1

SAM Paper Series 16 (2002)

M hnh ho cc thay i s dng t ti huyn Ch n viphng php CLUE-S

V Nguyna, Jean-Christophe Castellab, Peter H. Verburgc

a Vin Khoa hc K thut Nng nghip Vit Nam (VAS), Thanh Tr, H Ni, Vit Namb Vin Nghin cu v s Pht trin (RD), 213 rue Lafayette, 75480 Paris Cedex 10, France, v

Vin Nghin cu La Quc t (IRRI), DAPO 7777, Metro Manila, Philippinesc Phng Th nhng v a cht, Khoa khoa hc mi trng, Trng i hc Wageningen, H Lan

Tm tt

Ch n l mt huyn ca tnh Bc Kn, thuc lu vc Sng Hng. Pha Bc gip h Ba B huyn Ba B,pha nam gip huyn nh Ho tnh Thi Nguyn, Pha ng gip huyn Bch Thng, Phia ty gip huyn NaHang - Chim Ho tnh Tuyn Quang. Ton b huyn c 21 x v 1 th trn. Dn s l 46224 ngi, ch yul ngi dn tc Ty (75%), Dao (11%) v ngi Kinh (9%). Tng din tch ton huyn l 91590 ha, trong t dnh cho nng nghip l 239 ha, phn ln dn s sng da hon ton vo nng nghip.

S tng dn s gy ra nhng p lc i vi s dng t v ngun ti nguyn thin nhin. Do ch c qu t tnng nghip nn din tch t dc ang chuyn i sang t nng nghip sn xut lng thc p ng nhucu ngy cng tng. iu ny lin quan n vic bn vng lu di ca ngun ti nguyn thin nhin. bov h thng ny, chnh ph cm vic ph rng lm nng. Trong thp k va qua, nng thn Vit Nam c nhiu thay i, mt trong nhng thay i ln nht l giao t cho tng h nng dn, iu ny c ngha lngi dn c trch nhim trn mnh t ca mnh, v vic thay i s dng t s din ra nh th no thngi lp k hoch rt kh d bo c. Vic p dng m hnh ho m phng v d bo qu trnh s dngt CLUE-S (the Conversion of Land use and its Effects at Small regional extent) cho huyn Ch n, tnhBc Kn l mt cng c h tr c bit cho cc cp qun l, n gip ch cho cc nh lp chnh sch v lp khoch s dng t c th thy c nhng vng n nh v nhng vng d thay i trong s dng t do ccnh hng khc nhau. Cc thng tin khoa hc a ra t m hnh c th c xem nh l cng c nh gicc chnh sch s ra.

1. t vn D bo l cng vic cn phi lm trong cchot ng nghin cu cng nh qun l. Dbo chnh xc th cc chnh sch ra mip ng c yu cu i hi ca thc t.Vic chuyn i s dng t l vn mcc nh nghin cu cng nh cc nh qunl u rt quan tm. H thng s dng trt phc tp v c mi lin h cht ch vih thng x hi v h sinh thi. S dng tkhng ch ni n lp t v sinh khi trnmt t m cn bao hm c mc ch khaithc mt t ca con ngi. Vic thay i sdng t khng phi lc no cng em lili ch cho cuc sng con ngi. t rng

v s xy ho cc cht hu c trong t dnn hiu ng nh knh v do lm thay ikh hu ton cu. Trng trt thm canh trnt dc dn n thoi ho t, gim khnng s dng t dc cho sn xut lngthc trong khi nhim mi trng khngkim sot c.

trnh hu qu nh vy ca thay i sdng t, tip cn mt cch h thng c p dng. K hoch s dng t l mtqu trnh m con ngi d nh thay i sdng t da trn cc mc tiu ra kt hpvi cc chc nng ca h thng s dng thin ti.

H thngNng nghip

Min ni

M hnh ho cc thay i s dng t ti huyn Ch n2

2. Phng php nghin cu

Trong bi ny, s dng t thay i ngha ls thay th loi s dng t ny bng loi sdng t khc. S dng t thay i nichung c coi l do nh hng trc tip vgin tip ca nhiu yu t, nhng yu t nyc chia lm hai loi: Loi nh hng trc tip ti t l v s

lng s dng t (VD: Rng b cht lm nng nghip do tng dn s).

Loi xc nh vic phn b s dng t(VD: t ph hp vi trng la nc).

thy r mi quan h tng h gia thayi s dng t v cc yu t nh hng,CLUE s dng phng php truyn thng, l s dng phn tch tng quan v hmhi quy, nh phng php ny, h thngphc tp vi nhiu mi quan h qua li, kthp vi s ph thuc vo cp rt kh mt mt cch tng qut nhng c th lngho c.

