Homage to Ramon Marga/ef; or, Why there is such p/easure in studying nature 337 (J. D. Ros & N. Prat, eds.). 1991 . Oec% gia aquatica, 10: 337-349

MEOITERRANEAN WOOOY GROWTH-FORMS, BIOMASS ANO PROOUCTION IN THE EASTERN PART OF THE IBERIAN PENINSULA

JAUME TERRADAS

Centre de Recerca Ecológica i Aplicacions Forestals (CREAF). Universitat Autónoma de Barcelona. 08 193 Bellaterra. Barcelona. Spain.

Received: February 1990

SUMMARY The major physiognomic features of Mediterranean vegetation in the eastem part of the Iberian Peninsula are described considering a coastal and a continental gradient and oro-Mediterranean formations. The main communities include broadleaved evergreen forest, maquis, pine woodlands, "garigue", matorral, thom-scrub and dwarf- steppes along mesic-xeric gradients, and pine-juniper woodlands and xeroacanthic cushion-like formations as altitudinal stages. We discuss sorne morphologico- functional traits of dominant from these different formations as related to environmental conditions, and their corresponding energy use strategies. Even though there are relatively few data on biomass and production, a broad synthetic approach is given, with sorne reference values.

KEY WORDS : Mediterranean vegetation, growth-forms, biomass, production, energy use strategy

INTRODUCTION Different shifts could thus be expected in vegetation structure and plant-grawth forms Two major mesic-xeric gradients are following each gradient. Other factors, such observed in the eastern part of the Iberian as wind, soil, etc., can also affect plant Peninsula (Fig. 1). One runs from the fitness and modify adaptation features. Pyrenees to the south, fram areas with Moreover, there are local deviations fram 700- 1 000 mm annual rainfall to areas with climatic general patterns due to local 190-350 mm. The second runs fram the climatic circumstances that will not be northeast coast to continental areas, and its considered here. annual rainfall ranges fram 600-700 mm to Mediterranean climax ecosystems have 300-400. In what fo llows we refer to them been discussed on phytosociological as coastal gradient and continental gradient. grounds by BOLOS (1985) for most of the Different temperature changes occur along area (Catalan countries), RIVAS (1974) for both gradients. Along the coastal gradient, the southern part, and RIV AS (1987) for all there is an increase in summer length, Spain. BOLOS (1985) distinguishes average temperature and winter rninima. between a boreo-Mediterranean pravince, Along the continental gradient, both winter with climax cornrnunities corresponding to length and thermic amplitude increase, Quercion ilicis alliance, an austra­ whereas winter mínima decrease. Mediterranean pravince, with climax 338 TERRADAS

commumt1es corresponding to Rhamno­ (1974) identifies mature commumtles as Quercion coccife rae and Oleo-Ceratonion included in Asparago-Rhamnion oleoidis alliances, and a westem oro-Mediterranean and Periplocion angustifoliae alliances. province, corresponding to high and Ebro river valley vegetation is puzzling, moderately high Mediterranean mountains, and a Rhamno-Quercion cocciferae climax with Pino-Juniperion sabinae, Xeracantho­ has been classically assumed (BRAUN­ Erinaceion and Hypericion balearici climax BLANQUET & BOLOS 1957), but this communities, the last one found only in might be an incomplete view Majorca. (TERRADAS, 1986). In the southem end of the area, RIVAS

'l �4' oo --- .:.::. : ::.:. � Q::::�:: � - 7,6 { �-----::::--�- CONTINENTAL GRADIENT

400;¡¡'�.,oornrn EIVISSA .",-... Palma de Malior<:8 (10m) 400rnrn � ~

D Boreo-Alpine and Eurosiberian Regions D Boreo-Mediterranean Province • Au s tro-Mediterranean Province

FIGURE 1. The eastern lberían Península and major features referred to ín the text. MEDITERRANEAN WOODY PLANT PHYSIOGNOMY 339

