Conversion of Hyrcanian degraded forests to plantations: Effects on soil C and N stocks

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1 Aville online t Scholrs Reserch Lirry Annls of Biologicl Reserch, 2011, 2 (5) : ( ISSN CODEN (USA): ABRNBW Conversion of Hyrcnin degrded forests to plnttio: Effects on soil C nd N stocks Niloufr Hghdoost, Moslem Akrini, Seyed Mohsen Hosseini, Yhy Kooch Deprtment of Forestry, Fculty of Nturl Resources, Trit Modres University, Noor, Mzndrn, Irn _ ABSTRACT Hyrcnin forest ecosystem is coidered to e one of the most importnt nturl deciduous forests in the world. Tody, these forests re eing devstted y humn ctivities. So there hve een mny plnttion estlishments with endemic species in degrded forests of this re. But the effects of such conversio on soil C nd N stocks nd nutrients re still unknown. We investigted the effects of conversion of degrded nturl forest to Alnus sucordt.l, Acer velutinum.boiss nd Cupressus sempervire. vr.horizontlis plnttio on soil C nd N stocks nd nutrients fter 18 yers. The studied stnds re locted in the county of Chmestn in the province of Mzndrn, Irn. Some of soil chemicl nd physicl properties including ville nutrient concentrtio (C, Mg, P nd K) nd totl N nd orgnic C stocks in the soil were determined in three soil depths ( cm, cm nd cm). Soil ville nutrients were higher under plnttion stnds compred to the degrded nturl forest except for soil ville K which decresed under A. sucordt plnttion. We expect incresing the soil nutrient improvement with incresing the ge of plnttion stnds. A. velutinum nd C. sempervire hd incresed soil C nd N stocks ut A. sucordt decresed soil C stock nd incresed soil N stock in comprison to the degrded nturl forest. These results indicte tht conversion of degrded forests with pproprite species cn significntly improve soil C stocks, helping to mitigte the negtive impcts of the greenhouse effect. Keywords: Acer velutinum.boiss, Alnus sucordt.l, climte chnge mitigtion, Cupressus sempervire. vr.horizontlis, soil nutrients. _ INTRODUCTION Hyrcnin forest ecosystem is coidered to e one of the lst remnnts of nturl deciduous forests in the world. In comprison to Europen rod-leved forests, the Hyrcnin forests seem to hve remined from the Tertiry nd to e relic ecosystem [43]. Scholrs Reserch Lirry 385

2 Moslem Akrini et l Annls of Biologicl Reserch, 2011, 2 (5): In Irn, Hyrcnin (Cspin) forests re locted t green strip extending over the Northern Slops of Alorz rnge of mounti nd Southern costs of the Cspin Se. This zone hs totl re of 1.84 million h comprising 15% of the totl Irnin forests nd 1.1% of the country s re [27]. These forests stretch out from se level up to n ltitude of 2800 m nd encompss different forest types [44]. Originl old-growth northern forests of Irn re essentil sources of genetic vrition, iodiversity, commercil woody products, nd vrious environmentl services (e.g., ground wter reservtion, uxiliry forest products provision, wildlife hittion, nd erosion control) [39]. The presence of pproximtely 146 ntive woody species, some of which re ecologiclly endemic [45], the diverse rnge of climtic conditio over the pproximtely km2 of horizontl/verticl forest expion, nd exteive wildlife hitt, highlight the importnce of the originl northern forests of Irn [39]. Fgus orientlis (Orientl Beech), Crpinus etulus (Europen hornpen), Acer velutinum (Velvet Mple), Quercus cstneifoli (Cucsin Ok ), Acer cppdocicum (Cppdocin Mple), Alnus sucordt (Alder), nd Tili pltyphyllos (Lrge-leved Linden) re the most importnt tree species in these forests [46]. Also these forests support such importnt species like Prunus divrict (Cherry Plum), Pterocry frxinifoli (Cucsin Wingnut), Buxus hyrcn (Boxwood), Pltnus orientlis (Orientl plne), Zelkov crpinifoli (Cucsin Zelkov), Ulmus cmpestris (Field Elm), Celtis ustrlis (Lote tree), Morus l (White Mulerry), Roini pseudocci (Blck Locust), Populus cspic (Poplr), Alizi julirissin (Persin Silk tree), Txus cct (Europen Yew), Cupressus sempervire (Tuscn Cypress) etc. [44]. Tody, these forests re depleting rpidly due to popultion growth, nd ssocited socioeconomic prolems, industril development, urnism, nd more recently inteive/irregulr tourism [39]. Aout 60% of Hyrcnin forests re mnged for timer production nd the reminders re degrded to vrying degrees [46]. The existence of different lnd-uses, nd their incresing ltertion, minly y locl communities, mismngement of nturl resources over