The giant reed invasion is of immediate concern in the Russian River watershed. Based on information from river systems in southern California and other riparian areas throughout the world, it is clear that giant reed may be one of the most serious impacts to the remaining riparian habitat in the Russian River system, having a direct impact on the salmonid fishery. Given the fact that the Russian River watershed is home to federally listed salmonid species - steelhead trout, coho and chinook salmon - as well as the federally listed freshwater shrimp and red legged frog, it is imperative that riparian zone management in these ecosystems take into account the impacts of invasive plants. Preservation of the remaining riparian habitat, as well as restoration of fisheries resources, will be more successful, and far more cost effective, if the giant reed issue is addressed during the early phase of this invasion.
*The above information that describes the Sonoma County orthophotogrpaphy was largely taken from the original metadata provided along with the images. For more detailed information describing the county orthophotography, please contact: (707) 565-3819 or via E-mail at gis@sonoma-county.org.
Methods:
The procedures listed below describe methods used to survey and
map the extent of Arundo donax invasion occurring
within the alluvial zone along significant tributaries of the Russian
River. As part of this project Circuit Rider Productions, Inc. (CRP)
mapped the extent of the giant reed invasion using Geographic Information
Systems (GIS) software ArcView GIS version 3.1, donated by Environmental
Systems Research Institute, Inc. (ESRI), Environmental Conservation
Program.
CRP has surveyed the majority of the salmonid-bearing streams in
the watershed to document the level of Arundo invasion.
Because Arundo tends to be found predominantly in alluvial
areas, CRP has focused the aerial reconnaissance and mapping program
to the alluvial sections of the tributary streams.
Two sets of imagery data were used as base maps for the project due to differences in available digital aerial photography data for Sonoma and Mendocino counties. For Mendocino county, USGS Digital Orthogonal Quarter Quadrangles (DOQQ) were used for the raster-format underlay for display of the final mapped stands of Arundo. Mendocino County USGS DOQQ were developed from 1993 National Aerial Photography Program imagery (1:40,000 photo scale). The project 3.75-minute DOQQ are in the Universal Transverse Mercator coordinate system on the North American Datum of 1983 and have a ground pixel distance of 1 meter.
For infestations mapped in Sonoma county, newly released orthophotography was used as the base imagery. The county orthophotogrpahy utilized in this project was a "Beta Version" of the orthophotography in Mr. SID-Compressed format. The data are stored in California Stateplane Zone II, NAD 83 (survey feet) II coordinates, and have been corrected to the ground using aerial and ground-based global positioning system (GPS) survey coordinates. At the time of use, the image data was being quality checked by County staff and may have contained irregularities. Available photo resolution varies within the orthophoto coverage with one-foot resolution or better in urban or incorporated areas and two-foot resolution in forested, mountainous, or other unincorporated areas of the County. In both counties, Arundo stands were interpreted from photographs taken during a series of low-level fixed wing aircraft flights.
In the fall/winter months of 1998, low-level fixed wing aircraft test flights were conducted to determine the best film type, weather conditions, season, photo angle, and plane flight altitude for photographing Arundo in a riparian setting. The significant tributaries were photographed during several low level flights conducted during the winter months (Jan./Feb. 2001), when riparian plant species were dormant, providing the clearest view of Arundo stands. A series of sequential, overlapping photographs was taken for both banks, at an approximate altitude of 500 feet, at a 45 degree angle, using Kodak Gold color film. Arundo polygons not clearly seen in the photographs were identified in the GIS database as being sites that require further surveying or base imagery with improved resolution.
Subsequent to the development of the hand held camera photographs, the photos were cataloged in a Microsoft Excel datasheet, indicating the roll number, photo number a general locational descriptor and the name of the tributary that the photograph captures. The features determined to be Arundo infestations were then digitized directly onto the USGS DOQQ base maps using ESRI ArcView 3.1 and ArcView 3.2 software. When possible, the area boundary of the infestation was digitized, producing a polygon feature to describe the infestation. However, in many cases the resolution of the base imagery was inadequate for mapping the infestations as polygonal data features. Consequentially, a majority of the tributary infestations were mapped as points, representing approximate locations of the centers of infestation stands. The differences in polygonal and point data have been accounted for by creating centroids of the digitized polygons. The resulting points were merged together into one GIS format file (ESRI .shp file) that illustrates and describes the extent of Arundo infestations along significant tributaries to the Russian River. Additionally, a GIS format (ESRI .shp file) has been created that describes the Russian River tributaries that have Arundo donax infestations along them.
Data Summary:
764 points were identified as approximate locations (point data)
of Arundo donax infestations within this study.
A significant number of tributary infestations are located near
the confluence of the tributary and the mainstem. After the mapping
was completed, this study required a mechanism for determining which
infestations within proximity to the confluence are tributary infestations
and which infestations biologically belong to the mainstem. Using
ArcView 3.2, a buffering method was used to facilitate this determination.
A buffer of thirty feet was applied to the hydrology of the Russian
River. Infestations located within a thirty foot radius of the mainstem
and tributary confluence were assigned to the tributary while those
that were within proximity to the confluence but did not intersect
the thirty foot buffer were attributed as being mainstem infestations.
After applying this filter, the data resulted in 227 points as tributary
infestations.
Though the extent of Arundo growth and general locations of feature polygons were the main focus of this mapping project, the determination of stand growth-patterns in relation to surrounding vegetation was considered important due to the implications for eradication efforts and long term monitoring.
43 tributaries in the Russian River watershed were identified as having Arundo infestations. Of these tributaries, 15 were unnamed tributaries according to the 1:24,000 hydrographic GIS dataset (hydro_121.shp) produced by CDF FRAP (http://frap.cdf.ca.gov/data/frapgisdata/select.asp). Map readers are able to identify these unnamed tributaries using the LLID value which is a unique numeric ID assigned to each hydrographic line feature in the 1:24,000 dataset. Certain tributaries are indicated as having Arundo infestations without corresponding information in the GIS point file indicating the approximate location of the infestation. This is a result of tributaries that have been identified as having Arundo through field surveying however, the point location information was unable to be mapped due to either inadequate base imagery resolution or complications in recording GPS information at the site. The method through which each the point data (representing approximate infestation locations) as well as the line data (representing infested tributaries) has been recorded in the "Methods" field of the two GIS databases.
Methods
AP- information is from an aerial photograph
LK- information is from local knowledge, such as someone telling us
he/she knows Arundo is present in a general area
FC- the Arundo was seen in the field and either was mapped
or a GPS reading was taken