HQI NGHj KHOA HQC T O A N Q U O C V £ SINH THAI V A T A I NGUYgN SINH V A T L A N THl> 5 + Pliuang phdp nghien ciru: De giai quyet tdt cac nhi?m vy dgt ra, da sir dyng nhieu phuang phap khic nhau, trong dd cic phuang phip chu dao la:
- Phucmg phdp hdi cuu sd U^u: Cic sd lieu ve quy md, mat dg phun rai CDC dugc xac djnh dya tren cic sa dd bang phun rai do quan ddi MJ cung cap [9]. Ben cgnh do, so Ii$u ve di§n tich rimg bj phun rii CDC va hoat dgng cua chien tranh dugc tham khao tu cic tai li$u khic nhau, la kit qui nghien ciru cho cic viing d mien Trung vi Tiy Nguyen [1,4, 6, 7].
- Phuang phdp nghien ciru dja thi,rc vdt: Nghien cim dia thuc vat dugc tien hinh theo cac tuyen va tgi cic d tieu chuan tgm thdi. Xac djnh cac Ioai ciy dugc tien hinh tren ca sd nghien cuu tdng hgp cic diu hi?u ve hinh thii. Ngoii thyc dja, viec dinh danh cay chii yeu tdi bge chi. Vifc xic djnh ten loai dya theo tai lieu cua Pham Hoing Hd "Cay cd Viet Nam" tgp I, 2 vi 3 [2]. Ten ggi hg vi chi cua thuc vat cd hoa theo he thong phan logi cua A. Takhtajan (1987). Khi xem \it die diem cau triic dirng ciia quan xa thyc vat, tien hanh md ti chi tilt theo cic ting cay dimg.
- Phirang phdp bdn dd, h? thong tin dia ly (GIS): Phuang phap nay giiip nhan biet linh tho Gio Linh mgt each khai quit vi nhanh nhit. C a s d d i i lieu dudi dang bin do khdng nhOng cdy nghTa ve mat phin bd khdng gian cua cac thinh phan mdi trudng nghien ciiu ma con chi ra nhirng thugc tinh ciia ddi tirgng theo tirng khu vyc cu the. Phuang phip nay cung dugc ip dung de thinh lap ban dd he sinh thai nhan sinh huy?n Gio Linh d ty le I/IOO.OOO phyc vy cho vijc
md ti cic don vj, cac quan xa thuc vat die trung. I - Phuang phdp so sanh, ddnh gid long hgp: De phin tich vi dinh gii sy bien ddi cia h^
sinh thii, quin xa thyc vat vi cic thinh phan mdi trudng, viec so sanh sd lieu thu th§p dugc la fit quan trgng. Co sd tii li^u dimg so sanh la kit qua nghien ciru ciia chiing tdi tgi rit nhilu dja diem d mien Nam Viet Nam vi sd lieu thu dugc tgi Khu Bao tdn thien nhien Dak Rdng, tinh' Quang Trj-noi khdng chju tac ddng ciia CDC de ddi chiing.
H. KET QUA NGHIEN ClTU VA THAO LUAN
1. Hoat dgng chien tranh hda hoc d Quang Tri va huy|n Gio Linh
Vdi vi tri dia chiln luge vi quin sy quan trgng, Quing Tri dugc xem la tuyen lira ciia cupi chien tranh chdng My. Dl thiet lap vanh dai tring, quan dgi My da su dyng nhilu bi?n phi|
khac nhau, trong dd tic dgng ndi bgt ddi vdi tii nguyen va mdi tnrdng la vifc sii dung CE)C o chira dioxin rii xudng nhij'ng khu vyc cd thim thyc vat, die biet Ii thim thyc vat ty nhien.
Theo kit qua thong ke tir nhilu ngudn tai Ii?u khac nhau, trongdd cdtii li?u ciia Bp Quo ^ phdng My, dien tich rimg bi tic dgng trong gidi han huyen Gio Linh tip trung nhieu nhatl tuyen lua vT tuyIn 17 dgc sdng Ben Hai, keo dai tir khu vyc Cdn Tien-Doc Mieu len giap bi6 gidi Viet Lao thugc dja bin cic xi Linh Thugng, Hal Thai, Linh Hai, Gio San, Gio Hoa, Gi^
Chau [5, 9]. Mirc do va pham vi phun rai rat khic nhau, trong dd cd mdt s6 di?n tfch chju non dg phun rii tren l.OOOgal/km^ Nhieu dien tich cdn Iai cd nong do phun rii trong khoing201 I.OOOgal/km^ Ciing vdi tic ddng hdn hgp cua bom dan va bom chay napal, nhiitig di|n tich ,|
phun rii da trd thinh dit trdng hoac trang cd. Sau nay chi cd mgt phin dien tich rat nhd ph|
hdi thanh rimg.
