An Evaluation of Oak Woodland Management in Northeastern Illinois, USA

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1 R E S E A R C H A R T I C L E An Evlution of Ok Woodlnd Mngement in Northestern Illinois, USA Jneen R. Ltsch' Roger C. Anderson Deprtment of Biologicl Sciences Illinois Stte University Cmpus Box 4120 Norml, IL USA ABSTRACT: We exmined vegettion chnge over time t mnged nd unmnged ok woodlnd sites locted in Cook County, Illinois, forest preserves. The mnged site (Cp Suers Holding) ws dominted by red nd white ok (Quercus rubr nd Q. lb) in 1995, nd density ws 313 trees h-'. Historicl records indicte tht white ok dominted the site nd tree density ws between 5 nd 50 trees h-'. Mngement initited in 1989 included prescribed burning nd woody plnt removl. Vegettion ws surveyed in 1988 nd No significnt chnge in totl ground cover or in cover of ntive or exotic species (plnts <1 m tll) ws detected in However, herbceous species s percent of the totl ground cover incresed from 58% in 1988 to 81% in Woody species decresed from 42% of the totl cover in 1988 to only 19% in Selected tx white snkeroot (Euptorium rugosum), enchnter's nightshde (Circe lutetin), woodlnd knotweed (Polygonum virgininum), nd ok species (Quercus spp.) significntly incresed in cover between the 1988 nd 1995 surveys. Exotic shrubs decresed by 3139 stems h- 1, ntives decresed by 2635 stems h-', nd the cnopy cover of exotic nd ntive shrubs decresed significntly. Tree cnopy cover t the mnged site did not chnge significntly between yers. In contrst, t the unmnged site (McClughry Springs Forest Preserve), totl ground cover (plnts <1.4 m tll) significntly incresed over four yers, mostly due to increses in woody vegettion. Density of woody species in ll size clsses incresed, nd there ws significnt increse in Virgini creeper (Prthenocissus quinquefoli). Invsive shrubs substntilly incresed in the suppressed (stems <1.4 m tll) nd intermedite (stems >1.4 m tll but <11 cm dbh) lyers. Mngement t Cp Suers Holding, while not hving conclusive positive effect on herbceous species, hs substntilly reduced the density nd cover of invsive nd exotic shrubs nd mintined tree cnopy cover, ll of which incresed t the unmnged site. The results of this study indicte tht mngement, in the form of prescribed burns nd removl of woody species, chieved some restortion gols t this site. Index terms: ground-lyer vegettion, ok woodlnd, prescribed burning, restortion, vegettion chnge 1 Current ddress: Missouri Deprtment of Conservtion, Nturl History Division, 2302 County Prk Drive, Cpe Girrdeu, MO USA. mil.conservtion. stte.mo.us Nturl Ares Journl 20: INTRODUCTION In 1820 forested ecosystems dominted by ok (Quercus spp.) covered 40 45% (5.6 million h) of Illinois, mostly long river vlleys nd steep slopes. Tody bout 1.7 million h, or 31%, of tht re remin in forest (Anderson 1991, Illinois Deprtment of Energy nd Nturl Resources 1994). Fctors influencing the distribution nd chrcter of Illinois forests since Europen settlement include fire suppression, deforesttion, effects of herbivores, nd exotic species invsion. With Europen settlement fires were suppressed, llowing woody species to invde grsslnds nd leding to the conversion of svnns nd woodlnds to closed forests (Gleson 1922, Curtis 1959). Between 1820 nd 1980, nerly 4 million h of forested lnd in Illinois were converted to griculture nd bout 203,000 h were converted to urbn res (Illinois Deprtment of Energy nd Nturl Resources 1994). Live- stock grzing degrded nturl communities, chnging the chrcter of mny svnns (White 1978); nd in the lter twentieth century, the white-tiled deer (Odocoileus virgininus), ntive herbivore, hs become thret to nturl res in the estern United Sttes (Anderson nd Loucks 1979, Alverson et l. 1988, Anderson 1997). Further degrdtion of forests hs occurred s result of exotic species invding frgmented or degrded res nd competing with ntive forest-understory species (White 1978, McCune nd Cottm 1985, Ptterson 1992, Illinois Deprtment of Energy nd Nturl Resources 1994). Some of the most troubling species re woody shrubs (Illinois Deprtment of Energy nd Nturl Resources 1994, Schwegmn 1994). Restortion Activities To counterct or prevent further forest degrdtion cused by historic nd con- Volume 20 (3), 2000 Nturl Ares Journl 211

2 temporry fctors, mny forested res re now being mnged or restored (Ptterson 1992). Restortion gols include protecting nd preserving the ntive flor nd fun, returning sites to historic conditions, nd reestblishing ecosystem functions such s hbitt structure nd wter-shed protection (Pckrd 1993, Jckson et l. 1995, Stevens 1995). Restortionists often seek to chieve their gols by reintroducing ntive processes such s fire into degrded ecosystems. Fire is thought to be n effective mngement tool to restore forests to historic conditions. It cuses decrese in tree cnopy cover nd in the number of woody species nd chnge in herbceous species composition nd bundnce (Anderson nd Brown 1986, Tester 1989, Anderson nd Schwegmn 1991). Reducing cnopy cover increses the mount of light reching the forest floor, which fvors the reproduction of shde-intolernt oks (Curtis 1959, Abrms 1992). Absence of fire in firedpted ecosystem cuses species ssemblges to shift towrd greter numbers of shde-tolernt, mesic forest species (Abrms 1992). Fire controls excessive woody growth s well s growth of some exotic species, which often re