Feature Article: After ten years of oak wilt management, where are we??

By Susan Burks, DNR-FHU

The year 2002 marked 10 years of active oak wilt (OW) management within the Minnesota Department of Natural Resources (MN DNR). Active management began with a federal pest suppression grant in 1992. In 1998, the effort was incorporated into a community assistance program called Minnesota Releaf. The Releaf Program broadened its scope in 2003, to include other forest health practices in an attempt to integrate traditional urban forestry with ecosystem management at the community level.

In the meantime, the status of oak wilt across the state had evolved as well. Early in the program, aggressive outreach enrolled a large number of communities. Their involvement increased legislative support, while at the same time decreasing the incidence of OW, in spite of continued pressure from urban development. In 1997 and 1998, a series of spring windstorms across central Minnesota damaged large numbers of oaks at the height of the oak wilt infection period. As a result, numerous new OW infection centers sprang up across the area.

In response to increasing disease pressures, requests for community OW funding exceeded available grant dollars for the first time in 2001-2002. As a result, a system of prioritization was needed to determine the level of community funding. However, developing one that would withstand close scrutiny from the state legislature, participating communities and partner organizations proved to be a difficult task.

On the program's tenth anniversary, the change in program goals and the increasing need to upgrade the technologies used to collect, manage and interpret treatment data, prompted an evaluation of the Minnesota oak wilt program. A preliminary analysis of the existing data was completed in 2002. In 2003, a formal assessment of the status of OW in Minnesota was initiated with the support of both state and federal funds.

The Federal Suppression Project

While the Minnesota effort began in the 1970's with the research of Dr. David French, it reached program status in the late 1980's with the a formal survey done in 1988. Color infrared photography (CIR) was taken of Anoka, Ramsey and Washington Counties plus parts of Isanti, Sherburne and Chisago Counties. Scattered areas in southeastern Minnesota were flown in 1989. Dr. French worked with a local contractor, to develop the protocol to interpret and digitize the photography back before anyone else had done anything similar. A massive outreach effort was launched by a coalition of the University, government agencies, industry professionals and concerned individuals to inform landowners and garner public and legislative support for disease management. The slogan 'Don't Prune in April, May and June' was advertised across the state and soon most Minnesota residents in the affected area had heard of oak wilt and its potential to kill trees. The MN DNR then presented the CIR data to the US Forest Service in a grant request for oak wilt suppression. The out-reach effort paid off and a $500,000.00 grant was awarded. Thus the first federal cost-share program (CSP) was launched.

The overall goal was to lower the incidence of oak wilt to levels manageable by local units of government and thus build local capacity to sustain long-term community forest health. Based on research that described the average rate of spread and satellite infection development, the density of oak wilt manageable by local government was determined to be one infection pocket per square mile. The control zone or focus area was defined as the six county area known to contain the most oak wilt. Dakota County was added to the list the following year. The original project objectives were to reduce the incidence of oak wilt within 75% of this control zone to one active infection center per square mile and to do so within five years through active community assistance.

Program and Data Management

One of the driving forces in the suppression project was outreach and citizen involvement and that focus influenced the way the program was designed, what data was collected and how it was managed. Public involvement required a better understanding of oak wilt and the factors that influenced disease incidence. Public support required a system to track program accomplishments across a wide area. These needs provided the impetus to develop new user-friendly, inexpensive GIS software that would allow program managers and participating communities to view and assess management activities in their particular area. EPIC, a raster-based GIS system was developed as a joint venture between thee MN DNR and the MN Land Management Information Center (LMIC) to serve program objectives.

