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USDA F o r e s t Service
G e n e r a l Technical Report INT- 16
September 1974
HANDBOOK FOR INVENTORYING
DOWNED WOODY MATERIAL
James K. Brown
INTERMOUNTAIN FOREST AND RANGE EXPERIMENT STATION
F o r e s t Service
U. S. Department of Agriculture
Ogden, Utah 84401
Roger R. Bay, D i r e c t o r
THE AUTHOR
JAMES K. BROWN received his bachelor's degree from the
University of Minnesota in 1960, his master's from Yale
University in 1961, and his Ph. D. from the University
of Michigan in 1968, all in forestry. From 1961 to 1965
he did research on field measurement of fuel properties
and fire-danger rating systems while with the Lake
States Forest Experiment Station. In 1965 he transferred to the Northern Forest Fire Laboratory, Missoula, Montana, where he i s responsible for research
on the physical properties and inventory of fuel.
CONTENTS
Page
...........................
NUMBER AND SIZE O F SAMPLING PLANES . . . . . . . . . . .
3
........................
4
INTRODUCTION
FIELD PROCEDURES
1
..................... 4
Sample Point P r o c e d u r e s . . . . . . . . . . . . . . . . . . . . 4
Tally Rules . . . . . . . . . . . . . . . . . . . . . . . . . 9
Heavy Slash Options . . . . . . . . . . . . . . . . . . . . 11
Utilization Options . . . . . . . . . . . . . . . . . . . . . 12
F i e l d Equipment . . . . . . . . . . . . . . . . . . . . . . . . 12
CALCULATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
FURTHER APPLICATIONS . . . . . . . . . . . . . . . . . . . . . 19
LITERATURE CITED . . . . . . . . . . . . . . . . . . . . . . . . 20
APPENDIX1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Sampling Intensities . . . . . . . . . . . . . . . . . . . . . . 21
Number and Size of Sampling P l a n e s . . . . . . . . . . . . . 21
Sampling P r e c i s i o n f o r Depth M e a s u r e m e n t s . . . . . . . . . 22
APPENDIX I1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Specific G r a v i t i e s of Sound M a t e r i a l . . . . . . . . . . . . . 23
APPENDIX I11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Calculating Needle Quantities . . . . . . . . . . . . . . . . . 24
Locating Sample Points
To facilitate debris management, procedures for inventorying downed
woody material a r e presented. Instructions show how to estimate weights
and volumes of downed woody material, fuel depth, and duff depth. Using
the planar intersect technique, downed material is inventoried by 0- to
0.25-inch, 0.25- to 1-inch, and 1- to 3-inch diameter classes; and by
1-inch classes for sound and rotten pieces over 3 inches. The method is
rapid and easy to use and can be applied to naturally fallen debris and to
slash. The method involves counting downed woody pieces that intersect
vertical sampling planes and measuring the diameters of pieces larger
than 3 inches in diameter. The piece counts and diameters permit calculation of tons per acre.
OXFORD: 431
KEYWORDS: fire causes (forest), fuel inventory, forest fuels, debris,
planar intersect method, sampling methods.
T h i s Handbook t e l l s how t o i n v e n t o r y weights, volumes, and depths o f downed woody
m a t e r i a l . Downed woody m a t e r i a l i s t h e dead t w i g s , branches, stems, and b o l e s o f t r e e s
and brush t h a t have f a l l e n and l i e on o r above t h e ground. T h i s m a t e r i a l i s u s u a l l y
c a l l e d s l a s h o r logging d e b r i s i f man c r e a t e s it by c u t t i n g ; it i s c a l l e d f u e l ,
n a t u r a l d e b r i s , o r d e t r i t u s i f it accumulates w i t h o u t c u t t i n g .
Inventorying downed woody m a t e r i a l can h e l p land managers p r a c t i c e f u e l management, p l a n f o r p r e s c r i b e d f i r e , and e s t i m a t e u t i l i z a t i o n p o t e n t i a l . For example,
u n d e s i r a b l e f u e l h a z a r d s can b e i d e n t i f i e d and p l a n s made f o r h a z a r d r e d u c t i o n . F i r e
behavior i n w i l d e r n e s s a r e a s can be p r e d i c t e d t o a i d i n implementing l e t - b u r n f i r e
p o l i c i e s . The volume of downed f i b e r can be e s t i m a t e d t o p l a n f o r s a l e s , removal,
and u t i l i z a t i o n . Managers can communicate i n e x a c t terms about t h e i r d e b r i s problems.
The i n v e n t o r y can be done t o provide a l l o r any p a r t o f t h e following i n f o r m a t i o n :
1.
Weights and volumes p e r a c r e of downed woody m a t e r i a l f b r
a.
Diameter s i z e c l a s s e s of 0 t o 0.25, 0.25 t o 1, and 1 t o 3 i n c h e s ; and
b.
Diameters of 3 i n c h e s and l a r g e r f o r sound and r o t t e n c o n d i t i o n s .
2.
Average diameter o f d e b r i s l a r g e r t h a n 3 i n c h e s .
3.
Depth o f f u e l and f o r e s t f l o o r d u f f .
This Handbook a p p l i e s most a c c u r a t e l y i n t h e western United S t a t e s because it
c o n t a i n s average p a r t i c l e d i a m e t e r s f o r western c o n i f e r s ; however, t h e procedures a r e
a p p r o p r i a t e f o r f o r e s t s everywhere. The i n v e n t o r y procedures a r e r a p i d and easy t o
u s e . For average amounts o f downed d e b r i s , about 5 t o 6 minutes p e r sample p o i n t a r e
r e q u i r e d f o r t h e measurements. More time i s u s u a l l y s p e n t i n t r a v e l i n g and l o c a t i n g
sample p o i n t s t h a n i n making t h e measurements. I f o n l y downed woody m a t e r i a l i s
i n v e n t o r i e d , a two-man crew can complete 20 t o 40 p l o t s a day, depending on how much
debris is present.
The i n v e n t o r y o f volumes and weights i s based on t h e p l a n a r i n t e r s e c t technique
(Brown 1971; Brown and Roussopoulos 1974), which h a s t h e same t h e o r e t i c a l b a s i s a s
t h e l i n e i n t e r s e c t t e c h n i q u e (Van Wagner 1968)
The p l a n a r i n t e r s e c t technique
i n v o l v e s c o u n t i n g i n t e r s e c t i o n s o f woody p i e c e s with v e r t i c a l sampling p l a n e s t h a t
resemble g u i l l o t i n e s dropped through t h e downed d e b r i s . Volume i s e s t i m a t e d ; t h e n
weight i s c a l c u l a t e d from volume by applying e s t i m a t e s o f s p e c i f i c g r a v i t y of woody
m a t e r i a l . The p l a n a r i n t e r s e c t technique i s n o n d e s t r u c t i v e and avoids t h e timeconsuming, c o s t l y , and o f t e n i m p r a c t i c a l t a s k of c o l l e c t i n g and weighing l a r g e quant i t i e s of forest debris.
.
