FOR 306. Forest measurements. Forest Inventory Variable Radius Plots

Transcription

1 FOR 306 Forest measurements Forest Inventory Variable Radius Plots

2 Fixed vs. variable radius plots Fixed area plot Variable radius plots The chance of a tree to be inside plot depends on stand density (i.e., # trees) The chance of a tree to be inside plot depends on the size of the tree 2

3 Variable radius plot sampling Each tree has a given plot size in relation to it s size. Cruiser location - Plot center How many of these plots does the location of the cruiser fall into? 3

4 Variable radius plot sampling A method of sampling based on a tree s size, rather than its frequency of occurrence. Size: Diameter or Height The probability of tallying a tree depends on its diameter (DBH) and the device used. Objective: stand and stock tables Challenge: expand to per unit area (acre) Solution: assign weights to each tree according to its probabilities of selection 4

5 Variable radius plot sampling Sampling based on Fixed plot sampling Frequency of occurrence Variable radius plot sampling Tree size Expansion factor Same for all trees Varies by tree Prob. Prop. Frequency Prob. Prop. Size 5

6 Variable radius plot sampling Device ensures a ratio between DBH / tree plot = 1:33 1 tree can 33 6

7 Variable radius plot sampling 7

8 The tree Factor Each tree surrounded by a circular area that can ensure inclusion of the tree in the sample The circular area around the tree ensures the expansion from tree level to per acre level Tree Factor expansion from tree to per unit area (acre or hectare) VARIABLE TF i sample unit area area element BA Factor expansion from BA of a tree to BA of one acre (unit area): BAF = BA x TF of i 8

9 Basal area factor BA Factor expansion from tree BA to acre BA How much BA does each sampled tree represent at per unit area (one acre)? BAF depends on the tree size AND the device Example: BAF DBH Distance Device with angle gauge 1 : 33 BAF = (1/33) 2 =. 2 9

10 devices Relaskop, prisms Offset tree bole in prism DOES overlap actual tree bole Offset tree bole in prism DOES NOT overlap with actual tree bole 10

11 Basal area factor Related to the sighting angle size of the prism. Chosen to provide a tally of 5-12 trees / point Eastern U.S.: 5, 10, 20 Western U.S.: 20, 40, 60 Example revisited: Device with angle gauge 1 : 33 BAF = (1/33) 2 =... each sampled tree represents.. ft 2 /ac BAF=BA TF TF = BAF / BA A tree with DBH=10 TF =.... each sampled tree represents.. trees/ac 11

12 Plot radius factor The value used to determine the maximum distance between plot center and a tree of a given diameter such that the tree would still be tallied. Depend on the device specifications Example: Prism with angle gauge 1:33 means that a tree with DBH=1 can be at most 33 far from the plot center to be counted in: PRF=33 /12 = 2.75 a tree 1 dbh can be 2.75 away 12

13 Plot radius factor Plot Radius Factor (BAF 10) = 2.75 ft. For each inch of dbh, a tree can be 2.75 feet from the point to still be included in the point s tally. Thus a 12 inch tree can be up to 33 feet (12 x 2.75) from the point and still be included in the point s tally. Plot Radius Factor (BAF 20) = For each inch of dbh, a tree can be feet from the point to still be included in the point s tally. Thus a 12 inch tree can be up to 23.3 feet from the point and still be included in the point s tally. 13

14 Plot radius factor Basal Area Factor [ft 2 /ac] Plot Radius Factor [ft] PRF BAF

15 Computations Basal area BA acre Total trees number of tallied points BAF Example: BAF 20 prism 402 trees tallied 25 points 402 BA sq. ft. / 25 acre 15

16 Computations Trees / acre Requires diameter of each tree (diameters of tallied trees were measured during cruise) Requires calculation of Tree Factor unit area BAF TF sample area BA per tree Tree factor depends on tree s DBH TPA DBH (# class trees tallied in DBH class i) ( conversion total number of factor points to per unit area for DBH class i ) TPA DBH i (# trees with DBH # points i ) TF DBH i 16

17 COMPUTATIONS TREES/ACRE Example: BAF 10 prism 12 points TF DBH 10" TF BA BAF per tree # trees in the 10-inch diameter class: 27 TPA 10 " n 10" n TF p 10" TPA 10" TPA 41.3 TPA for the 10-inch diameter class 17

18 Computations - volume Two methods: 1. Volume Factor (VF) method 2. Volume - Basal Area (VBAR) method Both methods require calculation of Tree Factor Both methods require diameter and height measurements from some or all sampled trees 18

19 VF - Method First, compute volume factor for each diameter-height class using a volume table and Tree Factor: VF i TF i v i Example: for a BAF 10 prism TF 10 = Volume of a 10" /2-log tree is 63 bf.- it is v i v i is determined from a published volume table 19

20 Stand and stock table 4 plots were used to cruise a 30 acre stand using a prism with BAF 10 the following tally sheets were obtained DBH Plot 1 Plot 2 Plot 3 Plot 4 Logs Logs Logs Logs * * * * 14 * * * * * * * 16 * * * * 20

21 Stand and stock table International ¼ in rule Form class 80 DBH Plot 1 Plot 2 Plot 3 Plot 4 Logs Logs Logs Logs *98 *98 *127 *98 14 *141 *186 *141 *186 * *141 * *256 *190 *256 *256 21

22 Stand and stock table DBH Plot 1 Logs BA/ tree TF Per acre Trees BA Vol 12 * * * DBH Plot 2 Logs BA/ TF Per acre tree Trees BA Vol 12 *98 * * *

23 Stand and stock table DBH Plot 3 Logs BA/ tree TF Per acre Trees BA Vol 12 * * 141 * * DBH Plot 4 Logs BA/ tree TF Per acre Trees BA Vol * * * *

24 Stand and stock table DBH Trees/ac BA/ac Volume/ac P1 P2 P3 P4 P1 P2 P3 P4 P1 P2 P3 P DBH Trees/ac BA/acre Volume/ac Total

25 Stand and stock table dbh Trees/ac BA/ac Volume/ac P1 P2 P3 P4 P1 P2 P3 P4 P1 P2 P3 P Total Mean # tree / acre Variance 4 i 1 ( x 2 x ) 4 1 Std. error of the mean s i ( ) x var 2.. ( ) 3 iance n CI= CI= =. 25

26 Stand and stock table Stand and stock table with confidence intervals DBH Trees /ac BA/ac [ft 2 ] Volume/ac [bd.ft.] Trees/ tract Volume/ tract Total 36.3 CI ±