Eastern White Pine - Threats to a Historically Important Species

Eastern white pine's current status belies its political past and potential future. Once demanded by the King's Royal Navy for its straight, tall ship masts, Pinus strobus inspired the White Pine Acts of 1691 and 1711 and fueled colonial resistance. Surveyors for the "King's Woods" blazed the largest white pines with the "King's Broad Arrow," a series of three hatchet slices. The Pine Tree Riot of 1772, where local townspeople chased and beat the King’s mast surveyors with pine switches, may have inspired the Boston Tea Party.

Widely distributed (10.6% of the Eastern United States area) and the tallest conifer, some consider white pine the Sequoia of the East. A popular landscape tree used for screening (although it naturally loses its bottom branches over time), and it has a delicate five-needled bundle of fine-textured leaves. White pine provides both important ecosystem benefits and enhances health. One mature white pine can intercept up to 4,000 gallons of rainwater annually in its canopy. Stroking its leaves can activate an immune response of T-cells in the human body.  Due to its susceptibility to drought, air pollution, and salt, sometimes white pine requires special siting and care in an urban environment.

White Pine Decline

White pine decline refers to a complex of environmental and biotic factors negatively influencing the tree's short- and long-term health. The result is a decline in the overall health of the tree. Environmental factors leading to white pine decline include soil and moisture conditions, which white pine is not adapted to growing in. Avoid those factors by choosing a site for your tree to succeed in! Proper soils for best growth include sandy or loamy non-compacted soils (not clay), a pH between 5.5 and 6.5, and good drainage. Above-ground canopy space should accommodate a 50–100-foot future height with 20 to 40 feet of spread and plenty of sun. White pine tolerates neither root disturbance, street-side planting requiring heavy winter salt maintenance, nor moisture extremes. Unless a needle cast disease (as described below) occurs, retain the fallen needles as a natural moisture and pH buffering mulch, or provide up to 3 inches of mulch up to the drip line for young, planted trees.

White Pine Needle Diseases

Browning needles and sparse tufts of new growth often signal the first obvious symptoms of an ailing white pine. Distinguish this from the normal yellow coloration and drop of the oldest needles in the fall (on the interior of the canopy).  Looking at the needles themselves, you may notice brown tips or the entire discoloration from a disease complex known as White Pine Needle Disease or WPND.

Hot sunny days with air pollution danger warnings can allow the gas ozone to damage needle tips. Needle blight pathogens associated with WPND include the fungi Lecanosticta acicula, Lophophacidium dooksii (brown spot needle blight), Bifusella linearis, and Septorioides strobi. Lesions or banding in older needles that develop into brown and yellow expanding areas can cause death to the distal part of the needle. The extent of damage to the affected needles varies. The bases of needles can remain green, and not all needles in a bundle may get infected. Wyka et al. (2017) determined that increased precipitation from May to July — when white pine needles are elongating — positively correlates with damage from needle blight pathogens. However, as is the case with many conifer needle pathogens, that effect has a one-year delay. This means an initial infection of current-year needles happens in spring/early summer, and the needles show symptoms the following year. Trees commonly shed entirely infected needles, with substantial needle drop occurring in June or with rain. Tree crowns begin to look sparse a year after the initial infection. Hence, the stress of late spring frosts, drought, and wet spring weather favors needle disease outbreaks.

Septorioides strobi, recently described as a new species, uncharacteristically affects the current season's needles. In many cases, troubled trees exist directly adjacent to healthy trees in the landscape. Most often, needle tips were straw‐colored to brown, while the needle base remained green and healthy. Chemical management for this fungal organism differs from that of other needle disease organisms, so check with your local County Extension office for recommendations.

The Eyelash Fungus

Caliciopsis pinea causes smooth, reddish-brown branch and trunk depressions (cankers), which exude resin. The bark appears rough and cracked if the canker starts below a branch whorl. With distinctive fruiting, the fungus forms visible, curved, black-colored stalks resembling eyelashes. Pole-sized white pine in dense stands and landscape trees in dense groves or screens are most susceptible. White Pine Bast Scale (Matsucoccus macrocicatrices or WPBS), feeds on fluids of the phloem’s bast cells. Both organisms cause relatively little harm to white pine by themselves. Recently, researchers found that Caliciopsis readily colonizes feeding sites of WPBS, and they now consider it a potentially serious pest-pathogen complex that attacks stressed and weakened trees. Saplings regenerating in the understory become regularly infected and die.

Keeping White Pines Healthy

Management includes chemical control and measures to increase light and airflow, as well as remove dead, diseased, or dying branches and fertilize. White pines have adapted by increasing photosynthetic rates in remaining needles, increasing water-use efficiency, and prioritizing carbon storage over annual growth. Close inspection of affected white pine may reveal undersized shoots and stunted needles. These trees save energy by not allocating resources to new growth to ensure future vitality, thereby betting on better times. Going into dormancy, trees normally pull nitrogen out of the naturally senescing foliage in the fall, a process known as resorption. When prematurely shed needles drop from WPND, white pines lose foliar nitrogen that fall senescence would have retained. Judicious fertilization may improve vigor the most in a WPND-affected white pine.

In addition, forestry practices such as thinning to lower forest density promote crown vigor and radial growth and significantly reduce WPND severity. On a landscape scale, thin white pine groves and rows, or remove neighboring less desirable plants. Eliminate unnecessary stresses on white pine by avoiding moisture extremes and following proper cultural practices.

Whether it's three hatchet chops or the microscopic fungal spore on a needle that's causing injury to white pine, one can argue that white pine is resilient. Climate change may induce its range to move farther west to survive, even while it changes its biological processes to withstand stress and biotic attack. The more we understand the environmental and biotic stresses any tree species faces, the more we can make the choices that ensure its survival in the landscape and forest.

Sources

Beale, J. and N. Gauthier. 2015. When White Pines Turn Brown... (PDF) Plant Pathology Factsheet PPFS-OR-W-22. University of Kentucky College of Agriculture, Food and Environment. 4 pp.

Brazee, N.J. 2021. Dieback of Eastern White Pine (Pinus strobus): Pathogens, Pests, and a Changing Climate. University of Massachusetts at Amherst Center for Agriculture, Food, and the Environment.

Gandhi, K. J. K., Livingston, W. H., Munck, I.A. Eds. 2018. Resilience and Health of Eastern White Pines under Novel and Historical Factors. Forest Ecology and Management. Vol. 423. 1-120 pp.

Li Q, Kobayashi M, Wakayama Y, Inagaki H, Katsumata M, Hirata Y, Hirata K, Shimizu T, Kawada T, Park BJ, Ohira T, Kagawa T, Miyazaki Y.  2009. Effect of phytoncide from trees on human natural killer cell function. Int J Immunopathol Pharmacol. 22(4):951-959.

Rogers, S.A. 2013. The Tree that Sparked the Revolutionary War: Eastern White Pine’s Colonial History. Northeastern Lumber Manufacturers Association (NELMA).

Wyka, S.A, Smith C., Munck, I.A., Rock, B.N., Ziniti, B. L, Broders, K. 2017. Emergence of White Pine Needle Damage (WPND) in the northeastern U.S. is associated with changes in pathogen pressure in response to climate change. Global Change Biology, Vol. 23, Issue 1, pp 394-405.