Woody p i e c e s l e s s t h a n 3 i n c h e s i n diameter a r e t a l l i e d by s i z e c l a s s e s . P i e c e s
3 i n c h e s and l a r g e r a r e r e c o r d e d by t h e i r d i a m e t e r s . S i z e c l a s s e s o f 0 t o 0.25, 0 . 2 5
t o 1, and 1 t o 3 i n c h e s were chosen f o r t a l l y i n g i n t e r s e c t i o n s because:
1. The c l a s s i n t e r v a l s p r o v i d e t h e most r e s o l u t i o n f o r f i n e f u e l s and a r e small
enough t o permit p r e c i s e e s t i m a t e s o f volume.
2 . They correspond, i n i n c r e a s i n g s i z e , t o I - , lo-, and 100-hour average
moisture t i m e l a g c l a s s e s f o r many woody m a t e r i a l s (Fosberg 1970)
[These a r e s t a n d a r d
moisture t i m e l a g s used i n t h e National Fire-Danger Rating System (Deeming and o t h e r s
1972) ]
.
.
I n v e n t o r y chosen a r e a s a s f o l l o w s :
1.
Decide on l e n g t h o f sampling p l a n e s and number of sample p o i n t s .
2.
Complete t h e f i e l d w o r k .
3.
C a l c u l a t e weight o r volume, s i z e , and depth of d e b r i s .
NUMBER AND SIZE
OF SAMPLING PLANES
Choose sampling p l a n e l e n g t h s from t h e f o l l o w i n g t a b u l a t i o n :
Diameter o f debris
Downed material
Nons l a s h ( n a t u r a l l y f a l l e n m a t e r i a l )
Discontinuous l i g h t s l a s h
Continuous heavy s l a s h '
6
6
3
10-12
10-12
6
35-50
35-50
-15-25
For any a r e a where e s t i m a t e s a r e d e s i r e d , 15 t o 20 sample p o i n t s should b e l o c a t e d
u s i n g t h e sampling p l a n e l e n g t h s shown i n t h e t a b u l a t i o n . This sampling i n t e n s i t y
w i l l o f t e n y i e l d e s t i m a t e s h a v i n g s t a n d a r d e r r o r s w i t h i n 20 p e r c e n t o f t h e mean
e s t i m a t e s . Areas l a r g e r t h a n approximately 50 a c r e s t h a t c o n t a i n a high d i v e r s i t y i n
amount and d i s t r i b u t i o n o f downed m a t e r i a l should be sampled w i t h more t h a n 20 p o i n t s .
I f m a t e r i a l l a r g e r t h a n 3 i n c h e s i n diameter i s s c a n t y o r unevenly d i s t r i b u t e d , t h e
l o n g e r sampling p l a n e s i n t h e t a b u l a t i o n should b e used.
The amount and d i s t r i b u t i o n of downed woody m a t e r i a l vary g r e a t l y among and
w i t h i n s t a n d s . Thus, t h e s e sampling recommendat i o n s should b e c o n s i d e r e d approximate
because a g r e a t e r o r fewer number of p l o t s may be r e q u i r e d t o f u r n i s h adequate p r e c i s i o n f o r any given a r e a . Sampling i n t e n s i t i e s a r e d i s c u s s e d f u r t h e r i n Appendix I .
Locating Sample Points
Locate p l o t s s y s t e m a t i c a l l y ; two methods a r e :
1 . Locate p l o t s a t a f i x e d i n t e r v a l along t r a n s e c t s t h a t l a c e r e g u l a r l y a c r o s s
a sample a r e a (uniform sampling g r i d ) . For example, on a sample a r e a , mark o f f p a r a l l e l t r a n s e c t s t h a t a r e 5 t o 10 c h a i n s a p a r t . Then along t h e t r a n s e c t s l o c a t e p l o t s
a t 2- t o 5-chain i n t e r v a l s .
Locate p l o t s a t a f i x e d i n t e r v a l along a t r a n s e c t t h a t r u n s d i a g o n a l l y
2.
through t h e sample a r e a . To minimize b i a s , have t h e t r a n s e c t c r o s s obvious changes
i n f u e l s . Before e n t e r i n g t h e sample a r e a , determine a t r a n s e c t azimuth and d i s t a n c e
between p l o t s .
Sample Point Procedures
Step 1:
Mark the sampling point with a c h a i n i n g p i n (No. 9 w i r e o r s i m i l a r i t e m ) .
Avoid d i s t u r b i n g m a t e r i a l around t h e p o i n t . Accurate e s t i m a t e s r e q u i r e
measurements o f u n d i s t u r b e d m a t e r i a l . I f s t a n d i n g t r e e measurements (d. b .h .
and h e i g h t ) a r e a p a r t of t h e i n v e n t o r y , measure downed m a t e r i a l f i r s t .
Step 2:
Determine d i r e c t i o n o f sampling plane by t o s s i n g a d i e t o i n d i c a t e one o f
s i x 30" a n g l e s between 0" and 150" ( f i g . 1 ) . The 0" heading i s t h e t r a n s e c t
d i r e c t i o n . Turn a f i x e d d i r e c t i o n , such a s clockwise, t o p o s i t i o n t h e
sampling p l a n e . A s an a l t e r n a t i v e f o r i n d i c a t i n g d i r e c t i o n of t h e sampling
p l a n e , u s e t h e p o s i t i o n o f t h e second hand on a watch a t a given i n s t a n t .
To avoid b i a s i n placement of t h e sampling p l a n e , do n o t look a t t h e f u e l o r
ground while t u r n i n g t h e i n t e r v a l .
Figure I . --Locating sampling
plane b y using die t o pick
one of s i x directions.
Step 3:
Denote position of the sampling plane by running a t a p e o r s t r i n g out from
t h e sampling p o i n t paralleZ t o the ground i n t h e d i r e c t i o n determined i n
S t e p 2 ( f i g . 2 ) . Extend t h e t a p e t o t h e l e n g t h o f t h e l o n g e s t sampling
p l a n e . A f i b e r g l a s s rod o r 1/2-inch aluminum t u b e p l a c e d along t h e s t r i n g
beginning a t t h e sampling p o i n t f a c i l i t a t e s counting p i e c e s l e s s t h a n
1 inch i n diameter. The rod should b e 6 f e e t long, t h e l e n g t h o f sampling
p l a n e f o r small p a r t i c l e s . The t a p e and rod f i x t h e p o s i t i o n of v e r t i c a l
sampling p l a n e s .
/
Grid Line
or Transect
\
30° For
\
\
each dot on die
\
-1-3
\
in Tally
1L
3+
in Tally
d
Figure 2. --Top view of smnplirzg plane and location of fuel depth measurements.
5
Step 4:
Step 5 :
Measure or estimate slope by s i g h t i n g along t h e sampling p l a n e from t h e
sample p o i n t u s i n g an Abney l e v e l o r s i m i l a r d e v i c e . Ample p r e c i s i o n i s t h e
n e a r e s t 10 p e r c e n t , which can be coded u s i n g one d i g i t (10 p e r c e n t = 1,
90 p e r c e n t = 9 , e t c . ) .
