View of Northern agriculture: constraints and responses to global climate change

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Northern agriculture: constraints and responses

to global ^climate change

Timo J.N. Mela

AgriculturalResearch Centreof^Finland,^Institute of^Cropand Soil Science, FIN-31600Jokioinen,Finland

Inthe northerncircumpolarzone, the areabetween the 600°Cd and 1200°Cdisoplethsof effective temperature^sumabove5°C,the annualreceiptof solar energyis limitedbythe lowangleof radiation arrivingat the earth’s surface. This is theprimarycauseoftheclimatic constraints observed inthe

zone, suchas low temperatures, ^ashortgrowing season, frostsduring thegrowing season,long and cold winters and thicksnow cover.In Finland,thelengthof thegrowingseasonvaries from 180 days in the south(60°N) to 120 days inthe north (70°N). Consequently, thegrowing time for cropsfrom sowingtoripening is alsoshort, which limits their abilitytoproduce high yields.

The most advanced forms offarming inthe high-latitude ^{zone are} encountered towards the south in NorthernEurope, central Siberia and theprairies of Canada, i.e. mainly inthephytogeographical hemiboreal zonewhere the effective temperaturesum is higherthan 1200°Cd. Conditions foragri- culture then deteriorategradually further north with thecoolingof theclimate,and this is reflected as anincrease incattlerearing at the expense ofgraincultivation.^In^northernEurope farmingis practised asfar north astothe Arctic Circle, at about 66°N latitude. In NorthAmerica, fields extend^to

about ^55°N,In Asia,there arefew fields north of 60°N. Finland is the most northern agricultural country intheworld,with all its field area, about2.5millionhectares, located north of latitude60°N.

Changes in the climate and atmospheric ^C0₂ predicted for the future are likely tohave a strong influence, either beneficial ordisadvantageous, onthe conditions forgrowth innorthernareaswhere the annual meantemperature is 5°Corless.

Key words: Finland, circumpolarzone,crop production, growth conditions, growing season, solar radiation, temperature sum, winter damage

Introduction

The northern circumpolarzone, defined by climatic and vegetationalcriteria, delimitsahigh- latitude zone which comprises about one sixth

of the world’s landarea.In these marginal areas adjacenttothe polar region, manandnature ap- proach the limits of their adaptability and the area is very thinly inhabited.

The zoneis ^notuniform with regard tocon- ditions for living organisms, as canbe seen,for

©Agriculturaland Food ScienceinFinland Manuscriptreceived March 1996

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instance, in thestructure ofagriculture. It is thus often divided into subzoneson a biogeographi- cal basis (Hämet-Ahti ^1981).The circumboreal zone,characterized by dominance of coniferous forests,coincidestoagreat extent with the area between the600 °Cd and 1200 °Cd isopleths of accumulatedtemperatureaboveabasetempera- tureof 5°C (effective temperature sum,^ETS).

Considerable differences withrespect toag- riculture, forestry, reindeer herding, and other activitiesare to be found within this zoneboth between northern and southernareas and in an east-west direction. The most advanced forms of farming in the high-latitudezone(Fig. 1)are encountered towards thesouth, in northernEu- rope,central Siberia and the prairies ofCanada, i.e. mainly in the phytogeographical hemiboreal zone where the effective temperature sum is higher than 1200°Cd (Varjo 1984). Conditions for agriculture then gradually deteriorate towards north with the cooling of theclimate,and this is

reflected as an increase in cattle rearing atthe expense ofgrain cultivation until, ateffective temperature sums of around900 °Cd, farming gradually gives way ^toforestryasthe predomi-

nant form of economic activity.^Innorthern^Eu- ropefarming is practisedasfar north asthe Arc- ticCircle, atabout latitude66 °N. In North Amer- ica,fields extend^to about 55°N. InAsia, there arefew fields north of 60°N.

InFinland, agriculture is concentrated south of the 1000°Cd isopleth. The largest field^areas, up to 50% of the total landarea, arepredomi- nantly located south of the 1200°Cd isopleth.

North of the !000°Cd isopleth fields are^rare;

theycoverless than5% of the total landarea.In the neighbouring countries agriculture is more southern than inFinland, in Sweden 90% and in Norway 50% of cerealsaregrown south of60°N, as in Finland the total fieldarea, about 2,5 millionhectares, is located north of latitude 60°N.