long periods of time, pl for industril development (e.g., estlishment of industril tow djcent to the forested res), pulic rod cotruction without detiled environmentl coidertio nd shortge of humn/finncil resources for sustinle monitoring nd mngement of the forest resources re thretening the existence of the Cspin forests [39]. Wht is ovious is tht the nturl forests hve een under continuous degrdtion over the lst few decdes in this re nd there is n urgent need to mintin the functio of this unique forest ecosystem. So Ntionl forest mngement officils hve cknowledged this fct nd hve initited ctio for sustinle mngement of the Cspin Forests, Different forms of mngement schemes re plnned for implementtion, such s documenting nd exhiiting the forest disturnce nd supervision nd mngement of the remining nturl forest ecosystems in the region [39]. Agriculturl ndonment nd tree plnting for commercil or restortion purposes re lso two min methods for the forest restortion [16, 41, 11]. So there were mny plnttio with endemic nd exotic species in degrded forest res which certinly hd mny effects on ecosystem specificlly on soil fertility nd nutrients. Forest plnttio were introduced to supply fuel-wood, chrcol, fodder, sticks nd uilding mterils. They were lso plnted to restore degrded lnds, to control soil erosion or to serve s uffer zones round rods nd res of nturl forests [15, 19, 24 34]. Although the re of forest plnttio hs incresed, there hs een concern over their ecologicl nd environmentl effects. It is elieved tht: they sustin low diversity of wildlife; they re high coumers of wter nd nutrients, nd increse soil cidifiction [10, 24]. This hs led to studies of soil properties under Scholrs Reserch Lirry 386

3 Moslem Akrini et l Annls of Biologicl Reserch, 2011, 2 (5): forest plnttio in comprison to nturl forests, pstures, nturl svn nd croplnds ll over the world [29, 57, 19, 25, 34, 53]. Hitherto, coiderle reserches hve een crried out concerning species influence on soils in Hyrcnin forests of Irn, ut results re not coistent nd generliztio re not possile nd lso most of these reserches re not pulished in English lnguge. Also there re no reserches focusing on effects of forest plnttio on soil C nd N stocks in comprison to nturl forests or degrded forests in Northern forests of Irn. Therefore, this study intended to fill this gp y focusing on soil ttriutes under similr environmentl nd soil conditio, 18 yers fter conversion of degrded nturl forest to three species plnttio. These species selected mong the endemic nd most used y foresters in North of Irn. MATERIALS AND METHODS 2.1. Study re The study re is locted t the Chmestn region in Mzndrn province, on the northern of Irn (36 o 29' N, 52 o 7' E). Study stnds were locted t n ltitude of 90 m ove se level nd with low slope (0-5%). Annul rinfll verges 803 mm, with wetter months occurring etween Septemer nd Ferury, nd dry seson from April to August monthly rinfll usully verges < 40 mm for 4 months. Averge dily tempertures rnges from 11.7 o C in Ferury to 29.5 o C in August. The soils hve the textures of lom nd cly lom with n cidic ph in top lyers nd in deep lyers soil textures were cly nd silty cly nd soil ph ws less cidic. Previously this re ws dominted y degrded nturl forests contining ntive tree species such s Quercus cstneifoli, Zelkov crpinifoli, Prroti persic, Crpinus etulus, Diospyros lotus nd Buxus hyrcn. But 18 yers go fter cler cutting (in smll res in degrded nturl forests), reforesttio hs een estlished (with 2 2 m spces) in this re with three species including: Alnus sucordt.l, Acer velutinum.boiss nd Cupressus sempervire. vr.horizontlis [3] Smpling method For investigte the effect of Conversion of degrded nturl forests to plnttio on soil cron nd nutrients, four experimentl sites were chosen in Chmestn region of Hyrcnin forests in Northern Irn. Three plnttion stnds including: Alnus sucordt.l (), Acer velutinum.boiss () nd Cupressus sempervire. vr.horizontlis () nd one degrded nturl stnd of Quercus-Zelkov (), ech with re of 10 h. At ny stnds four 5 5 m plots with rndomly systemtic sttisticl method selected nd in ech plot the soils were smples in three depths: cm, cm nd cm, fter removing the litters. To minimize the inccurcy, one dditionl comined smpling ws implemented: the soil smples of the four corners of ech plot were picked nd then these smples were mixed together. So then in every stnd for ech depth totlly ten smples were collected [33, 32, 37, 30, 20] Lortory Methods After ir drying, soil smples were pssed through 2.0 mm (20 mesh) sieve to remove roots prior to chemicl nlyses. Then, Soil ph ws determined using n Orion Ionlyzer Model 901 ph meter in 1:2.5, soil: wter solution. EC (electricl conductivity) ws determined using n Orion Ionlyzer Model 901 EC meter in 1:2.5, soil: wter solution. The soil texture ws determined y Bouyoucos hydrometer method [7]. The ulk deity (g/cm³) ws studied with volumetriclly [6]. Soil orgnic mtter ws determined using the Wlkley-Blck method [1]. Totl N ws determined using the Kjeldhl method [9]. Aville P ws determined with Scholrs Reserch Lirry 387

