HQI NGH! KHOA HQC TOAN Q U 6 C V £ SINH THAI VA TAI NGUY£N SINH VAT L^N THLf BA NGHIEN CUtJ TAC T>QNG CUA CHAT DIET CO VA BOM NAPAN LEN RlTNG NHIET DCH GIO MUA Cf MIEN NAM VIET NAM KUZNETSOV A N , KUZ[.]
HQI NGH! KHOA HQC T O A N Q U C V £ SINH THAI V A TAI N G U Y £ N SINH VAT L^N THLf BA NGHIEN CUtJ TAC T>QNG CUA CHAT DIET CO VA BOM NAPAN LEN RlTNG NHIET DCH GIO MUA Cf MIEN NAM VIET NAM KUZNETSOV A.N., KUZNETSOVA S.P IPHAN LUONGI, NGUYEN DANG HQl Trung tdm Nhi^t dai Viet - Nga Trong thdi gian chien tranh My tiln hanh d Vift Nam, lan dau tien lich sir can dai, sy tan phi, buy hoai da dugc tiln hinh tren quy md ldm, rgng khip mgt vimg rimg nhiet ddi, nai dudi nhiing tang tin rimg che chd, quin dgi nhan dan Vift Nam vin ngiy dem hanh quan, thiet lap cac cin cii boat ddng Giai doan tir 1963 den 1971, rimg ngap man cung nhu rimg ddng bing vi rimg chin nui d cic tinh mien Nam v i mien Trung Vift Nam, ciing vdi dit canh tic ndng nghifp da bi khdng quan My xir ly mgt cich hf thdng bang cic chit lam ryng Ii, chat dift cd (sau day ggi chung Ii chit dift cd) Theo cich dd, vifc sir dyng tap tmng cac loai chat dift cd khac keo dai nhieu nam Ii mgt nhimg hinh thirc mdi de tien hinh chien tranh Theo thdng ke, tdng difn tich rimg bi phun rai chit dift cd khoang 2,2 trifu (trong 1,4 trifu d miln Nam) (Bethel J.S., 1975; Wesring, 1976; Phiing Tim Bdi, 1994; Socolov, Tsilova, 1996) Quan dgi My da ket hgp chat diet cd vdi bom napan vi cic loai bom dan khic dl buy dift tham thyc vat rimg Trong nhieu nam chien tranh hoi hgc d mien Nam Vift Nam, mgt khoing rdng rimg ngap man da bj hiiy dift C) cac tinh nhu Tay Ninh, Sdng Be (hifn la tinh Binh Duomg vi Binh Phudc) hom mgt nira tham thyc vat rimg ciing bi bien mit Difn tich rimg ciia tinh Ddng Nai ciing bj suy giim dang ke Hf qua cua nd d i lam cho mdi lien hf giira rimg d mien Nam Viet Nam va rimg ciia Campuchia bj phi buy Trong nhtmg nim sau chien tranh, nhu cau ve gd xay dyng va thuomg mai cing tang de dip limg cho cdng cudc kien thiet dat nude nen rimg ciy cd than gd cao cdn sdt lai d •viing ddng bang cung deu bi ddn Dieu dd dan den sy thu hep difn tich rii'ng nhift ddi nguyen sinh sau Nghien cuu dugc thyc hifn nham phin tich hau qui tic dgng tdng hgp ciia chien tranh (hda chat, bom napan, cic loai bom dan khic, boat ddng can quet quan sy) len cic kieu rimg khac cua mien Nam Vift Nam, giii thich nguyen nhan sy tdn tai ciia nhumg cinh rimg cay gd vdi thinh phin da dang ve loii vi cau triic thing dung, ddng thdi phuc vy cdng tic danh gia kha ning ty hdi phyc ciia rimg nhift ddi sau tham hga bdi tac dgng nhan sinh L PHLTOTSG PHAP VA DOI TlTQNG NGHIEN ClTU Tir nim 1989 din nim 2008, nhdm tac gia cua Trung tam Nhift ddi Viet - Nga, co quan nghien ciru thudc Bd Qudc phdng Vift Nam v i Vifn Hin lam Khoa hgc Nga da tien hanh nghien