S dng t b rng buc bi cc yu t mitrng nh l tnh cht t, kh hu v ahnh, trong khi nhn t con ngi xcnh v tr s dng t: u?, lm g? t m quy m, phm vi s dng t mtni no b thay i. xc nh c ccyu t gii thch c cu s dng t, chngta thit lp mt b s liu gm cc tt c ccyu t m c cho l c nh hng nvic s dng t. Hu ht cc s liu ctng hp t cc iu tra cp thn bn kthp vi cc s liu thng k ca huyn nngnghip nm 1998 theo a gii hnh chnhx, cc s liu v l-sinh hc c t cc bn t mt s nghin cu khc, cc s liukh hu c c t cc trm kh tng.Ring bn s dng t c gii on tnh v tinh nm 1998.

c th s dng c hm hi quy, victrc tin l phi to mt b s liu ph hp.Tt c cc bn v s liu c chuynsang cp li c kch thc l 250 x 250mt, tc l trn mi ca huyn s cha thng tin: loi s dng t, mt dn s, cao, dc,kh nng tip cnBin phthuc trong phn tch l cc loi s dng tkhc nhau.Khi p dng CLUE phm vi ln nh cpquc gia vi phn gii ln (kch thc li ln) v cp ny, s dng t cbiu th bng phn trm ca mi loi sdng t trong mi , chng hn 30% ttrng trt, 40% c v 30% rng. Khi p

dng CLUE phm vi nh, cc loi s dngt da trn bn s dng t hoc cgii on t nh v tinh s c biu thbng loi s dng t chim ln nht trongmt v c coi l ng nht trong .V vy khi chuyn sang dng li th chc mt loi s dng t trong mt . Do bin ph thuc c biu th bng s 1 (c)hoc s 0 (khng c) trong mi li. Dos khc nhau trong biu din s liu v tnhcht ca cc cp p dng nn i vi huynCh n, p dng CLUE-S (the Conversionof Land use and its Effects at Small regionalextent) l thch hp. Nh vy CLUE-S cp dng cho cp vng vi phn gii cao,n bao gm mt m hnh khng gian v phikhng gian, cp vng p dng trong m hnhny l cp huyn, ri n cp li.. Ccthnh phn chnh ca CLUE-S c biudin trong hnh 1.

2.1. Cc yu t trong m hnhXc sut. Do cc bin ph thuc trong mhnh l nh nguyn nn m hnh thng ktrong CLUE-S da trn phn tch hm hiquy logistic xc nh v lng ho ccc nhn t nh hng n s xut hin cacc loi s dng t. Cc phn tch cthc hin i vi s dng t hin ti chotng loi s dng t ring bit. Cc h sca hm hi quy c dng tnh xc sutca mi dnh cho tng loi s dng ttrong nm phn tch.

Khu vc c bo v. Thnh phn ny ch ranhng no c a vo tnh ton trongm hnh thay i s dng t. Tt c nhng khng c a vo trong tnh ton l vchng c coi l s dng t n nh. Phnny c dng xc nh nhng nothuc vo vng c bo tn, vng m cgi thit l khng c thay i g v s dngt trong thi gian m phng.Nhu cu. Chng ta ang nghin cu s thayi s dng t nn yu t thi gian cngc a vo m hnh. u t ny c xemvo nh l s thay i s dng t theo nhucu. Phn ny s xc nh mi loi s dngt cn thit cho mi nm cp vng (cphuyn) m khng cn ch n yu tkhng gian. u t phi khng gian ny c thxc nh bng mt m hnh kinh t, cc nhhng cho tng lai hoc ch suy lun tuyntnh n gin v s tng din tch s dngt.

M hnh ho cc thay i s dng t ti huyn Ch n3

Hnh1. Nhng thnh phn chnh trong m hnh CLUE-S

S n nh. S n nh ch ra mt loi sdng t no d thay i nh th no.Thnh phn ny cung cp cho ta co dnca chuyn i. Ni cch khc, s chuyni ca mt loi t no sang loi sdng t khc l d hay kh. Gi tr ca n nh c th thay i t 0 n 1. Vi s 0tc l loi s dng t d thay i nht, s 1l loi t n nh nht. u t n nh l yut phi khng gian c xc nh cho miloi s dng t cp vng.Nhn t n nh ny rt kh tham s hoc, do chng cn c suy lun davo qu kh hoc kt hp vi cc kin thcchuyn gia.

Ma trn i. Ma trn ny ch ra s chuyni s dng t no l c php. y l matrn y x y, trong y l s cc loi s dngt. Trong ma trn: hng biu th cc loi sdng t hin ti; ct biu th loi s dngt c th c chuyn sang trong tng lai;gi tr 1 ch ra rng s chuyn i l cphp, gi tr 0 tc l khng c php.Trong ma trn ny cng c th ch ra thigian ti thiu hoc ti a mt loi s dngno cn phi n nh trc khi thay i.Thi gian ti thiu c ch ra bng s 100+ thi gian, thi gian ti a c ch ra bngs 100 thi gian. bc u tin ca mhnh, cc loi s dng t c gi s rng tn ti v tr ca chng c 5 nm ri.

