By Robin Y Rivet.
Is your neighborhood lined with large, mature street trees? The odds are against it.
· Older communities once revered their elder trees, but that archetype is waning.
· Magnificent veteran shade trees are hitting the chopping block every day - getting hacked or disappearing completely.
· The reasons may be good, bad, or very ugly; but the end result is fiercely unsustainable.
Possibly benevolent causes:
· Dwarf trees are associated with edible fruit, reduced litter, and less infrastructure problems, but the reality is larger species are more vigorous, resilient and longer-lived. Choose wisely.
· Advocates for wildlife habitat suggest that native trees are superior, but many are diminutive in stature, while our incredibly colossal and spreading native oak canopies - struggle to thrive in urban conditions.
· Many trees imported into Southern California haven’t adapted here long enough to confirm whether their lifespans will improve or falter, but natural pest predators don’t always arrive with introduced species.
What is bad?
· People view tree mortality through an anthropomorphic lens. Urban trees may seem to be shorter-lived than their counterparts in open forests. But why is that?
· High value of land and the need for more housing, often translate into tiny, soil-level footprints and minimal setbacks, so large trees depart – and smaller scale plants typically take their place. A few extra stories are worth improved soil exposure and bigger scale trees.
· A common misconception is that as trees age, they become useless and frail. Studies however tend to defy that conclusion. A concept called “negative senescence”, is a phenomenon where the durability of older trees may mean they have a greater chance of survival than younger ones. If they don’t perish young, they may develop tolerances that compensate for future adverse conditions. Big trees with extensive roots systems are generally less likely to topple than younger saplings, and these larger specimens store carbon at disproportionately higher rates.
What is truly ugly?
· Some neighborhoods do value their impressively regal heritage trees[1], but litigation-weary governments tend to err on the side of hasty removals[2], rather than thoughtful preservation when any doubts are raised.
· Perceived solar installation conflicts, unjustified fears about cost of irrigation or the imagined danger of senescenceoften prompts residents to remove otherwise stately, mature specimens unnecessarily.
· In considering resiliency to climate changes, species that adapt best to environmental changes, are frequently also considered “invasive”; while many native species struggling to adapt - are dying off.
· Monoculture still prevails, and pest and diseases need smarter and more diverse urban design.
Is there a bottom line?
· Environmental conditions affect tree longevity more than age, and some species have both juvenile and senescent parts on the same tree, so care must be taken to clearly evaluate when chainsaws should prevail over life. Every person’s actions matter, and societies that don’t respect their elders often suffer.
· Ultimately, we need urban trees for our sense of well-being, and we need to plan better to accommodate future canopy needs now.
· Most aging urban trees acquire some decay over time, but the processes are quite complex and sometimes remaining heartwood is strong, and removals become largely unnecessary. The western tree species failures reports don’t document many cases in San Diego County.
· I think this blog nails the sensitive link between healthy human function and healthy trees.
References:
[1] https://www.nbcsandiego.com/news/local/effort-to-save-century-year-old-trees-continues-in-kensington/2523078/ [2]https://www.cbs8.com/article/news/local/kensington-pepper-trees-cut-down/509-d9b6f031-3d4f-418f-a3a5-729e3f68ff9e
Member Robin Rivet is an
ISA Certified Arborist – contact her: treetutor@gmail.com
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