Fig. I.The circumborealzoneand its transcontinental subzones. (1) Northernboreal,(2) middle boreal,(3) southernboreal,(4) hemiboreal and (5) arctic andcomplex, mountain areas (Hämet-Ahti

1981).

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Climatic constraints

In the circumpolar zone, the annual receipt of solar energy is limited by the low angle of radiation arriving atthe earth’s surface. This is the primary cause of the climatic constraints observed in this^zone, suchaslow temperatures, a short growing^season,frosts during the growing season, long and cold winters and thick snow cover.Only in the middle of thesummer, when days are at their longest (between 18 and 24 hours) does the daily incoming radiation_corre- spondtothat of the middle and low latitudes. At this time, the gross C0₂assimilation rate of plants is correspondingly high.

The growingseasonin the circumpolarzone is short. In^Finland, the length of the growing season (defined as the period with daily mean temperature exceeding 5°C) varies from 180 days in the south (60°N) to 120 days in the north (70°N) (Mukula and Rantanen 1987). Conse- quently, the growing time for crops from sow- ing toripening is also short, which limits their ability toproduce high yields. Compared with countries in central Europe, the growing season in Finland is significantly shorter. For example, in Germany the season is one to three months longer than in southern Finland.

The long wintersexertaconsiderablestress onwinterannual and perennial plants. An ample storage ofreservecarbohydrates is necessary _to maintain vital functions through sixtonine cold months. Low temperatures and winter diseases (Microdochium nivaleFr., Samu^&Hall,Typhu- la ishicariensis Imai,Myriosclerotinia borealis

Bub. ^& Vleug, Sclerotinia

trifoliorum

^Erikss.)

often damage and kill wintering plants. Winter diseases thrive in hightemperatures under thick snow cover in the central and northern_partsof Finland and theyare the main_reasonfor winter damage of perennial grasses and winter cereals.

In the_western coastal region, hard icecover of-

ten suffocates wintering cereals and grasses.

Other climatic hazard factors include night frosts in the earlysummer orearlyautumn, which occurannually in someregions (Fig. 2, Solantie

1980).The average number of night frosts varies from threetofour in the agricultural areain June and from 1.5to2.5 in August. Inaweather observatory 100 km north of the southerncoast (Jokioinen 60°49’N, 23°30’E), every second year the last spring frost hasoccurred, onaverage, after 17 June and the last hard spring frost(under -3°C) after 1 June. Every fourth year there has been a hard spring frost on 8 June or later.

The dates for the corresponding first frosts in autumn are20 August, 9 September and 28 Au- gust, respectively. The average duration of the period without hard frosts is 100to 114 daysat inland locations away from lakes and_onemonth longer ^atsites adjacent tolakes, which _are safe areas for growing crops sensitive tofrosts.

Another typical characteristic of the Finnish climate is aprecipitation shortfall_atthe begin- ning of thesummer. It is especially harmful for spring _sown crops and grass grown forpasture and silage. Losses from drought are greatest in the coastal _{area on}clay and silt soils. There isa high variability in climate from yeartoyear, and cool,rainy summers occur acouple of times ina decade causing yield and quality losses. Varia- Fig. 2.Number ofnightfrostsinJune-July(Seläntie 1980)

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tions of yields are large (Mela and Suvanto 1987).

The number of crops whichcan be grown during the short growing _season in the circumpo- larzoneis small,and theyaremainly annual. In Finland, autumn-sown winter wheat and winter rye as well as spring-sown spring wheat for bread, spring turnip rape for oil and protein for feed, and sugar beetare grown in the southern partsof the_country. Themostcommon cereals in Finland, spring-sown barley and oats, are mainly grown for feed andare more widely dis- tributed northwards. Commercialpotatoproduc- tion, some for export, is practised in the north because under the northern conditions the number of aphids which transmit virus diseases is low. Perennial grasses and red clover are grown for forage asfar north_asthe Arctic Circle and beyond.

Under northern conditions yields of all agricultural cropsarelow comparedtothose in middle latitudes.^Incentral Europe, winter forms of wheat and barley aswellaswinter rape arepre- dominantly grown and their yieldsareinherent- ly higher than yields of spring cereals and spring turnip rape suitable for the Finnish conditions today. Growth of sugar beet is regularly ^cutshort byautumn frosts in Finland.However,yields of field crops have doubled in thepast 30 years in Finland due ^to increased fertilization, higher yielding varieties and improved crop husband- ry. This trend is continuing and may even accel-

erateas aresult of climate change.

