Neither Wild Nor Planted: Essential Role of Giesta (Cytisus, Fabaceae) in Traditional Agriculture of Beira Alta, Portugal1

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Neither Wild nor Planted: Essential Role of Giesta (Cytisus, Fabaceae) in Traditional Agriculture of Beira Alta, Portugal1

George F. Estabrook

Estabrook, G. F. (Department of Ecology and Evolution, The University of Michigan, Ann Arbor, MI 48109; e-mail: [email protected]). Neither Wild nor Planted: Essential Role of Giesta (CYTISUS, Fabaceae) in Traditional Agriculture of Beira Alta, Por- tugal. Economic Botany 60(4):307Ð320, 2006. Giesta (Cytisus) is the dominant or only woody plant on about one-quarter of the land area of the high granite mesas of interior Beira Alta, Portugal, where for at least the past 800 years the main cereal crop has been rye. During this time, a substantial fraction of this crop has been sold and taken to cities to feed the urban population, carrying with it nitrogen in the proteins of the grain. These farms have remained sustainable for nitrogen in the face of this outﬂow because farmers have allowed and even encouraged giesta, which is a nitrogen ﬁxer, to occupy a substantial fraction of the land area, from which it is harvested and buried in the cultivated soil to restore its fertility. Stable N15 analysis and ecological techniques estimate quantitatively the importance of this practice.

Nem bravia, nem semeada: A função indispensãvel da Giesta (Cytisus, Fabaceae) na agricultura tradicional da Beira Alta, Portugal. As giestas (Cytisus spp.) são as plantas lenhosas dominantes em cerca de um quarto das áreas montanhosas graníticas do interior, nomeadamente na Beira Alta (Portugal), onde durante os últimos 800 anos, o principal cereal cultivado era o centeio. Nessa altura, uma fracção substancial deste cereal era ven- dida e enviada para as cidades, para alimentar a população urbana, transportando consigo nitrogénio nas proteínas dos grãos. Estes campos cerealíferos mantinham um fluxo susten- tável em nitrogénio, porque os lavradores permitiam e até auxiliavam o crescimento das giestas, que sendo fixadoras de nitrogénio e ocupando uma grande parte dessa área, cortavam- nas e enterravam-nas no solo de cultivo, mantendo, assim, a respectiva fertilidade. Análises “Stable” N15 e técnicas ecológicas confirmam quantitativamente a importância desta prática camponesa. Key Words: Nitrogen, soil fertility, rye, stable isotope, sustainable agriculture, traditional ecological knowledge, Cytisus, Portugal.

For the past many hundreds of years, agri- agro-chemicals to complement this high- cultural technology in Europe changed very energy fertilizer and the new crop varieties that little until the early 20th century, when tech- respond to it soon followed. By the third quar- nology was developed that consumed large ter of the 20th century, yields had increased amounts of (fossil fuel) energy to break the dramatically, but in many cases so had contam- stable bond of N2 to transform atmospheric ni- ination and erosion of soil, and pollution of the trogen into ammonia and nitrate. This technol- air, the water, and even the crop itself. In some ogy soon came to be used to manufacture ni- cases, this new technology is not sustainable trogen fertilizer, the availability of which because it depletes or contaminates the soil and stimulated the development of new varieties of water on which it depends. (especially) cereal crops that could use large By the last quarter of the 20th century, many quantities of soil nitrogen. Machinery and agronomists and other scientists had become aware of the need to address this situation. A more ecological approach to agricultural re- 1 Received 27 March 2006; accepted 14 June 2006. search was initiated in which sustainability was

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included explicitly as an objective (Altieri accept Rhizobium to form nodules, where nitro- 1987; Gliessman 1990; Loomis and Conner gen from the air is made biologically available, 1992). Some researchers became aware that tra- using energy from the sun captured by the ditional agrarian communities contain valuable stems and leaves of the giesta. Thus much of ecological knowledge (Hunn 1999), which is the nitrogen in the giesta twigs and branches often expressed in cultural rather than scientific that are buried in the cultivated soil to restore terms (Estabrook 1994). The study of a tradi- its fertility has recently entered the biosphere tional, solar energy-based technology that has from the atmosphere. This replaces the nitrogen been practiced sustainably for hundreds of in the protein of the rye seeds carried away to years in the same place may help us access and feed urban populations. Although traditional preserve traditional ecological knowledge and farmers in these villages had no concept of ni- cultural diversity (Hunn 2001), and provide un- trogen or nitrogen fixation, their traditional eco- derstandings of the natural world that may con- logical knowledge and culturally informed tribute to healthier and more sustainable mod- technology have instructed them to keep about ern agricultural technology. one-quarter of the land area that participates in One approach to the study of sustainable a village agro-ecosystem covered with what ap- agriculture is to investigate a traditional agricul- pears to be wild, but is in fact deliberately man- tural system that has produced for hundreds of aged, giesta. years without depleting the resources on which The results reported here arise from a study it depended. This paper reports the essential of traditional farming practices of Beira Alta, role played by two apparently wild species of in the mountainous interior of Portugal, located Cytisus (Fabaceae) and the way they are man- as shown on the map of Fig. 1, where rye has aged in the traditional agriculture of interior been produced using basically the same tech- Beira Alta, Portugal, to achieve sustainability of nology for at least 800 years (Raposo 1994), nitrogen soil fertility over the hundreds of years even though the New World crops, corn and this region has served as a “bread basket” for potato, joined the rotations in the mid-17th the populous area of northern interior Portugal century, and the land reforms of the early 19th north of the Serra da Estrela and south of the century increased the number of resident own- Douro River. ers (Oliveira 1980). A 19th century account of An earlier quantitative study of nitrogen flux agricultural technology in Beira Alta is given in traditional agriculture is reported by Loomis by Almeida (1882). Two or more generations (1978). He made very plausible estimates of have passed since the advent of agricultural compartment sizes and flux rates based on his technology based on large inputs of fossil-fuel considerable experience in ecological agricul- energy in America and Europe, where few liv- ture. This work remains a useful landmark to ing people have even witnessed the practice of compare and contrast nitrogen pools and fluxes traditional agricultural technology. However, under more modern technology. Loomis and during the middle half of the 20th century, Por- Conner (1992) in Fig. 8.2 show a generalized tugal was ruled by a dictator who did little to nitrogen flux diagram for a modern agricultural develop its interior (Bruce 1975). During the system, and in Fig. 8.5 give estimated fluxes for last quarter of the 20th century, traditional agri- a traditional agricultural system based on the culture was still practiced, although by fewer work of Loomis (1978). In the farm analyzed in and fewer people, in the mountainous interior that work, only minor roles are played by nitro- of Portugal. As a consequence of the economic gen fixation and the maintenance of shrub lands decline of this region, younger people moved for the main purpose of bedding animals kept away and unchecked fires destroyed much of primarily to maintain soil fertility. the forest cover (Damaso 1992). Most of the Nitrogen flowed out of the agro-ecosystems older people who remained just retired from of the farming villages distributed over the high agriculture instead of replacing traditional granite mesas of interior Beira Alta with the rye technology with modern. Thus, much of the grain that was carried away to Viseu, Lamego, land and equipment, although no longer in use, Guarda and other smaller cities nearby. Giestas has been left as it was, and many people still are nitrogen fixers, i.e., the roots of the giesta remember the technology. For these reasons, 31508_U01.qxd 11/30/06 12:30 PM Page 309

