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1200 m
Quadrant 1
Quadrant 2
Quadrant 4
Quadrant 3
Figure 4.7
Multiple quadrant design used at the Fairystone and Umstead sites. The 1200-
1200-m region
approximates a MODIS LAI pixel, with a 100-m buffer on each edge. Quadrants are randomly
located within each 600-
600-m quarter.
(Figure 4.8) and the spherical densiometer (Figure 4.9) (Becker et al., 2002). Measurement estimates
were also performed using the TRAC instrument and hemispherical photography.
Measurements of forest structural attributes (forest stand volume, basal area, and density) were
made at each quadrant and subplot using a point sampling method based on a 10-basal-area-factor
prism. Point sampling by prism is a plotless technique (point-centered) in which trees are tallied
on the basis of their size rather than on frequency of occurrence on a plot (Avery and Burkhart,
1983). Large trees at a distance had a higher probability of being tallied than small trees at that
same distance. Forest structural attributes measured on trees that fell within the prism angle of
view included (1) diameter at breast height (dbh) at 1.4 m, (2) tree height, (3) tree species, and (4)
crown position in the canopy (dominant, codominant, intermediate, or suppressed).
At each quadrant, forest structural attributes were sampled at the 10-, 50-, and 90-m stations
along the A, C, and E hemispherical photography transects (Table 4.2). Point sampling was per-
formed at the subplot 25-m transect intersection. Physical site descriptions were made at each
Top View
Bottom View
Sighting Hole
Figure 4.8
Schematic of vertical tube used for crown closure estimation.
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