Variability of Plant Diversity and Soil Features Following Gap Creation in Caspian Beech Forests of Iran

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1 Aville online t Annls of Biologicl Reserch, 22, 3 (9): ( ISSN CODEN (USA): ABRNBW Vriility of Plnt Diversity nd Soil Fetures Following Cretion in Cspin Beech Forests of Irn Ktyoun Hghverdi *, Hdi Kidliri 2, Khosro Sghe -Tlei 3, Yhy Kooch 4 Scientific Memership, Deprtment of Nturl Resources, Svdkooh Brnch, Islmic Azd University, Svdkooh, Irn 2 Deprtment of Forestry, Science nd Reserch Brnch, Islmic Azd University, Tehrn, Irn. 3 Reserch Institute of Forests nd Rngelnds, Tehrn, Irn. 4 Fculty of Nturl Resources nd Mrine Sciences, Trit Modres University, , Noor, Mzndrn, Irn. ABSTRACT Due to study the effects of gp size nd position on herl diversity indices nd soil fetures, twelve cnopy gps with n re etween < 2 m 2 nd m 2 were selected in reserve orientl eech (Fgus orientlis Lipsky) stnd in the north of Irn. For ech cnopy gp, one non-gp plot (closed cnopy) 4 m 2 squre smpling qudrte ws considered lso. Ground vegettion ws ssessed within five smple plots (2 2 m re) from gp center to the edges. Soil smples were tken ( 2 cm depth) from within gp nd closed cnopy positions. Some of soil chrcters including ph, orgnic mtter nd cron, totl nitrogen, phosphorus, potssium, clcium, mgnesium nd sturted moisture were mesured t the lortory. Results indicted tht diversity nd richness indices incresed with incresing of gp re wheres, evenness indices were decresed. Furthermore, the highest mount of diversity nd richness indices were oserved in gp center compred with gp edge nd closed cnopy. But, closed cnopy position hd the gretest vlue of evenness indices. Anlysis of dt showed tht soil ph, orgnic mtter nd cron nd lso totl nitrogen incresed with incresing of gp re. Also the highest vlues of these chrcters were detected in within gps. Wheres, sturted moisture mounts decresed with incresing of gp re nd the highest vlue of this chrcter ws detected in closed cnopy. Compre mens of ville phosphorus, potssium, clcium nd mgnesium in the gp size indicted tht medium gps hd the greter mounts thn in the smll nd lrge gps. These chrcters were significntly greter in within gps in comprison to closed cnopy. Greter mounts of cron to nitrogen rtio were found in medium gp nd closed cnopy position. In generl, our reserch results provide useful sis for evluting the implictions of forest mngement prctices. Keywords: gp size, gp position, diversity, richness, evenness, nutrient elements, soil. INTRODUCTION Beech (Fgus orientlis Lipsky) is the most industril commercil tree species mong more thn 8 rod - leved trees nd shrus in Irn. In the north of Irn, pure nd mixed orientl eech forests cover 7.6 per cent of the surfce lnd re nd represent 3 percent of the stnding iomss. This species is the most vlule wood