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Fig. 1. Beira Alta region of Portugal in the high divide between the Mondego and Douro river drainages. Shaded rectangle of insert shows location within the Iberian peninsula. District capitals shown with large solid circle. County seat of Trancoso shown with small solid circle. Parish centers of Sebadelhe and Aldeia Nova shown with small open circles.

the mountainous interior of Portugal is a good farmers on the granite mesas and valleys of place to study traditional Portuguese agricul- Beira Alta manage and use giesta to maintain ture. the fertility of their cultivated soil, and then es- Over the past two decades, I have studied timate quantitatively the rate at which these the traditional agriculture of this region, living plants and practices bring new atmospheric ni- there for periods of from a few weeks to sev- trogen into the traditional agro-ecosystem. eral months during 1984, 1987, 1991, 1993, These estimates use two kinds of techniques: 1996, 1997, 2002, and 2003, talking to life- those of plant ecology to measure primary pro- long residents and observing their practices, ductivity of giestas; and those of mass spec- and sampling soil, plant, and animal material trometry of stable N15 isotopes to measure to measure quantitatively the effectiveness of percent total nitrogen in giesta, and to estimate these practices. For example, Estabrook the fraction of that nitrogen derived from the (1998) described how some of the techniques atmosphere. These quantitative results will of traditional agricultural practiced on the demonstrate clearly the importance of the tra- shale hillsides of the parish of Cabril, Portu- ditional practices that manage giesta in main- gal, maintained the fertility of their cultivated taining the nitrogen sustainability of the agro- soil. ecosystems of Beira Alta over the past In this paper, I will describe how traditional centuries. 31508_U01.qxd 11/30/06 12:30 PM Page 310

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Fig. 2. Farmers in Sebedelhe parish center, county of Trancoso, Beira Alta, Portugal, transporting estrume (composted giesta with sheep excrement) to cultivated ﬁelds in a cart drawn by two cows, yoked by their horns.

to regenerate before they cut it again, when it Management and Use of Giesta has reached 70 to 80 cm in height. In the sheep by Traditional Farmers shelters, the giesta is enriched with sheep ex- Two species of giesta commonly occur on the crement. It is removed and replaced about once granite mesas and upper erosion valleys of Beira a week. The resulting organic matter is called Alta: giesta branca (Cytisus multiflorus [L’Her.] “estrume” by Portuguese farmers, who trans- Sweet); and giesta negral (C. grandiflorus [Brot] port it to their cultivated fields and bury it in the DC.). These giestas are bushes from about 0.5 to soil at the rate of 8 to 15 metric tons dry weight 3.0 meters tall, with long, flexible photosyn- per hectare to restore its fertility before planting thetic stems that keep their leaves for only a few rye. Giesta branca produces relatively few months in the year. Because of their physical ap- seeds, investing instead in vegetative spread and pearance, they are often called “broom.” In Por- regeneration. I have looked carefully in all sea- tugal, an area dominated by giesta is called a gi- sons of the year and never found a naturally oc- estal. Giesta branca is allowed/encouraged to curring giesta branca seedling. grow where it would be difficult to plow be- Giesta negral grows around the edges of cul- cause the soil is rocky and shallow above the tivated rye fields. In April and May, its copious, granite bedrock. Large areas dominated by gi- large yellow flowers are conspicuous. These de- esta branca include grasses among these shrubs, velop large numbers of seeds, which are re- but rarely any other woody plants. Sheep graze leased toward the end of the dry summer. After the grass and farmers cut the giesta to bed the about six years of cultivation, a rye field is al- sheep when they are housed in stone shelters lowed to remain fallow. At this time, seeds from during the cold, rainy winter. the surrounding giesta negral, which are abun- Giesta branca is cut just above ground level. dant in the rye field, germinate and grow. The Farmers allow four years for a cut giesta branca habitat of these seedlings is fertile relative to 31508_U01.qxd 11/30/06 12:30 PM Page 311