Tally the number of particles t h a t i n t e r s e c t t h e sampling p l a n e by t h e
following s i z e c l a s s e s :
0 t o 0.24 i n c h (0 t o 0.6 cm)
0.25 t o 0.99 i n c h (0.6 t o 2.5 cm)
1 . 0 t o 2.99 i n c h e s ( 2 . 5 t o 7.6 cm)
The i n t e r s e c t i o n s can be counted one s i z e c l a s s a t a time o r "dot t a l l i e d , "
which t a k e s s l i g h t l y l o n g e r t h a n counting ( s e e sample d a t a form, page 1 4 ) .
The a c t u a l diameter o f t h e p a r t i c l e a t t h e p o i n t o f i n t e r s e c t i o n determines
i t s s i z e c l a s s . A go-no-go gage w i t h openings 0.25 i n c h , 1 i n c h , and 3 i n c h e s
works w e l l f o r s e p a r a t i n g b o r d e r l i n e p a r t i c l e s i n t o s i z e c l a s s e s and f o r
t r a i n i n g t h e eye t o r e c o g n i z e s i z e c l a s s e s ( f i g . 3 ) .
The v e r t i c a l p l a n e i s a p l o t . Consequently, i n counting p a r t i c l e i n t e r s e c t i o n s , it i s v e r y important t o v i s u a l i z e t h e p l a n e p a s s i n g through one
edge o f t h e p l o t rod and t e r m i n a t i n g along an imaginary f i x e d l i n e on t h e
ground. Once visualized on the ground, the posit<on of the line should not
be changed while counting particles ( f i g . 4 ) . See t a l l y r u l e s f o r q u a l i f y i n g
particles.
Figure 3. --Dimnet&
the intersected
i s checked with
no-go gage. The
rod marks the sa
pling plane.
Figure 4. --The sampling
plane i s exactly
defined b y one edge
of the plot rod.
@ Intersections
Step 6 :
Take three measurements of dead fuel depth. Record depth a s t h e v e r t i c a l
d i s t a n c e from t h e bottom o f t h e l i t t e r l a y e r t o t h e h i g h e s t i n t e r s e c t e d
dead p a r t i c l e f o r each o f t h r e e a d j a c e n t 1-foot-wide v e r t i c a l p a r t i t i o n s o f
t h e sampling p l a n e ( f i g . 5 ) . L i t t e r i s t h e s u r f a c e l a y e r o f t h e f o r e s t f l o o r
and c o n s i s t s o f f r e s h l y f a l l e n l e a v e s , n e e d l e s , t w i g s , b a r k , and f r u i t s .
Begin t h e v e r t i c a l p a r t i t i o n s a t t h e sample p o i n t . Record t o t h e n e a r e s t
whole i n c h .
1 -Foot
Fuel
/
0
Sample
Point
/
9
Figure 5. --Cross sect i o n of a fuel bed.
Depth i s measured
along the arrows
i n each l - f o o t wide partition.
0
0
-Wide
Vertical Partitions
Depth should b e measured from o n l y t h o s e p a r t i c l e s i n c l u d e d i n t h e
i n v e n t o r y f o r loading. For example, p a r t i c l e s a c c e p t a b l e f o r measurement
by t h e p l a n a r i n t e r s e c t technique a r e a l s o a c c e p t a b l e f o r determining depth.
I f o t h e r t e c h n i q u e s a r e used t o e s t i m a t e weight p e r a c r e o f g r a s s and f o r b s ,
t h i s v e g e t a t i o n would a l s o q u a l i f y f o r determining depth.
Stev 7 :
Measure v e r t i c a l depth o f d u f f t o t h e n e a r e s t 0 . 1 inch u s i n g a r u l e r along
t h e sampling p l a n e a t two p o i n t s : (1) 1 f o o t from t h e p l o t c e n t e r ; and
( 2 ) a f i x e d d i s t a n c e of 3 t o 5 f e e t from t h e f i r s t measurement.
Duff i s t h e f e r m e n t a t i o n and humus l a y e r s of t h e f o r e s t f l o o r . I t does
n o t i n c l u d e t h e f r e s h l y c a s t m a t e r i a l i n t h e l i t t e r l a y e r . The t o p o f t h e
d u f f i s where n e e d l e s , l e a v e s , and o t h e r c a s t o f f v e g e t a t i v e m a t e r i a l have
n o t i c e a b l y begun t o decompose. I n d i v i d u a l p a r t i c l e s u s u a l l y w i l l be bound
by f u n g a l mycelium. When moss i s p r e s e n t , t h e t o p o f t h e d u f f i s j u s t below
t h e green p o r t i o n o f t h e moss. The bottom of t h e d u f f i s mineral s o i l .
C a r e f u l l y expose a p r o f i l e o f t h e f o r e s t f l o o r f o r t h e measurement. A
k n i f e o r h a t c h e t h e l p s b u t i s n o t e s s e n t i a l . Avoid compacting o r loosening
t h e d u f f where t h e depth i s measured.
When stumps, l o g s , and t r e e s occur a t t h e p o i n t of measurement, o f f s e t
1 f o o t p e r p e n d i c u l a r t o t h e r i g h t s i d e of t h e sampling p l a n e . Measure through
r o t t e n logs whose c e n t r a l a x i s is i n t h e d u f f l a y e r ( f i g . 6)
.
Yes= center of log is
duff layer or below.
No= center of log is above duff layer.
Figure 6.--Duff depth i s measured through a r o t t e n Zog when i t s
centraZ a x i s Zies i n or b e l m the d u f f .
Step 8:
Measure or estimate the d i m e t e r s o f a l l p i e c e s 3 i n c h e s i n diameter and
l a r g e r t h a t i n t e r s e c t t h e sampling p l a n e . Measure t h e diameters a t t h e
p o i n t o f i n t e r s e c t i o n t o t h e n e a r e s t whole i n c h .
Record d i a m e t e r s s e p a r a t e l y f o r r o t t e n and n o n r o t t e n p i e c e s . Consider
p i e c e s r o t t e n when t h e p i e c e a t t h e i n t e r s e c t i o n i s obviously punky o r can
be e a s i l y kicked a p a r t .
A r u l e r l a i d p e r p e n d i c u l a r l y a c r o s s a l a r g e p i e c e of f u e l works s a t i s f a c t o r i l y f o r measuring diameter. Be s u r e t o avoid p a r a l l a x i n r e a d i n g t h e
r u l e r . C a l i p e r s a l s o work w e l l f o r measuring d i a m e t e r . A diameter t a p e ,
however, i s u n s a t i s f a c t o r y f o r p i e c e s i n c o n t a c t w i t h t h e ground.
Use a s many c o n s e c u t i v e l i n e s on t h e d a t a form ( s e e page 14) a s n e c e s s a r y
t o r e c o r d diameters.