2. Bac diem cau triic cac quan xa thuc vat nhan sinh dac trung '
* Qudn xa thirc vgt rirng nhdn sinh & dp cao 100-300m
Quin xi nay cd di?n tich khoang 1.590ha, phan bd chii ylu d khu vyc phia Tiy, Tiy Bac'
Linh Thugng. '
HQl NGHj KHOA HQC T O A N Q U 6 C V £ SINH T H A I V A TAl NGUYEN SINH V A T L A N THCf 5 Da ghi nhan nhirng ciy gd non vi cic chdi nhinh mgc len tir nhirng gdc cyt, cd chilu cao tir 1,5 din 4m vdi cac chi: Chi Budi bung Acronychia (Rutaceae); chi Sua Alstonia (Apocynaceae), chi Doi Archidendron (Mimosaceae); chi Trie Dalbergia (Fabaceae); chi Cam ngugi Ardisia (Myrsinaceae); chi Mit Artocarpus, chi Rudl Slreblus (Moraceae); chi De gia Breyniopsis (Euphorbiaceae); chi Mdc Caryota (Arecaceae); chi Que Cinnamomum, chi Bdi ldi litsea, chi Bdi Id! nude Neolitsea va chi Khio Phoebe (Lauraceae), chi Thinh nganh Cratoxylum, chi Bira Garcinia (Clusiaceae); chi Dirc diep Daphnyphyllum (Daphnyphyllaceae);
chi Thj Biospyros (Ebenaceae); chi Cdm Elaeocarpus (Elaeocarpaceae); chi Cd ke Grewia (Tiliaceae); chi Dan Ixora, chi Liu Psychotria, chi Gang Randia (Rubiaeeae); chi Miu chd Knema (Myristicaceae); chi Bing ling Lagerslroemia (Lythraceae); chi Sim Memecylon (Melastomataceae); chi Nhgc Polyalihia (Annonaceae), chi Trdm Slerculia (Sterculiaceae); chi Den Fi/eJT (Verbenaeeae).
Day leo khi phong phu v i da dang, vdi cic dgi dien thugc chi Bac thau Argyreia (Convolvulaceae); chi Miy Calamus (^Arecaceae); chi Gim Gnetum fGnetaceae); chi Ngiy Rubvs (H.osaceae); chi Chac chiu Telracera (Dilleniaceae); chi Bii de Uvaria ^Annonaceae), mOt sd loii thugc hg Connaraceae, hg Menispermaceae. Cac loai than thao cd chi Re quat Dianella fPhormiaceae); chi Huyet giac Dracaena (Dracaenaceae); chi Da cim Hedyotis Rubiaeeae). Ben cgnh dd, cung da ghi nhin dugc nhirng dai dien thyc vat die trung ciia khu vyc bi phi huy nhu chi La nen Macaranga (Euphorbiaceae); chl Hoing mgc Zanthoxylum Rutaceae), chi Thdi haAlangium ('Alangiaceae).
Nhu vgy, vdi nhimg thinh phan trong quan xa hien tgi, ciing vdi nhirng ket qui qua phdng van cu dan dia phuang, hdi cuu so lieu cho phep di den nhin djnh; Tgi khu vyc nay trudc chien tranh di tirng tdn tgi kidu rirng kin nhiet ddi thudng xanh die trung ciia viing dat thap mien Trung Vi?t Nam.
Kieu quin xi nay hi?n tgi cung ghi nhgn dugc tren cac dang dja hinh thip vi dgc theo nhung bd sudi, song vdi cic dien tich nhd (400-500m"). Trong thanh phan td thanh loii, da ghi nhan dugc cic loii nhu Ka nia Irvlngla malayna (Irvingiaceae), Sti'a Alstonia scholaris (Apocynaceae), chi Thinh nganh Cratoxylum fClusiaceae), chi Cd ke Grewia (Tiliaceae), chi Xang miu Horsfieldia fMyristicaeeae), chi Sdi Lilhocarpus (Tagaceae), chi Cg Livislona (Arecaceae), chi Ngii gia bi Schefflera (Araliaceae), chi Tram Syzygium (Myrtaceae).
