2003. Proceedings of the Indiana Academy of Science 1 12(2): 160-1 68

EARLY SUCCESSION IN A TALLGRASS PRAIRIE RESTORATION AND THE EFFECTS OF NITROGEN, PHOSPHORUS, AND MICRONUTRIENT ENRICHMENTS

Paul E. Rothrock and Edwin R. Squiers: Randall Environmental Center, Taylor University, Upland, Indiana 46989-1001 USA

ABSTRACT. The past decade has witnessed increased effort to restore prairie on former agricultural land in Indiana. We used the Upland Prairie Restoration to document changes over a five year post-planting period and to examine the effects of acute fertilization with soil amendments. Growing seasons I and II were characterized by rapidly changing communities of annual weeds. Dominant species included Hibiscus trionum, Cyperus esculentus, Setaria glaiica followed in Year II by Setaria faberi and Ambrosia artemisiifoUa. Prairie grasses {Andropogon gerardii and Sorghastrum nutans) and forbs domi- nated by Rudbeckia hirta and Ratibida pinnata became evident during Years III-V. Prairie species density and cover, as well as their diversity, reached mature stage by Year V. The prairie restoration community showed no important responses to acute additions of phosphate, micronutrient mix, and a combination of phosphate and micronutrients. Nitrogen enrichment, however, promoted weed cover in early stages of community establishment. Weed persisted throughout the five-year period of observation and strongly inhibited the establishment of native prairie species. Our results suggest that successful prairie restoration on former agricultural land should consider management practices that control nitrogen avail- ability.

Keywords: Prairie restoration, succession, fertilizer, nitrogen, phosphorus, micronutrients

In pre-settlement Indiana, prairies made up one commercial nursery (Spence Nursery, about 15% of the area, primarily in the north- Muncie) has focused on developing a product west and west-central portions of the state. line suitable for ecological restoration of prai- Unfortunately, most of the original prairie has rie and wetland . been lost to drainage, urbanization and agri- In 1993, we initiated a tallgrass prairie res- culture (Samson & Knopf 1996). Only a few toration on a 25-acre site (10 ha) in Upland, high quality remnant areas, such as Hoosier Indiana. Previously, this site had a long agri-

Prairie in Lake County, have been preserved; cultural history, first to raise row crops and and fewer than a dozen small examples of di- more recently as pasture. The significant size verse kinds of prairie are part of our state na- of the Upland Prairie Restoration effort af- ture preserve system (Division of Nature Pre- forded opportunity to investigate questions re- serves 1999). lating to the successional changes associated The growing public awareness of this loss with tallgrass prairie restoration on former ag- of a fascinating part of our natural heritage is ricultural land and the potential effects nutri- one reason that prairie and its restoration have ent amendments might have on that early become subjects of intense interest to many community development. people in the American Midwest (Sayer The earliest recorded tallgrass prairie res- 1999). Within the scientific community, the toration at University of Wisconsin attempted first attempts at reconstruction in- to establish a prairie community through the volved the tallgrass prairie at the University crude transplantation of blocks of sod (Bonta of Wisconsin Arboretum between 1935-1941 1991). Since that pioneering effort, we have (Bonta 1991). In Indiana over the past decade, learned much about seed acquisition, site prairie restoration has become a familiar tool preparation, and planting (e.g., Schramm for the Division of Nature Preserves (Rich 1978, 1992). Likewise, the use of herbicides Dunbar pers. comm.) and the Nature Conser- as a management tool has received significant vancy (Nathan Simons pers. comm.). At least attention (Packard & Mutel 1997) and a par-

160 .

ROTHROCK & SQUIERS—SUCCESSION IN A PRAIRIE 161

ticularly rich literature regarding the use of Vit. plantings (Foster &l Gross 1998j. Forb fire has developed (e.g., Collins & Wallace species, more than grass species, appear sen- 1990). Surprisingly, the role of soil amend- sitive to adverse effects of nitrogen enrich- ments seems to have had scant attention as a ment (Gibson et al. 1993). factor for enhancing (or inhibiting) the estab- A few studies have ](X)ked at the effects of lishment of a prairie restoration (Parkard & phosphorus amendments in prairie communi- Mutel 1997). Some types of ecological resto- ties. On mature Konza Prairie, Gibson et al. ration clearly benefit from fertilizer applica- (1993) saw no effect on herbaceous cover fol- tion. These include coal mine spoils (Singh et lowing three years of phosphate enrichment. al. 1996), post limestone-quarry grasslands Most studies of phosphorus enrichment ha\c (Richardson & Evans 1986), grass swards and focused on their interaction with m\c()rrhi/ai Salix scrub (Marrs et al. 1983), and montane fungal. Eom et al. (1999) observed decreases forest (Tanner et al. 1990). in extraradical mycorrhizal hyphae under con-

