NE1601: Eastern White Pine Health and Responses to Environmental Changes

(Multistate Research Project)

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Issue(s) and Need:

Eastern white pine (Pinus strobus) is a crucial ecological and economic component of forests in the eastern U.S. and Canada. In the southeastern U.S., white pine is an especially critical associate of forests in the Appalachian Mountains as hemlock trees have been in decline due to the exotic hemlock woolly adelgid (Adelges tsugae). Yet throughout the eastern U.S., from Georgia to Michigan to Maine and adjacent areas in Canada, white pines have experienced unprecedented damage in recent years due to native pests and pathogens that reduce the species’ growth, productivity, and economic value.

For many decades, white pine health has been adversely affected by the non-native white pine blister rust (Cronartium ribicola) and the native white pine weevil (Pisodes strobi).  In this proposal, we describe additional native white pine stressors that have received little or no attention, but are nonetheless linked to declining health of white pine stands throughout North America.

In the northeastern US, Caliciopsis pinea, a stem canker pathogen, poses a significant threat to white pine health. In the past 10-15 years, white pines have succumbed to an increase in the occurrence and severity of C. pinea infestations; these infestations result in excessive resin production, leading to serious growth declines and commercial defects in lumber. External symptoms include crown thinning, cankers and profuse pitching. From recent surveys conducted on 360,000 acres of white pine forest (defined as >75% white pine basal area) in Maine, Massachusetts, and New Hampshire, we know that C. pinea cankers occur on 36% of the surveyed land(27).  With white pine being such an important forest product in the northeastern U.S., it is critical to understand the extent to which C. pinea reduces wood quality and lumber yield.

White pine stands in the northeast are also facing an emerging foliar disease complex, “white pine needle damage”, that will likely remain a problem in years with excessive springtime moisture. White pine needle damage results from one or several fungal pathogens native to North America. In addition to brown spot caused by Lecanosticta acicola (=Mycosphaerella dearnessii), several other species of fungi have been isolated from diseased pine needles at a high frequency that may represent novel white pine pathogens. Unfortunately, there is still limited information on the basic etiology, epidemiology, and managment of these pathogens on eastern white pine. While mortality resulting from white pine needle damage has not been reported, continued defoliation will weaken trees, making them more susceptible to other biotic and abiotic stresses.

In the Lake States region, unusual white pine health problems were first detected in 2006 in the Au Sable and Manistee River corridors located in Michigan’s north-central Lower Peninsula. By 2012, the crown symptoms of dying branches also appeared in the Upper Peninsula region, where it was reported in the Munising District of Hiawatha National Forest. Symptomatic white pine has been primarily associated with stem and branch cankers induced by native fungal pathogens (primarily Diplodia spp.) and the native pine spittlebug (Aphrophora parallella).

In the southern Appalachians there has been an increase of dieback and mortality symptoms in white pine since 2006, especially in the mountains of Georgia, Virginia, and West Virginia. These symptoms include branch flagging, canker presence, high resin pitching associated with cankers, and mortality across a range of tree diameters. In Georgia’s Chattahoochee National Forest, one region documented 44% of the white pine trees as dead and another 30% of the trees showed >50% dieback. In both Georgia and Virginia, the majority of mortality was observed on trees with <30 cm diameter. Preliminary examination of cankers yielded primarily C. pinea, which was found on 86% of branches. Embedded within these various cankers were immature pine scale insects, which were later identified via DNA analysis as Matsucoccus macrocicatrices, the first report of the scale in the southeastern U.S.  Surprisingly, M. macrocicatrices is common in the northeastern U.S. and Canada and is known as the “Canadian pine scale,” but the insect has not been investigated as an associate of C. pinea infestations. Because the scale is frequently associated with C. pinea infections on white pine trees in the southeast, this indicates a previously undescribed relationship between insect and fungus affecting white pine health that should be further explored(25).

The above reports on declining health of white pine indicate that the stresses may vary from region to region.  However, the reported symptoms are similar, given the frequent reference to canker formation, needle loss, declining growth, dieback, and mortality.  The label “white pine health issues” will be used here to refer to the range-wide phenomenon of declining health in numerous eastern white pine stands. 

White pine has enormous economic value throughout its range.  Over the region, the net volume of white pine saw logs is over 186 billion board feet (USDA Forest Service, Forest Inventory and Analysis).  With a typical market price of $100/1,000 bd ft, the potential value of standing white pine is $18.6 billion.  To help guide the white pine and other forest product markets, market models are being developed for predicting the impacts of changes in forests and the forest products industry, regardless of whether the changes are intentional or not. Models have been used extensively in other parts of the country to help the forest products industry understand the impacts of changes in the resource supply and demand, to better prepare for potential future scenarios, and to help policy makers assess potential impacts of policies. These forward-looking models can be used to assess impacts of any factor affecting wood supply, including diseases and pests that affect tree growth and mortality.  Therefore, the market models should consider the impact of white pine health issues on white pine markets. 

From an ecological perspective, white pine has significant impact on the eastern forest.  White pine attains the largest dimensions of any eastern tree serving as a critical habitat for many species of wildlife that depend on emergent crowns and large snags and downed woody debris.  More information is needed on white pine health issues to better understand how well white pine can continue to provide these ecosystem features and identify effective management strategies to enhance white pine health and resilience in the face of these threats.