2.2. Cc bc phn b s dng ttrong CLUE-S.

Khi chy m hnh CLUE-S, cc loi s dngt khc nhau s c phn b vo cc khc nhau ca vng m phng. Quy tcphn b t ln lt theo nhng bc sauy:1. Tt c cc c php thay i c

xc nh (din tch bo tn v loi sdng t n nh b loi ra).

2. Vi mi cn li, xc sut ton b ctnh theo kt qu hm hi quy, nnh v nhn t lp. Nhn t lp c thlm thay i xc sut ton b nu loi sdng t c phn b khng p ngc nhu cu.

3. Phn b u tin c tin hnh vi gitr nh nhau ca bin lp bng cch phnb loi s dng t c xc sut cao nhtcho mi .

4. Tt c cc loi s dng t c phnb s c so snh vi nhu cu. Nudin tch c phn b nh hn dintch nhu cu, gi tr ca bin lp ctng ln.

5. Bc 2 v bc 5 c lp li khi nhucu cha c tho mn. Khi s phn bbng nhua cu th s phn b cui cngc ghi li v s tnh ton c tip tccho nm tip theo.

Ton b th tc phn b t c cho tronghnh 2.

Bo v

n nhNhu cu

Cp li, khng gian

Cp huyn, phi khng gian

M hnh ho cc thay i s dng t ti huyn Ch n4

Hnh 2. Th tc phn b t ca CLUE-S

2.3. Phng php thng kMt phn quan trng ca m hnh CLUE-Sl tnh hm hi quy logistic. Dng hm nyc s dng khi bin ph thuc l nh phn(0 hoc 1) v bin c lp l lin tc hocphn loi. Mi loi s dng t (bin phthuc) trong CLUE-S c gi tr 0 hoc 1 chra s c hay khng c loi s dng t trongmi . Hm logistic c dng nh sau:

Log(Pi / 1-Pi ) = 0 + 1X1i + 2X2i +...+ nXni

Trong Pi l xc sut ca xut hinloi s dng t ang xt v X l cc nhn tnh hng. Phng php hi quy tng bccho php chn nhng nhn t c lin quantrong tp hp v s cc nhn t c gis l c lin quan n c cu s dng t.Cc h s ca hm hi quy c a ra trctip t m hnh. Trong m hnh hi quylogistic bi ny, ch nhng bin c nghanht trong tp hp nhng bin c lp mic a vo m hnh lm gim s cngtuyn. S cng tuyn l s tng quan giacc bin c lp, cc nhn t nh hng. Stng quan ny c gi s l bng 0 nhngvn xut hin khi cc bin c lin quan vinhau c s dng, chng hn fluvisol vkhong cch ti sng sui. Tuy nhin vnkhng th loi ht s cng tuyn ca mhnh theo cch ny.

S ph hp ca m hnh tuyn tnh bi cth m t bng t l gii thch ca phngsai (R2). Gi tr R2 ny ni ln ng hiquy gii thch s liu nhiu hay t. Cch phhp nh gi hm hi quy logistic l sdng ROC (Relative OperatingCharacteristics), y l phng php m tmi quan h gia d bo ng v sai i vinhng gi tr cut-off khc nhau ca xc sut.

Gi tr cut-off trong m hnh c mc nhl 0.5, ngha l vi cc gi tr nh hn 0.5 thloi s dng t c coi l khng xuthin, v vy nu gi tr cut-off cng nh thdin tch ca loi s dng t c d bocng nhiu. M hnh l tng nht a rang cong. c din tch di ng congl ln nht.

Din tch di ng cong thay i t 0.5ti 1.0, nu m hnh d bo s xut hin camt loi s dng t no khng tt hnxut hin ngu nhin th din tch ding cong s l 0.5, chnh l ng chotrong th.

2.4. S liuCc thnh phn khc nhau ca m hnh ihi cc s liu u vo khc nhau, do cnphi chun b mt b s liu ph hp.Phng php la chn s liu c ch ratrong hnh 3.

Nhu cu n nh Cp huyn,phi khng gian

Cp li,khng gian

Nhn t lp

Xc sut DT bo tnXc sut tng

Vng lp

Phn b sdng t

ngcong ROC

Hnh 3. ng cong ROC cho Cy bi, dintch di ng cong (AOC) l 0.875

M hnh ho cc thay i s dng t ti huyn Ch n5

Hnh 4. Nhng s liu cn cho m hnh CLUE-S

3. p dng cho huyn Ch n

Mt bn s dng t nm 1998 c sdng to thnh s liu biu din cc lois dng t. Cc bin c lp bao gm ccs liu sinh hc - a cht, kinh t - x hi,kh nng tip cn v kh hu.

