Saturday, July 25, 2009

Hockomock Swamp, Old Growth Cedars

Back in the late summer of 2003, I walked through the old Old Colony Railroad bed through the heart of the Hockomock Swamp near the Easton/Raynham town line and found a number of stands of very large, very old Atlantic white cedar (Chamaecyparis thyoides). Only on my birthday in July 2009 was I able to return to this spot with a camera, and only for a short time. Luckily, the sun had come out after a torrential thunderstorm the night before.

Despite the conventional wisdom, the Hockomock Swamp is not muddy nor filled with mud. It is certainly wet, during the wet season, but the water is as clear and clean as spring water. In the place where I found these old growth cedars, the water in the Hockomock is perhaps more clean and pure than any water in the world, because it is filtered by miles of undisturbed swamp. It is probably the safest, cleanest water to drink that can be found.

And contrary to conventional wisdom, the Hockomock is not hard to walk in. Yes, you need to let your feet get wet, but in the summer, on a sunny day, the feeling is like walking along a beach with the waves lapping over your shoe tops. Apparently, what I found in this deepest part of the Hockomock is a mature Atlantic white cedar swamp that has not been cut or logged or disturbed for at least 150 years -- and possibly ever. The trees are large and tall with branches beginning 20-30 feet above their trunks and an understory of smaller trees and shrubs scattered among beds of sphagnum moss. And contrary to most wisdom, plenty of light reaches the swamp floor, because the canopies of the mature trees do not completely meet and intermingle, but instead leave gaps often as wide as their crowns.

Make no mistake. In the photos above you are seeing a place that almost nobody has seen or walked in for centuries. Yet it is just a 15 minute walk from the Raynham Dog Track. Judging by the size of the Atlantic white cedars here and the lack of any cut cedar stumps (which are easily visible right alongside the railroad bed), these stands have never been cut and have rarely, if ever, been visited by humans.

The first photo in this sequence shows a forest of sphagnum moss. Sphagnum moss is the little engine that could of the Hockomock. It is what makes all of the life possible in the swamp, because it prefers to grow with its feet constantly wet. Beneath this bed of electric green sphagnum is a bed of old, dead sphagnum 40 feet deep -- peat moss. You would have to dig down the length of a telephone pole to find a single bit of soil, or rock, or dirt, or sand. It is all vegetation. That's why the Hockomock is not muddy. To be muddy, there must be mud. And mud is made mostly of mineral soil. There is no mineral soil in the Hockomock, except so deep that it is where early humans followed caribou on a tundra 10,000 years ago and built tiny fires from twigs of trees only shoulder high. Somewhere, down very deep in this peat, many feet below the living layer of sphagnum moss are the footprints and fluted points and graves of those who watched as the mountainous glaciers receded to the north.1

How old are these cedars?

The biggest white cedar I found is 25 inches in diameter. Not having a tape measure, I estimated the tree's diameter by putting my arms around it, and my hands could not touch each other. Back home, I measured the distance of my outstretched arms and got a figure of 72 inches. Adding six inches to this (since it seemed that my hands were a few inches shy of touching when wrapped around the trunk) gives a circumference of 78 inches, which divided by pi, gives a diameter of 24.8 inches.

A "honker" Hockomock cedar with Queequeg T. Dog, Ph.D providing a size comparison. This Atlantic white cedar is approx. 25 inches in diameter at breast height.

The next question is whether this stand of white cedar regenerated from a stand that was cut when the Old Colony Railroad railbed was cut through the swamp in 1866.2 A stand that regenerated from a cut in 1866 would now be 140-150 years old. Given the documented growth rates and age vs. diameter of white cedar studied in southern New England, it would be very possible that the seedlings and small trees that were left from an 1866 cut would be in the average size range seen in this stand, ie. 14-16 inches in diameter.

However, a 25 inch diameter cedar in southern New England is of sufficient size to be as much as 200 years old. This cedar may predate the 1866 construction of the Old Colony Railroad bed by 50 years. This tree suggests that some parts of this cedar stand were logged lightly or not at all when the railbed was built; and strongly suggests the stand has not been logged in the 143 years since the railbed was built.

Atlantic white cedar is noted for being extremely resistant to rot and decay. For this reason, past logging should be shown by cedar stumps. The white cedar in this part of the Hockomock grow on massive humps or hummocks elevated three or more feet above the wetted part of the swamp. The humps created by the trunks and roots of these cedars are the highest ground in the stand. You have to literally climb up these hummocks in order to stand alongside the trees and examine them. In order for 19th century loggers to cut these trees with two-man saws, the cuts would have been made about three feet above ground level, leaving behind a considerably large stump well above the swamp floor. At least some of these stumps, particularly those from large cedars, should still be visible today.

Interestingly, there are cedar stumps of this type just outside the railbed, where the carted-in gravel and fill was used to raise the railbed above the swamp. But once you walk more than 100-150 feet away from the railbed and into the swamp , there are no cedar stumps. Because on this most recent visit I was focussed on documenting the character of the cedar stand with video and still cameras, I was not specifically searching out evidence of stumps in the part of the stand farthest from the railbed. As such, it is possible that a focussed effort to search for stumps deeper in the stand might reveal them.

