Effects of Seedling Protectors nd Weed Control on Blue Ok Growth nd Survivl 1 Dougls D. McCrery 2 Jerry Tecklin 2 Astrct: Two fctors limiting successful recruitment of plnted lue ok (Quercus douglsii) seedlings re dry soils nd niml dmge. Mny pproches hve een used to mitigte these fctors including severl types of protective cges nd lterntive methods of weed control. This study exmined how treeshelters, screen cges nd vrying intensities of weed removl ffect the estlishment nd growth of lue ok seedlings. After 5 yers, seedlings protected with treeshelters hd higher survivl, greter dimeter, nd were tller thn those in screen cges. Seedlings receiving no weed control hd lower survivl, shorter height, nd smller dimeter thn those with the two highest intensities of weed removl. This study suggests tht treeshelters re promising tool for regenerting lue oks in Cliforni nd tht providing dequte weed control cn improve the growth nd survivl of plnted seedlings. Blue ok (Quercus douglsii) is one of severl species of ntive Cliforni oks tht is reported to e regenerting poorly in some loctions (Bolsinger 1988, Muick nd Brtolome 1987). Recent studies indicte tht vriety of fctors limit nturl recruitment, including herivory y deer, livestock, nd rodents; defolition y insects; root clipping y gophers; girdling y voles; nd limited soil moisture induced y competing vegettion. These sme fctors cn lso prevent successful estlishment of plnted seedlings or corns (McCrery 1990). Mny devices re used to protect plnted seedlings from dmge y nimls, with vrying degrees of success. Some of the more common products re plstic mesh cges, cylinders mde from luminum window screen, cges of chicken wire, nd hrdwire cloth uried in the ground. One reltively new product is clled treeshelter. These re rigid, trnslucent, doule-wlled plstic cylinders, developed in Englnd nd used there for more thn 10 yers (Potter 1988). They re reported to not only protect seedlings from vriety of nimls, ut lso stimulte oveground growth. Another fctor tht cn severely limit the survivl nd growth of ok seedlings on mny rngelnd sites is severe competition from grsses nd fors. Such competition cn crete extremely dry soil conditions tht cn e lethl to oth nturl seedlings nd plnted oks (Griffin 1971). Some reserchers elieve tht plnt competition on mny hrdwood rngelnds is greter tody thn it ws efore the introduction nd estlishment of exotic Mediterrnen nnuls, which hve displced mny ntive perennils (Welker nd Menke 1987). These nnul plnts sor more soil moisture in the spring thn the ntive perennil grsses, nd consequently, crete drier environment. This mkes it more difficult for ok seedlings to ecome estlished. Becuse of the dverse effects of such competition, reserchers nd prctitioners hve found controlling weeds round ok plntings necessry to otin dequte survivl nd growth. Without weed control, niml dmge prolems re lso generlly greter, ecuse dense weeds provide fvorle hitt for nimls such s grsshoppers nd voles, which cn seriously dmge young plnts (Tecklin nd McCrery 1993). A vriety of techniques hve een used to eliminte weeds, including mulch, hericides, sclping nd mowing. Though studies compring weed control to no weed control hve demonstrted the dvntge of weed removl (Adms nd McDougld 1995), we re wre of no reserch on the effectiveness of vrying intensities of weed removl on the field performnce of lue ok seedlings. 1 An revited version of this pper ws presented t the Symposium on Ok Woodlnds: Ecology, Mngement, nd Urn Interfce Issues, Mrch 19-22, 1996, Sn Luis Oispo, Clif. 2 Nturl Resources Specilist nd Stff Reserch Associte, respectively, with the Deprtment of Environmentl Science, Policy nd Mngement, University of Cliforni, Berkeley. Miling ddress: 8279 Scott Fores Rod, Browns Vlley, CA 95918. USDA Forest Service Gen. Tech. Rep. PSW-GTR-160. 1997. 243