2 producing species in the Cspin forests [45] nd reches in mture stge to more thn cm dh nd out 5 meters height. They re found in smll groups up to 5 m.s.l. while individuls hve een reported from m up to 265 m [38]. When trees strt to dry lone or collectively, gps will e creted in forest cnopy. Such gps increse the forest iodiversity y settling new species. Since the 98s, these cnopy gps hve therefore een mjor focus of forest ecologists. They studied not only environmentl conditions [46] nd effects on tree regenertion [], ut lso her lyer response [2]. Studies on the her lyer species composition generlly report tht plnt species numer, her lyer cover nd the undnce of mny species re higher in gps thn under closed cnopy [27]. These differences increse with incresing gp size [23, 4]. Although ptterns of her lyer response to cnopy gps hve een frequently studied, severl questions re still open. In eech forests of Irn, formtion of gps y wind throw is chrcteristic nturl disturnce event. size vries gretly from the size of only single crown to vst open fields with dimeters of mny tree lengths. However, chnges in iotic nd iotic conditions depend oth on gp size nd within gp position [32, 37]. Consequently, it is not esy to predict how soil properties rect to gp formtion. Although it is recognized tht gps modify soil resources, few studies hve focused on elow - ground processes [28]. Most studies of gps hve ddressed vegettion dynmics, regenertion through seedling estlishment, effects of microclimte vriles on the regenertion nd, in generl hve concentrted on oveground processes [46, 4]. Reltively few studies hve ddressed elowground effects of cnopy gps on soil chemicl nd iochemicl properties. Thus, the ojectives of this study were to exmine the impcts of smll, medium, lrge gps on herl diversity indices nd soil properties, "sink" nd "source" of plnt nutrients in eech stnds in northern Irn. The present pper ssesses experimentlly the effects of gp cretion on soil nutrient supply. Also this study is helpful to understnd mechnism of the development of vegettion influenced y different gp size, nd to derive some rules for nture - sed mngement of Irn eech forests with gp dynmics. MATERIALS AND METHODS Study re: This reserch performed in the reserve orientl Beech (Fgus orientlis Lipsky) stnd t Lng - Kelrdsht, wter ctchment 36 in Mzndrn province, north of Irn with the re of 43 h. (Between , northern ltitude, , estern longitude). The mximum elevtion is 65 m nd minimum is 35 m. Minimum temperture in Ferury (7 C) nd the highest temperture in August (26 C) re recorded, respectively. Men nnul precipittion of the study re were from 289 to 32 mm t the Tonekon city metrologicl sttion, which is 3 Km fr from the study re. The soils re semi - deep, modertely well drined. They hve textures of cly lom with ph of 4.2 to 6. Bedrock is sndstone with silting nd rgillite stone. Presence of logged nd re roots of trees is indicting rooting restrictions nd soil hevy texture [3]. selection: For this study, twelve cnopy gps with n re etween < 2 m 2 nd m 2 were selected in reserve orientl eech stnd. Moreover, for ech cnopy gp, one non - gp plot (closed cnopy) 4 m 2 squre smpling qudrte ws considered. Cnopy gps res were mesured in the field ccording to common method [5]. The smpling protocol ws uilt up y locting nd mesuring two perpendiculr lines in ech gp: one long the longest line visile nd one perpendiculr to it t the widest section of the gp. The gps were clssified in three clsses: four gps in 8-2 m 2 re clss (smll gp with re men of m 2 ), five gps in 2-5 m 2 re clss (medium clss with re men of m 2 ), nd three gps in 5 - m 2 re clss (lrge clss with re men of m 2 ). Ground vegettion ws ssessed within five 2 2 m smple plots from center to the gp edges (Fig ). 4623