cim hf sinh thai rimg mien Nam Viet Nam Qua ket qui khao sit v i nghien cim, da xic djnh dugc die diem phan khu hf thyc vat vi cau triic thing dumg cua rimg nhift ddi nguyen sinh sinh trudng d cac dieu kifn ty nhien khac (do cao, dia hinh, thd nhudng, dieu kifn thiiy van va hau d timg vimg) Trong qui trinh nghien cii'u da tim hieu die trumg sinh hgc cua hf cay than gd, loai cay chinh tao nen tang cho quan hf rimg, cu the: chu ky thien nhien, cic die trumg phan bd ciia qua va hat, dieu kifn de bao tir phat tan mam, phit trien cay gidng va cay non Vdi myc tieu mang tinh tdng hgp dugc dit nhu tren, da ip dung cic phuong phip cd tinh truyen thdng hifn dang dugc sir dyng rdng rii nghien cum sinh thii hgc cd tinh den die thii nghien ciru rirng nhift ddi De nghien cum td chirc khdng gian rimg, da sir dung bieu dia Iy thyc vat cd cic chi tiet md t i dieu tra dinh gii sy che phii ciia rimg tren nhtrng difn tich mau rimg bat bien va tam thdi d cic quy md khac Vifc nghien 1390 HQI NGH! KHOA HQC T O A N Q U O C V £ SINH THAI V A TAI NGUYgN SINH VAT LAN THLf BA ciru cau true Idp dat thd nhudng vi che nude dat rimg da dugc tiln hanh cd sir dung cic phuong phip truyen thdng nhu: dao phau dien Idn vi nhd, khoan Id thiing thd nhudng Da quan sit che tieu hau dudi nhirng tan rimg Ben canh do, de phyc vy hifu qui cdng tic nghien cim, da tham khao cd phan tich chgn Igc cac tai lifu, ban do, inh tu lifu va phdng vin cac nhan chiing - nhtmg ngudi tryc tiep tham gia va chimg kien cic tic ddng cua chien tranh n KET QUA NGHIEN CLTU VA THAO LUAN De huy diet thim thyc vat rimg nhiet ddi d Vift Nam, hiu het cic tmdng hgp, quan ddi My deu sir dung chat dift cd dugc tao tir hdn hgp axit diclorphenoxitaxetic (2,4 - D) va axit triclorphenoxitaxetic (2,4,6 - T) vdi ty If ngang Nhumg loai chat dift cd niy thugc nhdm hda chit kich thich tang trudng manh Chat dift cd tham sau vao thyc vat qua phien Ii, mim va re cay Hf va thim thyc vat bj buy hoai bieu hien qua cic hinh thii ben ngoai nhu heo iia, cong queo, van xoiy va cac bien ddi khac ve kich cd ciia Ii vi mim Rirng ngap man sinh trudng viing nude trieu cuomg ven bien d phan cudi phia Nam ciia bin dio Ddng Duong vi viing chau thd sdng Mekong dugc xem Ii vimg bj tdn thuang nhieu hon ci Mgt phin ldm Ii cay bi rung tic dgng ciia chat dift cd vi ldp hoi chit rii roi tren be mat ciia re sinh, re thudng va re hd hap dan den sy phi buy ning ne tinh trang cin bang mudi va gay dift vong hing loat cac loai cay gd Dudi tic dgng ciia chit dift cd mgt viing rdng Idn rimg ngap man cung da bj hiiy diet Hifn nay, tren khu vyc trudc timg Ii rimg dang dugc tien hinh ddc canh bang cich trdng cic loai cay than gd thugc chi Dude Rhizophora Rimg cay go hg Dau Dipterocarpaceae (trong dd cd rimg khgp) hinh thinh d mien Nam Vift Nam chii ylu tren dja hinh bang va