S la chn s liu a vo m hnh phthuc vo nhng nhn t m c coi lquan trng. i vi min ni pha bc VitNam th nhng vn sau y thng cngh ti: Cc hn ch v a cht ( cao, dc,t ngho axt, phn b ma khng ngu,...)

Mi trng (Thoi ho t, kh hu bchia thnh cc tiu vng khc nhaunhiu,...)

C s h tng km (H thng thng tinv giao thng cha pht trin)

Kinh t (Ch da vo nng nghip, thtrng ngho nn)

p lc dn s (T l sinh cao, tht nghipnhiu)

Trnh vn ho (Trnh gio dcthp, nhiu dn tc khc nhau)

Nhng vn ny cng s nh hng tivic s dng t, cc bin c lp c lachn a vo hm hi quy do chng clin quan ti cc hn ch trn, cng nhchng c coi l nhng nhn t quan trngc th nh hng ti s thay i s dngt.

3.1. Chun b s liuS liu ch yu c lm trong ArcView.Trc ht cc s liu kinh t x hi cnhp vo bn hnh chnh (cp thn bnhoc x), cc yu t a cht, kh hu, a l,kh nng tip cn,... l cc bn c sn tcc nghin cu khc, tip theo ton b bn c chuyn sang dng raster ( li) vikch thc nh trc. Kch thc yc nh l 250 x 250 mt. Sau tt ccc bin c xut ra ASCII files, dng nyc th nhp vo SPSS phn tch thng k.

S liu k hoch

S liu thng k

S liu k hoch

M hnh pht trin

Quy tc quyt nh vkin thc chuyn gia

Nhu cu n nh Cp huyn,phi khng gian

Xc sut Bo v Cp li, khng gian

Bn s dng t

s liu khng gianS liu

khng gian

Hi quyChnh sch

M hnh ho cc thay i s dng t ti huyn Ch n6

Bng 1. Cc bin, loi bin, n v v cc lp trong b s liu c s dng cho m hnh CLUE-Shuyn Ch n

Bin Loi n v LpBin ph thuc

S dng t Nh phn 0 - 1

La ncNngVn tpng cRngCy biKhu dn c

Bin c lpt, a cht, a hnh

Loi t Nh phn 0 - 1

CambisolsLeptosolsFluvisolsRegosols

Tnh cht a cht Nh phn 0 - 1

SchistSandstoneGraniteLimestone

Thoi ho t Nh phn 0 - 1KhngNhKh

cao Ri rc mt

dc Lp 0 - 1

KhngtTrung bnhKh

Kinh t x hiDn s Ri rc Dn s / thnMt dn s Ri rc Dn s trung bnh / haT l ngho i Ri rc % h / thnT l m ch Ri rc % ngi / xPhn trm ngi Dao Ri rc % h / thn

V Nguyn\ Jean-Christophe Castella\ Peter H. Verburg7

Phn trm ngi Ty Ri rc % h / thnPhn trm ngi Kinh Ri rc % h / thnS tru b Ri rc S tru b / thnMt tru b Ri rc S tru b / haS ln nui Ri rc S ln nui / thnMt ln Ri rc S ln nui / haC in li Nh phn 0 - 1Giu c Ri rc S lng tivi,i / thn

Kh nng tip cnKhong cch ti sng Lin tc mtThi gian ti cc ch, y t,trng, u ban Lin tc pht

Thi gian ti th trn, th x Lin tc phtS lng gio vin, bc s trongvng Ri rc ngi

Kh hu

S thng kh Nh phn 0 - 1 3 thng4 thng

S thng lnh Nh phn 0 - 1 0 thng1 thng

3.2. M t s liu:

Cc bin ph thuc:Bn s dng t ca d n SAM cgii on t nh nm 1998 di dng vectorgm c 7 loi s dng t: La nc,nng, t vn tp, cy bi, ng c, rngv khu dn c.

Cc bin c lp:

Thoi ho t: T mt s tnh cht nh lxi mn v cc mc thoi ho t khcnhau, sau khi cn i li, nguy c thoi hot c phn loi thnh 3 loi cho n ginhn: Khng thoi ho t, t thoi ho vthoi ho trung bnh.

Dn s: S dn trong mt thn.

Mt dn s v mt gia sc (tru b vln): Mt dn s bng tng s dn trongthn chia cho din tch thn. i vi gia sccng lm tng t.

T l ngho i: Nu trong 1 h m thu nhpt hn 15 kg thc / ngi / thng th h c coi l ngho (tiu chun h ngho nm1998). T l ngho i tc l % s h nghotrong thn.

T l m ch: % ngi trong x di 35 tuikhng bit ch.

Phn trm dn tc Ty, Kinh, Dao: L % sh l ngi Ty, Kinh hoc Dao c trongthn.

