Details of the
Hubbard Brook Phytosociology programThis page contains Tom's notes about the details of the phytosociology programming for Watershed 5 (post-harvest). They are here as much for our remembrance of what we did as for the benefit of anyone else who needs to know the minutia.
There are some quick notes:
1. Snags are "standing dead trees" without branches but with a bole left above dbh. Dead trees are "standing dead trees" which still have most of their branches.More detailed notes:
2. "All live trees" includes healthy and sick trees. "All dead trees" includes standing dead and snags.
3. For all W5 post-harvest surveys, all trees >1.5 cm dbh were measured in each of the selected plots for that survey. In 1990, the plot system included 199 circular plots (1.37 radius) on the lower two-thirds of the watershed. In 1994, plots consisted of a 1 m strip (1 x 25 m) in each of 38 watershed grid units selected at random from the whole watershed. In 1999, plots again consisted of a 1 m strip (1 x 25 m) in each of 101 randomly-selected watershed grid units.
4. You should study the year-specific data documentation for the special details and access to the original raw tree by tree data.
1. The first W5 post-harvest survey was conducted on the spur of the moment in 1990 when it was realized how quickly the saplings were growing. A series of 199 circular plots, radius 1.37 meters (the length of a dbh stick), were sampled along transects on the lower two-thirds of the watershed. At higher elevations most saplings were not large enough to register a dbh. These plots do not correspond to the numbered W5 grid units, nor can they be located within the grid system since they were never marked. This is why they cannot be mapped or assigned an elevation. Seventeen plots had no trees large enough to measure (8, 19, 20, 54, 62, 83, 84, 86, 93, 100, 107, 120, 133, 145, 165, 177, 195).
The 1994 survey (conducted by Wayne Martin) included 38 of the 360 25x25m grid units. All trees were measured in a one meter strip along one side of the grid unit. Since the corner stakes have shifted over time, the actual length of the sample plot was measured and recorded and is used in the calculations.
The 1999 survey included 100 of the 360 25x25 m grid units that had been designated for vegetation studies (plus an extra one, probably surveyed accidentally). All trees were measured in a one meter strip along the west side of each of these 101 grid units, except in a few cases when using the south side made more sense. Since the corner stakes have shifted over time, the actual length of the sample plot was measured and recorded and is used in the calculations. There is some confusion about the lengths of Plots 2 and 8 in this survey. They are both recorded as 49.5 m, double the normal length. We know that for at least one survey plot, the operators missed a corner stake and set their tape the length of two grid units and measured all the trees in the extra large plot. If this was Plot 2, then starting at the top and measuring down the west side (field notes confirm the west side was measured) for about 50 meters would land one at the bottom of Plot 8. Thus it seems Plot 2 at 49.5 m in the 1999 survey should likely include the strip in grid unit 8 and there should be no separate field sheet for Plot 8. But there is a separate field sheet for Plot 8 which does not appear to have any duplicate trees. It in not clear whether someone tried to separate the trees from the extra large plot into two plots, forgetting to alter the recorded length of each of those plots, or whether there were actually two separate plots each with lengths of 49.5 m. We will probably never figure this one out, but note that the low basal area and density of these plots may or may not be reality.2. In designing the diameter distribution per hectare graph, some "fudging" was necessary to even out diameter classes. The program lumps all the trees that belong in each 1 cm diameter class (e.g. 3.5 to 4.4 for the 4 cm class, 4.5 to 5.4 for the 5 cm class, etc.), and when run with the default size class choice all diameter classes end up even. This is because, in contrast to many of our other surveys where trees < 2.0 cm were not included, (thus eliminating half of the diameter class--see Footnote 6), the W5 post-harvest surveys include trees >1.5 cm thus encompassing the full 2 cm diameter class (trees 1.5 to 2.4 cm). However, if the "select a diameter" option is used and the selected lower or upper diameter is an integer, then really only half of the diameter class for these endpoints is included in the calculation (e.g. 5 to 10 includes only 5.0 to 5.4 for the 5 cm class and 9.5 to 10.0 for the 10 cm class). So that the 1 cm classes on the ends of the selected range don't come up short, the program doubles the stem count for the lower diameter and upper diameter values. This doubling is based on the assumption that there will be about the same number of stems in either half of a 1 cm diameter class. It was assumed most users will enter integers in the "select a diameter class" option, so this only works if the entered value is an integer. If the selected range is 4.5 to 10.4, nothing will be doubled, but because this choice includes whole 1 cm diameter classes (4.5 to 5.4 for the 5 cm class and 9.5 to 10.4 for the 10 cm class), the graph will be correct anyway. However, if the selected range is 4.8 to 10.1, nothing will be doubled and both the 5 cm and 10 cm diameter classes will look short in the graph (4.5 to 4.7 trees are not accounted for, nor are 10.2 to 10.4 trees). Therefore, it is recommended to use either integers or whole 1 cm diameter classes (X.5 to X.4) in the "select a diameter" option.
3. The option for "zones" corresponds to five general areas of the watershed which are loosely defined forest community types existing at the time of the survey in 1982. The "high spruce-fir" was on a portion of the ridge and was largely dominated by red spruce, fir and white birch - it comprises 73 of the 25 x 25 m grid units (zone 1 in the raw data file). The "middle spruce-fir pocket" includes 15 plots there were isolated from the high spruce-fir and was dominated by spruce and yellow birch (zone 2). The "high hardwoods" includes 33 plots which are on the ridge and shoulder of the ridge and were mostly sugar maple and beech (zone 3). The "middle hardwoods" includes 146 plots and were the portion of the watershed above the middle rain gauge clearing and below the start of the steep ledges (zone 4). The "lower hardwoods" were sugar maple, beech and yellow birch and include 93 plots (zone 5). For the sake of continuity, we decided to keep these zones for summarizing post-harvest surveys even though the regrowth vegetation does not initially show distinct differences among these previously-defined zones.
4. The following table includes tree species found in our vegetation surveys.
# Acronym Common name Scientific name 1 ACSA Sugar maple Acer saccharum 2 American beech Fagus grandifolia 3 Yellow birch Betula alleghaniensis 4 White ash Fraxinus americana 5 Mountain maple Acer spicatum 6 Striped maple or moose wood Acer pensylvanicum 7 Pin or fire cherry Prunus pensylvanica 8 Choke cherry Prunus virginiana 9 Balsam fir Abies balsamea 10 Red spruce Picea rubens 11 White or paper birch Betula papyrifera 12 Mountain ash Sorbus americana 13 Red maple Acer rubrum 14 Eastern hemlock Tsuga canadensis 15 unknown, used for unidentifiable rotten snags 16 Quaking aspen Populus tremuloides 17 Black cherry Prunus serotina 18 Shadbush Amelanchier sp. 19 Big-tooth aspen Populus grandidentata 20 Willow Salix sp. 21 Alternate-leaved dogwood Cornus alternifolia 22 Cherry (unspecified) Prunus sp.
For any further questions, please email thomas.siccama@yale.edu.
Web page created March 2004
by Thomas Siccama and Ellen Denny