Street Tree Risk Factors and Care
Urban trees play a vital role in our communities, providing shade, beauty, and critical environmental benefits. However, these trees face numerous threats that can jeopardize their health and longevity. This page is dedicated to informing you about the various risks urban trees encounter, including pests and diseases, environmental challenges, and improper management practices. By understanding these risks, we can work together to protect and preserve our urban forest for generations to come.
Pests and Diseases
Ficus Dieback – The Southern California region is currently experiencing an outbreak of branch dieback and associated cankers on the popular Indian Laurel Fig (Ficus microcarpa). The City of Santa Monica Public Landscape Division has been engaging local stakeholders and third-party experts to develop an ongoing management plan. This plan includes reducing non-emergency Ficus pruning, removing infected trees quickly, sterilizing tools and spraying wounds with bio-fungicide.
Dotted Paropsine Leaf Beetle – “Although small, the dotted paropsine leaf beetle and its larvae can cause significant damage to the leaves of a host tree. If they do not eat the whole leaf, they will leave behind distinct notches in the leaves like other eucalyptus leaf beetles. Severe infestations can cause defoliation and eventual death in stressed or young trees.”
Environmental Challenges
Drought– Urban trees need our help during drought conditions. With an increasingly dry climate on the horizon, it's crucial to water them deeply and infrequently, add mulch to retain moisture, and choose drought-tolerant species. The City of Santa Monica has published a guide to help understand watering guidelines during drought.
Wildfires – According to CalFire, living trees in
urban settings are at greater risk of the homes near them catching fire and
harming the trees than the reverse. This is due to the high moisture content of
living trees and the high flammability of homes. We encourage you to view resources
from CalFire on creating defensible space and preparing for the next natural
disaster.
Human Activities
Improper Pruning - Topping is one of the worst
pruning practices to do to a tree, yet it is unfortunately very common to see. It
is the indiscriminate reduction of the tree size, without consideration for the
long-term structure or health of the tree. Proper pruning promotes healthy
growth and maintains the tree's structural integrity, whereas topping leads to
large wounds that can cause decay, introduce disease, and permanently disfigure
a tree. Other improper pruning practices include "lion's-tailing" or
excessive thinning of interior growth. This practice leads to excessive
wounding, sun scalding, and altered wind dynamics, making trees more susceptible
to branch failure.
Development – Urban trees are at great risk of being removed as part of increased development pressure. Through careful planning and intent, trees should be preserved where possible. Consulting with an ISA Certified Arborist at the start of your project can help create a Tree Protection Plan, to preserve the aesthetic and environmental benefits provided by existing trees throughout construction and after. As part of a multi-year urban tree canopy assessment, the City of Santa Monica has learned that while the tree canopy coverage on public lands has increased, it has decreased significantly on private property.