The original CIR data was interpreted using a stereoscope and transferred to 1:24,000 quad maps, by projecting the maps over photographic prints and matching key features. Later on, additional CIR was taken and added to the data (see CIR map). 1 map of oak wilt infected areas, and 1 map of releaf program areas Once the infection pockets were drawn in, they were digitized in Arc/Info. Macros were developed in Arc/Info to produce community maps of all known infection pockets and their current status. These maps were printed and distributed to participating communities. The communities did any ground truthing necessary and updated the maps on an annual basis by hand drawing in any corrections and/or additions to the known infection pockets (see map of CSP & Releaf participants). These data were generalized into treated versus active infection pockets and exported into EPIC. Raster analysis in EPIC allowed rapid assessment of oak wilt density, spore loading and the acres of oak forests at risk of future infection. The information facilitated reporting and furthered on-going outreach.

In the initial inventory, 3006 infection pockets were identified in 44 townships. By 1997, 8387 infections centers had been identified across an expanded control zone of 79 townships. Participating communities had treated 5164 infection pockets or 61.5% of the known pockets. Even though the combined survey data indicated that the density was nearly twice as high as expected, the cost-share program lowered the density of oak wilt from 2.97 centers per square mile to 1.58. Within 53% of the control zone, the density was lowered to one infection center or less (see annual charts). Given the high initial density, this is a significant accomplishment. The other significant program accomplishment was the high level of public awareness and involvement achieved. During the five years of the first federal suppression project ('92-97), communities and private citizens spent $3,043,294.00 to match $1,950,000.00 in federal funds, for a project total of $4,993,294.00!!

2 images of annual accumulation of acrea affected by oak wilt

The federal suppression project ended in 1997 and the state incorporated oak wilt management into the Minnesota Releaf program. Since then funding has been uncertain with funds available some years and not others. Intermittent and/or delayed funding has impacted the level of management activities and in a few cases, community participation. Yet public support has remained high as demonstrated by the number of letters and testimonies given in support of state budget requests during the '02-03 legislative session.

During this same period, the incidence of oak wilt began to increase. Factors included funding levels for community programs, increased urban development and a series of severe spring windstorms that whipped the north metropolitan area in 1997 and 1998.

The storms damaged trees over a wide area at the height of the oak wilt infection period. By 1999, the incidence of oak wilt had reversed previous gains in several areas, particularly in Sherburne County; hit the hardest by the storm events, and the numbers have continued to climb since then (See 1997 and 2001 maps).

Map of oak wilt in metro 1997 & 2001

In response to increasing questions about program accomplishments and necessary funding, the data was exported to Arc/View and for the first time the treatment histories were assessed. The fact that this was the first time the treatment data was evaluated may seem odd unless you understand the nature of raster data and the original program design. Rasters or pixels can contain only one set of attributes, for instance forested or not. The attribute could be the species, such as oak, elm or ash, but not pole-sized maple, versus mature basswood, unless you create a large number of categories for the one attribute possible to cover all possible size/species combinations - something that is not usually feasible. In this example, the size data would be put in one data layer or file, while the species data would be put in a different data layer. Any number of data layers can be laid one on top of the other. Because each layer shares the same geographical reference, i.e. the raster or pixel, each data layer can be compared to the others to determine patterns and correlations between data sets. Although file sizes are small, the power in spatial analysis is huge. And EPIC was designed to provide that kind of power to participating communities at no charge. But in the process, it took the treatment data and generalized it down to treated versus not treated. When an individual pocket was treated, how it was treated or how often was not known until the data was moved to a different platform. In response to increasing questions about program accomplishments, necessary funding and the increasing incidence of disease, the data was exported to Arc/View and for the first time the treatment histories were assessed.

2001 treatment summary

Treatment Summary

Sites were considered 'treated' if they had received any combination of treatments or if it were determined (by the community) that no treatment was necessary (i.e. the pocket was no longer active). Communities reported VP treatments alone on 25% of the treated sites and PSP alone on 42% of the sites. Only 16% of the sites received both VP and PSP treatments. Fungicide injections were becoming more common. Data collected for the first time in 2001 indicated 4.37% of the sites received fungicide injections in combination with other treatments and 2.47% received fungicide injections alone (see treatment charts).

