The Slow Storm

The Slow Storm: Tree and Stand Mortality in CT during 2018 from drought, insects and diseases.

by Thomas E Worthley, UConn Associate Extension Professor, Forestry

During the last decade most tree-related front-page-newsworthy stories resulted from disruptions related to severe storm events that caused power outages, transportation disruptions and property damage that folks will long remember. Such events are sudden and dramatic, are certainly newsworthy and result in visible changes in our landscapes and neighborhoods. Less sudden and dramatic, but perhaps more intensively and extensively altering our wooded landscapes visibly and ecologically, is the slow and relentless “perfect storm” of weather patterns, invasive insects and opportunistic pathogens the last few years causing severe and extensive tree mortality, most noticeably in eastern CT. We are witnessing a landscape-scale change in forest species composition, age structure and stand condition such as not been experienced in a generation.

90% oak canopy loss due to drought and gypsy moth defoliation at Beaver Brook State Park, 06/2018.
90% oak canopy loss due to drought and gypsy moth defoliation at Beaver Brook State Park, 06/2018.

During the early summer of 2018 it became apparent that numerous trees throughout eastern and central Connecticut did not produce leaves this spring, having died sometime during the winter. It’s not unusual to lose a tree or two to natural causes at any time of year, but the massive scale and extent of oak tree (Quercus spp.) mortality during the winter of 2017 to 2018 was striking and concerning. The combination of drought conditions during 2015 through 2017 followed by widespread and intense gypsy moth (Lymantria dispar) infestations and defoliations in 2016 and 2017 is the primary cause. Many trees already stressed by drought conditions upon being defoliated simply were not able to produce sufficient carbohydrate reserves to survive. In some places a secondary mortality phenomenon is also evident. Early and mid-season browning of leaves on individual trees that leafed-out and seemed fine during spring of 2018 indicates that other pests or diseases continue to affect previously stressed trees, the main pathogens responsible being two-lined chestnut borer (Agrilus bilineatus), a native pest, and armillaria fungus, also known as “shoestring” fungus (Armillaria mellea). Both of these agents are known to opportunistically attack stressed trees.

Damage on a red oak limb caused by two-lined chestnut borer, 08/2018
Damage on a red oak limb caused by two-lined chestnut borer, 08/2018

Combined with the anticipated loss of ash trees (Fraxinus spp.) in our area due to the invasive emerald ash borer (Agrilus planipennis)  moving across Connecticut, the sheer numbers of LARGE standing dead trees throughout the state presents what might be described as a slow-moving environmental disturbance. For some property owners the word “disaster” might be more appropriate, given the value of standing timber losses or the expenses associated with removals of large dead trees near homes.

A long period of detection sampling and information dissemination raised awareness about emerald ash borer with professionals, elected officials and members of the public, so we’ve been somewhat prepared for it. But the sheer degree and extent of oak tree mortality in central and eastern CT was unexpected and unprecedented and has overwhelmed many homeowners, Tree Wardens, foresters and others. 

Implications of a sudden shift in forest composition and structure

What can woodland owners in affected areas expect to happen next? At this time some continued mortality from two-lined chestnut borer and armillaria fungus is anticipated and gypsy moth egg masses remain abundant in some spots. A wholesale loss of oak forests from the landscape is not expected, but stand structure and composition, habitat features and wildlife populations, and future stand growth patterns will be different.

  • Many mature oak stands will become young oak stands, in upland settings where the oak canopy was dominant and the losses severe. A strong acorn crop in 2016 combined with abundant advance oak regeneration (seedlings that have been present for many years) at many upland sites will ensure a future oak forest at those locations. Landowners can encourage an oak component by means of forest improvement practices that eliminate competition. 

 

  • Some stands exhibiting partial oak mortality will transition to mixed-species stands. Much of the southern New England forest resource is comprised of “even-aged stratified mixtures”, in forestry jargon, where forest canopies are arranged in layers. The uppermost part of the canopy is occupied by oaks and other species that are not-so-tolerant of shade, and just beneath these crowns reside the more-shade-tolerant maples, beech and birches. In many cases these individuals can be expected to grow into and occupy canopy gaps left by dying oaks. It will be up to landowners to decide whether that is a desirable future condition.

 

  • Habitat conditions are changing and wildlife populations will compensate. Birds that require large areas of unbroken forest canopy and animals that depend on abundant acorns will move to places where those conditions still exist. Observers can expect to see more birds that utilize canopy gaps and early successional structure, along with rabbits, mice, other rodents and ground-nesters. Insect-eating birds will find abundant forage, predators will enjoy numerous perching sites and as dead trees decay and topple over during the next few years, amphibian and reptile populations might benefit from unique habitat and food sources associated with decaying wood.

 

  • Invasive species will invade even more. Near roads, fields, power lines and other forest-fragmenting features, where invasive species such as Japanese barberry and oriental bittersweet are already an issue, even partial canopy loss will worsen the problem. Ticks will thrive in these places. Management activities that control invasives will yield long term benefits.

 

  • Hikers and hunters will need to look up! Constantly. Anyone making recreational use of woodlands in affected areas MUST be aware that dead branches and limbs can and will drop at any time under any conditions. Temporarily closing some popular recreational sites to the public might be advisable.

 

  • Think twice before acting on the temptation to salvage that dead tree. The risk of brittle broken limbs falling and causing injury to a person cutting a dead tree is extremely high. If a dead tree needs to be removed, and you are not properly equipped and trained, the advice of a professional is essential. (Besides, we’ve already mentioned the tree is an awesome perching site and insect buffet!)

“Forest”, in all its variations, is the natural vegetative cover for most of southern New England, indeed, it’s estimated that 75% of Connecticut is under some sort of tree canopy. The forest is also resilient, relentless, creative and patient. Regardless of what we humans do to the land, trees will, ultimately, find a way to grow back and as we observe the effects of this “Slow Storm” we can be encouraged to remember this. While we can’t control the effects of slow or sudden storms, we can observe and enjoy the dynamics of re-growth, watch the changes that take place, help to encourage what’s desirable and control what’s not, slow down and be part of the process.

Posted by Amanda Bunce in