3 Fig.. disply nd collected smples Then, different indices of iodiversity (diversity, richness nd evenness of the her lyer) such s Shnnon nd Simpson diversity, Menhinick nd Mrglef richness nd Sheldon nd Pielou evenness indices were clculted y pst softwre. Soil smpling nd nlysis: For this purpose, two positions were distinguished including within gp nd closed cnopy. Soil smples were tken t - 2 cm depths from ll positions using core soil smpler with 8cm 2 cross section [44]. Roots, shoots nd peles in ech smple were seprted y hnd nd discrded. The ir - dried soil smples were sieved (ggregtes were crushed to pss through 2 mm sieve) to remove roots prior to chemicl nlysis. Soil ph ws determined using n Orion Ionlyzer Model 9 ph meter in :2.5, soil: wter solution. Sturted moisture ws mesured using of weighting method [26, 52]. Soil orgnic cron ws determined using the Wlkey - Blck technique []. The totl nitrogen ws mesured using semi Micro - Kjeldhl technique [9]. The ville P ws determined with spectrophotometer y using Olsen method [33]. The ville K nd C (y mmonium cette extrction t ph 9) were determined with Atomic sorption spectrophotometer (AAS) [8]. The vlues of Mg were mesured y ICP AES (Spectroflme) [26] t the Lortory. Sttisticl nlysis: Normlity of the vriles ws checked y Kolmogrov - Smirnov test nd Levene test ws used to exmine the equlity of the vrinces. Differences etween gp different res nd gp positions in diversity indices nd soil chrcteristics were tested with two - wy nlysis (ANOVA) using the GLM procedure. Interctions etween independent fctors were tested lso. Duncn test nd Independent smple t-test were used to seprte the verges of the dependent vriles which were significntly ffected y tretment. Significnt differences mong tretment verges for different prmeters were tested t P.5. SPSS v..5 softwre ws used for ll the sttisticl nlysis. RESULTS Cnopy gp chrcteristics. Twelve cnopy gps with different res were detected in study site (Tle ). s clssified in three clsses: four gps in 8-2 m 2 re clss (smll gp with re men of m 2 ), five gps in 2-5 m 2 re clss (medium clss with re men of m 2 ), nd three gps in 5 - m 2 re clss (lrge clss with re men of m 2 ). Result is indicting the most present gps in study re hve 9-3 m 2 re. Tle. Chrcteristics of cnopy gps in study re clss (m 2 ) numer re men (m 2 ) Minimum nd mximum of gp re (m 2 ) Biodiversity indices: Results indicted tht the Shnnon nd wever nd Simpson diversity indices, Menhinick nd Mrglef richness indices for her lyer incresed with incresing of gp re (Fig. 2 nd 3). Wheres, Pielou nd Sheldon evenness decresed with incresing of gp re (Fig. 4). Shnnon nd wever nd Menhinick indices were 4624

4 significntly (P <.5) higher in lrge gps compred with smll gps (Tle 2 nd Figs. 2 nd 3). But, the highest mount of Sheldon evenness index (P <.5) ws detected in smll gps in comprison to lrge gps (Tle 2 nd Fig. 4). Aout the effects of gp positions on iodiversity, the results showed tht the highest mount of diversity nd richness indices were oserved in gp center in comprison to gp edge nd closed cnopy (Tle 2 nd Figs 5 nd 6). Wheres closed cnopy position hd the gretest vlue of evenness indices in comprison to the other positions (Tle 2 nd Fig. 7). Shnnon nd wever nd Menhinick indices were significntly (P <.5) greter in gp center positions thn closed cnopy (Tle2 nd Figs 5 nd 6). cnopy position devoted in the gretest vlue (P <.5) of Sheldon evenness index in comprison to the other positions (Tle 2 nd Fig. 7). Tle 2. Three - wy nlysis of herl diversity indices in gp different res nd positions Vriles Source Diversity indices df SS F-Vlue MS Sig Shnnon nd wever Simpson Menhinick Mrglef Pielou Sheldon Shnnon nd wever Simpson Menhinick Mrglef Pielou Sheldon Shnnon nd wever Simpson Menhinick Mrglef Pielou Sheldon re position re position Diversity Indices vlues Shnnon nd wever Simpson Smll Medium Lrge Diversity Indices Fig. 2. Men of diversity indices in gp different res 4625

5 Richness Indices vlues Smll Medium Lrge Menhinick Mrglef Richness Indices Fig. 3. Men of richness indices in gp different res Evenness Indices vlues Smll Medium Lrge Pielou Sheldon Evenness Indices Fig. 4. Men of evenness indices in gp different res Diversity Indices vlues center edge cnopy Shnnon nd wever Simpson Diversity Indices Fig. 5. Men of diversity indices in gp different positions 4626

6 Richness Indices vlues center edge cnopy Menhinick Mrglef Richness Indices Fig. 6. Men of richness indices in gp different positions center Evenness Indices vlues edge cnopy Pielou Sheldon Evenness Indices Fig. 7. Men of evenness indices in gp different positions Soil fetures: Anlysis of dt showed tht soil ph, orgnic mtter nd cron nd totl nitrogen incresed with incresing of gp re. Soil ph ws significntly (P <.5) higher in within gps in comprison to closed cnopy. Also the highest vlue of orgnic mtter nd cron nd totl nitrogen were detected in within gps (Tle 3 nd Fig. 8, 9, nd ). Greter mounts of cron to nitrogen rtio were found in medium gp nd closed cnopy position (Fig. 2). Wheres sturted moisture of soil decresed with incresing of gp re nd the highest vlue of this chrcter ws detected in closed cnopy (Fig. 3). Compre mens of ville P, K, C nd Mg in the gp size indicted tht medium gps hd the higher mounts thn in the smll nd lrge gps. Also, these chrcters were significntly (P <.5) greter in within gps in comprison to closed cnopy (Fig. 4, 5, 6 nd 7). 4627