Soils in east-central Indiana frequently have ditions of phosphate enrichment. Hetrick et al. concentrations of nitrogen, phosphorus, and (1989) found that the of big bluestem micronutrients that may limit productiv- seedlings was unresponsive to phosphorus fer- ity. Studies of whether micronutrient amend- tilizer. However, their greenhouse studies in- ments might enhance prairie or grassland dicated that warm-season grasses, when \\ ant- communities appear lacking. A few relevant ing in mycorrhizal fungi, responded positi\ ely studies with phosphorus and especially nitro- to phosphorus fertilizer (Hetrick et al. 1990). gen soil amendments are available. In some At the time of initiating the Upland Prairie rangelands, low nitrogen levels can limit plant Restoration, we had reasons to expect that the growth (Ownesby et al. 1970; Rains et al. site had a compromised mycorrhizal commu- 1975; Ownesby & Smith 1979; Hipp 1986; nity (McGonigle & Miller 1993). The site had Brejda et al. 1995). Furthermore, individual no recent history of supporting prairie species. species such as Panicum virgatum L. respond Instead, it had experienced poor soil manage- to nitrogen by increases in ramet size and ment under a regime of row crop productiem flowering and seed production (Hartnett and pasture, conditions poorh suited for 1993). In other cases, nitrogen increases dry maintaining diverse and abundant m\conhi- matter production (Stubbendieck & Nielsen zae. Consequently, we were interested in 1989), especially in forbs (Seastedt et al. whether phosphorus fertilizer might supple-

