Caliciopsis Pine Canker in New England

 Caliciopsis pinea , a fungal pathogen that causes cankers on conifers, has been reported causing damage to eastern white pine (Pinus strobus) in eastern North America. In order to better understand the extent and severity of the disease, surveys were conducted from 2014-2016 at randomly selected sites throughout Maine, Massachusetts, and New Hampshire. Initially in 2014 cankers were observed at 42 of the 58 sites surveyed (72%). Soil type and stand density were found to be promising predictive variables associated with the disease. Symptoms were most frequently observed on trees growing in excessively drained (86%) or poorly drained soils (78%) than in well drained more fertile soils (59%). Stand density was found to be greater for stands with Caliciopsis than for stands without the pathogen. Subsequent surveys during 2015-2016 were done to further investigate the relationship of soils and stand density at 62 sites with 50 of these (81%) having symptoms of the canker disease. Again results show that poor soils and high stem density are associated with incidence and severity of Caliciopsis canker disease.

A modified version of the New Hampshire Important Forest Soil groups was developed specifically for conditions potentially related to white pine growth and productivity. Soils from Belknap, Merrimack, and Hillsborough counties in New Hampshire (NH) and Oxford, Androscoggin, Sagadahoc, and York counties in Maine (ME), where eastern white pine is abundant, were classified into four soil groups. Layers of these modified soil groups for use in Geographic Information System (GIS) were generated for New Hampshire and Maine counties with the greatest concentration of eastern white pine basal area.

In 2015, at least 12 sites per soil group with more than 75% basal area of eastern white pine were randomly selected for sampling. The sites visited were sawtimber stands because most of the eastern white pine resource in New England is mature. Previously, Caliciopsis canker symptoms were more frequently observed on pole-size trees. In addition, during 2015, Caliciopsis cankers and fruiting bodies were frequently observed on white pine regeneration. In 2016, therefore, poletimber stands and eastern white pine regeneration within these were surveyed to better quantify probability of Caliciopsis canker symptoms in these stands at greater risk of damage by C. pinea.

In the field, a GPS receiver and compass were used to locate the center point of each site generated by the intersection of GIS soil groups and white pine layers. A 10 basal-area-factor prism was used at plot center to select sample trees (DBH > 11.5 cm). Three more prism plots at 120 degrees (0, 120, and 240) and 17 m from the initial plot center were installed for a total of four prism plots per site). Trees per prism plot were converted to trees per hectare by calculating an expansion factor unique to each tree’s DBH.

In addition, the following data were collected for each eastern white pine: live crown ratio, presence of C. pinea fruiting bodies, incidence and severity of Caliciopsis canker symptoms. Caliciopsis canker symptom severity was visually assessed by dividing the bole of the tree into thirds (bottom, middle, and upper stem) and counting the number of resin streaks in each section up to ten streaks per section. This assessment was conducted on two opposing faces of each tree and added for a maximum score of 60 resin streaks per tree. Resinosis associated with white pine blister rust symptoms, insect boring, decayed branch stubs, or mechanical damage was not considered in Caliciopsis canker disease severity assessments. In 2015, the presence of C. pinea in understory regeneration was recorded for each prism plot, but not for individual seedlings. In 2016, consequently, the presence of Caliciopsis fruiting bodies from the five closest eastern white pine seedlings (DBH < 2.54 cm, height > 30 cm) to each prism plot center as well as maximum distance to prism plot center were recorded. Caliciopsis fruiting bodies and infected plant tissue were collected from symptomatic eastern white pines trees or seedlings during 2015 for diagnoses.

A total of 62 white pine stands or sites were sampled in Maine and New Hampshire during 2015–2016. Fifty of these (81%) had symptoms associated with Caliciopsis canker. During 2015, 50 sawtimber stands, at least 11 in each soil group were sampled in New Hampshire and Maine, 13 of which were privately owned. For 2015, mean stand diameter was 34 cm, mean tree density per stand was 336 trees per hectare, on average eastern white pine comprised 80% of the stand basal area, and 20% of eastern white pines exhibited symptoms associated with Caliciopsis canker. During 2016, 12 poletimber stands, at least three in each soil group were sampled in New Hampshire all on lands owned and managed by the State. For 2016, mean stand diameter was 23 cm, mean tree density per stand was 459 trees per hectare, on average eastern white pine comprised 86% of the stand basal area, and 66% of eastern white pines exhibited symptoms associated with Caliciopsis canker.

