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White Oak Regeneration, Is It a Crisis or Not?

Monday, July 17, 2017, by Nicholas Patel
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[Using an increment borer to core the 234 year-old white oak at the Mohawk Trail State Forest that has only very recently reached the canopy. Photo by Neil Pederson]Scientists and foresters have documented and monitored the increasing mortality of oak trees in the United States for over the past century. This decline has become a high-profile issue because oaks account for one third of our nation’s hardwood saw timber volume, most of which is coming from eastern states. Of the 20 commercially valuable oak species, white oak is the most important in the United States’ timber market. White oak is a slow-growing species with a territory ranging from northern Florida to southern New England. One part of this decline is that many forest ecologists and forestry manuals report a widespread lack of young white oak saplings in the understory of forests with white oaks in the canopy.  However you can still find some oak saplings in the understory of these forests.  In the absence of this younger generation, there is the concern that white oaks will disappear from many forests after all of the canopy white oak trees have died. Fire exclusion, insect defoliators, and climate change are some of the factors that have been implicated with this failure to regenerate.

Following European settlement, approximately 60-80% of New England forests were cleared for agriculture. Much of this land was then allowed to revert back to forests in the mid to late 1800s when agriculture moved to the Midwest. Consequently, much of New England’s forests are relatively young (100-150 years old) second growth forests. This is important because when land is reclaimed for forests, it takes over a century at least for it to mature enough to the point where it has enough light from the canopy gaps of dead trees to support understory regeneration.

[Mounted and labeled tree cores. The top core is not sanded or dated, while the bottom core has been sanded and its annual rings measured and dated. Photo by Nick Patel]I am spending this summer investigating this “regeneration crisis” and exploring how dire the current situation really is for white oaks. At its core, I wanted to establish how long white oaks can persist in the low light conditions beneath the canopy. This knowledge is important because the longer a tree can persist in the understory, the greater chance it has to live a long life and continue to reproduce. My mentors, Neil Pederson and David Orwig, and I hypothesize that because many New England forests are still relatively young, they are likely still in the early phases of development and therefore we would not expect to see much understory regeneration anyway. If white oaks can endure understory conditions for a long time, then maybe only a relative few trees need to survive during the understory re-initiation phases in order to establish a new generation of white oaks.

[The sinewy, twisting trunk of this small diameter tree exhibits the characteristics of extreme persistence that define older trees. Photo by Neil Pederson]We sampled approximately 100 trees of different canopy statuses and sizes at four different sites across Massachusetts: Wright Woods in Concord, Lincoln Conservation Trust in Concord, the forest around Harvard Pond in Petersham, and in the Mohawk Trail State Forest in Charlemont. The first three sites are younger, second growth sites while the Mohawk Trail is an old growth site. For each tree we took a tree core and performed an assessment of the competition for light from the surrounding trees. The tree cores are taken by drilling into the trunk at chest height (Picture 1) with an increment borer. The borer only removes a small section of the living cambium and therefore does not significantly harm the tree. Back in the lab, I mounted and sanded the tree cores (Picture 2), dated their rings, measured the width of each ring using a measuring stage, and crossdated the cores using a statistical program in order to verify that I had assigned the correct date to each ring.

[Scenic outlook at summit of Todd Mountain from our sampling field day at the Mohawk Trail State Forest. Photo by Dave Orwig]I am still in the process of generating and analyzing the results of this study. However, our initial findings indicate that the so-called regeneration crisis may not be as severe or irreversible as many people think. At all of our sites we have found trees that have survived under the canopy for over 150 years, with one tree (Picture 1) having persisted in this stressed position for almost 230 years. This tree is fascinating because as can be seen from its small size, it highlights the misconception that old trees are always large trees. There are still further questions that I want to answer with my data. Can white oaks typically recruit to the canopy without canopy gaps forming? Is there a relationship between our competition index and tree growth and age? Answering these questions is significant because it could suggest the possibility of far cheaper forestry management practices. Instead of selectively burning and cutting lands in order to allow the oak seedlings to grow without competition, this research shows that if forest managers just let the forest grow through its normal development trajectory then there will still be ample opportunity for white oak regeneration to occur.

So far my summer has been packed with things that make the experience both informative and incredibly enjoyable. I have two excellent mentors who have taught me all about dendrochronological techniques and methods (and the tree ring lab has AC), the food is fabulous, my fieldwork takes me all over the state to many scenic vistas (Picture 4), and our lab group trip to the Adirondacks last weekend was spectacular.

Nicholas Patel currently attends Swarthmore College and is studying Biology and Environmental Studies.