7 Tle 3. Two - wy nlysis of soil fetures in gp different res nd positions Soil chrcter Vriles source F - Vlue Sig. re Sturted moisture (%) position re position ph Orgnic mtter (%) Orgnic cron (%) Cron to nitrogen rtio Totl nitrogen (%) Aville P (mg/kg) Aville K (mg/kg) Aville C ( me/l ) Aville Mg (me/l ) re position re position.52 3 re position re position re position re position re position re position re position re position 37 re position re position re position re position.3 79 re position re position re 8.55 position re position ph Smll Medium Lrge Within cnopy re position Fig. 8. Men of soil ph in gp different res nd positions 4628

8 6 Orgnic mtter(%) Smll Medium Lrge Within cnopy re position Fig. 9. Men of soil orgnic mtter in gp different res nd positions Orgnic cron (%) Smll Medium Lrge Within cnopy re position Fig.. Men of soil orgnic cron in gp different res nd positions Totl nitrogen (%) Smll Medium Lrge Within cnopy re position Fig.. Men of soil totl nitrogen in gp different res nd positions 4629

9 Cron to nitrogen rtio Smll Medium Lrge Within cnopy re position Fig. 2. Men of soil C/N rtio in gp different res nd positions 56 Sturted moisture (%) Smll Medium Lrge Within re position Fig. 3. Men of soil sturted moisture in gp different res nd positions Aville P (mg/kg) Smll Medium Lrge Within cnopy re position Fig. 4. Men of soil ville P in gp different res nd positions 463

10 2 Aville K (mg/kg) Smll Medium Lrge Within cnopy re position Fig. 5. Men of soil ville K in gp different res nd positions Aville C (me/l) Smll Medium Lrge Within cnopy re position Fig. 6. Men of soil ville C in gp different res nd positions Aville Mg ( me/l ).4.2 Smll Medium Lrge Within cnopy re position Fig. 7. Men of soil ville Mg in gp different res nd positions DISCUSSION 463

