The Annihilation of our Arbutus

No matter how you refer to our Pacific madrone (Arbutus menziesii), it is a tree species that will always remain close to our hearts. Being the Pacific Northwest’s only broad-leafed evergreen, it is a true native, found along the west coast, all the way from British Columbia down to the Baja. From inauspicious beginnings that belie its current reverential status today, it was once thought of as a weed and cut down to make room for prized fir or cedar specimens.

The microhabitat of the madrone happens to also be favoured by humans in search of a room with a view. Madrones like to cling to rocky cliff-sides and have their branches take on a wind-swept look. Their roots can penetrate bedrock in search of water and a stronger foothold, in fact studies have proved that their tenacious roots are a contributing factor to slope stability on a bluff that has previously experienced landslides.

Tragically it is these very sites that are prized by people who would rather gaze upon it idly from a lofty perch ensconced safely and hermetically behind triple pane glass, than walk the land and enjoy it in its natural and wild untamed state. They are blivious to the interconnectedness of all things, and how their construction changes can have unforeseen negative repercussions in a system so incredibly complicated and diverse as nature.

So what is causing the classic symptoms of arbutus decline? Lets start with abiotic stresses first, the biggest being urbanization, including vehicular and marine traffic and their pollutants. Climate change has made the trees more susceptible to infection. Madrones store their nutrients underground and healthy saplings can sprout from a stump if the tree is cut down or burned. Quite possibly the suppression of wildfires may also be weakening the trees. Arbutuses don’t like their roots bothered so root disturbance and damage, competition for resources, shading and drought stress can also cause stress to these sensitive treest.

The biotic stresses endured are prolific, starting with pathogenic fungi. There are at least 21 different species that have been identified; this fact comes from Marianne Elliott and her paper on Diseases of Pacific Madrone. Most of these fungi are not a serious threat to the long life of a healthy arbutus but there are three that Dr. Elliott names most likely to cause tree death. Phytophthora cactorum is a fungal-like protist that causes a root rot, belonging to the same genus as the dreaded Phytophthora ramorum, the pathogen that causes Sudden Oak Death. Nattrassia mangiferae is also known as Arbutus canker, and madrone canker caused by Fusicoccum aesculi.

Although, we can’t seem to pinpoint exactly what is causing the death of the madrones, there is a consensus that that they are dying at an alarming rate and have been in steady decline for the past decade or more.

What can you do? The most important step is to try and minimize human influence around them. Avoid disrupting roots and damaging above-ground portions of the trees. Do not prune, as any wound is an entry point to disease causing pathogens and micro-organisms. Do not irrigate established plants because it will encourage surface rooting, which is typically short-lived and considerably less resilient than deep rooting. Summer irrigation is not advised, as arbutus are well adapted to our Pacific Northwest conditions where grow naturally and are semi-dormant in the summer. Planting more arbutus is an option, but there's no guarantee that the plants will survive the next drought or our well-intentioned interfering, but better to be on the optimistic side.