Khong cch ti sng sui: Khong cch tmi ti sng hoc sui c tnh ton tbn , n v l mt.

Thi gian ti cc ch, y t, trng, u ban:Thi gian trung bnh i ti cc ch, trm yt, trng hc gn nht v bng phng tinnhanh nht. (Kt qu t nghin cu khnng tip cn).

Thi gian ti th trn, th x: Thi giantrung bnh i ti th trn, th x hoc sanghuyn th trn ca huyn khc. (Kt qu tnghin cu kh nng tip cn).

S lng gio vin, bc s trong vng: Slng gio vin hoc bc s c th tm thyc trong vng 60 pht. (Kt qu t nghincu kh nng tip cn).

Cc loi t: c 12 loi t trong bn tc lm t nh v tinh v phn tch mut cho ton tnh Bc Kn. gim s bin,s phn lp c lm li da trn tnchnh ca loi t (4 loi): cambisol,leptosol, fluvisol, regosol.

Cc loi bin v a cht: c 40 loi trongbn a cht, s phn lp li da trn tnca 4 loi chnh: schist, sandstone, granite,limestone.

cao: c sn trong bn cao vi phn gii l 24 x 24 mt nhng trong mhnh ny c chuyn thnh 250 x 250 mt.

dc: c sn trong bn dc vi phn gii l 24 x 24 mt nhng trong mhnh ny c chuyn thnh 250 x 250 mt.

M hnh ho cc thay i s dng t ti huyn Ch n8

Cc yu t kh hu: S liu lng ma vnhit trung bnh theo thng c thu thptrong 25 nm (ngun t LUPAS). Thngkh l nhng thng c lng ma t hn 50mm. Thng lnh l thng c nhit thphn 120C.

3.3. Cc kch bnHai kch bn c a ra da trn nhhng pht trin ca tnh v huyn.

Kch bn 1: m bo cung cp lngthc cho dn s ngy cng tng ca huyn.T dn s 1998 ca huyn Ch n, tnhtheo t l tng dn s ton tnh s c s dnd bo trong huyn theo tng nm. Do nhu cu din tch t dnh cho lng thc

cng phi tng. Vi t l rng hin ti cheph 45%, theo nh hng pht trin nnm 2010, t l ny phi t 60%, t tnhc din tch rng phi tng tng nm.Din tch rng c gi thit l pht trin tcy bi. Cn din tch trng la c th tngln t nng. Nu yu t k thut c avo, tc l nng sut la s tng ln th dintch trng lng thc c th tng khngnhiu (bng 2).

Kch bn 2: Vi nhu cu v nh hng phttrin rng nh trn nhng ng thi tngdin tch ng c pht trin chn nuitru b nhm tng sn lng tht, ci thini sng hoc tng thu nhp cho nng dn(bng 3).

Bng 2. Kch bn 1: m bo lng thc v mc tiu trng rng

Nm Dn s La nc Rng

1998 42783 5075.0 39687.5 (45%)

1999 43703 5098.7 40847.1

2000 44643 5208.4 42006.7

2001 45604 5320.4 43166.3

2002 46585 5434.9 44325.8

2003 47587 5551.8 45485.4

2004 48610 5671.2 46645.0

2005 49656 5793.2 47804.6

2006 50512 5893.1 48964.2

2007 51383 5994.7 50123.8

2008 52269 6098.0 51283.3

2009 53170 6203.2 52442.9

2010 54087 6310.1 53602.5 (60%)

V Nguyn\ Jean-Christophe Castella\ Peter H. Verburg9

Bng 3. Kch bn 2: m bo lng thc v mc tiu trng rng, ng thi pht trin ng c chn nui b.

Nm Dn s Din tch la Din tch rng S tru b Din tch ng c

1998 42783 4406.3 39687.5 (45%) 21737 7212.5

1999 43703 5098.7 40847.1 23065 7653.1

2000 44643 5208.4 42006.7 24474 8120.6

2001 45604 5320.4 43166.3 25969 8616.6

2002 46585 5434.9 44325.8 27555 9142.9

2003 47587 5551.8 45485.4 29238 9701.4

2004 48610 5671.2 46645.0 31024 10294.0

2005 49656 5793.2 47804.6 32919 10922.8

2006 50512 5893.1 48964.2 34930 11590.0

2007 51383 5994.7 50123.8 37064 12298.0

2008 52269 6098.0 51283.3 39328 13049.2

2009 53170 6203.2 52442.9 41730 13846.3

2010 54087 6310.1 53602.5 (60%) 44279 14692.1

Vng c bo tn

i vi 2 kch bn trn, din tch cn botn c xc nh, din tch ny s khngthay i trong qu trnh chy CLUE-S v nc coi l khng chuyn t loi s dngt ny sang loi s dng t khc. Chnghn khi chnh ph cm ph rng th trongcc kch bn a ra rng s l khu vckhng th chuyn sang loi s dng tkhc.Trong huyn Ch n th din tchrng c coi l khu vc c bo tn.

