TV056
Comparisons among five canopy-cover estimating methods in five Douglas-fir/western hemlock structure types in the western Oregon Cascades

CREATOR(S): Anne C.S. Fiala McIntosh

PRINCIPAL INVESTIGATOR(S): Anne C.S. Fiala McIntosh

ORIGINATOR(S): Anne C.S. Fiala McIntosh

OTHER RESEARCHER(S): Steven L. Garman, Andrew N. Gray

METADATA CONTACT: Anne C.S. Fiala McIntosh

METADATA CREATION DATE:

1 Sep 2004

MOST RECENT METADATA REVIEW DATE:

29 Jun 2017

KEYWORDS:

Populations, community structure, populations, photo point imagery, canopies

PURPOSE:

To compare four ground-based techniques for estimating forest overstory cover -line-intercept, spherical densiometer, moosehorn, and hemispherical photography-and cover estimates generated using the Forest Vegetation Simulator (FVS) in five Douglas-fir/western hemlock structure types in western Oregon.

METHODS:

Experimental Design - TV056 :

Description: This study was a split-plot design with stand-structure type as the whole-plot level treatment and the technique for estimating cover as the sub-plot treatment. Each stand was an experimental unit.

Field Methods - TV056 :

Description: Canopy measurements for the four ground-based methods were collected for five subplots in each of the 52 stands. In each subplot, canopy measurements were recorded along 3 17-m slope- corrected line transects radiating out from the center of each subplot (azimuth 0, 120 and 240). The numbers and locations of canopy measurements differed for the four methods being compared, with replicate measures for the same technique located to minimize overlap. Densiometer measurements were recorded at the center of the subplot, and at slope-corrected distances of 8.5 and 17 m along each transect. Moosehorn measurements were recorded at the center of the subplot, and at 4.25-meter slope-corrected horizontal intervals along each of the three transects. Hemispherical photo-points were located at the center of each subplot, and at distances of 11.3 m along each transect.

Instrumentation - TV056 :

Description: Convex spherical densiometer, moosehorn, hemispherical photography.

Algorithms - TV056:

Description: Statistics/algorithms (include name, description, and citation): The Forest Vegetation Simulator (FVS; Donnelly and Johnson 1997) is an individual tree, distance-independent growth and yield model (Donnelly and Johnson 1997), commonly used by the Forest Service to compare alternative forest treatments. Canopy cover is estimated by summing individual tree crown areas, using crown radii formulae developed for each species from regional inventory plots. The final stand-level canopy cover corrects for crown overlap by assuming random distribution of canopy elements (Crookston and Stage 1999). We calculated uncorrected and overlap-corrected cover for live trees on the sampled subplots in each stand using the unpublished FVS Region 6 crown radii formulae. However, in the PSP stands trees between 5-15 cm were only measured on a subset of the area, and this area could not be determined. Therefore, these tree sizes were omitted when calculating FVS cover for the PSP stands. [Crookston, N. L., and Stage, A.R. 1999. Percent canopy cover and stand structure statistics from the Forest Vegetation Simulator. USDA For. Serv. GTR. RMRS-GTR-24.]

SITE DESCRIPTION:

The study was conducted in 52 forested stands located in the Mt. Hood and Willamette National Forests of the Oregon Western Cascades during June - September 2001 (Fig. 1). Plots were located in the Tsuga heterophylla forest zone (Franklin and Dyrness 1973) and represented a range of Douglas-fir/western hemlock structure types. Stand-structure types included: young stands (38-52 years old) that were unthinned, lightly thinned, or heavily thinned; mature (120-180 years); and old-growth (> 250 years). Eight stands were sampled for each of the three types of young stands (Table 1). Half of these stands were from the Young Stand Thinning and Diversity Study sites harvested between 1994 and 1996 (CCEM 1996): control (unthinned, n=4), light thin (247- 375 trees per ha =[tph], n=4), and heavy thin (114-200 tph; n=4). The other half of these stands were from the Uneven-Aged Management Project stands harvested from 1999-2000 (CCEM 1999): control (unthinned, n=4), multi-storied stand (which we classified as light thin based on mean relative density [Husch et al. 1972] of 30; n=4), and single-tree selection (which we classified as heavy thin based on mean relative density of 20; n=4). Within each stand, there were 20-m apart parallel transect lines (North-South or East-West) and tree data were collected on multiple 0.1-ha subplots that were located along these transects. We randomly selected five of these subplots from each of the stands for use in this study. The mature and old-growth stand-structure types in this study each had 14 replicates (Table 1). The plots were comprised of USDA Forest Service Current Vegetation Survey National Forest Inventory plots (CVS) and Permanent Sample Plots (PSP; Acker et al. 1998). CVS plots were circular fixed-area plots systematically located on a 1.7-mile grid (3.4 miles in designated wilderness areas), with five systematically-located subplots in each plot. Subplots were arranged around a center subplot, with four subplots in cardinal directions with subplot centers 40.8 m from the middle subplot center. PSP plots were rectangular stem-mapped 1-ha plots. The PSP plots were subjectively located in the region around the HJ Andrews Experimental Forest (44.2N, 122.2W) to represent different community types of mature and old-growth forests. The mature stands in this study were randomly selected from 35 PSP and CVS plots that were between the ages of 120-180 years and dominated by Douglas-fir. The old-growth stands were randomly selected from 73 CVS and PSP stands that were > 250 years. We used the systematic five-subplot arrangement established by the CVS program for all the PSP and CVS plots used in this study. Additional information is included in Anne Fiala's MS Thesis: Forest Canopy Structure in Western Oregon: Characterization, Methods for Estimation, Prediction, and Importance to Avian Species on file in the FSL reprint room and the library.

TAXONOMIC SYSTEM:

Garrison et al., 1976

GEOGRAPHIC EXTENT:

The western hemlock zone of the western Oregon Cascades encompassed within the Willamette and Mount Hood National Forests.

ELEVATION_MINIMUM (meters):

350

ELEVATION_MAXIMUM (meters):

1200

MEASUREMENT FREQUENCY:

Each of the 52 stands was visited once.

PROGRESS DESCRIPTION:

Complete

UPDATE FREQUENCY DESCRIPTION:

notPlanned

CURRENTNESS REFERENCE:

Ground condition

RELATED MATERIAL:

Anne Fiala has the fisheye negatives that were used to calculate the percent cover of the hemispherical photographs. Additional data for the plots that were examined in this study can be found in FS1181 and FS1191and the information on the permanent sample plots is housed by Howard Bruner and Kari O'Connell.