Working Around Trees
June 3, 2020 | By mendservices
In Central Texas, nature plays a key part in our lives! We enjoy being outside with friends and families. Many of us are fortunate to have beautiful trees around our homes providing a cool reprieve from the Texas heat in the form of shade. We want to take advantage of those outdoor spaces for entertaining guests or relaxing on the weekend. So, how can we best utilize and incorporate those trees into design without harming them?
Understanding Your Trees
When considering work around existing trees, it’s important to understand what can and can’t be done. The first step in that process is to conduct a tree survey. This process involves identification and location of trees on site including species and size. Additionally, inspection from a licensed arborist may help in identifying the overall health of your trees and how potential work may impact their health and longevity.
Heritage Trees
A protected size tree is determined by measuring the tree trunk at 4.5′ above the ground. This is commonly known as DBH (diameter at breast height). A tree within the Austin city limits is protected once it reaches a DBH of 19″.
In the City of Austin, removal of a heritage tree is prohibited unless the Planning and Development Review Department has issued a permit for its removal. A permit to remove a heritage tree can only be granted if a variance is approved. The Director of the Planning and Development Review Department may grant a variance and issue a permit for removal of a heritage tree if the city arborist determines that the tree is dead, diseased or in an imminent hazard to life or property and the hazard can’t be reasonably mitigated without removing the tree.
Learn more about protected trees at: http://www.austintexas.gov/faq/what-size-trees-are-protected-are-permits-required
Critical Root Zones
Taking care of what’s below the ground is equally as important as taking care of what’s above the ground for trees. Protecting and nurturing the roots of our trees helps to ensure their health and longevity.
City of Austin code requires that proposed developments demonstrate that trees are preserved to the maximum extent reasonable and feasible. These codes include both commercial and residential scenarios and encompass any work that may encroach on trees, specifically those defined as protected or heritage.
A Critical Root Zone (CRZ) is assigned to each tree based on Diameter Breast Height (DBH).
CRZ = DBH (in inches) x 2, then convert to feet
So, a tree with a 20″ DBH would have a 40′ CRZ.
20″ x 2 = 40″ = 40′ CRZ
A minimum of 50% of the CRZ is required to be left undisturbed during development. Trees are depicted on plans with a CRZ circle centered on the tree base location. Those CRZ circles are superimposed to better understand the impact of development on the health of the trees.
Further limitations on construction are in place for tighter areas around Protected and Heritage trees. The Half-Critical Root Zone (1/2 CRZ) can have minimal disturbance during construction. No cut / fill deeper than 4″ shall be performed, and any work in the 1/2 CRZ must be approved during plan review. Disturbance in the Quarter-Critical Root Zone (1/4 CRZ) of a Protected / Heritage tree is prohibited.
Protecting Trees During Construction
Construction around trees brings significant stress to their health! Any tree in or around the designated work area (including areas of access but not construction) should be protected for the duration of the project.
For Protected or Heritage trees, even if no work is being performed within the 1/2 CRZ, that area must be protected during construction to prevent root damage caused by equipment, material storage or heavy foot traffic. A construction fence must be installed at the perimeter of the 1/2 CRZ and the area defined by that perimeter must be loosely filled with mulch to decrease compaction of the soil above the roots and allow for adequate drainage and moisture retention.
For smaller trees that are not considered Protected or Heritage, consider installing protection around the trunk or major overhanging branches of the tree to minimize damage associated with impact.
Mend Services can help navigate the planning and permitting, specifically associate with tree plans for your project. We can also help ensure you have the proper measures in place to ensure the safety and health of your trees during construction so that they provide you with years of enjoyment for your new outdoor space!
If you have questions about a specific tree, contact the City of Austin Arborist: http://austintexas.gov/page/tree-reviews-and-permitting