The simplification of traditional vineyard based agroforests innorthwestern Portugal: some ecological implications

M.A. Altieri* and C.I. NichollsDivision of Insect Biology, University of California, 201 Wellman Hall #3112, Berkeley 94720-3112, USA;*Author for correspondence (e-mail: nicholls@uclink.berkeley.edu)Received 22 January 2001; accepted in revised form 13 February 2002

Key words: Diseases, Insect pests, Traditional agriculture, Vineyard

Abstract

In northwestern Portugal, peasants have developed complex vineyard (Vitis vinifera) systems comprising agro-forests composed of host trees, vines, annual crops and in some cases animals. Until recently these vineyardssuffered very few pest problems and received relatively low pesticide loads. In the last few years, new policy andmarket forces have prompted the conversion of many of these systems to monoculture thereby decreasing thebiodiversity inherent to traditional vineyards. Many scientists are concerned that with accelerating rates of vine-yard simplification insect pest and disease problems may increase due to lack of habitat and resources for naturalenemies or to a concentration of preferred host plants for specific pathogens and herbivores. During the growingseasons of 1997 and 1999 we conducted several farm surveys of traditional agroforestry and modernized, mono-culture farms. We conducted field measurements to elucidate trends in insect pest and disease incidence in bothtypes of vineyards. Our surveys revealed that monoculture vineyards exhibited lower number of species ofpredators and parasites and correspondingly higher densities of two grape herbivores (Lobesia botrana and Em-poasca vitis) than diverse vineyard agroforests. Botrytis bunch rot seemed more prevalent in the monoculturesystems, which also received increased fungicide applications when compared to the traditional vineyards. Al-though preliminary, our studies suggest that new vineyard designs may be more productive, but such gains occurat the expense of biodiversity and agricultural sustainability, reflected on higher pest vulnerability. Further agro-ecological studies are needed to account for the full ecological costs of the modernization of traditional vineyardagroforests.

Introduction

Portugal is a country still rich in traditional agricul-ture. The peasant population is still numerous (tradi-tional and small farms amount for 98% of all produc-ers in the Northwest) and economically significant,playing an important role in the countrys economyand food self-sufficiency. The agricultural landscapeof Northwestern Portugal is characterized by a patternof small, fragmented farms that produce mainly forfamily consumption, interspersed with somewhatlarger and more mechanized farms that specialize incommercial crops.

At least since the ninth century, Portuguese peas-ants have developed complex farming systems, the

sustainability of which has stood the test of time.These traditional agroecosystems, which consist ofcrop polycultures surrounded by vines (Vitis vinifera)upon tree-hosts, reflect the priorities of peasant farm-ers, meeting the needs of a simple, largely self-suffi-cient peasant society. These vineyard-based agrofor-estry systems are found mainly in the designatedregions of Vinho verde including Minho and a por-tion of northern Beira Litoral (Stanislawski 1970).

Since Portugals incorporation into the EuropeanUnion, agricultural policies have had a major impacton traditional agriculture. Technological moderniza-tion of small farms, through monocultures and agro-chemicals is perceived as a critical prerequisite forincreasing yields, labor efficiency, and farm incomes.

185Agroforestry Systems 56: 185191, 2002. 2002 Kluwer Academic Publishers. Printed in the Netherlands.

New varieties are being substituted for old ones, andthe area is being planted to grape monoculture, fea-turing continuous fields of short, vertical trellises thatpermit easy mechanization (Pearson et al. 1987). Theshift away from arbor-style diversified vineyards re-presents a clear pattern of landscape homogenizationand loss of agrobiodiversity. Such simplification maycontribute to increased pest and disease levels andlosses, by creating more favorable conditions to her-bivorous insects and fungi (Jones 1998).

