Plant biomass dynamics in old-growth Watersheds 8 and 9 at the Andrews Experimental Forest, 2003 to present

ORIGINATOR: Kari B. O'Connell
OTHER RESEARCHER: Robert J. Pabst, Frederick J. Swanson, Mark E. Harmon
ABSTRACTOR: Kari B. O'Connell
29 Jun 2005
29 Jun 2005
Organic matter, Primary production, biomass, community composition, species composition, plant species composition, primary production, thinning, organic matter, forests, understory vegetation
On the HJ Andrews Experimental Forest, OR, studies on paired small watersheds compared site productivity for locations with diverse environmental attributes. For study ID TP115, Watershed 8 and Watershed 9 were measured in 2003 with a series of 17.82 m radius plots on multiple transects in each watershed. Watershed 8 is an unmanaged small watershed (median elevation 3600 feet) with a dynamic and varied history of fire disturbance. Watershed 9 is lower (median elevation 1750 feet) unmanaged small watershed and has less disturbance apparent in the extant forest. Trees, shrubs, and herbal vegetation were measured. The understory vegetative cover by species and species-specific structural characters were measured in 4 m square quadrats, while the all trees = 5.0 cm DBH were tagged and measured for diameter. Tree crown closure in each plot was measured by ocular estimate. Biomass estimates for each watershed was generated from the plots with equations in Biopak (Means, et al., 1994).
Experimental Design - TP115 :
Description: There are 4 transects and a total of 22 circular 0.1 ha plots in WS8, and 5 transects with a total of 16 0.1 ha circular plots in WS9 for tree measurement and whole plot species lists. Each plot has two 2*2 m quadrats for the vegetation measurements.
Field Methods - TP115:


Ground surface cover types and growth forms:

Cover of each type (substrate, moss, vegetation) < 2 m in height in the 2 x 2 m plot.


  • BARE = mineral soil, rock, gravel, anything not organic
  • CWD = large (greater than 10 cm diameter) woody detritus. This includes logs, stumps, and exposed roots.
  • BOLE = total cover of bole of any live tree of any size (for species classified as trees see the list Species Codes, Names, and Growth Forms).
  • LITTER = fine litter, organic matter, any dead branches less than 10 cm in diameter.

Moss: moss species lumped.


  • NON-TREE VEGETATION = total cover of vegetation (less than 4 m in height) other than trees such as grass, herbs and shrubs.

Estimates for canopy closure:

  • Tree and shrub foliage cover = all foliage of any kind greater than 4 m in height within vertical projection of veg quadrat. This number will vary from 0 to 100%.

Species cover and biomass data

Percent cover should be estimated for every species that is in the vegetation quadrat (less than 4 m in height). For example, if a species is rooted outside the quadrat, but its foliage is hanging inside the quadrat, the species and cover should be assessed. Also, if a species is rooted inside the quadrat but some of its foliage is hanging outside the quadrat, only include the cover of the part of the plant inside the quadrat. Biomass measures are taken only when a stem is rooted in the quadrat.

Species Name. Write it out fully if you are at all uncertain about the acronym. This will allow us to correct erroneous acronyms. If unknown, record descriptive material here … (e.g., "grass with long awns"). Identify grasses to species if possible. If not possible, list 'GRASS' in the species name and species code columns.

Species Code. Based on Garrison et al. 1974. See the complete list of species names and acronyms. If a plant can only be identified to genus, record the first 5 letters of the genus. If a plant cannot be identified in the field, record it as "UNKN#" (where # is a unique #-# for the plot-quadrat). Collect a specimen from outside the quadrat and include a label in/on the bag with collector's name, date, and WS/transect/plot/quadrat number. Describe the morphology or draw a picture on the data form (back if necessary).

LC. Line count. LC = 1 for the 1st record of a species in a quadrat. If more than one line is necessary to record biomass measures, increment LC as necessary (e.g., 2, 3, etc.). All records for a species do not need to be recorded in order; species can be interspersed.

