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omit rehabilitation of degraded ‘Espinales’ diterranean-climate region of central Chile

Be ecologmcal and economtc condlttons m the -It-acla carcn dominated Espmales’ of tne Medtterra- nean-chate mne af central Chrle, we have undectaken a long-term project armed at combmmg sustamable resource development of the regron wth ecological rehabrlrtdtton of Espmal ecosystems and landscapes. The central hypothesis m this project IS that the mtroductlon of compatrbte and appropriate legume/Nt-fixing mtcrosymbtont ‘couples’ can ( 1 ) optrmrze the amount of atmosphenc nitrogen fixed 1~1 a degraded artd or semiarid land ecosystem, (2) promote the devel- opment of associated plants, and (3) rmprove so,rlc and enhance posstbtlttles for the spontaneous or asststed return of natwe plants and ammals A schematsc model IS presented of ecosystem degradation u-t the Chilean Espmales together wtth three alternative responses to It ( restoration, rehabthtatron and reallocation ) The roles of ‘arttfktal negative selec- tlon’ and ‘powwe selection’ m these processes are discussed Fmally, we compare the landscape of a typtcal farming vtllagc m south-central ChtPe as seen today, and as rt could become when bto- and agro-ecologtcal diversity are recognrzed as the best guarantors of ecosystem stablhty. resrlrence, and long-term producttvtty.

Five hundred years ago, the Central Depres- sion of Chile was covered by dense, sclerophyl- lous matorral vegetation typical of Mediterra- nean-climate regions (Parsons, 1976; Gasto, 1979; Fuentes et al., 1989 ). Today, virtually all of this region has been ‘artificialized’, and is used for agricultural systems and rangelands of generally low productivity (Bahre, 1979; Ovalle et al., 1990). Except where intensively managed (e.g. in vineyards) or else irrigated (no more than 4--Y% of the area), the region is thoroughly invaded by the spiny legume ilee Acacia caven (‘espino’) or, in some cases, by shrubby Baccharis spp. (Asteraceae), both of which taxa are exotic to the region, and by a wide assortment of Eurasian and Mediterra- nean Basin annuals. The resulting A. caven

‘Corresponding author.

dominated pseudo-savannas, or ‘Espinales’, cover more than 2 000 000 ha of the Central Depression of Chile, and provide the frame- work for land use management for some 300 000 people (Ovalle et al., 1990). How- ever, as mentioned, productivity of most Chil- ean Espinales is low compared with other rainfed farming systems of similar precipita- tion regimes (Crespo, 1985 ). This is presum- ably due to the combined effects of decreased biodiversity and soil fertility, both of which were sacrificed in the name of short-term gains over the past few centuries. Moreover, it can be argued that an inverse relationship exists between biodiversity and short-term produc- tivity (Fig. 1). However, if the qualifier ‘short- term is removed, there need be no conflict between the two, provided that the initial structure and functioning of the natural eco-

system are preserved more or less intact.

0 1993 Elsevier Science Pubhshers B.V. Ail rights reserved 0 I69-2046/93/$06.00

Natural ccarJyetcm Atrurture and fuactlontng

SHORT-TERM

FIR I The balancmg act bctwccn blodlLcrsll> and shon-term productI\ It\ Where natural ecos)stcm structure d func-

tlonmg arc rcspcctcd. then ccoslstcm stablilt> (lncnla and rcslhcncc) cnsurcs the compatlbllll> of long-term or sus- tamed producti\ IQ and blodl\ crsl!).

Acacia caven has merit in agroforestry for its edible pods, nitrogen-fixation capzity (Aron- son et al., 199 I ) and, above all. its out-of-phase phenological pattern that all contribute to the productivity and pasture value of the stratum of herbaceous plants growing under it (Ovalle and Avendaiio, 1987: Aronson et al.. 1993a.b). These positive effects are appreciated. how- ever, only when the tree is managed in a silvo- pastoral or agrosilvopastoral system.

