Which Loblolly Pine Seedling Has a Higher Survival Potential -a Deep Planted J-root or a Shallow Planted I-root?’

Two schools of thought exist regarding the planting of bare-root seedlings. One school favors the “pull-up” m e t h o d w h e r e t h e s e e d l i n g i s p u l l e d u p 3 t o 1 0 c m a f t e r p l a c i n g t h e r o o t s i n t h e p l a n t i n g h o l e . A l t h o u g h t h i s a c t i o n p u r p o r t e d l y s t r a i g h t e n s t h e taproot, d a t a a r e l a c k i n g t o s h o w t h i s e x t r a s t e p a c t u a l l y i m p r o v e s f i e l d p e r f o r m a n c e . P u l l i n g u p t h e s e e d l i n g u s u a l l y r e s u l t s i n “ s h a l l o w ” p l a n t i n g ( w h i c h c o u l d i n c r e a s e m o r t a l i t y o n s o m e s i t e s ) . T h e “ p u s h d o w n ” s c h o o l a d v o c a t e s m a k i n g a d e e p p l a n t i n g h o l e a n d p l a c i n g t h e r o o t s n e a r t h e b o t t o m o f t h e h o l e . T h e y s a y t h a t s h a l l o w h o l e s k i l l s e e d l i n g s : b e n t r o o t s d o n o t . P l a n t i n g g u i d e l i n e s s h o u l d b e r e w r i t t e n t o : ( 1 ) e m p h a s i z e t h e “ p r o p e r ” d e p t h o f p l a n t i n g ( t o i n c r e a s e s e e d l i n g s u r v i v a l ) ; ( 2 ) d e e m p h a s i z e i n t u i t i v e b e l i e f s t h a t r o o t s s h o u l d l o o k “ n o r m a l ” a f t e r p l a n t i n g ; ( 3 ) e l i m i n a t e u n n e c e s s a r y r e f i n e m e n t s i n p l a n t i n g t e c h n i q u e ; ( 4 ) e x p l a i n t h e a d v a n t a g e s o f m a c h i n e p l a n t i n g ; ( 5 ) e x p l a i n t h e s p e c i e s / s i t e / p l a n t i n g d e p t h i n t e r a c t i o n f o r s u r v i v a l ; a n d ( 6 ) c i t e r e f e r e n c e s t o s u p p o r t r e c o m m e n d a t i o n s . INTRODUCTION In the South, many planted seedlings (40 to 80 percent) can be classified as having deformed roots (Gruschow 1959, Schultz 1973, Hay and Woods 1974a, Mexal and Burton 1978, Harrington and others 1989). However, just because a planted pine seedling has a bent taproot, this does not mean the performance will be less than seedlings that originate from direct seeding. In fact, sometimes 32 percent of loblolly pines (finus taeda L.) originating from seed have bent taproots (Harrington and others 1989). Therefore, bends in the taproot can be “natural” as well as “man-made.” Even so, some claim that J-roots (table 1) will kill seedlings and that utmost care should be exercised during planting to ensure the taproot is straight. They claim that planting seedling roots deeply will bend the roots and, therefore, they say the “proper” planting depth is so the root-collar is slightly below groundline. In my opinion, tree planting guidelines for loblolly pine overemphasize the dangers of both J-rooting and deep planting. Planting guidelines should be rewritten to eliminate the unimportant aspects of planting and to stress the important. Most data with loblolly pine indicate that bent roots, per se, do not affect early seedling survival or growth. On many sites, planting loblolly pine or slash pine (Pinus elliottii Englem.) deep in the hole increases survival (Slocum and Maki 1956, Malac and Johnson 1957, Malac 1965, Blake and South 1989). This paper reviews the J-rooting L-rooting studies that have been conducted with bare-root pines in the southern United States. It does not cover root-strangulation occasionally caused by growing seedlings in containers or when twisting bare-root seedlings during planting. It reviews data mainly from the compression method planting where root systems are compressed into a vertical plane (also know as slit planting). TWO SCHOOLS OF THOUGHT REGARDING THE PROPER PLANTING TECHNIQUE Two schools of thought exist regarding the planting of loblolly and slash pine seedlings. The older-school favors the “pull-up” technique where the seedling is placed into the planting hole and then pulled up 3 to 10 cm (and the rootcollar is about 1 to 5 cm below the soil surface). This action purportedly improves field performance by straightening out the roots. Several tree planting guides recommend this technique even though empirical trials by Wakeley (1954) show no advantage of this technique when compared to planting with a mattock. We even do not know if pulling the seedling up 3 cm is really enough to straighten out the roots. To avoid yl-roots, members of this school allow some pruning of long fibrous roots by tree planters. “Graduates” of this school prefer straight taproots to deep planting. They claim the “correct” planting depth is to have the root-collar at or slightly below the groundline. The other school recommends the “push-down” technique (which favors deep planting over straight taproots). Due to an increase in probability of success, members of this school prefer machine planting to hand planting (average planting hole depth for machine planting is about 30 cm and the root-collar is typically about 15 cm below the soil surface; this sometimes results in a high percentage of Lroots). On sites where hand-planting is required, leaders in this school recommend making a wide (15 to 18 cm) and deep (27 to 34 cm) planting hole. The roots are placed at the bottom of the hole and there they remain. As a result, the root-collar ends up at least 5 to 10 cm deeper than recommended by the “pull-up” school. For many sites, the “correct” planting depth for loblolly pine will result in the rootcollar 15 cm below ground (and the bottom of the roots will be 25 to 34 cm deep). They allow J-roots, L-roots and r-roots but prohibit shallow planting holes (less than 25 cm deep) as well as pruning or stripping of roots by tree planters. However, due to a three-way interaction between species, site, and planing depth, members of this school do not recommend the same planting depth for all pine species or for all sites. Deep planting on sites where the water table is near the surface can decrease survival of loblolly pine (Switzer 1960). Therefore, the “correct” planting depth varies with site. Because less time is required to make narrow, shallow holes, hand planters prefer recommendations from the “pullup” school. Making a deeper planting hole by hand increases planting costs which is one reason those from the “push-down” school favor machine planting. ’ P a p e r p r e s e n t e d a t t h e T e n t h B i e n n i a l S o u t h e r n S i l v i c u l t u r a l R e s e a r c h C o n f e r e n c e , S h r e v e p o r t , L A , F e b r u a r y 1 6 1 8 , 1 9 9 9 . * P r o f e s s o r , S c h o o l o f F o r e s t r y a n d A l a b a m a A g r i c u l t u r a l E x p e r i m e n t S t a t i o n , A u b u r n U n i v e r s i t y , A L 3 6 8 4 9 5 4 1 8 .