134 W e a t h e r and Climate (1991) 11: 134-138 IMPACTS OF CLIMATE ON AGRICULTURE : A SOUTHERN PERSPECTIVE M J Salinger National Climate Centre, N Z Meteorological Service Global climate change will particularly affect agricultural patterns i n temperate and subtropical latitudes o f the southern hemisphere. Many countries in these latitudes have a maritime, or semi-maritime climate in comparison with their northern counterparts. Best estimates o f future climate place temperature increases at 1.5°C, with a range from 0.5 to 2.5°C by 2030 AD. Here the impacts of these and associated changes in other climate factors on southern agricultural systems are considered. IMPACTS ON CROP DEVELOPMENT Crop development is the progress a plant makes from germination to maturity for an annual crop; and the annual cycle from bud initiation to maturity for a perennial crop. The rate of development in the field is generally determined by temperature, and to some extent by daylength. Temperature Temperature increases change the length o f the potential growing season in the southern hemisphere, resulting in substantial shifts o f agricultural potential. For a 1°C increase in temperature, present crops and pasture could be grown at 200 metres higher in altitude and about 200 km further polewards. An increase in mean temperature increases thermal time (degree-day) accumulation above threshold base temperatures. As the thermal time requirement for a crop variety to mature is constant, crops will mature earlier. About 200-300 degree-days are added to the growing season, decreasing crop maturation time by two to four weeks. Similarly, an increase in mean temperature decreases the number of days of frost and lengthens the frost free season, the interval between the last frost in spring and the first frost in autumn. I n continental northern hemisphere environments the season lengthens by 10 days per 1°C increase in mean temperature. For maritime southern hemisphere environments the increase i n frost free season is between 25 and 30 days. Many temperate crops bred in the more continental north have winter chilling requirements (a period of low temperatures in winter) to initiate or accelerate the flowering process. As temperature increases reduce the amount of chilling in the southern climates, these crops have their potential range contracted polewards. Ultimately, year-to-year temperature variability will still be crucial in determining the success o f arable and horticultural crops, especially where crops are grown at the extreme margins of their range. Daylength The greatest daylength effects would be felt with the latitudinal shifts in crop and pasture varieties as a consequence o f warmer temperatures. Crops would need to adapt to a new light environment.
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
134 W e a t h e r and Climate (1991) 11: 134-138
IMPACTS OF CLIMATE ON AGRICULTURE : A SOUTHERNPERSPECTIVE
M J SalingerNational Cl imate Centre, N Z Meteorological Service
Global c l i m a t e change w i l l pa r t i cu l a r l y a f f e c t ag r i cu l tu ra l pa t te rns i n temperateand sub t rop ica l l a t i t udes o f t h e sou the rn hemisphere. M a n y c o u n t r i e s i n t h e s elatitudes h a v e a m a r i t i m e , o r semi -mar i t ime c l i m a t e i n compar i son w i t h t h e i rnorthern c o u n t e r p a r t s . B e s t e s t i m a t e s o f f u t u r e c l i m a t e p l a c e t e m p e r a t u r eincreases a t 1.5°C, w i t h a range f r o m 0.5 t o 2.5°C b y 2030 A D . Here the impacts o fthese a n d associated changes i n o t h e r c l i m a t e f a c t o r s o n sou the rn ag r i cu l tu ra lsystems a r e considered.
IMPACTS O N CROP DEVELOPMENT
Crop development i s t h e progress a p l an t makes f r o m germinat ion t o ma tu r i t y f o ran a n n u a l c r o p ; a n d t h e a n n u a l c y c l e f r o m b u d i n i t i a t i o n t o m a t u r i t y f o r aperennial c r o p . T h e r a t e o f development i n t h e f i e l d i s genera l l y determined b ytemperature, a n d t o s o m e ex ten t b y daylength.
T e m p e r a t u r e
Temperature increases change t h e l e n g t h o f t h e po ten t ia l g r o w i n g season i n t h esouthern hemisphere, r e s u l t i n g i n substant ia l s h i f t s o f agr icu l tu ra l po ten t ia l . F o ra 1 ° C increase i n temperature, present c rops a n d pasture c o u l d b e g r o w n a t 2 0 0metres h i g h e r i n a l t i tude a n d abou t 2 0 0 k m fu r the r polewards.
