Garden Notes : Seeing the forest and the trees
Photo by Susan Safford
As the year progresses and summer draws to its climax, the light shifts. In its annual solar cycle, Earth has tilted away from the sun and the wavelengths of sunlight reaching Earth have shifted towards the infrared. Observing backlit foliage, nature's solar panels, gives the impression that there is a difference, a distinctive quality, to that sunlight: practically quivering and glowing, more interesting and vital — almost as if commanding, "photosynthesize, NOW."
It is generally agreed that forests, one of Earth's largest carbon sinks, are under increasing amounts of stress as a result of climate change. According to a BBC article, carbon sinks play a key role in the global carbon cycle and are promoted as a way to offset rising emissions.
All forests are facing conditions differing from those under which they evolved, although coniferous forests are particularly vulnerable. Now, the BBC article continues, a report has been released that purports to show that European forests' ability to act as carbon sinks is slowing. Published in Nature Climate Change, it said this was a result of a declining volume of trees, deforestation, and the impact of natural disturbances.
The carbon cycle is the process by which carbon — essential for life on the planet — is transferred between the geosphere, biosphere, hydrosphere, and the atmosphere. Carbon sinks are where key components of the cycle store carbon, preventing it from being recycled.
Since the Industrial Revolution, human activity has modified the cycle as a result of burning fossil fuels and land-use change. Burning fossil fuels has resulted in vast amounts of carbon previously locked in the geosphere being released into the atmosphere. Land-use change, such as urbanization and deforestation, has reduced the size of the biosphere, which removes carbon from the atmosphere through photosynthesis.
The conclusions of the researchers, based at Wageningen University and Research Centre in the Netherlands, appear to contradict an earlier 2011 report on the State of Europe's Forests, which said that trees covered almost half of Europe's land mass and absorbed about 10 percent of Europe's annual greenhouse gas emissions. However, a sizeable proportion of forests were mature stands of trees, which were mainly planted in the early 20th century or post-World War II.
A spokesperson for the new report, co-author Gert-Jan Nabuurs, explained that these forests are now 70–80 years old and are beginning a phase in the life of a tree where the growth rate starts to come down. "So you have large areas of old forest and even if you add these relatively small areas of new forest, this does not compensate for the loss of growth rate in the old forests."
Weighing the carbon sink value of younger forests against the biodiversity and wildlife/habitat value of older ones is an issue that also faces landowners and conservation organizations on Martha's Vineyard.
I surmise that young, fast-growth trees such as locust, sassafras, red cedar (juniper), and pitch pine are critical carbon accumulators at that nurse stage of forestation, but are often disdained, however, for their invasive qualities when what is wanted is picturesque field and pasture, or stately woodland.
An Island tree, the black locust, Robinia pseudoacacia, which functions as a nurse tree for reforestation of other tree species and is known for fast growth (which equals greater carbon sequestration), appears to be in trouble. Furthermore, locusts are a rich source of bee forage and fragrant, delicious honey.
Wherever one looks, the locusts are defoliating and showing signs of dieback. It is normal for locust to die once the woods it has helped to nurture have engulfed it. However, many of the struggling trees are in open areas where they might have been expected to live for decades more.
According to Wikipedia, "In 1900 it was reported that the value of Robinia pseudoacacia was practically destroyed in nearly all parts of the United States, beyond the mountain forests which are its home, by locust borers which riddle the trunk and branches.
"Were it not for these insects, it would be one of the most valuable timber trees that could be planted in the northern and middle states. Young trees grow quickly and vigorously for a number of years, but soon become stunted and diseased, and rarely live long enough to attain any commercial value."
Is this a banner cycle for locust borers, or is there a new, different affliction of these trees?
My home gardens are suffering from the presence of stately white oaks, seven of them, if "suffering" is the right word. It may be only myself that is suffering this Procrustean dilemma. Although ornamental gardens' design can adapt and evolve through changing light conditions, the gardens are losing light, critical for vegetables. When I contemplate removing the seven white oaks, all of which must be between 90 and 125 years old, I feel as if I simply cannot do it. Then I look at my vegetable garden, sitting there, unable to ripen its crops properly.
In the Garden
Onions, harvested several weeks ago, have cured to the point where the stems are dry and almost non-existent. I use an old, discarded screen door on sawhorses in a ventilated shed, and lay them out on this to air dry. Now, the stems and remnants of roots can be cut off with kitchen shears.
Be choosy about what you plant. It is really laborious to get rid of something that has outstayed its welcome, such as adenophera. It invades all its neighbors, all of which must be lifted and cleansed of its roots, so I am working on "sanitizing" a portion of border. Every perennial in one section has been dug up and set aside. Contact me for divisions of Siberian and intermediate bearded iris.