McCrery nd Tecklin Effects of Seedling Protectors nd Weed Control Our ojectives in this study were to determine how different types of oveground protection, nd different intensities nd durtions of weed control, would ffect the growth nd survivl of trnsplnted lue ok seedlings. Study Are nd Methods In erly Ferury 1991, we plnted 160 1-yer-old lue ok seedlings t the University of Cliforni Sierr Foothill Reserch nd Extension Center, 30 km northest of Mrysville, Cliforni. Seedlings hd een rised t the Cliforni Deprtment of Forestry nd Fire Protection Nursery in Dvis, Cliforni, nd were from corns collected from single tree growing pproximtely 5 km from the plnting site. Seedlings were plnted on 2.1-m spcing in fenced reserch re inccessile to deer nd livestock. Tretments included four levels of weed control (none, nd weed-free circles of 0.6-, 1.2-, nd 1.8-m dimeter), nd two types of protection (60-cm-tll screen cges or 1.2-m-tll treeshelters). Four locks of 40 seedlings were estlished. Within ech lock, ech weed-control tretment consisted of two djcent 5-seedling rows, which were rndomly positioned. One of these rows ws rndomly ssigned to e protected with screen cges, while the other row ws covered with treeshelters. At the time of plnting, through summer s end, the weed-free circles were creted nd mintined y sclping with hoes nd occsionl hnd-pulling. Before plnting, plnting holes were ugured to depth of 60 cm using trctormounted 15-cm dimeter uger. A 21-g, slow-relese fertilizer tlet (20-10-5 NPK) ws plced pproximtely 30 cm deep within ech hole. At the end of ech of the next five growing sesons, we evluted survivl, totl height, nd sl dimeter of ll seedlings. During the second growing seson, two of the four replictions were rndomly selected for continution of the weed-control tretments. Tht is, during this second seson, those plnting spots receiving the three weed-control tretments (0.6, 1.2, nd 1.8 m circles) were mintined y comintion of hoeing nd hnd pulling. The other two replictions were not treted, so there ws reinvsion of some weeds in the circles, though these res hd fewer weeds thn the untreted res. After the second yer, no dditionl weed removl ws provided. All survivl dt were initilly collpsed to frequencies nd nlyzed y chi-squre test. In instnces where chi squre indicted significnt (P < 0.5) differences mong weed-control tretments, survivl percentges were clculted for ll weed-control/protection comintions within locks, trnsformed y n rcsine trnsformtion, nd nlyzed y n nlysis of vrince for split-plot design with protection tretments nested within weedcontrol tretments. Height nd dimeter dt were lso nlyzed using ANOVA for split-plot design. When we oserved significnt (P < 0.05) differences mong weed-control tretments, Tukey s multiple comprison test ws performed to determine which tretments were significntly different from ech other. We lso tested for interctions etween seedling-protection nd weedcontrol tretments. To determine if there were significnt differences etween seedlings receiving weed control for either 1 or 2 yers, split-split plot ANOVA ws performed. All differences stted s significnt re t the P < 0.05 level. Results Survivl During ech growing seson, survivl of seedlings in treeshelters or tues ws significntly higher thn survivl in screen cges (tle 1). The solute differences etween shelter types incresed ech successive yer: survivl of 244 USDA Forest Service Gen. Tech. Rep. PSW-GTR-160. 1997.
