Details of the
Hubbard Brook Phytosociology programThis page contains Tom's notes about the details of the phytosociology programming for Watershed 5 (pre-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 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 the 1982 pre-harvest survey, all trees >10 cm dbh were measured in each of the 360 25 x 25 m grid units. Trees 2.0 - 9.9 cm dbh were measured on a stratified random set of 42 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. 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).
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. 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.
3. Trees 2 to 9 cm dbh were not measured on all plots; only on 42 of the 360 25 x 25 m plots. When running the program for trees 2 to 9 cm, the list of plots will show up as the entire list or group you have selected but in reality the program will only include those plots within this group which have data for the 2 to 9 cm trees. It is also possible to select a group of plots you want to do for which none had the 2 to 9 cm trees measured - you will get no results in this case.
4. 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). This latter area is probably more typical of the "Northern Hardwood Forest" than the "high hardwoods".
5. 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 2003
by Thomas Siccama and Ellen Denny