Sampling Vegetation Attributes - Natural Resources Conservation ...

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End Point of Transect 100-Meter Tape Midpoint of Transect Beginning Point of Transect Figure 4. Study layout for the linear technique. STUDY DESIGN AND ANALYSIS Transect Bearing Stake Quadrats Study Location Stake 13
14 STUDY DESIGN AND ANALYSIS d From a sampling perspective, it is the study site that constitutes the target population. The collection of all possible sampling units that could be placed in the study site is the target population. 2. Random Sampling Critical to valid monitoring study design is that the sample be drawn randomly from the population of interest. There are several methods of random sampling, many of which are discussed briefly below, but the important point is that all of the statistical analysis techniques available are based on knowing the probability of selecting a particular sampling unit. If some type of random selection of sampling units is not incorporated into the study design, the probability of selection cannot be determined and no statistical inferences can be made about the population. (Directions for randomly selecting the location of transects to be run off of a baseline using random number tables are given in Appendix D). 3. Systematic Sampling Systematic sampling is very common in sampling vegetation. The placement of quadrats along a transect is an example of systematic sampling. To illustrate, let’s say we decide to place ten 1-square-meter quadrats at 5-meter (or 5-pace) intervals along a 50-meter transect. We randomly select a number between 0 and 4 to represent the starting point for the first quadrat along the transect and place the remaining 9 quadrats at 5-meter intervals from this starting point. Thus, if 10 observations are to be made at 5-meter intervals and the randomly selected number between 0 and 4 is 2, then the first observation is made at 2 meters and the remaining observations will be placed at 7, 12, 17, 22, 27, 32, 37, 42, and 47 meters along the transect. The selection of the starting point for systematic sampling must be random. Strictly speaking, systematic sampling is analogous to simple random sampling only when the population being sampled is in random order (for example, see Williams 1978). Many natural populations exhibit an aggregated (also called clumped) spatial distribution pattern. This means that nearby units tend to be similar to (correlated with) each other. If, in a systematic sample, the sampling units are spaced far enough apart to reduce this correlation, the systematic sample will tend to furnish a better average and smaller standard error than is the case with a random sample, because with a completely random sample one is more likely to end up with at least some sampling units close together (see Milne 1959 and the discussion of sampling an ordered population in Scheaffer et al. 1979). 4. Sampling vs. Nonsampling Errors In any monitoring study, it pays to keep the error rate as low as possible. Errors can be separated into sampling errors and nonsampling errors. a Sampling Errors Sampling errors arise from chance variation; they do not result from “mistakes” such as misidentifying a species. They occur when the sample does not reflect the true population. The magnitude of sampling errors can be measured. b Nonsampling Errors Nonsampling errors are “mistakes” that cannot be measured.
Page 1 and 2: SAMPLING VEGETATION ATTRIBUTES INTE
Page 3 and 4: TABLE OF CONTENTS SAMPLING VEGETATI
Page 5 and 6: TABLE OF CONTENTS TABLE OF CONTENTS
Page 7 and 8: I. PREFACE PREFACE The intent of th
Page 9 and 10: 2 INTRODUCTION values when individu
Page 11 and 12: 4 INTRODUCTION represent the “pul
Page 13 and 14: 6 INTRODUCTION G. Coordination Moni
Page 15 and 16: 8 STUDY DESIGN AND ANALYSIS A. Plan
Page 17 and 18: 10 STUDY DESIGN AND ANALYSIS Macrop
Page 19: 12 STUDY DESIGN AND ANALYSIS Becaus
Page 23 and 24: 16 STUDY DESIGN AND ANALYSIS b Cove
Page 25 and 26: 18 STUDY DESIGN AND ANALYSIS sideoa
Page 27 and 28: 4 3.5 3 2.5 20 5 STUDY DESIGN AND A
Page 29 and 30: 22 STUDY DESIGN AND ANALYSIS C. Oth
Page 31 and 32: 24 ATTRIBUTES Frequency is the numb
Page 33 and 34: 26 ATTRIBUTES 2. Advantages and Lim
Page 35 and 36: 28 ATTRIBUTES b Standing crop and p
Page 37 and 38: 30 ATTRIBUTES
Page 39 and 40: 32 METHODS—Photographs c Angle ir
Page 41 and 42: METHODS—Photographs Hinge Rod sta
Page 43 and 44: METHODS—Photographs angle iron st
Page 45 and 46: 38 METHODS—Frequency • One tran
Page 47 and 48: 40 METHODS—Frequency transected,
Page 49 and 50: 42 METHODS—Frequency (3) Total fr
Page 51: Page of Frequency 44 Study Number D
Page 55 and 56: METHODS—Frequency The frame is ma
Page 57 and 58: 50 METHODS—Dry Weight Rank C. Dry
Page 59 and 60: 52 METHODS—Dry Weight Rank After
Page 62 and 63: D. Daubenmire Method METHODS—Daub
Page 64 and 65: METHODS—Daubenmire b Ten Cover Cl
Page 66: Page of Daubenmire Study Number Dat
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50 cm Six Cover Class Frame 20 cm R
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METHODS—Line Intercept b Pilot St
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METHODS—Line Intercept Hanley, Th
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70 METHODS—Step Point F. Step-Poi
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72 METHODS—Step Point the boot an
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74 METHODS—Step Point measures AN
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78 METHODS—Point Intercept G. Poi
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80 METHODS—Point Intercept 8. Sam
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82 METHODS—Point Intercept b Tran
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METHODS—Point Intercept Examples
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86 METHODS—Cover Board H. Cover B
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88 METHODS—Cover Board g Study Do
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Page of Cover Board Method Profile
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94 METHODS—Density I. Density Met
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96 METHODS—Density (often very mu
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98 METHODS—Density able to make s
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Page of Density Study Number Date E
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• Herbage Yield Tables for Trees
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METHODS—Double Weight Sampling (4
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METHODS—Double Weight Sampling d
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Page of Production Study Number Dat
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112 METHODS—Harvest K. Harvest Me
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114 METHODS—Harvest 7. Taking Pho
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116 METHODS—Comparative Yield L.
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118 METHODS—Comparative Yield (1)
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120 METHODS—Comparative Yield Tab
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M. Visual Obstruction Method - Robe
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METHODS—Visual Obstruction—Robe
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Sampling Interval Study Location 1
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130 METHODS—Other N. Other Method
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132 GLOSSARY browse: (1) the part o
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134 GLOSSARY grazable woodland: for
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136 GLOSSARY sample: a set of sampl
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138 GLOSSARY
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140 REFERENCES Crocker, R.L. and N.
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142 REFERENCES Hironaka, M. 1985. F
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144 REFERENCES Nie, Norman H., C. H
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146 REFERENCES Society for Range Ma
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148 REFERENCES Whitman, W.C. and E.
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Location 150 APPENDIX A Study Locat
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APPENDIX B APPENDIX B—STUDY AND P
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APPENDIX B 3. Label 3 A placard on
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APPENDIX C Photo Identification Lab
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160 APPENDIX C
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162 APPENDIX D The formula for usin
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Form Approved OMB No. 0704-0188 Pub
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