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PBYSTOQOGY SILVICULTURE OF BLACK WALNUT

PO2 COMBINED TIMBER AND NUT PRODUCTION

J. W e Van Sambeek and George ~ i n l d - 1

Abstract.--Research l i t e r a t u r e was reviewed f o r evidence suppor t ing the management of black walnut p l a n t a t i o n s f o r combined timber and nut production. The s i l v i c u l t u r e of the spec i e s is d iscussed Zn r e l a t i o n t o dua l cropping. S t imula t ion and phenology of f lowering m d f r u i t i n g a r e reviewed.

: Diameter growth, f lowering, phenology,

Walnut growers face t he same economic vaga r i e s a s o the r businessmen, The eLznt surges i n t he c o s t of c a p i t a l have made s tandard economic f o r e c a s t s bsoie te . Current i n f l a t i o n i n t e k e s t r a t e s may make p l a n t a t i o q establ ishment

cos t s p r o h i b i t i v e when pro jec ted over the l eng th of walnut r o t a t i o n s . Nut crops could provide one source of e a r l y income t o o f f s e t such c o s t s (Kincqid and h r t z 1981)

I n d u s t r i e s marketing nut meats and s h e l l s would l i k e a more r egu la r yea r ly volume of mats, al tkough walnut is considered a f a i r l y cons i s t en t bearer (Wylie 1466). Managers of seed orchards a l s o need methods f o r enhancing nut product isn if they are to annual ly supply n u r s e r i e s wi th g e n e t i c a l l y improved seed.

Evidence is presented showing t h a t ya lnu t can be managed f o r timber and improved nut y i e l d s *

EYLANAGEmNT STRATEGIES FOR TIMBER AND NUTS

Maximizing timber y ie ld c o n f l i c t s with maximizing nut y i e ld s . Maximizing production of q u a l i t y timber r equ i r e s g r e a t e r stem pruning and c l o s e r spacing of trees to favor a longer branch-free bo le , whi le i nc reas ing nut y i e l d involves growing t rees at a wider spacing t o favor l a r g e r t r e e crowns. Optimizing both nu t and timber product ion involves compromises i n spacing a s wel l a s i n t iming and extent of pruning (Schles inger and Funk 1977).

Initial tree spacing i n p l a p t a t i o n s intended f o r combined nut and t imber p roduc t ion is recornended t o be 15 t o 20 f e e t square compared t o %O t o 12 feel square f a r timber alone. P l an t ing t r e e s a t a c lo se spacing provides more opportunity for s e l e c t i o n of supe r io r c rop t r e e s , It a l s o n e c e s s i t a t e s an ea r l i e r thinning (Schlesinger and Funk 1977, Funk -- e t a l . 1978)*

--- Research Plant Phys io log i s t and Research P l a n t G e n e t i c i s t , North Cent ra l F o r e s t Experiment S t a t i o n , OSDA Fores t Serv ice , Carbondale, I l l i rko is

A c r i t e r i o n for degermingng the necessity arnd timfng of thinning i s crown competition factor (CCF). For nut production, the CCF should nof exceed 90. A CCB o f 90 means that rhe plsratation w f S 1 have 010 be thislned when the t o t a l crown area covers 90 percent o f the plantation's land surface (Schlesinger ar~d Punk 1977). The plantation may have t o be thinned three or more times during a rotatione Psr emmpfe, in simu1aling an 80-gear roEatfsn, Foster and Kung (1980) proposed thinning a plantation s i x times. W i t h a 20-f oat-square spacing, the f i r s t thinning (around age 20) wsufd be after the trees have begun flowering and f rukt ing , Crop trees csu%d be 8eBected on the basis o f seed prsduceion, seed qua l i ty , and sten form,

Lateral pruning should begin when the trees are f O to 15 f ee t t a l l (approximately age 5) and should be continued in stages untFl Bore than 9 f ee t a% clear stemwood i s obtained on every crop eree, The leagth of clear stem should not exceed 50 to 60 percent of t o t a l tree heighf. Only crop trees need to be prunedb Corrective pruezing w i l l probably not be necessary because grees wlth poor form w i l l be removed i.burizrr;g thinning8 (Seh%lesinge.g-, in press)*

Ma research dara are available on combfnad =at and tiaber production fraa walnut plasltations. Using skaulation techniques, Foster aad Kung (1980) compared the economic efficrency of managing walnut p lanta t ions fo r aut and timber production versus -waging E s r timber alone, They found that aanagbng for coabiaed nut and tfabar pro$actian was aore prafitsble than managing for t imber alone, as long as ehe annuax compound interest race exceeded 6 3f4 percent and rotations Wske Ponger than 40 years, Similar concfusAons b v e been made by (1966), Gallahan and Smith f19f4), Garrett aad Kurtz (L980), and Kincaid and Kurtz (1981) wing different economic and tree growth assumptions.

