Sunday, June 30, 2013
State of the Union Address: The Wavering Health of the Eastern Forest
(Red River Gorge sandy hill-top dry-mesic forest in November)
Education is power. I'd like to empower readers to empower others about the threats caused by globalization, human disturbance and other natural factors, on our forests of the Midwest and East. In this blog post I will outline the greatest threats to the security of our forests, outside of logging, agricultural development and urban sprawl. Foreign insects and diseases, by no fault of their own, are devastating and/or weakening the composition of our forests by using native trees as hosts without any effective natural controls unimplemented by man. With climate change, the threats grow. Studies tie increasing wildfires, droughts and floods to man perpetuated climate change posing long-term threats. The icing on the cake is within the disturbance of our forested regions, invasive species are taking advantage of newly broken ground quicker than a good diversity of our forest canopy species can, changing the whole process of natural succession. The logging projects of the pioneers, and first settlers would have not yield such beautiful second growth forests as we have throughout most of the East if today's invasive plants were as established as they are now, back then. Today, from Ornamental Pear, to the Honeysuckles, and Kudzu we have major disruptors to the regenerative process of our forest systems that will compound the problem of many species being weakened or push to extinction by foreign pests and pathogens. Once again, education is power, and I hope to empower many to begin to turn the wheels of innovation and dedication, so that we may preserve/restore as much of our native forest communities as possible for the future.
This post will focus on species of trees that are dominant or common in forest communities of primarily Midwestern, Eastern, and Northeastern America.
( A Red Oak- Quercus Rubra, in fall color)
With the demise of the American Chestnut (Castanea dentata), the role of mass producing proteins and fats within the forest ecosystems has been largely shifted to Hickories, Beech, and Oaks which often make up large portions of today's second growth forests. The Oak species (Quercus), in American has been found to support the larvae of over 500 different kinds of moths and butterflies, the most of any single tree genus. The number of other insects that directly rely or that are supplemented by the Oak genus is imaginably large also. Oaks face threats from many fronts even though they are one of the most disease resistant, extreme weather tolerant, and long lived species of the American forests.
The Red Oak Borer (Enaphalodes rufulus) threatens currently in the Central Hardwood Region, having already done severe damage to ecosystems in the Ozark Highlands. This pest attacks the young and old, it prefers Quercus rubra (northern red oak), Q. velutina (black oak), and Q. coccinea (scarlet oak). Other species are also less often attacked.
Twolined Chestnut Borer (Agrilus bilineatus) today attacks oaks in decline, under abnormal stress, or suppressed by shade. First signs are wilted foliage that turns brown and hangs upon the branches, then the branches die and/or will make no foliage for the following year that have been bored into. Death of the tree usually occurs within 3 years of the initial attacks.
The Gypsy Moth (Lymantria dispar) was introduced by a french scientist in the late 1800's. This moth's larvae feeds upon oaks, apple, sweetgum, speckled alder, basswood, gray and white birch, poplar, willow, hawthorn, cottonwood, hemlock, southern white cedar, and native pines and spruces. When populations rise, over 50% defoliation is common. When severe consecutive defoliation occurs mixed with environmental, pathogen, or other insect stress, trees will die after a last significant defoliation.
The Oak species aren't under indefinite demise such as the Ash species (Fraxinus sp.), but over time the above threats can worsen or expand their range taking advantage of environmental stress factors and human disturbance weakening mature specimens. The succession of shade tolerant species (Beech-Fagus sp., Maple-Acer sp.), which most argue is natural, are a direct threat to Oaks in the forest communities. Oaks remain one of the most ecologically valuable trees of all of America. Their large savannah open grown canopies offer a generous amount of shade and cooling to developed areas making them a very attractive candidate for combating heat islands and reforesting communities. But when reforesting or planting for heat relief for cities, diversity is always a must, as the next generalist or specialist insect brought in from overseas may be only 10, 30, or 50 years away which could potentially wipe mono-culture plantings like the American Elm (Elmus americana) catastrophe. For now, Oaks remain a very viable and valuable tree selection for the Midwest throughout the northeast with it's biggest threats being natural succession and gypsy moths.