The lack of any obvious stumps in the cedar stand away from the railbed suggests, pending a more detailed survey, that the builders of the Old Colony Railroad bed confined their logging operations to the immediate vicinity of the railbed and did not venture deeper into the adjoining swamp to cut trees purely for their value as sawlogs. If this was the case, it is possible that the stand of Atlantic white cedar documented here may not have been cut at all during the construction of the railbed in 1866. And because this part of the swamp was completely inaccessible and pathless prior to construction of the railbed in 1866, it is doubtful this stand of cedars was ever cut prior to 1866. This history presents the possibility that some or all of this cedar stand was never cut at all.

Another clue to the age of the stand is found in the ratio of cedars (C. thyoides) to red maple (Acer rubrum). The cedar stand documented here is atypical for the Hockomock. It is not a thick, pure, even-aged stand of white cedar with trees just a short distance apart from each other in an impenetrable and nearly lightless tangle of live, dead and fallen trees. This type of thick, dense cedar swamp forest is characteristic of the species throughout its range. The density of trees in Atlantic white cedar swamps is a key reason why they were so commercially valuable and so aggressively clearcut. It is estimated that more than 98 percent of the Atlantic white cedar swamps in the United States have been destroyed by logging.

Atlantic white cedar tend to grow in pure, dense, even-aged stands. Prior to the onset of logging in the 1700s, forest fires, windstorms and hurricane periodically created large openings in cedar swamps which destroyed enough of the standing trees to allow a new generation of trees to seed and replace them. A key clue which supports this theory is that young cedar require a sunny, well-lit, open forest floor to germinate and grow.

Unlike many New England trees, young cedar cannot survive for more than a few years in the deep shade created by their parents towering over them. For this reason it is believed that cedar swamps require periodic disturbances which remove large sections of the mature cedars in order to regenerate. Absent such disturbances, a mature Atlantic white cedar swamp would, after several centuries, become dominated by red maple (Acer rubrum). This is noted by Stoltzfus and Good:

"The pattern suggested in these earlier studies is that A. rubrum eventually replaces C. thyoides over time. As large canopy individuals die within even-aged stands, Acer rubrum individuals invade the gaps and eventually dominate. The mature-state or old-growth stand thus becomes dominated by A. rubrum rather than C. thyoides. Wetland forests dominated by C. thyoides can be maintained only by continued disturbance whereby the canopy and shrub layers are removed, providing open conditions in which C. thyoides can regenerate."3

Modern silvicultural research shows that the germination of Atlantic white cedar is almost completely halted if the cones fall into a leaf litter of hardwood and shrub leaves, ie. the typical floor of a red maple swamp.4 In other words, what we know about Atlantic white cedar suggests that mature cedar swamps eventually "go out of business" due to their own success and become red maple swamps when they remain undisturbed for a period of time longer than the natural life expectancy of the existing cedar stand (ie. 2-3 centuries).

If this successional model is true, we should expect that a very old cedar swamp that has not been disturbed by fire or hurricane-induced blowdown would be comprised of a fair number of large, old even-aged cedars in a swamp dominated by red maple and other deciduous trees and shrubs.

This perhaps describes the origin of the mature Atlantic white cedar stand in the Hockomock west of the railroad bed at the Easton/Raynham town line.

Tree Companions of the Hockomock White Cedars

This is a black gum or tupelo (Nyssa silvatica), growing beneath an old growth Atlantic white cedar.

This is a yellow birch (Betula alleghaniensis), growing beneath an old growth Atlantic white cedar.

Canopy view of the Hockomock old growth cedar stand with mature Atlantic white cedar at the top and mature red maple (Acer rubrum) at the bottom. All trees shown are approx. 50-60 feet in height. Note the significant gaps in the canopy.

1Stone tools from the Early Archaic period (9,000-8,000 years ago) have been found along the shore of Lake Nippinicket, at the southern end of the Hockomock. See Kathleen Anderson and Ted Williams et al. 1968. "The Hockomock: A Wonder Wetland." Privately published. See also,"Taunton River Wild & Scenic Study, Notes from Archaeology Experts Meeting, 5/14/2003."
2Easton Historical Commission. 2008. "Town of Easton Historic Preservation Plan." Town of Easton, Mass. Available as 3.5 mb pdf file.
3Dwight L. Stoltzfus & Ralph E. Good. 1998. "Plant Community Structure in Chamaecyparis thyoides Swamps in the New Jersey Pinelands Biosphere Reserve, USA." in Coastally Restricted Forests, Aimlee D. Laderman, editor. Oxford University Press.
4 Aimlee D. Laderman. 1989. "The Ecology of Atlantic White Cedar Wetlands: A Community Profile." U.S. Fish & Wildlife Service. Biological Report 85 (7.21). Washington, D.C.

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