Unfortunately. in Chile. as elsewhere in southern South America, A. car~n has suffered from ‘artificial negative selection’ (Aronson, 199G ). This term refers to the nearly universal process whereby people and animals tend to cut, graze, and otherwise harvest plants in re- verse order to that which would be in their own long-term interest. Instead of preserving the best individuals in wild plant populations as ‘mother plants’ and ‘nurst plants’, they exploit the largest, most valuable, and most palatable trees, shrubs and grasses first, the next best next, and the worst last. It is true that certain espino trees are left standing in some farmers’ fields 9s ‘pajareros’ (roosting sites for birds), but this does not affect the general tendency. When its consequences are evaluated at higher levels of organization, artificial negative selec-

tion can also bc seen as contributing to and even accelerating the destabilization of piant

communities and ecosystems, as well as the degradation of entire landscapes. In central Chile over the past four centuries, it has re- sulted in the progressive loss of biodiversity and long-term productivity - throu a pro- cess called ‘retrogressive succession’ (Gasto, 1979; Allen, 1989 ) .

Our research and development programme seeks to reverse the trends of desertification and retrogressive succession in the Chilesln Es- pinales. We pursue a strategy of seeking long- term, sustainable productivity, at the ecosys- tem level, by re-establishing as much biodiv- ersity as possible in an ‘artificialized’ land- scape, and as is comnfi+;bia par1 uz Wit I IUd tXO?iOii?iC . I-

realities. Artificial negative selection must be eliminated for such goals to be achieved.

One hypothesis being tested is that the intro- duction of compatible and appropriate leg- ume/&-fixing microsymbiont ‘couples’ can ( 1) optimize the amount of atmospheric ni- trogen fixed in a degraded arid or semiarid land ecosystem, (2) promote the development of associated plants. and ( 3 ) improve soils and enhance possibilities for the spontaneous or assisted ret:lm of native plants and animals. However, a more general model is also being followed, as described below. It is oniy in the presence of alternative visions of the future that local people can be expected to alter their patterns of bioresource exploitation and management.

In our view, fighting desertification and ret- rogressive succession in degraded ecosystems can follow two main pathways: restoration or rehabilitation ( Aronson et al., 1993b,c). Both share as primary goals the improvement of soil structure and fertility, the re-inauguration of ‘progressive’ as opposed to ‘retrogressive’ succession oi plant communities and, finally, increased biodiversity, and stability (inertia and resilience) at the landscape and ecosystem levels.

Restoration aims at re-establishing the en-

tire assemblage of species presc~t prior to t onset of human disturbance, if it I~ doubtful whether this can ever be fu achieved (Simberloff, 1990; Sprugel, I99 I ).

McJiterranean lands, where people so firm inhabit the landscape and so strongly mani late the flora and fauna of land, air and water (e.g. Naveh, l990), such a goal seems partir- ularly unobtainable.

The alternative path of rehabilitation take< as its primary goal the rapid amelioration o’ general ecosystem function without necessar - ily restricting itself to the use of indigenous eld - ments. and without seeking to reconstitute ;1 predetermined inventory of native spectcs (Aronson et al., 1993~). Instead, it seeks create a simplified ecosystem whose structu and, especially, functioning are roughly deiled after the original, or pre- man )disturbance ecosystem. However, for reason stated above, in Mediterranean 1 agro-ecological diversity should prob taken into consideration along with naturaI biodiversity, and instead of a pre-( he- man)disturbance condition, it is that con tion found prior to the onset of severe, anar- chic overexploitation which must be sought.

Finally, ‘reallocation’ describes what hap- pens when a piece of land is assigned an alto- gether new use or uses and the original ecosys- tem’s structure and functioning are no longer taken as a model to be followed (Aronson et al., 1993~). In its broadest sense, reallocation covers a wide range of land uses, from energy- intensive, irrigated farming systems to low- energy run-off systems, parking lots, or even nuclear waste dumps. In a well-managed land- scape, reallocation is confi,-ted to those land- scape klnits best suited for the new uses im- posed upon them. However, a problem arises when less well-suited lands aie reallocated to a new use to the detriment of biodiversity, fertil- ity, and long-term productivity at the ecosys- tem and landscape levels. In arid and semiarid lands of developing countries, such as central Chile, this is increasingly the case as a result of L

escalating demographic pressure, rural POV- efty, and related phenomena

Figure 2 illustrates the application of these concepts to the Chilean Espinales. Given the

presence of a large rural, resource-based pop- ulation, the full restoration or rehabilitation of ecosystems in central Chile to a state resem- bling their presumed pre-Conquest diversity, cover and productivity is impractical, not to say impossible, outside of nature reserves or national parks. A more useful goal is the res- toration or rehabilitation of a presumed vege-

tational Steddy St&e that we call a ‘mixed Es- pinal’. It corresponds to the Espinales of 100, 200 or 300 years ago, when according to his- torical accounts (Molina, 18 10; Mufioz Schick, i 975 ), anarchic exploitation and retrogressive succession had not yet proceeded very far.