4 Moslem Akrini et l Annls of Biologicl Reserch, 2011, 2 (5): spectrophotometer y using Olsen method [21]. Aville K, C nd Mg (y mmonium cette extrction t ph 9) were determined with Atomic sorption Spectrophotometer [8]. The verges of soil ulk deity, C nd N concentrtio were used in this study. The totl stocks (C t, g cm -2 ) of soil orgnic C nd totl N were clculted s following [17, 12]: Where BD is the soil ulk deity (g cm -3 ), C the soil orgnic C nd totl N concentrtion (%), nd D is the soil smpling depth (cm) Dt nlysis The dt otined hve een sttisticlly nlyzed using the SPSS 17 softwre. The normlity of dt exmined with Kolomogorov-Smirnov test nd the homogeny of vrinces ws investigted y Levene test. Attending to the normlity nd vrince homogeny of dt, Two-wy nlyses of vrince (ANOVA) were used to compre soil properties mong experimentl sites. Duncn tests were used to seprte the me of dependent vriles. Person correltion ws used to ssess the correltion etween soil properties cross ll studied stnds. RESULTS 3.1. Soil ttriutes Prticle size of ll three depths coidered were significntly different (p <0.05) etween stnds except for the silt nd cly frctio of the cm soil lyer nd the snd frctio of the cm soil lyer. The soil under the degrded nturl stnd () hd higher cly nd lowest snd frctio thn the soils of the plnttio (Tle 1). This my e ttriuted to the effects of plnting prctices nd ssocited disturnce on the soils of the plnttio. Severl other studies conducted on similr soil s the soil of our study site hve reported rpid ltertion of stle soil properties including prticle size distriutio within reltively short periods when suject to deforesttion nd susequent cultivtion nd plnttion. In the cm soil lyer, Bulk deity (g/cm 3 ) did not differ significntly etween degrded nturl stnd () nd A. sucordt (), A. velutinum () nd C. sempervire () plnttio. But in the two other soil depths it ws significntly different (p <0.05) etween the stnds (Tle 1). In the depth of cm the soil under the CHS stnd hd highest Bulk deity nd in the cm soil lyer the stnd hd highest Bulk deity. Soil ph nd EC of ll three depths (, nd cm) differed significntly (p <0.001) etween nd plnttio. Soil ph ws lowest under in ll three soil lyers nd hd highest soil EC (Tle 2). As it is seen in tle 2, plnttion with A. velutinum nd C. sempervire significntly incresed soil EC in compred to the degrded nturl stnd. Soil orgnic C nd totl N in the depths of the nd cm were significntly different (p <0.05) etween degrded nturl stnd nd plnttion stnds. But there were no significnt differences in soil orgnic cron nd totl N in the soil lyer. Therefore, it cn e sid tht conversion of degrded nturl forest to plnttio prtly hd improved soil C nd N contents. Also C:N rtio differed significntly (p <0.05) etween stnds in two top lyer of soil nd the degrded nturl stnd hd higher rtio thn the plnttion stnds (Tle 2). As cn e oserved in the results tht shown in tle 2, conversion of degrded forest to plnttio hd significntly improved soil ville nutrients (P, C, Mg nd K). Plnttio hd significntly (p <0.05) incresed soil ville P in the top lyer of soil. But in two other soil depths the Scholrs Reserch Lirry 388