bang phing cd dg cao - 6m tren myc nude bien vdi die dilm dit cd tinh chit din luu kem Den nay, nhtimg cinh rimg nhu vay dugc tri d tinh Tay Ninh chi Ii nhiimg khoanh rimg nhd (sit bien gidi Campuchia) Nhiimg khoinh rimg Icin chii ylu trii rgng gin vl phia vT dg cao ban (Rimg Qudc gia Yok Ddn, tinh Dik Lik) Trong ciu true rimg ciy gd hg Dau cd gin 40 loii cay than gd; ciu true dan giin v i die trumg thucmg cd ting ciy, tang tren phit trien tdt, tang dudi bj phin minh (hinh 1) Hinh 1: SOT mat dt ciia rung cay go hp Dau Trong do: Ap - Aporusa, Bmb - Bombax, Br - Bridelia, But - Butea, D.in - D intricatus, D.ob Dipterocarpus obtusifolius, D.t - D tuberculatiis Dill - Dillenia, Sh.o - Shorea obtusa, Sh.s - Shorea siamensis, Sind - Sindora, T - Dun moi, T.al - Terminalia alata, XI -Xylia Cic loai uu thi trgi gdm: Dipterocarpus obtusifolius, D tuberculatus, Shorea obtusa, S siamensis (Dipterocarpaceae) va Terminalia alata (Combretaceae) Ben canh^dd, cdn ghi nhan cic loii: Albizia chinensis, Bauhinia malabarica, Butea monosperma, Sindora siamensis, Xylia xylocarpa (Mimosaceae), Bombax aneeps (Bombacaceae), Bridelia glauca (Euphorbiaceae), Careya arborea (Lecythidaceae), Cratoxylum cochinchinensis (Guttiferae), Dillenia pentaginata (Dilleniaceae), Schleicherea oleosa (Sapindaceae), Gardenia sootepensis, Morinda 1391 HQI NGHI KHOA HQC T O A N Q U O C V £ SINH THAI V A TAI N G U Y £ N SINH VAT LAN THLf BA tomentosa, Mytrogyna rotundifolia, Neonauclea sessilifolia (Rubiaceae), Irvingia malayana (Irvingiaceae), Premna latifolia (Verbenaceae), Pteroearpus macrocarpus (Papilionaeeae), Quercus kerri (Fagaceae), Spondias pinnata, Semecarpus sp (Anacardiaceae), Strychnos nuxplanda (Loganiaceae), Terminalia mucronata (Combretaceae), Vitex peduncularis (Verbenaceae) Die diem ndi bat ciia rimg khgp Ii tang cay than thao phat trien tot vdi dai difn \k Amndinaria pusila, cd dg cao 0,5-1,5m, dg che phii dat 70-100%) Nhtmg khu rimg khgp d tinh Tay Ninh, thugc vimg timg bj phun rai tap tmng chit dift cd va bom napan, diu da bj buy dift Hien tren dien tich rimg trudc deu da dugc canh tic bing cay ndng nghifp hoac cay than go phit trien nhanh thugc cac chi Acacia va Eucalyptus, d nhirng vimg dat khdng dugc cai tao da hinh nhiimg quan xa thyc vat than thio vc^ri dai difn ciia hg Cd nhu Imperata cylindrica, Pennisetum cf polystachyon va Themeda amndinacea chilm uu thi d day khdng dien sy tai sinh ciia cic cay than gd va hoi smh cua nhtmg canh rimg Tren nhiimg vimg dit feralite thoit nude tdt d dong bang mien Nam Vift Nam, dg cao 30 70m so vdi myc nude bien di hinh nhtimg canh rimg cay go hg Dau cd than cao vdi to chiic khdng gian phiic tap, cd tir - ting (hinh 2) Die tnmg cua rimg cay go hg Diu than cao dugc xic djnh qua ket qui khio sit d nhirng manh rimg d Hieu Liem, Ma Da va VTnh