The proportion of trees (DBH > 11.5 cm) or seedlings (DBH < 2.54 cm, height > 30 cm) with symptoms associated with Caliciopsis canker differed significantly across soil groups (p < 0.0001) and stocking categories. Trees in poletimber stands were more likely to have Caliciopsis canker symptoms than trees in sawtimber stands. For example, the probability (ranging from 0 to 1) of having Caliciopsis canker symptoms was 0.7 for trees in poletimber stands in the dry soil group compared to 0.3 for trees in poletimber stands in the dry soil group.

Trees in loamy soils and understocked stands were less likely to be damaged by Caliciopsis canker than trees in other soil groups or adequately stocked stands. The proportion of live trees with symptoms associated with Caliciopsis canker was less for loamy soils than any other soil group, and greatest for dry soils. The proportion of live trees with symptoms associated with Caliciopsis canker was less in understocked stands than in adequately stocked stands. Pinus strobus seedlings in poletimber stads were more likely to be damaged by C. pinea in sites with loamy soils and understocked over story. Stand density was not related to soil groups (for basal area per hectare: p = 0.47, F-value = 0.86, df = 3, 58; or for trees per hectare: p = 0.9, F-value = 2.3, df = 3, 58). In contrast to results from the tree density analyses, seedling density of seedling in poletimber stands was related to soil type (p = 0.0239, F-value = 3.49, df = 3, 42). Seedling density was greater in poletimber stands on loamy soils than those on shallow soils. Live crown ratio of eastern white pines decreased with increasing Caliciopsis canker symptomseverity (Figure 6), ranging from 28% for trees without symptoms to 20% for trees with high disease severity (p = 0.002).

In this study 62 eastern white pine stands across a variety of soils was sampled. No prior knowledge of Caliciopsis canker incidence was known in these sites prior to sampling. The 62 sites had an average slope of 3.4% ranging from 0% to 25%, therefore, soil was the most salient topographic feature differing among sites. Incidence of symptoms associated with Caliciopsis canker in mature white pines was greater in drier and shallow soils compared to loamy soils. Conceivably, white pine trees growing in soils with more nutrients, and adequate but not excessive water-holding capacity, likely have more resources to grow and allocate towards defense than trees growing in more nutrient poor and excessively or poorly drained sites.

The water holding capacity of soils affects the amount of water available for tree growth. Drier soils are more conducive to drought stress which might render trees more susceptible to damage by Caliciopsis canker because these trees might have less water to allocate towards growth and defense. In contrast to mature trees, white pine regeneration in loamy soils exhibited greater incidence of Caliciopsis canker symptoms than seedlings growing in other soil groups. Seedling density was also greater in loamy soils compared to other soils. Stem density increases the probability of damage by Caliciopsis canker. For example, mature trees in stands that were adequately or fully stocked were more likely to have Caliciopsis canker symptoms than trees in understocked stands.

Stem density could affect disease development because trees in denser stands or seedlings growing at high densities have less resources to allocate towards defense due to competition. Stem density could also influence disease development by creating an environment more favorable to pathogen reproduction and dissemination. Thickets of white pine regeneration are probably more likely to retain moisture and create high humidity conditions that could favor reproduction and dissemination of C. pinea. Furthermore, stem density could also affect tree physiology. Trees growing in denser stands typically have thinner bark, which is associated with greater Caliciopsis canker severity, allegedly because the pathogen is better able to penetrate thinner bark. Currently, all these hypotheses are highly speculative because the epidemiology of C. pinea has not been investigated. For example, we do not know what temperature and humidity favor growth and reproduction of C. pinea. The time of the year at which inoculum is most abundant and how inoculum is disseminated are both also unknown.

The objective of this study was to further investigate the relationship between soil and stocking in eastern white pine forests of New England. Eastern white pines growing in excessively drained, poorly drained, and nutrient poor soils are at greater risk of being damaged by Caliciopsis canker. Stem density was also positive correlated with Caliciopsis canker damage for mature trees and regeneration. Poor soils and high stem density could predispose trees to Caliciopsis canker or could affect environmental conditions that favor disease development. The epidemiology of Caliciopsis canker is not understood at this time. Given the prevalence of Caliciopsis canker in important white pine growing regions, this topic deserves further investigation. Foresters will have to take C. pinea into account in eastern white pine management.