5 Moslem Akrini et l Annls of Biologicl Reserch, 2011, 2 (5): chnges ws not significntly different. Aville C nd Mg were significntly (p <0.001) higher under thn under, nd in ll three soil lyers. Also hd the lowest mount of ville C nd Mg compred to the plnttion stnds in ll three coidered depths. Aville K lso ws significntly different etween the studied stnds. In ll three soil lyer hd the lowest mount of ville K thn the other studied stnds (Tle 2). So it cn e sid tht the conversion of degrded nturl stnd to A. sucordt () plnttion hd negtive effects on soil ville K 18 yers fter the conversion. Tle 1- Soil physicl properties in the degrded nturl stnd nd plnttio in three soil lyers with their stndrd error (elow) ANOVA (9.66) (7.84) (2.88) (2.5) Silt (%) (3.5) (4.69) (2.69) (2.06) (3.69) (4.78) (4.78) (2.21) (3.4) (2.88) (4.03) (2.21) Snd (%) (2.5) (4.79) (4.57) (1.91) (2.06) (2.06) (2.64) (1.82) (9.21) (5.9) (3.3) (1.29) Cly (%) (3.96) (5.68) (4.03) (0.957) (2.87) (3.36) (3.86) (0.5) (0.245) (0.246) (0.132) (0.292) Bulk Deity (g/cm ) (0.1355) (0.171) (0.103) (0.444) (0.502) (0.318) (0.188) (0.487) - ANOVA results: Men vlues with the sme letter within the soil lyer do not differ significntly with ech other. show the significnt t the 0.05 level. The output of nlysis of vrince of soil ttriutes in three depths the four studied stnds with interctive effects of stnd nd depth re presented in Tle 3. The stnd tree vegettion significntly influenced ll soil ttriutes except for orgnic C. The depth effects on Cly (%), Bulk Deity (g/cm 3 ), Orgnic C (%), Totl N (%), C:N rtio, Exchngele C (mg/kg), Exchngele Mg (mg/kg) nd Exchngele K (mg/kg) ws sttisticlly significnt. The interctive effects of stnd nd depth ws significnt only in soil orgnic C (%). Results of Duncn test etween three soil lyers (, nd cm) properties indicted different results for ech of stnds. As under degrded nturl stnd (), EC, OC, totl N, C:N rtio, ville C nd ville Mg were significntly differ etween three soil lyers. Bulk deity, OC, totl N nd C:N rtio were significntly differ etween three soil lyers under A. velutinum () plnttion. Under A. sucordt () plnttion, OC, totl N, C:N rtio nd ville P were significntly differ etween three different soil depths. Also under C. sempervire (), silt nd cly percentge, OC, totl N, C:N rtio, ville C nd ville P were significntly different etween three coidered soil depths (Fig 1). Scholrs Reserch Lirry 389

6 Moslem Akrini et l Annls of Biologicl Reserch, 2011, 2 (5): Tle 2- Soil chemicl properties in degrded nturl stnd nd plnttio in three soil lyers with their stndrd error (elow) ANOVA (0.125) (0.186) (0.082) (0.206) ph c (0.211) (0.107) (0.051) (0.224) 5.96 c (0.086) (0.149) (0.173) (0.127) c c 8.81 (0.444) (1.75) (0.287) (1.39) EC (ds/m) c c 6.67 (0.018) (1.43) (0.35) (1.64) (0.021) (1.55) (0.21) (1.07) (0.029) (0.03) (0.003) (0.045) Orgnic C (%) (0.115) (0.066) (0.053) (0.054) (0.051) (0.101) (0.135) (0.123) (0.033) (0.0739) (0.02) (0.023) Totl N (%) (0.023) (0.055) (0.51) (0.013) (0.027) (0.039) (0.028) (0.022) (0.534) (0.571) (0.174) (0.314) C:N (0.958) (0.722) (0.726) (0.41) (1.61) (0.975) (0.589) (0.482) (0.029) (0.101) (0.042) (0.045) Aville P (mg/kg) (0.059) (0.31) (0.021) (0.035) (0.025) (0.362) (0.019) (0.007) (5.92) (9.1) (22.3) (8.342) Aville C (mg/kg) (0.868) (10.69) (24.34) (9.004) (1.3) (7.28) (17.49) (3.31) (3.44) (2.02) (8.23) (6.04) Aville Mg (mg/kg) (2.36) (3.83) (6.27) (6.95) c (0.5) (3.88) (2.25) (3.37) (8.94) (19.96) (9.27) (9.55) Aville K (mg/kg) (36.57) (65.77) (6.23) (65.91) (46.58) (22.48) (10.41) (63.58) - ANOVA results: Men vlues with the sme letter within the soil lyer do not differ significntly with ech other., respectively show the significnt t the 0.05 nd.001 level. Scholrs Reserch Lirry 390

7 Moslem Akrini et l Annls of Biologicl Reserch, 2011, 2 (5): Tle 3- Anlysis of vrince of soil ttriutes in three depths with the interctive effects of stnd nd depth Stnd Depth Stnd Depth Error d.f ph EC (ds/m) Silt (%) Snd (%) Cly (%) Bulk Deity (g/cm 3 ) Orgnic C (%) Totl N (%) C:N Exchngele P (mg/kg) Exchngele C (mg/kg) Exchngele Mg (mg/kg) Exchngele K (mg/kg) , respectively show the significnt t the 0.05 nd.001 level. d.f. - Degrees of freedom As cn e oserved in the results tht shown in fig 1, in ll three plnttion stnds soil chemicl properties contents took the order: > > 30-50, ut under degrded nturl stnd they followed the order: > < Pttern tht oserved in soil under the degrded nturl stnd is proly duo to erosion nd leching which cused y humn ctivities nd the degrdtion ecuse of tht Soil C nd N stocks The three plnttion stnds exhiited no significnt differences in soil C nd N stocks t the depth of nd cm in comprison to the degrded nturl stnd while there were significnt differences in soil C nd N stocks of cm soil lyer. In this soil lyer the stnd hd the highest mount of these stocks nd the hd the lowest mount compred to other stnds. Also soil C stock ws differ significntly etween stnds cross the 0-50 cm depth rnge ut soil N stock ws similr etween studied stnds t this rnge (Tle 4). Assuming