Theo quan sit qua nhieu dgt khao sat, mac dii cac cay gd rirng ra hoa, ket qua, nhung nhirng cay non cua chiing khdng thi phat trien dugc vi bj dim ciy hda thio che phii, khdng the thoat ra ngoii chd trdng. Ket qui la nhung manh rirng kieu "kham" khdng cd dugc xu hudng phit trien rgng. Nhu viy, d day khdng ghi nhan dugc qui trinh dien the ma trong do cic cay gd rimg phit trien cd the lin chiem dugc nhiing lanh thd mdi, loai bd cic tring cd-cay bui (tham chi khi nhu'ng lanh thd dd nam ngay canh cic khu rirng).
* Quim xd thitc vgt rirng nhan sinh & dp cao tren 300m
Tren dja ban huy?n Gio Linh, kieu quin xi niy c6 di?n tich I.lOSha, phan bd khu vyc phia Tiy, Tay Bic xa Linh Thugng. Cic don vi cua kieu quan xi nay nam ndi tiep ngay phia tren ciia dai 100-300m.
Ket qui khio sit cho thay, tai cic khu vyc tiep giip vai cac quan xa cay cd cho den nay vin cdn duy tri dugc nhung manh rung ty nhien, mac du chimg da bj lac ddng vi bi phi buy mgt phan. Cay gd rirng mang ti'nh da trgi. Tuy vgy, tai mgt sd dia diem, tinh trgi chi cd d mgt sd hg va ciu triic rirng dugc phan hda thanh 3 ting tuang doi ro ret
1365
HQl NGHj KHOA HQC T O A N Q U O C V £ SINH THAI VA TAl N G U Y £ N SINH VAT L A N T H Q 5 - Ting tren cimg (ting 1) cd chieu cao 17-20m, dudng kinh thin ciy 40-70cm, d gdc nhilu loai cay phit triln nhirng re banh ve nhd; tan day, nen chat, hinh oval hoac ciu, ban kinh tan khoing 2-3m. Td thinh loii gdm Siia A. scholaris (Apocynaceae), Ka nia /. malayana (Irvingiaceae), Bing ling di Lagerslroemia caliculata (Lythraceae), Dau tam Morus album (Moraceae), Huynh Tarrieiia javanica. Long mang Pterospermum heierophyllum (Sterculiaceae), Thau ITnh Alphonsea sp. (Annonaceae), cic Ioai De Caslanopsis spp., Soi Lilhocarpus spp. (Fagaceae), Que Cinnamomum sp. (Lauraceae), Cdm Elaeocarpus sp., Nhim nude Sloanea sp. (Elaeocarpaceae), Boi ldi Litsea sp. (Lauraceae), Chan chim Schefflera sp.
(Araliaceae). C) khu vyc chin sudn, nai cd nhilu suoi va thic nude, tinh trgi thugc vl loii Chan chim Schefflera sp., trong khi tren dgng dia hinh sudn vi dinh, tinh trdi thugc ve cac loii ciia hg De (Fagaceae).
Hinh 1. Mat cat dimg quan xa thirc vdt rung nhdn sinh & do cao tren 300m khu v\rc go doi huyen Gio Linh
{Mst'Alslonia, dn-Cinnamomum, Dios-Diospyros, E\-E!aeocarpus, Eur-Eurycoma, Vk-Ficus, Gdi-Garcinia, Gir-Gironniera, Gon-Gonocarium, Lag-Lagersiroemia, Laur-l^auraceae, Lilh-Lilhocarpiis, Lils-iiaea, Liv-Ln'islona, Ma^-Mangifera,
?oii.T\-Podocarpus nertfoHus, ?o\-PoIyallbia, Ptct-Plerospermum, Q-Quercus, Scf-Scheffiera, Su-Slreblus, TaT-Tarrietia, Vit-Viiex sp.)
Ting 2 cao 6-11 m, ciu triic tir cac loai Budi bung Acronychia pedunculata (Hutaceae), Lgc virng Barringtonia sp. (Lecythidaceae), Thanh nganh Cratoxylum sp., Biia Garcinia sp.
(Clusiaceae), Chdm chdm Nephelium sp. (Saplndaceae), Nhgc Polyalthia sp. (Annonaceae), Trim Syzygium sp. (Myrtaceae), Den Viiex sp. (Verbenaeeae). Dilm dgc trung ciia ting 2 la sy cd gdp mat cua loii Cg kich thudc ldn Livislona sartbus (Palmae), cay cao tdi 6-8m. Tgi mgt so dja dilm, loai Cg L. saribus mgc thanh khdm. Loai nay ghi nhgn dugc ca d khu vyc chin, suim vi dinh ddi.
