On a beautiful October afternoon not long ago, a young friend showed me the remaining plants in the small garden that she and her sister had planted. I noticed that there were still some lovely basil plants with perfect leaves that would be scrumptious chopped and sprinkled on slices of the few last tomatoes in our garden—we could share! Suddenly she pulled some leaves off a woody shrub nearby, “Look! These are sourwood leaves — if you are ever really hungry, these are edible.” She’s right — young tender sourwood leaves are edible, and they can be used to make tea. It is best, however, not to eat very many of them because they are quite sour and can be an effective laxative.

Sourwood trees (Oxydendrum arboretum) are native to eastern North America, one of the few endemic trees that are not found in other continents unless planted there. It is the only species in the genus Oxydendrum, i.e., there are no other plant species in the heath family (Ericaceae) related to it so it has its own species name. Although native sourwood trees typically grow from southern Pennsylvania south to northwest Florida and west to southern Illinois, they are most common in the Southern Appalachian Mountains. They are most often a component of oak-heath forests because, like most members of the heath family, sourwoods prefer acidic soil. Sourwood is a fairly common understory tree, often bush-sized in areas like ours with dry, acidic soil, usually growing no taller than about 25-30 feet with a slender trunk with gray fissured bark, and often leaning toward the sunlight because it has a rather narrow crown. However, sourwood trees can grow straight and tall, as high as 60+ feet, if there are not many trees around competing for root space and/or sunshine.

Sourwood is an attractive tree with fragrant sprays of small white flowers in late spring/early summer and brilliant scarlet/dark purple leaves in fall. Sourwood leaves are often the first to turn color because their sap is less acidic than most trees. Their leaves alternate and are about 3-5 inches long with finely toothed margins. The dense clusters of small, bell-shaped flowers produce fragrant nectar and are actively pollinated by bees in the spring. The nectar is well known for the delicious sourwood honey that the bees produce, and the juice from the sourwood blossoms can be used to make sourwood jelly. Deer browse the new leaves in the spring and summer, and it is a popular tree for fall webworms to use for their large grey webs that protect their larvae as they browse on the late summer leaves. The shoots of sourwood trees were used by the Cherokee and the Catawba to make arrow shafts, and the mature wood of the trees is heavy and close- grained and can be polished to high shine.

Photo credit: barkandgarden.com

Finally, as you embrace all the virtues of sourwood trees, search the Internet for a popular old-time Appalachian tune, Sourwood Mountain—several musicians from Andy Griffin to the Carolina Chocolate Drops have recorded it. And definitely make plans to attend the 42nd annual Sourwood Festival in Black Mountain NC next August.

Resources:
Will Cook Carolina Nature website
Jeff Pippen North Carolina Wildflowers, Shrubs and Trees website
Tim Spira Wildflowers & Plant Communities of the Southern Appalachian Mountains and Piedmont, 2011 UNC Chapel Hill Press
Photo credit of red sourwood tree leaves , djbones Flickr

Photo from Pixabay

Richland Ridge Nature Notes Volume 1 Number 6
 June 2015
by Linda Martinson Certified Blue Ridge Naturalist

You may remember walking on the Richland Ridge trails last fall and noticing acorns everywhere, like ball bearings underfoot. And then noticing this spring a proliferation of small oak seedlings in every open space. It was “a good mast year” for acorns and therefore for the wildlife at Richland Ridge.

Mast is the accumulation of nuts on the forest floor, usually acorns in the Southern Appalachians. Approximately every three to five years, an entire population of trees across a fairly wide geographical area, produces together an over-abundance of wild nuts, as many as five to ten times more than during an average year. These bumper crop years are “good mast years,” and there is often a bumper crop of wildlife, such as bear cubs, the following spring because acorns are the most important wildlife food in most deciduous forests.

Why and how can trees coordinate a synchronous over-abundant nut production in a given year? The variable nut production of individual trees must have evolved as a survival strategy: if the nut production was constant from year to year, the animals that depend on mast would adjust, and almost every nut would be eaten every year. Certainly, the synchronous production of mast among a large number of trees is a superior survival strategy: when there is suddenly an over-abundance of mast produced in the forest one year, the wildlife population cannot eat all of it, leaving plenty to sprout and grow.

The big question is how masting trees manage to coordinate the same cycle with other trees over a large area in a given year? And it can be a large contiguous area; synchronous masting has been found among a million trees as far away from each other as 1500 miles. Despite extensive research on synchronous masting, until recently scientists had not developed a complete and definitive answer even though they had identified several factors that affect masting.

Weather, such as seasonal temperature extremes, wind, rain, drought, and other environmental stresses such as fire or pests do affect oak trees, but only in specific areas. Oaks are monoecious, i.e., they bear their male and female flowers on the same tree, so a late spring frost that kills all the flowers on oak trees in a given area certainly precludes a good mast year there. Also, oaks are wind pollinated and there are chemical signals carried from tree to tree by what is called pollen coupling, but pollen is usually effective only within a range of about 200 feet so it cannot account for all of the synchronous tree communication among masting trees. There has to be another component to tree communication beyond weather and other environmental factors and chemical communication through pollen coupling.

An emerging hypothesis explaining tree and other plant communication is from recent research proposing that an extensive underground network exists connecting plants by their roots and that it serves as a complex interplant communication system, kind of a “Plant Internet”. The organism that creates this immense biochemical highway is a type of fungus called mycorrhizae. The tiny filaments of the fungi form a symbiotic relation with plants, including trees, by colonizing the roots and sending extremely fine filaments far out in every direction into the soil, like extensions of the plant roots. Mycorrhizae increase the nutrient absorption of the plant 100 to 1,000 times, and these fungi also provide communication networks among the plants allowing them, for example, to develop natural chemical defenses against common pests such as aphids after they receive signals from a plant that has been attacked.

In one thimble full of healthy soil, there are several miles of fungal filaments releasing powerful enzymes that make communication and synchronicity among plants possible. One network of mycorrhizae was found weaving its way through an entire Canadian forest with each tree connected to dozens and hundreds of other trees through enormous networks of
mycorrhizae. These fungi networks also connect plants of different species, thereby possibly facilitating interspecies plant communication.

One characteristic of oak tree germination is its interesting life cycle. Soon after acorns fall, if they aren’t eaten almost immediately, they start to germinate, but they send out roots not shoots. Root growth continues until the ground gets too cold, then it continues in the spring along with the growth of shoots. It is possible that the immense mycorrhizae network connecting the plants in a healthy forest, including oak trees, can determine whether a sufficient number of acorns have developed roots and signal this information to oak trees in a large geographic area. It does sound like science fiction, but it is possible given the size and capabilities of mycorrhizae networks, and it could form a more complete explanation of the widespread synchronicity of masting trees in large forested areas.

Mycorrhizae underground networks have been found to have symbiotic relationships with more than 90 percent of plant species, and what is absolutely necessary for these fungal networks to exist and flourish is that the soil must be undisturbed. Soil erosion, tillage, compaction and other disturbances to intact healthy soil destroys beneficial fungi, and they are slow to recolonize once they are disrupted. If indeed the trees and plants in forests of Richland Ridge are able to communicate with each other through an extensive underground mycorrhizae network, kudos to us for keeping our forests healthy with relatively undisturbed soil. And hooray for good mast years, because as Ralph Waldo Emerson reminded us, “The creation of a thousand forests is in one acorn.”

References:
W.D. Koenig and Johanes Kropp American Scientist. The Mystery of Masting in
Trees. July – Aug 2005 Volume 13, Number 4. Page 340
BBC News Summary Science and Environment Fungus Network Plays Role in Plant Communication 10 May 2013