A PHYSIOGNOMIC DESCRIPTION phanerophyte with long shoots and short OF VEGETATION shoots (dolichoblasts and brachiblasts) and marked seasonal heteromorphism, and the From a morphological point of view, dwarf palm Chamaerops humilis. mature vegetation along the coastal gradient Floristically, they are similar to maquis and changes from the broadleaved evergreen so they are inc1uded by phytosociologists in forest to tall thicket matorral and maquis the Rhamno-Quercion alliance, but the (Oleo-Ceratonion), and thom-scrub physiognomy has shifted. We are near the commumt1es (Oleo-Ceratonion and tree border (which is found somewhere Asparago-Rhamnion). Broadleaved between 350 and 400 mm of annual evergreen forests are dominated by Quercus rainfall). AIso replacing communities after ilex ssp. ilex or, on sandy soils in the disturbance are c1early different: large northem part of the area, by Quercus suber. surfaces are covered by chamaephytes, i. e. These forests are often replaced by "tomillares" (Thymo-Siderition leucanthae), pine-oak mixed forests, by Quercion-ilicis or halophytic, nitrophilous or gypsophylous maquis with Arbutus unedo and Erica commumtIes, and by dry therophytic scoparia, or by matorral: Cistion grasslands. The typical thorny shrub mediomediterraneum on siliceous soils and growth-form diversifies to the south, when Quercus coccife ra "garigues" or c1imate becomes drier, with plants like Rosmarino-Ericion scrub on limestone, all Maytenus europaeus, Periploca of them often with pines. Forests, maquis angustifolia, Ziziphus lotus, Asparagus and "garigues" are commumt1es with albus or intricatum added to phanerophytes with plane leaves, often lycioides (Asparago-Rhamnion coriaceous or sc1erophyIlous and entire, as and Periplocion alliances). the dominant plants, whereas matorral The continental gradient begins at the commumt1es are richer in northeast edge with the broadleaved nanophanerophytes or chamaephytes with sc1erophyl1ous forest or maquis near the soft (malacophyllous) leaves, sometimes coast, which is soon replaced by an plane (like in Cistus species) but in other impoverished ssp. cases leptophyllous (Erica) or linear. rotundifolia forest with Quercus coccife ra The austro-Mediterranean Oleo- "garigues " , Rosmarino-Ericion matorral or Ceratonion maquis is also dominated by pine woodlands as successional stages. At phanerophytes with coriaceous or sc1erophyllous leaves, mostly medium or ME IC small sized or divided (as in Ceratonia Quercus ilex evergreen sclerophyllous forest siliqua Pistacia lentiscus). . or But this () Continental "- sc1erophyllous vegetation has very often ffix Pine Q.rotundifolia Maquis. "garigue" Steppe een been replaced by Cistion or Rosmarino­ �:�;�� '-- Mato rral Ericion cornmumtles. Malacophyllous ;�:�:��iS '" : Maquis plants beco me more frequent and diverse in Matorral o '---- this area. () In the southem part of the territory,

eciduous forest maquis broadleaved evergreen Thorn-scrub phanerophytes like Olea europaea, Quercus Ev����:�n-oak "---- Dwarf-shru coccifera Pistacia lentiscus b and are XERIC steppe progressi vely replaced in mature F I GURE 2 . Major plant formations along the two communities by a thom-scrub. These mesic-xeric gradients and on Mediterranean communities are at first dominated by mountains. For the coastal gradient, degradation series Rhamnus lycioides, a malacophyllous are shown. 340 TERRADAS