When protected from grazers and browsers, some natural re-invasion of native woody spe- cies does occur in disturbed ecosystems of cen- tral Chile, thanks to the nurse plant effect pro- vided by certain pioneer shrubs (Fuentes et al., 1989). However, contrarv to other Mediterra- nean-climate regions, most native tree and shrub species of the Chilean matorral lack post- disturbance regeneration mechanisms (re- sprouting from lignotubers, fire-induced seed germination, etc. ) (Armesto and Pickett, 1985 ). Furthermore, the soil-borne seed bank at most Espinal sites is completely devoid of most indigenous trees and shrubs, such that long-distance dispersal is the only possible means (short of human intervention ) for the return of these species. (Moreover, once re-in- traduced, it is not certain that they could sur- vive in competition with the exotic invaders that have occupied these lands for several cen- turies.) Thus, even the limited goal of increas- ing biodiversity in shrub and tree layers is unobtainable without major intervention, and intensive management for a prolonged period, i.e. rehabilitation. Needless to say, realloca- tion is a viable option in some areas, but only when important outside ‘subsidies’ (i.e. en- ergy, irrigation, water, fertilizers, etc. ) can be

Rl!AABfLItATlON USALLOCATION -e

FIN 2. Pathwjs of rcsto;atlon. rehablhtatlon. and reallocatlon followng a departure from current degradation patterns III Ch~l- can Esplnalcs NFTs. mtrogen-fixing trees. AS. agrovlko. SP. sll\opastoral. ASP. agrosIl\opastoral ( Qonson et A.. 1993b).

supplied. Such inputs are usually reserved for the most productive lands available. and not for so-called ‘marginal’ lands.

One further characteristic of rehabilitation hinges on the s te1y intro- duced exotics, e.g. fodder shrubs or fast-grow- ing. nitrogen-fixing trees. Where indicated by pragmatic concerns, exotic species can be sub- stituted for, or added to, native ones in the re- habilitation pathway. provided they are in- tended to become part of a self-sustaining dynamic system. In other words, if these useful exotics become naturalized, and come to play an ecological role comparable with that of some formerly present native species, then it is ap- propriate to speak of successful rehabilitation having taken place. If, on the contrary, the in- troduced exotics never become self-sustaining parts of srlccessional communities, then the project in which they form a part is one of reallocation.

As described by Gvalle et al. ( 1992 ), a three-

tiered approach is pursued in our research and development programme. The first step is the introduction and selection on a regional basis of ecotypes of the naturalized annual medic ( Medicago polvmorpha), in combination with - selected strains of rhizobacteria. Where suc- cessfully established and integrated in farming systems. such nitrogen-fixing ‘couples’ should increase levels of available nitrogen in the soil, while also contributing to organic matter con- tent and increasing yields of wheat crops sown in rotation with the medic and the natural pas- ture exploited during fallow years in the result- ing ‘ley-farming’ rotat ion system ( Puckridge and French, 1983 ).

Secondly, low-cost ways of improving soil fertility and microbial biomass are being tested, notably the introduction of nitrogen-fixing shrubs and trees, together with appropriate microsymbionts. Finally, we seek to establish both natural and simplified ‘mixed Espinales’ whose tree and shrub layers would show greater

Fig. 3. Current landscape around a village in the subhumd portlon of the Mediterranean-&mate re&o? of south-central Chile. Virtually all of the shrubs are Acana cat-en suffenng from ‘artlficlal negatwe selectlon’

diversity in bcth their horizontal and vertical structure than existing Espinales and whose productivity and successional trajectories would be more promising than those seen at present.