Ting 3 cau tgo tir nhiitig cay cao 2-5m, bao gom cic loii: Diing dinh Caryota miiis, Mdc cgc Licuala sp. (Palmae), Bach benh Eurycoma longifolia (Simaroubaceae), Thy dio Gonocaryum siibrostratum (Icacinaceae), Chdi mdi Anlidesma sp., De Breynia sp., Diep hg chau Phyllanthus s^.
(Euphorbiaceae), Cam ngudi Ardisia sp., Dan nem Maesa sp. (Myrsinaceae), Cong Calophyllum sp. (Clusiaceae), Dan Ixora sp., Xu huang Lasianthus sp., Liu Psychotria sp.
(Rubiaeeae).
Hi?n tugng ciy non cua nhiJng cay gd rimg khdng thi phit triln ra ngoai dim cd, ciy bgi
HQI NGHI KHOA HQC TOAN QU6C V£ SINH THAI VA TAI NGUYEN SINH VAT LAN THC 5 tnhSn djnh ban diu ve khi nang phyc hdi rimg sau tie ddng ciia CDC hoac khdng diln ra, hoic dien ra vd ciing cham chap.
* Trdng cd cdy b^i nguon g6c nhan sinh
Do tic ddng manh liet cua CDC va bom napal, nhieu dien tich rimg da bj phi huy va hinh tiianh n6n cic kilu tring cd, tring cay bui, phan bd rgng khap trong viing, tir do cao dudi 100m den nhirng khu vyc tren 300m. Dii vay, trong thinh phin cau tnic, td thanh loai thyc vat ft cd sy khac biet. Diem khic biet thi hien chi d miic do phong phu vi sire sdng thyc vat theo tinh chit cua dit va tilu khi hau. Theo dd, thyc vat trong tring cd cay bui li nhirng quan xa cd thanh phin ddng uu tr^i la Cd dudi voi nhieu gie Pennisetumpolystachyon va Lau Eryanthus arundinaceus.
Mgt si dien tich ghi nhin dugc loii trdi la Cd tranh Imperaia cylindrica. Loii Cd dudi voi nhilu gie dgt tdi chilu cao 120-150cm va Lau cd ki'ch thudc dat tdi 220cm chilu cao.
Ngoai nhifng loii cd kl tren, trong khu vyc nay cdn ghi nhan dugc nhu-ng loai thuc vat nhu Duong xi Pteridium aquylinum, chilu cao tdi 120cm, Cd lio Eupalorium odoratum, Eupatorium spp. (Asteraeeae), Re quat Dianella nemorosa (Tormiaceae), Ludi thio Lindemia spp.
(Scrophulariaceae)...
DO che phii tai nhung khu vyc nay dat tdi gan 100%>. Ting cd cd mat do day dac nhit d do cao 30-80cm. 0 mgt vai nai, nhirng khdm cay cd nim cinh nhau khoang 30-50cm. Vao miia kho thyc vat vin tiep tuc phat trien mgnh va nhu'ng phan cay Ii tren mat dat khdng bi kho vi chet. Tren mgt dat van quan sit thiy nhirng la cd chet, nhung chiing khdng dii dl tgo thinh Idp la ryng.
Trong nhu'ng tring cd ciy byi niy, da ghi nhan dugc nhu'ng loai tien phong va mdt sd cay go rimg. Nhirng loai tien phong thugc chi Ba soi Macaranga, Ba bet Mallotus /Euphorbiaceae), chi Mua Melasloma (Melastomataceae), chi Hu day Trema (Ulmaceae) va chi Hoing mdc Zanthoxylum (Rutaceae). Chieu cao ciia cay tdi 2,5m. Nhimg loai tien phong nay thudng la cic cay thich nghi vdi vdi ddi sdng cd do chieu sang manh (ven dudng vi d nhirng noi ma ldp cd da bi con ngudi phi huy). Tai nhiJng dia diem nay, khdng quan sat thay trudng hgp khi _ma cic nhdm cay tien phong hinh thanh, tin ciy sit vio nhau, che inh sing mat trdi va loai bd dugc ldp cay cd ben dudi, gidng nhu quan sat thay d nhirng rirng cay dang phuc hoi.
NhCfng cay rirng cd chieu cao tdi 6m, thudng la nhung loii thugc tang thap nhat cua rirng cay gd nhu Triic tiet Caralha sufriiticosa (Rhizophoraceae), Chdi mdi Anlidesma sp.
(Euphorbiaceae), Dirc diep Daphnyphyllum sp (Daphnyphyllaceae), Dan Ixora sp. (Rubiaeeae).