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that of giesta branca, and the seedlings grow in this traditional system, I measured the rate at rapidly. By their third year they are about 1.5 which giestas grow (primary productivity), how meters tall and producing a few flowers. By the much of giesta dry weight is nitrogen, and the fourth year they may exceed two meters and fraction of that nitrogen that had been fixed flower abundantly. Then, in the middle of the from the atmosphere. This estimated amount dry season in July, they are all cut just above per unit area can be applied to the amount of ground level and removed. Their side branches area maintained in giesta, and compared with are cut off and used, along with the branches of the area under cultivation. giesta branca, to bed sheep and make organic Primary productivity. Because pilro makes matter to bury in the soil. The main stems may such a small fraction of the nitrogen fixers man- have reached a diameter of up to 5 or even 6 cm aged by the farmers in a village, I estimated near the ground. These are dried and used to productivity only for giesta branca and giesta fire the communal bread ovens. Cut giesta ne- negral. In conversation with residents of the gral does not regenerate. During the last couple town of Sebedelhe da Serra, in the Concelho of of months of the dry season, its roots die and Trancoso (located on the map of Fig. 1), I are removed with a large hoe before the field is learned that the town has a common hillside enriched with estrume and plowed at the onset where giesta branca can be harvested by day of the rainy season when rye is again sown. workers (who do not own or rent plow-land but Another shrubby nitrogen fixer, called pilro have a small door-yard vegetable patch), and I (Genista cineria [Villars] in Lam DC.) grows in received permission to cut a small area. People wetter areas, such as seeping ground near harvest giesta branca after it has been regener- springs or on banks of streams, but occupies ating for about four years, so in an area where very little area compared with giestas. Because others had recently been harvesting giesta, I of its high resin content, its primary use is to clear cut at ground level (as do the residents) an start cook fires. area 2 m × 3 m. I weighed the cut giesta with a This use of giesta has long been a part of the hand-held spring scale, selected a representative traditional technology in Beira Alta. Although half-kilo, including the full spectrum of stem its role in soil fertility maintenance is essential, diameters from about 1.5 cm down to 2 mm, farmers do not describe and explain its use for and sealed it in a bag, which I took with me soil fertility, but instead describe its use in the when I returned to Coimbra a few days later. In care of their animals. Farmers’ explanations do the plant physiology laboratory of the Botany not evoke agro-ecological concepts, which only Department of the University of Coimbra, I relatively recently have come to be well under- weighed, then oven-dried, then reweighed the stood by agronomists and ecologists. These sci- sample to estimate the fraction dry weight. To entific explanations serve a scientific purpose. estimate annual primary productivity, I multi- However, the preferred explanations of these plied this fraction by the wet weight of the gi- traditional farmers help them remember the de- esta removed from the 6 square meter area I tails and timing of their practice, while placing had cut and divided by the four years it had the real purpose outside the realm of their re- been growing there. sponsibility, eliminating the need for a boss or Giesta negral does not regenerate but grows decision-maker to implement it, and protecting from seed spontaneously in fallowed rye fields. it from question during years when yields are Antonio Sovral Dias, one of the farmers who low. Although the effectiveness of traditional was still actively working his land in Sebedelhe knowledge can be evaluated using modern eco- da Serra, was about to remove some giesta ne- logical concepts and technology to measure the gral from some land he had not cultivated for consequences of traditional practice, these cul- just over five years. He collaborated with me to tural explanations help to encode traditional estimate the productivity of this giesta. He used ecological knowledge and to inform its practice an axe to cut just above the ground the approxi- (Estabrook 1994). mately 5 cm diameter stems of these 3+ meter tall bushes. When he had worked for about 45 Methods minutes, he allowed me to measure the area he To estimate the rate at which new, atmo- had cleared. The cut giesta was arranged in spheric nitrogen becomes biologically available seven piles, each small enough to be weighed 31508_U01.qxd 11/30/06 12:30 PM Page 312

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with the hand-held spring scale. About a kilo that are the result of chemical transformations sample, with the full spectrum of stem diame- that take place in living plants and animals, or ters from 5 cm down to 2 mm, was sealed in a after organic matter leaves living plants and bag and used as described above to estimate animals. On the ground, in the animal bedding fraction dry weight. Giesta negral germinates or later within the soil, chemical transforma- after the rains start in late October, so in this tions continue, many mediated by fungus and case the time this giestal had been growing microbes (Harris 1988). Often, these reactions from seed could be determined, within a month produce ammonia and dinitrogen, which enter of accuracy, at five years and six months. the air as gasses. Some of the products that re- How much new nitrogen? Agronomists have main in the soil are leached into ground or sur- long recognized the importance of measuring face water, others are taken up soon by plant quantitatively the rate of biological nitrogen fix- roots, and others become part of the soil humus. ation under natural conditions. Hardy et al. These chemical transformations often have a (1968) described an assay based on the reduc- preference to bring forward into the product rel- tion of the triple bond in acetylene to form the atively more of one or the other of the stable double bond in ethylene to measure N2 fixation isotopes of nitrogen, with the result that the under field conditions. Although it required the stable isotope ratio of the nitrogen in soil or- transport of heavy and awkward equipment into ganic matter varies from one area to another, the field and several hours to use it, this acety- and can be quite different from the nearly con- lene reduction technique was widely and enthu- stant ratio for nitrogen in air. siastically used during the 1970s. Now its use Chalk and Smith (1994) compare Delta val- has been abandoned for a variety of reasons, of ues for nitrogen in tissues of two crops, one but which the most decisive was the development not the other a nitrogen fixer. Plants of the two of more convenient, accurate, and efficient tech- crops were grown close together so that their niques using stable 15N isotope analysis with roots might exploit the same soil. It is assumed mass spectrometry. that the nitrogen derived from the soil by plants Essential to the development of these new of either crop comes from the same pool of soil techniques was the discovery (Marioti 1983) organic matter and thus has the same Delta that the ratio, a = [15N]/[14N], of the concen- value. Under this assumption, the Delta value trations of 15N and 14N stable isotopes of ni- of the nitrogen in the tissues of the nitrogen trogen in air is nearly constant at a = 0.0036765 fixer is a mixture of nitrogen with a Delta value anywhere near the surface of the earth. A mass equal to that of the non-fixer plus nitrogen with spectrometric analysis measures the ratio, s = a Delta value of zero for the nitrogen biologi- 15N(sample) / 14N(sample), of the 15N and cally fixed from the air. Chalk and Smith (1994) 14N stable isotopes of nitrogen in a sample, then used these Delta values, together with compares it to a, the ratio in air, and expresses other considerations, to estimate the fraction of the result as the nitrogen in a nitrogen-fixing plant that came from the air. Alves et al. (2000) confirmed the Delta(s) 1000 * (s a)/a (1) potential accuracy of this approach by carefully measuring all factors under controlled labora- Delta is a measure of the fraction of nitrogen tory conditions. Boddy et al. (2000) review re- in organic matter that is heavy nitrogen relative cent studies that apply this basic approach to ni- to that fraction in air; Delta will be positive if trogen fixation by woody perennials, and Lajtha organic matter has a higher fraction of heavy ni- and Michener (1994) review a variety of appli- trogen than air. In this study, values for Delta cations of stable N15 technology in ecological fall between −3.0 and 6.0. studies. If chemical nitrogen fertilizer has not been To apply stable N15 technology to the pres- added to soil, then organic matter in soil pro- ent study, I looked for a giesta growing so close vides virtually all nitrogen to most non- to a non-nitrogen-fixing plant of similar size nitrogen-fixing plants. The dynamics of soil or- that that their branches intertwined. For each ganic matter (Jenkinson 1988) and its nitrogen plant, many small amounts of the leaves and turnover (Groot et al. 1991) are complex. In this stems were taken from a number of different soil organic matter, nitrogen occurs in molecules places and combined to make a sample. Figure 31508_U01.qxd 11/30/06 12:30 PM Page 313

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Fig. 3. Giesta branca (Cytisus multiﬂorus) growing right next to sargaco (Halimium lasianthum) sampled for stable nitrogen isotope analysis by mass spectrometry, county of Trancoso, Beira Alta, Portugal.

