Ordinance No._____- 2012 AN ORDINANCE ... - San Juan County

eing transported and deposited in more sensitive locations.
Page 7 of 56
Ord. ____-2012
While in most cases the proposed buffers should be adequate, a potential area of risk for lakes and
ponds where the water has a longer residence time, is that 760% pollutant removal will not be
adequate, and that harmful quantities of pollutants will be deposited or incorporated into the food
chain, adversely impacting functions and values. This risk could be reduced by applying a larger buffer
with a greater pollutant removal capability to lakes and ponds with little or no outflow.
i. The tree protection zoneTree Protection Zone for Type Np and Type Ns streams flowing 6
months or more per year are 50 feet and 30 feet respectively, which is consistent with the requirements
under the Forest Practices Act. For streams flowing less than 6 months per year, a tree protection
zoneTree Protection Zone is not required but stream bank vegetation must be retained, which is
consistent with Wenger and Fowler (2000). In nearly all cases, these distances will be supplemented by
the water quality component of the buffer which is described above.
j. Under certain conditions, limited tree removal within tree protection zoneTree Protection Zones can
occur without significantly affecting FWHCAs. Adequate numbers and configurations of trees must,
however, be retained to preserve wind firm conditions (to prevent blow down), to provide shade, and
to maintain normal hydrologic and habitat functions.
Figure 3-3 of the BAS Synthesis provides information on distances necessary to reduce wind speed,
with a tree protection zoneTree Protection Zone equivalent to one SPTH approximately 70-75%
effective at reducing wind speed. Kleinschmidt (1999) also provides guidance on the management of
buffers and tree protection zoneTree Protection Zones to prevent blow down, with a 35 foot no cut
zone required next to the water (Zone 1), and at least another 35 feet (for a total of 70 feet) where
some tree removal is allowed if minimum stocking levels are retained (referred to as Zone 2). Blow
down rates can, however, vary depending on the spacing of trees within a tree stand (i.e., clusters),
topography (tree stand orientation relative to the strongest winds), usual duration and depth of soil
saturation, and other factors that are impractical to assess site-specifically in a County program.
Chapter 4 of the BAS Synthesis cites a research study (Reid & Hilton 1998) that found tree protection
zoneTree Protection Zones of 100 feet width were inadequate to protect adjoining trees from blow
down, and that tree fall rates were abnormally high for a distance of at least 656 feet from edges. A
wide range of buffer widths (55 to 800 feet) have been reported as being necessary to maintain the
microclimate (soil temperature, moisture) within forested areas.
In the outer zone (Zone 2) where the ordinance allows some tree removal, Kleinschmidt (1999) was
used to establish minimum stocking levels necessary to protect wind firm conditions. For softwood
stands such as Douglas fir, stocking levels are shown both in terms of basal area (which may be
difficult for those without a forestry background to determine) and canopy cover. For softwood stands,
80 s.f./acre of basal area (the amount that needs to be retained) was estimated to be approximately
equivalent to 21% canopy cover based on the ratio of canopy cover to basal area for a fully stocked
condition. From the State forest practice regulations, the basal area target at 140 years for all soil site
classes is 325 s.f./acre, and the maximum attainable canopy cover for Douglas fir is approximately
85%.
A potential area of risk, where the regulations may depart from the science, is in allowing the
construction of a primary structure within Zone 2 of the tree protection zone, which is proposed to
allow property owners more flexibility in the siting of their homes. Kleinschmidt (1999) does not
permit the construction of impervious surfaces within Zone 2 (which ranges from a width of 35 feet to
195 feet). Their buffer sizing procedure, however, combines the water quality and tree protection
components, while the procedure outlined in this ordinance separates them, with the construction of a
primary structure only allowed outside the water quality-sensitivity component of the buffer. This may,
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