Ecosystem dynamics in a mature (Hagan block) and old-growth (Watershed 2) forest, Andrews Experimental Forest, 1981 to present

ORIGINATOR: Jerry F. Franklin
OTHER RESEARCHER: Robert J. Pabst, Charles B. Halpern, Kari B. O'Connell, Steven A. Acker
ABSTRACTOR: Mark W. Klopsch
15 Apr 2003
13 Aug 2019
Organic matter, Primary production, communities, community structure, stand structure, Long-Term Ecological Research (LTER), soil chemistry, plant ecology, biomass, tree age, community composition, species composition, plant species composition, soil properties, primary production, mortality, soil nutrients, organic matter, soil horizons, forests, understory vegetation
The terrestrial vegetation plots are designed to meet a number of LTER needs in mature and old growth forests including (1) tree growth and mortality information, (2) biomass information for both overstory and understory, and (3) leaf area estimates to test leaf area hypothesis. Additionally, the sampling must include baseline environmental information to evaluate the measurements.
Experimental Design - TP091:
Description: Plots were established at 100 m intervals along transect lines. In the Hagan block transect lines ran NW-SE at 400 m intervals. In WS2 transects ran N-S at 200 m intervals. The distance to the initial plot on a transect was randomly generated. The plots are 1000 square meter circular plots, which are not slope corrected. The biomass of herbs and shrubs will be estimated on four 2 meter radius subplots (microplots) within the main plot. Plot boundaries are established at 8 points (with, across, and diagonal to the slope) by measuring 17.84 meters from the center stake. The stakes marking the subplots for shrub and herb biomass are 10 meters from the center stake along the diagonals.
Field Methods - TP091:

Each plot consisted of an 1000 square meter circular plot used for tree tagging, log mapping, mortality and whole plot cover. Inside this plot located 10 m from the center diagonally to the slope were four 12.5 square meter circular plots used for shrub biomass measures, subplot covers, and (nearby) soil sampling. A soil pit was dug below the center and detailed data (height, age, sapwood, growth) was taken on four trees.

Estimate cover on microplots. In 1993, two methods to measure plant cover were employed, (1) estimation on microplots and (2) line intercept. Future remeasurements will use the line intercept. However, the original measurement was made using estimation on microplots and a comparison of the two methods is needed. In 1993, measurements in microplots will be limited to one transect in each watershed: transect 7 in Watershed 2, and transect 6 in Hagan Block. Cover is estimated by mentally combining the ground area covered by all aerial portions of plants of each species present.

Also in 1993, in order to estimate cover of ecologically significant groups of mosses, cover of six different categories of mosses will be estimated : 1) mosses on the ground, less than 1 cm thick ("MOSSG1"); 2)mosses on the ground, greater than or equal to 1 cm thick and less than 3 cm thick ("MOSSG2"); 3)mosses on the ground, greater than or equal to 3 cm thick ("MOSSG3"); 4)mosses on logs or tree boles, less than 1 cm thick ("MOSSL1"); 5)mosses on logs or tree boles, greater than or equal to 1 cm thick and less than 3 cm thick ("MOSSL2"); 6)mosses on logs or tree boles, greater than or equal to 3 cm thick ("MOSSL3"). Moss cover was assessed on a surface area, not horizontal area, basis, and include moss on tree boles up to 1 m. Thus moss cover can exceed 100%.

In addition to estimating cover of all vascular plants (excluding tagged trees), and the moss categories, the collective cover of the following groups were estimate separately: all mosses (including liverworts), herbs, shrubs, tree regeneration (recorded as "REGEN", these are trees too small to be tagged), fresh logs ("LOGF"), decayed logs ("LOGD"), bare ground ("B.G."), and rock. Note that other than mosses, no cover values can exceed 100%.

Measure biomass variables in microplots. One goal of the understory measurements is to assess the contribution of understory species to the biomass of each watershed. For many species, adequate regression equations can be constructed to predict biomass from cover alone. For others (especially trees, shrubs, and ferns), additional measurements are necessary. In 1993, these measurements were only taken within microplots on the two transects listed above.

There is a list of common species that indicated which species require additional measurements, and which measurements are required. The abbreviations on the species list stand for the following measurements: dbadiameter at the base of the stem, measured with dial calipers to the nearest 0.1 cm, len* for woody plants (and the herb Stachys cooleyae), length of longest stem from ground to tip, measured with tape measure to nearest 5 cm, * for ferns and forbs, average length of fronds or leaves, to nearest 5 cm, numnumber of fronds or leaves measured as a single group.

Measure cover with line intercept. The microplot stakes are used as endpoints of two lines for line intercept sampling. The intercept line can be thought of as a linear quadrat, within which each segment occupied by each species is recorded.

The intercept lines are numbered as follows: Line #1 will run from microplot stake #1 to microplot stake #2, Line #3 will run from microplot stake #3 to microplot stake #4. In 1992, four intercept lines per plot were initially measured. Lines #2 and #4 were dropped in 1993, but the numbering system previously used was maintained. The total length of the line to the nearest cm is recorded. The starting and ending position of each portion of a vascular plant or moss intercepted by the line, either above or below the line, also to the nearest cm, is recorded. Moss is recorded using the six categories described above. Intercepts of tagged trees are not recorded.

Measure biomass variables in belt quadrats. The additional measurements needed for biomass estimation are taken in belt quadrats running along the intercept lines. The quadrats are a one half-meter strip along the intercept line.The quadrats are the same number as the intercept line on its edge and the total length of the line recorded above is used to determine the belt area.

The sites were considered representative of mature (Hagan block) and old-growth (Watershed 2) forests. The Hagan has 2 age classes, 85 and 125 years, with little understory hemlock. Watershed 2 is a 450 yr old PSME forest much of which was underburned 150 - 200 years ago.
Garrison et al., 1976
Hagan Block and Watershed 2 in the H.J. Andrews
Ground condition