the Ebro valley, rainfall decreases fast and A dense forest is rarely obtained. broadleaved trees disappear, and are Summits of Iberían mountains and southem replaced by a pine woodland with a shrub "sierras" are occupied by spiny cushion-like understory also c1assified Xeracantho-Erinaceion communities, in a phytosociologically as Rhamno-Quercion poor forro if compared with Sierra Nevada coccife rae. Therroophyllous species of thís and Atlas equivalents. community, inc1uding the pine itself, are Spiny cushion-like are also gradually disappearing to the centre of the present aboye 1100 m in Majorca Ebro valley, where the winter c1imate (Hypericion balearici), with a different becomes colder. There, on gypsic ground, floristic composition. Xeroacanthic shrubs slopes and shallow soils are mostly covered can be considered as an interesting case of by a nitrophilous or gypsophilous evolutionary convergence in oro­ chamaephyte semidesert or steppe Mediterranean c1imates: different families (Salsolo-Peganion, Gypsophylion), whereas are represented by species with similar fine-textured loams are occupied by morphology in these highly fluctuating hemicryptophytic or rhizomatous geophytic windy environments. Similar forros are also perennial grasses (Agropyro-Lygeion). In found on the coasts of the Balearic islands, this landscape, a high diversity of in windy environments too. therophytes covers the free spaces between perennial grasses or shrubs during the short wet periods. Halophytic chamaephytes or DOMINANT WOODY GROWTH nanophanerophytes appear on saline soils, FORM near the bottom of undrained valleys. Further up the mountains in the northem We will now try to summarize the major part of the territory, extra-Mediterranean woody plant growth forros that dominate conditions are soon fo und, which Mediterranean landscapes in our terri tory . correspond to the Euro-Siberian or MARGARIS (198 1) has suggested two Boreo-Alpine regions. But in the Iberían main adaptation syndromes for and southem (sub-Betic, Betic and Mediterranean environments: maquis Penibetic) mountains, sorne features of plants, corresponding to typical Mediterranean c1imates reach higher sc1erophyllous woody plants, and phrygana altitudes. According to BOLOS (1985), plants (equi valents are said to be Israeli oro-Mediterranean vegetation covers a very "botha", Iberian "tomillares", Portuguese limited area in sorne scattered isolated "barocales", Italian "gariga" and sorne other patches, occurring aboye Quercus forroations). Similar views have been rotundifolia and deciduous sub- discussed by ORSHAN (1983). Mediterranean forests. Pino-Juniperion Maquis plants are called isomorphic sabinae communities of IberÍan mountains because they maintain the same kind of are made up of large carpet-like patches of leaves all through the year. The average life Juniperus sabina or J. communis ssp. span of the leaf is usually between 1-2 hemisphaerica, with Ísolated individuals or years, but can be shorter in sorne species c1umps of Pinus sylvestris or Juniperus like Pistacia lentiscus (7.9- 15.7 months thurifera emerging from shrub cover and a according to DIAMANTOGLOU & therophytic grassland as a background. In MITRAKOS, 198 1). Leaf fall peaks tend to more exposed environments this seems to be advanced in early summer. Leaves are be very dynamic vegetation, because pine rich in structural components (lignine, growth overshadows Juniperus carpets and hemicelluloses) that make them rigid and can suppress them, but pines gerrninate have low nutrient contents. This last only under the carpet protection. condition also means that nutrient MEDITERRANEAN WOODY PLANT PHYSIOGNOMY 341

requirements are low. In Quercus ilex we isomorphic plants use soil water gradually have found accumulation of nutrient by developing roots to deeper soil leveis reserves in branches (ESCARRÉ et al, when surface horizons become dry. This 1987) and these reserves are used to build process can help to control activity rates, new leaves. Sc1erophyllous plants may use thus al lowing the plants to reach the end of wood reserves as a way to deaden the summer with predawn water potentials that effects of environmental fluctuations. In are not too negative : -5 MP has been any case, plant function is usually based on measured in Arbutus unedo (TENHUNEN a conservative nutrient economy. Canopy et al., 1985), less stable than other structure is shaped by light availability sc1erophylls like , acting as a key factor (GRACIA, 1983). whereas in the malacophyllous Rosmarinus Phrygana strategy consists in a marked off icinalis MERINO (1988) measured -7 seasonal heteromorphism, with large leaves MP. Gas exchange can be controlled by a during the wet-season, appearing on high number of stomata in isomorphic dolicoblasts just with the first autumn rains, plants; stomata number in heteromorphic and showing high photosynthetic rates plants is usually lower. The ecophysiology (almost twice the rates of the sc1erophyllous of maquis plants has been studied by leaves of maquis plants). During the spring, authors like LARCHER (1972) and phrygana plants have their maximal growth BRECKLE (1966); recent important rates. Then wet-season leaves are shed, advances in that subject have been reported and they are replaced by drought-season by Lange and co-workers in several papers leaves. Meanwhile, dolicoblasts elongate on Arbutus unedo, Ceratonia siliqua, and lignify. Before leaf fall, there is a Quercus suber, Phyllirea, etc. (LANGE et retranslocation of most leaf nitrogen stocks al., 1982; TENHUNEN et al., 1987). Daily to other plant organs (data on Timbra and seasonal cyc1es c1early show effective capitata, Phlomis fruticosa, Cistus spp. and stomatal control of transpiratory and Sarcopoterium spinosum are given by photosynthetic rates. Nevertheless, MARGARIS, 1981). The morphological considerable differences are found between traits of summer leaves differ from those of species: Arbutus unedo has larger decreases wet-season leaves (palissade parenchyma in both maximal photosynthetic rates and thickness, stomata distribution, etc.) and xylem potential than Quercus coccifera; they are more xeromorphic. Dimorphism this seems to be related to much shallower seems to be controlled by day length. Soft roots in Arbutus (TENHUNEN et al. , leaves can fo ld, which reduces their 1985). Pistacia lentiscus, which has low exposed area in transpiration. Light is not a gas exchange control and short leaf span, major factor for canopy organization. A can be considered as a maquis plant with shallow root system enables these plants to sorne transltlOn characters to the respond faster than maquis plants to early malacophyllous strategy, enabling it to live auturnn rains. in rather xeric environments. ORSHAN (1989) has pointed out that To these two morphologico-functional heteromorphic plants have much larger types, we must add sorne others. One is fluctuations of transpiratory rates during the constituted by pines, with only a few year than isomorphic plants. In fact, species, but dorninant over large areas. Pine isomorphic plants are regulated by deep growth-form is c1early not a specifically water use at the end of surnmer (higher Mediterranean adaptation pattern. In fact, it rates are thus possible in this period); is found in many other climates. Besides, it moreover, the properties of sc1erophyllous does not represent specific adaptations to leaves impose sorne lirnitations on spring any Mediterranean environment because it transpiration. These authors as sume that is found in most conditions. But we should 342 TERRADAS

