Shel­ter low­ers stock stress

Matamata Chronicle - - Rural Delivery - By BALA TIKKISETTY

It’s win­ter again, the time of year that is best for tree plant­ing on farm.

Us­ing trees for stock shel­ter is one of the ways farm­ers can lessen the cli­matic stress an­i­mals feel dur­ing win­ter.

Nor­mally an an­i­mal liv­ing in its nat­u­ral habi­tat would find its own shel­ter but farmed an­i­mals may not be pro­vided with suf­fi­cient op­tions, es­pe­cially if they are in a field of grass sur­rounded only by a wire fence.

Plant­ing a shel­ter belt is the op­tion open to some live­stock farm­ers for re­duc­ing the ad­verse ef­fects of wind.

Ar­ti­fi­cial wind­breaks also play a part in pro­tect­ing live­stock where cost al­lows and rapid pro­tec­tion is es­sen­tial.

When es­tab­lish­ing a shel­ter belt, care­ful con­sid­er­a­tion needs to be given to site se­lec­tion and the tree species that are to be used.

An un­der­stand­ing of the ter­rain and lo­cal weather con­di­tions is im­por­tant, along with an ap­pre­ci­a­tion of the in­ter­ac­tion with live­stock be­hav­iour.

Strate­gic plant­ing is likely to be more worth­while than blan­ket plant­ing and be­cause of the longterm com­mit­ment, a care­ful de­ci­sion should be made.

Be­sides pro­tect­ing stock, the tra­di­tional view has been that the shel­ter belts help to re­duce evap­o­ra­tion of soil mois­ture and tran­spi­ra­tion from the grass. Strong winds in par­tic­u­lar en­hance tran­spi­ra­tion rates from the grass and, if the wa­ter ab­sorp­tion rate by the roots is lower than the tran­spi­ra­tion rate, the plant de­vel­ops an in­ter­nal mois­ture deficit.

The re­duced growth rates were re­flected in re­duced dry weight, leaf area, and height but leaf area was much more sen­si­tive to wind than growth of whole plant weight, which sup­ports the con­cept that leaf cell ex­pan­sion is specif­i­cally lim­ited.

Wind can cause phys­i­cal dam­age to grasses, lead­ing to stunt­ing or des­ic­ca­tion. At higher wind speeds, grass blades knock and rub to­gether, bend over, and fre­quently ro­tate about their lon­gi­tu­di­nal axes. Such move­ments could pro­duce per­ma­nent lat­eral frac­tures as well as wilt­ing and des­ic­ca­tion of the leaf tips.

In ad­di­tion to en­vi­ron­men­tal ben­e­fits such as ero­sion con­trol and soil con­ser­va­tion, shel­ter can have com­ple­men­tary ef­fects by achiev­ing mul­ti­ple goals for both the landowner and the en­vi­ron­ment.

Re­cent re­search re­ports re­veal that shel­ter­ing and feed­ing ewes be­fore lamb­ing has a ma­jor im­pact on re­duc­ing lamb losses.

The re­ports also say that shel­ter­ing and feed­ing ewes two weeks be­fore lamb­ing has a big­ger ef­fect on lamb sur­vival.

The types of species used in the shel­ter belts will make a dif­fer­ence in the num­ber of in­ver­te­brates.

Broadleaf shel­ter har­bour more ground-liv­ing spi­ders than conifer shel­ter belts and there will be a greater va­ri­ety of na­tive species of spi­ders and bee­tles in shel­ter belts made up of na­tive species.

These spi­ders and bee­tles can play an im­por­tant role on pas­toral farms by help­ing to re­duce the num­bers of pas­ture pests.

Roots hold the soil to­gether, pro­vid­ing sig­nif­i­cant re­in­forc­ing.

Root ten­sile strength is im­por­tant, but dif­fers be­tween species.

The ef­fect of trees in re­duc­ing ero­sion is a func­tion of tree size, tree stock­ing per hectare, root ten­sile strength, and rate of de­cay af­ter har­vest.

Shel­ter trees can be a haven for birds, give shel­ter for homes and build­ings, stock yards, be aes­thet­i­cally pleas­ing, and in­crease the tree species in an area.

This is one of the largest ways of in­creas­ing bio­di­ver­sity.

Shel­ter can also screen noise and re­duce odours associated with live­stock op­er­a­tions.

The use of na­tive plants, par­tic­u­larly those nat­u­rally oc­cur­ring in the lo­cal­ity, help to pre­serve the lo­cal char­ac­ter and pro­vide for­age for bees.

Shel­ter belts con­trol the re­moval of top soil by the wind, when the es­tab­lish­ment of shel­ter is un­der­taken si­mul­ta­ne­ously with other sus­tain­able land use prac­tices such as min­i­mum tillage.

Good shel­ter im­proves the mi­cro­cli­mate of plants and soil by im­prov­ing plant wa­ter re­la­tions and con­serv­ing heat and re­duc­ing phys­i­cal dam­age. It is very im­por­tant to know that the prin­ci­ples of shel­ter and the tech­niques of es­tab­lish­ing wind­breaks as a sus­tain­able land man­age­ment prac­tice.

There are four main con­tribut­ing fac­tors or prin­ci­ples re­lat­ing to ef­fec­tive­ness of shel­ter – ori­en­ta­tion, per­me­abil­ity, length, and height.

Shel­ter is most ef­fec­tive when sited at the right an­gles to the erod­ing wind.

The wind bar­rier should be sited di­rectly across the most harm­ful wind to give max­i­mum pro­tec­tion.

If east-west belts are re­quired they should in­clude de­cid­u­ous species to lessen the win­ter shad­ing of pas­tures.

Poros­ity of the shel­ter belt de­ter­mines the wind be­hav­iour on the lee­ward and to a some ex­tent on the wind­ward side.

Prac­ti­cal ex­pe­ri­ence has shown clearly that belts of medium poros­ity (about 50 per cent) pro­duce a much more even wind flow over a much wider area.

Good poros­ity can be achieved by cor­rect species choice and sub­se­quent man­age­ment.

When poros­ity is low, the wind pro­file is changed; tur­bu­lence oc­curs at a fac­tor of about five times the shel­ter height.

It is im­por­tant that shel­ter fil­ters the wind to avoid tur­bu­lence.

This is achieved by plant­ing at pre-de­ter­mined spac­ings and prun­ing.

The longer the wind­break the bet­ter the pro­tec­tion.

Short plant­ings have a dis­pro­por­tion­ate edge ef­fect, where wind slips around the ends re­duc­ing the area of pro­tec­tion.

Gaps in a shel­ter belt cause the wind to fun­nel through at ex­ces­sive speed.

This can hap­pen where there are miss­ing trees or when there is a draughty space at ground level.

Be­cause of the na­ture of wind pat­terns through the gaps it is ex­tremely dif­fi­cult to fill them in later.

Any early fail­ure must re­placed as soon as pos­si­ble.


Height of the shel­ter di­rectly in­flu­ences the area of wind re­duc­tion on the lee­ward and wind­ward side.

The greater the height greater the area in­flu­enced.

Gen­er­ally, good wind shel­ter is pro­vided for 15 times with some ef­fect up to 20 times the shel­ter height on the lee­ward side and up to five times on the wind­ward side, where a high de­gree of pro­tec­tion is re­quired.

Tall shel­ter gives the most eco­nomic pro­tec­tion as the area pro­tected is di­rectly re­lated to the height of the wind­break

For fur­ther de­tails and ad­vice, please call Bala Tikkisetty at the Waikato Re­gional Coun­cil on 0800 800 401.


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