Khong thi gian m phng trong mhnh

Trong m hnh, thi gian m phng ct l 12 nm, t 1998 n 2010 bi v trongcc mc tiu phn u, cc nh lp chnhsch thng ly nm 2010 lm im kt thcmt giai on. Nh vy vi mi kch bn, tac th a ra 12 bn d bo ca tng nmmt, t 1999 n 2010.

Ch s n nh (kh nng chuyn i)

Cc quy tc quyt nh nh hng n ch sn nh ca cc loi s dng t khc nhau.Do ch s n nh ny ni ln vicchuyn cc loi s dng t sang cc loikhc l d hay kh. Trong m hnh, ch sn nh c t nh sau, c tham khokin thc chuyn gia tnh Bc Kn:

Loi s dng t Ch s n nh

La nc 1Nng 0.3Vn tp 0.3ng c 0.25Rng 0.75Cy bi 0.2Khu dn c 1

Theo kin ca cn b a phng, c c 2loi: loi c trn t cn, khng th mcc cc loi cy khc m ch mc c cmay th kh n nh, ch s c th ln n0.4 v kh ci to chuyn sang loi sdng t khc, cn loi c mc sau nng(nng b b ho) th khng n nh, chngd dng pht trin thnh mt trong cc loisau: nng, cy bi - rng, vn tp hoc

M hnh ho cc thay i s dng t ti huyn Ch n10

khu dn c, ch s n nh khong 0.1nhng trong bn s dng t t gii onnh th khng th phn bit 2 loi c ny, do ch s n nh c ly trung bnh l0.25. Cy bi cng khng n nh mc dcng n nh hn c (ch s n nh = 0.2),n d dng chuyn thnh nng, c hocrng. Ngc li, rng cng d dng b suythoi thnh cy bi. La nc ch sng c rung, khng th sng c ni nokhc, khi t trng c la nc th domc tiu m bo lng thc nn khng thchuyn sang trng loi cy khc (ch s nnh = 1). Tng t i vi khu dn c.

Tiu chun hi t

Tiu chun h t ch lch ti a chophp gia s thay i ca nhu cu v s thayi ca phn b d dng t hin ti theophn trm. t ch s ny s lm tng tci hi t ca m hnh m phng. Gi trny trong m hnh c mc nh l 0.35%nhng cng c th tng hay gim tu thucvo tng m hnh. i vi Ch n, ch sny ch l 0.2

3.4. Kt qu t phn tch thng kHm hi quy c chy nhiu ln cho ccmu ngu nhin ca ton b b s liu kho st s n nh ca m hnh. Sau mtvi hm hi quy trn cc mu ngu nhinkhc nhau, kt qu c v khng n nh, ccbin khc nhau vi cc h s ca hm hiquy khc nhau xut hin trn cng mt lois dng t. tng n nh ca mhnh, mt vi bin php c p dng.1. Mt s bin b loi ra khi m hnh,

nhng bin ny l nhng bin c binng nh trong huyn v khng giithch r trong hm hi quy ca cc lois dng t.

2. Gim cc xc sut tiu chun a vo va ra ca cc bin trong hi quy tngbc gim s cng tuyn. iu nylm tng n nh ca m hnh. Xcsut a vo v a ra khi m hnh y ln lt l p = 0.01 v p = 0.02.

3. Cc kch thc mu khc nhau cngc phn tch xt xem kch thcmu c nh hng n n nh cam hnh hay khng. Mu cng nh thbiu din b s liu cng km. Mt viloi s dng t ch xut hin mt s t, m bo nhng loi s dng t

ny biu din b s liu th t nhtphi c 75 . Loi s dng t c s tnht l khu dn c, ch c 124 , do mu ngu nhin l 60% c chn.

cho m hnh gn hn, ch gi li nhngbin c nh hng r rng n d dng t,nhng bin c h s hm hi quy nh hnhoc bng 0.0001 b xo khi m hnh.Nhng nu ROC gim ln hn hoc bng0.01 do xo bin th bin c gi litrong m hnh.

Hm hi quy c nh gi bng s phhp theo trung bnh ca phng php ROC.S ph hp ny c ch bng gi tr gia0.5 v 1, s 1 l ch s ph hp nht. i vib s liu ca huyn Ch n, ROC ctnh t 0.635 cho rng ti 0.85 cho la nc.Gi tr thp ca ROC c nhiu nguyn nhn: chnh xc khi gii on t nh, cc yut nh hng a vo m hnh cha,s phn lp cc yu t nh hng hp lcha, ....

ch s quan trng ca cc yu t nhhng ti cc loi s dng t, exp(B) c tnh ch ra rng xc sut ca mtloi s dng t no trong mt l tng(ln hn 1) hay gim (nh hn 1) khi tngbin c lp.