3. Sir bien ddi va dien the thyc vat sau tic dgng ciia CDC
Viec sir dung CDC lam cho cay go rirng va diy leo bi rung la. Tuy vay, sau khi rirng bi phun rai lan dau thi phan Idn cay gd rirng deu cd kha nang phat trien la mdi. Neu rirng bj phun rai nhieu Ian se dan den ciy gd vi cac loai thyc vit khic bi chet va sau dd bom napal dugc su dyng de huy diet hoan toin tham thyc vgt rirng.
Tren nhirng khu vyc bj mat di thim thuc vit rirng, hat cua cac loai thyc vat tien phong dugc gid dem tdi, ma chii yeu li cac Ioai cd vdi dai dien ciia chi Imperaia, Penimetiim, Themeda (Poaceae) va Eupalorium (Asteraeeae). Sau mot miia mua, cac loii cd niy phat trien dat chieu cao tdi 2in, hinh thanh cac bui cd, ra boa vi cho hat rat nhieu. Nhu vay, chi sau mdt thai gian ngan cic khu vuc trdng da bi nhirng loai cd than cung xam chiem. Vao thdi ky miia khd, nhung trang cd nay thudng bj ddt do chii y hoac vd y ciia con ngudi.
Ket qua nghien cuu cho thiy, nhung khu vyc rirng bi huy diet bdi CDC thi sau do khdng lau, tgi dd da hinh thanh nhirng quin xa thyc nhan sinh vat gom clui ylu tir cac loai than thio.
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HQl NGHI KHOA HQC T O A N Q U O C V £ SINH THAI V A T A I N G U Y £ N SINH VAT L A N THU 5
Sau chiln tranh va cho den hien nay, van chua cd hogt ddng cai tao dit nio (thim chi cd nai vin chua ra phi xong bom min). Dien hinh trong sd dd phii ke den dja bin xa Linh Thugng, la mgt trong nhiJng nai chju hau qui ngng ne nhit. Tgi diy, tring cd va tring cd cay bui khdng dupe thay ddi theo hudng thay thi bing quin xa thyc vat rimg, tham chi nhilu khu vyc cdn chua dgt tdi kilu tring cd ciy bui dac trung. Dien tich tring cd tren nen dit bi bio mdn d Gio Linh dgt tdi 12.000ha trong tdng sd khoang 18.300ha tring cd, trang cd cay bui (hinh 2).
Dieu dang luu y la trong dieu kign ty nhien, nhiing Ioai ciy gd tao rimg lai phyc hdi dugc tren dit ddc bing dien the "man rirng-cua sd". Cay rirng khdng cd ca che ty phat tan hgt ra cy ly xa. Hat v i qui cua mot s6 loii cay chi cd thi phit tin di xa nhd gid. Ddi vdi nhieu loii chim-chu thi gieo hgt thi chimg can phai cd cho dau, nhung d tring cd thi khdng cd dieu kien nay. Tuy viy, theo quan diem cua chimg tdi, dieu ca bin li ciy gd rimg nhiet ddi khdng cd khi nang phat trien tren nhiJng khu vuc trdng la do dac diem sinh hgc ciia chung.
Khac vdi cac loii cay gd rirng, cic loii cay thugc nhdm tien phong Iai phat trien rat tit trong dieu kien nhiet do, mirc do chieu sang gin vdi dieu kien d khu vyc trdng trai. Ket qua nghien ciru d Gio Linh va nhieu khu vuc khac d Viet Nam trong khoang 20 nim qua cho thay, nhu'ng loai thuc vat nay thugc cac hg: Araliaceae (Dan chau chau Aralia arinala);
Euphorbiaceae (Sdi tia Sapium discolor, Sdi tring S. sebiferiim; 14 loai thugc chi Macaranga, trong dd d mien Nam cd loai dac trung Ba soi long sao M. irichocarpa va 30 loai thugc chi Mallotus); Lauraceae (Mang tang Lilsea cubeba); Melastomataceae (14 loii thugc chi Melasloma, trong dd d mien Nam cd loai Mudi an bich M. osheckoides); Ulmaceae (Hu day Idng Trema orientalis, Hu day T. velutina); Rubiaeeae (Gio tiu Anihocephalus chinensis);
Rutaceae (Ba chac Euodia lepla, Cdc hdi Zanthoxylum rhetsa); Simaroubaceae (Khd sim nam Bruceajavanica); Verbenaeeae (khdng dudi 26 loii thudc chi CalUcarpa).
