Intro to Ecology, ECOL 100
Sampling techniques
Laboratory on techniques to sample vegetation
A bit on background information (modified after D. Ressler, 2004)
The two forests we will visit are Tall Timbers Natural Area and Shade
Mountain. We will consider Tall timbers as an old-growth stand of hemlock
(Tsuga canadensis) and white pine (Pinus strobus) that was never logged. The
forest plants and soil in this area are the closest remnants of what the landscape
would have looked like 300-400 years ago. This area is underlain by the Juniata
Siltstone and Bald Eagle Sandstone. The former is a grayish red siltstone and
sandstone, and the latter is grayish red sandstone.
Shade Mountain has been logged at least three times, on or about 1850, 1920,
and 1950. Local residents know blueberries grow best when the forest is thin, so
the mountain has been illegally burned on several occasions since the last
logging (1950). This mountain represents a frequently disturbed landscape.
Shade Mountain is underlain by the white Tuscarora Sandstone, a highly
resistant, cemented sandstone and conglomerate. On the western edge, the
older bald eagle Sandstone, grayish red sandstone is exposed.
The study locations are only about ten miles apart, lie on virtually the same
bedrock formations and are only separated by a small valley. Geologically, they
have the same materials from which soils can form, both lie between 1,800-2,200
feet above sea level, so they should have the same climate. During the
investigation, make specially note of the soil depths and features, the species
present, their characteristics, and their density (number of individuals per area).
You will compare these and other characteristics for your lab report.
Once you get to the forests, you should take notes of:
-Identification of the place
-Site description
-Diversity
-Dominant spp & Spp list
-Spatial distribution
-Understory architecture
-Look at organic matter, detritus, and leaf cover at both forests
Sampling Tech - # 1
FOREST ANALYSIS
(After G. Boone, circa 2000)
The analysis of community structure can be a daunting task. The size of a
community may prevent you from getting an overall view of the composition and
determination of dominant organisms.
A forest presents a unique problem because of its size and the size of individual
members of the forest. The size also limits observations as to the common and
rare members in the forest.
Using commonly accepted sampling techniques we can determine species;
frequency, density, dominance, and importance value, among others.
Normally it is impossible to count all the individuals in a community (a census) so
we settle for a sample of the community. In doing so, we must then calculate
estimates of the total community based on a few measurements.
There are many different approaches to sampling a community including plot and
plotless methods. Plots may be square, rectangular, circular or some other
shape. The term quadrat is often interchangeably used for plot, but strictly
speaking, a quadrat is a square plot. Quantitative plant sampling methods then
can be divided in Plot methods and Plotless methods. Within plot methods, we
will mention “Quadrats method” & “Line-Intercept method”. Among plotless
methods we will see (and use) “Point-quarter method” (see table).
Quadrats method
A quadrat is usually a square sample unit or plot, which in a vegetation survey
may be divided into subplots. Quadrats vary in size, shape, number and
arrangement, depending upon the nature of the vegetation and the objectives of
the study. In some studies, a quadrat is rectangular, although often circular plots
are done. Circular plots can be the easiest to layout, requiring only a center stake
and string of desired length. Rectangular plots appear to furnish a more accurate
sampling of vegetation composition.
Line-Intercept method
Line-intercept sampling is one-dimensional, and is most useful for sampling
shrub stands and woody understory of the forest. The method consists of taking
observations on a line or lines laid out randomly or systematically over the study
area.
Using any plot method, you will determine the plot size, and then you need to lay
out plots, and gather data such as species name, number of individuals per plot,
and circumference or diameter of each stem at breast height (CBH or DBH).
Sampling Tech - # 2
Point-quarter method
Point-quarter sampling is useful in sampling communities in which individual
plants are widely spaced or in which the dominant plants are large shrubs or
trees. The method is especially useful for surveying large tracts of land in which
many data points should be obtained, but each data point should not require a
long time for data acquisition. Thus, this method can sometimes represent a
"quick and dirty" technique for canopy surveys.
In point-quarter the height of each tree may be obtained as a method of
indicating the age of certain tree stands. Using a plotless technique is less time
consuming because the researcher does not spend time laying out the plots.
PLOTLESS METHOD
This method, as the name implies does not require
the construction of plot boundaries. We select a
random point and use a compass to create 4
quadrants (see figure). Locate the tree nearest the
point in each quadrant, identify the tree to species
and measure the distance from the point to the
tree and the CBH (or DBH) in meters. Use only
living trees and trees with a CBH > 15 cm. Record
these three pieces of data (species, distance,
circumference).
The easiest way to record data is to assign each species a number. Then when
you record a species, distance, circumference, etc. all you need to do is record a
number rather than a name.
For example, 1-15-.89
might read 1 = white pine (Pinus strobus), 15 meters from the central point and
.89 meters CBH.
You can use this for all methods. Many authors recommend a minimum of 25
points or samples of data.
Sampling Tech - # 3
Table 1 - Plant Composition
Tall Timbers
Species
Shade Mountain
Red maple, Acer rubrum
Hemlock, Tsuga canadensis
Turkey oak, Quercus laevis
Yellow birch, Betula alleghaniensis
White pine, Pinus strobus
Witch hazel, Hamamelis virginiana
Pitch pine, Pinus rigida
Poplar, Populus sp
Sampling Tech - # 4
Intro to Ecology, ECOL:100 Sampling techniques
Datasheet for recording Point-Quarter data
(SP is the species name or number; D is distance from the center point to the
plant, in meters; CBH is circumference at breast height, in meters)
Date:
Point
Number
Locality:
Compass Quadrant
SP
Northeast
D
CBH
SP
Northwest
D
CBH
SP
Southeast
D
CBH
SP
Southwest
D
CBH
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
Sampling Tech - # 5