Most projections f a r dianreter growth a8~'t;tnn-e tt i s 8 linear function a f age with an average annual increment o f 0.33 inchlyear (Naughton 19701, 0.33 to 0.5 inch/year (Garrett and Kurtz 1980), or up t o 0.56 inch/year (Wylie 1966). Projections for nut y ie lds as a linear function of diameter at breast height for open grown Crees are Plluserated i n figure I (Foster and Kung 1980, Garrett and Kurtz 1980),

Id kernel formrtfo

January Marre9r Y a y July Bltptccmbet ~ o v @ G b @ r

MONTH

Figure 2,--SeQuence sf flower development, pollination, and nut maturation f o r black walnut i n southern I l l i n o i s .

Walnuts bear separate w l e and fenale flowers on the same treeo Self-pollination i s unlikely, however, because flowers of d i f f e r e n t sexes normally mature at d i f f e r e n t times; female % I s w e u s most o f t e n precede the mles. However, sp r ing Elora l develpment is definitely temperature dependent and w a r m cewperakures at the t i m e of flowering tend to increase the overlap between male and female flower naturation (Masters 1974) .

Male flowers axe found on wood grown in the previous season; t hey are i n i t i a t e d in vegetative buds during the period of rapid shoot elongat ion early in erle growing season o f the previous year. Female flowers are found at the tip o f the current growing shoot , developing in dormant buds set after completion of t he previous year's growth ( f i g . 2 ) (Ramina 1969, Masters 1 9 7 4 , Funk 1978),

Several factors influence flowering abundance, A I L f lowers are essentially borne on t he crown surface. h y cultural practices increasing the crown surface area, or nu~bnber of new branches, will increase the n m b e r of p o t e n t i a l Elowering s i t e s , In Engl i sh walnut the naunber of female flowers increases as growth i s increased (Link 9961), Likewise, Increased nut y i e l d s i n black walnut in response t o fertilization (Ponder 1979) and weed control (Holt and Voeller 1973) may be related to improved vigor resulting in more branches and branch growth and consequently more flower productiona

Figure 1.--Pro ject ions o f average nut product ion by d i f f e r e n t diameter walnut trees. So l id l i n e i s f o r air-dried weight after Foster and Kung (1980); dashed l i n e f o r f r e s h l y hu l led weight af ter Garrett and Kurtz (1980).

Management guidelines are now available for improving diameter growth o f black walnut on marginal s i t e s (Schlesinger and Funk 1977). But what l i t t l e information i s available about improving nut y i e l d s has not been tested. Bef o we can reasonably expect t o manipulate stands to improve nut y ie lds , we must understand the physiology o f flowering and f r u i t i n g fo r walnut. Most research on flowering and f r u i t i n g i n Juglandaceae has been wi th English walnut and pecan, but i t i s assumed tha t much of t h i s information also a p p l i e s to black walnut,

FLOWERING BIOLOGY

Black walnut normally begins flowering about mid-April in the southern part o f the range and mid-June in the northern p a r t of the range, although wi th in indiv idual s tands trees may vary by as much as a month in flowering dat (Plasters 1974, MeDaniel 1956). Flower development and leafing out occur at approximately the same t i m e , early enough f o r possible damage by late spring frosts ( f i g . 2). Pollination and f e r t i l i z a t i o n normally occur a few weeks a f t t h e mean f rost-free date and are less l i k e l y to be affected by l a te spring f ros ts*

La te sp r ing f r o s t s o f t en reduce the number sf f lowers reaching matur i ty . Compared with clean cultivation, maintenance 05 legumin~us or grass covers in walnut p lanta t ions m y delay bud break by as mu& as 4 t o 12 d a y s , thereby decreasing the p r o b a b i l i t y of darilage to new growth and flowers (MaLstenholne 1970). Overtree i r r i g a t i o n i n the spring w i l l a l s o de l ay bud break and f lowering fron 5 to 6 days (Beineke and H u d e y 1979)0

L i t t l e research has been done an the use of chemical sprays to alzer new shoot growth and subsequent flower production. Marth and Mitchell (1965) found t h a t g i b b e r e l l i n treatments promoted walnut shoot e longa t ion , F o l i a r spray app l i ca t ion may increase flower production kh rowh hproved branch growth, Langrova and Sladky (1971) Sound t h a t auxin-containing sprays a p p l i e d to English walnut when male f lowers were forming decreased the amber of catkins foraed the f ollawfng year; anti-auxin sprays appl ied after male flowers formed increased t h e a m b e r of catkins, many of which contained female flowers* The formation o f male and female flowers is apparently controlled by the interaction of g ibbere l l ins , auxins, and growth i n h i b i t o r s within t h e developing shoots (Sladky 1974), Fur the r research i s needed on c u l t u r a l a d chemical methods t o stimulate flower formation and nut development,