The purpose of this study was to test this assertionand to determine whether the best way to improve theproductivity of traditional vineyards is through theuse of new varieties, agrochemicals and the latest viti-culture techniques. We examined whether yield in-creases resulting from modernization entailed envi-ronmental costs, such as increased pest levels, andthus affected the ecological sustainability of smallfarms. The main indicators used provided an assess-ment of changes in vine health and incidence of in-sect pests or diseases following conversion of agro-forestry systems to monoculture.

The biophysical and socioeconomic context

The Minho region where virtually all the Portuguesevinho verde is produced lies between 41 and 42 de-grees north latitude, facing west towards the AtlanticOcean. Rainfall is high (about 1500 mm/year) withirregular distribution, reaching low intensity in Julyand August. Average daily temperature is about 12degrees Celsius, varying according to distance fromthe sea, topography, exposure and altitude. Most soilsare alfisoils with sandy loam texture, acidic, and arepoor in calcium, phosphorous, and potassium, but fer-tility levels have been improved in most small farmsthrough copious additions of organic matter overtime.

Approximately 26% (74,000 hectares) of the agri-cultural area in the vinho verde region is devoted togrape production. Farm size averages 2.5 hectareswhere wine grapes are grown on trellises (ramadas)on the borders of cultivated fields. The actual areadevoted to grapes per farm is quite small, about 2,200square meters. Production per farm averages 1.82tons of grapes, or about 1,400 liters of wine. Around70% of the vinho verde produced in the region is red,however, due to recent market incentives, many farm-ers are shifting from red to white grape varieties. Al-though the majority of the vinho verde is still home-

processed, cooperatives have begun to seek a widershare of the domestic market. A small number of pri-vate farms produce nationally marketed quality winesfrom their own grapes or the grapes of other farms(Pearson et al. 1987).

The vineyard-based traditional agroforestrysystems

Vinho verde grapes traditionally are grown on treesbordering crop fields. The combination of high vineand maize is characteristic of the area. There are anumber of traditional agroforestry patterns, all ofwhich represent an ingenious response to land con-straints by allowing vertical agriculture (Stanislawski1970):

1. Association of vines and trees dispersed withinfields. This simple system consists of a tree with48 vines planted around the base. The vines as-cend and follow the branches.

2. The festoon system where younger cross-branches of the vines join together every year fromthe nearest trees planted along field margins.

3. The arjoado system is a form of festoon, but withvertical wires attached to the wire that runs be-tween the trees. In addition to planting vinesagainst the tree trunks, several vines can beplanted in the intervening area.

4. In the ramada system, grapes are grown on el-evated arbors (about three meters high and fourmeters wide) supported by stone columns withiron crossbars connected to steel wires.

In systems ac, preferred host trees are PortugueseOak (Quercus lusitanica), elm (Ulmus sp.), poplar(Populus sp.), and wild cherry (Prunus sp.). The treestolerate heavy trimming, have deep roots, grow fastand are long lived. Most yield products such as wood,bark, and fruits. Many trees provide additional ben-efits such as altering the microclimate (interception ofwinds and lower evaporation rates) and protectingvines from winter frosts of the valley bottom. Treescan also reduce dispersion of weed seeds, insects, andpathogen inocula by forming a physical barrier.

The centers of the fields are available for grain(mostly maize, Zea mays), legumes, and vegetables.Normal crop rotations include oat grain (Holcus lana-tus), rye grain (Lolium multiflorum) and the legumesOrnithopus sativa and Trifolium incarnatum, all used

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as fodder. Some fields are left fallow for the growthof volunteer legumes (mostly species of Ulex andSpartium) used for cattle beds in the stalls. Afterbeing mixed with urine and feces of the cattle, thesemi-decomposed materials of the beds are workedinto the soil of the farms as organic amendment.