not dpted to burning (Anderson nd Schwegmn 1991, Nuzzo 1991). At some restortion sites, degrded ground-lyer vegettion is being enhnced through the sowing of seeds of ntive woodlnd herbs (Pckrd 1997). Exotic shrubs re often cut nd removed, nd the invsive herbceous species grlic mustrd (Alliri petiolt) is hnd-pulled (Schwegmn 1994). (Vsculr plnt nomenclture follows Swink nd Wilhelm [19941.) Rtionle nd Gols for the Study We used monitoring dt nd sttisticl methods to evlute mngement in woodlnd locted in Cook County Forest Preserve in northestern Illinois (Cp Suers Holding, Figure 1: CSH). The site ws surveyed in 1988, mngement of the study re begn in 1989, nd we resurveyed the vegettion in All monitored res t the mnged site were treted. For comprison to Cp Suers Holding, we exmined vegettion chnge t ner- by unmnged site (McClughry Springs Forest Preserve, Figure 1: McCS), which hd been surveyed in The forest preserve district's stted mngement gol for the Cp Suers Holding site ws "to reestblish ntive vegettion." We subdivided tht gol into three objectives for which specific predictions could be mde to ssess progress towrd the overll gol. The objectives re to improve the qulity of the ntive ground-lyer vegettion, control woody vegettion (especilly exotic shrubs), nd increse the mount of light reching the understory, s mesured by reduction in tree cnopy cover. We predicted tht successful mngement would led to the following chnges: (1) increse in richness nd cover of ntive species; (2) decrese in richness nd cover of exotic species; (3) decrese in density nd cover of shrubs, especilly exotic shrubs; (4) decrese in totl tree cnopy cover; nd (5) increse in ok seedling cover. We compred vegettion chnge between smpling times for ech site. Then we compred the direction of chnge t the mnged site to the direction of chnge t the unmnged site. We evluted chnge in the context of chieving the objectives outlined bove. METHODS Mnged Study Site--Cp Suers Holding Forest Preserve Site Description Cp Suers Holding is 615-h forest preserve in Cook County, Illinois, encompssing vriety of nturl communities including wetlnd, pririe, svnn, nd forest. We studied wooded re on rolling topogrphy in the western portion of the preserve. Government Lnd Office (GLO) surveys from 1821 suggest tht the study re, in Section 19 of Plos Township, ws svnn with density of 5 50 trees h-' (Nyberg nd Nyberg 1993). Level lnd immedite- ly southwest of the study re ws pririe. Of the nineteen witness trees recorded in the survey for Section 19, seventeen were white ok (Quercus lb); there were single trees of blck ok (Quercus velutin) nd blck wlnut (Juglns nigr) (Nyberg nd Nyberg 1993). Mngement The Cook County Forest Preserve District's mngement gol is to "reestblish ntive vegettion." Mngement prctices include periodic prescribed burns, cutting nd removing stems of invsive woody shrubs, removing exotic species, nd sowing smll mounts of seed of some forest herbs (seeding informtion vilble in Ltsch [1997]). Prescribed burns were pplied to the site t irregulr intervls, with no re being burned more frequently thn every two yers. The seson of the burn (fll or spring) ws held constnt for ech re. Ninety percent of the study trnsects' totl length lies in spring-burned res nd the reminder lies in fll-burned res. Fifty percent ws burned once in seven yers. The remining res were burned either two or four times in seven yers. Figure 1. Loction of Cp Suers Holding (CSH) nd Mc- Clughry Springs (McCS) Forest Preserves in Cook County, Illinois, USA. 212 Nturl Ares Journl Volume 20 (3), 2000

3 Vegettion Surveys Vegettion ws surveyed in July 1988 nd July 1995 long four permnent monitoring trnsects with combined length of 1200 m. Dt were collected on ground cover plnts (ll vegettion <1 m tll), shrubs (woody plnts 0)1 m tll nd <5.1 cm dbh), nd trees (woody plnts 0)5.1 cm dbh) (Apfelbum 1989). We estimted percent ground cover of ech species in 1-m' qudrts using cover ctegories modified from Dubenmire (1959): (1) 0-2%, (2) 2-20%, (3) 20-50%, (4) 50-80%, (5) %. A totl of 120 qud-rts were smpled in ech yer. Shrub density ws estimted by counting stems of ech species in 1-m-wide belt trnsect. Tree density nd bsl re were estimted by counting nd mesuring the dbh of stems by species in 2-m-wide belt trnsect. Shrub nd tree cnopy cover were estimted to the nerest centimeter nd summrized s meters of intercept of ech species directly over the trnsect. Belt trnsect nd line intercept surveys were completed in 50-m sections of trnsect nd dt were nlyzed using ech 50-m section s smple unit. Sttisticl Anlyses Due to the lrge numbers of species nd zeroes in the dt set, dt were pooled into more inclusive vribles: ntive, exotic, woody nd herbceous ground covers; densities nd cnopy covers of ntive nd exotic shrubs; totl tree cnopy cover; nd ok, non-ok, nd exotic tree species cnopy covers. In ddition, for ground cover it ws necessry to pool dt from three consecutive 1-m 2 qudrts to normlize the dt set. Dt were trnsformed to chieve normlity when necessry, nd were nlyzed for differences between yers nd the rndom effect of trnsect with twowy (yer nd trnsect s fixed nd rndom effects, respectively) nlysis of vrince (ANOVA) nd multivrite nlysis of vrince (MANOVA) using the SAS GLM procedure (SAS Institute 1989). When the results of MANOVA were significnt, pooled vribles were tested individully using protected ANOVA (Scheiner 