1991). In some prairie communities, a high ment or replace the nutrients normal 1\ gar- frequency of fire is one apparent cause of lim- nered by mycorrhizal fungi. ited nitrogen. Burning depresses nitrogen In summary, our objecti\es in this multiple availability through volatilization and immo- season study were: 1) to describe the pattern bilization of labile soil nitrogen (Seastedt et of community succession on a tallgrass res- al. 1991; Benning & Seastedt 1995). toration initiated on agricultural soils, and 2) While some studies of prairie communities to examine the effects of phosphate, micro- support a positive role for nitrogen amend- nutrient, micronutrients plus phosphate, and ments, others issue caution. Excess nitrogen nitrogen enrichment on the dexek^pmcnt and can enhance the growth of annual weeds and structure of this communit\ exotics (Berg 1995; Milchumas & Lauenroth METHODS 1995; Paschke et al. 2000). This weedy growth could have particularly adverse effects The Lapland Prairie Restoration consists of during the critical stage of establishing seed- a 25-acre (10 ha) site o\\ uclI b\ A\ is Indus- lings of native prairie species. Because of in- trial Corp.. l^pland. Indiana (N4(V2~.2 . creased weed content, the tempo of ecological W85''0'). Before the onset of restoration, the succession in which native perennials, partic- rolling field produced row crops icorn and ularly grasses, displace annual weeds may be so\beans) and pasture of Kentuck\ blue-grass slowed (Wedin & Tilman 1990). In addition {Foa pnHi'tisis L.). fescues {Fcsiucli spp.i. and to enhancing weed content, nitrogen enrich- \arious \\eed\ and oldtield forbs. Routine ment may lead to a reduction in species rich- anahsis (b\ Central Uaborator\. Indianapolis. ness, as reported for native grasslands (Collins and A c'v: L Great Lakes Laboratories. Fort et al. 1998) as well as in Audropogon gcnudii Wa\ne. Indiana) indicated that fertilit\ of the 162 PROCEEDINGS OF THE INDIANA ACADEMY OF SCIENCE site varied. The eastern half overall had higher forbs-LBS area levels of soil nutrients. The western half was A2y especially deemed low or very low in phos- phorus (Bray PI of 4-10 ppm) and the mi- CI cronutrients boron and zinc, while the eastern half had medium phosphorus levels (8—26 ppm) and mostly adequate micronutrient con- [MDbi centrations. Across the study area, total Kjel- C2 dahl nitrogen ranged from 0.13-0.28%. In April 1993, the vegetation was treated with Round-up® herbicide (glyphosate - a product of Monsanto Agricultural Chemicals) area rich in tall at recommended rates. In early June, after grass species plant die-back, the ground was tilled, disked, & forbs and planted with cold-treated, hand-collected tall grasses prairie seed mixes. The seed mixes were pre- sumed to contained regional genotypes since Rt. 26 they were gathered from prairie fragments in Figure 1 . —Schematic showing layout of research eastern Illinois and western Indiana. Across plots on the 25-acre (10 ha) Upland Prairie Resto- most of the area, big blue-stem {Andropogon ration site. Not drawn to scale. Blocks Al and A2 gerardii) and Indian grass {Sorghastrum nu- are situated in an area rich in forbs and little blue- tans (L.) Nash) predominated in the seed mix. stem (LBS); the grass rich area of block Bl and B2 Although these grasses formed the bulk of the was planted with less than 10% forbs in the seed seed mix, it contained a diversity of other mix; blocks CI and C2 were planted with approx- grasses and forbs with a total count of ap- imately 20% forbs in the seed mix. Each experi- proximately 50 species. mental block encompasses an area of 36 X 17 m. Before seed germination, we laid out six treatment blocks in a randomized complete block experimental design. One pair of blocks April 1994—1997, we applied nutrients with a (Al and A2) occupied flat topography in the hand-held spreader. The micronutrients in- northeast corner of the field (Fig. 1). The par- cluded boron (2.3 g/m-), manganese (1.6 ticular seed mix for this area contained an g/m^), and zinc (1.2 g/m-^). Nitrogen, in the of forbs and little blue-stem (Schi- form of 46% urea, was spread at a rate of 40 zachyrium scoparium (Michx.) Nash) but had g/m- and 46% phosphate at 30 g/m-. During minimal seed from tallgrass species. A second the 1993 and 1994 growing seasons, we at- pair of blocks (Bl and B2) was placed in the tempted no weed control within the treatment center of the 25-acre (10 ha) site, a flat area strips. However, field thistle {Cirsium arvense near the base of an east-facing slope. This (L.) Scop.) proved persistent and necessitated seed mix was rich in several tallgrass species spot treatment in May 1995 and each subse- (<10% forb content). The final pair of treat- quent year. ment blocks (CI and C2) was sited on a well- Starting with the 1993 season, sampling of drained, east-facing slope near the west mar- density and canopy cover of each weed and gin of the field where the seed mix was prairie species took place in late July—early enriched with forbs (approximately 20% of August. During the first two growing seasons, seed content). sampling consisted of 15 random 0.25 m- Each of the 36 X 17 m blocks contained quadrats per treatment strip. Thus, the total five randomly assigned treatment strips: con- quadrats sampled across the experimental de- trol, micronutrients, nitrogen, phosphate, and sign was 450 per year. As prairie species phosphate + micronutrients. The treatment gained size, their quadrat size was increased strips, separated from each other by 2 m wide to 1 m-. buffer zones, were 17 X 5 m. This provided Total density and total cover of prairie spe- sufficient area for two sampling zones 15 m cies and of weeds were calculated for each in length for a total of 30 potential sample quadrat. In the context of this experiment, we areas per treatment strip. In June 1993 and late define weeds to mean those species not in- )

