Wind chal­lenges for BoP or­chards

New Zealand has a tem­per­ate mar­itime cli­mate that offers unique op­por­tu­ni­ties for grow­ing pro­duce. But be­ing tem­per­ate and mar­itime also has draw­backs. The con­se­quent vari­abil­ity of cli­mate can pro­vide chal­lenges for grow­ers.

The Orchardist - - Orchard Management - By Toni String­field, Fruition Hor­ti­cul­ture

Too much rain at times, which has cer­tainly been an is­sue for many North Is­land grow­ers this sea­son, and oc­ca­sion­ally too lit­tle rain. Tem­per­a­tures are fairly re­li­able and in the ‘Goldilocks range’, i.e. not too hot and not too cold, be­cause we lack the ex­tremes of tem­per­a­ture seen in more con­ti­nen­tal cli­mates. Grow­ers have also gen­er­ally been care­ful to se­lect crops suit­able for the tem­per­a­tures in their area.

The other thing that comes with a tem­per­ate mar­itime cli­mate is wind. Most or­chard blocks are well shel­tered to pro­tect trees and vines from cane or branch break­age and fruit mark­ing. Many grow­ers, how­ever, know that one side of a block, or tran­sect through a block, does get wind dam­age as land drops away to one side. Higher parts of the block may not be ad­e­quately shel­tered from the pre­vail­ing wind, or wind comes through gaps in the shel­ter which are there for ac­cess or to en­sure views from the house are not com­pro­mised!

Bay of Plenty grow­ers may have no­ticed this last sea­son that wind dam­age was par­tic­u­larly bad where shel­ter is not ideal on some parts of their or­chards.

WIND MEA­SUR­ING

Wind is mea­sured as wind run and wind gust. Wind run is mea­sured as kilo­me­tres per 24 hours. It is the dis­tance the wind trav­els, in one place, that day. It is fre­quently mea­sured us­ing a cup anemome­ter. See pic­ture 1.

As the wind blows the cups turn; the wind speed can be de­rived by count­ing the num­ber of full ro­ta­tions of the cups.

Be­cause wind changes di­rec­tion dur­ing the day there is no di­rec­tional data avail­able with the wind run mea­sure­ment from NIWA. It is the wind gust data from NIWA that pro­vides us with di­rec­tional in­for­ma­tion. As gusts oc­cur within the stream of the pre­vail­ing wind, not against it, we are ad­vised of the di­rec­tion of the stronger wind on that day. All data used to write this article is pro­vided by NIWA via the CliFlo web­site and is based on Tau­ranga data.

The Tau­ranga weather sta­tion at the air­port, near the har­bour, records higher wind speeds than the Te Puke weather sta­tion in the midst of the Te Puke ki­wifruit grow­ing area. The Te Puke sta­tion is bet­ter shel­tered from the wind, though lo­cated in a rel­a­tively open area. There are many or­chards lo­cated on the fringes of Tau­ranga har­bour and fur­ther down the coast to Maketu and be­yond, so us­ing Tau­ranga weather sta­tion data is valid.

UNITS OF WIND MEA­SURE­MENT

Wind is mea­sured by a num­ber of units. The ear­li­est scale, still used to­day to de­scribe wind speed, is the Beau­fort Scale. The Beau­fort Scale was based on ob­ser­va­tions of sea con­di­tions and how those re­lated to sail­ing ships in the early 1800s, rang­ing from so lit­tle wind it was hard to steer the ship, to winds that would rip the sails. It was later ex­tended to in­clude ob­ser­va­tions of land con­di­tions. Ranges ex­pressed in me­tres per sec­ond (m/s) and kilo­me­tres per hour (km/h) were added for each of Sir Fran­cis Beau­fort’s 13 de­scribed wind cat­e­gories.

For the pur­poses of this article I have di­vided wind run data into units above or be­low 500 kilo­me­tres per 24 hours. A wind run of 500km/day equates to an av­er­age wind speed of 21km/hour which is de­scribed on the Beau­fort Scale as be­ing at the lower end of a mod­er­ate breeze. A mod­er­ate breeze ‘raises dust and loose paper; small branches moved’. If small branches are moved then the rapidly grow­ing canes of ki­wifruit vines with their large leaves will be quite mo­bile. Also 21km/h is only the av­er­age wind speed, there is con­sid­er­able

Pic­ture 1

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