Application of Self-Thinning in Mesquite (Prosopis glandulosa var. glandulosa) to Range Management and Lumber Production

8/9/2019 Application of Self-Thinning in Mesquite (Prosopis glandulosa var. glandulosa) to Range Management and Lumber Pr…

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Forest Ecology and Management,

31 ( 1990 ) 225-232 225

Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

A p p l i c a t i o n o f S e l f T h i n n i n g i n M e s q u i t e

P r o sop i s g l a n du l o sa v a r . g l andu l o sa ) t o R a n g e

M a n a g e m e n t a n d L u m b e r P r o d u c t i o n

PETE R FELKER, JOSEP H M. MEYER and STEVEN J. GRONSKI

Center for Semi-Arid Forest Resources, Caesar Kleberg Wildlife Research Institute Texas A I

University, KingsviUe, TX 78363 (U.S.A.)

(Accepted 27 January 1989)

ABSTRACT

Felker, P., Meyer, J.M. and Gronski, S.J., 1990. Application of self-thinnin g in mesquite (Prosopis

glandulosa var. glandulosa) to range management and lumber production. For. Ecol. Manage.,

31: 225-232.

To gain a better understanding of the relationships between stand density and tree volume in

mesquite, seven native stands were examined. Stand densities ranged from 6 to 19 000 stems h a- 1,

and e stimat ed biomass ranged from 0.65 to 1300 kg stem -1. Regression equations were used to

estimate biomass from basal diameters. A plot of estimated tree biomass vs. stand density was

defined by the estima ted self-th inning line: log W-- - 1.17 log d+5. 22 (r e=0.9 5), where: W

is stem fresh weight (kg); and d stand densi ty (stems h a- 1 . Regressions of stand dens ity on basal

diameter, lumber volume stem-1 and tot al biomass ha-1 were also examined. When plots deemed

to not be at full stand occupancy were excluded from the data set, a regression predicted that

densities of 100 stems ha -1 would produce 35-cm-basal -diameter stems. This density also gave

the highest lumber yield.

I N T R O D U T I O N

M e s q u i t e

Pr osopis landul osa

ar .

glandulosa)

r e e s c a n o c c u r a t d e n s i t i e s

o f 1 0 0 0 0 s t e m s h a - 1 , w i t h b a s a l d i a m e t e r s o f 3 - 4 c m , a b o u t t e n y e a r s a f te r

l a n d - c le a r i n g . T h e s e d e n s e s t a n d s a re a p r o b le m o n r a n g e l a n d s , w h e r e t h e y

c o m p e t e w i t h f o ra g e s p e c i e s fo r li g h t , w a t e r a n d n u t r i e n t s ( F i s h e r , 1 9 5 0 ) . L a r g e r

m e s q u i t e t r ee s g i v e s h a d e t o l i v e s t o c k a n d p r o d u c e a b u n d a n t b e a n s , u s e f u l f or

a n i m a l fe e d i n d ry y e a r s ( F e l k e r , 1 9 7 9 ) . F u r t h e r m o r e , m e s q u i t e t r e e s im p r o v e

s o i l f e r t i l i t y t h r o u g h n i t r o g e n f i x a t i o n ( R u n d e l e t a l . , 1 9 8 2 ) . L a r g e t r e e s c a n

p r o v i d e t i m b e r w i t h p r o p e r t i e s s u i t a b l e f o r q u a l i t y h a r d w o o d f u r n i t u r e a n d

f l o o r i n g ( W e l d o n , 1 9 8 6 ) .

F o r m e r l y , w h e r e d e n s e s t a n d s o f m e s q u i t e e x i s t ed , e r a d i c a t io n w a s a t -

t e m p t e d ( F i s h e r et a l ., 1 9 7 2 ) , u s u a l l y w i t h o u t s u c c e s s . I f s e l f - t h i n n i n g o c -

0378-1127/90 / 03.50 © 1990 Elsevier Science Publishers B.V.