1993). Pilli's trce ws the test sttistic used to interpret MANOVA results. MANOVA nd ANOVA tbles re vilble in Ltsch (1997). Tree density nd bsl re were clculted from belt trnsect dt collected in Importnce vlues for tree species were clculted s (reltive density + reltive dominnce)/2 (Adms nd Anderson 1980). The Wilcoxon nonprmetric test (corrected for multiple tests using Bonferroni procedure [Sokl nd Rohlf 19951) ws used to test individul species for differences between yers. Species occurring most frequently in qudrts were chosen for testing. Ok ws lso included to test the prediction regrding cover of ok seedlings. The SAS NPAR1WAY procedure ws used to perform nonprmetric tests (SAS Institute 1989). Significnce ws ccepted t P<0.05 for ll tests unless otherwise indicted. Since the tretment t the mnged site is not replicted, sttisticl interprettion reltive to the study re my not be more brodly pplicble. Unmnged Study Site McClughry Springs Forest Preserve Site Description McClughry Springs, n 80-h Cook County forest preserve is locted 3.2 km est of the Cp Suers Holding study site. The study site is wooded nd on level uplnd surrounded by steep slopes. Historic tree density t the site (lso derived from the 1821 GLO surveys) ws <125 trees h- 1. As t Cp Suers Holding, the mjority of witness trees for this section (10 out of 12) were white ok (Nyberg nd Nyberg 1993). No prescribed burning or removl of woody or exotic vegettion hd been conducted in the study re s of the 1995 survey. Vegettion Surveys Ground-lyer vegettion ws surveyed in June or July 1991 nd July 1995, nd woody vegettion ws surveyed in July 1992 nd July Surveys employed two permnent trnsects, ech 325 m in length. Percent ground cover for ech species <1.4 m tll ws estimted in 0.25-m 2 qudrts using strtified rndom smpling t 10-m intervls for 150 feet of the trnsect. Fifteen qudrts were smpled on ech trnsect for totl of 30 qudrts. Woody vegettion ws surveyed t 25-m intervls using the point-qurter method for three size clsses: suppressed, intermedite, nd dominnt. Suppressed vegettion includes woody stems less thn brest height (<1.4 m tll), intermedite vegettion includes smll trees greter thn brest height, but not reching the uppermost cnopy lyer (in generl <11 cm dbh). Dominnts re trees reching the upper cnopy (in generl stems 11 cm dbh). Thirteen points were smpled on ech trnsect for totl of 26 smpling points. Sttisticl Anlyses Totl ground cover ws nlyzed for differences between yers with nonprmetric Wilcoxon test using SAS NPAR1WAY procedure (SAS Institute 1989). Wilcoxon tests were lso used to test for differences between yers for ntive nd exotic, nd woody nd herbceous species groups, nd for Virgini creeper (Prthenocissus quinquefoli), gry dogwood (Cornus rcemos), nd flse Solomon's sel (Smilcin rcemos). Totl density of suppressed vegettion, nd totl density nd bsl re of intermedite nd dominnt vegettion, were clculted from point-qurter dt. In ddition, density of individul suppressed species, nd density nd bsl re of intermedite nd dominnt woody species were clculted. For the dominnt clss, importnce vlues were clculted s (reltive density + reltive dominnce)/2. We tested for chnges in woody species bundnce (chnges in the reltive proportions of species) using contingency Chi-squre test. Density by species ws used to test suppressed vegettion for chnges between 1992 nd Bsl re by species ws used to test for chnges in bundnce of intermedite nd dominnt species during this time period. Volume 20 (3), 2000 Nturl Ares Journl 213

4 RESULTS Cp Suers Holding Forest Preserve Ground Cover Vegettion Species richness in the ground lyer of the mnged site incresed between the two survey yers. Eighty species were recorded in 1988 nd 98 species were recorded in 1995, n increse of 18 species. In 1988, 67 species were ntive nd 13 were exotic, nd in 1995, 87 species were ntive nd 11 were exotic. Abundnt exotic species in this lyer in 1995 were glossy buckthorn (Rhmnus frngul), creeping smrtweed (Polygonum cespitosum vr. longisetum), nd Spnish needles (Bidens bipinnt) with 3.4% cover, 3.1% cover, nd 2.8% cover, respectively. Of the 80 species recorded in 1988, 52 were herbceous species nd 28 were woody species, while in 1995, 77 of the 98 species were herbceous nd 21 were woody. The species present were primrily woodlnd species common to the Chicgo region. Totl ground cover did not chnge signif- icntly from 1988 to 1995 (ANOVA, F=0.05, df=1,66, P=0.8244); it ws 49.6±3.2% (men ± SE) nd 48.6±3.2% for ech yer, respectively. Pooled cover of ntive nd exotic species ws lso unffected by yer (MANOVA, F=0.733, df =2,2, P=0.577). Ntive species hd pproximtely 40% cover or bout four times the percent cover of exotic species in both yers. Cover of pooled woody species decresed from 20.8±1.9% to 9.6±1.9% between 1988 nd 1995, nd pooled cover of herbceous species incresed from 28.9±2.8% to 40.3±2.8%; but these chnges were not significnt (MANOVA, F=6.6738, df=2,2, P=0.1303) (Tble 1). However the proportion of herbceous to woody species chnged significntly (c 2 =30.19, df=1, P<0.001). In 1988 herbceous species comprised 58.1% of the ground cover while woody species comprised 41.9%. In 1995 herbceous species comprised 80.8% of the ground cover nd woody species comprised 19.2%. Nonprmetric Wilcoxon tests showed significnt increses in ground cover between 1988 nd 1995 for enchnter's nightshde (Ci- Tble 1. Percent ground cover (men ± 1 SE) of species groups nd selected ground lyer species t Cp Suers Holding in 1988 nd N SPECIES GROUPS Ntive ± ± 2.8 Exotic b ± ± 1.6 Woody ± ± 1.9 Herbceous ± ± 2.8 Totl cover ± ± 3.2 SELECTED SPECIES d Euptorium rugosum ± 0.2 **8.0 ± 1.0 Rhmnus frngul ± ± 0.9 Circe lutetin ± 0.5 **2.8 ± 0.4 Quercus spp ± 0.0 **0.4 ± 0.1 Polygonum virgininum ± 0.7 **3.5 ± 0.7 Snicul gregri ± 2.0 " 1. 