Plant formations on ultramafic rocks in New Caledonia

ABSTRACT New Caledonia is known for the diversity of its geological substrates, which have shaped its highly original and diverse flora. Here, the effect of the soil on the vegetation is described for several contact zones between ultramafic and other substrates. The main vegetation formations on soils derived from ultramafic rocks are described: low and medium altitude rainforests, high altitude rainforests, and maquis. The main types of maquis and the biological characteristics of maquis species are also presented.


Introduction
The New Caledonian archipelago lies in the South West Pacific, between 20S and 22S latitude and 164E and 167E longitude. It includes a main island (Grande Terre) approximately 500 km and 50 km wide, and a number of other islands including the Loyalty Islands and isle of Pines. According to Takhatjan (1969), New Caledonia represents a floristic domain, "the New Caledonian subkingdom", one of five units within the Paleotropical realm. The uniqueness and richness of the New Caledonian flora has struck every botanists who visited the territory.
About a third of the main island, a portion of the isle of Pines, and most of the Belep islands, are covered with ultramafic rocks (c. 5500 km 2 ). They contain the principal mineral resources of the territory: mostly nickel ores, but manganese, cobalt and chromium have also been sporadically exploited. The extraction of these metals is made in open cast mines and implies a destruction of the plant cover. The regrowth of the vegetation is very slow (Jaffré et al. 1977).
In his paper describing the history of New Caledonian botany, MacKee (1966) stated that the history of formal botany of New Caledonia started with the work of Johann & Georg Forster, Cook's companions, who were in 1774 the first to make botanical specimens in this region. They were followed in 1794 by La Billardière who wrote the first major document entirely dedicated to the New Caledonian flora (Labillardière 1824). Then came Montrouzier, who stayed for almost half a century in New Caledonia and wrote a flora of the Belep islands (Montrouzier 1860), Pancher and Balansa who, from 1860 to 1880 collected for the Muséum National d'Histoire Naturelle (Balansa 1872), Schlechter and Däniker published annotated checklists of their collections in New Caledonia (Schlechter 1906(Schlechter , 1908Däniker 1932). The many specimens collected were studied in Paris' Museum from 1860 by Baillon, Brongniart and Gris, then by Guillaumin, who ventured into the writing of a comprehensive flora of New Caledonia published in 1948.
The second phase in our knowledge of New Caledonian botany started with Virot's book « La végétation canaque » (Virot 1956), which was the major ecological study of New Caledonia, Sarlin's book « Bois et Forêts de la Nouvelle-Calédonie » (Sarlin 1954), the many taxonomic contributions of Guillaumin, and then the work by Schmid. They gave a more precise picture of the New Caledonian botany, while questioning the causes of the uniqueness and richness of this flora The occurrence of special edaphic conditions derived from ultramafic rocks probably played a significant role in the differentiation of the New Caledonia flora (Schmid 1978). Therefore, detailed studies of the vegetation in these particular environments seem necessary to understand the link between soil and vegetation, and to understand the requirement and tolerance of the species that form these ecosystems. commonly observed elsewhere, as Krause (1958) indicated in a synthesis of serpentinites throughout the world, and later Whittaker (1954Whittaker ( , 1960 and Kruckeberg (1969aKruckeberg ( , 1969b for the USA, Spence (1959Spence ( , 1970, Proctor and Woodell (1971) for Great Britain, Lyon et al. (1971) for New Zealand, Duvigneaud (1966) for France, Pinto da Silva (1970) for Portugal, and Wild (1965Wild ( , 1970 for Zimbabwe; here, the plant formations of ultramafic rocks are not necessarily lower, more stunted or sparser than those occupying different geological substrates in their vicinity.
Contact zones are generally found at relatively low elevations where forests are poorly represented: -In most cases, the ultramafic rocks, and more precisely the serpentinites, are in contact, at the base of the mountain massifs, with basalts. The latter harbor grassy savannas or woody savannas which, on ultramafic rocks, give way to a more or less dense sclerophyllous shrubby formation, or maquis. At the serpentinite-basalt contact, the change of vegetation takes place abruptly, without transition. A radical transformation of the flora accompanies this physiognomic change; this is the case at the Nekoro Pass, at the base of the Boulinda Massif ( Figure 1). The changes in vegetation and flora coincide with an important modification of the chemical composition of the soil in close relation to the nature of the geological substrates. The degradation of the plant cover can explain the presence of a lower formation on basalts due to fires, which are facilitated by a well-developed grassy layer, thus preventing any evolution towards a shrub or tree formation. In contrast, on serpentinites, the absence of a continuous herbaceous layer generally prevents the progression of fires, except during exceptionally dry periods when sufficiently dense shrubby maquis can burn.
-Where ultramafic rocks are in contact with siliceous rocks (Figure 2), as is the case for the isolated serpentinite veins in the northeastern part of Grande Terre, there is an interruption of the niaouli savanna (Melaleuca quinquenervia) or of the very open maquis if the underlying soil is acidic and eroded. This is usually to the benefit of a dense maquis (typical vegetation on typical serpentinite soils) or of a short savanna dotted with a few groves of magnesicolous shrubs, Casuarina collina, Xanthostemon spp. (a typical vegetation on serpentinite soils that have generally received allochthonous inputs). As in the previous case, the savanna formations regularly burn, preventing any evolution towards taller and more closed formations. The maquis, on the contrary, both on siliceous rocks and serpentinites, burns less frequently. Generally, the maquis on serpentinites are higher and bushier than the maquis on siliceous rocks, but the serpentinite sectors of the north of the territory are less eroded and less dry than the sectors occupied by the maquis on siliceous rocks.
-In the south of Grande Terre, contacts of the peridotites with the gabbros or granodiorites ( Figure 3) are hardly noticeable in the vegetation cover, except in the lowlands on mixed hydromorphic soils, where niaouli becomes dominant. However, on gabbros and granodiorites, a close examination of the vegetation reveals the presence of a lot of hydrophytic species (Gahnia sieberiana, Grevillea gillivrayi, Tetraria comosa, Schoenus brevifolius), which, on peridotites, are found in lower topographic situations. The more clayey soil on gabbros seems to create conditions of hydromorphy, which influence on the vegetation appears more significant than the chemical nature of the geological substrates. Indeed, in these contact zones, the vegetation does not always clearly reflect the chemical composition of the upper horizons of the soil.
-If the contact between ultramafic rocks and another geological substrate is located in a forested area, the physiognomy and composition of the vegetation do not vary dramatically, and only a detailed study of the flora could identify the boundary.
In conclusion, it appears that the differences in vegetation and flora between the ultramafic and the nonultramafic domains are always present but sometimes subtle. The changes in vegetation are remarkable at the base of the ultramafic massifs, where we find mainly Magnesic Cambisols associated with Magnesic Leptosols and, in flat areas, with Magnesic Vertisols. They are more difficult to detect in small nonultramafic enclaves within the peridotites, the two types of substrates often concealed by a relatively thick and uniform cover of colluvium resulting from the dismantling of the initial Ferralsols (south of the territory). They are also more difficult to detect in forested areas. Mineral nutrition of plants in contact zones are described in Jaffré (2023a).