An i n c r e a s e i n m e a n t e m p e r a t u r e i n c r e a s e s t h e r m a l t i m e ( d e g r e e - d a y )accumulat ion a b o v e t h r e s h o l d b a s e t e m p e r a t u r e s . A s t h e t h e r m a l t i m erequirement f o r a c r o p v a r i e t y t o ma tu re i s constant , c r o p s w i l l m a t u r e ear l ie r.About 2 0 0 - 3 0 0 degree-days a r e a d d e d t o t h e g r o w i n g season, decreas ing c r o pmaturation t ime b y t w o t o f o u r weeks.
Similarly, a n increase i n mean temperature decreases t h e numbe r o f days o f f ros tand lengthens t h e f r o s t f r e e season, t h e in te rva l between t h e l a s t f r o s t i n sp r ingand t h e f i r s t f r o s t i n au tumn . I n con t inenta l no r t he rn hemisphere env i ronmentsthe season lengthens b y 1 0 d a y s p e r 1 ° C inc rease i n m e a n temperature. F o rmaritime sou thern hemisphere env i ronments t h e increase i n f r o s t f r e e season i sbetween 2 5 and 3 0 days.
Many temperate c r o p s b r e d i n t h e m o r e cont inenta l n o r t h h a v e w i n t e r c h i l l i n grequirements ( a per iod o f l o w temperatures i n w in te r ) t o i n i t i a te o r accelerate t h eflowering process. A s temperature increases reduce t h e amoun t o f c h i l l i n g i n t h esouthern c l imates , t hese c r o p s h a v e t h e i r potent ia l r a n g e cont racted polewards.
U l t imate ly, y e a r - t o - y e a r t e m p e r a t u r e v a r i a b i l i t y w i l l s t i l l b e c r u c i a l i ndetermining t h e success o f arab le a n d hor t icu l tu ra l c rops , espec ia l l y w h e r e c ropsare g r o w n a t t h e ext reme marg ins o f t h e i r range.
D a y l e n g t h
The greatest daylength effects w o u l d b e f e l t w i t h t h e la t i tud inal sh i f t s i n c r o p andpasture var ie t ies a s a consequence o f warmer temperatures. C r o p s w o u l d need t oadapt t o a n e w l i g h t environment.
Climate Change and Agriculture
IMPACTS O N CROP GROWTH
Growth i s r e g a r d e d a s t h e i nc rease i n d r y w e i g h t o f a p l a n t because o fphotosynthesis. I t i s m a i n l y a consequence o f amb ien t C O 2 concent ra t ion , l i g h tinterception a n d m o i s t u r e .
Carbon D i o x i d e
In t h e m i d s t o f a l l t h e c l ima te uncertainties, atmospher ic C O 2 l e v e l i s present lyincreasing b y 1 . 5 ppm/year and i t w i l l cont inue t o r i se f o r some t ime. H ighe r CO2levels w i l l increase p l a n t g rowth , especia l ly t hose adapted t o a temperate c l ima te(C3 plants). H o w much w i l l b e expressed as y i e l d i s uncertain. T h e effects w i l l b emost pronounced u n d e r h i g h w a t e r st ress a n d h i g h temperatures. T h e w a t e r u s eefficiencies o f a l l c r o p s w o u l d i m p r o v e s ign i f i can t ly.
C3 p lan ts use t h e C 3 biochemical pathway f o r photosynthesis, w h i c h i s l i m i t e d b yC 0 2 concen t ra t ion . T h e C 4 p a t h w a y, u s e d b y C 4 p l a n t s , i s n o t l i m i t e d b yatmospheric C O 2 concent ra t ion. M a n y temperate c e r e a l a n d ho r t i cu l t u ra l c r o p suse t h e C 3 pathway. Subtropical pasture a n d ma ize a r e C 4 crops a n d t h e i r g rowthrates w o u l d b e o n l y s l i gh t l y affected.