11 Effects of gp on iodiversity As the results showed diversity nd richness indices for her lyer incresed with incresing of gp re, wheres evenness indices decresed. Also results indicted tht the highest mount of diversity nd richness indices were oserved in gp center in comprison to gp edge nd closed cnopy, wheres closed cnopy position hd the gretest vlue of evenness indices. In forest ecology, the fetures of the gps (re, shpe nd ge) nd the lndscpe (territory) re importnt ecuse of richness nd species comintion. The gp re is more importnt thn the ge [8]. However; the ge hs its own importnt effects which cn cuse the smll gps to close quicker fter while. In the lst decdes, numerous studies hve een done on the effects of gp size on the understory vegettion [27, 53, 23, 4]. Cnopy openings s result of tree flls crete n environment different from the djcent forest, which influences plnt regenertion. In ddition, gp processes prtly determine forest structure nd ply n importnt role to mintin plnt species richness [4, 9]. microclimtes my enhnce seed germintion nd increse growth rtes of hers nd woody species in comprison with rtes in the forest understory [27]. However, chnges in iotic nd iotic conditions depend to oth on gp size nd within-gp position [32, 37]. Severl uthors hve stressed tht on n undistured forest floor sptil ptterns my e mintined for mny yers fter gp cretion [34, 27, 32]. Understory plnts lredy present in the re (including in the seed - nk) increse in numer nd size in response to chnged environmentl conditions, in ddition to other species tht cn invde. Shrus nd hers exhiit sensitivity to vriety of forest disturnces [39], including forest mngement prctices [49, 6], nd re likely to respond individulisticlly to the chnging environment creted y cnopy tree removl [56]. However, the species composition in gps is often very similr to tht under closed cnopy, lthough in severl cses certin gp species could e identified [53]. Plnt species typiclly or exclusively occurring in gps re often descried s shde-intolernt nd typicl for non-forest hitts [27, 2]. Erly succession species nd midsuccession species hd higher density in gps in comprison to closed cnopy wheres shde tolernt species were oserved in closed cnopy.s hve higher totl plnt species richness in the understory thn closed cnopy, wheres Higher evenness ws oserved in closed cnopy thn in gps. Also size ws positively correlted with the totl density of splings, the density of severl species, nd species richness [53]. Sptil extent of gp influence on understory species diversity did not follow simple pttern. In generl, edge loctions pper to support lower understory plnt species diversity thn surrounding thinned forest or gp interiors. influence on diversity exhiited oth n interior (high diversity) component nd n edge (low diversity) component [2]. Furthermore, plnt diversity will incresed with incresing of opening res in cnopy gps [54] tht re oserved in study re, lso. Nf nd Wulf [4] reported tht species composition ws reltively homogenous in different gps size ut significntly determined y gp size, light vilility, with more fvorle light conditions, n incresing proportion of generlist species occurred within gps. The fll of cnopy trees results in incresed totl incident light levels t the ground nd in some cses lso in incresed nutrient nd moisture vilility [6]. As shown y mny studies, light vilility increses with gp size [3, 23]. The incresing effect of re on species numers is known for long time [4]. Higher species numers in gps due to more fvorle light conditions were found in most gp studies [2, 53]. Ritter, et l. [46] indicted tht size hd significnt effect on the cover of tree regenertion.it cn e interpreted s the fvoring effect of higher resource vilility in lrger gps comprising more light, more spce nd less root competition y cnopy trees. Richness, composition nd totl cover of herceous vegettion were different in smll versus lrge gps.much of this difference ws ttriuted to the presence of specific reltive light intensities nd lso to the incresed mount of ville soil moisture in gps. Species were differently ffected y the comined effects of light nd soil moisture, s well s y differences in ville sustrtes. All this resulted in species - specific distriution ptterns within gps [23]. Smll gps my hve een dominted y competitor species in prt ecuse of the lower levels of ground - lyer disturnce ssocited with this gp size [2]. In the sence of high levels of disturnce, ruderl species re unle to tke dvntge of cnopy removl nd susequent reduction in undnce of stress-tolernt species. In smll gps, levels of direct rdition my not hve een elevted enough to cuse competitive reduction of stress - tolertes except t the very center of the gps, resulting in the negtive gp influence extent oserved in smller gps [2]. In smll gps, the trees round the gp put remrkle shdow on inner prts of the gps nd mrginl effect of such trees exist in centrl prts of the gps [24]. If such circumstnce continues nd the crown closes in following yers [22, 3], lrge numer of species, especilly those which shde-intolernt, re not le to grow [27]. 4632

