Assessment of Sudden Oak Death in Bear Creek Redwoods Open Space Preserve

Study conducted by students of the Summer section of Mission College's Field Ecology class



Introduction and Purpose History and Methodology
2004   2005   2006  
Future Work


Introduction and Purpose

Sudden Oak Death is a plant disease caused by the water mold Phytophthora ramorum that causes the rapid death of tanoaks and other oak species as well as twig dieback and foliar lesions on other susceptible species such as California Bay Laurel and Rhododendron. Since the first P. Ramorum-infested nursery stock was found in Santa Cruz county, California in 2001, the disease has been found spreading through northern California plus Oregon, Washington and British Columbia in the U.S. It has also spread to forests from nursery stock in the U.K. and Netherlands in Europe. The pathogen thrives in cool, moist climates and its spores can be spread through water, the movement of infected plant material and soil and human activity.

Our study was designed to observe the extent of Sudden Oak Death infestation on the Aldercroft section of Bear Creek Redwoods Open Space Preserve and the adjoining McNamara property in Los Gatos, California (see Figure 1 and Figure 2.) Each year, students of Mission College's Field Ecology (Biosc 7) class work with instructor Jean Replicon to record characteristics of trees from randomly selected sample sites along the forested trail from the McNamara residence to the spring house on Bear Creek Preserve at the head of Aldercroft Creek. The study is intended to be ongoing, recording any changes in forest health and composition over time.


Figure 1 - Map of the Aldercroft section of Bear Creek Redwoods OSP

Map of Aldercroft
	section of Bear Creek Redwoods OSP


Figure 2 - Aerial photo of study site (study area in yellow)

Aerial photo
	of study site


History and Methodology

Year 1: June 19-20, 2004

Students placed blue flag trail markers to demarcate 20m segments of the trail and numbered them sequentially. All potential 10m x 10m study plots were then designated on both the right and left sides of the trail. The plots which were not good for study due to steepness of terrain were noted. The remaining plots were numbered sequentially, starting with #1 on the left side, then going back down on the right side of the trail, skipping the inaccessible plots.

A random number table was used to randomly select ten plots for study, assigning two for each of the five student teams (see Figure 3.) The GPS coordinates of the study site and plot were noted by two operators using two different GPS units. The waypoints were plotted onto a topographic map.


Figure 3 - Plot mapping

Plot mapping


With blue flags and string, the students marked off their assigned 10m x 10m plots. The trees in each plot were tagged with permanent numbered aluminum tags. Other trees of interest outside the plots were also tagged. Tags were placed on the side of the tree facing the trail.

Information about the plots and the tagged trees was collected and recorded as time and conditions allowed. The data collected includes tree species identification, diameter at breast height (DBH), tree height with tangent height finder, visual inspection for signs of SOD, canopy cover using a densiometer, insect life revealed through tray beating, bark rubbing, leaf samples, and an overall map of plot showing tree locations. At least one digital photograph of most tagged was taken for a visual database of the trees. This visual database is available by request. Based on the data collected, each tree was assigned a score between 1 and 10 to indicate its overall health, where 1 is considered very healthy and 10 is a dead tree.

Small sections of selected California Bay Laurel trees were used to asceptically inoculate PARP selective medium. These trees were located within and outside of the sample plots designated for study. Plates were examined for the presence of Phytophthora ramorum by Karl Buermeyer, Regional SOD Coordinator.

At the end of the study all equipment and footwear were disinfected using Lysol to prevent the potential spread of SOD.


Year 2: June 25-26, 2005

Students placed permanent wood markers to demarcate 20m segments of the trail and used the same numerical sequence as the 2004 class. All 10m x 10m plots were re-measured with DBH measuring tape and marked with a blue flag trail marker.

The ten plots that had been selected for study by the first year students were assigned for re-evaluation to the second year student teams.

Tagged trees in each plot were inspected and data collected. If there were trees present within the plot with a diameter greater than 6 cm, they were given tags as well. The data collected from trees included: tree species identification, diameter at breast height (DBH), visual inspection of signs of SOD and apparent insect life. An overall map plot was drawn for each plot indicating the location of all trees in the plot as well as the location of the tagged trees. A photo was taken of the tree tag and visible symptoms. Based on the data collected, each tree was assigned a score between 1 and 10 to indicate its overall health, where 1 is considered very healthy and 10 is a dead tree.

Additionally, individual trees outside of the plots were tagged for study by the 2004 class. These trees were inspected and data recorded.

At the completion of the study all equipment and footwear were again disinfected using Lysol to prevent the potential spread of SOD.

Year 3: June 24-25, 2006

The ten plots that had been selected for study by previous classes' students were assigned for re-evaluation to the third year student teams. Previously-tagged trees outside the plots were also evaluated. Blue flags at each corner of each 10m x 10m plot were given designations of A, B, C or D, assigned in a clockwise direction along the right-hand side of the trail (when facing the spring house) and a counter-clockwise direction along the left-hand side, to aid with locating trees within each plot. As before, tagged trees in each plot were inspected and data collected and untagged trees with a diameter greater than 6cm were given markers as well. A plot map was drawn for each, indicating the location of each tagged tree.

Dead
	      tan oak
Tan oak killed by SOD - photo by Stacie Wolny, 2006

Using a standardized data sheet (.doc), more specific data were collected on each tree this year than previously, including:

The overall health of each tree was again assigned a score between 1 and 10, this year based on the number of visual signs that were present (listed above.) For every sign present, the health score was degraded. Also, the following score categories were created:

All data collected from this year and previous years were entered into a database and made available online by student Matt Crampton. It can be accessed at http://www.mattcrampton.com/sod_study/ and includes the following:

At the completion of the study all equipment and footwear were again disinfected using Lysol to prevent the potential spread of SOD.


Future Work

The 2006 class came up with suggestions for improvement for next year's round of study, based on our experiences this year:

Tan
	    oak acorn
Tan oak acorn - photo by Stacie Wolny, 2006



Page prepared by Stacie Wolny (email: barefoot at sculptors dot com), Field Ecology student, Summer 2006