2/8

6 P FELKE R ET AL

curr ed in mesqui te stands, t he livestock problems caused by small trees could

be eliminated. Large mesquite trees, grown at wide spacings, might compete

against seedlings and maintain a savannah. In search of economical and self-

sustaining techniques for rangeland manag ement, we evaluated self-thinning

in mesquite. Could large trees pre vent dense stands of mesquite from becoming

established? If self-thinning occurred in mesquite, what would be the ultimate

tree size and sta nd-density for lumber production?

The natural thinni ng of other forest communities has been described by a

plot of stand density (stems ha -1) vs. plant diameter or weight (Long and

Smith, 1984). Research with other species has examined dens ity/ diam eter re-

lationships at full-stand occupancy. In mesic areas, this can be assumed to

occur at crown closure.

Mesquite trees grow in semi-arid and ar id regions, where self- thinning might

occur at low stand densities. The root: shoot biomass ratio of arid-land trees

could exceed 1, with la teral roots ex tend ing beyon d the canopies. Indeed, Cable

(1977), using neutron access tubes, found tha t mesquite trees used water at

10-15 m beyond the ir canopy zones. In arid-land forests there is seldom canopy

closure; the spacing of trees increases as an nual rainfall decreases. Thus, full-

stand occupancy in mesquite trees may depend more on root competition than

canopy competition. This could complicate the estimati on of a self -thinning

line.

MATERIALS AND METHODS

Since mesquite stands seldom have closed canopies, it is difficult to know

when full-site occupancy occurs. We measured large trees, at spacings several

times the canopy diameter, to obtain an upper limit for tree size with minimal

competition. Mesquite plantations do not exist, except for research plots. Hence,

it was impossible to measure densit y/volu me relationships of trees at known

ages. Instead, sites with co ntra sting density: volume ratios were chosen. Native

mesquite stands between Kingsville and Nixon, Texas, were measured for basal

diameters, tree heights, and canopy diameters. The mean annual rainfall in

both locations was about 650 mm. Selection criteria were based on absence of

irrigation and fertilization. The first, second, and fourth locations were near

Kingsville; the other four encompassed a 15-km distance near Nixon, Texas.

Plot sizes varied according to s tand density, with smaller plots used in denser

stands (Table 1 ).

A regression from the harvest of 194 young South American rosopis alba

trees in Kingsville, Texas (Felker, unpublished data, 1986) was used for esti-

mating the biomass of small stems at sites 1 through 3. The equation was:

log W=2.70 lo gd b - l. l l (r2=0.957, SE=0.041)

where: W is stem fresh weight (kg); and db, stem basal diameter (cm). The


3/8

SELF-THINNING IN MESQUITE 227

TABLE 1

W e i g h t s a n d d e n s i t ie s o f s t e m s i n s u r v e y e d m e s q u i t e Prosopis

glandulosa

var.

glandulosa

s t ands

S i t e P l o t D i a m e t e r B i o m a s s D e n s i t y

m 2 ) cm s t e m 1 kg s t e m 1 s t em s h a 1

1 50 1.88 0.72 18 800

1 50 1.85 0.60 13 800

1 50 3.61 4.16 10 200

1 50 3.40 3.20 10 000

2 144 4.87 9.36 7180

2 144 6.08 13.67 5110

2 144 5.76 16.6 4760

2 144 5.96 12.3 3590

3 100 5.67 11.2 5800

3 100 6.18 15.0 4900

3 100 7.04 19.3 2900

4 900 20.7 183 280

4 900 18.8 148 320

4 900 18.0 137 350

4 900 15.5 95 470

5 900 22.0 213 311

5 900 24.7 281 244

5 900 25.8 298 222

6 900 30.6 452 167

6 900 31.2 467 122

6 900 42.4 885 111

7 11800 43.7 943 13.9

7 7100 49.2 1190 9.92

7 6500 50.9 1290 5.93

b i o m a s s o f s t e m s a t t h e o t h e r f o u r s it e s w a s e s t i m a t e d b y a r e g r e s s io n o n 1 0

l a r g e m e s q u i t e

P. g landu losa

var.

g landu losa)

t r e e s t h a t w e r e w e i g h e d a n d

m e a s u r e d i n S o u t h T e x a s ( E l F a d l e t al ., 1 9 8 9 ) :

l o g W=1 05 log A b+ 3.8 3 r2--0.800, SE----0.187)

w h e r e : A b i s s t e m b a s a l a r e a ( c m 2 ) .

L o g a r i t h m s o f fr e s h w e i g h t ( k g s t e m - 1 w e r e e s t im a t e d w i t h t h e s e r e g re s -

s i o n e q u a t io n s , a n d p l o t t e d o n t h e l o g a r it h m s o f s t a n d d e n s i t y ( s t e m s h a - 1 ) .

A r e g r e s s io n d e s c r i b i n g t h i s s e l f - th i n n i n g r e l a t i o n s h i p w a s p l o t t e d o v e r t h e

p o i n t s .

A s t u d y c o n d u c t e d b y R o g e r s ( 1 9 8 4 ) i n L u f k i n , T e x a s r e g r e s s e d s a w n l u m -

b e r , g r a d e 2 lu m b e r , a n d g r a d e 1 l u m b e r y i e l d s o n t h e l e n g t h s a n d d i a m e t e r s o f

1 0 5 m e s q u i t e l o g s. B o a r d s w i t h a c l e a r s u r fa c e o f 5 .1 c m × 1 5 .2 c m w e r e c l a s s i-


4/8

8 P F ELKERE T AL

f l e d a s g r a d e - 2 l u m b e r ; b o a r d s w i t h a c l e a r s u r f a c e o f a t l e a s t 5 . 1 >< b y 6 0 c m

w e r e c o n s i d e r e d g r ad e - 1 l u m b e r . T h e m e t r i c c o n v e r s i o n s o f t h e s e r e g r e s s i o n s

w e r e u s e d t o p r e d i c t l u m b e r v o l u m e s :

SL = 1 . 8 6 D s e + 0 . 1 7 0 L - - 3 6 . 0

G 2 = 1 . 1 6 D , ~ +0 .0 8 5 L - 2 0 . 0

G 1 = 0 . 4 8 2 D s e + 0 .0 2 3 L - 9 . 2 1

( r e = 0 . 7 1 )

( r 2 = 0 . 5 3 )

( r 2 = 0 . 4 5 )

w h e r e : D~e i s s m a l l - e n d d i a m e t e r o f a m e s q u i t e l o g ( c m ) ; L , m e s q u i t e l o g l e n g t h

( c m ) ; S L, s a w n l u m b e r ( m 3 ) ; G 2, g r a d e - 2 l u m b e r ( m 3 ) ; a n d G l , g r a d e - 1 l u m b e r

m3).

I n e s t i m a t i n g t r e e v o l u m e s , E1 F a d l e t a l. ( 1 9 89 ) e q u a t e d b r a n c h s e c t i o n s t o

c y l i n d e rs , w i t h d i a m e t e r s e q u al t o t h e m e a n o f s m a l l - e n d a n d l a r g e - e n d

t h i c k n e s s e s . L u m b e r v o l u m e s , p r e d i c t e d f r o m R o g e r s ( 1 9 8 2 ), w e r e r e g r e s s e d

o n t h e b a s a l a r e a s ( m 2 ) o f t h e s e t r e e s t o o b t a i n :

l og V = 1 . 2 7 l o g A b + 0 . 7 1 8

l o g S L = 1 . 3 7 l o g A b + 0 . 4 5 3

log G2 = 1 .35 log Ab + 0 .228

log G1 = 1 .65 log Ab-- 0 .202

( r2 = 0 .9 1 , S E = 0 .1 4 1 )

( r2 = 0 .9 3 , S E= 0 .1 3 9 )

(r2 = 0 . 9 3 , S E = 0 . 1 3 6 )

( r 2 = 0 . 9 0 , S E = 0 . 1 9 7 )

w h e r e : V i s t r e e v o l u m e ( m 3 ); a n d r 2, c o r r e l a t i o n f o r t h e r e g r e s s i o n s o f p r e -

d i c t e d l u m b e r v o l u m e s o n s t e m b a s a l a r e a.

R o g e r s l u m b e r g r a d es w e r e b e l o w c o m m o n g r a d es f or o t h e r h a rd w o o d s , d u e

t o d e f e c t s i n m e s q u i t e w o o d . B o t h R o g e r s ( 1 9 84 ) a n d E l F a d l e t a l . ( 1 9 8 9 ) u s e d

r e g r e s s i o n s b a s e d o n l o g s g r e a t e r t h a n 1 0 c m a t t h e s m a l l e n d . S i n c e i t is d if -

f i c u lt t o p r o c e s s s m a l l l o gs , w e c o n s i d e r e d t h e l u m b e r v o l u m e t o b e n i l i n t r e e s

w i t h d i a m e t e r s l es s t h a n 1 5 c m .

RESULTS

D e n s i t y s t a t i s t i c s o f t r e e s i n t h e s u r v e y a r e a s ( T a b l e 1 ) a r e u s e f u l fo r p r e -

d i c t in g th e b i o m a s s o f n a t i v e m e s q u i t e s t an d s . B i o m a s s s t e m - 1 r a n g e d f r o m

0 .6 5 k g a t a s t a n d d e n s i t y o f o v e r 10 0 0 0 s t e m s h a - 1 , t o 1 3 0 0 k g a t a s t a n d

d e n s i t y o f 1 0 s t e m s h a - 1. S t e m v o l u m e c a n b e o b t a i n e d b y d i v i d i n g m a s s b y a

m e s q u i t e w o o d d e n s i t y o f 7 00 k g m - 3 ( W e l d o n , 1 9 8 6 ).

S e v e r a l r eg r e s s io n s w e r e e x a m i n e d f o r p r e d i c t i n g s t e m b i o m a s s f r o m s t a n d

d e n s i ty . W e a s s u m e d t h a t f u l l - s t a n d o c c u p a n c y d i d n o t e x i s t a t s i te 7 , a n d

c o m p u t e d a r e g r e s s io n t h a t e x c l u d e d t h e s e t r e e s. T h e e q u a t i o n , s h o w n g r a p h -

ica l ly in F ig . 1 , i s :

l o g W = 1 . 1 7 l o g N + 5 . 2 2 ( r2 = 0 .9 5 , S E = 0 . 0 64 )

w h e r e : N i s s t a n d d e n s i t y ( s t e m s h a - 1 ) .


5/8

S E L F - T H I N N I N G I N M E S Q U I T E 9

3 5 - -

0 o

3.0

E 2 .5

~ 2.o-

~ 1 .5-

E

C~

x5

1.0

0

23

~ 0.5-

0

0.0

I

0.5 1.0

I I I

1,5 2.0 2.5

o

o

310 3.5 4.0 4.5

I o g l O o f s t o n d d e n s i t U ( s t e m ha -1)

F i g . 1 . S e l f - t h i n n i n g l i n e f o r h o n e y m e s q u i t e

Prosopis glandulosa

v a r .

glandulosa)

s t a n d s . T h e

r e g r e s s i o n l in e : l o gl o f r e s h w e i g h t k g s t e m - 1 ) = _ 1 .1 7 X l o gl o s t a n d d e n s i t y s t e m s h a - 1 ) + 5 .2 2

d o e s n o t i n c l u d e t h e t h r e e s i t e s i n t h e u p p e r - l e f t c o r n e r o f th i s g r a p h . )

R e d u c i n g s t a n d d e n s i t y i s b e n e f i c ia l f or c a t t l e g r a z in g a n d l u m b e r p r o d u c -

t i o n . A r e g r e s s io n o f b a s a l d i a m e t e r ( c m ) o n s t a n d d e n s i t y ( s t e m s h a - 1 ) i n -

d i c a t e d w h a t t h i n n i n g r e g i m e w o u l d p r o d u c e a g i v e n- s iz e lo g. W h e n t h e l a r g es t

t r e e s a t s i t e 7 , w i t h d e n s i t i e s b e l o w f u l l - si t e o c c u p a n c y , w e r e e x c l u d e d , t h e

e q u a t i o n w a s:

l o gD b - - - - 0 . 5 1 l o g N + 2 . 5 9 ( r 2 = 0 . 9 6 , S E ---- 0.0 22 )

w h e r e : D b is b a s a l d i a m e t e r ( c m ) .

T h i s r e g r e s s i o n e q u a t i o n p r e d i c t s t h a t 3 0 - c m a n d 4 0 - c m - b a s a l - d i a m e t e r lo g s

c o u l d b e g r o w n a t s p a c i n g s o f 8 . 3 m a n d 1 0 .9 m r e s p e c t i v e l y ( F ig . 2 ) . H o w e v e r ,

t h e s l o p e i s d i f f e r e n t f r o m t h e - 1 . 5 f r e q u e n t l y r e p o r t e d ( H a r p e r 1 97 7; L o n g

a n d S m i t h , 19 8 4 ). T h e ' m i n u s 3 / 2 l a w ' s h o w s t h a t b i o m a s s h a - 1 i n c r e a s e s i n

p r o p o r t i o n t o t h e r e c i p r o c a l o f t h e s q u a r e r o o t o f s t a n d d e n s i t y . F o r e x a m p l e ,

i f s t a n d d e n s i t y d e c r e a s e s f r o m 1 0 00 t o 1 00 s t e m s h a - 1, t h e n b i o m a s s h a - 1

i n c r e a s e s b y a f a c t o r o f 3 .1 6 . T h e s u b s t i t u t i o n s a r e a s f o ll o w s :

l o g W = - 3 / 2 l o g N + l o g K o

log ( W N a /2 = l o g K o


6/8

2 3 P. FELKER ET A L.

2.0

t .6

u

L

(])

~J

E 1.2

©

8 o B

x~

©

D

o.4

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I I I I I I I

0.5 I.O 1.5 2.0 2.5 3.0 3.5 4.0 4.5

1 0 9 1 0 o f s t o r q d d e n s i t y s t e r n s h u -1)

F i g . 2 . S e l f - t h i n n i n g l i n e f o r h o n e y m e s q u i t e (Prosop is g landu l osa v a r . glandu losa) s t a n d s . T h e

r e g r e s s io n l i n e: lo g lo b a s a l d i a m e t e r c m ) = - 0 . 5 1 × l og l o s t a n d d e n s i t y s t e m s h a - ~ 4 - 2 . 5 9 d o e s

n o t i n c l u d e t h e t h r e e s i t e s i n t h e u p p e r - l e f t c o r n e r o f t h i s g r a p h . )

O 5

g O / / ; i

I 0

80 / I ~; 40

70 / I \ i

/ I I (0 I , 0

, , , ~ o ,

2 0 . 0 . . . . . i

0

I0

£~" 4 0 l / / [ \P , L:)O J ~"

30 / .6 [] I

/ / o ~ E

o~ 2o / / . . . . . . . ' . > . . , , / I ~o L

o ~ s z S . ' " . . .. .. .. .. .. .. .. . , , . , , . , , , . " 2 ~ _ I

J

0.7 1.2 1.7 2.2 2.7

3 . 2

3.7 4.2

S t G m d D e n s i t y l o g l O o f s t e m s h Q -1 )

3

F i g . 3. G r e en m e s q u i t e b i o m a s s O , t h a - 1 ) a n d l u m b e r v o l u m e s m h a - ) a s i n f l u e n e e d b y s t an d

d e n s i t y l o g lo s t e m s h a - 1 ) . . , g r a d e -1 l u m b e r ; A , g r a d e -2 lu m b e r ; [Z , t o t a l s a w n l u m b e r .

S i n ce W N = B ,

K o = B N °s


7/8

SELF THINNING IN MESQUITE

231

and B

=

W o / N m-- 1)

where: B is biomass ha-1; and m, slope of a self-th inning line.

This implies that when the absolute value of the slope is greater than 1,

biomass ha-1 increases with decreasing stand density, as in mesquite stands.

Whe n the slope is 1, biomass ha -1 does not change with sta nd density; when

the slope is less than 1, biomass ha -1 declines with decreasing stand density.

Max imum biomass ha - 1 occurred at densities of about 100 stems h a - 1. Large

trees at low stand density, and small trees at high stand density, had lower

biomass ha-1. The sawn lumber (grade I and grade 2 lumber ) for stems larger

tha n 15 cm diameter is presen ted in Fig. 3. At densities above 3000 st ems h a- 1,

no lumber was produced. But, as s tand densi ty decreased to 470 stems

h a - 1

lumber increased rapidly. Th e volum e/de nsity relationship was described by

the following regression:

log SL=-- 0.77 lo gN+ 2. 84 (r2=0.70, SE=0.180)

The largest stems, and s tems below 15 cm in diameter, were excluded from

this regression. Sawn lumber was maximized (23 m 3 ha- 1) at densities of about

111 stems ha -1, or stem spacings of 9.5 m. At retail prices of US 425 m- 3, non-

select lumber from these trees would be worth US 9775.

DISCUSSION

Plotting mesquite biomass h a-1 on stand density indicated maximum bio-

mass at about 100 stems ha-1. The self-thinning line developed for mesquite

had a slope tha t was different from the - 3 / 2 often reported in literature. Re-

cently, Weller (1987) s tate d tha t the - 3 / 2 slope is not applicable to all tree

species. The difference between mesquite trees, and other species with differ-

ent thin ning slopes, may relate to the extensive root system in mesquite; full

site occupancy may occur without canopy closure in mesquite.

The number of mesquite stems ha-1 shortly after seedling establishment

has exceeded 10 000. In this condition, mesquite is a thre at to grass production

on rangeland. The mini mum density we observed was 6 stems ha-1, but these

trees were not at full-site occupancy. Under this condition, seedlings become

established in open areas. Medium stand densities ( 100-150 stems h a- 1 could

prevent this problem.

Controlled thinnn ings may increase the quality of mesquite lumber. Most

hardwoods are phototropic and develop misshapen boles when grown under

the c rowns of other trees. Thus, it is beneficial to establish ha rdwoods in dense

and unif orm stands (Smith, 1962). Although full-stand occupancy should be

maintained to prevent seedling establishment, tree spacings in mechanical-

thinn ing operations should be based on desired tree-size. Regression equations

predict that 100 stems ha-1 would achieve basal diameters of 36.5 cm, and


8/8

232 P. FELKERET AL.

sawn-lumber volumes of about 19.8 m 3 (8391 fbm 1 . It is questionable whether

the same dens ity/volum e relationships would hold in regions with different

rainfall, but stem spacings of about 10 m would be a good man age men t objec-

tive for this study area.

C O N C L U S I O N S

Regressions of stand density on stem volume, biomass ha-1, basal diamete r

and three grades of sawn lumber were estimated for mesquite stands. The

regression of stem volume on stand density had a slope slightly less than - 1,

indicat ing that mesquite biomass increased little with lower stand density. Yet,

decreasing stand densities for mesquite lumber production was compatible with

lumber production and land ma nage ment for cattle grazing. Maximum pre-

dicted lumber volume (22 m 3 ha - 1 occurred in 42-cm-diameter stems at spac-

ings of 9.5 m.

Mesquite lumber is superior to most oaks, walnut, and Philippine mahogan y

in hardness and shrink/swe ll characteristics; cultivating it could enhance land

revenues, which, from cattle alone, are currently only about 6 ha-1 y ea r- '.

R E F E R E N C E S

C ab le , D .R . , 1977. Seas o na l u s e o f s o i l wa te r by ma tu re ve lve t mes qu i t e . J . R ang e M a nage . , 30 : 4 -

11.

E l F a d l , M . A . , G r o n s k i , S . J . , A s a h , H . , T i p t o n , A . , F u l b r i g h t , T . E . a n d F e l k e r , P . , 1 9 8 9. R e g r e s s i o n

e q u a t i o n s t o p r e d i c t f r e s h w e i g h t a n d t h r e e g r a d e s o f l u m b e r f r o m l a r g e m e s q u i t e

Prosopis

glandulosa

va r .

glandulosa)

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