1 ± 0.3 Dt were trnsformed s the rcsin of the squre root of the proportion (P<W: ). b Dt were trnsformed s the log of the proportion (P<W: ). C Totl cover is the sum of cover vlues for ll species. d Significnce is indicted by sterisk (** P<0.01). correction (e.g., 0.05/6=0.008). Criticl vlues were djusted with Bonferroni ce lutetin), white snkeroot (Euptorium rugosum), woodlnd knotweed (Polygonum virgininum), nd ok. Blck snkeroot (Snicul gregri) declined significntly; glossy buckthorn did not chnge significntly (P>0.10) (Tble 1). Observed trends in species cover tht we did not test sttisticlly were increses in creeping smrtweed, Spnish needles, nd white grss (Leersi virginic), nd decreses in poison ivy (Rhus rdicns), Virgini creeper, nd gry dogwood. Frequency nd cover of ll ground-lyer species in ech yer re listed in Ltsch (1997). Litter cover ws estimted t 79% in 1988 nd 82% in Percent of ground without vegettive cover ws 53% in Shrub Lyer In 1988, 25 shrub lyer species were recorded including 6 exotic species; there were 7 species of shrubs, 4 vines, nd 14 tree species. In 1995, 27 shrub lyer species were smpled of which 7 were exotic; there were 11 shrubs, 3 vines, nd 13 species of trees. Shrub density declined significntly over time. This decline ws significnt t the 10% level (MANOVA, F= , df=2,2, P=0.0588). Becuse the P-vlue for the MANOVA ws close to the 0.05 level, we proceeded with protected ANOVA for ech of the response vribles. There ws significnt decline for pooled ntive species (ANOVA, F=32.65 df=1,40, P=0.0001) nd pooled exotic species (ANOVA, F=60.48 df=1,40, P=0.0001) (Tble 2). Stndrdized cnonicl coefficients showed tht the decline in exotic species (1.67) ws more responsible for the significnt difference between yers in shrub density thn ws the decline in ntive species (0.25). Exotic species de-cresed by 3139 stems h-' nd ntives decresed by 2635 stems h-' between the two smples. Species with significnt de-clines in stem density, ccording to Wilcoxon tests, were two exotic shrubs, glossy buckthorn nd rrow-wood (Viburnum denttum), nd gry dogwood, ntive shrub. Other species tht incresed or decresed between smples, but were not tested sttisticlly, re listed in Tble Nturl Ares Journl Volume 20 (3), 2000

5 Tble 2. Shrub density in stems/h (men ± 1 SE) for selected woody species in 1988 nd 1995 t Cp Suers Holding. Species re grouped bsed on whether decrese, mintennce, or increse of density ws observed between the two yers. Tree Lyer Species P-vlue b DECREASING Rhmnus frngul 3208 ± ± 573 *(0.0001) Cornus rcemos 1067 ± ± 17 *(0.0001) Viburnum denttum 867 ± ± 158 *(0.0064) Crtegus spp. 567 ± ± 58 (0.1263) Prunus serotin 483 ± ± 30 Rhmnus cthrtic 292 ± ± 20 Prunus virginin 208 ± ± 17 Frxinus mericn 142 ± ± 35 Corylus mericn 142 ± ± 0 Frxinus pennsylvnic 83 ± 38 0 ± 0 Rhus rdicns 58 ± ± 17 Cry ovt 50 ± 37 8 ± 9 UNCHANGED Quercus rubr 42 ± ± 21 INCREASING Rubus llegheniensis 0 ± ± 247 Ros multiflor 8 ± ± 207 Vitis spp. 42 ± ± 68 SPECIES GROUPS Ntive 3418 ± ± 357 Exotic 4288 ± ± 642 These species were tested for significnt chnges between yers using the Wilcoxon test. Significnt chnges re mrked with *. b Four tests were performed so significnce ws ccepted t P < 0.05/4, or In 1995 tree density ws 165 nd 313 trees h-' for trees >25 cm dbh nd >10 cm dbh, respectively. Twenty-two species were recorded in the tree lyer during the study. All of these re ntive except for pple (Mlus spp.), glossy buckthorn, nd common buckthorn (Rhmnus cthrtic). Species with the highest importnce vlues in 1995 were red ok (Quercus rubr) nd white ok followed by blck cherry (Prunus serotin) nd bur ok (Quercus mcrocrp), respectively (Tble 3). The density of ded blck ok stems (17.4 trees h-') ws higher thn tht of live stems (4.4 trees h-'). Bsl re of trees >10 cm dbh ws 32.5 m 2 h-'. Totl tree cnopy cover did not chnge significntly between yers (ANOVA, F=0.53 df=1,40, P=0.4727). There ws no difference between yers for pooled ok, non-ok ntive, nd exotic species groups (MANOVA, F=3.7466, df=3,1, P=0.3589). Oks dominted the cnopy in 1995 with 83.5±6.3% cover, nerly four times tht of non-ok ntives (19.4±3.6%) nd exotics (2.3±1.3%) combined. Red ok hd greter cnopy cover thn white ok in both survey yers. Ok species, including white, red, bur, nd blck ok, decresed slightly between smples while non-ok ntives, including blck cherry, hwthorn (Crtegus spp.), Americn elm (Ulmus mericn), nd shgbrk hickory (Cry ovt), incresed slightly. McClughry Springs Forest Preserve Ground Cover Vegettion Nineteen species were recorded t Mc- Clughry Springs in 1991 nd 30 in 1995; totl of 37 species over both yers. Thirty species were ntive nd seven were exotic. Of the totl species for both yers, 17 were herbceous nd 20 were woody. In 1991 nd 1995, 8 out of 10 of the most bundnt ground cover species were woody, nd woody species hd seven to eight times the cover of herbceous species in both yers. Percent cover of ntive species ws bout ten times the cover of exotics in both yers (Tble 4). Wilcoxon