Step 9 :
For the entire s q l e area, record the pcedominate species o f t h e 0- t o
1-inch-diameter branchwood. An average diameter f o r t h e 0- t o 0.25-inch,
and 0.25- t o 1-inch s i z e c l a s s e s w i l l be s e l e c t e d from t h i s information. I f
s e v e r a l s p e c i e s comprise t h e downed d e b r i s , e s t i m a t e t h e p r o p o r t i o n o f t h e
two o r t h r e e most common s p e c i e s . Base t h i s e s t i m a t e on a g e n e r a l impression
o f what e x i s t s on t h e sample a r e a and r e c o r d a s p e r c e n t a g e s o f t o t a l 0- t o
1-inch branchwood. O r , f o r a s l i g h t r e d u c t i o n i n accuracy, omit t h i s s t e p
and i n t h e c a l c u l a t i o n s u s e an average diameter f o r a composite o f s p e c i e s
(page 16)
T m L Y RULES
The f o l l o w i n g r u l e s apply t o downed woody p i e c e s o f a l l d i a m e t e r s :
1. P a r t i c l e s q u a l i f y i n g f o r t a l l y i n c l u d e domed, dead woody m a t e r i a l
( t w i g s , stems, branches, and bolewood) from t r e e s and s h r u b s . Dead branches
a t t a c h e d t o b o l e s o f s t a n d i n g t r e e s a r e omitted because t h e y a r e n o t downed
v e g e t a t i o n . Consider a p a r t i c l e downed when it has f a l l e n t o t h e ground o r
i s s e v e r e d from i t s o r i g i n a l s o u r c e of growth. Cones, b a r k f l a k e s , n e e d l e s ,
l e a v e s , g r a s s , and f o r b s a r e n o t counted. Dead woody stems and branches
s t i l l attached t o standing brush and trees are not counted.
2 . Twigs o r branches l y i n g i n t h e l i t t e r l a y e r and abdve a r e counted.
However, t h e y a r e n o t counted when t h e i n t e r s e c t i o n between t h e c e n t r a l a x i s
o f t h e p a r t i c l e and t h e sampling p l a n e l i e s i n t h e duff ( f o r e s t f l o o r below
the l i t t e r ) (fig. 7).
Does Not Qualify
Figure 7.--Regardless o f s i z e , pieces are t a l l i e d only when i n t e r section l i e s i n and above the l i t t e r ( r i g h t of arrow).
9
3. I f t h e sampling plane i n t e r s e c t s t h e end o f a p i e c e , t a l l y only i f
t h e c e n t r a l a x i s i s c r o s s e d ( f i g . 8 ) . I f t h e plane e x a c t l y i n t e r s e c t s t h e
c e n t r a l a x i s , t a l l y every o t h e r such p i e c e .
0
YES
#
NO
Sampling Planes
F i p r e 8.--An i n t e r s e c t i o n a t the end of a brnnch or log must
include the central axis t o be t a l l i e d .
4 . Don1t t a l l y any p a r t i c l e having a c e n t r a l a x i s t h a t coincides p e r f e c t l y with t h e sampling plane. (This should r a r e l y happen.)
5. I f t h e sampling plane i n t e r s e c t s a curved p i e c e more than once,
t a l l y each i n t e r s e c t i o n ( f i g . 9 ) .
Figure 9.--Count both intersections for a curved piece.
6. T a l l y wood s l i v e r s and chunks l e f t a f t e r logging. V i s u a l l y mold
t h e s e p i e c e s i n t o c y l i n d e r s f o r determining s i z e c l a s s o r recording diameters.
7. T a l l y uprooted stumps and r o o t s n o t encased i n d i r t . For t a l l y i n g ,
c o n s i d e r uprooted stumps a s t r e e b o l e s o r i n d i v i d u a l r o o t s , depending on
where t h e sampling planes i n t e r s e c t t h e stumps. Do n o t t a l l y undisturbed
stumps
.
8. For r o t t e n logs t h a t have f a l l e n a p a r t , v i s u a l l y c o n s t r u c t a
c y l i n d e r c o n t a i n i n g t h e r o t t e n m a t e r i a l and e s t i m a t e i t s diameter. The
c y l i n d e r w i l l probably be s m a l l e r i n diameter t h a n t h e o r i g i n a l log.
9. Be s u r e t o look up from t h e ground when sampling because downed
m a t e r i a l can b e . t a l l i e d up t o any h e i g h t . A p r a c t i c a l upper c u t o f f is about
6 f e e t . However, i n deep s l a s h it may b e necessary t o t a l l y above 6 f e e t .
When s t a n d i n g t r e e s a r e i n v e n t o r i e d along with downed m a t e r i a l , i t i s necessary
t o f i x a limit above t h e ground f o r sampling downed m a t e r i a l . An upper l i m i t h e l p s
d e f i n e a owned t r e e s o t h a t inventory of s t a n d i n g and downed m a t e r i a l s w i l l not
overlap.- 13
HEAVY SLASH OPTIOIVS
1. A y a r d s t i c k a t t a c h e d t o a J a c o b ' s s t a f f i s u s e f u l f o r marking t h e sampling
E r e c t t h e Jacob Is s t a f f
plane and speeds t h e counting of small p a r t i c l e s ( f i g . 10)
a t t h e sample p o i n t . Aline t h e y a r d s t i c k with t h e d i r e c t i o n o f t h e sample plane and
l e v e l i t u s i n g an a t t a c h e d bubble l e v e l .
.
:gure 10. --A yardstick or
meter s t i c k attached t o
a Jacob ' s s t a f f defines
the sampling plane i n
heavy slash.
2 . I n a r e a s with c o n s i d e r a b l e s l a s h , sampling e f f i c i e n c y i s improved by
o c u l a r l y e s t i m a t i n g t h e number o f 0- t o 0.25-inch i n t e r s e c t i o n s and a c t u a l l y counting
t h e number o f i n t e r s e c t i o n s a t a subsample of p o i n t s . The o c u l a r - e s t i m a t e s a r e
a d j u s t e d using t h e r a t i o o f o c u l a r e s t i m a t e s - t o - a c t u a l counts. This method, i n c o r p o r a t i n g 3P sampling, i s described i n d e t a i l by Beaufait and o t h e r s (1974).
~ / 1 nt h e USDA Forest S e r v i c e Northern Region, a r u l e has been e s t a b l i s h e d t h a t a
stem is "downed" and thus q u a l i f i e s f o r t a l l y i n g when t h e i n t e r s e c t i o n o f t h e sampling
plane and c e n t r a l a x i s is 6 f e e t o r l e s s from t h e ground. I f t h e midpoint o f t h e b o l e
i s more than 6 f e e t above ground f o r t r e e s encountered i n f i x e d and v a r i a b l e r a d i u s
p l o t s , they a r e i n v e n t o r i e d a s "standing. l 1
For each sampling plane, e s t i m a t e t h e p r o p o r t i o n o f 0- t o 1-inch-diameter
3.
branchwood t o t h e n e a r e s t 10 p e r c e n t f o r t h e t h r e e most common s p e c i e s .
UTILIZATION OPTIONS
For p i e c e s over 3 inches i n diameter, t h e following a d d i t i o n a l measurements can be
useful f o r describing u t i l i z a t i o n potential :
1.
2.
3.
4.
Species
Length o f p i e c e
Diameter a t l a r g e end
Degree o f checking, r o t , and o t h e r d e f e c t s t h a t apply t o t h e e n t i r e p i e c e .