tht the C stock of the degrded nturl stnd is equivlent to the C stock of the plnttion stnds efore the conversion, we concluded tht the soil C stock incresed under A. velutinum (35.47 t/h) nd C. sempervire (31.06 t/h) nd decresed under A. sucordt (20.18 t/h) in 18 yers fter the conversion. There were no significnt differences in soil N stock under studied stnds cross the 0-50 cm depth rnge, ut ll three plnttio hd incresed soil N stock in comprison to the degrded nturl stnd. Wht is interesting is tht even though A. sucordt is one of the nitrogen fixing species, soil under the plnttion hd lower mount of N stock compred to nd. EC (ds/m) Silt (%) Scholrs Reserch Lirry 391

8 Moslem Akrini et l Annls of Biologicl Reserch, 2011, 2 (5): Cly (%) OC (%) C:N Aville C (mg/kg) c c Fig 1- Comprison of soil properties of three different depths under ech stnd Bulk Deity (g/cm) Totl N (%) Aville P (mg/kg) Aville Mg (mg/kg) c Tle 4- soil C nd N stocks under degrded nturl stnd nd three different species plnttio ANOVA C stock (t/h) ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 25.8 N stock (t/h) 7.31 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ANOVA results: Men vlues with the sme letter within the soil lyer do not differ significntly with ech other. show the significnt t the 0.05 level. Scholrs Reserch Lirry 392

9 Moslem Akrini et l Annls of Biologicl Reserch, 2011, 2 (5): Out of ll possile correltio, 43 correltio were sttisticlly significnt, nd only four exceeded correltion coefficient of 0.70 (Tle 5). Wht is importnt to us is the soil ttriutes which correlted to orgnic C nd totl N. There ws strong positive correltion etween Orgnic C nd totl N. Orgnic C showed positive correltio with ville C (mg/kg), percentge of snd nd C:N rtio. There were negtive correltion etween orgnic C nd percentge of cly. Totl N ws positively correlted with EC, ville C (mg/kg), ville Mg (mg/kg) nd percentge of snd. Also there were negtive correltio etween totl N with C:N rtio, ville K (mg/kg) nd percentge of cly (Tle 5). Tle 5- Person correltion coefficients (r) mong soil ttriutes cross studied stnds ph EC (ds/m) Silt (%) Snd (%) Cly (%) Bulk Deity (g/cm 3 ) Orgnic C (%) Totl N (%) C:N Aville P (mg/kg) Aville C (mg/kg) Aville Mg (mg/kg) Aville K (mg/kg) ph 1 EC (ds/m) Silt (%) Snd (%) Cly (%) Bulk Deity (g/cm 3 ) Orgnic C (%) Totl N (%) C:N Aville P (mg/kg) Aville C (mg/kg) Aville Mg (mg/kg) Aville K (mg/kg) , respectively show the correltion is significnt t the 0.05 nd 0.01 level. DISCUSSION 4.1. Effects of conversion on soil ttriutes As the results of this study showed, conversion of Hyrcnin degrded nturl forest to plnttio of three ntive species hd coiderle influences on soil physicl nd chemicl properties. Results of tle 1 indicted tht ech of three studied species hd different effects on soil physicl properties. Other studies lso reported differences mong soil physicl properties etween different species [18; 28; 51]. In our cse, the differences etween plnttion nd the nturl stnd my e cused y the effects of plnting prctices nd ssocited disturnce [28]. The oserved differences etween plnttion species my e ttriuted to their different influences on soil iologicl community [18]. Lemenih et l., [28] suggested the species dependent difference on soil properties is proly n ccount of difference in iomss production nd nutrient cycle vi litter fll nd root turnover etween the species. Scholrs Reserch Lirry 393

10 Moslem Akrini et l Annls of Biologicl Reserch, 2011, 2 (5): The results of tle 2 showed tht in comprison to the nturl stnd, the plnttion stnds hd huge effects on soil chemicl ttriutes. Plnttio hd incresed soil ph compred to the nturl stnd. Removl of nutrients y intee hrvest [36] could hve een the min fctor controlling the cidity mesured under degrded nturl stnd. It cn e lso explined y slower litter decomposition of degrded nturl stnd s species (dominnt species ws Quercus cstneifoli), which leds to the production of orgnic cids nd delys the return of se ctio to the soil [18]. Ymshit et l., [56] suggested tht this cidifiction under nturl forest could e cused y lower se sturtion nd relted lower mount of exchngele se ctio. Results showed tht plnttio hd significntly incresed soil slinity in comprison to the degrded nturl stnd. As cn e seen in tle 2, soil EC ws higher in ll three plnttio nd they took order: A. velutinum > C. sempervire > A. sucordt > degrded nturl stnd. These differences my e cused y different