Appendix 1: Correspondence with Midpeninsula Regional Open Space District Vegetation Mapping
An independent vegetation mapping effort was completed in March, 2000 by Aerial Information Systems, a contractor hired by Midpeninsula Regional Open Space District (MROSD). The mapping was completed using 1: 24000 aerial photographs that were taken in April of 1999. A full description of the process can be obtained in the "Aerial Information Systems Project Report", dated March 31, 2000. For an image of the MROSD mapping, see Map 2.
Overview: Vegetation Mapping Strategies
The mapping of ‘vegetation type’ (which also could be called the mapping of plant assemblages, or plant communities) is a fundamentally different concept than the mapping of a species distribution. Most vegetation mapping efforts are primarily concerned with ‘vegetation type’ such as those employed by the Manual of California Vegetation (used in the MROSD mapping).
Such mapping efforts define and name categories based on the dominant species, and may or may not include ‘associations’, which could define a secondary species. Each of these series usually includes many other species in a ‘common’, or ‘representative’ species list. For example, a unit of land mapped as “California Bay Series” may consist of 60% California Bay, 20% Tanoak, 15% Coast Redwood, and small amounts of other species such as Coast Live Oak and Canyon Live Oak.
The distribution of California Bay Laurel is thus much larger than an area mapped as “California Bay Laurel Series”, the same is true for the Coast Redwood and Douglas-fir Series. When mapping the distribution of a species, the goal is to delineate the land that particular species occupies, regardless of whether there may be another dominant species present.
The FPR defines “Timberland” as land capable of growing commercial species, which for our purposes is Coast Redwood and Douglas-fir, and in some circumstances Group B species. Therefore, mapping the distribution of Coast Redwood and Douglas-fir is more consistent with the legal definition of Timberland than is the mapping of vegetation types, which would include only areas dominated by Coast Redwood and Douglas-fir, and would list areas with lower densities of Redwood and Douglas-fir under vegetation types with different names.
Our analysis followed guidelines for mapping a species distribution, the mapping dicussed below, conducted by Midpeninsula Regional Open Space District, was concerned with a larger, more broad goal of mapping vegetation type and dominant plant assemblages across a very large area.
Specifics of MROSD Vegetation Mapping
The MROSD maps were very useful in helping us delineate and understand various vegetation classes. Overall, this mapping effort is an exemplary and very detailed data set that is of great value to any ecological work in this area. However, we realized after examining these maps with respect to the high-resolution images taken by our helicopter, that it would be difficult to use these vegetation classes in any estimate of legal timberland owned by SJWC for the following reasons:
1) MROSD was not primarily concerned with mapping vegetation on SJWC lands, the entire effort mapped 55 square miles in the Sierra Azul area, but 556 acres of SJWC land were not mapped.
2) MROSD was not concerned with mapping vegetation types in a way consistent with the legal definitions of timberland. Some of the vegetation classes were defined as unequivocally containing Douglas-fir and Coast Redwoods, but another large set of vegetation classes were defined as sometimes containing lower densities of Douglas-fir and Coast Redwood.
DETAILS:
The classification of vegetation was conducted in accordance with the "Manual of California Vegetation" published by the California Native Plant Society (online version can be found here). Four of the vegetation classifications (see Supplement 4) can be considered as unequivocally comprised of timber species (either listed as Coast Redwood or Douglas-fir Series). For comparison with our data, we have grouped these four classifications as one mapping unit, referred to as "PRIMARY SERIES."
Five of the vegetation classes list either Coast Redwood or Douglas-fir as a common species in their definitions, but may or may not actually contain individuals of these species. The California Bay Series (including subsets California Bay - Coast Live Oak Association and California-Bay Canyon Live Oak Association) includes common species as Coast Redwood, and the Group B timber species Pacific Madrone and Tanoak. The Tanoak Series includes the common species Douglas-fir and Pacific Madrone. For comparison with our data, we have grouped these classifications as one mapping unit, referred to as "SECONDARY SERIES." We found that when these areas were located adjacent to conifer forests, they often contained smaller Douglas-fir individuals; when they were mapped at higher-elevations or drier sites they often did not contain timber species. For these areas, the MROSD report contains phrases such as "Douglas-fir may be present, with less than 20% cover".
SJWC owns 1866 acres of land designated as "PRIMARY SERIES" and 1719 acres of land designated as "SECONDARY SERIES".
