t trc l mt bin php k thut dng la lm gim 50 70% khi lng vt liu ngay t u ma kh. Vi ngn la yu t trc khng lm tn hi ng k n sinh trng ca cy rng, n iu kin th nhng v hon cnh sinh thi ni chung. Do lm gim khi lng vt liu chy, ch yu l vt liu chy tinh, m t trc c tc dng lm gim kh nng bn la gy chy rng vo thi k nng hn nht.

Rng khp Ty Nguyn vo ma kh

Hin nay, t trc c p dng nhiu ni, trong thc hin trit nht l t trc cho rng trng thng Lm ng. Ngoi ra t trc cn c thc hin Gia Lai, c Lk, Ngh An, Thanh Ho, Qung Ninh v.v... Tuy nhin, phn ln cc khu vc ngi ta tin hnh t trc theo kinh nghim, vic nghin cu hoc tng kt cng ngh t trc vi mi loi rng mi khu vc cn hn ch. Bi bo ny trnh by mt phn kt qu ca ti KC0824 v mt s ni dung trong cng ngh t trc nh ma t trc, thi im t trc, thu gom vt liu trong t trc, kim sot m chy trong t trc, an ton trong t trc v chu k t trc:

- Ma t trc

Ma t trc c xc nh l khong thi gian trong nm m vt liu di rng cha kh hn, lp pha trn kh song lp di cn m, lp thm kh c th chy song mt phn cy bi v c cn ti cha nhiu nc, kh chy. V vt liu chy cha kh nn khi b t chng khng chy ht m vn cn li 30 50%. Khi t trc m chy c hnh thnh, song la yu v tc lan trn chm, d b tt ni vt liu cn m hn hay ni t vt liu hn. Bng vic to ra nhng ng bng nh c co bt vt liu kh, bng cy xanh chng chy, gii rng c v sinh, hay vic dng dng c th cng p trc tip vo ngn la con ngi c th khng ch c m chy trong t trc. Trong thc t ma t trc thng l vo u ma kh khi nhng m chy u tin c th xut hin, v kt thc khi cc m chy sp tr nn ph bin, kh kim sot. Phn tch quy lut bin i ca thi tit v c im vt liu chy cho thy ma t trc Ty Nguyn cn bt u vo cui gia thng 1 v kt thc vo gia thng 2 hng nm. Tuy nhin, t trc vi rng t nhin thng mun hn so vi rng trng, nn bt u vo thng 2.

- Thi im t trc,

Thi im t trc l thi im trong ngy c th thc hin t trc mt cch an ton. N c xc nh trn c s phn tch quy lut din bin ca m vt liu chy theo thi gian trong ngy. Trn thc t thi im t trc l thi im m m vt liu chy vt qu mt gii hn nht nh c th kim sot c m chy, theo kt qu nghin cu ca ti ny th t trc rng thng cn thc hin khi m vt liu chy 30-50%, rng khp l 20-25%. Ph hp vi yu cu ny th thi im t cn bt u vo khong 18 gi hng ngy v kt thc trc 9 gi sng hm sau.

- Thu gom vt liu cho t trc,

t trc cc rng trng non c th lm cht cy. V vy, cn gom vt liu chy vo gia nhng hng cy ngn la khng lm cht cy trng. Khong cch gom vt liu phi cch xa tn cy trng t nht 2 ln chiu cao ngn la. Vic thu gom vt liu chy i vi nhng rng mi trng tng i tn cng sc. Vt liu chy trong trng hp ny ch yu l c v cy bi. V vy, phi ct trc khi thu gom. Trong ti ny vic vic t trc vi nhng rng mi trng c xut theo cng ngh t hai ln lp, c th m t bng mt s bc sau:

(1)- Ct v lm kh c gia nhng hng cy trng. Sau khi kt thc ma ma chng 1 thng s dng my ct c cch gc chng 30-40cm theo bng gia nhng hng cy trng. Chiu rng bng bng khong 2/3 khong cch gia hai hng cy.

(2)- t c ln 1. Ch cho n khi cc thn c b ct kh nhng nhng cy c khng b ct vn ti tin hnh t ln 1. Ln t ny khng lm chy gc c bng ct nhng lm chng b cht nng. Mt phn vt liu chy tinh bng c cn ti cng b chy song chng khng to ngn la ln lm cht cy con.

(3)- t c ln 2. Ch cho n khi cc gc c bng ct b cht kh, tin hnh t ln 2. Cc c quanh cy trng vn ch b chy mt phn pha ngoi, do , khng lm cht cy trng.

Sau hai ln t phn ln gc c cng vi nhng chi mi mc ca chng bng trng b chy. Mt t cn li nhng tn than v gc c b cht nng. Chng to thnh bng trng ngn cn s lan trn ca cc m chy c th hnh thnh trong thi k nguy c nguy c chy cao.

Theo cng ngh ny nhng c ti khng b ct c tc dng nh nhng lp o che ch cho cy trng. Ngn la do t trc to ra lm cho chng b chy tp mt phn v khng cn l vt liu nguy him to thnh m chy ln trong thi k c nguy c chy rng cao.

- Kim sot m chy,

Kim sot m chy l mt trong nhng ni dung quan trng ca t trc. Kim sot s m bo duy tr cng chy v tc ln trn ca la khng vt qu gii hn nht nh, khng bng pht thnh chy rng, khng lm cht cy trng v dng li nhng ranh gii nh trc.