3 pictures a giesta branca with such a neighbor- Observe that f/(1+f) is the fraction of total ni- ing sargaco negro (Cistus monspeliensis L. Cis- trogen in the nitrogen fixer that is heavy. Simi- taceae) that were sampled in this way. Each larly, for the non-fixer that fraction is n/(1+n), sample was dried at 60 C, ground and homoge- and for air that fraction is a/(1+a). The fraction nized, and then Delta values were determined of nitrogen in the fixer that is heavy is a mixture by mass spectrometry at Laboratorio de Isoto- of the fraction in the soil and the fraction in the pos Estaveis at the Faculdade de Ciencias of the air, in which we weight the soil fraction by b University of Lisboa, Portugal. Mass spectrom- and the air fraction by (1−b), as shown. etry also measured the fraction of dry weight of each sample that was nitrogen. Fraction of nitrogen from atmosphere. To es- f / (1+f) b *(n / (1+n)) (2) timate the fraction of the nitrogen in a giesta +(1 b)*(a / (1+a)) that came from air, using the Delta values reported by mass spectrometry analysis, I rea- Solving for b gives soned as follows. Denote with b the fraction of b = ((n+1) / (f+1)) * ((f−a) / (n−a)). the nitrogen in the tissues of the nitrogen-fixing Now, consider the quotient (n+1)/(f+1). In giesta that was derived from the soil. Denote the results reported below, n never exceeds with f the ratio of 15N/14N for the nitrogen in 0.005 and f never exceeds 0.0025; thus this the tissues of the nitrogen-fixing giesta, and quotient is between 0.992 and 1.007, which dif- with n the ratio of 15N/14N for the nitrogen in fers from 1.0 by far less than the proportional the tissues of the non-fixer. We assume that the variation in repeated mass spectrometric analy- roots of the nitrogen fixer are sampling the same ses of the same sample. So we set this quotient soil organic matter as are the roots of the non- to 1.0 and estimate b = (f−a) / (n−a). fixer. Thus, we assume that n is also the ratio However, the sample analyses are expressed 15N/14N for the soil derived nitrogen in the ni- in Delta units, so it would be convenient to ex- trogen fixer. press the estimate of b with Delta units. 31508_U01.qxd 11/30/06 12:30 PM Page 314

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Delta(s) = 1000 * (s − a) / a (3) was chosen to estimate the rates of nitrogen fixation by giesta. Although SS is regularly which implies grazed, the giestas occur fairly densely as does (s − a) = a * Delta(s)/1000 the bushy non-fixer sargaco negro, the perennial forb leiteira (Euphorbia characias L. Euphor- for any sample, s. Substituting f for s gives biaceae), and the less common nitrogen fixer (f − a) = a * Delta(f)/1000 pilro. At a distance of 4 or 5 kilometers from the village center, on the higher exposed ridges and substituting n for s gives (altitude 900m) above Quinta Baralhada (an (n − a) = a * Delta(n)/1000 isolated farm), another giestal, designated QB, not presently very actively grazed but whose gi- Now, b = (f−a) / (n−a) implies that esta and pilro are still harvested for fuel or bed- b (a * Delta(f)/1000) / (a * Delta(n)/1000) ding, was also chosen to estimate the rate of ni- (4) Delta(f)/Delta(n) trogen fixation of pilro, using sargaco branco (Halimium lasianthum [Lam] Spach) that grows Thus, we use the quotient Delta(f)/Delta(n) with pilro on wetter soils. to estimate the fraction of the nitrogen in the Another giestal sampled for this study is in tissues of a giesta that was derived from the soil the parish of Aldeia Nova (altitude 460m). This organic matter. giestal, designated AN, is actively managed by It is desirable to estimate fixation rates of gi- a farmer with sheep who, during the past 22 estas growing under conditions resembling years, has regularly cut giesta from this giestal those of the traditional agriculture of Beira to make sheep bedding, which he ultimately Alta. However, giesta usually occurs in the tra- buries in his cultivated fields. This giestal has a ditional farming systems of Beira Alta as dense great deal of frequently grazed grass cover over monocultures of giesta negral growing rapidly which grow well-spaced giestas. No non- for a short time on fallow rye fields, or as nitrogen-fixing woody shrubs grew here, so dense monocultures of giesta branca growing plants of the non-nitrogen-fixing perennial for many years as a regenerating, rhizomatous forbs, rosmaninho (Lavandula stoechas L. perennial on rocky infertile slopes and hilltops. Menthaceae) and dedaleira da serra (Digitalis In these two vegetation types, nitrogen fixation thapsi L. Scrophulariaceae) growing in giestal rates could not be measured because the gies- AN in close physical association with giestas tas are so dominant that no plausible non-fixer were sampled instead. was ever found thriving in close physical prox- To complement data from locations actively imity. Occasionally a giesta is found growing managed with traditional technology, I took near enough to entwine branches with another samples of giestas growing in places where large non-nitrogen-fixing bush, which can be they were no longer actively managed, where sampled to apply the technique described non-fixing close neighbors of comparable size, above to estimate nitrogen fixation. Some- age, and woodiness had been allowed to grow. times, the only relatively large long-lived During the past decade, a giestal of giesta ne- plants found growing near giestas are perenni- gral has been growing unmanaged on an aban- als, which regenerate their aboveground parts doned rye field about 5 kilometers south west annually from underground storage organs. of Trancoso. These plants have reached height When nearby bushy non-fixers were not avail- of about 2 meters, as have closely associated able to estimate nitrogen fixation rates, I sam- plants of urze (Erica arborea L.). Samples from pled nearby perennials whose root systems this Trancoso site are designated TR. Samples seemed to be exploring some of the same soil were taken from a similar old giestal near the as the nitrogen fixer. village of Mende Gordo (designated MG), Samples for this study were taken from a about 8 kilometers east of Sebedelhe da Serra, number of actively managed locations in the which contains large urze the size of nearby gi- Concelho of Trancoso, District of Guarda, in esta negral. Samples were also taken a few kilo- Beira Alta, Portugal, shown on the map of Fig. meters south near the village of Terrenho, des- 1. In the parish of Sebedelhe da Serra, at 860 m ignated TE, from a six-year-old giesta negral altitude, giestal, designated SS, currently ac- and a nearby flourishing sargaco negro in a tively grazed and harvested for sheep bedding, young pine plantation planted seven years ago; 31508_U01.qxd 11/30/06 12:30 PM Page 315

