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Forest Biometry Lecture Number 11 Outline n Basics of variable plot cruising n How variable plot cruising works Variable plot cruising I n Instruments for variable plot cruising n Borderline trees Forest Biometry Lecture No. 11 2 Basics of variable plot cruising Basics of variable plot cruising “The Bitterlich method” n In un-evenaged forests, there are always many small trees and much fewer large trees n In variable plot sampling – or point n In fixed area plots, most of the time is sampling – trees are tallied according to invested measuring the small trees their size n However, large trees determine the basal n The probability of tallying a given tree area and the timber volume of the stand depends on its basal area n Sampling for timber volume would be most n The bigger a tree the more likely it is to efficient, if we could focus on the large trees, be selected without ignoring smaller ones completely Forest Biometry Lecture No. 11 3 Forest Biometry Lecture No. 11 4 Basics of variable plot cruising How variable plot cruising works “The Bitterlich method” n The decision if a tree is ‘in’ a plot depends on n The system is extremely efficient and both, its basal area and its distance from the accurate, because larger trees are more plot center important when it comes to estimating n Small trees are only included when they are basal area and timber volume close to the plot center n The system was developed in 1948 by n Large trees are also included at further Walter Bitterlich, a forester and distances biometrician from Salzburg, Austria Forest Biometry Lecture No. 11 5 Forest Biometry Lecture No. 11 6 1 How variable plot cruising works How variable plot cruising works n More precisely, the decision which tree to n Example include is based the ratio between diameter Ratio Tree 1 Tree 2 Tree 3 and distance to plot center Diameter 6 6 6 n A tree is ‘in’ a plot when this ratio is equal to, or larger than, a predefined ratio Distance 12 16.5 33 n One commonly used ratio is 1/33 in feet Distance 144 198 396 in inches 1/33 Diameter/ 0.0417 0.0303 0.0151 0.0303 distance Forest Biometry Lecture No. 11 7 Forest Biometry Lecture No. 11 8 How variable plot cruising works How variable plot cruising works n Example n The BIG advantage of variable plot cruising is Ratio Tree 1 Tree 2 Tree 3 that counting trees is all that is necessary to measure basal area per acre Diameter 12 12 12 n A ratio of 1/33 is equal to a basal area factor (BAF) of 10 Distance 12 16.5 33 in feet n This means that each tree ‘in’ a plot Distance 144 198 396 represents a basal area of 10 square feet per in inches acre 1/33 Diameter 0.0833 0.0606 0.0303 0.0303 /distance Forest Biometry Lecture No. 11 9 Forest Biometry Lecture No. 11 10 How variable plot cruising works Instruments for variable plot cruising n In the field, all that is necessary is n Angle gauge u Tree are counted “in” when they are wider than u tostand at the center of the plot the intercept at the end of the gauge u examine each tree in the surrounding u User’s eye must be placed over the plot center u decide if the tree is ‘in’ or ‘out’ u Good for dense stands u multiply the number of tree by 10 u Usually designed for a BAF of 10 n Result is an accurate estimate of total basal u Slopes > 15% require slope correction, which is area per acre cumbersome with the angle gauge Forest Biometry Lecture No. 11 11 Forest Biometry Lecture No. 11 12 2 Instruments for variable plot cruising Instruments for variable plot cruising n Penny n Cruz-All u Same idea as the angle gauge u Also based on the angle gauge principle as the u The penny must be 24” away from the eye, eye u Difference is that that you look at an opening and must be over the plot center decide if a trunk fills the opening completely u At this distance, the BAF is 10 u The distance to the eye is measured via a little u Slopes also problematic chain that you hold with your teeth u Less precise than the angle gauge, u Eye must be over the plot center but easier to carry around u Slopes also problematic u Has four BAFs built in (5, 10, 20, and 40) Forest Biometry Lecture No. 11 13 Forest Biometry Lecture No. 11 14 Instruments for variable plot cruising Instruments for variable plot cruising n Wedge prism n Wedge prism u Trees are “in” when their shifted image in the u Slope correction in three steps prism still overlaps with the rest of the trunk F Point the long side of the prism at eye u Low cost and light weight level towards the tree u The prism must be placed over the plot F Maintain the slope angle while rotating the NOT THE EYE! prism 90 degrees u Allows slope correction F Make the decision if tree is “in” Forest Biometry Lecture No. 11 15 Forest Biometry Lecture No. 11 16 Instruments for variable plot cruising Instruments for variable plot cruising n Spiegel relascope n Contra spiegel relascope u Trees are counted “in”, when they are wider than u Problematic on dark, rainy days the predetermined number of stripes inside the u Takes a little bit more training viewing field u Costly u The relascope must be positioned over the plot center n Pro spiegel relascope u Built in topographic correction, great for steep terrain u Contains several BAF thus flexible Forest Biometry Lecture No. 11 17 Forest Biometry Lecture No. 11 18 3 Borderline trees Borderline trees n Trees that are neither clearly “in” nor n More accurate is to actually measure “out” borderline trees u Multiplying the dbh (in inches) with the plot radius n The simple way of dealing with is to factor gives the maximum distance (in feet) from count every second borderline tree “in” the sampling point for a given tree to be “in” u For a ratio of 1/33, the plot radius factor is 2.75 n The first borderline tree is “out” u The plot radius factor depends on the BAF, n When you cruise multiple plots, for a BAF of 5, the plot radius factor is 3.89, continue the in-out list from one plot to and for BAF 20 1.94 the next n In the field, a table is used to check the critical distance for a given dbh Forest Biometry Lecture No. 11 19 Forest Biometry Lecture No. 11 20 Outline n Basics of variable plot cruising n How variable plot cruising works n Why variable plot cruising works n What size Basal Area Factor? Forest Biometry Lecture No. 11 21 4 Walter Bitterlich 1 2 3 4