Hmh 2. Sir hinh thdnh qudn xd cdy thdn thao sau tac dgng cua chiSn tranh hoa hgc (I-Rimg cay g6 than cao diln hinh; 2-Khai thic quy md cdng nghifp (khai thic tring); 3-R£rng b| phun rai nhilu lin chit doc hoa hoc; 4-Su dyng bom chay napal; 5-Sy phat triln quin xS thyc v|t vdi uu the \i
HQl NGHI KHOA HQC T O A N Q U Q C V £ SiNH T H A I V A T A I N G U Y £ N SINH VAT L A N THO" 5
Kit qui nghien ciru cung cho thay, trong dieu kien binh thudng, sau 1 miia mua, cic loai M trichocarpa. T. velutina, A. chinensis da cd chieu cao tdi 150cm. Trong khi dd, chilu cao Idn nhat khi trudng thanh ciia 2 loai M. Irichocarpa, T. velutina li 8m, cdn loai A, chinensis la 20m.
Sau mdt thdi gian sinh trudng ngin cay da ra hoa, ket trii. Quan sit thyc te cho thiy, T. velutina da ra hoa chi sau 3 thing sinh trudng. Vdng ddi cua cac cay tien phong, theo udc tinh cua chiing t6i, ia tir 10 den 15 nam. Hang nam, cac cay tien phong deu ra trai va rat sai qui, tuy viy khdng thiy nh&ng cay con ciia chiing mgc ngay dudi tin ciy me. Nhihig loai cay tien phong kl tren thudng cd mat d nhifng "cua s6" rung, tren nhirng nai rimg bi khai thic chgn va ci nhiJng bai trong. Tai Gio Linh cung nhu nhieu viing bi rai CDC d Mien Nam Viet Nam, cac cay gd tien phong mgc quanh, bao bge lay rimg ciy than cao, hinh thanh mgt dai dem, cdn ggi la ddi chuyen tiep rit die thii gi&a rirng tu nhien (cd the nguyen sinh) va cac quan xa cd, thyc vit dang savan (hinh 3). Chieu rdng ciia ddi chuyen tilp dao dgng phd bien trong khoing 3 den 7m. Cac cay tien phong vdi toe do sinh trudng nhanh, cd vai trd quan trgng la bao ve be mat dit tranh bj birc xg mat trdi va trinh bj nude mua bao mdn. Ddng thdi, day ciing li eon dudng khdi phyc lgi nh&ng tham sd vi khi hgu d sit mgt dit rirng (ldp khdng khi tir 0 den 20cm).
Dudi tan nhung cay gd tien phong, theo thdi gian (3-4 nam), mim ciia nhuTig loii cay phit tan tu phia rirng cd the se phit trien tdt. Trong ddi chuyen tiep, da phat hien mam va cay non ciia cac loai Thinh nggnh C. formosanum (Cllusiaceae), Ka nia /. malayana (Irvingiaceae), Sao den Hopea odorata. Sen cat Shorea roxburghii (Ditperocarpaceae) v i Cim Parinari annamense (Chrysobalanaceae). Qua trinh niy dien ra tir khi nhung canh thip nhat ciia tin ciy tien phong dgt tdi dg cao l,5-2m each mat dat. Song song vdi sy lorn len cua cac loii cay gd rirng, tan che do cay tien phong tgo ra trong ddi chuyen tiep bi chia cit, mac dii cay rimg mdi chi dat tdi do cao ciia ldp cd. Dii bdng ram do cay gd rirng tao ra ciing vdi cay non trong ddi chuyen tiep dan day liii ranh gidi ciia cic quin xa cd v i tgo dieu kien md rgng dien tich phia dudi thyc vat rimg.
S^i bien ddi din din dieu kien vi khi hau dudi tan cay theo hudng tiep can vdi cic tham sd vi khi hau trong rirng, ciing nhu sy xuat hien gin khu vuc dit trdng. Nhung cay den tudi trudng thanh, ra hoa ket qua thudc Idp tren ciing ciia rirng, se thiic diy qua trinh khdi phuc rirng cay nhi?t ddi ban dja tai khu vuc dd. Tuy nhien, qui trinh "quay trd lai" nay cua cac loii ciy thugc ting tren ciing ciia tan rirng (cho du chi la mdt sd Ioai cay nio do) dien ra trong thdi gian rat dai, khoang tir 50 den 80 nam. Trong dieu kien thyc tai tgi Gio Linh cung nhu nhieu viing khic d Viet Nam, do mdi qiian hg "con ngudi-rirng nhiet ddi", qua trinh dien the nhu vay da va se rat khd dien ra, vi nhu thudng thiy, hoat ddng ciia con ngudi khdng ngirng giy ra nhung tic dgng tieu eye len cic khu vyc niy.