According to Raposo and Amaro (1997), in north-ern Portugal, vineyards are affected by various patho-gens, insects, and mites. Among insect pests, the tor-tricid moth, Lobesia botrana, is the most persistentone. Of the three generations of this lepidopteran, thetwo first generations are of greatest economic signifi-cance. Leafhoppers are also present (especially Em-poasca vitis, cigarrinha verde), puncturing leaves andeventually causing leaves to fade, dry up and fall offthe vine. Downy mildew (Plasmopara viticolor),powdery mildew (Uncinula necator) and bunchrot(Botrytis cinerea) are the most prevalent fungalpathogens of grapes in the area. Most of these insectsand fungi reach, only sporadically, epidemic propor-tions in traditional agroforests.

During the past ten years, major economic policy-induced changes have occurred in the vinho verdewine industry. Farmers are encouraged to plant vari-eties that produce better-quality white wines andmove away from agroforestry based vineyards to thecordao monoculture system characterized by short,vertical trellises for easy mechanization. Although thesystems reduce labor costs and may enhance profitlevels, the cordao involves less-intensive land use.The modern system is totally integrated into the mar-ket, and little importance is given to production ofcrops and wine for home consumption (Avillez et al.1992). In addition the intensification of grape produc-tion changes the diversity and microclimate of thevineyard, creating new environmental conditions thatmay favor some pests.

Methods

During the summers of 1997 and 1999 we conductedfarm surveys and interviews with farmers and techni-cians throughout the northwest region of the Minho(Braga Guimaraes Barcelos Ponte de Lima).Thirty traditional and 20 modernized farmers wereinterviewed throughout the region to gather descrip-tive information on farm design, crop patterns, use oflocal resources, and farmers practices, as well as tounderstand why farmers adopt particular croppingsystems and production methods. The interviews

were also designed to assess factors affecting decisionmaking by farmers with respect to the use of croptechnologies, and how they avoid risk and adapt tonatural and socioeconomic constraints. Direct inter-views and observation provided detailed informationabout biotic constraints affecting productivity andcrop management practices, i.e., land preparation,planting, weeding, pest control, fertilization, harvest,etc., their timing, and the amount of inputs utilized infarm operations (Shaner et al. 1982).

Field surveys included the general description ofthe landscape, identification of existing vineyard pat-terns, and the actual interactions between the variousbiological components in the various agroforestrysystems. Field measurements were conducted in a fewselected fields to elucidate disease incidence and thepopulation trends of pest insects and associated natu-ral enemies, and the resulting degree of pest damagein two dominant vineyard systems:

1. Vineyards under traditional management relyingon family labor and low-input technologies (arjoa-do system).

2. Vineyards in the process of modernization undermonoculture and high input management (cordaosystem).

The entomofauna was sampled by randomly plac-ing 10 yellow sticky traps (10 17 cm, SeabrightLaboratories, coated with TanglefootR) in the middleof each of 10 vineyards (five arjoado and five cordao)to estimate densities of prevalent herbivores and pred-ators/parasitoids (Pedigo and Bunton 1994). Trapswere deployed from June through mid September andreplaced weekly during 1997 and 1999. Twenty ran-dom grape leaves and 20 inflorescences were visuallyexamined weekly in the center of each vineyard, forpresence of E. vitis and L. botrana adults or inmaturesrespectively. Egg parasitism was determined examin-ing the same 10 grape leaves under a dissection mi-croscope for the presence of parasitized or healthy L.botrana or E. vitis eggs.

Insect species diversity was estimated using Sim-psons measure of diversity (D) and the Shannon-Weaver index (H) (Pielou 1969). Species richness(MA) was calculated using the formula (vMA) = S 1/log 10 N. The evenness (J) component of speciesdiversity was measured using formulas reported byMagurran (1988).

Although powdery mildew (oidio) is the most se-rious and widespread disease in the region, B. cinerea

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was prevalent in some vineyards, which received un-timely or low dosages of fungicide applications. Ev-ery 20 days, 100 bunches per vineyard were randomlysampled and assessed for infected berries. The pro-portion of infected berries and disease progresscurves in a pair of modern and traditional vineyardswere then determined.