-
Item
Field Equipment
Hand compass
Gaming d i e
50-foot t a p e o r s t r i n g and one
chaining p i n
P l o t rod
Go-No-Go gage ( f i g . 11)
1-foot r u l e r o r s t e e l pocket t a p e
Hypsometer with p e r c e n t s c a l e
Sample forms
For s l a s h : Jacob I s s t a f f with a t t a c h e d
yard o r meter s t i c k and l e v e l
Use
Transect and p l o t l a y o u t .
Random o r i e n t a t i o n o f sampling p l a n e s .
Delineate t h e sampling p l a n e s .
Delineate sampling p l a n e s and i f
c a l i b r a t e d , measure f u e l depth.
Determine s i z e c l a s s o f b o r d e r l i n e
particles.
Measure duff depth and diameters o f
p i e c e s over 3 i n c h e s . Fuel depth
could b e measured with s t e e l pocket
tape.
Slope measurement.
Record d a t a .
Delineate sampling plane f o r counting
small p a r t i c l e s .
Figure 11 .--A Go-No-Go gage ean be
cut from 1/26 or 1/8-inch
sheet aluminum. Cut the notches
s l i g h t Zy t i g h t and fiZe smooth
t o f i n a l dimensions.
CALCULATIONS
and a r e a l s o easy u s i n g a
The c a l c u l a t i o n s can be r e a d i l y processed by computer:/
Sample c a l c u l a t i o n s a r e shown i n f i g u r e s 12 and 13. For a given
desk c a l c u l a t o r
s t a n d o r sample a r e a , f i l l i n t h e computation summary s h e e t a s follows:
.
1. C a l c u l a t e t h e average s l o p e c o r r e c t i o n f a c t o r (c) u s i n g s l o p e c o r r e c t i o n
f a c t o r s f o r each sampling p l a n e . Look up t h e c o r r e c t i o n f a c t o r s i n t a b l e 1 o r
compute them by:
No s l o p e c o r r e c t i o n i s needed f o r samples taken u s i n g t h e J a c o b ' s s t a f f .
Table 1. --Slope correction factors for converting weight/acre
on a slope basis t o a horizontal basis
:
S1ope
Correction
factor
Percent
c
0
10
20
30
40
50
1.00
1.00
1.02
1.04
1.08
1.12
:
Slope
Percent
60
70
80
90
100
110
Correction
factor
c
1.17
1.22
1.28
1.35
1.41
1.49
-
:/card punching i n s t r u c t i o n s and a FORTRAN program f o r computing t h e i n v e n t o r y
r e s u l t s a r e a v a i l a b l e upon r e q u e s t from t h e Northern F o r e s t F i r e Laboratory, Drawer G ,
Missoula, Montana 59801.
DOWNED
FUEL
INVENTORY
L
I;Y)WST
I
BLOCK
COMPlUT!m
SUL3COMPN<rIMT;S\Tr
ASPECT
STAND
ELEVATION
COVER TYPE
SIZE CLASS ( I n . )
HABITAT TYPE
-
3+
I
10
.35
FUEL DEPTH
3+ DI-
DUFF DFSTH
INTERSECTS
I
1 - 3
I
6
LENGTH OF SAMPLING PLANE ( ~ t . 1 :
r
NO. OF
1
0 - 1
:
w
-*
0
Z
rl
d
=
I
M
3
i
@
r-t
E l m
r
-
N
0
p
a
3
a
,
3
mQm
CG
3
4
?
13
I
I/
1/17
, I
:
,
I
I
4
I
1
I
I
I
,2 5
I
,g
1 2 10
I
,!?
I
1'7
I
L
/[email protected]
13
12
1
5
i
4
U
3
2l 2
i
2
a
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Q
215 / , O
I
1
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I
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I
l o 13
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Figure 12. --Sample data f o m .
14
1
I
I
I
I
I
,
I
DOWNED
WOODY
FOREST :
MATERIAL
COMPUTATION
COMPAR'MENT:
SUMMARY
STAND :
Formulas t o compute tons/acre:
(A)
0- t o 3-inch m a t e r i a l :
(B)
3+-inch m a t e r i a l
Size
class
Constant
=
.
11.64 X n X d2 X s X a X c
Na
,11.64X~d~XsXaXc
NJI
Tons/
acre
I
1d2 f o r 3+
3+ Sound
3/7
3+ Rotten
76 3
Sum o f 3+-inch
diameters
sound
:
Rotten :
3+ Sound & Rotten = IV + V
=
Total = I + I1 + 111 + VI
=
Number
of pieces
Average
diameter
3-3
L
8. 25 in.
37
2
18.5 i n .
Sum o f duff depths : :
3-
Number observations :
9
Average duff depths :
. /
in.
Sum of f u e l depths
:
Number observations :
in.
Figure 13. --Computation summary sheet.
Average f u e l depths :
45)
-4
6 .7
in.
in.
The input values are from figure 12.
15
2 . T o t a l t h e number o f i n t e r s e c t i o n s [n) o v e r a l l sample p o i n t s f o r each of
t h e 0- t o 0.25-inch, 0.25- t o 1 - i n c h , and 1- t o 3-inch s i z e classes.?/
3. From t a b l e 2, e n t e r t h e a p p r o p r i a t e squared average d i a m e t e r s (d2) f o r each
s i z e c l a s s on t h e computation s h e e t . I f s p e c i e s composition -has been determined,
c a l c u l a t e an average d2 a s :
Where P1, P2, and P3 a r e p e r c e n t a g e s f o r composition o f t h e s p e c i e s recorded i n Step 9
(page 9) *
I f s e v e r a l s p e c i e s a r e p r e s e n t and t h e i r composition unknown, t h e composite d2
v a l u e s can b e used a s approximate averages.
Table 2 . - -Squared average-quadratic-mean d i a m e t e r s f o r nons Zash and s l a s h
ground f u e l s
Size class
(inches)
Nons l a s h
.
:
Cover t y p e y
Slash
Average d2
speciesl/
:
Average d2
Inches
0 - 0.25
-
0.25
1 - 3
1
-Tnches2
PP
LP
S, DF, AF, C
L
Composite
0.0342
.0201
,0122
.0149
.0151
PP, LP
L
DF, GF, C , S
~om~osite~l
0 .0248
.0149
,0122
.0151
LP
S, DF, AF, C
L , PP
Composite
,344
.304
.238
.2 89
PP, C
DF, GF, LP, L , S
Composit e
.317
.278
.2 89
PP, AF
S, DF, C , LP
L
Composite
3.12
2.87
2.17
2.76
LP
DF, PP, GF
L , c, s
Composite
3.50
2.83
2.30
2.76
v ~ ~ = ~ o n d e r poi n
s ea (Pinus ponderosa) ; LP=lodgepole p i n e (Pinus
contorts) ; S=Engelmann s p r u c e ( P i c e a enge Zmannii) ; DF=Douglas - f i r
{Pseudotsuga m e n z i e s i i ) ; L=west e r n 1a r c h I L m i x o c c i d e n t a Z i s ) ; GF=grand f i r
(Abies g r a n d i s ) ; C=west e r n r e d c e d a r (Thuja p l i c a t a ) ; AF=subalpine f i r
(Abies Z a s i o c a r ~ a )
21~11composite v a l u e s a r e averages of nonslash and s l a s h f u e l s with
each cover t y p e and s 2 e c i e s weighted e q u a l l y .
