Notes and Research
Forest Inventories and Assessments
Stand Exams
A stand exam involves collecting data to determine per acre averages for measures of stand structure and composition. The primary measures that we report to you include:
- Volume measures include average cubic feet or board feet per acre, based on the volume of the stem above the root collar.
- Diameter distribution includes the average trees per acre in each given diameter class, broken down into species.
- Basal Area is the area of the cross-section of a tree measured at breast height (conventionally 4.5 feet from the groundline). Generally, basal area is reported on a per acre basis, as a sum of the cross-sections of all trees. It is based on diameter values and reported in square feet per acre.
- Crown competition Factor, an index of stand density that Interface Forestry uses, is derived from the above measures.
- Clumpiness derives from the per acre variation in the distribution of trees.
Depending upon the variability of the stand structure, a stand exam usually involves a sampling density of one plot to 2-5 acres distributed on a square grid. Generally, the ratio of plots to acreage will decrease with comparatively larger stands. In the field, we use variable-radius plots for trees 4.5 inches DBH and greater, and fixed-radius plots (usually 1/100 acre) for trees with smaller DBH values. Generally, the measurements that we take in the variable-radius plots include the following parameters:
- Species. The species of every "in" tree with a DBH value of 4.5 inches or greater
- DBH. We measure the DBH (in inches) of very "in" tree with a DBH value of 4.5 inches or greater, using a diameter tape, which converts circumference to diameter.
- Height. We measure the height (in feet) of 20-25% of the "in" trees using Relascope (ground- based measurement). The actual density of our height-sample depends upon your management objectives.
- Defect. For each height-measured tree, we also measure its variation from being perfectly straight, based upon the merchantability standards for the local mills.
- Taper. For every third height-measured trees, we measure the taper of the tree by measuring the height at which the diameter value is 80% of the DBH. As with height and defect measurements, the actual number of taper trees depend upon your objectives.
- Age. We determine age by counting annual rings in a core sample extracted using an "increment bore." Samples include trees of each species (or tolerance group).
In the fixed-radius plots, we generally measure:
- The species and diameter of any tree with a DBH over 1 inch.
-
The height class
of any tree with a DBH under 1 inch that is at least 6 inches tall.
We generally use two classes:
- 0.5-3.5 ft
- 3.6-8 ft
- The tree height of roughly every third tree over 1 inch DBH. (The actual ratio depends upon your management objectives.)
We enter and compile this data using a computer program called Forest Projection and Planning System (FPS). FPS is based on a relational data-base (ODBC-compliant), so we can serve stand data and information to a wide variety of database frameworks and to our geographical information system. Using FPS, we produce a forest stand table, which reports the above parameters (basal area, volume, clumpiness, CCF) in tabular form. To make this information meaningful to you, we supplement the stand table with an easy-to-read explanation and interpretation, which you can use in your management decisions.
Forest Inventories
Conducting a Forest Inventory involves several steps:
-
The first task is setting up a
GIS
map project, which involves a few sub steps:
- Firstly, we obtain or create a virtual geo-referenced aerial photo image. Geo-referencing an image correlates each point on the image to a specific longitude and latitude.
- Secondly, we use these photos to discern stand boundaries, which we then draw into our GIS using the mouse, our method of digitizing. These digitized drawings, which represent forest stands, are polygons, a type of GIS object. (Other objects include points and lines.) Because our image is georeferenced, we are able to obtain the latitude and longitude values for any point on our stand (or, on our polygon). Each polygon constitutes a record in a database that contains useful data about the stand (acreage, spatial coordinates of the boundary, and much more).
- Thirdly, we use the photos to digitize other geographical features that interest us, including roads, streams and riparian areas, historical and cultural artifacts, sensitive wildlife or flora habitat, and other features that we find significant. As with all drawings, these features will each constitute a record in a database that contains useful data about them.
- Finally, we print out field maps.
- The second task is field-checking every stand in our forest to discern their forest cover types and to georeference important landmarks, property boundaries, fence lines, and other significant features using a global positioning system unit (with resolution ranging from 10 meters to better, depending upon location and environmental conditions).
- The third task is inputting all cover type and field data into the GIS database and making adjustments to the GIS project. Often, remote and adjacent stands will share cover types (with the stand boundaries defined by geography, roads, or some other criterion).
- The fourth task involves conducting stand exams and fuel assessments on a representative number of stands within each cover type. (The sampling density will depend upon your management objectives.)
- The fifth task involves inputting and compiling data and extrapolating from sampled stands to non-sampled stands (all with FPS), and linking the resulting tables with the GIS database.
- The final task is to produce a report that the client finds useful and easy to understand, including clearly printed color maps, tables, images, and diagrams that might aid the reader.
For our mapping needs, Interface Forestry uses Manifold System GIS. For our database purposes, we are currently developing a MySQL database platform.