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Table 1. Common name, scientific name, author, family name and Estabrook’s collection number for taxa discussed in text.All voucher specimens are in the University of Mich- igan Herbarium, MICH.

Collection Common Name Scientific Name, Author, Family Number Giesta branca Cytisus multiflorus (L’Her) Sweet, Fabaceae 567 Giesta negral Cytisus grandiflorus (Brot) DC, Fabaceae 568 Pilro Genista cineria (Villars) DC in Lam., Fabaceae 577 Sargaco negro Cistus monspeliensis L., Cistaceae 576 Leiteira Euphorbia characias L., Euphorbiaceae 579 Sargaco branco Halimium lasianthum (lam) Spach, Cistaceae 578 Rosmaninho Lavandula stoechas L., Menthaceae 580 Dedaleira Digitalis thapsi L., Scrophulariaceae 575 Urze Erica arboria L., Ericaceae 582

these samples are near the usual age when landowner what area of his or her land was farmers cut them for animal bedding and cook used to grow each crop, such as rye, potato, fires. Samples were also taken a few more kilo- olive trees, chestnut trees, or grape vines, and meters south near the village of Castanheira, other cover such as pine trees or giesta. These designated CA, in a wet, sandy meadow near estimates were recorded in a series of books the headwaters of the Rio Teja co-dominated by that are still archived in the tax office of the city giesta branca and sargaco branco. Voucher of Trancoso, where Jorge Santos Costa, the re- specimens for all taxa sampled have been de- sponsible agent, generously allowed me to posited in MICH, the University of Michigan spend many days transcribing them for the vil- Herbarium, Ann Arbor, Michigan, USA. Their lages of Aldeia Nova and Sebedelhe. names are presented all together in Table 1. I took two approaches to estimating the area Results and Discussion of giestal relative to the area under cultivation. I From a 6.0 square meter area, 12.5 kg wet observed and conversed with three farmers who weight of giesta branca was harvested. The were still actively managing their land; Antonio fraction dry weight was determined to be 0.38. Sovral Dias, his cousin Jose of Sebedelhe, and This estimates an average yearly primary pro- Manuel Andrade of Aldeia Nova. In 2002/3, duction of about 200 g dry weight per square when I did these field studies, only a few tradi- meter, which is about 2 metric tons per hectare. tional farmers were still active. The Dias From a 7.5 square meter area, about 91.7 kg cousins, but especially Antonio, were able to wet weight of giesta negral was harvested. Its make credible estimates of land areas used in fraction dry weight was determined to be 0.41. different ways by their uncle Manuel Dias, who This estimates an average yearly primary pro- in about 1940 operated the large Quinta Baral- duction of about 900 g dry weight per square hada, a few kilometers from the village of meter, which is about 9 metric tons per hectare. Sebedelhe da Serra. On many occasions I It would have improved accuracy to have walked with Antonio Dias over the lands of the been able to make additional estimates of pri- Quinta Baralhada. I could see and measure ap- mary productivity in other giestais, but there proximately how much area Manuel Andrade were obstacles that made this impractical. I actively cultivated, so by measuring the rate at cannot cut people’s giesta without their permis- which he harvested giesta to bed his sheep, and sion. It is difficult to discover owners of giestais using the rates of primary productivity of gies- and locate them. Many of them do not live lo- tas, I could estimate the minimum amount of cally. Even if they are local, it is difficult to ask area in giesta required to sustain that harvest them for permission to cut their giesta without rate. first establishing a personal relationship with In addition, as part of a national rural land them, which is not always possible and in any survey for tax purposes, the government of Por- case takes time. Finally, this investment would tugal sent teams into the agricultural villages of be worthless unless it were possible to know Trancoso in 1974 to estimate for every rural when the giesta was last cut, which is rarely 31508_U01.qxd 11/30/06 12:30 PM Page 316

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Table 2. Estimates of %Nfixed using dilution of 15N/14N.

Name Place Date %N fixed %N Deltas giesta branca 52 (29, 68) 2.4 0.73 0.53 0.51 Pair 1 AN 30 Jan 03 rosmaninho non-fixer 2.2 1.58 1.14 1.03 giesta negral 35 (33, 44) 1.3 0.51 0.48 0.43 Pair 2 AN 26 Sep 02 dedaleira non-fixer 0.9 0.77 0.76 0.76 giesta branca 95 (99, 78) 2.5 0.45 0.11 0.09 Pair 3 SS 29 Jun 03 sargaco negro non-fixer 2.1 2.21 2.21 2.10 pilro 96 (97, 82) 2.4 0.27 0.08 0.04 Pair 4-b SS 20 Mar 03 leiteira non-fixer 2.3 1.58 1.53 1.48 giesta negral 47 (34, 51) 1.6 1.03 0.89 0.89 Pair 5 MG 7 May 02 urze non-fixer 0.8 1.82 1.73 1.54 pilro 92 (93, 86) 2.6 0.15 0.09 0.08 Pair 6 QB 29 Jan 03 sargaco branco non-fixer 2.2 1.21 1.12 1.06 giesta negral 82 (82, 79) 1.6 -0.50 -0.51 -0.56 Pair 7 TR 9 May 02 urze non-fixer 0.9 -2.65 -2.75 -2.82 giesta negral 40 (49, 27) 2.8 1.32 1.22 1.11 Pair 8 TE 28 Jan 03 sargaco negro non-fixer 1.9 2.19 2.03 1.81 giesta branca 88 (91, 84) 1.5 -0.20 -0.33 – Pair 9 CA 7 May 02 sargaco non-fixer 1.0 -2.00 -2.11 -2.15 giesta branca 88 (63, 53) 3.0 2.43 2.19 1.93 Pair 10 SS 20 Mar 03 sargaco negro non-fixer 2.4 5.28 5.27 5.16 giesta branca 73 (77, 71) 3.5 0.70 0.66 0.62 Pair 11 AN 21 Mar 03 rosmaninho non-fixer 2.8 2.67 2.42 2.42 giesta negral 68 (83, 66) 3.3 0.42 0.42 0.23 Pair 12 AN 21 Mar 03 rosmaninho non-fixer 2.5 1.37 1.30 1.23