CJ Gio Linh, cic cay thudc ddi chuyin tilp khdng cd khi ning xam lin thanh dien tich rgng Idn khi hoan toan khdng cd cay rirng bin dja. NhiJng nai nhu viy chi xuit hien nhiJng dai dien dan Ie va hiem khi gap nhirng cum 3-7 cay ddi chuyin tiep. Ben trong nhirng cum cay nhu vay, dudi tin ciia chung khdng dien ra qua trinh phuc hdi cay rirng. Ciy ddi chuyen tiep khdng chen lan dugc vao ting cd rim rap, khong phat trien dugc tren nen dat bi bao mdn, rira trdi, dd la nhung nai mi thinh phin ly-hda cua dit da bj thay ddi, thim chi mgt sd noi da hinh thanh ldp vd feralit rin chic khdng hoac it thim nude. Nhu vay, qui trinh canh tranh sy sdng ciia nhirng cay gd cd khi nang sinh sdi d khu vyc phuc hoi ben trong rimg, nhung lgi khdng cd kha nang tdn lai dugc d nh&ng khu vyc bi mit rirng, khdng hoan toan thoa man khai niem "tien phong"
da tung dugc thira nhin. Day Ii nhung cay chi tdn tgi dugc trong dieu kien chuyen tiep, hay con ggi li chuyen tiep sinh thii.
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HQl NGHj KHOA HQC T O A N Q U Q C V £ SINH T H A I V A T A I N G U Y E N SiNH VAT L A N THU 5
Hinh 3. Cdy go lien phong dai chuyen tiep giira rimg vd qudn xa cd
Khac vdi cay go, cic loii cd hoin toan cd kha nang xam Ian nh&ng khu vyc trdng trii. Tren nin dit vira Id ra sau khi rirng bj mat, ciing nhu dat bj bao mdn, rira trdi Ii dilu kign thich hgp cho cac Ioai cd va duang xi phat triln. Hgt ciia nhilu loai cd de ding phit tan nhd gid, cac bg phin dudi dat ciia chiing phit triln rit mgnh vi mim tii tgo ciia chiing van tdn tgi dugc sau nhung tran chiy rirng. Tren khu vyc rimg da bj tan pha, hinh thinh cic quin xa cd dgt tdi eye dinh ve khi hau. Tren dia hinh viing ddng bang, gd ddi d Gio Linh, trong nhimg quan xa nhu vay chiem uu thi vin Ii cac Ioai cd cgng to va cung. Qua trinh diln thi cua tham thyc vat tiep tyc dien ra trong chu trinh nhu vgy neu nhu khdng cd nh&ng dot bien ve dieu kign ty nhien hogc bign phip ky thuat tir phia con ngudi.
IIL KET LUAN
Trii qua thai gian dai, chiu nh&ng tac dgng cua CDC ciing nhilu tac ddng nhin sinh khac nhau da lam bien ddi ca bin quan xa thuc vat ty nhien huyen Gio Linh, tao nen nhung quan xa.
thyc vat nhin sinh cd ciu tnic dan gian vdi dai dien li tring cd cay bui va rirng nhan sinh.
Cau triic cic quan x i thyc vat rirng nhan sinh hinh thinh sau tac ddng cua CDC chua dat den do dn djnh vi cd nhieu khac biet, phu thudc vao mirc do tie ddng v i vj tri cua chiing: Trong quan xa thyc vat rimg thu sinh, thim thyc vgt cd tang tin chua dn djnh, nhieu day leo nhung d mdt sd khu vuc da cho thay su phan hda vdi 3 ting chii dgo; cic trgng thii tring cd, tring cd ciy bui cd cau tnic dan giin, vdi thanh phan gdm chii yeu la cac loii cd than to v i cung.
Theo xu hudng diln thi, trong dilu kien hien tai, kha nang phuc hdi cua cic quin xi thyc vat rung la hoin toin cd thi diln ra tgi nh&ng ddi chuyin tilp gi&a rirng va trang cd cay bui,
HQI NGHI KHOA HQC TOAN QUQC VE SINH THAl VA T A I N G U Y E N S I N H VAT LAN THO" 5 nh&ng yeu td tdi hgn mi thim thyc vat rimg khdng cd kha nang phat sinh vi tdn tgi, trong dd cd chl dg nhigt-im cua khdng khi vi dit; dg chieu sang va su bien ddi cic ylu td theo mua.