tests showed significnt increses in totl ground cover t McClughry Springs s well s significnt increses for woody nd herbceous species nd ntive nd exotic species (Tble 4). Between the two smples, there ws lrge nd significnt increse in ground cover for Virgini creeper (P<0.001). Gry dogwood nd flse Solomon's sel showed no significnt chnge nd hd less cover thn Virgini creeper (Tble 4). Woody Vegettion A contingency chi-squre test on density of suppressed woody vegettion showed significnt chnge in species reltive bundnce (x 2 = , df=7, P<0.001) between the two smples. Chnges in density included n increse in Virgini creeper, the most bundnt species. Poison ivy showed lrge decrese, while rrow-wood (Viburnum spp.), gry dogwood, nd buckthorn (Rhmnus spp.) ll more thn doubled in density from 1992 to 1995 (Tble 5). Bsl re of intermedite nd dominnt clsses incresed (Tble 7). Chi-squre tests on bsl re of intermedite nd dominnt vegettion showed no significnt chnge in reltive proportions of species between yers (dominnt: c 2 =2.54, df=7, P>0.9; intermedite: c 2 =2.09, df=14, P>0.995). Density (stems/h) of ll three size clsses incresed (Tbles 5, 6, nd 7). Severl tree tx in the intermedite clss blck cherry, sh (Frxinus mericn nd F. pennsylvnic), nd elm (Ulmus rubr nd U. mericn) tht hd densities of Volume 20 (3), 2000 Nturl Ares Journl 215

6 Tble 3. Density, reltive density, bsl re, reltive dominnce, nd importnce vlue (IV) for trees >10 cm dbh t Cp Suers Holding in 1995, nd verge importnce vlues for Wisconsin southern dry-mesic nd dry forests (from Curtis 1959). Species Density Reltive (stems/h) Density Bsl Are (m 2 /h) Reltive Dominnce IV' IV drymesic" Quercus rubr Quercus lb IV dry" Prunus serotin Quercus mcrocrp Ulmus rubr Crtegus spp Rhmnus cthrtic Frxinus mericn Tili mericn Cry cordiformis Cry ovt Quercus velutin Juglns nigr Rhmnus frngul Ulmus mericn Acer negundo < Acer scchrum Quercus ellipsoidlis TOTALS (reltive density + reltive dominnce)/2. b (reltive frequency + reltive density + reltive dominnce)/3. bout 400 stems h- 1 in 1995 hd pproximtely doubled their 1992 densities. Red ok, white ok, nd Hill's ok (Quercus ellipsoidlis) were found t lower densities thn blck cherry, sh, nd elm. For shrubs in this clss, hwthorn hd the highest density nd much greter bsl re thn ll other shrub nd tree species in the intermedite size clss. Shrub species in-cresing in density were hwthorn, rrow-wood, buckthorn, nd honeysuckle (Lonicer spp.). These chnges were not tested for significnce (Tble 6). In the dominnt size clss, white ok hd the highest density nd bsl re in 1995, followed by red ok. White nd red ok incresed in density nd bsl re between the two smples; gin this chnge ws not tested for significnce (Tble 7). Density for trees >10 cm dbh ws 275 trees h -1, which ws lower thn the 1995 density t Cp Suers Holding. DISCUSSION Evlution of Mngement We predicted tht with successful mngement, ntive species in the ok woodlnd would increse in richness nd cover over time nd exotic species would decrese, meeting the mngement objective of improving the qulity of ntive groundlyer vegettion. The totl number of species t the mnged site incresed between 1988 nd Other studies hve shown species richness to increse with prescribed burning in fire-dependent communities (Tester 1989, Anderson nd Schwegmn 1991, Mehlmn 1992). However, in this study n increse in species richness ws lso observed t the unmnged site. The predicted increse in ground cover of ntive species ws not observed t the mnged site. At the unmnged site, totl ground cover incresed, s did ntive nd exotic species cover. Much of this increse however, ws due to n increse in woody species, which composed >80% of the ground lyer t this site in This site hd fewer totl species thn the mnged site, with severl species overwhelmingly more bundnt thn ll others. At the mnged site, fire mngement probbly ws responsible for the decrese in woody species nd the chnges in bundnce of some herbceous species. Evidence for mngement positively ffecting the ground lyer is inconclusive. Species richness incresed nd proportions of ntive nd exotic species cover remined the sme t both sites. A second mngement objective ws to control woody understory vegettion, especilly exotic shrubs. We predicted decrese in shrub density nd cnopy cover with successful mngement. This mngement objective ws met during the seven yers of mngement t Cp Suers Holding, s evidenced by chnges in proportions of woody nd herbceous cover nd chnges in density nd cnopy cover of the shrub lyer. In the ground lyer t Cp Suers Holding, herbceous species outnumbered woody species by bout 3.5 to 1; this proportion of species numbers ws mintined with the mngement regime. In terms of cover, woody species tended to decrese nd herbceous species tended to increse such tht the proportions of woody to herbceous species chnged mrkedly. This is consistent with observed decreses in woody species fter burning elsewhere (Anderson nd Schwegmn 1991). Some woody species in the ground lyer, such s poison ivy, Virgini creeper, nd gry dogwood, tended to decline s well. Overll, glossy buckthorn showed no significnt chnge in the ground lyer. Nevertheless, glossy buckthorn decresed in ll mngement zones except in one tht hd received two fll burns since 1988, where it incresed. In ddition, this zone hd the smllest decrese for glossy buckthorn in the shrub clss (>1 m nd <5.1 cm 216 Nturl Ares Journl Volume 20 (3), 2000

