The City of Austin Tree and Natural Area Preservation code is based on
the fundamental precepts of sound urban forest management. These precepts
establish a diversification of species, with a mix of young, medium aged,
and mature trees. Proposed development projects are evaluated on a
case-by-case (and tree-by-tree) basis. The goal of each review is to
assure that, through a combination of preservation and re-forestation, a
final product is achieved which results in a diversified and sustainable
urban forest.
The review process entails evaluating the existing tree resources on a
site, understanding the dynamics of trees and development impacts, and
negotiating a solution that results in a development with a balanced
mixture of age classes of trees and a diversification of species. The
national tree regulation standard is based upon a replacement ordinance.
This typical approach is based upon a formula that allows for the removal
of any and/or all trees by satisfying a replacement amount. However the
City of Austin ordinance places greater emphasis on tree preservation. The
system relies upon staff evaluation and negotiation to achieve tree
related resolutions. Trees on sites other than single-family home lots,
that measure greater than 8 inches in diameter are scrutinized for
preservation potential. Trees greater than 19 inches in diameter are
classified as "protected size" and receive enhanced preservation
evaluation. The tree ordinance applies to sites within the zoning
jurisdiction of the City of Austin.
A permit is
required for the removal of or impact to any tree 60 inches in
circumference and larger (measured at 4.5 feet above the
ground). Sixty inches in circumference is equivalent to 19 inches in
diameter. Trees smaller than 60 inches in circumference are not
regulated .
City code requires that proposed developments
demonstrate that trees are preserved to the maximum extent reasonable and
feasible. Tree preservation is effectively defined as root system
preservation, a Critical Root Zone Area (CRZ) is assigned to each tree,
based on trunk diameter size. A minimum of 50% of the CRZ is required to
be left undisturbed to achieve minimal conformance with the regulations.
Trees are depicted on plans with a CRZ circle centered on the tree base
location (i.e. a twenty inch diameter tree is represented by a 40 foot
diameter circle). The formula is: Tree diameter in inches X 2, then
convert to feet = CRZ diameter. The CRZ circles are superimposed on the
proposed plan improvements so that review staff can discern the extent of
disturbance proposed near existing trees. Tree types and sizes are also
provided. Trees which are removed are generally required to be replaced at
a sliding ratio determined in part by the overall extent of tree removal
proposed.
City code requires that proposed developments
demonstrate that trees are preserved to the maximum extent reasonable and
feasible. Tree preservation is effectively defined as root system
preservation, a Critical Root Zone Area (CRZ) is assigned to each tree,
based on trunk diameter size. A minimum of 50% of the CRZ is required to
be left undisturbed to achieve minimal conformance with the regulations.