M o i s t u r e
This i s a v e r y impor tan t reg ional var iab le f o r agr icu l tura l product ion. T h e impac tof changes i n r a i n f a l l w i l l ove r r i de temperature e f f ec t s i f hea t requirements a r eadequate f o r c rop matu r i t y. L a c k o f s o i l mois ture i s t h e m a i n constraint t o y i e l dsin m a n y temperate a n d subt rop ica l a reas o f t h e sou thern hemisphere, espec ia l l yin t h e s u m m e r season. R e g i o n s w h e r e g r o w i n g season r a i n f a l l increases w o u l dhave h i g h e r y i e l d s , a n d reg ions w i t h r a i n f a l l decreases w o u l d exper ience l o w e ryields w i t h o u t i r r i g a t i o n .
Climate change poses v e r y s ign i f i can t i m p a c t s o n agr i cu l tu ra l p roduc t ion b y i t seffects o n ext reme events: i n some regions droughts w o u l d become m o r e frequent.The changes i n va r iab i l i t y o f extreme events w i l l cause impor tan t changes i n t h ecomparative advantages o r competit iveness o f d i f f e ren t c rops .
Soil m o i s t u r e i s t h e r e s u l t o f a n u m b e r o f w a t e r ba lance processes: r a i n f a l lduration a n d i n t e n s i t y , evapo t ransp i ra t ion a n d r u n o f f . U l t i m a t e l y i t i s t h edecrease o r increase i n s o i l moisture a n d resul t ing changes i n t h e number o f daysat w i l t i ng po in t , ( a d a y w h e n a l l t h e avai lable wa te r capacity i n t h e s o i l f o r p lan tgrowth i s deple ted) t h a t impacts o n c r o p g r o w t h a n d pasture y i e l ds . T h e h i g h e rthe number o f days a t w i l t i ng point , t h e more t i m e l o s t f o r p lan t growth.
Models s h o w t h a t areas t h a t rece ive 1 0 % m o r e prec ip i ta t ion g a i n f r o m 4 t o 1 5extra d a y s ava i l ab le f o r p l a n t g r o w t h pe rm i t t ed b y t h e w a t e r s u p p l y. I n t heseareas, y i e l ds w o u l d increase. Conversely areas w h i c h receive 1 0 % less have 1 2 t o17 ex t ra days o f w i l t i ng po i n t (drought days). Un less ex t ra wa te r can b e added b yirrigation, t h e a r e a s t h a t b e c o m e d r i e r w i l l h a v e l o w e r y i e l d s , a s t h e a c t u a lduration o f p lan t g rowth i s less o v e r t h e g row ing season.
W i n d
Arable a n d hor t icu l tura l c rops a r e a t m o s t r i s k f r o m increases i n w i n d . G a l e a n dstorm f o r c e w i n d s c a u s e mechanica l damage t o p l a n t s w h i c h m a y damage t h eplant t o such a n extent t ha t t h e p lan t needs replacing, o r t ha t t h e present season'scrop i s uneconomic .
135
136 C l i m a t e Change and Agriculture
Many areas i n t h e southern hemisphere a re i n i s land locations, a n d a r e exposed t ostrong w i n d s . A n y changes i n t r o p i c a l c y c l o n e (hu r r i cane ) f r e q u e n c y o r p a t h swi l l h a v e s ign i f i can t e f f e c t s o n c r o p product ion.
IMPACTS O N AGRICULTURAL PESTS A N D DISEASES
Climate change w i l l a l t e r t h e inc idence o f agr icul tural pes ts a n d diseases, o w i n gto c h a n g e s i n t h e w e a t h e r c o n d i t i o n s t h a t f a v o u r o r d i s c o u r a g e t h e m .Introduction o f n e w c r o p s a n d var ie t ies w o u l d b e accompanied b y n e w diseasesand p e s t s . T h e g r e a t e s t t h r e a t c o m e s f r o m t h e m i g r a t i o n p o l e w a r d s o r t h einadvertent in t roduct ion o f n e w pests a n d diseases, especial ly o n is lands.
Fungal a n d B a c t e r i a l D i s e a s e s
Rainfall a n d temperature a r e t h e t w o c l ima t i c fac to rs t h a t s ign i f i can t a f f e c t thesediseases. T h e y r e q u i r e f r e e w a t e r t o i n f e c t t h e h o s t c r o p . R a i n f a l l a n d t h efrequency a n d d u r a t i o n o f su r face l e a f wetness w i t h h i g h h u m i d i t y a r e m a j o rrequirements f o r d i s e a s e e p i d e m i c s . W a r m e r t empera tu res a l s o s h o r t e n t h egeneration t i m e , i nc reas ing t h e deve lopment r a t e o f ep idemics . I n t h o s e a reaswhich b e c o m e w e t t e r , t h e d i sease t h r e a t f r o m f u n g a l a n d b a c t e r i a l ep idem icsincreases.