Importance and Consequences if Work is Not Accomplished

Estimating losses due to white pine health issues creates challenges because symptoms can be difficult to recognize and quantify.  Unlike mortality caused by invasive pests, which happens quickly and is easy to recognize, the white pine health issues described in this proposal develop slowly and involve multiple stresses. For example, stresses associated with white pine health issues differ throughout its range.  Losses accumulate over time and are more related to reductions in growth losses and wood quality, losses that are more difficult to quantify than mortality.  As a result, land owners and managers are concerned that loss in tree productivity and allowable cut are occurring without immediate recognition.  Therefore, actions are not being taken to improve productivity by mitigating factors associated with white pine health issues. More targeted efforts are needed to recognize and quantify these losses throughout the range of eastern white pine.  For example, the extent to which C. pinea reduces wood quality and lumber yield remains poorly understood, and potential actions for reducing C. pinea damage have not been tested.  White pine needle damage has recently gained attention, but the long-term effects of repeated defoliation remain undocumented. Further, organisms native to North America, such as needle fungi and M. macrocicatrices, are associated with unprecedented white pine health issues, and it is uncertain if the situation is developing into larger problems that will affect white pine health and productivity on a broader scale. If we fail to quantify white pine losses associated with white pine health issues, the extent and severity of these complexes will continue to be poorly understood, poorly managed, and absent from market models.

What is happening to the white pine?  Native organisms are behaving in unprecedented, unexpected manners that need to be explained.  Explanations will involve a number of factors including distribution and genetic changes in both white pine trees and biotic stress agents, as well as changes in the climate and stand development patterns of white pine forests. Taken together, these factors raise the following questions related to biotic stressors:

  1. Why are cankers associated with pinea infections appearing at damaging levels in stands; is this due to increased precipitation in late spring favoring infestations, or is the stand development of white pine in abandoned fields predisposing the tree to infestations?
  2. Why are the needle fungi now causing damage, and why are some trees more affected than other trees co-existing in the same stand?
  3. To what extent are changes in climate associated with white pine needle damage, and to what extent is infection and subsequent needle loss the result of other stresses predisposing trees to infection?
  4. Why is macrocicatrices associated with damage in the south but not the north? Is this a behavior change or has the scale been associated with damage in the north but gone undetected?
  5. Is the presence of macrocicatrices and C. pinea in the same stand synergistic to the development of cankers on pine?

Without answers to these and other questions, it will not be possible to assess future losses associated with white pine health issues, and consequently, management recommendations cannot be developed to improve the health and productivity of white pine.

Although the multiple stress agents associated with white pine health issues make it a challenge to study, strategies aimed at improving white pine health are readily available.  White pine has long been successfully regenerated using silvicultural methods, such as shelterwood and seed tree cuts, and responds very well to thinning.  By gaining a better understanding of white pine health issues, we will be able to recommend treatments that reduce the risk of white pine damage due to these stressors, and we can evaluate the economic benefits of silvicultural practices that reduce white pine’s predisposition to health issues.   

Technical Feasibility

Funded projects are currently supporting surveys of white pine health issues in northeastern U.S., southern Appalachia, and Michigan. Market models for forest products are being developed for Maine and will be available to serve as a case study on how to utilize the results of this project in other market models.

Specifically, funded projects are supporting or have supported efforts to better understand (1) factors affecting C. pinea infestations in New England, (2) fungal infections and tree impacts associated with white pine needle damage, (3) interactions of pine spittlebug and stem fungi on white pine in Michigan, and (4) association of M. macrocicatrices with stem fungi and impacts on white pine in southern Appalachia.  Techniques are well established for using dendrochronology to quantify stress impacts on tree growth and onset of infestation, for sampling and identifying fungi and insects, and for measuring the physiological status of pine through stem flow measurements.  Funded projects are also helping to improve quantification of damage on white pine.

The critical role of eastern white pine in the region is well understood, timber values are high and quantifiable, and silvicultural practices are available for regenerating and growing high-value white pine.  As our understanding increases on the development of white pine health issues in the region, the results can be easily incorporated into the best practices for managing the species and reducing damage.  

Critical Role of Multistate Effort

Given the complexity and extent of white pine health issues, it is unlikely that major advances will be accomplished by any single research group working in relative isolation; such advances require collaboration among groups working in parallel. Collectively, potential project members have an enormous amount of expertise in various aspects of white pine health. However, when viewed regionally, the research effort appears fragmented. Bringing members together in a structured and active arrangement would create a synergism in research effort, thereby increasing research efficiency and productivity, with the ultimate goal of improving white pine health throughout the region.

Currently, the potential project members include researchers and outreach professionals from Land Grant Universities (Georgia, Maine, New Hampshire, Vermont), USDA Forest Service (New Hampshire, Georgia, Minnesota), and state agencies (Maine, New Hampshire, West Virginia).  Many of these participants work directly with stakeholders. The combination of researchers and outreach professionals creates an effective means of finding practical solutions for improving the management and health of white pine.  Creating the multistate project will allow project members to:

  • Review, synthesize, and share information on white pine health issues.
  • Identify critical knowledge gaps that currently hamper efforts to improve white pine health.
  • Avoid unnecessary duplication of research effort.
  • Establish a collaborative information-exchange network to provide better detection and understanding of factors affecting white pine health.
  • Standardize field, laboratory, and analytical protocols across the regions.
  • Develop additional multi-institutional research proposals for national-level grants in order to bolster and build upon this initial work.
  • Develop silvicultural prescriptions and other management recommendations to help mitigate potential white pine threats.
  • Ensure that new findings are communicated with land managers.

Impacts

Bringing together region-wide expertise on white pine health issues will allow assessment of the species’ responses to a changing environment.  The combination of land use changes and climate change may be initiating transformations in white pine’s responses to its environment that may dramatically alter the appropriate management prescriptions for the future.  The proposed working group will initiate this assessment and develop a range-wide understanding on the future health of white pine.  Finally, our goal of using this initial project to motivate an additional multi-institutional, national-level grant could lead to much broader impact than that outlined above.

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