Forest Succession

Dr. Frank Egler (1910-1996) devoted most of his life’s work to the research and study of vegetation, and plant and forest succession. Forest succession is about how such ecological communities start, grow and change over time at different scales in different places and bioregions.
 
After his studies and some initial academic research, he settled at age 35 in Norfolk. He actively studied and worked in the changing lands around him in the northwest corner of CT. He maintained plots where he manipulated existing vegetation and introduced new native and some non-native species. This was at a time when abandoned farms and fields were reverting to forest. Nowadays the state of  CT is 58% forested, up from just 10-20% at the peak of agriculture, charcoaling and industry in the late 1800s. The town of Norfolk is now 90% forested.

In large part the forests of Aton are Northern, Mixed or Transition Hardwoods (including oak-hickory and red oak), Red Maple and Hemlock Swamps. See The Vegetation of Aton Forest Summary. Most stands have trees averaging 100-120 years of age, within which there is variation, depending upon geology, aspect, soil and land management history. More intensive study could reveal that some of these stands are in excess of 150 years in age..
 
Forest succession was the overarching ecosystem phenomena which tied Egler’s work together:

– Initially Egler had pursued practical research programs for Right Of Way management, selectively using herbicides to manage growing and evolving communities of plants and trees. See: The Plight of the Right of Way Domain: Victim of Vandalism. Egler, 1975.
– For many decades he maintained research plots, pursuing “long-term, low-cost. low-key” management in the ever changing fields around the Norfolk family house, and wrote research papers.
– Finally, he practiced and wrote about naturalistic landscape gardening.
 
In a simple sense, succession is the process of plant species change in a given ecological community in space over time. There is the initial “colonization” in a new habitat (imagine a new island emerging from the ocean) or after a disturbance (think of a hurricane blow-down of an entire forest) of a pre-existing habitat. Succession that begins in new habitats, uninfluenced by pre-existing communities, is called primary succession (think of “pioneers”), whereas the succession that follows disruption of a pre-existing community is called secondary succession. Both are dynamic, with the latter often more complex, dependent upon initial conditions, climate, soil, the absence or presence of different species, and of course more.

His model “Initial Floristics” (Vegetation Science Concepts I. Initial Floristic Composition, a Factor in Old-Field Vegetation Development. Egler. Vegetatio, 1954, Vol. 4, No. 6 (1954), pp. 412-417) hypothesized that succession was importantly influenced by existing initial conditions (seed pack, prior disturbance, physical conditions) in a less predictable set of processes not adequately captured by “Relay Floristics”, the dominant Clementsian model of forest succession. This traditional model was known as “plant succession to climax”, where discrete plant communities not only succeed one another in a deterministic way, but each proceeding stage preparing the way for the next stage, almost like in a relay race. The stages are Nudation (bare area), Migration (arrival of species), Ecesis (establishment), Competition (species vying for resources), Reaction (habitat changes), and finally Stabilization into a climax community.

“Ecological research has long focused on understanding and predicting forest succession.” See “Review of Forest Succession Models” 2009. 50 years before Clements, Thoreau observed in his “The Succession of Forest Trees and Wild Apples” 1868 that: “When, hereabouts, a single tree or a forest springs up naturally where none of a kind grew, I do not hesitate to say it came from seed … no other tree has ever been known to spring from anything else. If anyone asserts that it sprang from something else, the burden of proof lies with him.” (p. 35).

Frank Egler was a highly gifted and opinionated academic who kept up with new developments in the field and corresponded feverishly with ecologists of the day, arguing about different models and theories of forest succession. His work was deeply informed by his applied research and outdoor field practical activities where he collected facts and tested out hypotheses. He reveled in argumentation and his style of writing was colorful and unique.

Frank E. Egler originally studied under a number of pioneering ecologists of the first and second generations. Some of Egler’s initial mentors included George E. Nichols, Egler’s Ph.D. mentor at Yale, William S. Cooper, his M.S. mentor at the University of Minnesota, and Henry C. Cowles, who Egler considered his undergraduate mentor at the University of Chicago. He also studied at the time of Henry A. Gleason, an elder statesmen of that first generation of ecologists.
 
In this period there was vigorous and rich debate about successional theories and underlying mechanisms. Clements’ observations were developed into theory with specific and original concepts and vocabulary, and he published perhaps the first scientific explanation for the process of succession in his book, Plant Succession: An Analysis of the Development of Vegetation. Clements held that different secondary plant communities were highly predictable and deterministic and converged on a climatically determined stable “climax communities” regardless of starting conditions.

Others like Henry Allan Gleason of the New York Botanical Garden believed in a succession model that was more complex and much less deterministic, suggesting a much greater role of chance factors, denying the existence of coherent, sharply bounded community types link, and pointing more to a “mosaic” of possibility and outcomes. Philosophically, Frank followed many of the viewpoints of Gleason who saw plants respond to environmental change according to their own tolerance limits, and with changing and unpredictable distributional patterns over long time spans.

From his Norfolk hilltop Egler was a vigorous participant in many of these often deadly academic debates, and a life-long outspoken critic of F. E. Clements’s model of ecological change, one that postulated a “climatic climax” end-point for vegetation types. This is all well chronicled in Magnificent Failure: Frank Egler and the Greening of American Ecology. An Epistolary Biography, by William Dritschilo.

Below are just some examples of Aton Forest research of forest succession, including Frank’s magnum opus, The Nature of Vegetation, 1977. See: The Nature of Vegetation: Its Management and Mismanagement

Behavior of Aton Forest Phytotaxa, 1925-1991. Civco
View PDF of the Behavior of Aton Forest Phytotaxa, 1925-1991. Civco

The Life and Death of Old Fields. Anderson, 2009
The Life and Death of Old Fields

Egler contributed meaningfully to the evolution of forest succession theory and study. For more about Frank, check out Frank Egler biographical page.