(The outlook on Hickories is very positive, but we must be careful not to over plant any species)
Hickories (Carya sp.) occupy a substantial amount of primarily upland forest habitats. Some hickories do specialize in bottomland habitats, but very few can withstand saturated soil for too long. The nuts and wood, are of high value to humans, and wildlife. This is a slow growing, large, long lived tree that has the kind of disease and pest resistance and climatic adaptability, that any heat island relief reforestation program would ask for. Though they do not grow as wide as the Oaks in open situations, they do grow as tall and often a bit taller depending on the species and site.
Deforestation and development is a threat to all tree species, but in some forest types Hickories share a similar succession problem as the Oaks do. Most hickories are shade intolerant, with a few species being intermediately tolerant. Research revealed no major insect or pathogen threats.
When researching threats to Hickories (Carya species) in the East and Midwest I was pleasantly surprised to find out there are no major insects or pathogens severely affecting them. One threat to all of our niche occupying trees is climatic change. By the end of the century Cincinnati's climate is projected to fall somewhere near being most similar to Middle-Tennessee at best, and Northern Alabama at worst. In city reforesting projects, or habitat reforesting, trees that range into the south should be prioritized over trees that are only dominant in Zones 5 or cooler (in reference to a project in Zone 6). Many Hickories such as the Shagbark Hickory pictured above range from the Southeast all of the way into Canada, perhaps making them a smarter choice for planting minding the future climate projections. When properly sited, Hickories are typically drought/heat tolerant, wind tolerant, and some species are even tolerant of poorly drained soils, the true challenge is finding hickories that are commercially available.
(Black Walnut-Juglans nigra is under a great threat of a canker disease spread by a beetle)
The Black Walnut is a sporadically occurring canopy tree throughout America, where which has been planted as an ornamental and for food in states it's not native to for centuries. It is a scattered forest tree preferring deep, well drained fertile soils, commonly found near streams and well-drained bottom lands. A toxic substance secreted by the roots (juglone) inhibits the growth of some plants beneath trees; this is know as allelopathy. Because of the high value of it's wood, it is now grown in plantations as a source of top-dollar veneer lumber. The nuts are only penetrable by squirrels and are a highly preferred food source to the species, but the formidable husk and shell prevent other animals from consuming them.
Walnut Twig Beetles (Pityophthorus juglandis) are the carriers of death for primarily the Black Walnut. The Beetle is native to Arizona, California, and New Mexico, but is invading states where Black Walnut has been planted and naturalized. Adult bark beetles carry fungal spores that are then introduced into the phloem where they create galleries. Small cankers develop around the galleries these cankers may enlarge and converge to completely girdle the branch. Trees die as a result of these canker infections at each of the thousands of beetle attack sites. The disease the beetle is spreading is also native to those above listed western states, being identified as Thousand Cankers Disease (Geosmithia sp.). On a side note: Butternut Canker (Sirococcus clavigignenti-juglandacearum) introduced to North America, has already seen the decrease of the Juglans cousin of Black Walnut, White Walnut (Juglans cinerea), in some states reach over 80%.
With large populations in the west already being decimated, and the disease/beetle combo already having made it's way into Tennessee, favorable climatic projects lead to the possibility of Black walnuts being similarly effected in Eastern Forests. Black Walnuts are also common components of disturbed metropolitan forests, second growth forests, and neighborhoods which poses the future threat of another mass dying and reduction of metropolitan tree canopy similar to what we are seeing with the Ash Trees (Fraxinus sp.) today. Personally, I would avoid planting Black Walnut until we are certain we have a biological or safe chemical control for the Thousand Cankers Disease. They recolonize very well after disturbance without our planting of them, probably because of forgetful squirrels, and there are many other trees with healthier outlooks.
(Yellow Birch-Betula alleghaniensis, a co-dominant species of northern forests)
Outside of the Birch trees natural ranges, these predominantly northerly trees are highly susceptible to insect and disease problems. The River Birch-Betula nigra is the most heat/humidity tolerant birch and is readily available through nurseries. All birches have several common features that help identify them. Most species of birch have papery, flaky bark of one varying color that has elongate, horizontal rows of lenticels. These medium sized mature trees have catkins that remain on the ends of the wings throughout the winter, usually clustered and obvious. Wildlife highly value the flowers and seeds of most birch species.