Effects of Seedling Protectors nd Weed Control McCrery nd Tecklin seedlings in treeshelters remined reltively constnt, while survivl of seedlings in screen cges decresed ech yer. From the third yer on, verge survivl in the treeshelters ws twice tht in the screens. After the first growing seson, no significnt differences in survivl mong weed tretments were detected (tle 1). By the second yer, however, there were significnt differences mong weed tretments, with the control hving significntly lower survivl thn the two tretments with the gretest intensities of weed removl. By the fourth growing seson (1994), verge survivl of lowest intensity weed removl (0.6-m circles) ws significntly greter thn the survivl of the no-weed-removl tretment. After the first growing seson, verge survivl decresed 20 percent for seedlings where weed control ws not mintined, ut went down only 10 percent in locks where the weed tretment ws continued. After ech susequent growing seson (when no further weed tretments were continued), survivl decresed slightly, ut t pproximtely the sme rte for seedlings provided with weed control for either 1 or 2 yers. There were significnt interctions etween protection nd weed tretment in 1993 nd 1995. Height From the first growing seson onwrd, seedlings in tues were significntly tller thn those in screens (tle 2). The solute difference in height etween these tretments lso incresed ech successive growing seson, nd y the third field seson, seedlings in tues were, on verge, pproximtely 1 meter tller thn those in screens. During the first yer of the study there were lso significnt differences mong weed-control tretments, with seedlings receiving the gretest weed control eing significntly tller thn those hving no weed control, or the smllest dimeter weed-free circles (tle 2). By the second growing seson, these Tle 1 Averge survivl (pct) of seedlings protected with different devices, nd receiving different intensities nd intervls of weed control 1 Growing Seson Tretment 1991 1992 1993 1994 1995 ------------------------------------------------------------------- pct ------------------------------------------------------------- Protection Screen cge 71.3 47.5 41.3 38.8 32.5 Treeshelter 90.0 83.8 83.8 81.3 81.3 Weed intensity None 67.5 42.5 40.0 37.5 32.5 0.6-m circle 80.0 67.5 57.5 60.0 57.5 1.2-m circle 87.5 75.9 75.0 70.0 65.0 1.8-m circle 87.5 77.5 77.5 72.5 72.5 Weeding intervl 1 yer 71.3 51.3 48.8 47.5 42.5 2 yers 90.0 80.0 76.3 72.5 71.3 1 Growing sesons nd tretment types with different letters re significntly different (P < 0.05) y chi-squre test for protection nd weeding-intervl tretments, nd y Tukey s test for weed-intensity tretments. USDA Forest Service Gen. Tech. Rep. PSW-GTR-160. 1997. 245
McCrery nd Tecklin Effects of Seedling Protectors nd Weed Control Tle 2 Averge height (cm) of seedlings protected with different devices, nd receiving different intensities nd intervls of weed control 1 Growing Seson Tretment 1991 1992 1993 1994 1995 ------------------------------------------------------------ cm ------------------------------------------------------------- Protection Screen cge 28.6 33.0 71.6 76.4 94.0 Treeshelter 45.8 96.1 163.8 183.4 211.9 Weed intensity None 30.2 39.2 81.1 105.0 106.8 0.6-m circle 30.7 54.7 113.1 110.9 149.9 1.2-m circle 39.9 c 71.4 c 127.4 137.0 162.0 1.8-m circle 48.0 c 94.8 c 149.4 166.7 192.9 Weeding intervl 1 yer 36.4 56.7 105.1 114.5 151.5 2 yers 38.0 72.3 129.0 139.2 157.5 1 Growing sesons nd tretment types with different letters re significntly different (P < 0.05) y Anlysis of Vrince for protection nd weeding-intervl tretments nd y Tukey s test for weedintensity tretments. differences were even greter. The solute difference etween controls nd weed-removl tretments ws gretest fter the fifth growing seson. In the second growing seson (1992), hlf of the plots received second yer of weed removl. Seedlings tht were mintined weed-free for 2 yers were significntly tller fter the second nd third growing sesons. During the next two growing sesons, differences in height etween these two groups were no longer significntly different. There ws significnt interction etween protection nd weed tretment in 1992 only. Dimeter Ptterns in sl dimeter were similr to those for height, ut did not commence s erly. During the first field seson, no difference in dimeter etween seedlings with different protectors ws detected (tle 3). By the second growing seson, however, seedlings in treeshelters hd significntly lrger dimeters. Over time, the differences etween these two tretments continued to increse, nd y the fifth yer, verge dimeter of seedlings in treeshelters ws pproximtely 2.5 times greter thn the dimeter of those in screens. During the first yer, we detected significnt differences in dimeter mong weed-control tretments; seedlings from the two tretments with the most weed removl were significntly greter in dimeter thn the two with the lest (tle 3). The solute difference in dimeter etween tretments tended to increse over successive yers. In contrst to height, the most pronounced increses in verge dimeter etween seedlings tht received weed removl for either 1 or 2 yers were during the lst two growing sesons. There were no significnt interctions. 246 USDA Forest Service Gen. Tech. Rep. PSW-GTR-160. 1997.
