Introduction
While growing up in Ottawa the street was lined with mature maple trees. About fifteen years ago, the neighbour next to my childhood home had to chop down the maple tree in their front yard as it was dying. Three years ago, my parents needed to do the same, and now the neighbour’s on the opposite side are facing the same situation. A single diseased and dying tree does not raise many questions or concerns and is only natural, but the progression of disease down the street becomes an ecological phenomenon.
Observation
The trees all showed, or continue to show the same symptoms, with unseasonal discolouration of leaves, smaller twigs dying, followed by the larger branches losing their bark and ultimately breaking. Larger pieces of bark and branches fall, or threaten to fall, and whole sections of the trees would die. The City would come and trim the large dead sections in an attempt to stem the disease progression, before finally removing the tree. Throughout the progression of disease and death the leaves would not only display unseasonal discolouration, but also, spotting, burns and other signs of stress.
Interpretation
My initial interpretation was that the first tree became diseased through a fungus or other source, progressing through the tree’s system, eventually expressing itself through the tree’s leaves. These leaves fell and were eventually blown onto the neighbouring property where the leaves, and fungus, decomposed into the soil. This fungus was then absorbed by the subsequent tree where the phenomenon continued. This sequence was my interpretation and assumption until this exercise cause me to investigate the phenomenon further.
Expert Consultation
I did not consult with any experts or colleagues regarding this phenomenon but I did conduct some primary research. The trees were likely infected with a soil-borne fungi, verticillium wilt and anthracnose are the likely culprits, but there was an additional stressor on the trees, maple decline (Zilke, 2014). Maple decline affects both urban and forest maples and is caused by repeated incidences of stress, though in urban environments trees undergo almost constant stress with poor water availability, nutrient-poor and compacted soil, road salt, and construction. These episodes of stress cause the trees to become more susceptible to other stress factors, such as soil-borne fungi, resulting in the trees succumbing to diseases that a healthy tree may survive (Houston, 1999; "Maple Decline: Various factors", n.d.).
Conclusion
http://plantclinic.cornell.edu/factsheets/mapledecline.pdf
Zilke, L. (2014). Maple trees in parts of the GTA threatened by soil-borne fungi. Global News.
Retrieved 17 April 2018, from https://globalnews.ca/news/1483357/maple-trees-in-parts-of-the-gta-threatened-by-soil-borne-fungi/