7 Tble 4. Percent ground cover (men ± I SE) for vegettion <1.4 m in height, t McClughry Springs in 1991 nd Dt shown re for species groups nd the three most bundnt species t McClughry Springs for the two survey yers. N P-vlue b SPECIES GROUPS Ntive ± ± 6.4 *(0.0001) Exotic ± ± 2.8 *(0.0006) Woody ± ± 6.4 *(0.0001) Herbceous ± ± 3.7 *(0.0027) Totl cover ± ± 6.9 *(0.0001) SELECTED SPECIES Prthenocissus quinquefoli c ± ± 1.9 *(0.0001) Cornus rcemos ± ± 1.9 (0.7780) Smilcin rcemos ± ± 3.3 (0.2458) Totl cover is the sum of cover vlues for ll species. The two yers were compred using Wilcoxon tests. Five tests were performed so significnce ws ccepted t P0.05/5 = b Significnt chnges re mrked with *. Three tests were performed; significnce ws ccepted t P50.05/3 = dbh) compred to the other zones. Fll (November) burns my be less successful thn spring burns in controlling buckthorn. The shrub lyer declined overll t the mnged site, with ntive nd exotic species showing lrge declines in density nd in cnopy cover. Despite these decreses, exotic shrubs still hd greter density thn ntive shrubs fter mngement. But in cnopy cover, ntive shrubs surpssed exotic shrubs before nd fter mngement. Trends of incresing density nd cnopy cover in the shrub lyer were seen only for species forming ggregtions-common blckberry (Rubus llegheniensis) nd multiflor rose (Ros multiflor), nd for vine species-virgini creeper, poison ivy, nd grpe (Vitis spp.). In contrst, t the unmnged site, woody species in the ground nd shrub lyers tended to increse. For exmple, the suppressed lyer t McClughry Springs incresed in density. Although this lyer ws dominted by vine nd shrub species (especilly Virgini creeper), some tree species were present, including sh, sugr mple (Acer scchrum), nd elm. Since sh nd elm lso incresed in density in the intermedite clss, t lest these species re pprently being recruited into the cnopy. The increse in hwthorn, rrow-wood, buckthorn, nd honeysuckle is the opposite of the pttern t the mnged site where ll of these species, excluding honeysuckle, showed significnt declines. Buckthorn, despite hving very low bundnce t McClughry Springs, incresed in the suppressed nd intermedite vegettion lyers between 1992 nd Little is known bout the historic shrub lyer t these sites, thus it is difficult to decide composition, density, nd cnopy cover pproprite for historiclly ccurte restortion. However, John Wlls, surveyor of Plos Township where both of these sites re locted, mentioned the understory only once in the entire township. Since it is unlikely tht shrubs were completely bsent from this lndscpe, the fct tht he only mentioned the understory once (in floodplin thicket), my indicte tht shrubs were present t low densities nd did not impede pssge through the woods (D. Nyberg, Deprtment of Biologicl Scences, University of Illinois t Chicgo, pers. corn.). Ntive shrubs my be n importnt component in this ecosystem, nd though site my benefit from control of their bundnce, cre should be tken not to remove them entirely from the community. For some sites, restortion of ntive shrub component my be dvisble (Wheln nd Dilger 1992). A third mngement objective ws to increse the mount of light reching the understory. We predicted tht mngement progressing towrd this gol would decrese tree cnopy cover nd increse frequency of ok seedlings, which re intolernt of shde (Curtis 1959). No increses or decreses were seen overll in tree cnopy cover t Cp Suers Holding, lthough it ppers tht cnopy composition is shifting towrd lower ok dominnce. Although cnopy cover of trees did not chnge significntly, the significnt decrese in shrub cover should llow more light to rech the understory. We found incresed cover of ok seedlings (<1 m) in the ground lyer t Cp Suers Holding, which my be due to incresed light vilbility in the understory. However, ok seedlings my not mture into splings without sufficient light. Incresed seedling cover does not provide enough evidence to rgue tht ok survivl hs incresed. In ddition, climtic nd biotic fctors, such s the timing of mst yers, re involved in ok reproduction. Chrcteriztion of Cp Suers Holding Forest Preserve Ltsch (1997) compred the ground-lyer species composition t Cp Suers Holding with the published species lists of vrious uthors (Med 1846, Curtis 1959, Pckrd 1988, Bowles nd McBride 1994, nd Pruk 1995). She found tht in 1995, ground-lyer composition t the site resembled forest community rther thn svnn or brrens community. Tree-lyer Volume 20 (3), 2000 Nturl Ares Journl 217

8 composition nd density ws forest-like, s ws tree cnopy cover (>80%), which clssifies the site s forest in most community clssifiction systems. Of the south-ern Wisconsin communities to which we compred Cp Suers Holding, it more closely resembled tree composition for drymesic forest thn for dry forest, mesic forest, ok openings, nd ok brrens (Ltsch 1997). To reestblish conditions similr to those of the erly 1800s t Cp Suers Holding, more rdicl reduction in tree density nd cnopy cover is necessry. Long-term Vegettion Chnge Cp Suers Holding shows pttern of incresed tree density over the lst 180 yers similr to tht of other studied ok sites (McCune nd Cottm 1985, Abrms 1992). However, in contrst to Noe Woods (McCune nd Cottm 1985), ok species composition hs shifted. McCune nd Cot- Tble 5. Density (stems/h) of suppressed vegettion (woody plnts <1.4 m in