not forget the success of the pine form in however, they are low on a soil surface Mediterranean countries. Mediterranean basis. AIso photosynthetic rates are high pines have relatively shallow root systems. during periods of leaf growth. But during Nevertheless, can endure long periods, the carbon budget must be rather xeric conditions. In that case, negative, because maintenance costs are morphological changes appear both in the high. Spines are probably an adaptation to canopy form and in leaf size. GINDEL reduce herbivory and maintain positive total (1973) found that leaf length was c10sely carbon budgets. In a Thymo-Siderition dependent on annual rainfall, both in P. community, we have observed Rhamnus halepensis and P. pinea. An interesting case lycioides roots passing through the to be studied is Chamaerops humilis, the petrocalcic layer, whereas chamaephyte only native European palm, which is a dwarf-shrubs had only shallow roots dominant plant in a large variety of maquis, branching within the top 15-30 cm of soil. matorral, "garigue" and thorn-scrub The biomass of thorny shrubs can be formations. It represents an atypical greater underground than aboveground, as successful growth-form in Mediterranean shown by MARTÍN (1984) in Withania environments, with very large fru tescens and Rhamnus lycioides. If sc1erophyllous leaves. However, very compared with other thorny shrubs, scarce data exist on its ecophysiological Rhamnus lycioides has sorne characteristics, characteristics, underground parts and other such as high chlorophyll content, low relevant features. Other morphologico­ nitrogen content and high specific leaf functional types are related to more local density, which are more similar to those of conditions. Let us discuss these conditions sc1erophyIlous plants. This might be related briefly. to the fact that its larger distribution range With increasing water stress and extends further to the north than most other unpredictability of water resources, woody thorn-shrub species. plants can follow different strategies. One In Quercus ilex forests is that of nanophanerophytes and evapotranspiration can amount to about 500 phanerophytes with both long and short mm in the course of a year: by using water shoots. These plants respond to rainfall by budgets in small catchments, 469 mm have producing either leaves from axillary buds been measured at La Castanya (Montseny) or from short shoots dispersed along the by A VILA (1989) and 495 mm at l' Avic branches (SHMIDA & BURGESS, 1988). (Prades) by ESCARRÉ et al. (1984). These leaves, generally small, are produced Under higher rainfall inputs, near quickly after episodic rains because few Montpellier, RAMBAL (1986) calculates, resources are invested in short internodal from a water . re lationships model, a growth, whereas during long wet periods 529-665 mm yr- I evapotranspiration for a long shoots elongate. So, leaf area can Quercus coccifera "garigue". Values can show pronounced changes (sorne plants certainly be reduced along mesic-xeric with these characteristics grow in relatively gradients, but c10sed woody sc1erophyllic dry habitats of temperate areas, such as canopies (forest, maquis, garigues) do not Berberis vulgaris). In extreme cases, seem to be able to develop below 350-400 summer deciduous plants are fo und (for mm of annual water supplies (from rain or instance, Asparagus albus, Withania lateral flow). fru tescens). Individual canopy structure is Below 300 mm of annual rainfall, or very open and leaves are arranged in a even aboye this value on slopes with diffuse way, making convective exchange shallow and eroded soils, and cooling easy. Transpiration rates per nanophanerophytes are replaced by leaf surface unit are relatively high; chamaephytes or hemicryptophytic and MEDITERRANEAN WOODY PLANT PHYSIOGNOMY 343

