Forest Stats Midterm 2 Notes

what is a t-test used for?

used to assess the statistical significance of differences between two means

what does the t-value measure?

it measures the size of the difference relative to the variation in your sample data

how is calculated t-value found?

through an equation

how is critical t-value found?

from the t-table

degree of freedom

n-1

if the calculated t-value is less than the critical t-value, then the null hypothesis is…

accepted—there is NO statistical difference between the means

if the critical t-value is less than the calculated t-value, then the null hypothesis is…

rejected—there IS a statistical difference between the means

a p-value set at 0.05 is

95% confidence

standard error=

mean +- t value * (s/n^0.5)

confidence interval =

mean +- standard error

when an initial sample doesn’t yield a useful estimate, what 4 possibilities should be considered?

- procedural or calculation error

- population is inherently variable and a sample cannot reduce the variation about the mean

- it might be necessary to subdivide the population to be sampled in a different way to reduce variation, ie keeping trees separate by species

- sample is too small and you need to keep measuring

sample size

n = ((s²)*(t²))/(e²)

options/methods for land measurement

- pacing

- hip chain

- GPS

- ultrasound

- tape or chain

- electronic distance meter or total station

pace

2 steps

Gunter’s chain

66 ft = 4 rods = 20.1 meters

Mile

80 chains = 5280 feet

Acre

660 chains = 43,560 sq ft

true north

aligns with the north star, the axis of earth’s rotation

compass measures direction from

magnetic north

declination

the angular difference between True North and Magnetic North

DD

decimal degrees

DMS

degrees minutes seconds

DD from DMS

DD = D + M/60 + S/3600

DMS from DD

D = integer part

M = integer of decimal part

S = 2nd decimal * 60

primary functions of GPS

- position and coordinates

- distance and direction

- travel progress reports

- accurate time measurements

what are the 3 segments of GPS?

1) space segment

2) control segment

3) user segment

forest stand

a community of trees that is more or les homogenous in composition, age, structure, spatial arrangement, and condition

stand parameters

species composition, height, age and growth, stand density, timber yield

100% cruise

used for scattered stands, high value stands, or small lots.

more accurate estimate of volume

high cost

BA/tree

0.005454(DBH²)

BA

sum of BA/tree * tree factor

tree factor/expansion factor

1/10th acre plot, 2 plots

TF/EF = 5

TF is constant for

area/plot centered

TF is variable for

probability proportional to size/variable radius plot

fixed area plots

probability proportional to frequency

advantages of circular plots

fewer decisions for trees near the plot boundary, no predetermined orientation, easier to correct slopover bias

advantages of line plot cruises

suitable for one person cruising, easy to spot check, allows for stratification by type/stand/area, and statistical analysis

methods of boundary slopover correction

- plot shifting

- plot enlargement

- plot area adjustment

- half plot

- mirage method

- walkthrough method

plot shifting

plot enlargement

plot area adjustment

half plot

mirage method

walkthrough method

Trees Per Acre (TPA)

total number of trees for all plots * tree factor

strip cruising

sample areas are taken in continuous strips at uniform intervals and of uniform widths

advantages of strip cruising

less travel time between samples, fewer edge trees, safety

disadvantages of strip cruising

not great for statistical analysis, underestimates tree heights

recording equipment used for establishing plots

- compass and/or GPS

- clinometer or laser for determining slope

- D-tape

- 100 ft tape or hipchain

- flagging and/or paint

- prism or angle gauge for point cruising

- hypsometer

steps to establish a plot

1) locate plot center

2) mark center temporarily

3) plot size targets 5-12 trees per plot

4) use same plot throughout

5) plot radius checked with hipchain