known by owners because most land is no fixed from the air were successfully calculated longer managed in the traditional manner, and for 12 samples of giesta, and are reported in my own serious attempt to discover anatomical Table 2. Results are presented in pairs: each gi- age markers such as growth rings or annual esta is followed by the non-nitrogen fixer grow- branching patterns, which are common for real ing in close proximity. Place is designated as trees, did not bear fruit. I was fortunate to have explained above. Total N is % of dry weight of been present when Antonio Dias was ready to plant tissue sampled. Three separate analyses of clear cut a stand of giesta negral of known age, material taken from the same dried, ground, and and to have established my welcome in a parish homogenized sample were made. Because total where a common of giesta branca was still N rarely varied by more than 0.2% among the being managed, so that we can have at least one three repeated analyses of the same sample, estimate of the primary productivities of these only their average is reported. Because Delta two giestas, under something resembling tradi- values were more variable, all three are re- tional management conditions. ported. Three estimates of the percent of total N Estimates of fraction of nitrogen in giesta fixed from the air are reported: the ratio of the 31508_U01.qxd 11/30/06 12:30 PM Page 317

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sums of the two most similar Deltas for each 45% of the dry weight of giesta is carbon and sample (if the three Deltas were equally spaced about 1.3% in some giesta negral up to 3.5% in then twice the middle value was used), fol- some giesta branca is nitrogen (Table 2). Thus lowed parenthetically by the maximum and C/N ratios for giesta can be estimated between minimum among the results using ratios of any a high of about 40 down to below 20 in some two Deltas with one from each sample. In con- cases. sidering these values, it is important to remem- In Aldeia Nova, with the help of Manuel An- ber that they may not be typical of the fixation drade, I buried giesta alone in the soil of a small rates of most of the giesta actually used to area of a larger plot to be sown in rye. Although maintain soil fertility, which grow in giestais there was enough giesta buried to supply all the where no other comparable non-nitrogen-fixing nitrogen needs of the growing rye, the rye there plant grows. grew very poorly compared to the rye growing According to Antonio Sovral Dias and his nearby in soil enriched with estrume. At the cousin Jose, when their uncle Manuel held the time of rye harvest, I dug up the soil in this Quinta Baralhada in about 1940, it comprised small area to discover that many of the larger about 220 hectares. About half of it was pine sticks and twigs of the buried giesta were still forest and about a quarter of it was giesta conspicuous. At the same time, digging nearby branca. About half the area of this giestal would it was rare to find any sticks or twigs at all. actually have giesta plants, the rest would be About 11 to 13 percent of dry weight of sam- rock or grass. Uncle Manuel had about 250 ples of sheep excrement analyzed in the na- sheep. He kept about 25 sheep for every hectare tional lab for agricultural chemistry in Lisboa cultivated, which estimates about 10 cultivated (LQARS) is nitrogen. To be effective, the hectares. About 8 would have rye, and the other sheep’s contribution to estrume needs to bring 2 hectares would have fodder crops such as rye- its C/N ratio down to about 20, which would be grass (Lolium perenne), beta root (Beta vul- about one part in five (dry weight) for the most garis) and rutabaga (Brassica napus, or pota- nitrogen poor giesta, but typically about one toes (Solanum tuberosum). In smaller plots part in seven or eight (dry weight). Adding a nearer the village, vegetables were grown. Be- seventh to the 8 or 9 metric tons of giesta per cause rye fields were fallowed about every eight hectare of rye estimated for Manuel Dias in the years, the 8 hectares with rye would imply an- Quinta Baralhada of Sebedelhe da Serra, brings other 4 temporarily in giesta negral. So we have it to about 10 metric tons (dry weight) of es- about 50 to 60 hectares of giesta branca produc- trume per hectare per year. ing at about half the rate I measured, and about People in these farming villages in the 19th 4 hectares of giesta negral, all supporting about and early 20th centuries probably did not know 10 cultivated hectares. This estimates about 50 about nitrogen or C/N ratios, so their culture metric tons of giesta branca and 36 metric tons must have informed them in some other way to of giesta negral buried every year in 10 culti- keep sheep. People in these villages do not eat vated hectares, which is about 8 to 9 metric tons sheep or lamb nor sell it before it is quite old. per hectare. The only meat they eat is pork and chicken (and Of course, estrume also contains the sheep’s occasional wild game). When sheep get too old contribution in addition to the giesta. In the (about six years) they are sold in the market past, farmers kept sheep primarily to lower the town about 30 kilometers away, as are old cows C/N ratio of estrume so that it would rot rapidly no longer reliable for their primary purpose, enough in the soil to fertilize rye, which was which is traction (Fig. 2). Sheep are shorn in the valuable crop. When the ratio of carbon to the spring, but their wool is not abundant and of nitrogen (C/N ratio) in fresh organic matter is low quality; it is used mostly for blankets and above about 30, it decomposes very slowly be- floor coverings. Sheep are not well fed so their cause these conditions do not favor large popu- birth rate is low, producing a lamb about every lations of the micro-organisms that rapidly rot other year. The small amount of milk, available fresh organic matter. When the C/N ratio is for a short time at weaning, is made into a below about 20, fresh organic matter can rot creamy cheese that is very much appreciated. quickly, releasing nutrients to the soil where Cows are milked briefly at weaning, but their they can be taken up by growing plants. About milk was traditionally fed to the pigs. Because 31508_U01.qxd 11/30/06 12:30 PM Page 318