Data on the number of leafhoppers L. botrana lar-vae and bunchrot infestation levels in modern andtraditional vineyards were statistically compared eachsampling date using a t-test.

Results and discussion

Patterns of insect diversity, abundance, and pestincidence

In both years (1997 and 1999), the number of insectspecies and the total number of individuals collectedper plot was greater in the agroforestry systems thanin monocultures (Table 1). According to both the Sim-pson and the Shannon measures (expressed as a meanof the D and H values for each plot obtained fromeight sampling dates) the species diversity of insectsin the agroforestry systems exceeded that found onmonocultures. The number of predator and parasitespecies was substantially greater in the traditional di-versified arjoado systems than in the cordao monoc-ultures. Main predator species included various spe-cies of Coccinellidae (Stethorum punctilum andothers), Syrphidae, Chrysoperla carnea, Orius spp.and others. Parasitoids belonged predominantly to thefamily Ichneumonidae, although we detected parasit-ism of L. botrana eggs by naturally occurring Tri-chogramma spp.

In the arjoado systems higher insect biodiversity isprobably the result of increased spatial heterogeneityand complexity of the agroforests. The presence of adiversity of crops and also of some weeds in the ar-joado increased the amount of food resources (flow-ers, extra floral nectarines, and alternate prey), whichmay explain the greater abundance, and diversity ofnatural enemies. In contrast, the lack of insect biodi-versity in mechanized systems was probably due tothe lack of plant diversity, and to the higher load ofinsecticides (mainly organophosphates and carbam-ates) that cordao systems receive (Altieri 1994).

Abundance monitoring of herbivores was difficultin the monoculture systems as insecticide applicationsprevented pest population buildup. However, delayedspraying in one modernized farm in 1999 allowed usto compare densities of L. botrana and E. vitisnymphs between this vineyard monoculture and aneighboring traditional vineyard. As observed in Fig-ure 1, densities of leafhopper nymphs tended to besubstantially lower from early June to mid Septemberon leaves in the agroforestry system than in thecordao monoculture. Similarly, from late June to mid-July, larval densities of L. botrana where higher inmonocultures than in the traditional system (Figure 2)which corresponded with a higher proportion of vineinflorescences infested by L. botrana larvae in mo-nocultures than in the vine agroforest (Table 2).

Disease incidence

From interviews we found that as farmers converttheir vineyards from the arjoado to cordao (monocul-ture) system, the amount of recommended fungicideapplications increases. The average number of fungi-cide sprays per year in cordao is 5.7 treatments for

Table 1. Species diversity measures for foliage insects associated with vines grown in traditional agroforestry and monoculture patterns inNorthwestern Portugal (1999)Diversity measurea Monoculture (cordao system) Traditional agroforestry (arjoado system)Total number of species, S 18 32# of predator species 3 6# of parasite species 3 8# of herbivore species 9 11Total number of individuals, N 79 196Shannon-Weaver H1 S.E. 2.03 1.7 2.47 1.8Simpson, D 0.14 0.08 0.36 0.06Species richness vMA 8.96 13.6Evenness, J1 0.671 0.810a All values are measures of 8 sampling dates and based on yellow sticky trap samples.

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downy mildew (mildio), 6.4 for powdery mildew(oidio) and 1.1 for Botrytis bunch rot. Copper formu-lations and several organic contact and systemic prod-ucts are the main fungicides used against the threemain fungal diseases. In traditional systems sulfur andBordeaux mixtures are the most prevalent treatments(3.5 average sprays/year), although some traditionalfarmers use fungicides.

Heavy applications of fungicides did not allow usto comparatively monitor disease development in

agroforestry and monoculture vineyards. However in1997 we were able to compare disease severity in twosystems (modern and traditional) both of which forvarious reasons did not receive applications of sul-phur or fungicides. Figure 3 shows the disease inten-sity over time, suggesting a reduction in Botrytis in-cidence in the traditional system. A number of factorsmay have contributed to such trends such as differ-ences in temperature and humidity between bothvineyards, including the fact that excessive use of

Figure 1. Nymphal densities of Empoasca vitis in modern and traditional vineyards in northwestern Portugal (1999).