An, noi cdn tri dugc cau tnic nguyen sinh sau tic dgng cua chat dift cd (Kuznestov, 2003) Trong phan cau t?io rimg cd hon 400 loai cay than gd (trong so dd cd 140 loai chu dao), hf thyrc vat phong phii vdi cic hinh thii cay day leo (hon 130 loai), thyc v|it bi sinh va thyc v^t bin bi sinh Hmh 2: Sff mat cat cua rirng cay go hp Dau than caoffviing dat sau thoat nude Trong dd: Acr - Acronychia, Agl - Aglaonema, Anc - Aneistrocladus, Ard - Ardisia, Bar Barringtonia, Bau - Bauhinia, Buch - Buchanania, Cin - Cinnamomum, CI - Calamus, Clph Calophyllum, D.d - Dipterocarpus dyeri, D.t - Dipterocarpus turbinatus, Dios - Diospyros, Dis - Dischidia, Dm - Drynaria, El - Elaeocarpus, Eur - Eurycoma longifolia Gar - Garcinia, Gon - Gonocaryum, Or Grewia, Irv - Irvingia, Kn - Knema, L - Lasianthus, Lag - Lagerstroemia, Le - Leea, Lie - Licuala, Lits Litsea, Mang - Mangifera, Met - Metadina, Neph - Nephelium, Part - Parthenocissus, Pin - Pinanga, Pit - Platycerium, Pol - Polyalthia, Pot - Pothos, Psy- Psychotria, Pter - Pterospermum, Rh Raphidophora, Rin - Rinorea, Sag - Sageraea, San - Sandoricum, Sap - Saprosma, Sc- Scaphium, Sh Shorea, Ster - Sterculia, Syz - Syzygium, T - dun moi, Tae - Taenitis, Tar - Tarrietia, Uv - Uvaria, Xr Xerospermum, Zin - Zingiberaceae Phan ting tren cimg (phan ting 1) chilm uu thi vdi dai difn la loii Dipterocarpus dyeri (Dipterocarpaceae), dg cao cua cay 40 - 55m Phan ting hinh tir nhirng loai dong trgi 1392 HQI NGH! KHOA HQC TOAN Q U C V £ SINH THAI VA TAI N G U Y £ N SINH VAT LAN THLf BA than gd hg Dipterocarpaceae nhu Dipterocarpus turbinatus, Shorea roxburghii, Anisoptera costata, Hopea odorata; nhumg loii cay khic cd: Irvingia malayana (Irvingiaceae), Mangifera cochinchinensis, Swintonia floribunda (Anacardiaceae), Parinari anamensis (Chrisobalanaceae), Lagerstroemia ealyculata (Lythraceae) va Tarrietia Javanica (Sterculiaceae) Phan tang gom cac loai cay than gd dugc cau hr ban 30 hg khac Phan ting dai difn co bin Ii hg Annonaceae, Lecythidaceae, Myrtaceae va Icacinaceae, cdn phan tang cd hg Euphorbiaceae, Melastomataceae, Myrsinaceae, Rhizophoraceae, Rubiaceae va Violaceae Ting thin thao bj phan manh dudi "bdng tdi" ciia rimg Ket qui phin tich mau chat diet cd cho thiy, rimg ciy go hg Diu d miln Nam Vift Nam bi tin phi d cic mirc dg khic Ngugc lai, d mgt so difn tich Icm cua rimg vin tri dugc md hinh td chirc khdng gian die tnmg ciia hf sinh thii rimg nhiet ddi nguyen sinh De hilu dugc hifn tugng niy can phii chii y den cac van de ve hf sinh hgc rimg va cic khia canh sinh hgc ciia nhtrng loai cay chii dao rimg De cd ddi tugng so sinh, chiing tdi da nghien cuu cac loai ciy gd hg Diu la loai cay gd ua sing, than thing, cd khdng gian thoing ciy cdn d cao thap va dan sit trudng Trong nhtmg quin the thyc vit rimg niy, cic loai ciy dugc sinh