Effects of Seedling Protectors nd Weed Control McCrery nd Tecklin Discussion Our dt suggest tht oth shelter type nd the intensity nd durtion of weed control cn drmticlly ffect the field performnce of plnted lue ok seedlings. From the first growing seson, seedlings protected with treeshelters grew much tller thn seedlings in screens. This is consistent with results from previous study tht compred these shelter types for vlley ok (Q. lot) (McCrery nd Tecklin 1993). In nother study with lue, vlley, nd interior live oks (Q. wislizenii), however, there ws little difference in survivl or height growth etween seedlings protected with treeshelters nd those protected with screen cges (Costello nd others 1996). Our study lso found tht seedlings in treeshelters did not initilly hve lrger dimeters, nd s result, were somewht spindly. Some erly studies with oks in Englnd found tht if shelters were removed fter only 3 yers, proportion of the seedlings hd not ttined sufficient girth to support the crown nd needed to e stked to the treeshelter stkes to keep them upright (Potter 1991). Our results suggest tht treeshelters do cuse n initil reduction in the dimeter-to-height rtios of lue oks. However, even during the second growing seson, seedlings in tues egn to increse in dimeter t fr greter rte thn those in screen cges. By the fifth growing seson, seedlings in tues hd not only lrger height nd dimeter, ut lrger dimeter-to-height rtios s well. In lte fll 1995, we removed ll ut the ottom 20 or 40 cm of ll treeshelters (which we left to protect the ses of the seedlings from voles nd to compre the effectiveness of different heights in providing this protection). None of the seedlings fell completely over, though four or five did len somewht fterwrds. These were ll very smll seedlings tht hd smll (<1.5 cm) sl dimeters nd either were shorter thn the tops of the tues or hd grown only slightly ove. All of the other lrger seedlings were not ffected y removl of the tues. Our generl impression is tht once the seedlings grow ove the top of the treeshelters nd egin to move in response to wind, they llocte more energy to Tle 3 Averge sl dimeter (mm) of seedlings protected with different devices, nd receiving different intensities nd intervls of weed control 1 Growing Seson Tretment 1991 1992 1993 1994 1995 --------------------------------------------------------------- mm --------------------------------------------------------------------- Protection Screen cge 4.8 4.9 7.8 9.2 10.8 Treeshelter 4.8 6.7 10.5 15.8 24.7 Weed intensity None 4.2 4.4 6.1 7.5 6.7 0.6-m circle 4.3 5.3 8.1 10.4 17.6 1.2-m circle 5.2 5.8 9.6 13.1 19.7 1.8-m circle 5.7 7.7 c 12.8 19.0 26.8 Weeding intervl 1 yer 4.8 5.0 8.2 10.2 15.6 2 yers 4.9 6.5 10.1 14.4 20.4 1 Growing sesons nd tretment types with different letters re significntly different (P < 0.05) y Anlysis of Vrince for protection nd weeding-intervl tretments nd y Tukey s test for weedintensity tretments. USDA Forest Service Gen. Tech. Rep. PSW-GTR-160. 1997. 247
McCrery nd Tecklin Effects of Seedling Protectors nd Weed Control rdil growth nd their dimeter increses. Simultneously, the rte of height growth slows down. The overll result is tht y the second or third growing seson, the seedlings re simply much lrger thn their screened counterprts. We elieve tht in wildlnd setting, greter initil growth rte will confer sustntil dvntge to seedlings, ecuse they will grow more rpidly to height t which they cn withstnd rowsing pressures. Without protection, ok seedlings cn remin stunted for yers (White 1966). By providing method to stimulte initil growth, treeshelters my not only improve the chnces tht young seedling will eventully ecome tree, ut gretly hsten the process s well. However, it is importnt to leve the shelters in plce until the seedlings hve grown well ove the tops of the tues, so tht they develop sufficient dimeter to support the crown. Determining exct cuses for fster growth of seedlings in treeshelters versus screened cges is somewht difficult. Treeshelters hve een reported to stimulte oveground growth of trees through comintion of moisture conservtion, incresed tempertures, nd elevted cron dioxide levels (Potter 1991). However, we oserved tht nimls