In order to rehabilitate such ‘mixed’ Esli;in- ales, we are testing the feasibility of inco-po- rating fast-growing, prolific cultivars of eqino (A. caven) and algarrobo (Prosopis scp. ) as well as other multipurpose trees and shrubs from the Chilean matorral or other lands (e.g. maiten (Maitenus boaria). belloto (Beilsch- Media spp. ) or introduced oaks (Quercus spp. ) ). All of these trees grow to be consider- ably taller and broader and, presumably, de- velop root systems deeper and vaster, than A. caven. Thus, they exploit different soil strata than espino and, together with their associated soil-borne micro-organisms, should improve soil structure and water infiltration of heavily compacted Espinal soils. They also show phen- ological and ecological features different from those of A. caven, and could thus aid in diver-

sifying plant community structure and func- tioning as compared with that of Espinales where only A. caven occurs. Diversification of the Espinales should bene% not only ungu- lates that browse young shoots, eat tree pods, and take shelter in their shade, but also bees and other pollinators (Peralta et al., 1992), and the herbaceous stratum growing underneath the trees (Ovalle and Avendafio, 1987 ).

Consider the landscape of a typical farming village in south-central Chile as it appears to- day (Fig. 3 ), and as it could become in the conceivable future (Fig. 4). At present, shrubby espino of no value whatsoever domi- nates all uncultivated fields, productivity and biodiversity are low, and soil erosion is ram;l- ant. However, by implementing the three- tiered programme we espouse, and by replac- ing artificial negative selection with positive selection at the ecotype, species and landscape levels, the landscape surrounding this village could become a mosaic composed of produc- tive, interlocking units. Reallocation would be

Fig. 4. One conceivable landscape of the future for the Chkan Espmales 13 the same subhumad zone as shown m Fag. 3. Appro- pnate land parcels are reallocated to vmculture. arch,. -Tds and firewood plantations More fragile landscape umts are bemg reha- bllitated with ley-farming. sllvopastoral. and agrosll\opastoral systems. Degraded h~lls~!es m the distance have been replanted with native trees, shrubs. and grasses, and are now managed as rarest and Nlldlife resents as well as for watershed management.

confined to the most appropriate topographic and hydrological units within the landscape; nature conservation would be enhanced in the areas least exploited by the villagers: rehabili- tation would be und&&en for rhe rest.

Transforming a ore easily done on paper than in the field, particularly when local people have strongly entrenched cultural traditions and the natural caution and conservatism that come from poverty. Yet we believe that unless bold new approaches are taken to fight desertification and retrogressive succession in the Chilean Espinales, the lot of the people there will decline in correlation with the loss of bio-agro-ecological diversity.

We are aware that even working at the land- scape level we will not be able to transform even one village economically and ecologically unless corresponding efforts are made at a na- tional level as well. As long as people cannot afford gas or oil, they will continue to cut and bum wood to cook their food and heat their

houses. (Yet firewood crops could be grown near villages. as in Fig. 4.) As long as poverty forces farmers to live from day to day, they will rarely be able to implement radical new pro- grammes or follow new paradigms. They need help on many different levels. Our purpose here has merely been to demonstrate that using na- tive plant resources primarily, and starting from the existing situation, new models and paradigms can be developed for degraded Es- pinales in central Chile. We intend to pursue these ideas experimentally over the next dec- ade or two; their implementation in working farms and villages remains the ultimate challenge.

Acknowledgements

We thank Lucho Alar&n, Teresa Aravena, Jose Cares, Marie Elena Ciiaz and Cesar Nor- ambuna for outstanding technical assistance in Cauquenes. We also thank Mary Abrams, Juan

ti

Armesto, Michel Etienne, Wesley Jarrell, Edouard Le Floc’h, Hem-i eel Le HouCrou, Arturo Lavin and Dan Simberloff for helpful discussions, although none of these colleagues are responsible for the opinions expressed here. RenC Ferris kindly drew the figures.

33rrhnae and rehabtlttataon of dts- d sotls: processes and practlses. Arx! Son! Res

and Pickett, S.T., 1985. A mechamstic ap- proach to the study ofsuccessmsn in the Chilean matorra!. Rev. Chil. Nat. Host., 58: 9- 17.

1990. Desert p!ants of use and charm from ‘Chile. Desert Plants, 10: 65-71,79-86. Ov alle. C. and 4~ endaiio, J . I 99 ! Early growth

rate and mtrogen fixation potential II? 44 legume species grown in two soi? types m central Ch le. For. Eco!. Man- age.. 47: 225-244.