height) t McClughry Springs in 1992 nd Species Prthenocissus quinquefoli 77,414 93,633 Rhus rdicns 13, Viburnum denttum ,578 Cornus rcemos Frxinus spp Rhmnus spp Crtegus spp b Acer scchrum 4361 Viburnum cerifolium 3271 Viburnum lentgo 2795 Lonicer spp Vitis ripri 1398 Rubus spp Ulmus mericn 1398 Ros multiflor 1398 Prunus serotin 1090 Acer negundo 1090 TOTALS 122, ,750 For these groups, gener were recorded in In 1995 species recorded were Frxinus mericn, Rhmnus frngul, nd Rubus llegheniensis. b No record of species is indicted by. tm (1985) reported lck of recruitment of the dominnt white nd blck ok t this site. At Cp Suers Holding, white ok ws the dominnt tree in 1821 nd red ok, pioneer species on mesic sites (Peet nd Loucks 1977, Adms nd Anderson 1980), hs been recruited s cnopy dominnt since tht time. Both species hve incresed in density since presettlement times, with red ok incresing proportionlly more thn white ok so tht they now shre dominnce. Perhps Cp Suers Holding is more mesic site thn Noe Woods, llowing red ok to increse t the former. However, in the bsence of disturbnce, community succession will likely led wy from dominnce of this pioneer species. Red ok hd low density nd cnopy cover in the shrub lyer t Cp Suers Holding in 1988 nd 1995, nd white ok ws completely bsent in this size clss. These conditions could led to lck of red nd white ok recruitment into the cnopy unless more effective fire mngement pro-grm is pplied (Abrms 1992). At McClughry Springs, tree density hs incresed since presettlement times nd oks hve in- cresed in density. White ok ws dominnt in 1821 (ccording to GLO surveys) nd hs mintined tht dominnce. White ok nd red ok densities incresed substntilly over three-yer period ( ). As t Cp Suers Holding, red ok incresed proportionlly more thn white ok since presettlement times, nd this trend continued between Tble 6. Density of intermedite vegettion (stems >1.4 m tll tht do not rech the cnopy) t Mc- Clughry Springs in 1992 nd Density (stems/h) Species T R E E S Prunus serotin Frxinus mericn 356 Frxinus pennsylvnic 98 Frxinus spp. (233) (454) Ulmus rubr 225 Ulmus mericn 172 Ulmus spp. (140) (397) Cry ovt Quercus rubr Quercus lb Quercus ellipsoidlis 16 Quercus spp. 47 Acer negundo Juglns nigr Tili mericn Acer scchrum Ostry virginin 16 S H R U B S Crtegus spp Viburnum denttum Rhmnus frngul 196 Rhmnus cthrtic 9 Rhmnus spp. (31) (205) Lonicer ttric Prunus virginin 60 Ros multiflor 27 Viburnum lentgo 18 Cornus rcemos 31 T O T A L S Numbers in prentheses represent totls for ll species present in prticulr genus. smpled yers. At this site, ok is present in the intermedite clss t low densities, but is gretly exceeded by blck cherry, elm, nd sh; blck cherry nd elm were reported to increse t Noe Woods in the bsence of disturbnce by fire (McCune nd Cottm 1985). Lck of ok recruitment nd the increse of smll-stture, shortlived trees re concerns to mngers of ok woodlnds. 218 Nturl Ares Journl Volume 20 (3), 2000

9 Tble 7. Density, bsl re, nd importnce vlue for dominnt woody species t McClughry Springs in 1992 nd Density (stems/h) Bsl Are (m 2 /h) Importnce Vlue Species Quercus lb Quercus rubr Quercus ellipsoidlis Frxinus spp. b Quercus mcrocrp Quercus velutin Cry ovt Prunus serotin Juglns nigr Tili mericn Ulmus mericn 3.0 < Populus deltoides TOTALS (reltive density + reltive dominnce)/2 bum nd Aln S. Hney, who led the originl survey. The Forest Preserve District provided us with previous monitoring dt from McClughry Springs. Jneen R. Ltsch is Nturl History Regionl Biologist for the Missouri Deprtment of Conservtion nd is interested in species conservtion nd functioning ecosystems. Her work involves restortion nd mngement of nturl communities s well s endngered species inventory nd recovery. Roger C. Anderson is Distinguished Professor of Biology t Illinois Stte University. He is on the Editoril Bord for Restortion Ecology nd served for six yers on the Illinois Nture Preserves Commission. His reserch interests include exotic plnts, the role of fire in pririe nd svnn vegettion, mycorrhizl ecology of pririe plnts, nd the effect of deer browsing on vegettion. b In 1995 Frxinus spp. included only Frxinus mericn. CONCLUSIONS The focus of this reserch ws to determine if existing mngement prctices were successful in ccomplishing the restortion gol for prticulr portion of Cp Suers Holding Forest Preserve. In the southwest portion of the preserve tht includes our study site, the gol of effecting n open cnopy woodlnd or svnn is true to historic (1821) community chrcter. It is likely tht this re burned frequently before the onset of fire suppression. Tree density nd bsl re t Cp Suers Holding nd McClughry Springs Forest Preserves hve incresed over the lst 180 yers, nd tree composition hs chnged. Mngement ctivity t Cp Suers Holding, while not hving conclusive positive effect on herbceous species, hs substntilly reduced the density nd cover of invsive exotic shrubs. The unmnged site showed n increse in ll woody size clsses nd substntil increses in invsive shrubs in the suppressed nd intermedite lyers, though species composition in the more mture clsses did not chnge. At the mnged site, species composition shifted somewht towrd more mesic species, but density, bsl re, nd cnopy cover of trees were mintined ner existing levels nd did not increse. Becuse of their contribution to invsive shrub control nd their potentil to restore historic