12 Under such conditions, only species which shde tolernt cn survive nd ecologicl condition turns to e tough for other species, thus, wood covering richness reduces [2]. Hrsh environmentl conditions, prticulrly regrding light condition, in closed cnopy nd smll gps cn cuse the reduction or omission of vrious species [48]; therefore species homogeneity increses nd is hrmony with the results of present study. However, the more the size of the gp, the more suitle conditions for the growth of vrious species. Thus, estlishment nd survivl of herceous species in cnopy gps of different sizes should e oserved more widely [27, 53]. Effects of gp on soil fetures Soil ph: The result is indicting tht lrge gps nd within gp position hd greter ph thn in the other gp size nd positions.menwhile, significnt different ws oserved etween gp positions. Smll gps tended to hve lower mounts of soil ph tht cn e relted to presence complexes of sustin orgnic cids s in gps with more openings these complexes re leching from soil upper lyers. Thus, gp lrger res tended to hve higher ph. Similr sttus cn e considered in different positions of gps s in gp center leching of cid complexes more occurred nd soil ph is incresed. Schrenroch nd Bockheim [52] detected no significnt differences in soil ph chrcter for gp different res. Orgnic mtter nd cron: The highest vlues of these chrcters found in lrge gps nd within gps. Density nd prticle size seprtions isolte district soil orgnic mtter pools for relting stiliztion nd turnover of cron in soil [3, 55 ].Soil orgnic mtter ssocited with silt nd cly prticles re considerly more reclcitrnt, with turnover times rnging from 4 to yers [42, 2]. In this reserch y reson presence of cly higher mounts in soil texture (result is unpulished) the orgnic mtter mounts were more considerle in lrge gps. Schrenroch nd Bockheim [52] reported the cnopy gps effects on soil orgnic mtter chrcter ws non significnt. Totl nitrogen: The most vlues of totl nitrogen found in gp lrge nd within gp positions. Ritter, et l. [46] lso found tht soil solution nitrte concentrtions nd nitrte losses were incresed s result of forest gps. Mny reserchers [43, 46] oserved the non significnt effects gp different res on soil nitrogen chrcter. Schrenroch nd Bockheim [5] climed tht cnopy gps re susceptile to nitrogen leching less, thus the mounts of this chrcter is less in opening res soil thn in closed cnopy. In generl, incresed orgnic mtter decomposition nd nitrogen minerliztion nd reduced root nitrogen uptke tends to fvor leching of inorgnic nitrogen in gps reltive to the undistured closed forest [, 58, 7]. Ritter nd Vesterdl [47] climed tht nitrogen concentrtion in growth seson is more in within gps thn to closed cnopy. In present study similr results detected py ttention to this reserch crried out in summer seson. But, it is ssumed tht nitrogen losses will occurred fter removl of the forest cover on lrge res. Incresed nitrogen concentrtion in the gps my prtly e ttriuted to lck of nitrogen uptke y regenertion or ground vegettion in the erly yers fter gp formtion, s lso found y Knight, et l. [35]. Cron to nitrogen rtio: The highest vlue of this chrcter detected in medium gps nd closed cnopy position. With considering the gretest mounts nitrogen oserved in lrge gps thus greter C/N rtio found in smll gps. Sturted moisture: The mximum vlues of sturted moisture oserved in smll gps nd closed cnopy. Temporl nd smll-scle sptil vrition in microclimte nd soil moisture in nd round cnopy gps hs often een studied in mnged forests [7, 5] or in nturl forests with different climte nd species composition to tht found in eech-dominted forests of Europe [25, 29, 57, 28]. Previous studies in temperte forests found tht on the whole gp scle light quntity increses with opening size, wheres the pttern of soil moisture is less strightforwrd: it does not lwys increse in gps, ut it is generlly more sptilly vrile thn light [3, 4,5]. Glhidy, et l. [23] indicted tht mximum of soil moisture ws the sme in smll nd lrge gps. This indictes tht even centers of smll gps (rdius < m) re eyond the rech of the root system of surrounding trees. Soil moisture nd temperture ptterns re lso ffected y locl vritions in soil depth nd stoniness. Ritter, et l. [46] indicted tht soil wter content in the gp ws ner field cpcity nd generlly higher thn tht under the closed cnopy during summer. Aville P, K, C nd Mg: Medium gps nd within gp position hd the gretest mounts of se ctions. In generl, solr rdition will incresed with incresing of cnopy opening res tht is due to ccelerting decomposition of litters [36]. But if the opening e very lrge, decrese in se ctions in gps is likely result of 4633