L
.
3/For c a l c u l a t i n g s t a n d a r d e r r o r s o f t h e e s t i m a t e , t h e number o f i n t e r s e c t i o n s
(step-2) and t h e sum o f squared diameters (Step 7) must be recorded f o r each p l o t .
16
4 . Determine s p e c i f i c g r a v i t y ( s ) o f m a t e r i a l s from known s o u r c e s o r from
l a b o r a t o r y s t u d i e s . Approximate s p e c i f i c g r a v i t i e s f o r c o n i f e r s a r e :
Diameter c l a s s (inches) : 0-0.25
Specific gravity
:
0.48
0.25-1
1-3
3+Sound
3+Rotten
0.48
0.40
0.40
0.30
Decay and v a r i a b i l i t y i n d e n s i t y make t h i s v a r i a b l e d i f f i c u l t t o handle w i t h accuracy.
More a c c u r a t e e s t i m a t e s f o r l a r g e sound m a t e r i a l can be o b t a i n e d by u s i n g s p e c i f i c
g r a v i t i e s from t h e USDA F o r e s t S e r v i c e (1955) Wood Handbook. S p e c i a l s t u d i e s , as
shown i n Appendix 11, a r e needed t o improve accuracy f o r t h e o t h e r p a r t i c l e c a t e g o r i e s .
5. For s l a s h , determine t h e n o n h o r i z o n t a l angle c o r r e c t i o n f a c t o r s (a) from
t a b l e 3 . For nonslash f u e l s , u s e t h e following c o r r e c t i o n f a c t o r s based on a composite
o f western s p e c i e s :
0 t o 3 inches: 1.13
3+ i n c h e s : 1.00
The c o r r e c t i o n f a c t o r a d j u s t s weight e s t i m a t e s f o r t h e f a c t t h a t a l l p a r t i c l e s do n o t
l i e h o r i z o n t a l l y a s assumed i n t h e p l a n a r i n t e r s e c t t h e o r y .
Table 3. --Average secant o f nonhorizontal p a r t i c l e angles for
eorreeting orientation bias for s lash
Size class
:
speciesL/
(inches)
0 t o 0.25
PP
Others
0.25 t o 1
PP
Others
Fresh
slash
Average
:
1 (a)
-yearand
:
olderslash
PP
Others
A l l (an
assumption)
1.00
1.00
l/~~=~onderp
o isnae ; Others=based on d a t a f o r Douglas- f i r ,
lodgepole p i n e , Engelmann s p r u c e , western r e d c e d a r , western l a r c h ,
and grand f i r .
6 . C a l c u l a t e t h e t o t a l l e n g t h of samplin2 l i n e (NR) f o r each s i z e c l a s s : NR =
number of sample p o i n t s m u l t i p l i e d by l e n g t h of sampling p l a n e ( f e e t ) .
7. For m a t e r i a l 3 i n c h e s and l a r g e r , s q u a r e t h e diameter o f each i n t e r s e c t e d
p i e c e and sum t h e squared v a l u e s (zd2) f o r a l l p i e c e s i n t h e sampled area..?./
Compute
L'd2 s e p a r a t e l y f o r sound and r o t t e n c a t e g o r i e s . To o b t a i n weights o r volumes f o r
c e r t a i n d i a m e t e r ranges ( 3 t o 9 i n c h e s , f o r example) , compute 1d2 f o r t h e s p e c i f i e d
range.
8. C a l c u l a t e t h e sum of d i a m e t e r s f o r a l l i n t e r s e c t e d p i e c e s 3 i n c h e s and l a r g e r
( c a l c u l a t e sound and r o t t e n m a t e r i a l s s e p a r a t e l y )
.
9.
C a l c u l a t e t h e sum of a l l measurements f o r d u f f d e p t h .
1 0 . C a l c u l a t e t o n s / a c r e , u s i n g formulas on t h e computation s h e e t ( f i g . 13)
d e s i r e d , c a l c u l a t e volumes :
Cubic f e e t p e r a c r e =
11.
If
grzvity
32.05 x t o n s
Specific
e r acre
C a l c u l a t e average d i a m e t e r s o f i n t e r s e c t e d p i e c e s 3 inches and 1-arger.
12. C a l c u l a t e average f u e l depth and duff depth a s t h e sum o f t h e depths d i v i d e d
by t h e number o f measurements.
13.
Appendix I11 shows how t o c a l c u l a t e n e e d l e q u a n t i t i e s i n s l a s h .
When i n v e n t o r y i n g l a r g e a r e a s t h a t hold many s p e c i e s i t i s p r a c t i c a l t o use
composite v a l u e s and approximations f o r d i a m e t e r s , s p e c i f i c g r a v i t i e s , and n o n h o r i z o n t a l
c o r r e c t i o n s . For example, a t i m b e r management and downed-debris i n v e n t o r y i n t h e
Northern Region of t h e USDA F o r e s t S e r v i c e u t i l i z e s composite average d i a m e t e r s , comp o s i t e average n o n h o r i z o n t a l c o r r e c t i o n f a c t o r s , and b e s t approximations f o r s p e c i f i c
gravities.
For t h e Northern Region i n v e n t o r y , t h e formulas i n f i g u r e 13 s i m p l i f y t o :
1.
0- t o 0.25-inch s i z e c l a s s : w = 0.09533 nc/NR
2.
0.25- t o 1-inch s i z e c l a s s : w = 1.825 nc/NR
3.
1- t o 3-inch s i z e c l a s s
: w = 14.52 nc/NR
4.
3+-inch sound
: w = 4.656 cd2c/N!L
5.
3+-inch r o t t e n
: w = 3.492 1d2c/N!L
where :
w = weight, t o n s / a c r e .
-
he formulas i n c o r p o r a t e an i n s i g n i f i c a n t b i a s because n , z d 2 , and c a r e t o t a l e d
s e p a r a t e l y . Summing n x c o r ~d~ x c o v e r a l l p l o t s would e l i m i n a t e t h e b i a s e s ; howe v e r , t h i s i s u n n e c e s s a r i l y troublesome.
FURTHER APPLICATIONS
I f only d e b r i s l a r g e r than 3 o r 4 inches i n diameter i s t o b e i n v e n t o r i e d , t h e
l i n e i n t e r s e c t technique d e s c r i b e d by Howard and Ward (1972) and Bailey (1969) might
be more a p p r o p r i a t e than t h e p l a n a r i n t e r s e c t method, e s p e c i a l l y i n logging s l a s h .
The l i n e i n t e r s e c t method employs a few long sampling planes; t h e p l a n a r i n t e r s e c t
method employs many small sampling p l a n e s . I f d e b r i s both g r e a t e r t h a n and l e s s t h a n
3 o r 4 inches i n diameter must be i n v e n t o r i e d , t h e p l a n a r i n t e r s e c t technique i s more
e f f i c i e n t . The p l a n a r i n t e r s e c t technique can a l s o be coordinated with o t h e r measurements o f v e g e t a t i o n taken on p l o t s ( f o r example, an inventory of timber volume)
.