rhizomatous grasses. Differences between continental gradient, the shift to colder and chamaephytes and grasses have recentIy longer winters comes along with a change been discussed by SHMIDA & BURGESS from mesic to xeric conditions, while the (1988). A high diversity of chamaephytic vegetational change shows analogies with dwarf shrubs exists in our territory. Small the change along the coastal gradient. On microphyllous or nanophyllous leaves are the mountains, the effects of colder largely dominant. Roots are often scarce conditions could be expected to lead to and relatively long; so, they can exploit different morphological types of plants. localized wet sites. Nevertheless, when a Nevertheless, carpet-like forms are also chalk crust exists they cannot usually pass found in extra-Mediterranean climates and through it and deep water resources are xeroacanthic communities are present in unavailable to these plants. An warmer Mediterranean c1imates on the opportunistic strategy is the response to Balearic coast. Pines and junipers dominate unpredictable and scarce water availability, cold oro-Mediterranean climates and either at the individual (leaf production and xeroacanthic cornmunities seem to be more growth bursts) or cornmunity (fast associated with strong wind exposure than population dynamics) level. High with temperature values or fluctuations. maintenance costs and short productive Obviously, there is also a variety of periods, as well as terminal shoot growth, conditions linked to soil differences, and would made chamaephytes vulnerable to we can especially distinguish rocks, sands, strong herbivory. As a result, chemical marshes and saline soils. Sandy, defence and unpalatability are frequent. waterlogged or saline environments sustain Sorne woody plants can exploit more similar vegetation forms under very permanent, local water resources, sueh as different climates, with only a few minor rock crevices or soil under rock protection, adaptations to local conditions. To sorne by developing a system of long roots. This extent, the same is true for rocky permits more conservative strategies of environments, although they are often energy use, thus allowing plants of the isolated refuges with a high level of maquis type, chamaephytes or thorny endemism. Perhaps the only fact worth shrubs to survive under climates drier than mentioning here is the increase in saline expected. mainland habitats along the mesic-xeric Other stress causes besides drought are gradients. present in Mediterranean countries. Both succulent leaves and stems are MITRAKOS (1980) has noted the double mostIy restricted to rocks, saline soils and stress, summer drought and winter cold, to salt-sprayed coastal environments. Sorne which Mediterranean plants are subject. succulent plants from xeric habitats have Winter cold depresses metabolism and can expanded after successful introductions also provoke frost-drought injur y , thus (Agave, Op untia). On gypsic soils we can reducing production, as we have shown for find sorne species with succulent leaves Quercus ilex along an altitudinal gradient (i.e. Helianthemum squamatum, Ononis (SA VÉ et al., 1986). Further inland or at tridentata). The thorny shrub Lycium higher altitudes, the Mediterranean flora intricatum also has succulent leaves. Only becomes clearly impoverished in our one species, the rhizomatous herb territory, as jndicated before. The Caralluma europaea, can be considered a vegetative period can be reduced either by spontaneous stem succulent linked to xeric increasing summer duration along the conditions, but it has a very restricted coastal gradient or by colder and longer distribution in the southern end of the winters as one proceeds into the continent territory. No desert succulent formations or up onto the mountains. Along the exist directly related to increasing aridity. 344 TERRADAS

