Plot sampling

FOREST MEASUREMENTS IIFixed area plot sampling

FIXED AREA PLOTSTwo general methodsStrip cruisingLine-Plot cruisingSample areaXSample areaUnderlying sampling design: Systematic sampling2

LINE - PLOT CRUISING3

LINE - PLOT CRUISING4

LINE - PLOT CRUISINGNominal cruise intensityHow much of the land was sampled?⎛I =⎜⎝Plot size in acresAcres represente d by⎞100plot⎟⎠Examples:1/10 acre plot on a 2 x 5 chain spacing:I⎛= ⎜⎝0.11⎞⎟100= 10%⎠1/5 acre plot on a 4 x 5 chain spacing:I⎛= ⎜⎝0.22⎞⎟100= 10%⎠5

PLANNING LINE - PLOT CRUISINGInput data:• 60 acre tract• 5% cruise (sample) → Area sampled = 3 acres• 1/5 acre plots1. Area to be sampled:Area sampled =( Tract area) (cruise percent)Area sampled = (60 ac) (0.05) =3.0acres6

PLANNING LINE - PLOT CRUISING2. No. of plots needed:⎛ Area sampled ⎞No.of plots =⎜⎟⎝ plot area ⎠⎛ 3.0 ⎞No. of plots = ⎜ ⎟ = 15 plots⎝ 0.2 ⎠3. Samples represent how much area?Representative area⎛Tract= ⎜⎝areaplots⎞⎟⎠⎛60 acres ⎞Representa tive area =⎜4 ac = 40 sq.ch.15 plots⎟ =⎝ ⎠7

PLANNING LINE - PLOT CRUISING4. Plot spacing?Representa tive Area=( Dist between plots)(Dist between lines)Distance between plotsPlot cruise planning:• 60 acre tract4 ac=40⎛ Representative area ⎞Dist between plots =⎜⎟⎝ Dist between lines ⎠Distbetween⎛ Representa tive arealines =⎜⎝ Dist between plots• 5% cruise → Area sampled = 3.0 ac• 1/5 acre plots → Plots size = 0.2 ac• No. plots : 15• each plot represent an area of 4 ac: Tract area / #plots40sq. chains = [int( 40 ) -1] ×= 5×8int( 40 ) -1⎞⎟⎠Distance between⎛plots = ⎜⎝40 sq. chains5 chains⎞⎟⎠= 8chains8

PLANNING LINE - PLOT CRUISINGSummary:• 60 acre tract• 5% cruise (sample)• 1/5 acre plots• Area sampled = 3.0 ac.• 15 plots needed• Each represents 4 acres (40 sq. chains)• 5 chain spacing between lines• 4 chain spacing between plots9

LINE - PLOT CRUISINGAdvantages1. Suitable for one-person cruising.2. Cruisers do not have to tally trees while following acompass line.2. Cruisers pause at plot centers, allowing more time tocheck measurements.4. Tree tally is separated by plots: can separate the plotsinto sets to calculate volumes for different timbertypes, etc.5. Easy to re-check the measurements10

LINE - PLOT CRUISINGCOMPUTATIONS• Line –plot cruising on a 34 ac tract• Plot size: 1/5 acre• # plots = 15•Computations: Simple Random Sampling MethodPlot Volume Plot Volume Plot Volume1 500 6 415 11 4702 710 7 310 12 5453 425 8 200 13 4504 900 9 490 14 6055 610 10 600 15 51011

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After cruising a 30 acre stand using 4 1/5 acre plotsthe following tally sheets were obtainedDBH Plot 1 Plot 2 Plot 3 Plot 4Logs Logs Logs Logs1 2 3 1 2 3 1 2 3 1 2 312 * * * *14 * * * * **16 * * * **

• International ¼ in rule• Form class 80DBH Plot 1 Plot 2 Plot 3 Plot 4Logs Logs Logs Logs1 2 3 1 2 3 1 2 3 1 2 312 *98 *98 *127 *9814 *141 *186 *141 *186 **141*18616 *256 *190 *256 *256

DBH Plot 1LogsBA/ Per acre …1 2 3 TREE TREES BA VOL12 *98 0.79 5 3.95 49014 *141 1.07 ……. …. …16 *256 1.40DBH Plot 4LogsBA/ Per acre …1 2 3TREETREES BA VOL12 0.79 0 0 014 ** 141*186 1.07 15 16.05 234016 *256 1.40 … … …

DBH Plot 2LogsBA/ Per acre …1 2 3 TREE TREES BA VOL12 *98 *127 0.79 10 7.90 112514 *186 1.0716 *190 1.40DBH Plot 3LogsBA/ Per acre …1 2 3TREETREES BA VOL12 * 98 0.79 5 3.95 49014 * 141 *186 1.0716 *256 1.40

DBH Trees/acBA/ac[ft 2 ]Volume/ac[ft 3 ]Trees/tractVolume/tract12 5 3.95 526.25 170 17892.514 8.7516 5Total 18.75

DBH Trees/acBA/ac[ft 2 ]Volume/ac[ft 3 ]Trees/tractVolume/tract12 5 3.93 526.3 170 17892.514 8.7516 5Total 18.75CI 3.98