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the value of these sheep products is not com- Baralhada, but accounted for only about 90 mensurate with their cost in labor and space, it hectares. Jorge Santos Costa assures me that for seems clear that the primary purpose for the a consideration, land owners could easily per- sheep was to help maintain soil fertility by con- suade members of these teams to under- tributing about 1/3 of the replaced nitrogen, estimate their holdings. However these records lowering the C/N ratios of estrume, and prob- are better than nothing, and almost certainly it ably also replacing other nutrients as well, such would be the area of valuable crops (grapes, as phosphorous, which is about two to three olive, grain, and, to some extent, pine) that tax- percent of the dry weight of estrume. paying owners would like to have underesti- Manuel Andrade, in Aldeia Nova, had 38 mated. Areas of giestal would probably be inac- sheep. At night he kept them in a shed with gi- curately estimated because they were not worth esta spread on the floor; he added fresh giesta enough for tax purposes to take the time to esti- about every other day. Every Saturday he re- mate accurately. Manuel Andrade moved onto moved all the giesta from the shed floor and the land he now holds in the mid-1980s when placed it in a pile outside the shed door. Before he bought some of the Quinta Pisao from Anto- cleaning his shed the next Saturday, he forked nio Fonseca of Aldeia Nova when he retired. this pile down the hillside to join a growing Thus the correspondence between what land he heap of estrume, which he would eventually held in 2003 and the 1974 tax survey was lost, bury in the soil of his cultivated fields. I mea- so I could not directly compare estimates. How- sured the volume of a weekly pile, which was ever, in 1974, the tax survey for another owner- just over one cubic meter. Two liters of this wet ship parcel of Quinta Pisao reported 1.6 ha gi- estrume weighed about 700 g and when dried estal, 0.135 ha in rye, and 0.390 ha in potato. about 300 g. A week’s worth of estrume from Potato is a low-nitrogen crop given less than 34 sheep is just over 1000 liters, so weighs half the estrume as rye, so at most 1.0 ha of gi- about 400 kg wet or about 160 kg dry. If this estal would fertilize the potato, leaving a ratio rate continues all year, it will fertilize some- of about 5 to 1 for the rye, or slightly higher if what less than a hectare at the usual rate of 10 some of the rye fields are fallow. metric tons dry weight estrume per hectare per Estimates from Table 2 of the percentage of year. This give us about 40 sheep per cultivated new nitrogen from the atmosphere present in hectare. However, Andrade is raising sheep to giesta negral vary in five samples from 35% to make cheese, not to sell rye, which in fact he 82%, with an average of about 54%; estimates grows to feed to his sheep. From Table 2 the of percentages in giesta branca vary in five percent dry weight nitrogen in giesta is some- samples from 52% to 95%, with an average of what variable around 2%, with branca running a about 80%. Applying these rates to the culti- little higher than negral on average. Samples of vated rye fields of Quinta Baralhada of Sebe- Manuel Andrade’s estrume are just over 4% dry delhe da Serra gives about 120 kilograms of weight nitrogen on average. Samples of the new nitrogen per ha per year. Observing and sheep excrement part contain about 12% dry talking with Antonio Sovral Dias determined weight nitrogen (some of the nitrogen was lost that rye seed was sown at a rate of about 80 as volatile ammonia before the sample was kilograms per ha. Traditionally harvests were taken). Combining these percentages implies quantified in seeds, i.e., the number of seeds that the sheep’s contribution is about one-fifth harvested for each seed sown. Harvests varied the dry weight of estrume. Thus, Manuel An- from as little as three seeds in poor years to as drade is harvesting about 130 kg dry weight much as 15 seeds in very good years, with (330 kg plant material) of giesta per week, or about seven seeds considered satisfactory, and about 700 metric tons per year. About 1/5 10 seeds good. Thus a rye harvest would hectare in fallow provides an average of about rarely exceed a metric ton of seed per ha. Rye 200 metric tons a year of giesta negral, so he seed is at most 3% nitrogen, so a rye harvest must have about 2.5 hectares of productive gi- would rarely remove more than 30 kilograms esta branca, which is likely to be actually about of nitrogen. Some seed was saved to plant the 5 or 6 hectares about half covered in giesta following year, and some rye was consumed branca, with the rest rocks and grass. by the farming family; so at most 20 kilo- Tax surveys from 1974 did include Quinta grams of nitrogen per ha cultivated in rye per 31508_U01.qxd 11/30/06 12:30 PM Page 319