The procedures i n t h i s Handbook can be a p p l i e d t o downed d e b r i s i n a r e a s o t h e r
than t h e western United S t a t e s by assuming o r measuring average diameters f o r t h e
t h r e e s i z e c l a s s e s of p a r t i c l e s . Average diameters have been determined f o r r e d p i n e
(Pinus r e s i n o s a ) , jack p i n e (Pinus banksiana) , and oak (Quercus spp. ) (Brown and
A convenient method f o r e s t i m a t i n g s l a s h weights o f s e v e r a l Lake
Roussopoulos 1974)
S t a t e s t r e e s p e c i e s has been r e p o r t e d by Roussopoulos and Johnson (1973).
.
If f i r e behavior i s t o b e mathematically modeled using models such a s Rothermells
(l972), weights of o t h e r f i n e f u e l s such as needle l i t t e r , dead g r a s s , and dead f o r b s
a l s o should b e determined by sampling o r by e x t r a p o l a t i n g from e x i s t i n g information.
Sampling f o r q u a n t i t i e s o f g r a s s , f o r b s , and l i t t e r r e q u i r e s methods o t h e r than t h e
p l a n a r i n t e r s e c t technique (USDA F o r e s t S e r v i c e 1959; Brown 1966; Hutchings and
Schmautz 1969).
Because p r a c t i c a l methods o f inventory have been lacking i n t h e p a s t , accumulat i o n s o f downed f u e l and d e b r i s have been described i n vague terms such a s " l i g h t , "
"medium,11 and llheavy.ll Using t h e simple f i e l d procedures i n t h i s Handbook, weight
and volume of downed woody m a t e r i a l can be i n v e n t o r i e d t o provide an o b j e c t i v e b a s i s
f o r managing d e b r i s .
LITERATURE CITED
B a i l e y , G . R.
1969. An e v a l u a t i o n o f t h e l i n e - i n t e r s e c t method of a s s e s s i n g logging r e s i d u e .
Can. Dep. F i s h . 6 For., For. Prod. Lab. I n f . Rep. VP-X-23, 41 p.
B e a u f a i t , William R . , Michael A . Marsden, and Rodney A . Norm
1974. I n v e n t o r y o f s l a s h f u e l s u s i n g 3P subsampling. USDA For. S e r v . Gen. Tech.
Rep. INT-13, 17 p . , i l l u s .
Brown, J . K .
1966. F o r e s t f l o o r f u e l s i n r e d and jack p i n e s t a n d s . USDA For. S e r v . Res. Note
NC-9, 3 p.
Brown, James K .
1971. A p l a n a r i n t e r s e c t method f o r sampling f u e l volume and s u r f a c e a r e a .
For. S c i . 17(1) :96-102, i l l u s .
Brown, James K .
1972. F i e l d t e s t o f a r a t e - o f - f i r e - s p r e a d model i n s l a s h f u e l s . USDA For. S e r v .
Res. Pap. INT-116, 24 p . , i l l u s .
Brown, James K . , and P e t e r J . Roussopoulos
E l i m i n a t i n g b i a s e s i n t h e p l a n a r i n t e r s e c t method f o r sampling small f u e l
volumes. For. S c i . ( I n p r e s s . )
Deeming, John E . , James W . L a n c a s t e r , Michael A. Fosberg, R . William Furman, and
Mark J . Schroeder
1972. N a t i o n a l f i r e - d a n g e r r a t i n g system. USDA For. Serv. Res. Pap. RM-84, 165 p .
Fahnestock, G. R.
1960. Logging s l a s h f l a m m a b i l i t y . USDA For. Serv. Res. Pap. INT-58, 67 p . , i l l u s .
Fosberg, Michael A.
1970. Drying r a t e s o f heartwood below f i b e r s a t u r a t i o n . For. S c i . 16 (1) :
57-63, i l l u s .
Howard, James O., and F r a n k l i n R. Ward
1972. Measurement o f logging r e s i d u e - - a l t e r n a t i v e a p p l i c a t i o n s of t h e l i n e
i n t e r s e c t method. USDA For. Serv. Res. Note PNW-183, 8 p.
Hutchings , S. S , and J E Schmautz
1969. A f i e l d t e s t o f t h e r e l a t i v e - w e i g h t - e s t i m a t e method f o r determining
herbage p r o d u c t i o n . J . Range Manage. 22:408-411.
Roussopoulos, P . J . , and V. J . Johnson
1973. E s t i m a t i n g s l a s h f u e l loading f o r s e v e r a l Lake S t a t e s t r e e s p e c i e s .
USDA For. Serv. Res. Pap. NC-88, 8 p.
Rothermel, R. C .
1972. A mathematical model f o r p r e d i c t i n g f i r e s p r e a d i n w i l d l a n d f u e l s . USDA
For. Serv. Res. Pap. INT-115, 40 p . , i l l u s .
Van Wagner, C . E .
1968. The l i n e i n t e r s e c t method i n f o r e s t f u e l sampling. For. S c i . 1 4 ( 1 ) :
20-26, i l l u s .
USDA F o r e s t S e r v i c e
1955. Wood Handbook No. 72, 528 p . For. Prod. Lab., Madison, Wis.
USDA F o r e s t S e r v i c e
1959. Techniques and methods o f measuring u n d e r s t o r y v e g e t a t i o n . Southern and
S o u t h e a s t For. Exp. S t n . Symp. P r o c . , 174 p.
.
\
. .
APPENDIX I
Sampling Intensities
NUMBER AND S I Z E OF SAMPLING FLANES
Sampling p r e c i s i o n can be c o n t r o l l e d by a l t e r i n g t h e number of p l o t s and l e n g t h
o f sampling p l a n e s . As a g e n e r a l r u l e , t h e more downed m a t e r i a l on an a r e a , t h e fewer
t h e number and s h o r t e r t h e l e n g t h o f sampling p l a n e s r e q u i r e d t o achieve a given l e v e l
o f p r e c i s i o n . F i g u r e 1 4 , based on average sampling v a r i a t i o n f o r number of i n t e r s e c t i o n s o f 0- t o 1-inch and 1- t o 3-inch p a r t i c l e s , can h e l p i n choosing number o f
p l o t s and l e n g t h o f sampling p l a n e s . The d a t a f o r f i g u r e 14 a r e from many s t a n d s o f
v a r y i n g composition and downed d e b r i s accumulations i n n o r t h e r n Idaho and western
Montana. Curves f o r a l l m a t e r i a l under 3 inches i n diameter would f a l l between t h o s e
f o r t h e 0- t o 1-inch and 1- t o 3:inch c l a s s e s .