cn lso influence seedling growth rtes. Becuse ground vegettion surrounding the sclped circles ws not controlled, vegettive cover ner seedlings ws extensive. This pprently provided fvorle hitt for oth voles nd grsshoppers. The screens were much hrder to mintin thn the tues, nd consequently these nimls dmged seedlings in the screen cges more frequently thn seedlings in the tues. Despite efforts to secure screen cges to the ground, voles were le to get underneth, strip rk, nd even completely girdle severl seedlings. Similrly, grsshoppers gined ccess to seedlings in screens fter they grew out the tops, nd then consumed considerle mounts of folige. Neither of these nimls seriously dmged seedlings in the treeshelters. Becuse we sunk the tues severl inches into the ground, voles were unle to urrow underneth. The ility of treeshelters to prevent vole dmge to ok seedlings hs een reported previously (Dvies nd Pepper 1989). While the grsshoppers te some folige tht grew over the tops of the tues, the seedlings were so lrge y this time tht overll dmge ws miniml. By modifying temperture, humidity, etc. nd protecting seedlings from insect nd rodent dmge, the treeshelters provided much more fvorle environment, resulting in greter growth nd survivl. In ll three instnces where we detected significnt interctions, the rnkings of protective types within weed tretments were the sme tht is, the verge survivl nd height were greter for seedlings in treeshelters thn in screen cges for ech of the weed-removl tretments. However, the mgnitude of the difference vried, cusing the interction. For survivl, seedlings in screens nd tues hd similr survivl under the gretest intensity of weed removl, ut much higher survivl in treeshelters under lesser intensities. The verge 1992 height of seedlings in tues for weed tretment 3 (1.2-m circles) ws more thn five times tht for seedlings in screens, while for the other three weed tretments, it ws only pproximtely two to three times s gret. There ws generl trend for seedlings to grow in proportion to the initil level of weed control. Though the verge sl dimeter of seedlings from the 1.8-m tretment ws only significntly greter thn tht of seedlings from the 1.2-m tretment in the third growing seson, it ppered tht oth dimeter nd growth tended to e greter for the lrger circles. We therefore do not know how lrge circles should e to promote mximum growth. It my e tht circles even lrger thn 1.8 m would stimulte even greter growth. However, the enefits of lrger circles must e weighed ginst the costs or difficulty of providing the tretment. In this study, weed control ws y hnd sclping, which ws oth difficult nd time consuming. The 1.8-m circles took pproximtely twice s long to sclp s the 1.2-m ones. The gin from such sclping my not e worthwhile. 248 USDA Forest Service Gen. Tech. Rep. PSW-GTR-160. 1997.
Effects of Seedling Protectors nd Weed Control McCrery nd Tecklin In such situtions, we recommend 1.2-m circles. However, if hericides re used for weed control, we recommend circles of t lest 1.8 m in dimeter, ecuse the dditionl expense nd effort would likely e miniml. As indicted previously, ll weed-control tretments were discontinued fter the second yer. There ppered to e n initil enefit from providing second yer of weed control, not only for survivl, ut lso for height nd dimeter growth. However, the enefits of this second yer of tretment t lest in terms of survivl nd height tended to diminish over time, in tht the verge survivl of seedlings from oth groups remined reltively constnt fter the second yer, nd height increments were similr. Thus, though n dditionl yer of weed control my offer some enefits in field performnce, these enefits re likely to e most pronounced during the first 2 yers the seedlings re treted differently. Though it took some time for the weeds to return to the sclped circles, differentiting etween treted nd untreted res is difficult tody. Both hve thick covering of weeds. Despite this similrity, seedlings in the treted plots continue to grow fster thn those from untreted plots. Clerly, these plnts otined n initil dvntge from which they continue to enefit. These dt suggest tht continued weed control is unnecessry for dequte growth nd