Environmental Engineering Reference
In-Depth Information
Although not technically statistically sound, ecologists often ignore statistical
assumptions in favor of a more representative sample. Sampling schemes including
combinations of regular and random sampling are typically favored by ecologists.
In this exercise, we will implement regular sampling with a random start so
as not to bias our samples and save time.
Global Positioning Systems (GPS)
GPS allows ecologists to locate their position on the earth. It relies upon a network
of 30+ satellites that encircle the planet, sending signals down to GPS receiver
antennas. The receivers differ in quality, some capable of sub-foot accuracy. You
will use GPS units to map the center of each plot by establishing waypoints.
Be careful to wait until you get roughly 10 m accuracy before plotting a waypoint.
Label your waypoint with the plot number. Later, you may download your points
into a GIS according to instructor-provided instructions.
Number of Plots
Each group will sample along transects in one of the forests using meter tape and a
compass. Take point measurements (as described below) every 20 m until you have
sampled at least five points.
Tree Identification
Your instructor will provide you with a tree identification guide and a list of
common trees and their abbreviations.
The Point Quarter Method
At each point, divide the surroundings into four quarters along the principal
compass directions (N, S, E, W). Use the data sheets provided to record the distance
(d, expressed in meters) from the center point to the nearest tree that has a DBH
(diameter at breast height)
4 cm in each of the four quarters (Fig.
5.12
). Also
record the DBH (in cm) and species of each of the four trees. These four
measurements constitute data for one point sample. Do not count dead trees.
Trees that have multiple trunks, but are separated at breast height are considered
multiple trees.
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