chrcter to the site, prescribed burns re highly pproprite here s they would be in mny ok-dominted ecosystems (Abrms 1992). Returning fire to ok svnns nd forests reestblishes n importnt ecosystem process upon which the system depends. Burn frequency could be incresed to ccomplish the gol of decresing cnopy cover. While some objectives were met t Cp Suers Holding, continued mngement is necessry to control exotic species nd mintin nd restore nturl community chrcter. ACKNOWLEDGMENTS The Cook County Forest Preserve District nd The Nture Conservncy provided support for this study during Also, the project would not hve been possible without the vilbility of monitoring dt tken t Cp Suers Holding in For this we re indebted to Steven I. Apfel- LITERATURE CITED Abrms, M.D Fire nd the development of ok forests. BioScience 42: Adms, D. nd R.C. Anderson Species response to moisture grdient in centrl Illinois. Americn Journl of Botny 67: Alverson, W.S., D.M. Wller, nd S.L. Solheim Forests too deer: edge effects in northern Wisconsin. Conservtion Biology 2(4): Anderson, R.C Presettlement forests of Illinois. Pp in G. Burger, J. Ebinger, nd G. Wilhelm eds., Proceedings of the Ok Woods Mngement Workshop, Est-ern Illinois University, Chrleston Ntive pests: the impct of deer in highly frgmented hbitts. Pp in M.W. Schwrtz, ed., Conservtion in Highly Frgmented Lndscpes. Chpmn & Hll, New York. nd L.E. Brown Stbility nd instbility in plnt communities following fire. Americn Journl of Botny 73: nd O.L. Loucks White-til deer (Odocoileus virgininus) influence on structure nd composition of Tsug cndensis forests. Journl of Applied Ecology 16: nd J.E. Schwegmn Twenty yers of vegettionl chnge on southern Volume 20 (3), 2000 Nturl Ares Journl 219

10 Illinois brren. Nturl Ares Journl 11: Apfelbum, S.I Studies of Illinois ok svnn remnnts in 1987 nd Unpublished Report for Applied Ecologicl Services, Inc., Brodhed, Wis. Bowles, M.L. nd J.L. McBride Presettlement brrens in the glcited pririe region of Illinois. Pp in J.S. Frlish, R.C. Anderson, J.E. Ebinger, nd F. Szfoni, eds., Proceedings of the North Americn Conference on Svnns nd Brrens, Illinois Stte University, Norml. Curtis, J.T The Vegettion of Wisconsin. University of Wisconsin Press, Mdison. 657 pp. Dubenmire, R A cnopy coverge method of vegettionl nlysis. Northwest Science 33: Gleson, H.A The vegettionl history of the Middle West. Annls of the Assocition of Americn Geogrphers 12: Illinois Deprtment of Energy nd Nturl Resources The chnging Illinois environment: criticl trends, Volume 3: Ecologicl Resources. Technicl Report ILENR/ RE-EA-94/05, Illinois Deprtment of Energy nd Nturl Resources, Springfield. Jckson, L.L., N. Lopoukhine, nd D. Hillyrd Ecologicl restortion: definition nd comments. Restortion Ecology 3: Ltsch, J.R Vegettion chnge in mnged nd unmnged ok woodlnd in northestern Illinois. M.S. thesis, Illinois Stte University, Norml. 87 pp. McCune, B. nd G. Cottm The successionl sttus of southern Wisconsin ok woods. Ecology 66: Med, S.B Ctlogue of plnts growing spontneously in the Stte of Illinois, the principl prt ner August, Hncock County. Pririe Frmer 6:35-36, 60, 93, Mehlmn, D.W Effects of fire on plnt community composition of north Florid second growth pinelnd. Bulletin of the Toney Botnicl Club 119: Nuzzo, V.A Experimentl control of grlic mustrd [Alliri petiolt (Bieb.) Cvr & Grnde] in northern Illinois using fire, herbicide, nd cutting. Nturl Ares Journl 11: Nyberg, D. nd G. Nyberg Mps of presettlement communities bsed on tree density for selected sections in Cook County forest preserves. Report prepred for The Nture Conservncy nd the Forest Preserve District of Cook County under contrct #ILFO 5/20/93. Pckrd, S Rediscovering the tllgrss svnn of Illinois. Article no in A. Dvis nd G. Stnford, eds., Proceedings of the Tenth North Americn Pririe Conference, Ntive Pririe Assocition of Texs, Dlls Restoring ok ecosystems. Restortion nd Mngement Notes 11: Interseeding. Pp in S. Pckrd nd C.F. Mutel eds., The Tllgrss Restortion Hndbook: for Priries, Svnns, nd Woodlnds. Islnd Press, Wshington, D.C. Ptterson, R Fire in the oks. Americn Forests (December): Peet, R.K. nd O.L. Loucks A grdient nlysis of southern Wisconsin ok forests. Ecology 58: Pruk, B Lists indicte recoverble ok svnns nd open ok woodlnds in southern Wisconsin. Restortion nd Mngement Notes 13: SAS Institute SAS/STAT User's Guide, Version 6. 4th Ed. Vol. 2. SAS Institute, Cry, N.C. Scheiner, S.M MANOVA: multiple response vribles nd multispecies interctions. Pp in S.M. Scheiner nd J. Gurevitch, eds., Design nd Anlysis of Ecologicl Experiments. Chpmn nd Hll, New York. Schwegmn, J Exotics of Illinois forests. Erigeni 13: Sokl, R.R. nd F.J. Rohlf Biometry: the Principles nd Prctice of Sttistics in Biologicl Reserch. 3rd Ed. W.H. Freemn nd Compny, New York. 887 pp. Stevens, W.K Mircle under the oks: the revivl of nture in Americ. Simon nd Schuster, New York. Swink, F. nd G. Wilhelm Plnts of the Chicgo Region. 4th Ed. Indin Acdemy of Science, Indinpolis. 921 pp. Tester, J.R Effects of fire frequency on ok svnn in est-centrl Minnesot. Bulletin of the Torrey Botnicl Club 116: Wheln, C.J. nd M.L. Dilger Invsive, exotic shrubs: prdox for nturl re mngers? Nturl Ares Journl 12: White, J.W Illinois Nturl Ares Inventory: Technicl Report, Volume I Survey Methods nd Results. Illinois Nturl Ares Inventory, Urbn. 427 pp. 220 Nturl Ares Journl Volume 20 (3), 2000