Details of the
Hubbard Brook Phytosociology programThis page contains Tom's notes about the details of the phytosociology programming for the Bird Area. 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.
2. "All live trees" includes healthy and sick trees. "All dead trees" includes standing dead and snags.
3. In 1981, 1991, and 2001, all trees >10.0 cm dbh were measured on each of four 2200 to 2900 m belt transects. Each transect was divided into plots 25 m long and 10 m wide for a total of 397 plots.
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!!
More detailed notes:1. There is some "fudging" in the calculations involved with filling out the 10 cm size class and care must be taken in selecting a diameter range that splits the 9.5 to 10.4 range (see Footnote 6). Since small tree data are not available for the Bird Area, this is not so much of an issue as with the some of the watersheds where you might want to enter a range of, say 5 to 10 cm. Using a lower diameter of 10 cm is fine so long as you understand that program automatically adds in an estimate for trees 9.5 to 9.9 cm dbh.
2. 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. 13.5 to 14.4 for the 14 cm class, 14.5 to 15.4 for the 15 cm class, etc.), and when run with the default size class choice of >10 cm dbh, the lower end of the range (10 cm) was 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 it is10, because this was 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 or whole 1 cm diameter classes (X.5 to X.4) in the "select a diameter" option.
3. Remember that one cannot expect to compare plots from 1981 to the other years. Trees were not tagged in 1981 and those on plot boundaries may have "drifted" in or out of the plot between 1981 and 1991 because the observer estimated the center of the tree to be in one year and out 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. Plots surveys with tagged trees (i.e. beginning in 1991) may be compared year to year.
4. The option for transect lines allows you to work with smaller spatial portions of the data, however there is no distinct difference in the vegetation among the transects like there is in the watershed "zones". The entire Bird Area is more or less similar to the "lower hardwoods" of the watersheds.
5. The following table includes tree species found in our vegetaion 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 November 2003
by Thomas Siccama and Ellen Denny