TAI LIfU THAM KHAO
1. Phdng Tuu Boi vd nnk., 2002. Anh huang cua chiin tranh hda hgc (1961-1971) ddi vdi ldi nguyen rimg Nam Vi4i Nam. Bao cao cic cdng trinh khoa hoc tai Hoi nghi Khoa hoc Viet-My v l dioxin H i NOi., tr 145-155.
2. Phgm Hoang Hg, 1999. Cdy co Viel Nam. t i p 1,2 va 3. NXB. Tre, Tp. H6 Chi Minh.
3 Nguyin t)3ng HOi (2000), "Ung dung phirang phdp ddnh gid tdng hgp cho vi?c khai thdc, sir dyng hgp ly va bao ve ldi nguyen rirng", Tgp chi Khoa hgc Lam nghiep (Sd 1 +2), tr. 31 -34.
*. NguySn Dang H^i, T r i n V i n Thjnh, Vu Van Lien, 2001. Tac dong lieu cue cUa chiin tranh hoa hgc len tdi nguyen moi Irudng tu nhien huyen Sa Thdy linh Kon Turn. TuyIn t i p Hgi nghi Khoa hgc Tii nguyen va Moi trudng Viet Nam. NXB. Khoa hgc-Ky thuat. Ha Ngi, tr. I73-183.
5 Nguyen Dang Hgi, Kuznetsov A.N., 2012. Nghien ciru hien trang vd biin ddi cac hi sinh thai l\r nhien dirdi tac ddng ciia con nguai va chiin tranh hda hgc huyen Gio Linh-Cam Lg, tinh Quang Tr;.
Bio cao de tai khoa hgc cap Uy ban phii hgp Vi^t-Nga, Ha Ngi.
6. Kuznetsov A.N., Kuznetsova S.P, Phan Luong, Nguyin Dang Hgi, 2009. Nghien aru idc dpng ciia chdi diet co vd bom Napal len rimg nhiel ddi gio miia a Miin Nam Viet Nam. Bao cao Khoa hgc tai Hgi nghj Khoa hgc toan q u l c lin thu 3 v l Sinh thai va Tai nguyen sinh vai nSm 2009, Ha N^i, tr. 1390-1396.
7. V6 Quj', Phan NguyCn Hong va nnk., 2004. Hgu qua Idu ddi ciia chiin tranh hda hgc ddi vai moi tnrdng. ldi nguyen rimg vd da dgng sinh hgc a Viel Nam. Ky ylu Hgi nghj Khoa hgc ve Tai nguyen va Moi tmdng 2003-2004, Trung tam Nghien ciiu Tai nguyen va Moi tnrdng, Dai hgc Qudc gia Ha Ngi S. Thii V i n Trimg, 1993. Phuc hdi nhSng he sinh thai rimg bj chdi diet cd hiry hoai a miin Nam Viet Nam.
B4o cio Khoa hgc H§i thio Quic tl lin 2 vl chit di^t co trong chiln tranh. Ha Ngi, U 120-128.
9 V3n phdng Chu'Ung trinh 33, 1999. Tap bdndo phum rdi chdt di4t cd cua qudn ddi My Irong chien Iranh d Viet Nam, H i Ngi.
STATUS AND SUCCESSION OF PLANTS IN THE ANTHROPOGENIC ECOSYSTEMS OF GIO LINH DISTRICT, QUANG TRI PROVINCE UNDER THE IMPACTS OF HERBICIDE
USING IN THE VIETNAM WAR
NGUYEN DANG HOI, KUZNETSOV A.N , KUZNETSOVA S.P.
During the Vietnam War, natural ecosystems of Gio Linh district, Quang Binh province had been adversely impacted due to the military operations, especially herbicide use. Over the decades, the vestiges of herbicide still exist in the ecosystems of Gio Linh district. As a result, natural ecosystems of this region have been changed into grassland, secondary forests and plantation The ecosystems, which were formed because of the impacts of herbicides, often have a simple structure and not even reached a stable status:
Secondary forests with unstable vegetation branches and many vines; grasslands with simple structure shnjb and mainly hard body grass According to the ecological succession, the ability of recovery of primary forest is highly possible in the transition zone between current secondary forests and grasslands, but with slow speed in current conditions. It is because several o'itical factors, which are not appropnvate for natural forest to develope to stable status, are existing in the current destroying ecosystems. These crilical factors include temperature-humidity regimes of air and soil and light level