IMPORTANT NOTE: It would be easy for a casual observer to assume that all of the legal timberland owned by SJWC would be included in this "PRIMARY SERIES" mapped by MROSD. This is not true. There are many, many, instances of obvious Coast Redwood and Douglas-fir trees outside of these zones, and the definitions of the "SECONDARY SERIES" zones are consistent with this fact. The purpose of the MROSD mapping was to map vegetation types in accordance with specific ecological definitions of vegetation type, not to map the distribution of Group A timber species.
For reference, 16% of the mapped NTMP zone is not within the "PRIMARY SERIES". The NTMP zone was designated by the foresters who prepared the plan as commercially viable timberland (with the exception of a few helicopter landing pads, etc). Therefore, these foresters who prepared the NTMP should agree with the fact the MROSD "PRIMARY SERIES" does not represent all of the Group A timber species on SJWC land.
3) The minimum mapping unit (MMU) in most cases was .5 hectares (1.2 acres), and the resolution of the aerial photographs was 1:24000, which was used by MROSD because the entire mapping effort covered a very large area of 55 square miles. As a byproduct of this MMU, developed or cleared areas, roads, and lakes, were often mapped as larger than their actual size. For example, a 1/4 acre parking lot surrounded by Douglas-fir trees would be mapped, at minimum, as 1.2 acres in size. There are some photographic examples of this phenomenon included below.
4) The MROSD vegetation mapping was completed using aerial photographs from 1999, we found many areas that had been mapped as hardwood zones, but that now have evidence of young Coast Redwood or Douglas-fir trees emerging from the canopy. See Supplement 5.
5) The mapping of linear wetlands is a problem in any vegetation mapping effort. The MROSD mapping effort attempted to map these areas at a resolution below their minimum mapping unit (.5 hectare), quote: "Linear wetlands that were often extremely narrow were also delineated when visible on the photography." However, the result of trying to designate a separate vegetation class for these riparian areas is that much of Los Gatos Creek and tributaries appears to have a 25-75 meter wide "buffer" of riparian vegetation. In most cases, there are individuals of the Group B timber species White Alder along the banks of the streams, but the primary vegetation cover within most of the "buffer" is Redwood or Douglas-fir. The practical effects of mapping wetlands in this area caused many acres which are in fact covered with timber species to be listed as "White Alder Series." We grouped the "White Alder Series" with our "SECONDARY SERIES" in comparing the MROSD data with our mapping.
How well does our mapping correspond with the MROSD mapping?
The following discussion is summarized in Supplement 4. MROSD had mapped 1866 acres, with four different vegetation classes, that we have renamed "PRIMARY SERIES". Of this series, we found 1789 acres that contained timber species. The high degree of concordance between the MROSD mapping of the four "PRIMARY SERIES" vegetation classes and presence of actual timber species was expected. The mostly pure stands of Coast Redwood or Douglas-fir that make up this vegetation class were likely some of the easier classes to delineate during the mapping process.
Outside of the "PRIMARY SERIES", we found evidence of Group A species on 339 acres that had not been mapped by MROSD, and 627 acres that had been mapped as various other vegetation classes within the "SECONDARY SERIES".
After reviewing the data, there seem to be several logical reasons why occasions of Coast Redwood and Douglas-fir were found outside of the "PRIMARY SERIES". First, any areas with lower densities of Coast Redwood and Douglas-fir were included in "SECONDARY SERIES" classes by the MROSD mapping. Secondly, young Douglas-fir trees appear to have grown into many areas previously mapped by MROSD as mainly California Bay. Thirdly, many riparian areas were mapped "White Alder" by default actually included a majority of Coast Redwoods and Douglas-fir. Fourth, the resolution of the MROSD mapping effort left out many small or young stands of Coast Redwood and Douglas-fir.
Our "SECONDARY SERIES" contains all land mapped by MROSD in vegetation classes that may be equivocal in terms of legal "Timberland". These areas by definition contain Group B timber species, but may or may not contain Group A species. Of the 1719 acres land owned by SJWC in the "SECONDARY SERIES", at least 481 acres (28%) contain clear evidence of mostly young Douglas-fir or Coast Redwood trees. This was also expected, because the CNPS definitions of these classes include Coast Redwood and Douglas-fir as common species. It is important to note that even within the NTMP boundaries, 98 acres had been mapped by MROSD as "SECONDARY SERIES". Thus the logic that much of this "SECONDARY SERIES" should be capable of growing Coast Redwood and Douglas-fir is consistent with the language expressed in the NTMP. It is likely that many more of the areas mapped within the "SECONDARY SERIES" also contain timber species, but it is also likely that they are still small and not readily visible by helicopter.