The birches have one potentially major threat already well established in the Northeast. This is the Birch Leafminer-Fenusa pumila, a small sawfly native to Europe that feeds on the tissue between the upper and lower surfaces of birch leaves. The birch leafminer causes damage to gray birch, European white birch, Erman birch, Asian white birch, monarch birch, and paper birch. Early season defoliation is particularly damaging. Severe defoliation weakens the tree and increases its susceptibility to invasion by secondary insect and disease pests. The host may show no symptoms of decline for several years, however, repeated leaf loss year after year could be fatal to the tree.
In comparison to the Emerald Ash Borer, Gypsy Moths, and other foreign insect threats, the Birch Leafminer causes fatality not nearly as often and is less damaging leaving the outlook for the Birch species neutrally positive depending on the development of this pest.
(The iconic American Beech-Fagus grandifolia, isn't without threats either today)
The long lived Beech tree is usually no more than 80 feet in height, while open grown trees have widely spreading crowns and short trunks. It preferes moist, well drained, fertilize soils dominating mesophytic types of forests through the mobility of it's nuts (by animals) and incredible shade tolerance. In drier, sandy forests it may be restricted to northern and eastern hillsides but where it is present, long-term, it will usually take up a significant amount of the canopy. The nuts are highly nutritious and attractive to wildlife, being small enough to be utilized and hoarded by birds which raise the mobility of it's crop. The cavity prone physical make up of the tree also makes it very high in value for cavity dwelling forest fauna.
When Beech Scale (Cryptococcus fagisuga), a soft bodied scale insect, feeds on the Beech tree, the damage caused by the introduced insect opens the door for Beech Bark Disease (Neonectria coccinea var. faginata). Beech Bark Disease has caused significant mortality, throughout Northeastern America and Southeast- Canada, it has also been cited as far west as Ohio, Tennessee and Wisconsin. On some trees, a red-brown exudate, called a slime flux or "tarry spot," oozes from dead spots. These dead spots are often the first symptom of Nectria infection.
While the Beech currently has only one major threat with the introduced insect/fungus combo, there currently is no biological or chemical control that can be replicated on a large enough scale to eradicate the growing and spreading damage these organisms are doing. There is possibly resistant populations within most tree species to their threats though, and sadly, one day it may come down to propagating from the Beech trees that remain after the scale and fungus have done their damage. But this is currently the only major threat to Beech trees so if we do create an economical widespread control, the outlook will be very healthy.
(Sugar Maples are doing very well, and some think too well, but do share a common threat)
Acer saccharum-Sugar maple, is a large, shade tolerant, dominant species occurring in mass throughout the Midwestern, Eastern and Northeastern mesophytic forests. The processes of natural succession may have been effected by man historically through prescribing and/or suppressing wildfires that would promote and/or control fire sensitive species like American Beech and Sugar Maple. Today Sugar Maples are displacing Oaks, Hickories, and pioneer species of second growth forest throughout their native range which isn't a positive for long-term diversity. Sugar maples are great landscape trees providing stunning fall color, and ample heat island relief with it's broad, but short trunk in open grown situations. It is less sensitive to drought than American Beech, and more tolerant of urban conditions also. But Sugar Maples do share a threat that potentially threatens many tree species.
The Asian Long Horn Beetle (Anoplophora glabripennis) is currently the Sugar Maple's, and all Maples biggest threat, more on this pest later.
Outlook-Tenatively, Very Positive
It's ability to reproduce and even change the composition of forest types within it's native range secures it's foothold as a dominant Eastern tree. But it's future greatly hinges upon future land use, deforestation, climatic change, and most importantly the control of the Asian Long Horn Beetle which I will elaborate on towards the end of this blog post.
(The future of Hemlocks in America, is not positively promising)
Hemlocks (Tsuga sp.) prefer acidic, cool soil habitats within mesophytic forests. It occurs sporadically throughout the East and upper Midwest, and in mass within the Northeast. These native evergreens can become 90 feet tall and grow rapidly in ideal conditions living as long as 600 years. This is one of the most shade tolerant Eastern trees, and easily one of the most shade tolerant evergreen trees making it a long-term community member where the habitat is suitable. In the right microclimates Hemlocks thrive in landscapes, but are sensitive to drought, salt, windy, and dry conditions requiring a well researched placement. Larger trees are favorite nest sites of many songbirds including black-throated green, blackburnian, and yellowy-rumped warblers, both kinglets, and purple finches. Seeds are small, but some-times crops are enormous and utilized heavily by pine siskins and crossbills.