ROTHROCK & SQUIERS—SUCCESSION IN A PRAIRIE 163

eluded in the planted seed mix. Statistical pogon gerardii), and Indian grass (Sorghas- analysis indicated that transect data, even trum nutans). In the case of black-eyed Susan, when transformed, did not fulfill the assump- the sharply-increased densities were due to tion of normal distribution. As a result, statis- high number of seedlings that sometimes car- tical comparisons between samples relied peted areas between young grass tussocks. On upon the non-parametric Mann-Whitney test. the other hand, increased grass densities re- In describing the development of the prairie flect vigorous tiller production in big blue- community, mean values for cover and for stem and Indiana grass. density were calculated from pooled transects Community succession over the remaining within each block. Effects of soil amendments two years involved further increases in tillers were tested by pooling similar treatments by perennial grasses accompanied by a de- across the six blocks. cline in forb seedlings such as black-eyed Su- san and prairie coneflower (Ratibida pinnata RESULTS (Vent.) Barnhart). As a result, the highest den- Development of the prairie communi- sities, averaging about 160 shoots per m-. oc- ty.—In the first growing season (1993 or Year curred in 1996 (Fig. 5). At the end of the li\e I) of the Upland Prairie Restoration, annual years of observation (1997), the four blocks weeds dominated. They reached average cov- (Bl, B2, CI, and C2) sown with grass rich er as high as 131% (Fig. 2) in the more moist mixes had an average prairie plant cover of sites (blocks Al and A2) located in the north- 45-61% (Fig. 4). east corner of field. In the first season (1993), The pattern of succession towards high co\ - abundant species included flower-of-an-hour er and density of prairie species was not uni- {Hibiscus trionum L.), nut-sedge {Cyperus es- form across the experimental design. Plots Al culentus L.), and yellow foxtail (Setaria glau- and A2, located on flat ground and planted ca (L.) R Beauv.). with a seed mix containing an abundance of During Year II (1994), the Upland Prairie forbs and little blue-stem, under-performed Restoration site was still heavily dominated over the period from Years III-V. The average by annual weeds (average within block cover cover by prairie species in these plots ranged ranged from 103-150%) but the species com- only from 10.5—16.1% (Fig. 4) and density position changed. Flower-of-an-hour and nut- only reached a maximum of 32 shoots per m- sedge were replaced by giant foxtail {Setaria (Fig. 5). Not surprisingly, the \\eed co\er in faberi Herrm.) and common ragweed {Ambro- these two blocks remained substantial!) high- sia artemisiifolia L.). Also during Year II, the er than those of blocks B2, CI, and C2 (Fig. total density of weed species reached a peaked 2), although the density of weeds did decline (Fig. 3); average within block weed densities to levels typical of other blocks (Fig. 3). ranged from 770 per m- in drier sites Response to soil amendments.— During to 2005 per m- in moister sites. each of the five years v>^ observation. scmI By Year III (1995), the Upland Prairie Res- amendments (micronutrients. nitrogen, phos- toration had undergone dramatic changes. The phate, and phosphate + micronutrient mix) density of annual weed species in 1995 were individually applied to strips w iihm each dropped precipitously (Fig. 3). Except for block. We expected that their addition might

block A2, average density returned to below stimulate prairie development, i.e.. merease 570 per m'. Weed cover (Fig. 2) also fell to the cover and/or densitv o{ prairie species. less than 75% for blocks BI, B2, CI, and C2 The results indicate that, relative to the con- but remained significantly higher (P < trol, none o( the amendments eonsisienilv en- 0.0005) for blocks Al and A2. This overall hanced the development oi the prairie com-

decline in weed density and cover was accom- munity (Figs. 8. 9). Bv ^ear 111 i h)^)>). cover panied by strong increases in dominance o( in the micronutrient. phosphate, and phos- prairie species (Figs. 4, 5). Average cover by phate + micronutrient treatments increased to

1-2. 5'( prairie species was as high as 70% (block C 1 an average o( M .7 — while the control

in the well-drained, forb-enriched areas in the reached 49<"r (Fig. 8). Slalisiieallv . (he Mnps

western portion of the planting. Three species treated vv ith micronutrienis or phosphate alone were particularly prevalent: black-eyed Susan had slightlv lower cover (/' \ 0.02) and den- {Rudbeckia hirta L.), big blue-stem {Andro- sity {F -^ 0.04) than the control (Fig. 9). How- —

