Have you noticed that some of the white firs (Abies concolor) in the Colorado Springs area are suffering? Many of these beautiful native trees seem to be having trouble this year, and experts are stumped. The needles start to turn a slightly lighter shade and drop, sometimes in a spiral pattern from the top down. Looking at the whole tree, it looks like it is declining gradually overall. The problem is affecting white firs of all ages and in all planting situations, non-irrigated, irrigated, sandy soil, clay soil, etc.
Of course, all evergreens naturally lose needles every year from the interiors of their branches. As the trees grow, those needles become shaded and no longer useful in the photosynthesis process. So the efficient trees drop those needles and concentrate their energy on the newer needles on the branch ends. With this condition, which has been informally dubbed “white fir decline,” all the needles along the branches are dropping. Another interesting feature is that these trees seem to have their upper branches covered with more cones (fully and not-yet-fully developed) than usual.
This week I noticed a white fir that had been hit by lightning in Monument Valley Park. It was a mature, tall tree and the strike toppled the tree about halfway down its trunk. I let Dennis Will from Colorado Springs City Forestry know about the tree, and he told me about this strange white fir malady. Apparently the downed tree was one of several suffering from it in the park. A tree expert from Colorado State University had been down to observe the trees and to take samples for diagnosis. His theory was that they might be suffering from a root disease. Root diseases are quite difficult to diagnose, and he was not successful in identifying any fungi that would cause such a disease. So it is still a mystery.
Dennis said he thought that the trees may be suffering from a complex of problems resulting from their being planted too far out of their native range. (This does bring up an interesting point. A plant may be a Colorado native, but that doesn’t mean it is native to every zone and environment in the state. These trees are happier in their native montane zone – a bit higher than the foothills – and in decomposed granite.)
Unfortunately, this doesn’t give us anything that we can do to help or save these trees.
Contributed by Carey Harrington, Colorado Native Plant Master