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Harvard Forest Symposium Abstract 2005
- Title: A Regional Context for Northern Red Oak Growth Rates at the Harvard Forest
- Primary Author: Neil Pederson (Harvard Forest)
- Additional Authors: Gordon Jacoby (Columbia University in the City of New York); Elizabeth Hammond Pyle (Harvard University); Steven Wofsy (Harvard University)
- Abstract:
Measurements at the Harvard Forest (HF) have indicated an average net uptake of roughly 2tC/ha annually in the second-growth forest surrounding the eddy-flux tower. The forest composition is dominated by northern red oak (Quercus rubra L.) (NRO) and red maple (Acre rubrum L.), with NRO the primary contributor to carbon uptake. We have created a tree-ring based network of NRO growth data covering the New York State and New England region (NYNE) from western NY to eastern Massachusetts and from northern New Jersey and coastal Rhode Island to the central Adirondack Mountains and northeastern Vermont. The network includes stands with a range land-use histories and stand-level productivity. Most populations are 100-140 years old. The network is used here to address the following question: “Is stand-level productivity of the HF Tower Plot NRO forest typical of NYNE?”
Increment cores were taken from at least 20 trees per population, processed and crossdated using standard dendrochronological techniques. A new methodology was used to determine stand productivity. Because disturbance is a significant constraint on growth in closed-canopied forests, we felt it necessary to reduce the influence of canopy disturbance to study site productivity. Each time series was examined for a step change increase in growth, which is evidence of a release from suppression. Suppressed growth was removed from each time-series. Each series was then realigned so that the first year of post-disturbance growth is Year One, even though the tree may be chronologically 100 years old. Average annual increment is calculated within each population to create an index of disturbance-normalized growth rates. Each index was placed into a NRO allometric equation to reconstruct average annual carbon uptake. This methodology reduces the influence of age and climatic trends as the averaging process for each year includes trees of different ages or from different time periods.
Rates of carbon uptake at the HF Tower Plot (thick red line) are lower than the NYNE average (thick green line) (Figure 1). Wachusett Mountain (purple line), the best example of old-growth NRO, has some of the lowest rates of carbon uptake. Growth rates of northern-range-margin sites (light blue lines) are also below the NYNE average.
The highest carbon uptake rates are found in the Lake Ontario Plain and Southern Tier of NY State (lines with inverted triangles). The exception to this trend is the population of NRO in Mohawk Trail State Forest, MA (orange line). The population with the highest rates of uptake (Niagara, NY – brown line) is growing on relatively fertile soil on the shore of Lake Ontario. The two populations in this subregion with the lowest rates of uptake are in forests on thin-soiled ridges (Naples and Hartwick College).
Our NRO carbon uptake network indicates that the HF Tower Plot is just below the NYNE average of potential productivity. Old-growth NRO forests tend to be found on sites with lower-productivity and support previous findings on the potential locations of extant old-growth. Highest rates of carbon uptake are found on sites with better soil development suggesting the new methodology presented here may reasonably capture stand-level productivity. These results suggest that HF is a typical NRO forest in our study region. This network will be further analyzed to identify the abiotic and biotic constraints on long-term growth rates.
- Research Category:
