27 $ by stand height 10.7 m compared with the unpruned stand.
Equation 12 predicts a basal area loss of about 13 % by stand height
10.7 m.
After thinning at stand height 10.7 m, the residual basal area estimated by equation 12 is closer to that estimated by Fenton
(1972 a) from plot measurements than is that estimated with equation
13* Between stand heights 10,7 m and 13*7 m the basal area
increment predicted with equation 12 is closer to that assumed by Fenton (1972 a) on the basis of plot measurements than is that predicted with equation 13*
Table 7 summarises predictions and the original data for
stand mean diameter, basal area and total stand volume at age 26 years. The increment loss from pruning predicted by equation 13 has a much greater effect on total volume production than does that predicted
8 1- • • • F e n t o n e t a l 1 9 7 2 - u n p r u n e d o Brown 1 9 8 2 ( , 27 • S h e p h e r d 1 9 6 1 ( 1 « 14 » O S t a n d h e i g h t - m e t r e s
Figure 11 Comparison of basal area g r o w t h predicted by
w ith e q u a tio n 12 , b u t b o th e q u a tio n s p r e d i c t a s m a lle r t o t a l s ta n d volume a t age 2
6
y e a rs th a n t h a t p u b lis h e d b y F e n to n (1972 a ) .TABLE 7; COMPARISON OF THE STAND MEAN DIAMETER, TOTAL STAND VOLUME, AND STAND BASAL AREA PREDICTED BY THE MODEL WITH DATA PUBLISHED BY FENTON (1972 a) S im u la tio n Model F e n to n 1972 a E q u a tio n
12
E q u a tio n 13 No p ru n in g D .B.H. (cm) 6 1 .7 3 9 .556.0
64.1
2
B a s a l a r e a (m /ha.) 59.156.0
4 9 .565.0
T o t a l s ta n d ■z volume (m /h a )676.0
639.0
656.3
742.9The e v id en c e su m n arised i n T a b le s 3 , 4 , 6 and 7 to g e th e r w ith th e ev id en c e from th e p ru n in g t r i a l d e s c r ib e d b y S u tto n e t a l (1 9 7 2 ), d is c u s s e d i n C h ap ter 4 s u g g e s te d t h a t th e u s e o f e q u a tio n 12 to c a l c u l a t e th e in c re m en t l o s s due to p rim in g would b e m a r g in a lly more a p p r o p r ia te th a n th e u se o f e q u a tio n 13* E x c e p t w here s t a t e d
t h e r e f o r e e q u a tio n 12 was u sed i n t h i s s tu d y .
I t has b e e n c l e a r l y shown t h a t th e e f f e c t o f p ru n in g on b a s a l a r e a in c re m en t i s c r i t i c a l to b o th clearw o o d and t o t a l volume
y i e l d s . A lthough th e e f f e c t o f p ru n in g on grow th h a s b e e n w id e ly s t u d i e d , i t s e f f e c t s a r e s t i l l n o t a c c u r a t e l y known. R ese arch o f a more d is c r im in a tin g n a tu r e i s r e q u ir e d to d e f in e p r e c i s e l y th e c o n se q u e rc e s o f p r u n in g f o r y i e l d p ro d u c tio n .
83
D e f i c i e n c i e s o f th e Model
The model i s n e c e s s a r i l y r a t h e r u n s o p h is ti c a te d b e c a u se i t i s b a se d on th e a v a i l a b l e d a t a ■which come from a wide v a r i e t y o f
s o u rc e s and which h as b e e n c o l l e c t e d f o r a v a r i e t y o f p u r p o s e s .
The e x p erim en ts w ith th e model d e s c r ib e d i n t h i s c h a p te r h ig h lig h te d a number o f d e f i c i e n c i e s i n th e m odel:
( i ) M ost o f th e p u b lis h e d d a ta d e a li n g w ith th e g ro w th and y i e l d o f r a d i a t a p in e i n Newr Z ealan d r e l a t e to s ta n d a g g re g a te s r a t h e r th a n to in d i v i d u a l ste m s. Clearwood p r o d u c tio n i s e s s e n t i a l l y a c h a r a c t e r i s t i c o f each i n d i v i d u a l lo g i n a s t a n d , and th u s a m odel b a se d on th e grow th o f in d i v id u a l t r e e s , r a t h e r th a n a s ta n d m odel as h as b e e n c o n s tr u c te d would be p r e f e r a b l e . However, th e com plete l a c k o f s u i t a b l e d a t a o b v ia te d any a tte m p t to c o n s t r u c t a t r e e b a se d s im u la tio n m odel.
( i i ) A s ta n d model ig n o r e s th e e f f e c t s o f s e l e c t i v e p ru n in g on th e gro w th o f i n d i v i d u a l ste m s. Where a p ru n in g i s imposed
th e model assum es t h a t a l l stem s i n th e s ta n d r e c e i v e th e seme tre a tm e n t and t h a t th e b a s a l a r e a grow th o f p ru n e d steams i s no d i f f e r e n t from th e a v e ra g e .
( i i i ) The e f f e c t s o f p ru n in g and th in n in g on t r e e form a r e n o t in c lu d e d i n th e m o d el.
( i v ) E q u a tio n 18 i s q u a d r a tic i n k n o t t y c o re d ia m e te r . However, i n th e m odel i t i s u sed to p r e d i c t th e clearw ood y i e ld
f o r th e s ta n d as a w hole. T h is w i l l c a u se a b i a s i n th e y ie ld s o f c learw o o d p r e d i c t e d , th e e x te n t d epending
th e d i s t r i b u t i o n o f d ia m e te rs a b o u t th e mean and th e upon
association of knotty core sizes -with particular final tree diameters.
(v) The model is deterministic. It assumes that the probability
of occurrence of the estimated outcome is unity. This is
obviously a gross over sinplification since any one regime of treahnent on a given site index -will produce a variety of outcomes in practice.
(vi) The model assumes that height growth is unaffected by
pruning: an assumption supported by research with species
other than radiata pine. However there are indications
that the assumption may be less valid for radiata pine in New Zealand, but there was no alternative other than to
accept the assumption in the absence of conclusive
quantitative data. If height growth is appreciably
affected by pruning, the yields predicted by the model will be biased upwards, and the extent of the bias will increase as pruning becomes more severe.
However, in spite of these deficiencies, the tests
described in this chapter indicated that the model could be used for predictive purposes with some degree of confidence.
Certainly the model makes best use of the data available, and it was therefore used to predict clearwood yields and total volume yields throughout the remainder of the study.
CHAPTER SIX
A DETERMINISTIC ANALISIS OF CIEARYOOD YIELDS FROM RADIAIA PINE
I n t r o d u c t i o n
Once a p a r t i c u l a r s i l v i c u l t u r a l s t r a t e g y h as b e e n s e l e c t e d , a know ledge o f th e s e n s i t i v i t y o f clearw o o d y i e l d to th e v a r i a b l e s u n d e r
th e c o n t r o l o f management i s i n p o r t a n t to e n su re t h a t management
o b j e c t i v e s a r e m et m ost e f f i c i e n t l y * I f clearw ood y i e l d i s e s p e c i a l l y s e n s i t i v e to a p a r t i c u l a r v a r i a b l e , th e n management m ust e n su re t h a t s i l v i c u l t u r a l o p e r a tio n s in v o lv in g th e v a r i a b l e a r e c o n t r o l l e d m ost c lo s e ly * C o n v e rs e ly , i f clearw o o d y i e l d i s i n s e n s i t i v e to a p a r t i c u l a r v a r i a b l e , th e c o n t r o l f u n c tio n c an b e t r a n s f e r r e d to more c r i t i c a l o p e r a t i o n s . A s i l v i c u l t u r a l s t r a t e g y s i m i l a r to one c o n s id e re d r e c e n t l y f o r u s e a t K a in g a ro a F o r e s t (K. C h a n d le r p e rs.co m m .) was s e l e c t e d , and th e clearw ood y i e l d s r e s u l t i n g from t h i s regim e and v a r i a n t s o f i t w are exam ined. The regim e was;
( i ) e s t a b l i s h 1 482 stem s p e r h e c t a r e , ( i i ) p ru n e 1 9 4 stem s p e r h e c t a r e to 2 .4 m a t s ta n d h e ig h t 6.1 m, ( i i i ) t h i n to 494 stem s p e r h e c t a r e a t s ta n d h e i g h t 6.1 m, ( i v ) p ru n e 3 7 0 stem s p e r h e c t a r e to 4 .3 m a t s ta n d h e ig h t 122 m, (v ) p ru n e 247 stem s p e r h e c ta r e to 6.1 m a t s ta n d h e i g h t 1 2.2 m, ( v i ) t h i n to 247 stem s p e r h e c ta r e a t s ta n d h e ig h t 1 2 .2 m ,
The E f f e c t o f T h in n in g on Clearw ood Y ie ld ( a ) th in n in g a t 1 2 .2 m
a s ta n d a rd s i l v i c u l t u r a l o p e r a tio n p r e s c r i b e c o m p le tio n o f p ru n in g and th in n in g b y s ta n d h e i g h t 9 .0 m to 15*0 m. P r e s c r i b e d r e s i d u a l s to c k in g s ra n g e f r o n 240 to 750 stem s p e r h e c ta r e (Bunn 1970), T h in n in g s to s to c k in g s ra n g in g from 247 to 998 stem s p e r h e c t a r e w ere s im u la te d a t a s ta n d h e ig h t o f 12,2 m i n a s ta n d e s t a b l i s h e d a t 1 482 stem s p e r h e c t a r e and p ru n ed b y th e sc h e d u le d e s c r ib e d above* C learw ood y i e l d s w ere c a l c u l a t e d a t r o t a t i o n ages r a n g in g from 20 to 3 0 y e a r s on a s i t e o f in d ex 29 m.
F ig u r e 12 shows t h a t clearw o o d y i e l d in c r e a s e d as th e th in n in g was made more s e v e re b e c a u se s ta n d mean d ia m e te r a t r o t a t i o n age in c re a s e d * The e f f e c t o f r o t a t i o n le n g th on c learw o o d y i e l d became more marked as th e th in n in g became more severe*