The xeroacanthic cushion-like growth­ but all the xeroacanthic Mediterranean form needs perhaps more comment. A cushions have a very c10sed and spiny general characteristic of this type of plants canopy, which gives a characteristic is the fact that they undergo not only the physiognomy to their formations. Although seasonal double stress, very marked in cushions can be merely morphogenic mountain plants, but also a continuous loss structures, this is not always the case. due to sprout mortality by wind mechanical Sometimes this morphology has a genetic effects or other associated physiological basis (BRAUN-BLANQUET, 1962). We factors. have tried to distinguish these two different So, this form is a result of heavy ongms in sorne cushion-like Balearic exploitation by the physical environment, coastal plants (TERRADAS et al., 1989). which adds to herbivorism, making it So, branching angles ranging from 10° to difficult to sustain a positive carbon budget. 15° in cushion shrubs are assumed to Spines, as well as very c10sed canopies, depend on genetic determinism, whereas reduce losses due to herbivory. Individual branching angles ranging from 45° to 90°, canopies have an extreme monolayer leaf or even more, are found in morphogenic arrangement: leaves are densely packed in a cushions (M. Riba, pers. comm.). 0.5-2 cm thick layer. Malacophyllous leaves are common, with sorne transition forms to sc1erophylly, in true cushion-like GROWTH-FORMS AND ENERGY plants. In coastal habitats under salt spray USE STRATEGIES influence, succulent leaves sometimes occur. So, leaf overheating would be SHMIDA & BURGESS (1988) expected under high irradiance, due to low recognize different strategies of desert convective cooling, except under strong plants using a two axis space. The first axis wind regimes that cause efficient eddy is oriented from poor to rich resources, transfers. Another factor to be taken into while the second axis goes from episodic to account with these plants is their nutrient stable resources. This seems to us a useful cycling. approach. Along a mesic-xeric gradient, Nutrient los ses by both litter wind rich resource availability becomes more carrying and soil erosion are very high, but episodic, then unreliable, whereas reliable the c10sed structure of these plants tends to resources beco me 10wer in concentration or minimize them. For instance, under summit quality. Near the mesic end of our cushions in the Aytana Sierra we have gradients, most dominant plants use 2 measured litter stocks of 0. 125 g cm- , a relatively (for this area) stable and rich quantity similar to that found in developed resources in a competltlve strategy forests with much larger aboveground (GRIME, 1979). Maquis-type isomorphic biomass. An external but growth-form plants in mature cornmunities are K controlled nutrient reserve is thus obtained. strategists, with slow energy use. Pioneer We have measured underground biomass in stages in disturbed sites can follow r sorne mountain and coastal cushion-like strategies. When approaching the xeric end Balearic plants. Astragalus balea rica has of the gradient, resource patchiness slightly more than 20 % of its total biomass increases over time and space. As a result, under ground and this rate is 26 % in K and r strategists (or competitive, ruderal Launaea cervicornis individuals; these are and stress resistants if Grime's not high values, if compared with many c1assification is preferred), find woody plants from arid zones. opportunities, and r-strategists are Cushion forms are often found on eventually more favoured. Resource mountains and coasts under other c1imates, availability fluctuations have effects similar MEDITERRAN EAN WOODY PLANT PHYSIOGNOMY 345

to disturbance, promoting high energy environment. Photosynthetic rates have not strategies (in the sense of SHMIDA & been measured, but they are likely to be BURGESS, 1988): short active periods relatively high to balance losses and long with high production per time of activity. inactive periods. Growth rate can be higher Transpiration and photosynthetic rates can than expected from poor cover, after be high, but leaf area is low and variable. observations on Centaurea balearica For instance, Rhamnus lycioides leaves colonizing disturbed sites on the coast of have on average much larger transpiration the island of Minorca. On the same, rates and water content changes than Anthyllis hermanniae and Launaea Quercus coccifera, Pinus halepensis or cervicornis are found on disturbed sites, Juniperus thu rife ra. The leaves, however, being replaced by Erica multiflora, have a diffuse arrangement and small Phillyrea media varo rodriguesii, Pistacia coverage, and leaf area can decrease lentiscus and Pinus halepensis scrubs and during drought periods (TERRADAS, woodlands in the succession to more 1973). So, Rhamnus lycioides has a higher mature stages. energy strategy than Quercus coccife ra and First growth is probably fast in cushions, is adapted to fast responses to rich episodic but it must slow down and take pl ace as resources, whereas Q. coccifera relies short bursts after a certain size (ruled by more on continuous use of poorer but stable local wind conditions) is reached. Studies resources. in population dynamics could also be very All along the gradients, man's use of the useful in order to understand fu lly the landscape can promote pioneer and less energy strategy of these plants. mature communities. As a result, we can When considering energy use, different expect r-strategists to increase in levels must be taken into account. importance. B ut other associated changes Individual survival is important to take place as well, thus reducing plant phanerophytes and nanophanerophytes, cover and modifying soil conditions. This because construction costs are high, but can open spaces to species adapted to more investment in structure assures either aerial xeric environments, and benefit the or subterranean space control. But certain northwards advance of southern xerophytic parts of the plants, such as leaves or fine r-strategists. A good example of this might roots, can be used in a way which is more be ¡nula viscosa. Original habitats of this or less economical in terms of energy. A Asteraceae deciduous shrub are the certain degree of opportunism is always south-Mediterranean "ramblas" (dry bed present. In an adult tree canopy, leaf watercourses), an environment under a high morphology, leaf size, leaf behaviour and disturbance regime by episodic waterflows. leaf span change along a vertical axis. We A ruderal strategist, this plant has expanded can consider woody plants as complex its area to the north, colonizing old fi elds systems or populations of organs inc1uding and waste lands. During the earlier years hierarchically organized structures, sorne of after field abandonment, it behaves like a them with high turnover rates protecting the chamaephyte, but as soil becomes others from external fluctuations or compacted it shifts to a hemicryptophytic exploiting episodic resources. Under mode (SORIA, 1980). appropriate conditions, Quercus species can True xeroacanthic cushion-like plants have more than one shoot growth periodo use stable and poor resources, with a high The very high capacity of resprouting and control of the external steps of nutrient increasing production rates after cyc1es. But they cannot easily be c1assified disturbance in Q. coccifera and other as K-strategists, because they are under K-strategists (as a result of use of heavy exploitation by the physical internalized resource stocks) allows them to 346 TERRADAS

