Rapid Assessment of Sudden Oak Death infestation rates on

FIA plots with known hosts in 12 California Counties

A study synopsis for 2002 FIA field work

26 March 2002

Jeremy Fried, California FIA Analyst

Introduction

We anticipate completion of data collection for the Rapid Assessment study, originally funded as two separate studies by FHM Evaluation Monitoring and USFS State & Private Forest Health funds, which will accelerate statistically based assessment of Sudden Oak Death (SOD) occurrence frequency and impact in 12 California counties and will provide baseline tree mortality estimates in those counties by the end of 2002. Beginning with the 2002 PNW-FIA protocol, we have also added a SOD search, recording and testing protocol that will be applied to all FIA plots in California (~1000 are visited each year).

Objectives

Principle objectives of the study are to:

Develop statistically based estimates of SOD areal extent that allow inference to the population from which the sample is drawn (forests containing known SOD hosts)
Provide baseline, pre-SOD mortality estimates for susceptible tree species against which future mortality can be evaluated (to assess impact in the future)
If a sufficient number of FIA plots are found to have SOD present, then we will also estimate ecological impacts of the disease and perhaps be able to identify factors (besides presence of known hosts) associated with its presence

Methods

In its normal course of business, PNW-FIA now visits 10% of FIA plots in California every year. USFS Region 5 provided funding to accelerate the transition to annual inventory on National Forest System (NFS) lands, so an additional panel of 10% is visited each year for the next 5 years (so that all NFS plots will have been measured by 2005). Retrospective analysis of FIA data from the Occasion 3 (1991-1994) inventory (which excluded NFS lands) undertaken in 2001 identified 96 plots in Sonoma, Marin, Napa, San Mateo, Santa Clara, Santa Cruz, Monterey, and San Benito counties where tanoak, live oak, or black oak were present in any quantity in the overstory. Most of these were not scheduled for measurement in 2001 or 2002 and were targeted for off-panel measurement. Forty-four of these plots were scheduled for visits in 2001 and 52 in 2002.

A second, retrospective analysis of FIA data from the Occasion 3 (1991-1994) inventory and from the USFS Region 5, late 1990s inventory, undertaken in 2002 identified 99 plots in Sonoma, Marin, Napa, San Mateo, Santa Clara, Santa Cruz, Monterey, Alameda, Solano, Mendocino, Del Norte, Humboldt and Placer counties where a Quercus species was present in the overstory or understory AND one of the following was also present (tanoak, rhododendron, toyon, California bay) in the overstory or understory, and the plot was not already scheduled for measurement in 2001 or 2002, either under the regular panel system or the 96 accelerated plots identified in 2001.

Because the annual inventory is on a slightly different spatial “grid” than previous, periodic inventories, some of the selected plots are not part of annual inventory; however, they are visited anyway because the Occasion 3 periodic inventory serves as the sample frame for this study. At each of the 212 identified plots in the 12 county infestation area (including those scheduled for full installation as part of the regular FIA panels), the old 5-subplot cluster is visited and mortality assessed. A new 4-subplot cluster plot footprint is established and monumented on plots that are now a part of the annual inventory. Inspection of known hosts for SOD symptoms occurs on both the old and, if applicable, new subplot footprints and if symptoms are identified, samples are collected for analysis and a full plot installation is undertaken, regardless of whether or not the plot falls within the current panel.

Expected Analysis

Because the plots are drawn from a statistically based sampling frame, we will be able to make inferences about the whole population (of forests with known hosts) from the results of this study. Expansion factors (number of acres represented by each plot) will vary from ~3000 acres to ~20000 acres depending on forest type and land ownership (e.g., NFS plots were installed at double intensity in some areas and oak woodland FIA were installed at less than half intensity because they were not considered timberland at Occasion 3).

Baseline mortality rates will be calculated from the data collected for this study. Earlier mortality rates generated from analysis of Occasion 2 (early 1980s) and 3 data will be compared to these calculated rates. Species-specific rates will be calculated if sufficient mortality data can be obtained.

A combined analysis of Occasion 3 and Region 5 inventory data should also facilitate estimates of potential impact of SOD at state and sub-state levels based on host species distributions. If SOD extent grows significantly over time, the annual inventory system should provide information on this trend.