survivl once seedlings re estlished. However, in slightly older reserch plot within 100 m of this study re, where weed control hs not een mintined, splings more thn 2.5 m tll nd 4 cm in dimeter hve een girdled y voles, nd rk hs een removed more thn meter up on the stem. We elieve tht vole popultions incresed drmticlly when we stopped controlling weeds severl yers go, nd tht without protection, the splings were vulnerle. So while it my not e necessry to continue weed control fter 2 yers to limit vegettive competition, filure to do so my promote such fvorle hitt for rodents tht even lrge unprotected splings my e seriously dmged. Conclusions This study indictes tht treeshelters cn promote sustntilly greter survivl nd growth of lue ok seedlings plnted on hrdwood rngelnds in Cliforni. Treeshelters pper to protect seedlings from t lest two dmging nimls nd stimulte oveground growth. We elieve this rpid, initil growth is highly eneficil ecuse it cn reduce the time needed for seedlings to grow to size t which they re less vulnerle to rowsing pressures. Additionlly, intensity of weed control significntly ffects performnce. Generlly, weed-free circles with lrger dimeters promote higher survivl nd fster growth. We elieve these circles should e minimum of 1.2 m in dimeter. Mintining weed-free res round seedlings for two complete growing sesons results in greter survivl nd growth thn tretment for only 1 yer. However, it ppers tht the enefits of this dditionl tretment tend to suside over time. Acknowledgments We thnk the stff t the Cliforni Deprtment of Forestry nd Fire Protection Lewis A. Morn Reforesttion Center for rering nd mintining the ok seedlings efore outplnting. This project ws prtilly funded y grnt from the University of Cliforni Sierr Foothill Reserch nd Extension Center. References Adms, Theodore E.; McDougld, Neil. 1995. Plnted lue oks my need help to survive in the Southern Sierrs. Cliforni Agriculture 49(4): 13-17. USDA Forest Service Gen. Tech. Rep. PSW-GTR-160. 1997. 249
McCrery nd Tecklin Effects of Seedling Protectors nd Weed Control Bolsinger, Chrles L. 1988. The hrdwoods of Cliforni s timerlnds, woodlnds nd svnns. Resour. Bull. PNW-148. Portlnd, OR: Pcific Northwest Reserch Sttion, Forest Service, U.S. Deprtment of Agriculture; 148 p. Costello, Lurence R.; Peters, Amy; Giusti, Greg A. 1996. An evlution of treeshelter effects on plnt survivl nd growth in Mediterrnen climte. Journl of Aroriculture 22(1): 1-8. Dvies, R.J.; Pepper, H.W. 1989. The influence of smll plstic gurds, tree-shelters, nd weed control on dmge to young rodlefed trees y field voles (Microtus grestis). Journl of Environmentl Mngement 28: 117-125. Griffin, Jmes R. 1971. Ok regenertion in the upper Crmel Vlley, Cliforni. Ecology 52: 862-868. McCrery, Dougls D. 1990. Ntive oks the next genertion. Fremonti 19(3): 44-47. McCrery, Dougls D.; Tecklin, Jerry. 1993. Treeshelters ccelerte vlley ok restortion on grzed rngelnds. Restortion nd Mngement Notes 11(2): 152-153. Muick, Pmel C.; Brtolome, Jmes. 1987. Fctors ssocited with white ok regenertion in Cliforni. In: Plum, Timothy R.; Pillsury, Normn H., technicl coordintors. Proceedings of the symposium on multiple-use mngement of Cliforni s hrdwood resources; Novemer 12-14, 1986; Sn Luis Oispo, CA. Gen. Tech. Rep. PSW-100. Berkeley, CA: Pcific Southwest Forest nd Rnge Experiment Sttion, Forest Service, U.S. Deprtment of Agriculture; 86-91. Potter, Mrk J. 1988. Treeshelters improve survivl nd increse erly growth rtes. Journl of Forestry 86: 39-41. Potter, Mrk J. 1991. Treeshelters. Forestry Commission Hndook 7. London, Englnd: HMSO Pulictions Centre; 48 p. Tecklin, Jerry; McCrery, Dougls D. 1993. Dense vegettion my encourge vole dmge in young ok plntings. Restortion nd Mngement Notes 11(2): 153. Welker, Jeffrey M.; Menke, John W. 1987. Quercus douglsii seedling wter reltions in mesic nd grzing-induced xeric environments. In: Proceedings, Interntionl conference on mesurements of soil nd plnt wter sttus. July 6-10, 1987, vol. 2, Plnts, Uth Stte University, Logn, UT; 229-234. White, Keith L. 1966. Structure nd composition of foothill woodlnd in centrl-costl Cliforni. Ecology 47(2): 229-237. 250 USDA Forest Service Gen. Tech. Rep. PSW-GTR-160. 1997.