Aronson. J.. Ovalle, C., Leon, P. and Agurlera. L., 1993a. Phenology of an “immigrant” savanna tree (.-fcacra caren, Leguminosae) m the mediterranean climate zone of cen- tral Chile J. Arid Environ.. m press.

Aronson. J., Ovalle. C.. Del Pozo. A.. Avendaiio, J. and Lavm. 4. 1 I.* i 993b. Rehabilitation of degraded ecosystems and outmoded farmmg systems in central Chile. l_ Historical overview and early field results wrth an annual medrc. Med~cago polwtorpha L., Agnc. Ecosystems, Environ.. m review.

Aronson. J.. Le F!oc’h, E., Floret, C.. Ovalle, C. and Por tan- ier. R.. 1993~. Restoration and rehabilitation of deg- lded ecosystems m arid and semiand regons. I. A view from the South. Restoration Ecol., 1: 8-l 7.

Bahre, C-J.. 1979. Destruction of the Natural Vegetation of North-Central Chile. Univ. California Press, Berkeley. I 17

PP. Crespo, D., 1985. IntenslficatIon of sheep production under

grazing on marginal lands of the Mediterranean regron. EEC/‘%AO Symposium, &ieVd, Switzerland. 18 pp.

Fuentes, E.R., Aviles, R. and Seguro, A.. 1989. Landscape change under indirect effects of human use: the savanna

of Central Chile. Landscape Ecol., 2: 73-80. Gasto. 3.. 1979 Ecologla. El Hombre y la Transformation dc

la Naturaleza. Edltorlal Umversltarra, Santiago, 573 pp. Moima, I.G., 1810. Saggla Sulla Stona Naturale de Chrlr.

(Second Edrtron ), Bologna. 345 pp Mui’i~z Schick. M , 1975. Geronrmo de Brlbar. nctable obser-

vador naturalista en la alborada de la Conquista. Bol., Mus. Nat. Host., Chile, 34: S-27.

Naveh, Z., 1990. Ancrent man’s impact on the Medlterra- nean landscape of Israel - ecological and evolutionary perspectives. In: S. Bottema, G. EntJes-Nleborg and W. van Zetst (Editors), Man’s Role m the Shapmg of the Eastern Mediterranean Landscape. Balkema, Rotterdam, pp. 43-50.

Ovalle, C. and Avendano, J , 1987. Interactions de ia strdte lrgneuse avec la strate herbacee dans les formations d’kacla caven (Mol. ) Hook et Am au Chrlr I Oeco!. Plant., 8. 385-404

Ovafle, C., Aronson, J.. De! Pozo, A. and Avendano, J , 1990. The espmal. agroforestry systems of the Medlterranean- type climate regron of Chile Agrofor Syst , IO. 2 I 3-239

OvaIle, C.. Aronson. J.. Avendafid. J.. De! Pozo. A. and Lavm. A., 1993. Rehablhtatlon of degraded ecosystems and out- moded farming systems m central Chr.,. II. Tagasaste muitlpurpose trees and a vlsron of the iuturs. Agnc. Eco- systems Envuon., m review.

Parsons, D.J., I976 Vegetation structure m the medlterra- nean scrub commumtres of Callfomla and Chile. J. Ecol., 64: 435-447.

Peralta, I., Rodnguez, J-G and Kalrn Arroyo, M.T., 1992. Breeding systems and aspects of pollmatron In Acacfa caren (MO!. ) Mel (Legummosae: Mrmosordeae) m the medl- terranean-;ype climate zone of central Chile. Bot. Jahrb , Syst., 1 14: 29 7-3 14.

Puckndge. D.W. and French, R J., 1983. The annual legume pasture In cereal-ley farming systems of southern Aus- tralia: a review. Agrrc. Ecosystems Environ., 9: 229-267.

Srmberloff, D., 1990. Reconstrtutmg the ambiguous - can IS- lands be restored? In D. Towns, C.H. Dougherty and IA-E. Atkinson (Ed-tars,, Ecologrcal Restoratron of New Zea- land Islands New Zealand Dept. Conservation, Welling- ton, pp. 37-5 1.

Sprugel, D.G., I99 1. Disturbance ecpulrbnum. and environ- mental variability: what IS “natural” vegetation In a changing environment? Brol. Conserv, 58: I - 18.