trudng tir hat Nhu da xic djnh, cay gd hg Dau gitr vai trd la loii lip quin Sy khic bift gitira cic kieu rimg dugc nhan biet qua md hinh td chuc khdng gian cua ting cay go (sd ting la 1-2 tang ddi vdi nhdm cay ua sing so vdi 4-5 ting d rimg tmdng thinh, cay mgc dan sit nhau), qua phan cau true va da dang hf thyc vat (cy the, nhtimg ciy d nhdm thugc 40 loii so vdi 400 loii cay d nhdm 2), qua sy tdn tai ciia tang cd mgc phit trien d rimg sing va mgc timg mang d nhtimg khu rimg kin Ngoai ra, ciing quan sit thay sy khac bift ve die diem sinh hgc ciia cic loai cay lip quan, sy khic bift d cic vimg tieu hau rimg, d sy cau vi CO che thuy vin cua dit trdng Cac nghien ciiu ciia chiing tdi cung chirng minh ring, d cic khu rimg cd cau tnic nhieu tang phiic tap, thing dimg, Ii phien mdng, cinh nhanh, than gd vi ldp thim myc khien nhtrng com mua nhd (lugng mua tir - 6mm) bj "chin ngang" di cjua cic tang cay va diy Ii nguyen nhin ngin cin sy xim nhap ciia nude quyen vao dat Cd the thay, so lugng the huyen phii cua chit dift cd phun ric len cic tin cay thap ban 1mm (tuong duong vdi mua quyen), vi vl cin bin, tren Ii, cinh nhanh, vdm Ii ciia ting tren cimg van cdn lugng thuoc ling dgng lai.-Cd le, chi d nhtrng noi "ciia sd" ciia rimg, chat dift cd mcii cd the roi ling xuong tang cay thap nhat vi ldp dat be mat Do dd, nghien cim nhimg khu rimg cd ciu true phirc tap, sy that chi Ii sy tiep xiic cua chit diet cd vdi re cay la khdng the Hoin toin chi Ii sy tiep xuc vcii cic re minh, ua boat dgng cua cay d ting phia tren, nhtimg re niy bi mit di theo miia (vao miia khd khdng bit gap nhdm rl nay) Nhd bin nang ciia cic kieu rimg ciy go hg Dau tmdng thanh, sau mdi dgt la rung, ldp Ii mdi dugc hinh (tuy nhien, qua quan sit, chiing thucmg bj iu trimg loai bd sit an mit), ldp la tren nhirng cay to ciing bj ryng, trd nen it hon sau qui trmh ty chong chgi lai chit dift cd Rd rang Ii nhimg cay niy bj ylu di, my nhien phin Idn cic tmdng hgp chiing khdng bj chit Thdi gian im ucit keo dai, sau miia mua da tao dilu kifn cho qui trinh phyc hoi tinh trang cic loai cay tren d mgt miic dg nhat dinh Vifc sir dyng chit dift cd theo cich khac ciing cd anh hudng din rimg ciy go hg Dau it tang (tang thip) Do ciu true thing dimg don gian ciia rimg (1-2 ting) vi khoang each thua giira cic cay, nen lugng chit dift cd phun rai cd dilu kien tilp xiic tdi da len cic tan cay Sau ryng Ii, than khdng cdn chira nhilu dudng chit dl nudi cay, rl ciy khdng in din ldp dit im, phan Idn nhtmg Ii mdi mgc khdng phat triln dugc, ciy bj ylu di vi chit Kit qui phdng vin nhtmg nhan chimg cua chiln tranh tai cac -vimg bi phun rii chat dift cd cung chi nhu vay 1393 HOl NGHI KHOA HQC TOAN Q U C V £ SINH THAI V A TAI N G U Y E N SINH VAT LAN THLf BA Rimg nguyen sinh Rimg sau nhieu \hn sii dung chat di$t c6 • Rimg bi huy ho?i