Figure 2. Infestation of grapes by Lobesia botrana in traditional and modern vineyards in northwestern Portugal (1999).

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chemical N fertilizer in the modern system may havepredisposed grapes to infection by Botrytis (Coley-Smith 1980; Jones 1998).

In addition our interviews with farmers, extensionagents, and researchers at the Estacao Viti-vinicolaAmandio Galhano provided some useful information:

1. Sulfur dust provides adequate control of powderymildew in traditional systems, but heavy lossescan occur if applications are insufficient or un-timely;

2. Fungicides used mostly in monoculture againstpowdery mildew (Mancozeb, Maneb, Zineb, andothers) can exert undesirable secondary effects,such as toxicity to the predator Typhlodromus py-ris and the egg parasitoid Trichogramma spp;

3. Vines growing on trees (arjoado system) are lessaffected by Botrytis. Vertical canopy developmentin such systems increases exposure of the grapeclusters to air and light, which creates a microcli-mate less conducive to development of bunch rot;

4. Arjoado systems with dense top foliage of treehosts shield lower vine foliage from dew, reduc-ing the attack of downy mildew on the lowerleaves; and,

5. Vines on trees are more protected than vines onlower trellises from winter frosts of the valley bot-toms.

Conclusions

Peasants in the vinho verde region of northwest Por-tugal have used traditional grape growing methods forcenturies. Vines grown on host trees circumscribesmall fields diversified with crops, vegetables, andforage for animals. In these systems, arbor style di-versified vines integrated into cropping systems mod-ify the environment of associated understory plants,influencing their growth, pest susceptibility, andyields. The greatest modification for crops apparentlyresults from the interception of wind and some solarradiation, but for vines growing in vertical structuresthere are clear microclimatic effects. These agrofor-estry systems are based on family labor and local re-sources and rely on traditional farming knowledge.Our observations and preliminary field data suggestthat agroforestry systems exhibit higher levels of in-sect biodiversity possibly linked to the higher vegeta-tional complexity of such systems, they are less de-pendent on external inputs (chemical pesticides), andtend to have fewer insect pest and disease problemsthan unsprayed modern vineyard monocultures.

Although the shift toward cordao monoculture po-tentially represents a more labor saving and profitablesystem, at the same time it can be a risky specializa-tion in production. In the few vineyards where wewere able to compare through systematic sampling,

Table 2. Proportion of vine inflorescences infested by Lobesia botrana in arjoado and cordao vineyard systems in northwestern Portugal(1999)

Monoculture (cordao system) (% inflores-cences with larvae)1

Traditional Agroforestry (arjoado system) (%inflorescences with larvae)2

Early June 18 a 17 aLate June 27 b 19 aMid July 52 b 37 a

1. The economic injury level for the first generation has been established in Portugal at 30100% of infested inflorescences, and 510% forthe second generation (Roehrich and Boller 1991).

2. Means in each horizontal column, followed by a different letter are significantly different (P < 0.05, t-test).

Figure 3. Progress of bunch rot (induced by Botrytis cinerea) dur-ing the 1997-growing season in a modern and traditional vineyardin northwestern Portugal.

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our findings suggest that promoted modern techno-logical schemes may be ecologically unsound. Vine-yards converted to monocultures exhibited largernumbers of leafhopper and lepidopteran pests, com-pared to more diversified traditional adjacent systems,featuring the same grape varieties. The fact that thesesystems, due to recommended practices, requiregreater application of fungicides is suggestive thatthese systems may suffer increased incidence of pow-dery mildew and Botrytis bunch rot. The strategy ofyield maximization with pest control left primarily topesticides has increased grape production by 2035%,but at the expense of higher vulnerability of the vine-yards and possible environmental risks.