conserve space control and dominance, in photosynthetic organs and show a higher succeeding each other as if there was a shift tumover at population levels. But in all in energy use strategy within the same kinds of plants, when large resources by genetical individuals. Leaves of young leaf area unit are either available in the resprouts show morphological and environment or are mobilized as a result of physiological differences from adult normal disturbance, a pattem of high energy is leaves (PERY et al., 1989): higher Chl developed. Relatively stable forest as well a/Chl b, transpiration rates, and osrnotic as maquis, no matter how rich they are in potential, lower specific weight, cuticle and resources, usually show closed canopies leaf thickness, proline and starch grain and low resource availability by leaf unit; content. In fact, resprout leaves have many thus, they behave in a low energy manner. more available resources than adult normal However, in transient conditions after leaves because they can use stocks. canopy rernoval due to disturbance, large Besides, the rate between leaf area and fine resource stocks are rnobilized and root root biornass is much higher in resprouts. systems are always present. So, new lea ves So, in the same individual low energy use have much higher resource availability by is dominant, but periods of high energy use leaf unit and they behave in a high energy occur seasonally or as a result of manner. Other less stable cornmunities limit disturbances, when high quantItIes of their activity to episodic periods of high resources are freely available. In phrygana resource availability, and always have open and thomy shrub types, leaves conserve and always maintain the high energy pattem. Woody structure is also maintained, but A) abo ve 350-400 mm leaf "populations" can fluctuate greatly, as Stable resources • Closed canopies¡ can individual leaf area (by folding). canopy removal lea! area is maximized in Moreover, thomy shrubs have a similar leaf transient low lea! area relation to available resources strategy but higher investrnent in woody related to available resources parts: they use deeper soil resources and t have longer individual life than low energy way phrygana-type plants or dwarf-shrubs. In canopy reconstruction very poor dry sites, as well as in heavily B) exploited and fluctuating environments, site Episodic resources • Open canopies conservation can beco me less important or not feasible, and individual tumover large available�'" resources available resources increase (steppe chamaephytes, under some threshold • , therophytes), giving a classical r-strategy lea! area and/or population bursts lea! area decrease or gradually adapted to the use of more mortality increase episodic energy pulses. high energy• way To sum up, sornepla nts tend to conserve � space control by means of large FIGURE 3. Two main ways of energy use are present investments in woody structures (which along our mesic-xeric gradients. ScJerophyIlous forest and maquis plants use a low energy strategy: they means a long individual life). We found a have low nutrient requirements, maintain long shift in these plants from slow gradual to continuous periods of activity, and show sorne fast pulsed changes both in leaf area and regulation due both to their internal stocks and their good stomatal control. Other plants, such as leaf activity as a response to increasingly maIlacophyIlous phrygana and sorne thorn-scrub episodic and unpredictable resource plants, have episodic pulses of high energy use due to availability in the environment. their high dependence on external patched reserves; they show high nutrient requirements, discontinuous Other plants sacrifice space control and growth bursts and regulation of gas exchanges by leaf long individual life, invest relatively more area changes_ MEDITERRANEAN WOODY PLANT PHYSIOGNOMY 347