164 PROCEEDINGS OF THE INDIANA ACADEMY OF SCIENCE

150 ever, during the last two seasons of observa- tion (Years IV—V), these differences largely O 125 O disappeared. When compared to the control, 100 Q. no significant differences in cover or density (O D 75 of prairie species were observed in Year IV (1996) and only cover within the phosphate o 50 treatment was statistically lower {P < 0.02) 25 than the control in Year V (1997). While no fertilizer amendment provided sustained, meaningful enhancement of the de- 2000 veloping prairie community, the negative re- sponse to nitrogen application was unequivo- o 1- 1500 0) 0) Q. Q. cal. In nitrogen treated strips, average cover ^ >r 1000 and density of prairie species remained near nil to extremely low throughout the duration > 0) 500 > Q of the study (Figs. 8, 9). Instead, the areas receiving nitrogen applications retained a community dominated by annual weed spe- 75 cies. These weeds included common and giant in ragweed {Ambrosia thfida L.), giant foxtail, O 1- lamb's quarter {Chenopodium album L.), and 0) o 50 Q. > CO o knotweeds {Polygonum spp.). Their domi- 0) *-' nance in nitrogen-enriched plots was not usu- 25 ally due to increases in density. In fact, in Years II-III (1994 and 1995) the density of annual weeds was actually lower where nitro- gen had been applied (Fig. 7). Clearly, how- 160 ever, the luxuriant nitrogen supply modified (A CM the size and, therefore, of individual <]> E cover 120 weed plants (Fig. 6). This response was par- (1) Q.S Q. ticularly evident in the first year of the exper- W >^ 80 0) iment (1993) when weed cover under nitrogen ^ (0 40 enriched conditions averaged near 140%. a. o Even at the end of the observation period (i.e.. Years IV-V), the cover of weeds was still ap- proximately 85% and substantially composed 1993 1994 1995 1996 1997 of annual as opposed to perennial weed spe- Year cies. A1 To clarify further the observed relationship •o- A2 between nitrogen enrichment and prairie spe- B1 cies, we plotted the five-year response to ni- V B2 trogen for each individual block against the 01 pooled results from control plots (Figs. 10, 02 11). Among five of the six blocks, cover of prairie species in nitrogen treatment plots con- Figures 2-5.—Changes in the Upland Prairie sistently remained below 6% (compared to Restoration, 1993-1997. 2. Weed species, mean 50% for control plots) throughout the study percent cover; 3. Weed species, mean density; 4. period (Fig. 10). At the same time, density Prairie species, mean percent cover; 5. Prairie spe- cies, mean density. Blocks (Al, A2, Bl, B2, CI, remained below 14 shoots per m^ (Fig. 11) C2) represent paired locations on the Restoration compared to up to 107 shoots per m^ in con- site (see Fig. 1 ). For clarity, standard error bars are trol plots. The cover and density of prairie not shown; variation was consistently less than 10% species in block CI, located in the well- of the mean value. drained western sector of Upland Prairie Res- toration site, was somewhat exceptional. By ! —

ROTHROCK & SQUIERS—SUCCESSION IN A PRAIRIE 165

150 60 o0) 125 o 1^ o 100 40 a a. > CO (/) o 75 0) o o L- 0) ?>5 20 0) 50

1500 i?n W CM o E inn o .2 E

*=* 80 fe 1000 £ Q. ^^ 60

z (/> 4U 500 2 Q. Q 20 > Q

75 o(0 O I. Control (pooled) 0) (D 50 a > Nitrogen - A1 (0 o Nitrogen - A2 fl) " Nitrogen 25 B1 Nitrogen B2 Q. — D-- Nitrogen C1 Nitrogen C2

Figures 10-11. —Response of prairie species to (A CM 120 nitrogen enrichment versus pooled control (1991- e 1997). 10. Mean per cent cover; 11. Mean density. 0) ^ control is pooled across the six blocks. Q. Q. 80 The from "^ ^ Individual nitrogen enrichment treatments are •c w shown for each block - Al. A2. B 1. 82. CI . and 40 2 S C2. Note the low and strongly oserlapping \alues for each nitrogen transect except the one from block CI.

1993 1994 1995 1996 1997 Year 1997, this block had a\crage co\er of ncaii\ Control 18% and densit\ of 38 shoots per ni\ Al- ••O Micronutrients though these \alues are signihcaniK higher

Nitrogen than those of other nitrogen plots. ihe\ are siill •-v- Phosphorus significantly lower than those obser\ed for P + M non-nitrogen treatments (e.g.. for co\er data: Figures 6-9. —Changes in response to soil P < 0.0008). Of interest, this same block sup- amendment treatments, 1993-1997. 6. Weed spe- ported a low weed eo\er during the tirst \ ear cies, mean percent cover; 7. Weed species, mean (1993) of the experiment, with an a\erage of density; 8. Prairie species, mean percent cover; 9. only 53% (Fig. 2). Ho\\e\er. in other \eais us = Prairie species, mean density. P + M phosphate weed cover and density were not excepiionai. plus micronutrients. Some standard error bars omit- ted for clarity. DISCISSION