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year would leave the area in exported grain. esta branca in relation to amount of area of cul- This leaves a surplus of about 100 kg of new tivated in rye, and the number of sheep per cul- nitrogen per ha per year. Even if the N15 tivated hectare all represent strategic balances stable isotope technology overestimated the that are a part of the culturally informed tech- percentages of biologically fixed new nitrogen nology of this tradition. in giesta by a factor of two, a substantial sur- Visit the Web site http://www.Personal.umich plus would remain. Nitrogen losses due to .edu/~gfe/ to download additional colored pho- other human activity seem probable, and there tos that illustrate and document this study. are natural soil nitrogen losses as well: using loss rate estimates given in Loomis and Con- Acknowledgments ner (1992) as a guide, perhaps as much as 40 Manuel Andrade of Aldeia Nova and Antonio kg per ha might be lost to denitrification, an- Sovral Dias of Sebedelhe, both experienced other 10 kg per ha to volatilization, and an- farmers raised in the traditional agriculture of other 5 kg per ha to leaching (but I captured Trancoso, Portugal, were valuable sources of and analyzed leach water from a half-meter information and help. Maria de Concecao below the soil surface under growing rye Alexandre of Trancoso provided valuable logis- throughout the rainy growing season, and at tic support. Dra. M. Regina Martins and Jorge most traces of nitrogen was detectable). I Santos Costa helped me access civil and land made no attempt to account for the nitrogen use records in Trancoso. Professor Helena Fre- lost in the sale of sheep and cows, and in the itas, Department of Botany, University of burning of wood to cook and bake. There also Coimbra, Portugal, made available laboratory may be other natural sources of new nitrogen space there for me to prepare specimens. I ap- such as nitrogen in rain water. preciate the welcome as invited professor ex- tended to me by the Anthropology Department Conclusion of the University of Coimbra. I am grateful to It is important not to overgeneralize these re- Professor Don Phillips, Department of Agron- sults. Agricultural sustainability depends on omy, University of California at Davis, for in- many factors, not just the sustainability of the troducing me to stable isotope techniques for nitrogen soil fertility examined in the study re- estimating in the field amounts of nitrogen bio- ported here. Replenishing other nutrients in the logically fixed by long-lived plants. I thank Pro- soil, keeping soil erosion rate below soil regen- fessor Cristina Maguas of the University of Lis- eration rate, avoiding soil pollution or contami- boa, Portugal, who facilitated my use of the nation or compaction, maintaining soil water Mass Spectrometry Laboratory of the Univer- table, and defending farmland from urban sity of Lisbon, and Rodrigo Maia, her techni- sprawl are examples of other important factors. cian, who performed the analysis of my sam- Indeed, very little agriculture is practiced in ples, for his skillful, careful, and patient work, Beira Alta at present, largely for economic rea- and for his advice for their preparation and sons not directly related to soil fertility mainte- preservation in transport. I admire the skill of nance. Most of the estimates presented here artist Vaike Haas who drew the map of Fig. 1. I were not made with high precision, but hope- appreciate financial support from Fundacao fully with appropriate accuracy to argue the Luso-Americano de Desenvolvimento, and the main points. Clearly, giesta makes a very sub- sabbatical leave program of the University of stantial contribution to the nitrogen sustainabil- Michigan. ity of the traditional farming practices of Beira Alta, Portugal, especially in the face of substan- Literature Cited tial 18th, 19th, and early 20th century exports Almeida, D. dos S. 1882. Estado actual de agricultura of nitrogen, in the form of rye seeds. This tradi- na Beira Alta. Relatorio. Final de Curso de En- tional farming system maintains giesta branca genheria Agronoma. Instituto Superior de on soils too poor to cultivate, and giesta negral Agronomia, Lisboa, Portugal. Altieri, M. A. 1987. Agroecology: The science of sus- in the vicinity of cultivated fields, ready to take tainable agriculture. 2nd ed. Westview Press, over during fallow to grow rapidly for four or Boulder, Colorado. five years. The amount of fallowed rye fields Alves, B. J. R., C. de P. Rezende, A. S. Rezende, R. with giesta negral, the area maintained with gi- Marcedo, R. Tarre, S. Urquiaga, and R. M. 31508_U01.qxd 11/30/06 12:30 PM Page 320

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Boddey. 2000. Estimates of N2 fixation in for N2 fixation: Laboratory and field evaluations. Desmodium ovalifolium from the relative ureide Plant Physiology 43:1185Ð1207. abundance of stem solutes: Comparison with 15N Harris, P.J. 1988. Microbial transformations of nitro- dilution and an in situ soil core technique. Nutri- gen. Pages 608Ð651 in A. Wild, ed. Russell’s soil ent Cycling in AgroEcoSystems 56:177Ð193. conditions and plant growth. Longman Scientific, Boddey, R. M., M. B. Peoples, B. Palmer, and P.J. Harlow, Essex, UK Dart. 2000. Use of 15N natural abundance tech- Hunn, E. S. 1999. The value of subsistence for the fu- nique to quantify biological nitrogen fixation by ture of the world. Pages 23Ð36 in V. Nazarea, ed. woody perennials. Nutrient Cycling in AgroE- Ethnoecology: Situated knowledge/Located lives. coSystems 57:235Ð270. University of Arizona Press, Tucson, Arizona. Bruce, N. 1975. Portugal: The last empire. David and ———. 2001. Prospects for the persistence of en- Charles, London. demic cultural systems of traditional environmen- Chalk, P.M., and C. J. Smith. 1994. 15N isotope dilu- tal knowledge: A Zapotec example. Pages 137Ð tion methodology for evaluating the dynamics of 144 in L. Maffi, ed. Biocultural diversity: Linking biologically fixed N in legume non-legume asso- language, knowledge, and the environment. ciations. Biology and Fertility of Soils 17:80Ð84. Smithsonian Institution Press, Washington, D.C. Damaso, E. 1992. Incendios florestais. Publico 2 sep Jenkinson, D. S. 1988. Soil organic matter and its dy- No 912. p 14. namics. Pages 564Ð607 in A. Wild, ed. Russell’s Estabrook, G. F. 1994. Choice of fuel for bagaco stills soil conditions and plant growth. Longman Scien- helps maintain biological diversity in a traditional tific, Harlow, Essex, UK. Portuguese agricultural system. Journal of Ethno- Lajtha, K., and R. H. Michener, eds. 1994. Stable iso- biology 14:29Ð37. topes in ecology and environmental science. ———. 1998. Maintenance of fertility of shale soils Blackwell Scientific, Oxford, UK. in traditional agricultural system in central inte- Loomis, R. S. 1978. Ecological dimensions of a me- rior Portugal. Journal of Ethnobiology 18:15Ð33. dieval agrarian system: An ecologist responds. Gliessman, S. R., ed. 1990. Agroecology: Research- Agricultural History 52:478Ð483. ing the ecological basis for sustainable agricul- ———, and D. J. Conner. 1992. Crop ecology. Cam- ture. Springer Verlag, New York. bridge University Press, Cambridge, UK Groot, J. J. R., P. DeWilligen, and E. L. J. Verbene. Marioti, A. 1983. Atmospheric nitrogen is a reliable 1991. Nitrogen turnover in a soil crop system: standard for natural 15N abundance measure- Modeling of biological transformations, transport ments. Nature 303:685Ð687. of nitrogen and nitrogen use efficiency. Kluwer Oliveira, A. de. 1980. A renda agricola em Portugal Academic Publishers, Dordrecht, The Nether- durante o antigo regime (seculo XVIIÐXVIII). lands. Revista de Historia 6:1Ð56. Hardy, R. F. W., R. D. Holsten, E. K. Jackson, and Raposo, J. R. 1994. Historia de rega em Portugal. R. C. Burns. 1968. The acetylene-ethylene assay Ministerio de Ambiente, Lisboa, Portugal.