Once the treatment data became available, a number of new questions arose. Correlations between disease incidence and differences in local program implementation began to become apparent. How annual treatment data was obtained (which varied by community) determined the level of detail provided. The size of the paper maps relative to community size seemed to influence the reported acreage. And the codes used to denote treatment methods were being confused at times and not corrected.

2 oak wilt treatment graphs

These issues created doubts about the reliability of the data. While the trends described help program managers understand where problems may exist in state program delivery, they couldn't be used to redesign the program to meet changing needs. Yet, the increase in disease incidence (and decreasing resources with which to control it) meant program adaptations were needed. But based on what?

2003-2005 Oak Wilt Assessment

A formal reassessment of the status of oak wilt in the state was initiated in 2002. New CIR photography was taken of 33 townships with another 76 townships flown in 2003. The data will be used to establish a baseline for the current federal CSP and to analyze the change in disease incidence based on a variety of factors. The primary goal is to evaluate our current management strategy; is it working at a program level and if not, why not. A secondary goal is to describe factors outside our control (like urban development and storm damage) and the influence they are having on disease incidence so we can incorporate that information into the way we prioritize treatments (and cost-sharing).

While the details are still being discussed, the assessment project will be divided into three phases. The first involves interpretation and digitization of all new CIR to establish a baseline. Digital ortho-rectified quad (DOQ) maps will replace the 1:24,000 K maps as the base layer. That will allow finer detail in the interpretations. The work will be done in Arc/View to avoid data distorts that can occur during translation to other formats.

The second phase will take data from the new CIR from a 20-township subset of the total and run a comparison against earlier CIR data to describe the change in disease incidence, i.e. density per square mile. Noted changes will be assessed by three factors; type of Releaf program, change in urban development and presence/absence of storm damage resulting from the 1997 or 1998 storms. The three categories of Releaf program will be 1) non-participant, 2) full-service, including a formal survey of the entire community, and 3) partial service, informal service or treatment by request only.

The third phase will use an additional subset of 12 townships. The older existing CIR will be reinterpreted using the latest technology. Both the new and old sets of CIR will be rectified. Then the two sets of data will be compared to describe the change in disease incidence. The same three factors will be used to assess any changes in the density of oak wilt, but this time individual pockets will be traced to explore the affect of various treatment practices.

The fourth phase of the project will be to compare the cost and the results of the two methods of change detection to determine the potential for future applications.

All of the new CIR photography was taken in 2003. Photo interpretation will happen this winter. A minimum of 10% of the mapped pockets will be ground truthed by the state, i.e. field checked, during 2004 to establish the level of accuracy. Change detection and analysis will occur during the winter of '04-05. The final results will be available in 2005, at which time Releaf management strategies will be reevaluated and modified as needed.

For those participating in the Releaf program, that means that the management strategies, mapping protocols and the system of prioritization for funding will stay the same for the next two years. That timing should work well since 2005 marks the end of the current Releaf grant period and the beginning of the new biennium.

In the meantime . . .

With the continuing increase in disease incidence, one of the biggest questions we face is whether or not it is possible to stay ahead of the spread of oak wilt. While some communities are doing an excellent job of staying current, others are falling behind. Modifying the means of program delivery and enhancing resident outreach may be all that's needed in some cases. Better enforcement of PSP removal for instance is one area where improvements can be made. But in other areas, disease incidence seems to be increasing in spite of well-run, full-service programs. Whether or not our strategies are inadequate, or outside factors are having a stronger influence, these areas serve as a source of continued disease pressure that may eventually overwhelm those that currently have oak wilt under control.

The situation resembles that seen in the gypsy moth slow-the-spread (STS) program. Those with the worst problem are tempted to throw up their hands because of the effort and expense involved in slowing the spread of oak wilt. However, continued management is critical to the well being of the oak resource as a whole. If those with the worst problem quit now, neighboring areas will be overrun. It is easy to focus only on those trees in your own back yard. But if we are to succeed, it is important that we all work together to preserve Minnesota's oak resource. Hopefully, the assessment project will provide the answers we need to regain lost ground and build on earlier accomplishments.