Sampling Vegetation Attributes - Natural Resources Conservation ...
Sampling Vegetation Attributes - Natural Resources Conservation ... Sampling Vegetation Attributes - Natural Resources Conservation ...
STUDY DESIGN AND ANALYSIS III. STUDY DESIGN AND ANALYSIS The rangeland monitoring methods described in Section V have a number of common elements. Those that relate to permanently marking and documenting the study location are described in detail below. Also discussed in this section are statistical considerations (target populations, random sampling, systematic sampling, confidence intervals, etc.) and other important factors (properly identifying plant species and training people so they follow the correct procedures). It is important to read this chapter before referring to the specific methods described in Section V, since the material covered here will not be repeated for each of them. Permanently Marking the Study Location Permanently mark the location of each study by means of a reference post (steel post) placed about 100 feet from the actual study location. Record the bearing and distance from the post to the study location. An alternative is to select a reference point, such as a prominent natural or man-made feature, and record the bearing and distance from that point to the study location. If a post is used, it should be tagged to indicate that it marks the location of a monitoring study and should not be disturbed. Permanently mark the study location itself by driving angle iron stakes into the ground at randomly selected starting points. The baseline technique requires that both ends of the baseline be permanently staked. With the macroplot technique, a minimum of three corners need to be permanently staked. If the linear technique is used, only the beginning point of the study needs to be permanently staked. Establish the study according to the directions found in Section III.A.2 beginning on page 8. Paint the transect location stake with brightly colored permanent spray paint (yellow or orange) to aid in relocation. Repaint this stake when subsequent readings are made. Study Documentation Document the study and transect locations, number of transects, starting points, bearings, length, distance between transects, number of quadrats, sampling interval, quadrat frame size, size of plots in a nested plot frame technique, number of cover points per quadrat frame, and other pertinent information concerning a study on the Study Location and Documentation Data form (see Appendix A). For studies that use a baseline technique, record the location of each transect along the baseline and the direction (left or right). Be sure to document the exact location of the study site and the directions for relocating it. For example: 1.2 miles from the allotment boundary fence on the Old County Line Road. The reference post is on the south side of the road, 50 feet from the road. Plot the precise location of the study on detailed maps and/or aerial photos. 7
8 STUDY DESIGN AND ANALYSIS A. Planning the Study Proper planning is by far the most important part of a monitoring study. Much wasted time and effort can be avoided by proper planning. A few important considerations are discussed below. The reader should refer to Technical Reference, Measuring & Monitoring Plant Populations, for a more complete discussion of these important steps. 1. Identify Objectives Based on land use and activity plans, identify objectives appropriate for the area to be monitored. The intent is to evaluate the effects of management actions on achieving objectives by sampling specific vegetation attributes. 2. Design the Study The number of quadrats, points, or transects (sample size) needed depends on the objectives and the efficiency of the sampling design. It should be known before beginning the study how the data will be analyzed. The frequency of data collection (e.g., every year, every other year, etc.) and data sheet design should be determined before studies are implemented. The sample data sheets included with each method (following the narrative) are only examples of data forms. Field offices have the option to modify these forms or develop their own. All of the methods described in this document can be established using the following techniques: a Baseline A baseline is established by stretching a tape measure of any desired length between two stakes (figure 1). For an extremely long baseline, intermediate stakes can be used to ensure proper alignment. It is recommended that metric measurement be used. Individual transects are then run perpendicular to the baseline at random locations along the tape. The location of quadrats along these transects can be either measured or paced. Transects can all be run in the same direction, in which case the baseline forms one of the outer boundaries of the sampled area, or in two directions, in which case the baseline runs through the center of the sampled area. If transects are run in two directions, the direction for each individual transect should be determined randomly. (Directions for randomly selecting the location of transects to be run off of a baseline using a random numbers table are given in Appendix D). Quadrats or observation points are spaced at specified distances along the transect. This study design is intended to randomly sample a specified area. The area to be sampled can be expanded as necessary by lengthening the baseline and/or increasing the length between quadrats or sampling points. This design may need to be modified for riparian areas or other areas where the area to be sampled is long and narrow. For these areas, a single linear transect may be more appropriate. b Macroplot The concept with this type of design is to allow every area within the study site or sample area to have an equal chance to be sampled. A macroplot is a large square or rectangular study site. The size of the macroplot will depend on the size of the study site. The macroplot should encompass most of the study site. From the standpoint of statistical inference, it is best, once the macroplot boundaries have been determined, to redefine the study site to equal the macroplot. Examples of macroplot sizes are 50 m x 100 m, 100 m x 100 m, and 100 m x 200 m, but much larger macroplots can be used to cover larger study sites. Macroplot size and shape should be tailored to each situation.
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STUDY DESIGN AND ANALYSIS<br />
III. STUDY DESIGN AND ANALYSIS<br />
The rangeland monitoring methods described in Section V have a number of common<br />
elements. Those that relate to permanently marking and documenting the study location<br />
are described in detail below.<br />
Also discussed in this section are statistical considerations (target populations, random<br />
sampling, systematic sampling, confidence intervals, etc.) and other important factors (properly<br />
identifying plant species and training people so they follow the correct procedures).<br />
It is important to read this chapter before referring to the specific methods described in<br />
Section V, since the material covered here will not be repeated for each of them.<br />
Permanently Marking the Study Location Permanently mark the location of each study<br />
by means of a reference post (steel post) placed about 100 feet from the actual study<br />
location. Record the bearing and distance from the post to the study location. An alternative<br />
is to select a reference point, such as a prominent natural or man-made feature, and<br />
record the bearing and distance from that point to the study location. If a post is used, it<br />
should be tagged to indicate that it marks the location of a monitoring study and should<br />
not be disturbed.<br />
Permanently mark the study location itself by driving angle iron stakes into the ground at<br />
randomly selected starting points. The baseline technique requires that both ends of the<br />
baseline be permanently staked. With the macroplot technique, a minimum of three<br />
corners need to be permanently staked. If the linear technique is used, only the beginning<br />
point of the study needs to be permanently staked. Establish the study according to the<br />
directions found in Section III.A.2 beginning on page 8.<br />
Paint the transect location stake with brightly colored permanent spray paint (yellow or<br />
orange) to aid in relocation. Repaint this stake when subsequent readings are made.<br />
Study Documentation Document the study and transect locations, number of transects,<br />
starting points, bearings, length, distance between transects, number of quadrats, sampling<br />
interval, quadrat frame size, size of plots in a nested plot frame technique, number of<br />
cover points per quadrat frame, and other pertinent information concerning a study on the<br />
Study Location and Documentation Data form (see Appendix A). For studies that use a<br />
baseline technique, record the location of each transect along the baseline and the direction<br />
(left or right).<br />
Be sure to document the exact location of the study site and the directions for relocating<br />
it. For example: 1.2 miles from the allotment boundary fence on the Old County Line Road.<br />
The reference post is on the south side of the road, 50 feet from the road.<br />
Plot the precise location of the study on detailed maps and/or aerial photos.<br />
7