In the Cpland Prairie Restoration, annual species doniinated the earl\ sueeessional eom- munit) (Years I-ll). Seedlings of prairie spe-

cies were present \\ ithin the subsiaiitial weed 166 PROCEEDINGS OF THE INDIANA ACADEMY OF SCIENCE

stands but did not become readily visible until This took the form of increased dominance Year III. By the end of the five-year study and persistence of annual weeds and a con- period, the overall Upland Prairie Restoration comitant reduction in prairie species. The ni- had a high cover and density of planted prairie trogen effects we observed have been reported grasses and forbs, including substantial pop- for other herbaceous communities such as old ulations of about 15 species. Subsequent sam- fields (Carson & Barrett 1988; Goldberg & pling (unpubl. data for 1998-2000) indicates Miller 1990), hay-meadows (Silvertown that this and quality has 1980), flatwood range (Kalmbacker & Martin changed little. 1996) as well as tundra and short-grass prairie The use of phosphate, micronutrients, or a (Gough et al. 2000). In our case, nitrogen en- combination of phosphate + micronutrients richment compromised establishment of prai- proved ineffective in enhancing establishment rie grasses as well as forbs. Under conditions of prairie grass and forb seedling and overall of nitrogen enrichment, individual weed community development. Instead, one of the plants may attain greater biomass and cover, most critical factors was simply the location. resulting in strong light attenuation at ground Within the topographic diversity of the site, a level (Wilson & Tilman 1993; Piper 1995; gentle east-facing slope proved most favor- Foster & Gross 1998). These low-light con- able. On lower, flat areas, heavy June rainfall ditions may, in turn, suppress seed germina- during Year I held the silt-loam soils at satu- tion, as seen in winter wheat (Valenti & Wicks ration for a prolonged period. These moister 1992), and/or the ability of seedlings to en- micro-sites had lower density and cover of dure strong interspecific . Regard- prairie species through most of the five-year less of the specific mechanism, the negative observation period. Some portions of the 25- effects of nitrogen enrichment may be of more acre (10 ha) site (outside the experimental consequence in this early stage of restoration. area) actually experienced short-term flooding As somewhat of a contrast to the observations and, as a result, only developed a sparse cover on the Upland Prairie Restoration, Seastedt et of big blue-stem. al. (1991), in their study of nitrogen addition Our inability to demonstrate effects due to to mature Konza Prairie, did not report in- phosphorus fertilization supports the findings creases in weed content but rather a change in the competitive environment that favored forb of Gibson et al. (1993) on natural Konza Prai- species over grasses. rie. In general, tallgrass species are obligate C4 Our results demonstrate the negative impact mycotrophs (Hetrick et al. 1994; Knapp et al 1998). In a study of the obligate mycotroph, of acute nitrogen enrichment of a restoration site. Can we also expect lower or chronic ni- big blue-stem, Hetrick et al. (1989) found no trogen enrichment to be a problem? Bobbink increase in biomass with phosphate. This lack et al. suggest that even air-borne nitro- of responsiveness extends to other warm-sea- (1998) gen deposition can alter community function. son grasses (Hetrick et al. 1990). According Nitrogen-fixing shrubs in California coastal to Hetrick et al. (1994), these obligate sym- prairie (Maron Connors 1996) and Thfoli- bionts would have less competitive advantage & iim repens L. in grasslands (Warren 2000) fa- in a phosphate-enriched environment (al- cilitate invasion by weedy exotics. These ob- though we were unable to demonstrate clear servations suggest a need to alter management detrimental effects of phosphate enrichment in strategies for nutrient-rich prairie restoration our field experiment). Forbs as well as cool- sites. One suggested strategy is soil impover- season grasses, on the other hand, often lack ishment, through the addition of saw-dust (To- a dependence upon mycorrhizal fungi. Yet, rek et al. 2000; Morgan 1994; Wilson & Ger- again in our restoration, phosphate failed to ry 1995), to immobilize nitrogen. Or, Collins enhance growth even in areas where forbs et al. (1998) recommend high mowing in or- were abundant. This was unexpected given the der to increase light at ground level and the results of Hetrick et al. (1990) in which fac- enhancement of seed germination and seed- ultative symbionts responded to either phos- ling development. phate enrichment or mycorrhizae. In contrast to the neutral response to phos- ACKNOWLEDGMENTS phate or micronutrient enrichment, nitrogen We wish to thank the Avis Industrial Cor- fertilization clearly had detrimental impact. poration for sponsoring the Upland Prairie ROTHROCK & SQUIERS—SUCCESSION IN A PRAIRIE 167