Mt nhc im ca exp(B) l n c biudin trn 1 n v tng ca bin c lp. Do tng 1 trong bin nh phn th lun c vnh l c nh hng ln hn khi tng 1 t Bca bin lin tc hoc ri rc v cc bin nylun c khong rng hn v gi tr.

Cc nhn t c tng quan nghch s lmgim xc sut ca mt loi s dng t no s c exp(B) gia 0 v 1 trong khi exp(B)ca nhn t c tng quan thun s lm tngxc sut ca ca loi s dng t no sc gi tr ca exp(B) ln hn 1. Do sosnh exp(B) ca nhn t c nh hng tchcc vi nhn t c nh hng tiu cc, tadng i lng so snh sau y:

exp(B*khong gi tr) = i lngso snh (vi B > 1)-1 / exp(B*khong gi tr) = i

lng so snh (vi B < 1)

Kt qu t hm hi quy c cho trongbng:

V Nguyn\ Jean-Christophe Castella\ Peter H. Verburg11

Lanc Nng

Vntp ng c Rng

Cybi

Khudn c

Loi tCambisol*Leptosol -0.36 0.19Fluvisol 0.95 -4.62 -0.69 -0.79 -0.76Regosol 1.84 1.33 -0.96 -1.25a chtSchist*Sandstone -0.37 0.22 -0.24GraniteLimestone 2.50 1.71 -0.59 2.28 cao -0.01 -0.01 -0.001 0.002 -0.005 dc 1 0.88 -0.97 0.21 -0.21 1.50 dc 2 -0.36 dc 3* dc 4t khng thoi ho 0.41 -0.45 0.27 -0.52t t thoi ho *t thoi ho trungbnh 0.47 -0.66 0.30

Kinh t x hiC / Khng in -0.17 0.24Dn s 0.006 0.003Mt dn s 0.41 0.40Tng s hT l m ch 0.08 -0.04 0.02T l h ngho -0.006 0.004Phn trm ngi Dao 0.005 0.006Phn trm ngiKinh -0.02 0.018 0.005

Phn trm ngi Ty 0.01 0.007 -0.01 0.008S lng tru b -0.01 0.001S ln nui 0.005Mt tru b/ha 0.73 -0.76 0.53Mt ln/ha 0.004S lng tivi, i -0.02 -0.005 -0.01Kh nng tip cnKhong cch tisng suiThi gian ti u ban,ch, trng x -0.012 0.006

S gio vin, bc sc trong 60 pht 0.002 0.007

T/g ti th trn, th xKh huS thng kh: 3 -0.54 1.06 0.79 -0.27S thng lnh*ROC 0.8497 0.6899 0.7895 0.6742 0.6345 0.6675 0.7979

Cc bin c du * khng c a vophng trnh hi quy v c nhng b binnu a y vo s to nn b bin phthuc tuyn tnh.

Cc bin: Tng s h, dc 4, t granit vkhong cch ti sng sui khng tham giavo cc phng trnh hi quy, chng tchng khng c ngha trong vic gii thch

M hnh ho cc thay i s dng t ti huyn Ch n12

cho cc loi s dng t. dc 4 l dcqu cao, con ngi kh c th khai thcc nn s dng t gn nh khngthay i. t granite chim a s din tchca huyn nn cng khng l nguyn nhnchnh trong vic thay i s dng t. Mts yu t v kh nng tip cn l kt qu camt nghin cu khc, cn khong cch tisng sui l tnh ton khong cch t mi ti sng hoc sui trn bn nn ch s nyc chnh xc khng cao v khng quantm n yu t a hnh.

Khu dn c c gii thch bi cc yu tbng phng, cao nh v mt dn s vloi t limestone. La nc c gii thchbi cao nh v trung bnh, phn trmngi Ty, mt tru b, t t dc, loit limestone, fluvisol, regosol. Ni chung,mt s yu t dng trong loi s dng tny th li m trong loi s dng t khc,iu chng t cc loi s dng t cngnh hng ln nhau. Tuy nhin nhng yu tny khng gii thch chnh xc ccloi s dng t bi v ROC khng cao lm.Ngoi cc bn d bo s dng t trongcc nm m phng, CLUE-S cn a ra bn xc sut cho tng loi s dng t. Bn ny cho ta xc sut xut hin ca tngloi s dng t trn cc . Xc sut ny lkt qu ca hm hi quy logistic v honton da vo cc yu t nh hng m taa vo. Nhn vo bn xc sut ta c ththy c kh nng xut hin loi s dngt no ti mt c th. Nu bn xc sutv bn s dng t cng ging

nhau th ROC cng cao. So snh hai bn ny ta s bit c hm hi quy c gii thchtt cc loi s dng t hay khng, cc yut c a vo m hnh l cha.

