Sunday, September 14, 2014

Beech Blight

American Beech (Fagus grandifolia) is a common and distinctive tree found across much of eastern North America. It is most often found on moist, acidic sites where it grows slowly, but lives long as a component of late successional, minimally disturbed forests.  

The smooth, silver bark gives American beech an almost elegant appearance compared to rough barked species it is often associated with.  However, this bark is quite thin and makes the tree susceptible to a variety of "damaging agents" (1).

Careful observation during the late summer & early fall may reveal signs of one of the more unusual of these "damaging agents".  There are at least 4 different but closely related signs to look for.  The first of these symptoms is defoliation or apparent die-off of limbs, usually evident on the lower branches, prior to normal leaves turning color or shedding.
Extensive defoliation of lower limbs; no living leaves present on the lower third of the trunk

In extreme cases, like the tree shown above, all lower limbs may be barren of live leaves. More commonly, only a single limb or two may be affected. Sometimes the culprit can be found in the process of causing defoliation on twigs that appear to be covered in a dense white, cottony fuzz. The fuzz is actually hundreds or thousands of colonial aphids. When approached closely, they wave and gyrate possibly as a defensive mechanism.  

The aphids (Grylloprociphilus imbricator) feed by sucking sap from the living beech tissue (possibly aided by the thin bark). Each colony includes individuals of different developmental stages or "instars". For example, on the image above, both winged and non-winged individuals can be observed as well as some individuals with varying degrees of plumage emanating from the rear abdomen (the later generations).  
Splotch of black tar-like material indicating feeding of aphids 

One of the many insect visitors feeding on aphid residues
As they feed, the aphids deposit "honeydew" or excrement on surfaces below. This honeydew begins to be colonized by sooty molds that give the appearance of black liquid tar. These patches are easy to spot and often persist for at least 2 seasons. 

The honeydew provides an attractant to numerous insects (see image left). For unknown reasons, possibly the quantity of honeydew, some substrates develop dense masses of sooty molds not just thin black films. 
Sooty Mold (probably Scoriosa spongiosa) in early development on Fagus leaf
Sooty Mold in later development on Fagus leaf
Sooty Mold mass on American Beech twigs

Sooty Mold mass advanced growth on Beech twigs

The sooty molds apparently don't penetrate leaves but dense patches seem to be able to limit or completely block photosynthesis.  Not surprisingly, tree seedlings underneath aphid colonies suffer greater mortality than unaffected seedlings (2).  I have observed several herbaceous and shrub species being negatively affected in this way, including Hepatica, Christmas Fern, and Mountain Laurel. 

This process could account for the relative lack of other species of plants around some American Beech stems (see image at top of page). 


(2) Cook-Patton. S.C., L. Maynard, N.P. Lemoine, J. Shue, and J.D. Parker.  2014. Cascading effects of a highly specialized beech-aphid-fungus interaction on forest regeneration. PeerJ.

Monday, September 1, 2014

Pine Barrens & Grasslands in New England; Part II

In a previous post I briefly discussed two examples of fire-maintained vegetation in southern New England ( Ecologically similar sites, often referred to as "pine barrens" or "pitch pine barrens" are scattered around the region.  I visited examples of this unique vegetation in Maine, New Hampshire, and Massachusetts in late summer (2014).

Pitch Pine barren near Waterboro, Maine
understory of lowbush blueberry, sweetfern, and bear oak

Some examples were enchanting forests; gnarly & twisted pines with charred boles, multiple age classes, and patchy ground cover openings. All sites occurred on "sandplains" or glacial outwash plains. These deep sandy soils supported two consistent species across all sites visited; Pitch pine (Pinus rigida) & Bear Oak (Quercus ilicifolia). Bear Oak was often heavily dominant as a tall shrub or dense midstory layer.
Pinus rigida bole displaying epicormic shoots
Bear Oak (Quercus ilicifolia)

Many areas I visited were thickly stocked with dense Pitch Pine, while others were open woodlands. Fire history could partially explain those density differences, with more frequently burned sites supporting the woodlands.

Much of the region around the Waterboro Barrens, was burned over in Maine's largest series of forest fires in 1947. Since that time (and prior to restoration work), a 93% decline in open canopy pitch pine has been documented (2).

In addition to the loss of open woodlands, Patterson (1) found that stands unburned since 1947 had developed highly volatile, well aerated fuels conducive to high intensity, fast moving fires.
Waterboro Barrens thinning;
dense forest (left) unthinned, open woodland (right) mechanically thinned. 
Not surprisingly, a proactive management strategy of mechanically thinning trees and brush around exterior boundaries of the site has been implemented. This strategy serves a dual purpose of minimizing fire behavior while "restoring" some of the open canopy woodlands that have been lost. This management strategy was also being implemented at a New Hampshire site I visited. Hand crews were actively cutting, clearing, and piling brush in much the same way we have done on fire reintroduction projects in North Carolina (one of which involved pitch pine). Examples shown here (below) were presumably thinned to achieve this open structure.

Waterboro, Maine
Concord, New Hampshire

Pitch Pine Woodlands:
(contrast both to image at top of page)

While appearing structurally similar, understory composition varied considerably; Concord (right) was much richer floristically and perhaps has a longer and/or more recent history of prescribed fire; prescribed burns began there in 2003 and ~ 20 acres or so have been burned in most years since then (3). Managers at Concord have a compelling reason to reintroduce fire. In addition to restoring a rare and declining natural community type, and reducing wildfire risk, their site is the only location in New Hampshire and the world's easternmost location known to support the Karner Blue Butterfly (4).
Karner Blue (Lycaeides melissa samuelis), Concord, NH
Thanks to Harry LeGrand for ID confirmation!
This federally endangered species (also found in the midwestern US, and mentioned in an earlier blog regarding the connection with Sundial Lupine) has been reintroduced to the site, along with Lupines by biologists in New Hampshire.  One relatively small portion of the site was exceptional for its grassy character (see image below). I observed a number of plants there, but in no other "barrens", including Big Bluestem, DogBane, New Jersey Tea, Ground Cherry, and others.
Grassy open Pitch Pine Barren@Concord, New Hampshire

Karner Blue (?) perched on Dogbane (Apocynum cannabinum)@ Concord, New Hampshire

It will be interesting to see what management activities, especially prescribed fires, are conducted across these barrens and the results they achieve. Reducing dangerous fuel loads while restoring more natural structure seems like a logical way forward (see below), but the real proof comes with fire.

Brush piles from hand clearing around large Pitch Pine @ Concord, NH