13 leching losses. Schrenroch nd Bockheim [52] reported the leching is the most importnt reson for decrese of se ctions in within gps. Their results suggest n incresed nutrient leching potentil s result of reltively lrge (3-2 m 2 ) gps in old growth northern hrdwood - hemlock forests. The results of current reserch is indicting tht se ctions leching potentil incresed with expnding of cnopy opening res from medium to lrge; thus soil is poor of nutrient elements in lrge cnopy gps. This importnt should e considered in forest mngement nd trees mrking for utiliztion to prevent of gps formtion with lrge opening res. CONCLUSION s promote recruitment nd growth of understory vegettion tht my eventully ecome dominnt trees y ltering the vilility of resources, including light, soil moisture, nd nutrients. The vilility of these resources, nd consequently species survivl nd vegettive growth, is function of gp chrcteristics, including re, orienttion, nd shpe. Findings show tht using vrious ut smll nd medium gps will provide etter condition for the forest stnds. Furthermore, the understnding of nturl disturnce nd stnd development processes is necessry for their incorporting into the prctice of ny type of close-to-nture silviculture. REFERENCES []Allison L E, Americn Society of Agronomy, 975, 2: [2]Anderson K L nd Leopold D J, J. Torrey Bot. Soc., 22, 29: [3]Anonymous, Kzemrood Forest Mngement. Orgniztion of Forest nd Rnge nd Wtershed Mngement, Islmic Repulic of Irn, 998, 45p (In Persin). [4]Arrhenius O, Journl of Ecology, 92, 9: [5]Brtsch N, Wter Air Soil Pollution, 2, 22: 3 6. [6]Bttles J J, Shlisky A J, Brrett R H, Held R C nd Allen-Diz B H, Forest Ecology nd Mngement, 2, 46: [7]Buhus J nd Brtsch N, Plnt Soil, 995, 22: [8]Bower C A, Reitemeier R F nd Firemn M, Soil Sciences, 952, 73(4): [9]Bremer J M nd Mulvney C S, Americn Society of Agronomy, 982, 2: []Brumme R, Plnt Soil, 995, 68 69: []Busing R T nd White P S, Oikos, 997, 78: [2]Buynovsky G A, Aslm M nd Wgner G, Soil Sciences Society Americn Journl, 994, 58: [3]Cnhm C D, Denslow J S, Pltt W J, Runkle J R, Spies T A nd White P S, Cndin Journl of Forest Reserch, 99, 2: [4]Collins B S nd Pickett S T A, Vegettio, 987, 7: 3-. [5]Collins B S nd Pickett S T A, Journl of Ecology, 988, 76: [6]Denslow J S nd Spies T, Cndin Journl of Forest Reserch, 99, 2:69. [7]Denslow J S, Ellison A M nd Snford R E, Journl of Ecology, 998, 86: [8]Didhm R K, Chpmn nd Hll, London,997, [9]Dupuy J M, Chrdon R L, Journl of Forest Ecology nd Mngement, 28, 255: [2]Fhey R T, MS thesis, Forest Science Deprtment, Oregon Stte University, Corvllis, OR, 25, 53 p. [2]Fhey R T, Puettmnn K J, Forest Ecology nd Mngement, 28, 255: [22]Frnklin J F, Spies T A, Vn pelt R, Crey A B, Thornurgh D A, Berg D R, Lindenmyer D B, Hrmon M E, Keeton W S, Shw D C, Bile K nd chen J, Forest Ecology nd Mngement, 22, 55: [23]Glhidy L, Miho k B, Hgyo A, Rjki K nd Stndov r T, Plnt Ecology, 26, 83: [24]Ggnon J L, Jokele E J, Moser W K nd Huer D A, Forest Ecology nd Mngement, 24, 72: [25]Geiger R, Arn R H nd Todhunter P, fifth Ed, Friedr, Vieweg nd Sohn, Wiesden, 995, Germny. [26]Ghznshhi J, soil nd plnt nlysis, Hom Puliction,997, 3p. [27]Goldlum D, Journl of Vegettion Science, 997, 8: [28]Gry A N, Spies T A nd Ester M J, Cndin Journl of Forest Reserch, 22, 32: [29]Gry A N nd Spies T A, Ecology,997,78: [3]Gregoriche G, Ellert B H, Boc Rton, FL, Lewis Pulishers, CRC Press Inc, 993, [3]Hlpern C B nd spies T A, Ecology Applied, 995, 5: [32] Holeks J, Plnt Ecology, 23, 68: [33]Homer C D nd Prtt P F, University of Cliforni, Agriculturl Sciences Pulictions, Berkeley, CA, 96, 39 p. 4634

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