The cone. It’s an integral part of any coniferous tree, and makes up a substantial part of the image that comes to mind when one hears the words “pine tree.”
Hemlocks belong to the order Pinales, which are distinguished by their possession of cones for reproduction. Hemlocks begin producing cones between 20 and 40 years of age and will continue to put out cones up to 450 years in age or more. Hemlocks are one of the highest producers of cones out of all eastern North American conifers and will produce at least some cones each year. However, a good, abundant crop of cones will only occur every two to three years. This is when one can look up at a hemlock and see hundreds of the small cones dangling from the ends of its branches. The cones start off a nice, light shade of green before taking on the dull brown color we typically associate with pine cones. Hemlock cones may seem like a fairly straightforward feature of the tree, like the hair on our heads, but there’s a lot more behind cone production and what their presence means for a tree than meets the eye.
Producing lots of seed is no easy task for a tree. It requires large amounts of resources and energy that could be used for other essential processes like food production, growth, and creation of new buds. A tree putting out many cones has made a calculated decision to invest heavily in reproduction, hoping to spread its genes on to the next generation.
Hemlocks naturally put forth the energy to produce a multitude of cones every few years, and intuitively, we may think that a tree producing many cones, and therefore seeds, is a healthy tree. However, many trees, including hemlocks, will produce high amounts of cones for a less intuitive reason.
“Distress crop” is a phenomenon that occurs when a tree becomes so stressed that its very survival is threatened. Dealing with the possibility of death, a tree will produce a bountiful amount of seed as a last ditch effort to reproduce. The tree will even use up critical food stores to do this, at the expense of its own life, so that its seed will hopefully spread. As eastern and Carolina hemlock face more and more stress from the infestation of hemlock woolly adelgid, it becomes increasingly likely that years of high cone production are related not to a natural cycle, but to the tree’s own assessment of its impending mortality.
This realization is important for those interested in assessing hemlock health. A large presence of cones may not be indicative of good health for a hemlock. Look for other signs of tree health like live crown ratio, crown density, and whether there is branch dieback or abundant new foliar growth. The assessment of these traits could indicate whether a large amount of cones is due to stress or simply the tree going through one of its natural years of high production.
Most people are aware of cones, but not many are aware that their overabundance could be a sign of tree decline, due to hemlock woolly adelgid or other factors. Spread the knowledge and let others know that the sight of a lot of these iconic seed carriers, while aesthetically pleasing, may indicate trouble for the tree from whence they came.