Vic kim sot m chy c thc hin bng phi hp nhiu yu t k thut khc nhau nh chn thi im t, to bng trng ngn cn chy lan, v sinh rng khng cho chy mt t tr thnh chy tn, t trc nhiu ln, v trc tip dp tt m chy khi bng pht khng theo d kin. :

(1)- Chn thi im t trc

Kt qu phn tch trn cho thy thi im t trc l thi im m m vt liu chy cn mc 20-30% vi rng khp (v cy l rng ni chung), 35-50% vi rng thng (v cy l kim ni chung). m ny m bo mt phn vt liu chy lp di khng b chy do cn m t. Lng nhit to ra ca qu trnh chy phi tiu tn phn ln cho sy kh cc vt liu chy.

Thi im t trc l vo sau 18 gi hng ngy cho n 9 gi sng hm sau. y l thi k nhit t khng kh h thp, vt liu chy ht nc ca khng kh lm m ca n tng ln, ngoi ra y cng l thi im nhit khng kh trong ngy gim xung, m khng kh tng ln v gi khng qu mnh. V vy, d dng kim sot ngn la.

(2)- To bng ngn cn chy lan

Ngn la trong t trc c th chy lan theo cc hng khc nhau. V vy, khng ch ngn la khng chy vo cy trng, khng chy ra ngoi din tch thit k cn to nhng bng ngn cch ngn la vi vt liu m hn hoc khng cn vt liu chy. Bng ngn cch c th l nhng di rng hn giao cc loi cy bn a. Chng l nhng loi cy thng xanh to nn tn che cao, c kh nng gi nc v lm cho t cng nh vt liu m t. Khi ngn la lan n nhng di rng ny s t tt v vt liu chy t hn hoc m hn.

Bng ngn cch cng c th c to ra bng vic gi li nhng bng cy bi thm ti khng b ct. Chng cn hm lng nc cao trong thn nn khi la trong t trc lan n s t tt do vt liu chy tr ln m t.

Bng ngn cch cng c th c to ra bng cch dn sch vt liu chy trn mt t. Khi la lan n s t tt do ht vt liu chy.

(3)- V sinh rng

Trong mt s trng thi rng mi trng c bit l rng thng th s kt hp ca c v cy bi mt t vi nhng cnh l kh phn di tn c th lm cho vt liu chy phn b tng i lin tc theo chiu cao. Khi ngn la mt t lan n chng d dng pht trin thnh chy tn v gy chy rng khng kim sot c. V sinh rng trong nhng trng hp ny lm cho la trong t trc c hn ch trong m chy mt t m khng pht trin thnh chy tn rng.

(4)- t trc nhiu ln

t trc nhiu ln kt hp vi k thut pht lm kh mt phn vt liu chy vo nhng thi im khc nhau s m bo to c s khc bit v kh nng chy ca nhng din tch khc nhau. Nh , nh hng c ngn la trong t trc lan trn nhng din tch ny m khng lan trn nhng din tch khc.

(5) Trc tip dp tt m chy khi bng pht khng theo d kin

Trong mt s trng hp nhng bng ngn cch c to ra ngn cn chy lan khng m bo, v sinh rng cha trit , hoc thi tit din bin khng nh d kin v.v... th ngn la trong t trc vn c th lan qua bng ngn cch ch ny hay ch kia, leo ln tn cy ch ny hay ch khc, hoc tn than cun ra khi din tch t trc v to thnh m chy ngoi d kin v.v... V vy, trong qa trnh t trc ngi ta phi b tr lc lng theo di v sn sng dp trc tip vo ngn la khi chng bng pht ngoi d kin.

- An ton trong t trc v

An ton l ni dung quan trng cn thc hin trong t trc. m bo an ton ngi thc hin c trc cn c tp hun nm vng k thut t trc, phi c trng b y bo h lao ng v nhng thit b dp chy khi cn thit. Ngoi ra hot ng t trc cn c thc hin theo nhng phng n c ph duyt bi cc c quan chc nng c chuyn mn v thm quyn.

- Chu k t trc v t l din tch t trc hng nm

Chu k t trc l khong thi gian lp li hot ng t trc tnh bng nm. Chu k t trc cng di th nh hng tiu cc ca n n hon cnh sinh thi cng t. Tuy nhin, trong mt s trng hp, chu k t trc di s lm cho khi lng vt liu chy tch t c tng v nguy c chy rng cng ln ln, vic kim sot ngn la trong t trc tr ln kh khn. V vy, ngi ta thng xc nh chu k t trc l khong thi gian di nht m ngn la trong t trc vn c th kim sot c. Nh vy, chu k t trc c quyt nh trn c s phn tch quy lut tch t vt liu chy v s ph thuc ca cng chy vo khi lng vt liu. Theo hng dn ca Cc kim lm th chu k t trc c xc nh chung cho cc loi rng l khong 5-6 nm v t l din tch t trc hng nm l khong 15-20%. Tuy nhin, nghin cu Ty Nguyn cho thy, trong iu kin cc k kh hn y th chu k t trc c xc nh l 3-4 nm vi rng khp v 4-5 nm vi rng thng. Nh vy, t l din tch t trc hng nm vi rng khp khong 25-30% cn vi rng thng l 20-25%

Tc gi:TS. B Minh Chu, PGS.TS Vng Vn Qunh

C gi tr thp, km cht lng, g cng bng chu thng chim, ln chim t ai ph hp nht pht trin thng.Loi khng mong mun c th m ng hay loi b nhng cy thng.Tuy nhin, vi vic s dng ng n chy theo quy nh, understory c th c qun l hn ch cnh tranh vi cc loi mong mun trong khi ng thi cung cp trnh duyt cho ng vt hoang d.

Summer t kim sot g cng.