canopies working in a pulsed high energy biomass is almost certainly between 50 and l manner (Fig. 3). 80 t ha- in most areas. RAPP (1978) has l measured 151 t ha- near Montpellier for the same species. Under much wetter 1 BIOMASS AND PRODUCTION conditions, 146 t ha - was found in a Pinus pinea forest studied by CABANETTES & There are few data on biomass and RAPP (1978) In southem France. production for the area considered, except Aboveground biomass in most Rosmarino­ for forests. A number of evaluations have Ericion and Cistion matorral cornmunities l been made in the last few years, mostly is less than 25 t ha- . Thymo-Siderition unpublished, on different types of natural dwarf shrub formations are elearly under 10 1 l cornmunities. They allow us a general t ha- (we have measured 4.3 t ha- in such overVlew. a community near Alicante; see also As far as broadleaved forests are FISHER et al., 1987), with underground concemed, accurate studies on Montseny biomass lower than aboveground biomass; and Prades holm-oak forests have been similar low values are found in most carried out. Aboveground biomass of a high Salsolo-Peganion communities. There are quality 60-90 years old stand from La no evaluations of thom-scrub community Castanya (Montseny) is 165 t ha-l (dry biomass in southem Spain, and in fact it is weight) for trees and 4.7 for understory, difficult to find well preserved l while root biomass is 65 t ha- . At Prades, representative formations. Isolated thomy a lower and denser holm-oak coppice has shrub individuals usually appear In l 100 t ha- aerial tree biomass and a 15 t dwarf-shrubs cornmunities. 1 ha- understory (ESCARRÉ et al., 1984). Xeroacanthic formations usually have Aboveground biomass values from 40 to less than 30% plant cover and I 270 t ha- have been measured in different corresponding low biomass: we have 1 holm-oak forests in the Mediterranean measured 1 t ha- with 15-20 % cover in region, and these values probably give us a Launaeetum cervicornis from the Balearic range estimation for this type of forest in coastal (much higher values can be our territory. Values for cork-oak forests expected in Aro-Phillyreetum communities, are probably a little lower, because these but these are constituted by morphogenic forests usually have more open canopies. cushions of maquis species); in the Arbutus unedo and Erica arborea maquis Hypericion balearici from the Balearic or heaths lie somewhere between 10 and 60 mountains, with a 60% cover we have 1 I t ha- , and Quercus coccifera "garigue" in found 4.2-4.8 t ha- biomass; on the summit l the 10-50 t ha- range, probably with a of Aytana sierra, cover, is 10-15 % and lower average than maquis. biomass is 3.3 t ha-l . Oleo-Ceratonion mature maquis are A vailable data on primary production are hardly found as a continuous cover, and very scarce. Moreover, spatial and temporal there are no good estimates of their variations can be very large. Whereas in the biomass. A Balearic community with Olea high quality Montseny holm-oak stand I europaea and Pistada lentiscus in patches production reaches a noticeable 9.7 t ha- l covering 40 % of the soil surface has a y- , similar to the values fo und for most l biomass of only 9 t ha- . Mediterranean mid-European forests, many mature holm­ l I pine forests and woodlands inelude very oak forests do not exceed 4-5 t ha- y{ (3 diverse communities, often rather open. A of them being leaves). Pine forests can Pinus halepensis woodland at Sierra show higher figures: the Sierra Espunya l Espunya gave 61 t ha- of aboveground forest, in the south of this area, reaches l biomass. Average P. halepensis woodland 8-9.5 t ha- yr- 1 . Obviously, there is a 348 TERRADAS

marked north-south decreasing gradient of chamaephyte steppes, whereas the rate of forest production associated with the photosynthetic organ production to total climatic gradient. GRACIA (in aboveground production increases. In TERRADAS el al., 1989) gives a range of general, increasing aridity implies more stem wood production between 12.2 and energy being invested in belowground and 1 1 0.64 t ha- y{ (provincial averages for any photosynthetic parts, as well as higher costs kind of forest, evergreen oaks excluded), of maintenance. following the same decreasing pattern. Biomass and production are not simple In maquis the above round production is responses to rainfall gradients. Man has l usually below 4 t ha-1f y{ , even though exploited the Iberian Peninsula resources during the first year after disturbance (fire, for thousands of years. As a result, we for instance) it can be higher. In Quercus cannot know to what degree soil 1 I coccife ra "garigue" we find 2-3 t ha- yr- degradation and nutrient los ses have been one year after fire and 0.5-1 .25 in most increased and water-holding capacity has other cases. Higher productions can be decreased by overgrazing, fire and found in old field scrub of Inula viscosa agriculture. A consequence of man's I 1 (SORIA, 1984), where 5-6 t ha- yr- has exploitation of the land could be a been measured in the early years after fi eld northwards shift of plant communities culture abandonment, but these values adapted to more xeric environments, decline rapidly. Rosmarinus matorral and especially along the coastal gradient. dwarf shrub communities are probably 1 l below 1 t ha- y{ , and the same must be true for xeroacanthic communities, but we AKNOWLEDGEMENTS lack direct measurements. The patterns of change in productivity Most data for this study result from along mesic-xeric gradients remain obscure projects funded by Fundació Enciclopedia because belowground productions are Catalana and CICYT. Many colleagues and unknown. Leaf production decreases clearly students of my biogeography courses have I 1 from a maximum around 3 t ha- yr- in contributed to their collection. F. Roda and broadleaved, pine forests and tall shrub A. Escarré have made helpful comments on forrnations with complete soil cover to the manuscript.

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