Photo by Dan Mullen licensed under CC BY-NC-ND 2.0
I must admit, I am not very savvy when it comes to trees. I love and appreciate them all the same, however, my attention is often paid to the species growing beneath their canopy. last summer changed a lot of that. I was very lucky to be surrounded by people that know trees quite well. Needless to say I picked up a lot of great skills from them. Despite all of this new information knocking around in my brain, there was one tree that seemed to stand out from the rest and that species is Juglans cinerea.
Afternoons and evenings at the research station were a time for sharing. We would all come out of the field each day tired but excited. The days finds were recounted to eager ears. Often these stories segued into our goals for the coming days. That is how I first heard of the elusive "white walnut." I had to admit, it sounded made up. Its as if I was being told a folktale of a tree that lived in the imagination of anyone who spent too much time in the forest.
Only a handful of people knew what it was. I listened intently for a bit, hoping to pick up some sort of clue as to what exactly this tree was. Finally I couldn't take it any longer so I chimed in and asked. As it turns out, the white walnut is a tree I was already familiar with, though not personally. Another common name for this mysterious tree is the butternut. Ah, common names.
I instantly recalled a memory from a few years back. A friend of mine was quite excited about finding a handful of these trees. He was very hesitant to reveal the location but as proof of his discovery he produced a handful of nuts that sort of resembled those of a black walnut. These nuts were more egg shaped and not nearly as large. Refocusing on the conversation at hand, I now had a new set of questions. Why was this tree so special? Moreover, why was it so hard to find?
The white walnut has quite a large distribution in relation to all the excitement. Preferring to grow along stream banks in well-drained soils, this tree is native from New Brunswick to northern Arkansas. Its leaflets are downy, its bark is light gray to almost silver, and it has a band of fuzzy hairs along the upper margins of the leaf scars. Its a stunning tree to say the least.
Sadly, it is a species in decline. As it turns out, the excitement surrounding this tree is due to the fact that finding large, robust adults has become a somewhat rare occurrence. Yet another casualty of the global movement of species from continent to continent, the white walnut is falling victim to an invasive species of fungus known scientifically as Sirococcus clavigignenti-juglandacearum.
The fungus enters the tree through wounds in the bark and, through a complex life cycle, causes cankers to form. These cankers open the tree up to subsequent infections and eventually girdle it. The fungus was first discovered in Wisconsin but has now spread throughout the entire range of the tree. The losses in Wisconsin alone are staggering with an estimated 90% infection rate. Farther south in the white walnuts range, it is even worse. Some believe it is only a matter of time before white walnut becomes functionally extinct in areas such as the Carolinas. No one knows for sure where this fungus came from but Asia is a likely candidate.
A sad and all too common story to say the least. It was starting to look like I was not going to get a chance to meet this tree in person... ever. My luck changed a few weeks later. My friend Mark took us on a walk near a creek and forced us to keep our eyes on the canopy. We walked under a tree and he made sure to point out some compound leaves. With sunlight pouring through the canopy we were able to make out a set of leaves with a subtle haze around the leaf margins. We followed the leaves to the branches and down to the trunk. It was silvery. There we were standing under a large, healthy white walnut. The next day we stumbled across a few young saplings in some of our vegetation plots. All is not lost. I can't speak for the future of this species but I feel very lucky to have seen some healthy individuals. With a little bit of luck there may be hope of resistance to this deadly fungus. Only time will tell.
Photo Credit: Dan Mullen (http://bit.ly/2br2F0Z)
Further Reading:
http://bit.ly/2b8GiMV
http://bit.ly/2aLUdMD