bang bom napan • Su phat trien cua quan the thuc v?t voi uu the ciia cic lo?ii co "tien phong" •Trong logi cay Acacia thay the nhimg lop rimg nguyen sinh da chet Hinh 3: Qui trinh bien doi rirng nhift doi Cic nghien cum thir nghiem vl chit diet cd ddi vdi thim thyc vat rung dugc tien hinh kit hgp ddt bing bom napan (md phdng thyc tl) Tuy nhifn thi nghifm diu tien cd sii dyng bom napan de buy diet rirng nhift ddi cay gd hg Diu mgc diy da cho thiy rimg khdng chiy, chinh xic hon la lira khdng Ian rgng rimg cay gd trudng Nguyen nhan Ii co chi tilu hau d tang rimg thap va trudc het la dg am khdng cao (d dg cao dudi 2m, quanh nim am tuomg ddi dat tren 70% vl ban va din ngudng 96 - 100% ve chilu mugn va dem) cic tang gin mat dat hau nhu khdng cd sy luan chuyin khdng Chilm vai trd quan trgng viec khdng de lira Ian rdng Ii ciy gd trudng ndi chung, cay go hg Dau ndi rieng, cd die tinh chay rit thip - O cic rirng cay gd hg Dau mgc thua hon, tinh trang xay ngugc lai Tai day bom napan kit hgp vai chit diet cd cang lim tang miic dg nguy hiem doi vdi rimg, tham chi nhumg khu rimg cdn sinh nhift rndt each ty nhien va cic cay chi cd nang chdng chju trudc tic ddng ciia nhumg dam chiy ngan, nggn lira thap Sau hr xir ly chat diet cd, cay bj rung la vi khdng thi hdi phuc, thim chi bj ylu di vi chit Sd lugmg cay chit cing nhilu va din Icin horn so cay cdn sdng Nhtimg cay khd dl dang bj boc chiy bj tie dgng ciia bom napan Cac vet chiy tir nhya tren than cay va canh nhanh ciia cay gd diu d rimg sang tao nhtrng d lira nhd giy 1394 HQI NGHI KHOA HQC TOAN Q U O C V £ SINH THAI VA TAI N G U Y £ N SINH VAT LAN THLf BA chiy Icin Nggn lira se cang manh len gap gid, nhat la im khdng thip (< 50%o), cd khd vi Ii rung nhieu _ Nhumg nhin td tie ddng neu tren chua dii dilu kifn dl nhumg khu rimg cd nhieu ting tin, ciu triic phirc tap chdng chiu tot vdi tic ddng cua chit dift cd Bdi le, nlu bj tic ddng nhilu lin ket hgp vdi sy phi buy ciia bom napan thi chimg cung bj hiiy dift Kit qui khao sit d khu vyc dgc mgt so tryc giao thdng cd tinh chiln luge thdi gian chiln tranh da minh chiing cho dieu dd Hon niira, theo Idi ke ciia mgt sd nhan chimg, nggn lira lan rit nhanh rimg bi "rot diy" bom napan Nhtimg khu rirng chay sau dd dugc dgn sach bing miy dio vi miy iii Die bift, dgc cic dudng loii cd Pennisentum polystachyon (Gramineae) da dugc gieo Sau chien tranh, khu vyc dugc dgn quang, din thdi dilm hien tai nhilu noi so dd da dugc phu bdi rimg trdng (mgt sd loai cay cd nguon goc tir Chau Uc nhu Acacia vi Eucalyptus) va cd xen lan cay luong thyc, hoa mau Nhumg viing dit chua dugc cii tao dl lam dit hifn vin dang bj cd phii kin, sd dd chii yeu Ii cic loai cd thin thio gidng lau, liia Dilu quan trgng can phii nhan manh, qua trinh khdi phuc, tai tao rimg tai nhimg viing dat da bj tin phi chien tranh (dat hoang) khdng hoan toan dien theo quy luat ty nhien Cic loai cd mgc chii ylu d day Ii Imperata cylindrica, Pennisentum polystachyon vi Themeda amndinacea (Poaceae), Eupatorium odoratum (Compositae).