There is strength in the diversity of traditionalvineyards, and it should not be reduced by extensivemonoculture, especially when consequences of doingso may result in serious ecological and social prob-lems. Instead, modernization should be guided byagroecological principles, principles whose source arethe very traditional systems that modernity is destroy-ing. As rural change occurs in Portugal given EECdriven agricultural modernization trends, knowledgeof traditional management practices and the ecologi-cal rationale behind them is gradually being lost. Forthis reason it is crucial to expand studies such as thisone in order to gain more insight into the ecologicalmechanisms that underlie the time-tested perform-ance of these diversified systems. Ecological princi-ples extractable from the study of traditional agroec-osystems can be used to design new, improved,sustainable agricultural systems in Portugal, moreadaptable to the socio-economic and environmentalconditions of the prevalent small farming systems.There is no doubt of the great need to design newsystems that are economically competitive, but suchsystems have to be environmentally sound and so-cially just as well as culturally compatible. Many tra-ditional vineyard systems provide elements for de-signing such new systems. However, agroecologicalresearch must proceed quickly before all the tradi-tional vineyards in the Landscapes of Bacchus aretransformed into large-scale monocultures.

References

Altieri M.A. 1994. Biodiversity and Pest Management in Agroeco-systems. Harworth Press, New York, 185 pp.

Avillez F., Jorge M., Jesus J. and Trimdale C. 1992. Small farms innorthern and central Portugal. In: Monke E., Avillez F. andPearson S. (eds), Small Farm Agriculture in Southern Europe.Ashgate, Aldershot, UK, pp. 5572.

Cavalloro R. 1989. Influence of Environmental Factors on the Con-trol of Grape Pests, Diseases and Weeds. A.A. Balkeme, Rot-terdam, 351 pp.

Coley-Smith J.R. 1980. The Biology of Botrytis. Academis Press,London, 318 pp.

Jones D.G. 1998. The Epidemiology of Plant Diseases. KluwerAcademic Publications, Dordrecht, 460 pp.

Magurran A.E. 1988. Ecological Diversity and its Measurement.Princeton University Press, Princeton, 167 pp.

Pearson S.R., Avillez F., Bentley J.W. and Finan T.J. 1987. Portu-guese Agriculture in Transition. Cornell University Press, Ith-aca, 283 pp.

Pedigo L.P. and Bunton G.D. (eds) 1994. Handbook for SamplingMethods of Arthropods in Agriculture. CRC Press, Boca Ra-ton, Florida, 340 pp.

Pielou E.C. 1969. An Introduction to Mathematical Ecology. WileyInterscience, New York, 286 pp.

Quartau J.A., Fancony A.I. and Andre G. 1989. Jacobiasa lybica, aNew Leafhopper Infesting Vineyards in Southern Portugal. BolSoc Port De Entomologia 114: 124133.

Raposo M.E. and Amaro P. 1997. Cultural Practices and Insect PestManagement in Vineyards. Actos de Horticultura (Port.) 18:171177.

Roehrich R. and Boller F. 1991. Tortricids in vineyards. In: GrantV. (ed.), Tortricid Pests, Their Biology, Natural Enemies andControl. Springer-Verlag, The Netherlands, pp. 5162.

Ruiz Castro A. 1950. La Lucha Contra las Plagas del Vinedo. BolPat Veg Ent Agr XVII: 111162.

Shaner W.W., Phillips P.F. and Schmehl W.R. 1982. Farming Sys-tems, Research and Development: Guidelines for DevelopingCountries. Westview Press, Boulder, 320 pp.

Stanislawski D. 1970. Landscapes of Bacchus: The Vine in Portu-gal. University of Texas Press, Austin, TX, 164 pp.

Tavares J.L.O., Teixeira R. and Arunuada L. 1989. Biological Con-trol of Lobesia botrana by means of Trichogramma cacoeciae.Bol Soc Port De Entomologia 103: 111.

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