Insect a n d M i t e P e s t s
The gene ra l e f f e c t s o f a w a r m e r c l i m a t e o n t hese pes t s a r e t o increase t h e i rdevelopment ra tes , resu l t i ng i n m o r e generat ions i n a g r o w i n g season. W h e r e anatural pes t enemy i s present, b io log ica l con t ro l m a y b e m o r e o r less e ffec t ive i nwarmer temperatures, depend ing o n t h e o p t i m u m temperature f o r t h e p e s t a n dnatural e n e m y conce rned .
Animal D i s e a s e s a n d P a r a s i t e s
The i n c i d e n c e o f m a n y e x i s t i n g l i v e s t o c k d iseases a n d paras i tes i s l i k e l y t oincrease w i t h temperature increases, because o f fas te r l i f e c y c l e comp le t ion a n denhanced s u r v i v a l . I n s o u t h e r n l i v e s t o c k a reas d iseases a n d paras i tes s u c h a snematodes, sa lmonel la a n d f a c i a l eczema w o u l d increase. A t t h e s a m e t i m e pestssuch a s midges, mosquitos a n d t i c k s w o u l d a l l spread polewards. These a r e vectorsfor a range o f new diseases w h i c h cou ld become established.
FIELD CROPS
Annual c r o p s a r e sens i t i ve t o c l i m a t e change, b u t because t h e i r r o ta t i on cyc lesare shor t , t h e y c a n b e replaced q u i c k l y, s o adjustment c a n b e rap id . T h e cur rentgenetic base o f crop types and varieties i s w ide. I t wou ld b e possible t o change thecrop t y p e s a n d var ie t ies g r o w n i n a n a r e a f as te r t h a n t h e c l i m a t e i s l i k e l y t ochange, p rov i ded p l a n t b reed ing a n d v a r i e t y t es t i ng a r e mainta ined.
The potent ia l f o r a m a j o r s h i f t i n la t i tude range poleward a n d t o h i ghe r elevationwould o c c u r w i t h temperature increases f o r a l l f i e l d c r o p s (whea t , b a r l e y, oa t s ,maize, s o r g h u m , p e a s , p o t a t o e s , soybeans , s u n f l o w e r , c o t t o n a n d r i c e ) . T h eincreases o f t e m p e r a t u r e a n d C O 2 w i l l i n c r e a s e t h e r a t e s o f b i o l o g i c a lproductivity, s o c r o p p roduc t i on r a t e s w i l l increase. O n t h e o t h e r hand , h i g h e rtemperatures w i l l i n c r e a s e c r o p d e v e l o p m e n t r a t e s a n d h e n c e t h e d u r a t i o n .Therefore t h e t i m e avai lable f o r accumulation o f y i e ld w i l l b e shorter.
The m a i n f i e l d c r o p s a r e annual species. There i s n o need t o encourage prematurerelocation o f c rop product ion t o n e w regions. T h e f a c t t h a t t h i s t y p e o f cropping
Climate Change and Agriculture 1 3 7
operates o n a n annual cyc le means t h e ac t i v i t y c a n s h i f t i n a v e r y shor t t ime.Plant b r e e d i n g p rogrammes, w h i c h ope ra te i n a l o n g t i m e f r a m e , s h o u l d b eencouraged t o m a i n t a i n s t r o n g s t ra teg ic bases s o t h e y h a v e t h e f l e x i b i l i t y t oproduce n e w var ie t ies adapted t o changed condi t ions.
HORTICULTURAL CROPS
Horticultural c rops a r e especial ly sensi t ive t o c l ima te change because t h e y h a v e along r o t a t i o n c y c l e a n d s o m e c r o p t y p e s h a v e a s m a l l g e n e t i c base . Va r i e t ydiversity a l l o w s s u b s t i t u t i o n s o f n e w v a r i e t i e s t o m a t c h n e w p a t t e r n s o fagr icul tural p o t e n t i a l .
