At Penn-Del’s 54th annual shade tree symposium, this year’s theme was trees, tools, threats and tech. There was a wide array of topics being discussed, but Dr. Lara Roman’s presentation on Urban Tree Mortality was most captivating for me in regards to how I think about the urban forest, especially in terms of ecosystem management and the role socio-economic factors influence the culture.
Two slides were provided that illustrated the concept of disease-decline spirals of trees in their respective environment.
In the above link, you can find Manion’s illustration of the disease-decline spiral that Dr. Roman used in her presentation. Upon the first observation of the illustration, I was overwhelmed with a feeling that trees in their respective dynamic natural environments are certainly doomed, eventually. And, once you introduce trees into the urban environment where resources become even less scarce, the odds are stacked more heavily against them.
So there is hope if a tree is lucky. But not much.
But, after considering the illustration a bit longer, I realized that it can also be looked at more of a comprehensive map rather than a pessimistic projection of a tree’s future.
Factors in the spiral illustration are classified into one of three categories affecting a tree’s ultimate decline: predisposing, inciting and contributing factors. You see, as we move through the spiral, there is the potential for cultural management each time a tree is presented with a stress factor in it’s unique environment, but that management becomes more difficult deeper into the spiral. When that management is focused and applied early on in the spiral, especially at the level of the predisposing factors, then arborists and managers have the ability to, even if for a short time, remove the tree from this downward spiral. In fact, in the urban environment, proper planning can be a great opportunity in mitigating such stress factors. Many times in example where planning is dynamic and well thought out, there is great success.
Dr. Roman presented us with 3 examples from her experience with urban tree management and mortality.
In the first example, Dr. Roman talked about her involvement in the Sacramento yard tree program in which the city took initiative to offer free trees to the residents of the city to expand and diversify the urban canopy. Rather than encouraging people to utilize the small space of tree lawns or other unsuitable urban sites, homeowners were encouraged to properly place the trees in their yards where they could be more beneficial towards the main goal of the program: reducing energy use. Responsibility for their care would then ultimately be left with the homeowner, which in a sense required a little more accountability on their end.
In 2008, at the time of Dr. Roman’s involvement with the program, there was a serious economic crisis. In hindsight, Dr. Roman also noted that there was a big problem with delivery and distribution of the trees. In fact only 15% of the total number of available trees were ever planted. On some sites it wasn’t even clear if trees were ever delivered, or ultimately what happened to them in terms of survivorship or mortality. This example lends itself to the notion that good intentions don’t always yield great results. Not only that, but other challenging factors such as microenvironment (Sacramento’s subject to drought and minimal irrigation opportunities) and also the socio-economic environment can be reflected in the poor results of the yard tree program during this period (I should note that I am only speaking of the yard tree program at the time of Dr. Roman’s involvement with the project as of 2008 as she reported on her experiences at this years shade tree symposium; this is not an accumulated summary of the yard tree program to date).
Dr. Roman provided us with two other examples of successful survivorship in tree planting programs, one located in East Palo Alto, CA, and the other at University City Green in West Philadelphia, PA. The survivorship in each was 96.3% and 90.7%, respectively. These results of course, are inspiring, and projects that we should certainly look to when trying to develop factors of successful urban tree programs. In other words, we see in these examples little progression through the disease-decline spiral.
http://ucgreen.org/index.php/about-us/programs
If we look at all three projects against the projection of the disease-decline spiral, success or failure starts with analyzing pre-disposing factors of the urban environment. Many times in the urban forest we see how influential abiotic issues can be in such a fractured setting. Things such as compaction, irrigation, placement, budget and monitoring create a dynamic web of factors that make programs such as these immensely challenging on the ground floor.
Who is ultimately responsible for the labor of tree care? In the Sacramento program, we see that homeowners and the community at large are sometimes not capable of the accountability necessary for healthy trees. On the other hand, when a ISA Board Certified Master Arborist is responsible for the direction and management of tree health and monitoring, there can be great strides of success. The labor of tree care is another heavily influencing factor.
Not every tree starts out with the same opportunities as others. We see this in the illustration of the disease-decline spiral, as well as in the two example programs discussed. Some trees, depending on species and environment, are more pre-disposed than others to certain stress factors. Some trees receive better design and planning, more care, more monitoring and more resources than others.
Is urban forest health and cover a direct result of the socio-economic environment in which a tree is located? Should everyone be entitled to have a healthy green space in their life? Are some urban forests more privileged than others?
These are just some of the questions I have been pondering since Dr. Roman’s presentation.
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