Cover (%). Projected cover in percent. Cover estimates for the 2 x 2 m slope corrected quadrat should be done mentally or with extra PVC to divide the quadrat into quarters. Minimum cover = 0.1% (even if cover is less than 0.1%, record 0.1%. Maximum = 100%.

BIOMASS measures: DBA, DBH, Ht. (Height), No. of stems (or fronds), Len (Length of fronds). These data are recorded for a subset of species: Consult the form entitled Biomass Parameters to Measure. These measures are taken for only those species listed and only when the plants are rooted in the quadrat (not if plants overhang the quadrat from outside the boundaries). If no stems are rooted in, check "Out?" column (see below). For large trees, "in" or "out" is based on the center of the tree. Only measure trees that are less than 5 cm in diameter.

DBA. For stems less than 5 cm in diameter rooted in the quadrat. Diameter at the base in cm (above major butt swell for tree species) using a caliper or small diameter strip. Measurements are to the nearest 0.1 cm. If a caliper is used on an oval-shaped stem, two measurements should be taken for the perpendicular axes of the stem and the values should be averaged. DBA should be recorded for (1) all tall shrub species (except RUPA), (2) trees without tags (DBH less than 5 cm). Each stem should be measured separately and its diameter placed on a separate line. However, if more than one stem occurs at a particular diameter, you can record the number of stems at that diameter in the "No. stems" column, thus saving additional data entry lines. The first DBA should be recorded on the line for which LC = 1 line (the one with the cover estimate).

Note: some herb species also require a DBA measurement: ARCA3, COCA2, LOCI, LOCR, PTAQ: caliper measurement at the base. XETE: gather the leaves into a tight bundle and wrap the diameter strip around the clump at its base.

Height. Either the modal height (ht) (the most common height in the quadrat), or the individual height of a stem, if listed as such on the attached form Biomass Parameters to Measure (these would be coded as i-ht). Measure stem length (rather than height off the ground) because plants often grow at an angle to the slope. Units are in centimeters; precision is to the nearest 5 cm for plants 0 - 1 m tall; to the nearest 10 cm for plants 1 - 2 m tall; and to the nearest 20-50 cm for plants > 2 m tall. Be sure to measure modal height (ht) for all grass species.

Number of Stems (or Fronds). Recorded for all ferns except POMU, and for PEFR2. The number of stems of a particular length (e.g., ADPE, ATFI, BLSP, POGL4) or diameter (PTAQ). For PEFR2 the number of leaves of a particular height. If different clumps have stems with significantly different lengths, list these clumps on separate lines. Likewise, for PTAQ, the number of stems of a particular diameter are listed on separate lines.

Length: Recorded for all ferns except POMU and PTAQ, and for PEFR2. The height of the fronds, or for PEFR2 the height of the leaf.

Out?. If a species with cover requires a biomass measure (e.g., diameter, height … see below), but it is not rooted within the quadrat, place a check mark here. This way we know that the biomass measure was not forgotten. Biomass measures are taken only when a stem is rooted in the quadrat.

Whole plot species list

All species encountered in the vegetation quadrats and tree measurements should be recorded on the datasheet entitled "Whole plot species list." A thorough inspection should then be made of the rest of the 0.1 ha plot to add any vascular plant species not previously recorded. If a plant cannot be identified in the field, follow the directions given above under "species code."


Use the data form "Watershed 8 and 9 Tagged Tree Measurement." Compete all information in the header. Each tree = 5 cm in the plot should be tagged at DBH with the tag facing the center of the plot. Begin tagging trees at the north side of the plot, and go clockwise around the plot in an orderly fashion to tag the rest of the trees. If tagging trees on a steep slope, always determine the correct height for DBH from the uphill side of the tree. Also, if a tree is forked below DBH, treat each stem as a separate tree. If a tree is forked above DBH, treat the tree as one tree.

Garrison et al., 1976
Andrews Experimental Forest , Oregon
Ground condition