Restoration and their continued hospitality in ferent res(^urce additions on species di\ersit\ in use of their facility. We also wish to acknowl- an annual plant coinmuniu. Ecokjgs 71:213- edge the willing labor of student researchers 225. Gough, L. C.W. Osenberg, K.L. Gross c^ S.L. Col- and the financial support from the Taylor Uni- lins. 2000. Fertilization elTccls on species den- versity Undergraduate Research Training Pro- sity and primary product] \il\ in hcrbacccjus plant gram. Additional thanks to Don Ruch and an communities. Oikos 89:428-439. anonymous reviewer for their helpful com- Hartnett, D.C. 1993. Regulation of clonal growth earlier draft ments on an of this paper. and dynamics of Panicum virgaium (Poaceaej in tallgrass prairie: Effects of neighbor remcnal and LITERATURE CITED nutrient addition. American Journal of Botany 80:1114-1120. Benning, TL. & TR. Seastedt. 1995. Landscape- level interactions between topoedaphic features Hetrick, B.A.D., G.W.T. Wilson & C.E. Ouensby. 1989. Influence of mycorrhi/al lungi fertil- and nitrogen limitation in tallgrass prairie. Land- and scape 10:337-348. ization on big bluestem seedling biomass. Jour- nal of Berg, W.A. 1995. Response of a mixed native Range Management 42:213-216. Hetrick, B.A.D., Wilson Todd. 1990. warm-season grass planting to nitrogen fertiliza- G.W.T & TC. Differential responses of grasses to tion. Journal of Range Management 48:64-67. C, and C4 mycorrhizal , phosphorus fertilization. Bobbink, R., M. Hornung & J.G.M. Roelofs. 1998. soil nf The effects of air-borne nitrogen pollutants on and . Canadian Journal species diversity in natural and semi-natural Eu- Botany 68:461-467. ropean vegetation. Journal of Ecology 86:717- Hetrick, B.A.D., D.C. Hartnett. G.W.T WiKon & 738. D.J. Gibson. 1994. Effects of mxconhi/ae. Bonta, M. 1991. Restoring our tallgrass prairies. phosphorus availability, and plant dcnsit\ on

American Horticulture 12 (Oct.): 10-1 8. yield relationships among competing tallgrass prairie grasses. Canadian Journal of Botany 72: Brejda, J.J., J.R. Brown & C.L. Hoenshell. 1995. Indiangrass and Caucasian bluestem responses to 168-176. different nitrogen sources and rates in the Hipp, B.W 1986. Fertilization and irrigation o\ Ozarks. Journal of Range Management 48:172- buffalograss in north Texas. Proceedings oi the 180. Tenth North American Prairie Conference. 04.03. Carson, W.R & G.W. Ban-ett. 1988. Succession in Kalmbacher R. & F Martin. 1996. Shifts in botan- old-field plant communities: Effects of contrast- ical composition of flatwoods range following ing types of nutrient enrichment. Ecology 69: fertilization. Journal of Range Management 4*-); 984-994. 530-534. Colfins, S.L., A.K. Knapp, J.M. Briggs, J.M. Blair Knapp, A.K., J.M. Briggs. D.C. Hartnett .^: S.L. & E.M. Steinauen 1998. Modulation of diversity Collins. 1998. Grass Dynamics: LcMig-term Eco- by grazing and mowing in native tallgrass prai- logical Research in Tallgrass Prainc. 0\t"ord rie. Science 280:745-747. University Press. Oxford. Englani.1. 3^4 pp. CoUins, S.L. & L.L. Wallace (eds.). 1990. Fire in Maron, J.L. & PG. Connors. l^)Oo. A naii\c niiro- North American Tallgrass Prairies. University of gen-fixing shrub facilitates weed inxasion. Occ- Oklahoma Press, Norman, Oklahoma. 192 pp. ologia U)5:302-312. Division of Nature Preserves. 1999. Indiana's Ded- Marrs, R.H., R.D. Roberts. R..A. Skeflingion .M icated Nature Preserves. Indiana Department of A.D. Bradshaw. 19S3. Nitrog^^n and the de\el-

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