatcher. While primarily focusing on one or two species, it is worth remembering that many species are irrevocably connected to each other.
Single-leaf pinyon (Pinus monophylla) and Utah juniper (Juniperus osteosperma) are often found together, making it difficult to decide if one is helpful to the other, in competition with, or indifferent. Where they are found together, biodiversity is naturally greater. Go downslope and eventually the P give way to J. March uphill, and one often finds tall, nearly pure stands of P with few or no J in sight. Oddly, where they do occur together, under every juniper over ten feet tall grows a pinyon, ranging from mere inches to three feet. This is known as “in-filling,” or simply filling open space in the woodlands with additional trees.
Pinyon pine does not venture north into Idaho more than 15 miles. It is found at mid-slope on the Albion, Jim Sage, and Black Pine Mountains. The best place to see, study, and simply enjoy pinyon is City of Rocks National Reserve. Here, over centuries past Shoshonean people travelled in late summer and autumn to gather pine nuts. The nuts were collected from mature cones, roasted, preserved, and consumed over the next several months. Whatever amount they could part with was traded between tribal bands and later with emigrants traveling the California Trail.
Scientists have documented the northward expansion of the pinyon territory. It is believed, based on packrat midden studies(1), that present-day pinyon arrived at City of Rocks about 2,800 years ago, long after the glaciers melted atop Cache Peak (10,339). As the climate became warmer and dryer northward, pinyon was able to propagate and enlarge its territory. However, right here the battle lines were drawn. Pinyon had invaded(2) long-held territory of the limber pine and to some extent lodgepole and Douglas fir. Perhaps we are witnesses to the end of a great ecological battle. Even though the pinyon might find the climate suitable for a northward advance, it is unlikely to surmount the relatively barren Snake River Plain physiographic province.
City of Rocks is the place to study and ponder where this species is in the continuum. The state champion pinyon is here, nestled in a slot canyon of granite. Many exceptionally large pinyons and a few limbers of advanced age are found together in what might have been the best fortress against loggers and wildfires. Yet look at the east slopes of Circle Creek Basin or north-facing Smoky Mountain and you will see that pinyons are in the fight of their lives. Kill-zones(3), pockets of dead or dying pinyon of an acre or more, are increasing in number and size. Each year, a piece of the woodland surrenders to a handful of pathogens that smell death in the global warmth.
Just as pinyon ends the protracted confrontation and subdues the limber pine, it must now turn its attention to this new and emerging threat – pathogens in alliance. For decades, forest pathologists and resource managers have recognized the occasionally devastating threat of Ips confusus, the pinyon Ips beetle. This critter is more than capable of orchestrating a kill-zone.
A few years ago, the superintendent of City of Rocks decide he had seen enough. He began to ask questions, investigate the root causes (so to speak!), and validate his concerns with the scientists. Surprisingly, the Ips beetle is not the primary culprit at City of Rocks. Black stain root disease caused by the fungal pathogen Leptographium wageneri is the silent killer. Tracked across the xylem like blood on the murderer’s shoe, tiny weevils track spores of the black stain fungus from one root system to the next.(4) The fungus gums up the xylem (or the tree’s “up elevator”) from sending water and other nutrient to the leaves. Like holding your breath too long results in a weakened body or even death, so too does black stain sap the life out of the tree.
Not only must pinyon withstand black stain, but also pinyon tip moth, pinyon pine blister rust, pitch moth, pouch fungus and of course the Ips beetle. And there are others that will take advantage once the stench of defeat is in the air. Of course, the pinyon is not without some defenses(5) . Where will it all end and what can or should be done by park stewards and forest resource managers? Range margins are places of active population dynamics, retreat and advance in response to climatic cycles, and more. With global warming, species are retreating from the hottest spots and extending their ranges northward.
Reluctantly and humbly, we must admit that for all we do know about pinyon pine, we know very little about the northern most range of the species in Idaho. Black stain is a native pathogen. Its killing instinct is perfectly legitimate. City of Rocks and national park units generally are set aside as places where natural processes are scientifically studied and celebrated. Active management rarely occurs, but when it does, it is because we messed up somewhere in the past and now, we are desperate to fix it. If the resource cannot be fixed, we try to perpetuate as many elements of the natural for as long as possible.
Pinyon is listed in Idaho as critically imperiled. In a few generations or a few centuries, pinyon pine might disappear from the Idaho landscape due to disease, climate change, or other woody competitors. Or it is possible that pinyons will adapt and advance into adjacent mountains such as the Deep Creek and Bannock Range. It is an interesting story to follow, and if we are wise, one which requires a good long read before we act too dramatically on what little we know about Pinyon Pine in Idaho.
Footnotes:
- Packrat nests contain excrement and vegetative materials that can be identified and dated more than 40,000 years.
- Did pinyon invade the territory of the limber pine, or did it simply find the land vacant of any competitors?
- Kill-zone: the author’s term for the acreage of woodland being attacked by black stain root disease.
- The disease can also spread between neighboring trees through root grafts.
- One of the pine’s best defensive weapons is pitch, the white, yellow, or pink sap that the tree produces to push out the beetle or moth invader.