This article is dedicated to the late Carl Mock, who was an experienced backcountry guide who was mauled by a grizzly bear in early April. He enjoyed hiking, camping, catch and release fishing, and wildlife photography. Carl is survived by his dad and stepmom Chuck and Pat Mock, his mom and stepdad Terri and Eric Nilsen, his sisters Tiffany (Robert) Cook and Lindsay Russell, his step brother Ryan (Nicole) Regan, his cousin Aaron Reisenbiglar whom was like a brother, his cats Beauford and Lucille and his bird Mabes. His death is a reminder that even wildlife experts are at risk when they enter or even come close to proximity of our Nation’s most wild places. To plant trees in memory, please visit the Sympathy Store.
At the end of June, I’m finally making my ecological pilgrimage to Yellowstone! Of course, I’m ecstatic to see the grazing herds of buffalo, packs of hungry wolves, towering moose, and the intimidating grizzlies, but the ecologist in me is researching trails that will cross paths with a specific plant. In the North-Western high elevation region of Yellowstone grows a plant integral to the functioning of these demanding areas. A community shaped by a tree species endemic to the area, the whitebark pine (Pinus albicaulis) is without a doubt a keystone species. Providing fat-rich pine nuts to mammals and birds throughout the harshest winter months, without healthy whitebark pines growing, competition for food resources increases, and other species lose out. I’m headed to see these trees first before it’s too late. Most of the adult individuals are infected with an invasive fungus that these trees will eventually succumb to. Intense restoration efforts are in place to plant juveniles that have been selected for with increased resistance to the fungal pathogen. I can’t wait to see these species and witness the ecological services they still provide in these high elevation regions.
Pictorial map of Yellowstone by Heinrich C. Berann.
Not to be confused with the towering, straight stemmed white pines of the East, (Pinus strobus) which actually grow to be the tallest tree species on the Eastern seaboard, whitebark pine is smaller in stature. It is also commonly found growing in a twisted and knotted way, a form we call ‘Krummholz’ which translates to ‘crooked wood’ in German. This is a common characteristic of trees growing in high elevation, cold and windy areas and highlights the environmental plasticity many plants possess. Even though they may not stand out against the landscape like the Eastern white pine, they do share a common threat with the whitebark pines. The white pine blister rust (Cronartium ribicola) was unknowingly introduced to North America most likely through the shipment of wood products inhabited by the fungus, or possibly the movement of ornamental plants from the genus Ribes; the main alternate host of this fungus.
A living Whitebark pine (Pinus albicaulis) displaying high elevation Krummholz characteristics.
Many of these fungal parasites commonly known as the rusts, have life-cycles requiring one, sometimes two host species. Pine blister rust has an exceptionally complex life-cycle, requiring two different host species consisting of five different spore stages. The individuals of infected alternate hosts (Genera: Ribes, Castilleja and Pedicularis) only show mild symptoms, like leaf spots and early leaf drop. It is during this alternate host infection where Cronartium ribicola lives through 3 of its 5 spore stages. The basidiospores produced at the last spore stage on the alternate host can then infect its primary whitebark pine host. Once the basidiospores land on the plants needles they quickly make their way into the plants vascular system, utilizing the sugars within. Pruning infected branches can help the plant live longer, but once the fungus makes its way to the main stem, it’s just a matter of time until the fungal growth essentially girdles the tree, halting the flow of water and nutrients up from the forest floor below.
Alternate and primary plant hosts. Left: Leaf spots on the underside of a leaf on a Ribes species (telial host). Right: Cronartium ribicola growing on Western Pine.
To make things worse, invasive pine beetles are also wreaking havoc in the West, and these little bugs don’t discriminate against North American pines. Many studies show that pine beetles are more likely to infect stressed plants that can’t muster up a proper defense as their resources and energy dwindle amongst this voracious fungus. The pine beetle could act as the final blow or initiate the infection from the start by flying from tree to tree, spreading spores around.
Additionally, us humans have wrongly been putting out natural forest fires, thinking we were helping these ecosystems for over 100 years. This fire suppression has helped this fungus immensely, as low intensity, high frequency forest fires common to these regions of Yellowstone before European settlers established themselves would kill many stages of the resting fungal spores. In addition to a direct interaction with the fungus, the lack of natural fires has allowed less fire-resistant species to grow and compete in places historically dominated be the whitebark pine.
Mountain pine beetle. (Dendroctonus ponderosae).
As humans spread invasive species around and alter fire regimes, we change the basic functioning of single keystone species, which ultimately radiates to other species. With whitebark pines declining from 40%-90% throughout their range, these high elevation regions are drastically being transformed. Grizzly bears depend on these fatty pine nuts to get them through the harshest winter months when little else is available. As these tree populations decrease, the fight for survival intensifies. It is time we all think about plant conservation and our role as humans in protecting these truly wild places. The bear that killed Carl Mock could have had a terrible winter with the few fat-satiating pine nuts available. Wildlife officials stated the bear was defending a moose carcass which was only 50 yards from where Carl was fishing. It is known that bears will defend large food items like this, regardless of the health of whitebark pines nearby. I’m here to remind you, and remind myself, that the struggle for survival in Yellowstone is ramping up, and that the decimation of one species radiates throughout the food web, which increases competition, which unfortunately increases the rates of human-bear conflicts.
To the friends and family of Carl Mock, I send my deepest condolences. I hope that this article sheds some light on the importance of the keystone species in the Greater Yellowstone region; a place that Carl loved and respected. RIP.