Changes in climate

Predicted changes in climateas a result of the increasing contentof so-called greenhouse gas- es,carbon dioxide(C0

2^),methane(CH

4^),nitrous oxide (N,O), troposphericozone(O,) ^{and halo-} carbons could have an important influence on the conditions for growth in northernareas.The most important greenhouse gas, C0₂, which alone is thought tobe responsible for about half

of the anticipated globaltemperatureincrease up

tothe middle of thenextcentury, also has adi- rectinfluenceonplant growth. Recent scenari- ospredict _adoubling of C0₂ in the atmosphere overpre-industrial levels approximately between 2060 and 2070 for_a“business-as-usual”_scenar- io, with no changes to present policy (IPCC

1995).

An increase of mean global temperature in the range I.5°Cto4.5°C is predictedasthe equi-

librium response to greenhouse gas forcing equivalent^toaofCO,(IPCC 1992).For the po-

lar regions the increase is higher than the global means. Recent scenarios for thenext centuryin Finland anticipate an increase in mean annual temperature of between 0.1 °C and 0.6 °C per decade with_acentral estimate of O.4°C per decade (Carter 1996).The central estimate ofa4°C warming by the end of the next century is ofa similar magnitude as the warming between the end of the last Ice Ages 10 000 years ago and the presentday atnorthern latitudes.

Under this scenario, in ahundred years the growing season in southern Finland would be prolonged by 6-7weeks, from 160-180 daysto 200-230 days, which corresponds ^to the growing season in northern Germany today. The re- sultant shift of climatic _zonesin Finland would be about 500 to650 km northwards (Carteretal.

1996).

Effects on agriculture

Achangeinmean temperatureof the magnitude envisaged musthave _asignificant effect _onag- riculture in the northern latitudes during thenext few decades. The impact may be beneficial or disadvantageous. In^Finland,increasing _temper-

atureis likely toenhance the growth of spring- sown cereals,especially in northernpartsof the country. However, low temperature is not the only growth-limiting factor for somecrops. For example, in southernFinland, lack of moisture during the early summer can be more harmful

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for the growth of spring barley (Kettunen etal.

1988).Moreover, a change in climate may benefit northern agriculture in several other ways than through temperature alone:

- An increase in carbon dioxide concentration in the atmosphere combined with arise in

temperature may increase the growth and yield ofcrops.However,increasedwaterdef- icit in the soil caused by increased_evapotran- spiration under elevatedtemperature candis-

rupt the growth of crops.

- The period ofsnow coveris likely ^tobecome shorter and the overwintering risk to crops may diminish.

- Cultivation of high-yielding ^autumn sown cropscan be expected^toincrease.

- A longer growing season may enable cultivation of higher yielding cultivars.

- Thezones of suitability for crop species will expandnorthwards,including _zonesof crops not currently grown inFinland, which may move into southern Finland.

- The growing period for grass will be prolonged and yields will increase.

Cultivars which havealong period of growth benefit fromalong growing seasonand develop slowlytoincrease the number oftillers,leafarea and ^root size, theirapparatus for subsequent production of a high yield. When the growing season extends earlier in the spring and crops form green leaves earlier, they_cantake advan- tage of the long, often sunny days in May. This

benefit, however, depends on a favourable fre- quency and timing of future spring frosts. Fur- thermore, the rapid shortening of days in the autumn may curtail the growth of crops in spite of continuing warmweather.

On the otherhand,climate change may have disadvantages, including:

- Existingpests, diseases and weedsarelikely tobecome moreabundant.

- Exotic pestsand diseases may appear.

- The need for plant protection will grow ^and, unless biological methodscanbe developed, theuseof pesticides and fungicides, withre- lated environmental problems, may increase.

- A reduction in soilfrost, prolongation of the frost-free season and possible increases in precipitation may increase the risk of nutri- entleaching.

- A warmer and longer growing season will accelerate the breakdown of soil organic^mat- ter,increasing problems of maintaining good soil ^structure.

Onbalance, however,the overall impact ofa changing climate_on crop yields in the circum- borealzone canbe expectedtobe beneficial. The expansion ofclimaticzonesnorthwards will lead to an increase in the agricultural potential of northern latitudes.Nevereless, the possibilities of the northern latitudes torespond ^to the increasing need of food in the worldare limited because of the unsuitable soil and topographical conditions in many regions.