folige properties nd the mount nd qulity of litter [18]. In two top soil lyers ( nd cm), soil orgnic C nd totl N were significntly higher under plnttio compred to the nturl stnd. It is ovious, tht the upper nd lower soil lyers re ffected y different fctors to vrious extents. Differences in oveground litter qulity s well s deposition inputs, mostly led to differences in chemicl properties of upper soil lyers. But if the differences in soil chemistry were cused y differences in root uptke nd turnover, they will e s seile in the lower lyers s in the upper lyers, ssuming tht the root distriution nd ctivity s well s wethering nd leching were reltively similr etween the lyers [18]. Results from other studies in tropicl nd temperte regio show tht soil C nd N chnges following fforesttion or reforesttion re quite vrile, with soil C nd N levels either incresing or decresing. For itnce, in study of ntive forest nd mture P. rdit plnttion, Turner nd Lmert [52] found tht soil orgnic C under Pinus ws lower thn tht under djcent ntive forest. In nother study under P. rdit nd E. grndis, Turner nd Lmert [53] oserved n ongoing decline in soil orgnic cron for 12 yers; therefter, soil C stilized nd incresed nerly ge 20 yers. Therefore, we conclude tht orgnic C nd totl N in forest soils re mrkedly vrile depending on tree species nd ge, soil type, climte, mngement prctices nd initil soil sttus. In the results A. velutinum nd A. sucordt plnttion hd more desirle effects on soil orgnic C nd totl N thn the C. sempervire plnttion which this might e due to the lower tree survivl nd deity tht oserved in the C. sempervire plnttion stnd. Soil C:N rtio is n index of N minerliztion [5, 50, 36]. The minerliztion rte is low t higher C:N rtios, nd s coequence soil nutrient levels decrese [36]. Lrge C:N rtios under degrded nturl forest likely resulted from low minerliztion rtes nd coequently their levels of totl N nd ville nutrients were low. As cn e seen in tle 2, in three coidered soil depths, ll studied soil nutrients were significntly differ etween the stnds except for ville P. Soil ville P showed significnt differences just in top soil lyer ( cm) which my e cused y differences in litter qulity nd deposition inputs. Results showed tht ll three plnttion stnds hd gret effects on soil ville nutrients. Most of nutrients significntly incresed fter conversion of degrded nturl forest to the plnttio ut under the A. sucordt plnttion soil ville K ws lower thn the degrded nturl forest. On the other hnd, A. sucordt plnttion hd higher concentrtio of ville P, ville C nd ville Mg thn other studied stnds. Our suggestion is tht P is one of the min elements Scholrs Reserch Lirry 394

11 Moslem Akrini et l Annls of Biologicl Reserch, 2011, 2 (5): which used in iomss productivity of A. sucordt trees, nd due to the utiliztion of this element, under A. sucordt plnttion concentrtion of ville P is lower thn nturl forest ut further study is necessry t this topic. Three fctors my explin the low levels of nutrients in soils of degrded nturl forest. First, cly prticles lose their cpcity to sor se ctio when soil cidity increses. As coequence, higher mounts of ctio re present in soil solution nd re free to lech into deeper soil profiles [29, 19, 25, 36]. Second, under low ph, the orgnic mtter is difficult to minerlize nd therefore, soil nutrient levels re not enhnced [36]. Third, degrdtion cused y humn ctivity hs led to reduction in tree deity nd cnopy cover nd so it led to increse nutrients leching. Chen nd Li [12] lso corroorte humn ctivities such s trees cutting, could ffect soil nutrient decomposition or loss. They sid fter humn ctivities (such s hrvesting nd logging), soil temperture nd precipittion on the forest floor will e incresed due to removl of cnopies, which increses litter decomposition. Therefore, rtes of litter decomposition will increse, ut mny nutrients will e lost with incresing runoff. Nutrient-rich needles, rnches, twigs nd corse litter frctio re importnt nutrient sources [12] fter the conversion these sources incresed y higher tree deities in plnttio. On the other hnd with incresing the cnopy covers, nutrient leching reduced under the plnttio. We elieve these re the most importnt fctors tht incresed soil nutrients under the plnttion stnds in comprison to the degrded nturl forest. As cn e oserved in fig 1, under plnttion stnds chnges in soil chemicl properties mong soil lyers followed the norml process nd decresed with