FRUITLNG BIOLOGY

Fertilization occurs w i th in 2 t o 5 days of po l l ina t ion , followed by a per iod sf r a p i d expansdon of the f r u i t during the next 5 EG 6 weeks ( f i g , 21, F r u i t s increase i n weight s u b s t a n t i a l l y before entering the shell-hardening stage i n early July, although increases i n s i z e are not noticeable at this t i m e , During the l a t t e r p a r t of the shell-hardening stage ( l a te J u l y ) , t h e embryo and cot yledsns begin t o enlarge r ap id ly , incorpora t ing most sf the prev ious ly depos i t ed emdssyerm, The kernel , csmpased of the embryo and cotyledons, usua l ly does not develop until 4 t o 5 weeks before the nuts are mture, By la te August, some nuts can germinate a f ter s t r a t i f i c a t i o n . Most nu t s , however, continue to increase in dry weight and do not d rop from the tree until s h o r t l y af ter Leaf f a l l in late September or early October,

Once the nutlets are formed, n u t l e t Loss is usua l ly due to disease or insect infestations. Blair and Kearby (1979) found tinah; more than 50 percent. of the potencia1 nut crop in Missouri walnu% plantations was destroyed by the walnut curculia a Epidemics o f walnut anthracnose early in the growing season can cause significant nutrek losses; later o r less severe disease outbreaks lead do poor nut f i l l i n g and darkened kernels called ambers (Funk 197Y),

Summer droughts can also lead to poor f i l l i n g of the kernels and may a l s o d e l a y seed maturity (Batchelor e t ale 1945 , Crane $ 9 4 9 ) , Jones (1975) found that June, J u l y , and Augu~t ra infa l l is an important variable in pred ic t ing annual nut crops in southwest Missouri. Irrigation during August and Septessber may be important for high nut y i e l d s , because these months often include long dry spel ls ,

Early f a l l frosts can injure new growth befare i t i s c o q l e t e l y l i g n i f i e d , preventing complete nut development aad causing undesdrable s h r i v e l (Funk 1979), This f r o s t danger is espec ia l ly per t inent because recomeadations f o r co l l ec t ing seed 200 miles south of the planting s i t e f o r g rea te r timber production inay resul t 3_n i m a t u r e nut crops (Sparks jb881), "E"I.lls problem may possibly be overcome by chemical treatment. I n English walnuts, f a l l spraying with ethephon produces a rnature nut crop I t o 3 weeks sooner, and fhe sprayed t r e e s produce higher q u a l i t y nuts than the unsprayed t r e e s (Plartin 1971, Sibbett -- et a l e 1974). Anogher alternative m y be underplanting with legminoas winter annuals ta acce le ra te t r e e d o r m m y (Buchter and Knapp 29%7),

The minimum seed-bearing age Esr comerclal q u a n t i t i e s of nuts i s about 12 years, although open-grown t r e e s produce some seeds as early as 4 years after outplanting (SehLesinger a& Funk 1977), The biggest challenge i n managing walnut for timber and nut productfan i s t o m l n t a i n regular annual yields* On spewgrown t r e e @ , nut craps a r e produced nost cornonly i n an al ternate-year cycle; some Lreea bear annually, o the r s bear i n 1 or 2 years out sf 3 , and m a y bear w i t h ns regular pattern a t all ( Z ~ r g e r et a l e L969), -- Alternate bearing is c h a r a c t e r i s t i c o f mast f r u i t t r e e s with late-season f r u i t maeuration and i s re la ted to the carbohydrate concentration In the plant (Sparks 1979), Late-seasan kernel develop~eat makes a high demand on available carbohydrates and stored reserves when the new female flowers are forming, Increasing lske l e a f area per un i t af fruit m y decrease t he alternate bearing tendency (Sparks 19791, Before thinning planeatisas, the manager jnay be able to identify those t r e e s with goad farm tha t are pers i s t en t bearers or trees tha t produce crops durfng "oEf" years. Mylie (1956) suggested annually spst-painting t r e e s tha t have above-average nut y ie lds f o r a period of 5 t o 10 years before thinning t o E a c i l i t a t e c r o p h r e e se lec t ion*

Nut qua l i ty ahauld also be considered when se lec t ing trees f o r yields. Kernel percentage, the dry weight of kernel a s a percent of the d ry weigh$ of the e n t i r e nut, is the key factor In nut quality and should be nore than 20 percent (Funk 1979), Such nuts can be expected es comaad a higher pr ice ( ~ a r r e t t ' a n d Kurtz 1980).

CONCLUSIONS

Managing f o r nuts and timber requires a lower level of stocking Gban f o r timber alone to ensure rapid growth of large-crowned trees* The Xandowader must a l s o prune t r e e s t o a minimum c l e a r height of 9 f e e t and s e l e c t f o r higher nut y ie ld ing t r e e s before the l a s t precomercia l thinning.

Managers o f seed orckrards mst s e l e c t trees f o r rapfd growth and nut production t o provide lasrdawaers with the desired tpgess Also, they may have to select for late bud break and use techniques like over t ree i r r i g a t i o n and herbaceous cover craps t o delay bud break a-nd flowering, Late-sumer i r r i g a t i o n mag be needed te ensure proper kernel development, and chernical r ipeners say be used t o mture nuts.

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