References

Carter,!.R. ^1996.Developingscenarios ofatmosphere, weather and climate for northernregions. Agriculturaland Food ScienceinFinland ^5:235-249(this issue).

- ,Saarikko,R. A.^&Niemi,K. J. 1996.Assessingthe risks and uncertaintiesof regional crop potential undera changingclimate in Finland. Agriculturaland FoodSci- enceinFinland ^5:329-350 (this issue).

Hämet-Ahti, L.^1981.The borealzoneand its biotic sub- division. Fennia ^159:^69-75,

IPCC 1992.Climate change 1992.The supplementary Report tothe IPCC scientific assessment. Houghton,J.T.

etal. (eds.). Cambridge University Press. 200p.

- 1995.Climate change 1994.Radiative forcingof climate changeandanevaluation of the IPCC 1992emis- sionscenarios. Houghton, J.T. el al. (eds.). Cambridge UniversityPress. 339 p.

Kettunen, L., Mukula, J.,Pohjonen,V., Rantanen, O.

&Varjo, U. 1988.The effects of climatic variations on

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agricultureinFinland. In:Parry, M.et al. (eds.). The impact of climatic variations onagriculture.Volume 1:^As-

sessments incool temperate and cold regions. Kluwer AcademicPublishers, ^Dordrecht,p. 511-614.

Mela,T.^& Suvanto,T. 1987.Peltokasvien satoennuste vuoteen2000.Peltokasvien satojen janiihinvaikuttavien tekijöiden kehitys vuoteen 2000 mennessä. (Prediction of the development of yields of field crops to the year 2000). Helsingin yliopiston kasvinviljelytieteen laitos.

JulkaisujaN:o14.201p.

Mukula, J.^&Rantanen, ^O. 1987. Climatic risks to the yieldand quality of field crops inFinland. I. Basic facts about Finnish field crops production. Annales Agriculturae Fenniae 26: 1-18.

Solantie, R. 1980. Kesän yölämpötilojen ja hallojen alueellisuudesta Suomessa. Maataloushallituksen Aikakauskirja1980,4: 18-24.

Varjo,U. ^1984.The high-latitude^zone:delimitation and characteristics,Nordia 18, 2: 93-104.

SELOSTUS

Maatalous pohjoisilla äärialueilla: ilmastolliset rajoitukset ja ilmaston muutosten vaikutukset viljelyyn

Timo J.N. Mela

Maatalouden tutkimuskeskus

Pohjoisella havumetsävyöhykkeellä auringon säteily- energian vuotuinenmäärä jäävähäiseksi säteilyn pie- nen saapumiskulman takia. Maataloutta harjoitetaan tällä alueella äärirajoillaan, sillä ilmastonkylmyys (matalat lämpötilat, lyhyt kasvukausi, hallat kasvukauden aikana, pitkät ja kylmät talvet sekäpaksu lu- mipeite) rajoittavat viljelyä. Suomessakasvukauden pituus vaihtelee etelän 180 päivästä pohjoisen 120 päivään. Tämän vuoksi viljelykasvien kasvuajan on oltavalyhyt,mikärajoittaaniidenkykyätuottaasuu- ria satoja.

Maatalousonedistyneintäalueen eteläosissa Poh- jois-Euroopassa, Keski-Siperiassa jaKanadan pree-

rioilla ns. hemiboreaalisella kasvimaantieteellisellä alueella, missäkasvukauden tehoisan lämpötilan

summa on^korkeampi ^kuin ¹²⁰⁰^°C. Viljelyolosuh- teetheikkenevät pohjoiseen päinilmastonkylmetes- sä, ja viljan viljely ^muuttuukarjataloudeksi. Pohjois- Euroopassamaataviljellään ainanapapiirille (66°N) saakka.Pohjois-Amerikassa pellot ulottuvat suunnil- leen leveysasteelle 55°N,Aasiassa muutaminpaikoin leveysasteelle 60°N. Suomi on ^maailman ^pohjoisin maa,jossakokopeltoala, 2,5 miljoonaa hehtaaria,si- jaitsee leveysasteen60°Npohjoispuolella.

Ilmaston ja ilmakehän hiilidioksidipitoisuuden ennustettu muutos vaikuttavat todennäköisesti voi- makkaasti kasvuoloihin näillä pohjoisilla alueilla, missä ^vuotuinen keskilämpötila on5 °C tai vähem- män.Vaikutukset ovatjokoedullisia taiepäedullisia.