P e r c e n t e r r o r s o f 20 p e r c e n t o r l e s s a r e probably adequate l e v e l s o f p r e c i s i o n f o r
a s s e s s i n g most f u e l problems. P e r c e n t e r r o r i s t h e s t a n d a r d e r r o r of t h e e s t i m a t e
d i v i d e d by t h e mean e s t i m a t e and expressed as a p e r c e n t a g e . More p r e c i s i o n , such a s
p e r c e n t e r r o r s o f 10 t o 15 p e r c e n t , may be d e s i r a b l e f o r e v a l u a t i n g u t i l i z a t i o n potent i a l o f downed woody m a t e r i a l
.
P r e c i s i o n i s maximized u s i n g a d i f f e r e n t l e n g t h o f sampling
c l a s s . However, c o n s i d e r i n g b o t h f i e l d e f f o r t and p r e c i s i o n , it
u s e t h e same plane l e n g t h f o r sampling t h e 0- t o 0.25- and 0.25The f o l l o w i n g s u g g e s t i o n s w i l l h e l p determine t h e most e f f i c i e n t
sampling p l a n e s f o r a given a r e a :
p l a n e f o r each s i z e
i s more e f f i c i e n t t o
t o 1-inch c l a s s e s .
number and l e n g t h o f
1. Record d a t a from about 20 sampling p l a n e s i n an a r e a and c a l c u l a t e t h e v a r i a t i o n f o r guiding f u r t h e r sampling.
10
20
30
40
50
60
70
80
90
100
110
Number of sample points
Figure 14.--Percent errors for number of particle intersections along 6- and
22-foot-length sampZing planes related t o number o f sample points for quant i t i e s of l i g h t slash and nonslash. Percent error i s 2OOX (standard error
of the estimate divided by the mean estimate).
2. For m a t e r i a l l a r g e r t h a n 3 i n c h e s i n d i a m e t e r , t h e sampling p l a n e should b e
long en ough s o t h a t on t h e average a t l e a s t one i n t e r s e c t i o n occurs w i t h t h r e e - f o u r t h s
o r more of t h e p l a n e s . A l a r g e sampling v a r i a n c e r e s u l t s when many zeros a r e recorded
f o r i n t e r s e c t i o n s . I n a r e a s where v e r y l i t t l e downed m a t e r i a l e x i s t s , sampling p l a n e s
should a c t u a l l y b e one t o s e v e r a l hundred f e e t long t o p r o v i d e r e s p e c t a b l e p r e c i s i o n .
Where many sampling p l a n e s have z e r o e n t r i e s , o t h e r methods such a s measurement of
l e n g t h and d i a m e t e r o f a l l downed p i e c e s may be t h e most e f f i c i e n t method of i n v e n t o r y .
3 . The number and l e n g t h o f sampling p l a n e s should be chosen s o t h a t f o r a p i e c e
s i z e of i n t e r e s t , such a s m a t e r i a l over 3 inches i n diameter, a t l e a s t 35 t o 50 i n t e r s e c t i o n s occur o v e r an e n t i r e sampled a r e a .
SAMPLING PRECISION FOR DEPTH MEASUREMENTS
To achieve p e r c e n t e r r o r s of 15 and 20 p e r c e n t u s i n g two-stage sampling, t h e most
e f f i c i e n t number o f secondary sampling u n i t s appears t o be t h r e e f o r f u e l depth and two
f o r d u f f depth ( f i g . 1 5 ) .
The d a t a f o r f i g u r e 15 r e p r e s e n t average v a r i a t i o n from sampling a wide v a r i e t y o f
f o r e s t and downed f u e l c o n d i t i o n s i n n o r t h e r n Idaho and w e s t e r n Montana. S e v e r a l thousand measurements were t a k e n u s i n g two secondary sample p o i n t s f o r d u f f depth and t h r e e
secondary sample p o i n t s f o r f u e l d e p t h . Vegetation q u a l i f y i n g f o r f u e l depth measurements i n c l u d e d a l l dead downed woody m a t e r i a l and dead b r u s h , g r a s s , and f o r b s
The
d a t a were s u b j e c t e d t o a n a l y s i s o f v a r i a n c e f o r two-stage sampling.
.
The number of sample p l o t s r e q u i r e d t o a t t a i n a given l e v e l of p r e c i s i o n v a r i e s
c o n s i d e r a b l y among d i f f e r e n t a r e a s . For choosing sampling i n t e n s i t i e s f o r s p e c i f i c
a r e a s t h e number of primary sample p o i n t s i n f i g u r e 15 could b e a d j u s t e d up o r down
c o n s i d e r a b l y , depending on homogeneity o f t h e dead v e g e t a t i o n s t r a t a .
S Dead fuel depth
f Duff depth
Number of secondary sample points
Figure 15.--Number of primary and secondary points needed t o achieve
percent errors o f 15 and 20 percent for fuel depth and duff depth.
APPENDIX II
Specific Gravities of Sound Material
The s p e c i f i c g r a v i t i e s i n t a b l e 4 a r e based on ovendry weight and a i r d r y volume
and can be used f o r c a l c u l a t i o n o f loadings.
Table 4 . - - S p e c i f i c gravity of uoody twigs
and branehes w i t h bark attached
Diameter s i z e c l a s s (cm)
Species
110 -
1
:.
1
-
10
o
-
i
1 1-
3
j
213
-
5
Ponderosa p i n e
Douglas-fir
Western l a r c h
Lodgepole p i n e
Engelmann s p r u c e
Subalpine f i r
Western redcedar
1' William R . B e a u f a i t and Charles E . Hardy. F i r e q u a n t i f i c a t i o n f o r s i l v i c u l t u r a l use. USDA For. S e r v . , I n t e r m t , For. 6 Range Exp. S t n . (In p r e p a r a t i o n . )
1
Brown (1972).
APPENDIX Ill
Calculating Needle Quantities
Weight o f n e e d l e s can b e determined by m u l t i p l y i n g r a t i o s of needle-to-branchwood
weights ( t a b l e 5) times e s t i m a t e d branchwood weight. The e s t i m a t e s i n t a b l e 5 a r e f o r
branches having a l l n e e d l e s a t t a c h e d . The d a t a a r e based on e s t i m a t e s o f n e e d l e s and
branchwood from t o t a l l i v i n g crowns f o r t r e e s between 2 and 30 i n c h e s d . b . h .
Tab l e 5. --Foliage- to-branchwood r a t i o s b a s e d on o v e n d q weight
Species
:
Diameter of branches
0- t o 0.25-inch
;
0- t o 1-inch
No. t r e e s
sampled
Western l a r c h
Ponderosa p i n e
Western w h i t e p i n e
Douglas-fir
Western hemlock
Engelmann s p r u c e
Western r e d c e d a r
Lodgepole
Grand f i r y
-
p
-
/'
-
-
Data by Fahnestock (1960).
QGPO 19794W1201475
Headquarters for the Intermountain Forest and
Range Experiment Station a r e i n Ogden, Utah.
Field Research Work Units a r e maintained in:
Boise, Idaho
Bozeman, Montana (in cooperation with
Montana State University)
Logan, Utah (in cooperation with Utah
State University)
Missoula, Montana (in cooperation with
University of Montana)
Moscow, Idaho (in cooperation with the
University of Idaho)
Provo, Utah (in cooperation with Brigham
Young University)
Reno, Nevada (in cooperation with the
University of Nevada)
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