- tao thinh mgt quin the ben vumg Khi ning khdng the phat trien hf thyc vat rimg d khu vyc trudc timg Ii rimg cd lien quan vdi sy thay ddi rd rft cua che tieu hau vi ket cau dat, ciing nhu gin lien vcii die diem sinh hgc cua hf thyc vat rimg Theo quan sit ciia chimg tdi, sau mat di tim chin la cic tin cay d ting cao (tang vi 2), cay gidng (tang dudi) ciia cac loai cay chii dao (dg cao khoing 46m) bj yeu di, cdn Icip cay mam va cay non thi bj chet Ciing theo nguyen nhan nay, khai thic trdng rimg d nhumg khu vyc Id thien, noi be mat dat dudi tic dgng tryc tiep ciia sire ndng mat trdi va nhift len den 50°C, bj xem nhu Ii khdng the Chiing tdi cung ghi nhan, tim chin Ii ldp vdm ciy bj mat di, be mat dat se bj thieu ddt cimg vdi sure ndng ciia mat trdi vi phii chju tic dgng xdi mdn nude mua Dieu dan den hifn tugng, chi qua miia mua, ting dat tren cimg bj phi hiiy vi tao ddng chiy nhd tain thdi, cdn tren be mat xuit hifn ket hach laterite chira oxit sit Dudi tic dgng ciia nhift dg cao, leap laterite tren cimg cd be diy - 5cm bj nung ndng vi ket thinh phien each difn ben vumg, lim cho cic loai re ciy khdng the xuyen qua dugc vafeonen die tinh khdng thim nude m.FCETLUAN Lay dien hinh la rimg nhiet ddi gid miia d mien Nam Vift Nam, ket qui nghien cum ciia chiing tdi da chimg minh, mac dii rat da dang ve thinh phan vi ciu tnic, sau rimg bj phi buy toin bg khdng thay cd sy khdi phyc, tai tao lai ciia cic loai thyc vat rimg mgt cich ty nhien Do dd, rd ring la mgt sy trii ngugc, nhung dieu kifn hiu nhift ddi "thuan lgi" lai Ii nhan td chu yeu, tran ip sy phat trien ciia hf thyc vat rimg Sy phi buy hf vi thim thyc vat rimg dan din vifc hinh thinh quan the ciy than thio mang die dilm cua thdi ky thd nhudng Nhtimg quin thi thyc vit nhu vay khdng phii Ii die trumg cua ty nhien vimg ddng bing Vift Nam Cinh quan trudc dugc bao phu bdi rimg, bj mit ludn ldp thyc vit rimg nguyen sinh Dilu quan trgng cin phai nhin manh, nhtmg loai ciy than thio mgc tai nhumg khu vyc niy khdng thich hgp dl chin nuoi gia sue Sir dung dit de canh tic cic loai cay ndng nghifp, cay cdng nghifp va trdng rimg ddi hdi cd kien thiic khoa hgc chuyen mdn de xay dyng nhimg bifn phap ky thuat vi img dyng chiing mgt cich thich hgp vdi mdi tmcmg sinh thii 1395 HQI NGHI KHOA HQC T O A N Q U C V £ SINH THAI V A TAI N G U Y £ N SINH VAT LAN THLf BA TAI L I f U THAM KHAO B e t h e l J S., Turnbull., 1975: Military defoliation of Vietnam Forests //American forester, 81(1): 26-30, 56-61 Phung Tuu Boi, Le Van Cham, 1994: The effects of herbicides on vegetation in forest of South Viet Nam// The 2"'' International Symposium