Elongate Hemlock Scale (Fiorinia externa), native to japan, attacks the lower surface of the hemlock needle, where it removes fluids from the mesophyll cells through piercing and sucking mouthparts. Mixed infestations of scales and adelgids can greatly hasten hemlock decline as scale populations build slowly on healthy trees, but much more quickly on stressed ones. Trees often die within the next 10 years, but some survive longer in a severely weakened condition with only a sparse amount of foliage at the very top of the crown and these weakened trees are unsightly and have little chance for recovery.
Treatments are available for protection of Hemlocks on small scales, but country wide would be not be economical. The combination of two foreign threats spreading through the native ranges of the hemlocks, makes this trees future nearly as bleak as the Ash Tree's (Fraxinus sp.) which I will describe next.
(The Ash trees (Fraxinus sp.) are a major loss ecologically, and economically)
Ash trees are large shade trees that acted as pioneer tree species and long-term dominant species of many mesophytic and hydrophytic forest types of the east. They are currently in the process of being wiped out within their native regions by a non-native insect, the Emerald Ash Borer (Agrilus planipennis). On small scales, the trees are treatable, much like the Hemlocks, but it is not feasible to do on a forest-wide basis. Genotypes are being preserved today, to one day restore the Ash trees back into the wild once the Borer has been declared extinct, which won't happen until it's food sources are all exhausted.
(Today the American Chestnut has been reduced to stump sprouts)
American Chestnut was the most common tree in the Appalachian Mountains until the mid-twentieth century, when an exotic fungus killed every tree in its natural range. Though it still exists a small trees sprouting from old stumps, and occasionally becomes large enough to produce fruit, the species is basically nonexistent compared to its former status among the trees of the Central Hardwoods. There is currently major efforts to reintroduce resistant trees into the wild by different organizations including the American Chestnut Foundation.
(A few American Elms also remain, sporadically, possibly resistant to Dutch Elm's disease)
Dutch Elm's Disease has seen the native Elms be reduced to sporadic specimens, many in decline, but some perhaps resistant to the Beetle/Disease combination. These trees were very ecologically, and economically important. The expanding flower buds are heavily sought out in the spring, probably from their high protein content. The seeds are also taken by a wide variety of birds and rodents once they fall in early summer, a time in which mast food production in the forest is at a low. A bit of hope remains of finding resistant elms, as for now, ornamentally resistant exotics are used, and some like the Siberian Elm have come very invasive.
(The Asian Longhorned Beetle-Anoplophora glabripennis)
The Asian longhorned beetle-Anoplophora glabripennis, is native to Japan, Korea, and southern China. Experts think that the beetle hitchhiked to the U.S. during the early 1990's in solid wood packing or crating materials on cargo ships arriving from China. In the U.S., where no natural enemies exist, the insect is extremely destructive to our landscape trees and forests. The beetle attacks many different hardwood trees, including maple (all species), horsechestnut, buckeye, poplar, willow, elm, birch, London plane tree, sycamore, mimosa, katsura tree, hackberry, ash, and mountain ash. Trees of any age may be attacked, however, trees 4 inches in diameter and larger are preferred. Beetles will attack both stressed and healthy trees, which makes them an even greater threat. Early detection, and then eradication is the best prescription for preventing this pest from moving throughout our Eastern Forests.
There is much that threatens the viability and composition of our forests today outside of insects and disease. Climate change increased temperature, wildfires, floods, and droughts will have there effects. Unyielding population growth, projecting for the amount of land use for agriculture to increase threatens legally unprotected forests. Invasive plants are established at such populations that they are preventing and changing the composition of forest succession/regeneration without human intervention. The challenge is before us today, for forever. If we do not educate one another, support the protection and proper management of forests-private and public, these parts of American history may only one day exist in photographs.
I've listed some valuable resources below. I hope you've enjoyed this sobering piece, and gained some insight on the challenges that face us today.