incresing in soil depths. But under the nturl stnd soil chemicl properties (such s EC, orgnic C, totl N nd ville nutrients) were higher in lower depth (30-50 cm) thn the middle depth (15-30 cm) which this proly cused y leching of the elements due to the degrdtion. In most reserches tht hve studied conversion of nturl forests to plnttio, the conversion hd negtive influences on soil orgnic C nd nutrients [17, 12, 28] ut in our study due to the degrdtion tht occurred in nturl stnd, the plnttion stnds hd positive influences on soil orgnic C nd nutrients. Soil ttriutes under plnttio depends on the prior plnttion estlishment site soil fertility. When estlished on degrded lnds, the effects re ssumed eneficil, wheres when grown on newly clered forest sites the effects re reported to e dverse [28, 58]. In this study the nturl forest ws degrded y humn ctivities. We ssumed tht the soil ttriutes of the degrded nturl forest re equivlent to the soil ttriutes of the plnttion stnds efore the conversion. Therefore, ccording to results of this reserch, within 18 yers since estlishment of the plnttio, they showed positive influences on most soil properties Soil C nd N stocks Plnts ply n importnt role in regulting the iogeochemistry of ecosystems y fixing cron nd nitrogen nd preventing the loss of nutrients [12]. Soil orgnic cron is very importnt in terrestril ecosystems since it plys crucil role in the formtion nd mintennce of soil structure, fertility, nutrient nd wter vilility [13, 49, 31]. On the other hnd, soil N increse is lso very importnt in degrded lnd rehilittion projects [31]. In ddition, soil C nd N stocks cn e n pproprite criterion to ssy the success of these rehilittion projects. In results, only in cm soil lyer C nd N stocks were significntly different etween the degrded nturl stnd nd plnttio. Across the 0-50 cm depth rnge, only soil C stock ws significntly differ etween studied stnds nd the differences were not significnt in soil N Scholrs Reserch Lirry 395

12 Moslem Akrini et l Annls of Biologicl Reserch, 2011, 2 (5): stock in this depth rnge. In comprison to the degrded nturl stnd, A. velutinum nd C. sempervire incresed nd A. sucordt decresed soil C stocks. After plnttion estlishment, there re reduced inputs of cron into the soil from prior lnd-use, together with ccelerted decomposition of soil orgnic mtter s result of disturnce, nd this leds to net loss of soil orgnic cron [53, 42]. Arevlo et l., [4] suggested tht soil C loss in the erly stges of plnttion development my e due to lesser orgnic C inputs thn orgnic C outputs. In some systems this loss of soil orgnic cron is not lnced until 5-10 yers fter estlishment nd on some sites, reduction in soil orgnic cron my remin until the end of the rottion. The ptter of ccumultion nd loss of cron vry ccording to loction, soil type, tree species nd plnttion mngement system [53]. So we think tht under A. velutinum nd C. sempervire plnttio, fter 18 yers of estlishment, soil orgnic cron lnced nd then even incresed in compred to the degrded nturl stnd. But under A. sucordt proly it will e tking longer time for soil orgnic cron to lnce. Erly soil C loss under young plnttio followed y incresed soil C stock with plnttion ge ws oserved y Arevlo et l., [4] so we expect n increse in soil C stock with incresing of the plnttio ge. Mny studies reported tht fter ntive forests were chnged into plnttio the soil cron stock declined [2, 17, 12, 26, 54]. They suggested tht species composition, ge of plnttion, nd precipittion hve significnt effects on soil cron stock in plnttio. While numer of studies did not oserve ny discernile ptter in soil C stock relted to or influenced y lnd use or forest ge [22]. Here due to the degrdtion of nturl forest, A. velutinum nd C. sempervire plnttion stnds hd improved soil C stock. Islm nd Weil [23] were similrly oserved n increse in soil C nd N stocks fter conversion of degrded nturl forest to Acci reforesttion. They suggested tht degrdtion of soil qulity my hve resulted from incresed disruption of mcroggregtes, reductio in microil iomss, nd loss of lile orgnic mtter due to fire, deforesttion, tillge nd ccelerted erosion. However, the rte of soil C stock increse will inevitly slow down s the soil C concentrtion increses with time [48, 47, 31]. According to Silver et l., [47], the nnul rte of soil C incorportion will e reduced to 0.20 (Mg/ h/ yer) in the next 80 yers, fter experiencing higher incorportion rte (1.3 Mg/ h/ yer) over the first 20 yers. At this point, it is importnt to emphsize the role of plnttion soils s C sink during the first yers. Mny studies hve found tht nitrogen-fixing species cn significntly increse soil N levels [40, 12, 31] while others found no correltion etween the presence of nitrogen-fixing species nd totl N ccumultion in the surfce soil [14]. It ws expected tht A. sucordt s nitrogenfixing species my hve greter soil N stock thn other studied species ut it hd lower one. There ws strong positive correltion etween orgnic C nd totl N (Tle 5). Mny other studies hve reported the sme reltion etween soil orgnic cron nd nitrogen [35, 42, 55, 38] while others found no correltion etween orgnic C nd totl N of soil [23]. Vrmesh et l., [55] in their studies on Roini pseudocci nd Cupressus rizonic in n urn forest of Tehrn oserved significnt correltio etween soil orgnic C nd grvel, cly, silt, snd nd ph. They lso found significnt correltio etween soil totl N nd cly, snd, orgnic mtter nd C:N rtio. They concluded tht volume nd qulity of cron storge re close relted to ction nd rection etween climte, soil, tree species, mngement nd chemicl composition of litter. Richrds et l., [42] proposed tht mnging the reltio etween orgnic C nd other soil properties my e crucil prerequisite for mintining nd incresing levels of soil orgnic cron under plnttio. Scholrs Reserch Lirry 396

13 Moslem Akrini et l Annls of Biologicl Reserch, 2011, 2 (5): CONCLUSION Our results showed tht conversion of degrded nturl forest to plnttio improved soil nutrients nd stocks of C nd N in soil. All three studied species hd incresed soil nutrients compred to the degrded nturl forest except for soil ville K which decresed under A. sucordt plnttion. We expect incresing the soil nutrient improvement with incresing the ge of plnttion stnds. Our study demotrtes tht conversion of degrded nturl forest to A. velutinum nd C. sempervire plnttio incresed soil C nd N stocks. But conversion to A. sucordt plnttion decresed soil C stock nd incresed soil N stock lthough differences were not significnt. These results concluded tht tree species nd ge of plnttion stnds cn e effective fctors tht influence the soil C nd N stocks. In ddition, it is importnt to coider tht such plnttio my hve n importnt potentil to trform degrded forest stnds into rehilitted res tht function s C sink, helping to mitigte the negtive impcts of the greenhouse effect. Therefore, estlishment of plnttion in degrded Hyrcnin forests will restore soil nutrients nd contriute to climte chnge mitigtion y incresing cron stock in soils nd it will ply fundmentl role in ecosystem productivity nd environmentl protection. Acknowledgements The uthors would like to thnk Trit Modres University for finncil, lortory nd scientific supports. We re grteful to the Orgniztion of Forest nd Rngelnds nd Wtershed Mngement of Irn for ccess to field sites nd logisticl support. We pprecite S. Vrmesh for his dditionl helps during this reserch. REFERENCES [1] L.E. Allison; Orgnic cron In: Blck, C.A. (Ed.), Methods of Soil Anlysis. Americn Society of Agronomy, Prt 2, Mdison,WI, 1975, [2] I. Ampoh, W. Meyer, Communictio in Soil Science nd Plnt Anlysis, 2000, 31, [3] Anonymous, Oshtorvsh Forest Mngement Plnning, Orgniztion of Forest nd Rngelnds nd Wtershed Mngement. Islmic Repulic of Irn, 1994, 370 p (In Persin). [4] C.B.M. Arevlo, J.S. Bhtti, S.X. Chng, D. Sidders, Forest Ecology nd Mngement, 2009, 257, 8, [5] G. Bengtsson, P. Bengtson, K.F. Mson, Soil Biology nd Biochemistry, 2003, 35, [6] G. R. Blke, K.H. Hrtge, Soil Science Society of Americ, 1986, 9, 1, [7] G.J. Bouyoucos, Agronomy Journl, 1962, 56, [8] C.A. Bower, R.F. Reitemeier, M. Firemn, Soil Science, , 4, [9] J.M. Bremmer, Journl of Agriculturl Science, 1960, 55, 13, [10] M.G.L. Cnnell, New Forests, 1999, 17, [11] R.L. Chzdon, Science, 2008, 320, [12] X. Chen, B.L. Li, Forest Ecology nd Mngement, 2003, 186, [13] E.T. Crswell, R.D.B. Lefroy, Nutrient Cycling in Agroecosystems, 2001, 61, [14] J.R. Cromck, R.E. Miller, O.T. Helgerson, R.B. Smith, H.W. Anderson, Soil Science Society of Americ Journl, 1999, 63, [15] J. Ev, New Forests, 1999, 17, [16] M.R. Gurigut, R. Ostertg, Forest Ecology nd Mngement, 2001, 148, [17] L.B. Guo, R.M. Gifford, Glol Chnge Biology, 2002, 8, [18] A. Hgen-Thorn, I. Cllesen, K. Armolitis, B. Nihlgrd, Forest Ecology nd Mngement, 2004, 195, Scholrs Reserch Lirry 397

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