Details of the
Hubbard Brook Phytosociology programThis page contains Tom's notes about the details of the phytosociology programming for Watershed 1. 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 a lot of 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. In 1996 and 2001, all trees >10 cm dbh were measured in each of the 200 25 x 25 m grid units. The 2.0 to 9.9 cm trees were measured in a 3 x 25 m subplot in each of the 25 x 25 m 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.
5. There are several ways of selecting plots which are redundant, and all the various selection processes are here because the author was trying to learn how to create all these options. The answers should cross check - so if you select plot 44 in option 2 and or enter plot 44 under the single plot option you should get the same results!!1. Watershed 1 differs from Watershed 6 in that there are two rain gauge clearings imbedded within the watershed area. The plot grid system includes these areas. Some plots are only partly forested and thus the plot area of forest is not the full 25 x 25 meters. In these cases we have estimated the area of the plot which is in forest and that is the area used in the calculations for that plot. In one instance there is a plot (number 144) which is entirely within the area of the clearing and has no trees on it. There is no data for plot 144 in the data set - the data goes from plot 143 to145. We think that the program accounts for this OK. We have left the plot number 144 in the list of plots but the program does not include it in the calculation of the forested area.
2. There is some "fudging" in the calculations involved with filling out the 2 cm and 10 cm size classes and care must be taken in selecting a diameter range that splits the 9.5 to 10.4 range or the 2.0 to 2.4 range (see Footnote 6).
3. In designing the diameter distribution per hectare graph, again 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 a standard size class choice, the lower ends of the range (either 2 cm or 10 cm) were already doubled to account for missing trees as explained above (and in Footnote 6). 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. 20 to 30 includes only 20.0 to 20.4 for the 20 cm class and 29.5 to 30.0 for the 30 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 (unless they are 2 or 10, because these were already doubled earlier in the program). 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 19.5 to 30.4, nothing will be doubled, but because this choice includes whole 1 cm diameter classes (19.5 to 20.4 for the 20 cm class and 29.5 to 30.4 for the 30 cm class), the graph will be correct anyway. However, if the selected range is 19.8 to 30.1, nothing will be doubled and both the 20 cm and 30 cm diameter classes will look short in the graph (19.5 to 19.7 trees are not accounted for, nor are 30.2 to 30.4 trees). Therefore, it is recommended to use either integers (except 10; see Footnote 6) or whole 1 cm diameter classes (X.5 to X.4) in the "select a diameter" option.
4. Remember that one cannot expect to compare plots from year to year. Trees on the plot lines may "drift" from one plot to the next between years because the observer estimated the center of the tree to be on one plot in one year and in the adjacent plot the next time (see Footnote 5). So there are situations where the basal area of a plot may jump or drop considerably because a single large tree is right on the line and may have ended up in one plot in one year and another plot the next time.
5. The option for "zones" corresponds to four general areas of the watershed which are loosely defined forest community types. The "spruce-fir" is on a portion of the ridge and is largely dominated by red spruce, fir and white birch - it comprises 23 of the 25 x 25 m grid units (zones 2 and 4 in the raw data file). The "high hardwoods" includes 34 plots which are on the ridge and shoulder of the ridge and is mostly white birch and beech (zones 1 and 3). The "middle hardwoods" includes 89 plots and are the portion of the watershed above the middle rain gauge clearing and below the start of the steep ledges (zones 5 and 6). The "lower hardwoods" are sugar maple, beech and yellow birch and include 54 plots (zone 7). This latter area is probably more typical of the "Northern Hardwood Forest" than the "high hardwoods".
6. 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 January 2003
by Thomas Siccama and Ellen Denny
Last Modified