3.5. Kt qu t CLUE-SCLUE-S c chy cho ba kch bn khcnhau. Kch bn 1 l m bo lng thcphc v cho dn s ngy cnh tng cahuyn, ng thi mc tiu ca huyn l ymnh vic trng rng, a din tch che phca rng nm 1998 l 45% ln n 60% nm2010. Theo kch bn ny, rung c din tchtng m bo lng thc nhng linvi nhng l rung theo bn s dngt 1998 v dc theo nhng sng, sui.

Nng nm 1998 nm ri rc gia rng vcy bi nhng dn dn cng c pht tringn rung v vn tp, xu hng nngcng ngy cng gn vi rung v vn l rrt. Din tch rng c m rng nhiunhng tp trung pha ty v ty nam, khuvc c nhiu sng sui. Cy bi trc y ri rc trong huyn th theo m hnh ch cnt nhng tp trung pha ty v ty bc cahuyn l vng c cao ln hn so vi ccvng khc ca huyn. ng c cn rt t vch tp trung pha ty ca huyn, c l ldo ph hp vi t cambisol v sandstone.Trong kch bn ny, rng c coi l vngbo tn v khu vc khng c phpchuyn i sang loi s dng t khc vchnh sch cm ph rng ca chnh ph vtheo kch bn th iu ny phi c thchin.

Kch bn 2: Ngoi cc mc tiu ca huyn lm bo t cp t tc lng thc cho s dnngy cng tng, a din tch rng che pht 45% ln n 60% nh kch bn 1 th mctiu ca tnh l a tng n tru b t108000 con nm 1998 ln n 220000 connm 2010, tc l tc pht trin hng nmca tru b phi l 0.061%. n tru b cahuyn nm 1998 l 21737 con, nu thc hinc tc nh mc tiu ca tnh ra ths lng tru b cng tng theo tng nm,do din tch ng c cng phi tng theov cc din tch ny c a vo kch bn2. Rng v ng c c pht trin nhngch trc y l cy bi. Trong kch bn nyth rng vn l khu vc c bo tn.

Theo kch bn ny th n nm 2010, do nhucu c pht trin chn nui, din tchng c tng ln nhiu nhng cng khngqu xa h thng sng sui, pht trin nhiu pha bc v phia nam ca huyn, ngoi racn ri rc xung quanh cc rung trng lanc. Din tch cy bi s cn rt t v chtp trung ch yu pha ng bc v mtphn nh pha ty bc ca huyn, ni c cao ln. T bn d bo nm 2010 cakch bn 2, c th kt lun rng vn tp rtph hp vi loi t limestone v khi dintch vn tp b gim th phn cn li ch tptrung vng c loi t ny, iu ny cngph hp vi kt qu hm hi quy.

V Nguyn\ Jean-Christophe Castella\ Peter H. Verburg13

Cc bn ca kch bn 1

Cc bn ca kch bn 2

20022006

2010

2002 2006 2010

M hnh ho cc thay i s dng t ti huyn Ch n14

4. Kt lun

M hnh CLUE-S l mt m hnh m t sthay i s dng t da trn mt lot cciu kin m cc iu kin ny c thhin trong cc kch bn. T kt qu ca hmhi quy, cc yu t nh hng tch cc haytiu cc n cc loi s dng t c xcnh. Nu cc chnh sch ra c lin quann cc yu t ny, chc chn s nh hngnhiu n thay i s dng t. S dngchnh sch to ra nhu cu s dng t ctnh n cc yu t k thut, th trng, ccnh lp k hoch hoc hoch nh chnhsch nhn vo bn s thy c v tr nos n nh, v tr no d thay i, v chnh l kt qu ca cc chnh sch khcnhau. Qua c th nh gi chnh sch sa ra, gii thch nguyn nhn ca s thayi s dng t.

CLUE-S c p dng cho huyn Ch n,l vng c phong cnh khng ng nht, skhng ng nht ny th hin trn bn d sdng t rt phn tn, nhng khng gp vn g trong vic phn bit cc loi s dngt c lp, mt phn do da nhiu vo kinthc chuyn gia, mt phn l do cc bcphn tch c lm k nhiu ln ly raphn n nh nht ca m hnh.

Nu coi din tch khu dn c c ch s nnh l 1, tc l kh chuyn i sang loi sdng t, th s khc nhau trong phn b ccloi s dng t khi coi khu dn c l vngc bo tn hay khng c bo tn l rtt.

Trong kt qu ca m hnh, cc loi s dngt c phn b k tip nhau theo trnh tph hp vi thc t xy ra Ch n.Vn cn li y chnh l kin nggp ca cc nh lnh o a phng vngi dn, kt hp vi kin thc chuyn gias c nng cp trong m hnh ccnghin cu tip theo.