Temperature increases m o v e t h e po ten t ia l l a t i t u d e r a n g e po leward a n d t o h i g h e relevations. H o w e v e r , t h i s c h a n g e i n r a n g e w i l l b e m o d i f i e d b y c h a n g e s i nrainfall. R e g i o n s t h a t b e c o m e w e t t e r f o r m a n y tempera te c r o p s w o u l d b e c o m emore unsui table because o f increased disease pressure.
Other s t ra teg ies t o a d a p t , a p a r t f r o m m o v i n g c r o p r a n g e s sou thward , i n c l u d ebreeding programmes f o r n e w var ie t ies w i t h d i f f e r e n t responses t o c l ima te . T h edegree o f adaptation strategies w o u l d v a r y. Perhaps t h e bes t strategies w o u l d b e amixture o f m o v e m e n t o f c r o p ranges po lewards a n d u p w a r d s i n t r o d u c i n g n e wvarieties o f t h e same c r o p w h i c h a r e be t te r su i ted t o t h e d i s t r i c t c l imate. F i n a l l y,the s e a r c h i n g f o r c r o p s t h a t n a t u r a l l y m a t c h t h e n e w c l i m a t e i s a n o t h e rresponse.
PASTURE
Pastures a r e sensi t ive t o c l imate change, b u t because t h e i r l i f e cyc le c a n b e shor tor t h e var ie ty c a n b e replaced qu ick ly, adjustment w o u l d b e rap id .
Temperate pastures a r e a t p e a k p roduc t ion i n s p r i n g . I n compar ison, subt rop ica lpastures p e a k i n summer. A l t h o u g h temperate grasses w o u l d spread po leward a n dupwards, s o t o o w o u l d subt rop ica l grasses. C l i m a t e w a r m i n g i n m a n y sou the rnlatitudes w o u l d increase t h e a rea covered b y subtropica l pasture a n d decrease t h earea i n t e m p e r a t e p a s t u r e . I f m o i s t u r e r e q u i r e m e n t s a r e m a i n t a i n e d , h i g h e ryields o f b o t h pas tu re t y p e s w o u l d o c c u r. T h e r e w o u l d b e m a r k e d e f f e c t s o nseasonality o f pasture product ion depending o n t h e ba lance o f temperate grasses,legumes a n d sub t rop ica l grasses.
With a s h i f t towards m o r e subtropical pastures, pasture product ion w o u l d increaseor decrease depend ing o n w h e t h e r t h e sub t rop ica l pas tu re w a s b e t t e r o r w o r s ethan t h e tempera te p a s t u r e i t rep laced . A m a j o r l e g u m e c o m p o n e n t o f b o t htemperate a n d subt rop ica l pastures i s w h i t e c l ove r.
For e x i s t i n g pas tures t h e e f f e c t s o f c l i m a t e c h a n g e o n p r o d u c t i v i t y w o u l d b eimmediate. H o w e v e r , t h e expans ion o f sub t rop ica l g rasses p o l e w a r d w o u l d l a gbehind c l ima te change. Fa rm ing systems w i l l need t o adapt t o t h e change i n f e e dquality a n d q u a n t i t y. Subt rop ica l grasses a r e character ised b y a s u m m e r g r o w t hpeak a n d a w i n t e r t r o u g h . Te m p e r a t e pastures. o n t h e o t h e r h a n d , w i l l t e n dtowards a l ess marked seasonal g r o w t h pat tern, excep t whe re mois ture i s l i m i t i n gin s u m m e r.
More impo r tan t l y, t h e th resho ld a l t i tudes f o r temperate pasture p roduc t ion w o u l dbe h igher. T h e u p p e r l i m i t o f g raz ing l a n d w o u l d r i s e b y 2 0 0 met res p e r 1 ° Ctemperature i n c r e a s e . I n h i g h e r e l e v a t e d a r e a s o f S o u t h A m e r i c a , s o u t h e r nAfrica, Aus t ra l i a a n d N e w Zealand such a w a r m i n g w i l l s ign i f i cant ly increase t h earea tha t c a n b e used f o r grazing l ivestock.
