Notice the 1860-1900, 1900-1920, and 1938-1940 periods, all caused by disturbance.
The final update! Well, here I am again to give you a final update of the going-ons of my project. Upon completing the remote sensing part of my study, I’m not surprised at the findings. The orientation of the downed tree boles are completely contained within 30 degrees of due west. This is consistent with east-southeasterly winds present during the Hurricane of 1938. It’s a relief knowing that now I can attach my data collection with a certain event.
After consulting with Charlie Cogbill, a historical ecologist and allometry enthusiast, I have reduced a set of allometric equations to describe biomass using only measured tree heights. Not only were the results surprising, but substantially large. The equations estimate that the Hurricane of 1938 downed about 15-35 , enough to substantially change the carbon pool and nutrient cycling of Watershed 6.
However, what does this say about the history of Watershed 6? Of the Hubbard Brook valley for that matter? Using the information gathered from my study, combined with that of Charlie Cogbill’s and building on others work such as Yamaski and Leak (2006) or Leak (1987) I have preliminary conclusions. What happened in Watershed 6? Here’s what a timeline of above ground living biomass (AGLB) of Watershed 6 would look like: I’d say that the Great Gale of 1815 reduced AGLB 15-35 followed by a 50 year recovery period. Then came the Spruce cull of 1870, which reduced the AGLB about 40 . By this point the AGLB is down to about 170 . Then comes the general cut, which slams the Watershed and reduces the biomass even further to 80 , followed by an 18 year recovery and regrowth period. The recovery period allowed the biomass to rise to 110 , before dropping another 50 from the Hurricane of 1938. Since 1938, the Watershed had gone basically undisturbed except for a few droughts and soil freezes.
The biomass curve looks as such:
Understanding the historic carbon flow through an ecosystem is particularly important at Hubbard Brook. Watershed 6 plays a major role as the biogeochemical reference watershed, giving understanding and significance to the watersheds in which experiments are performed. How much of the current carbon budget was supplied by the Hurricane of 1938? A lot? Any? Without a solid understanding and knowledge of previous nutrient cycling, can we really consider it a control?
Judging by the amount of biomass on the forest floor and the motives of the loggers to harvest primarily Spruce and Hemlock, a hardwood harvest seems unlikely. If the loggers were after hardwoods, the general cut would have been much more extensive. In addition to the merchantable interests of the loggers, the sawmill and Mirror Lake could simply not handle hardwoods nor could they river float them (Hardwood is too dense to float). Surveys provided by Bormann et al. (1970) confirm that cutting stumps were only present throughout half of Watershed 6 further confirming the Spruce theory. All evidence seems to paint a picture of what the dominant species of the forest once was. In addition to current dominants such as Beech, Yellow Birch, and Sugar Maple, Red Spruce could have possibly composed about 40% of the forest.