138 C l i m a t e Change and Agriculture
L IVESTOCK
Direct e f f e c t s o f c l i m a t e c h a n g e o n metabo l i sm, g r o w t h a n d pe r fo rmance o fanimals w o u l d n o t b e important, except tha t c o l d stress w o u l d b e reduced. Howeverheat stress w o u l d have s ign i f icant e f fec ts o n l o w e r concept ion ra tes i n l ivestock.
Indirect e f f e c t s w o u l d h a v e v e r y s i g n i f i c a n t i m p a c t s o n a n i m a l p r o d u c t i o n .Changes i n t h e amoun t a n d seasonal d is t r ibu t ion o f f eed ava i l ab i l i t y a n d q u a l i t y,and i n t h e t y p e a n d i n f e c t i v i t y o f pests, diseases a n d parasi tes w o u l d h a v e t h emain e f f e c t o n product ion.
Climate w a r m i n g w i l l r e d u c e t h e c h i l l i n g t h a t o c c u r s o f n e w b o r n l i v e s t o c k i nwinter a n d s p r i n g , r e d u c i n g m o r t a l i t y r a t e s o f s h e e p a n d c a t t l e . I n w a r m e rclimates, h e a t stress w i l l a f f e c t f eed in take , metabol ism, b o d y we igh t , m i l k y i e lds(dairy c a t t l e ) a n d rep roduc t i ve per formance.
Increased q u a n t i t y o f f e e d u s u a l l y r e s u l t s i n i m p r o v e d a n i m a l p e r f o r m a n c eprovided f e e d i n t a k e a n d d iges t i b i l i t y a r e n o t l i m i t i n g . I n temperate zones , t h eincrease i n CO2 a n d temperature s h o u l d m a r k e d l y inc rease s p r i n g , s u m m e r a n dautumn product ion o f pasture, p rov ided r a i n f a l l d o e s n o t decrease. H i g h e r w i n t e rtemperatures r e s u l t i n i m p r o v e d w i n t e r g r o w t h a n d q u a l i t y pas tu res dom ina tedby temperate C 3 pasture species. I n m a n y w a n n e r temperate a n d subtropical areastemperature increases w i l l a l l o w t h e spread o f subtropical C 4 grasses, w h i c h havea l o w e r d igest ib i l i ty a n d h ighe r f i b r e con ten t than temperate C 3 grasses. T h i s w i l lresult i n r e d u c e d a n i m a l i n t a k e s , g r o w t h r a t e s a n d m i l k y i e l d s f o r sou the rnlivestock product ion i n these areas. T h e h i g h e r CO2 l e v e l s s h o u l d i m p r o v e w a t e ruse e f f i c i e n c i e s , w h i c h p a r t i a l l y c o m p e n s a t e f o r r e d u c t i o n s i n r a i n f a l l o rincreases i n evapo t ransp i ra t i on .
Increases i n tempera ture a n d a l s o h u m i d i t y t e n d t o p r o d u c e m o r e f avou rab leconditions f o r an ima l pests, diseases a n d parasites.
A l l t hese changes r a i s e a n u m b e r o f adaptat ion strategies f o r l i ves tock fa rm ing .The change i n seasonal i ty o f f e e d product ion w i l l m e a n a change i n t i m i n g o freproduction a n d g r o w t h cyc les . H o w e v e r, a dec l i ne i n f e e d q u a l i t y i n w a r m e rtemperate r e g i o n s m e a n s r e l o c a t i o n o f l i v e s t o c k i n d u s t r i e s s u c h a s d a i r y i n gpoleward. Sheep f ann ing act iv i t ies shou ld b e ab le t o spread t o h i ghe r elevations.
Apart f r o m re loca t ion o f l i ves tock r e a r i n g a t t h e p o l e w a r d a n d h i g h e r a l t i t udemargins, w a r m i n g w o u l d inc rease t h e inc idence o f a n d po ten t i a l l osses d u e t opests, diseases a n d parasi tes, a n d hence increase t h e n e e d f o r e f f ec t i ve c o n t r o lmeasures. Changes i n f a r m management i n response t o chang ing pas tu re g r o w t hpatterns, together w i t h changes i n d is t r ibu t ion a n d a c t i v i t y o f pests, diseases a n dparasites w i l l r e q u i r e changes t o f a r m i n g c o n t r o l programmes.
Related Documents