Inventory of plant formations on ultramafic substrates
The vegetation of New Caledonia has been mapped at a scale of 1:1,000,000 (Morat et al. 1981), and the soils have been characterised and described on the Boulinda Massif (Jaffré and Latham 1974;Latham 1975aLatham , 1975b. Not all plant formations represented in New Caledonia are found on ultramafic rocks. Savannas are practically excluded as well as secondary thickets. The maquis however, is very diversified and the rainforests are usually represented by low and medium altitude forests and by high altitude forests. The forests on ultramafic rocks, as a whole, do not significantly differ physiognomically from New Caledonian forests in general. However, they present some particular communities (forests with Arillastrum gummiferum ("chêne gomme"), forests with lichens and Hymenophyllaceae, forests with Nothofagus, forests with Araucaria, forests with Agathis ovata), which are characteristic of the forest stands on mining sites. At the base of some massifs, the tall, closed-canopy maquis, have a physiognomic resemblance with certain formations of dry forest, but they remain floristically very close to the maquis. Similarly, the swampy vegetation of the south of the island, whose flora includes mainly floristic elements of the maquis, can be considered as swamp maquis or wetland maquis-like formations.

Lowland and medium-altitude rainforests
Lowland and medium-altitude rainforests are found on all the ultramafic rock massifs where they are most often located at altitudes between 500 and 1000 m, in areas receiving between 1500 and 3500 mm of rain per year. On the eastern slopes, which receive more rainfall, they generally extend further down, but below 500 m, they rarely cover entire slopes, remaining localised in a few talwegs and along watercourses. Typically, they occupy relatively humid sites where they have been sheltered from fires.
These forests ( Figure 4A) most commonly occur on steep slopes with eroded Ferritic Ferralsols and Leptosols, sometimes covered by scree. They occur less frequently on Magnesic Cambisols and Leptosols or on deep Ferritic Ferralsols (more than 10 m thick). This is partly because Magnesic Cambisols and Leptosols are generally found at altitudes below the limit of rainforests and because deep Ferralsols occupy subhorizontal areas that were prime sites for nickel ore exploration and where vegetation was therefore often destroyed by fire and mining. This could also be because soils with high stoniness are generally more favourable to a forest.
These forests, like all the forests of New Caledonia, are not very high. The canopy is generally between 15 and 25 m. It is commonly ovetopped by gymnosperms: Agathis lanceolata in the Southern Massif and in the Boulinda Massif, and various Araucaria (A. montana, A. subulata, A. biramulata, A. bernieri, A. laubenfelsii) on all the mining massifs. These forests are pretty dense. The very discontinuous herbaceous layer is composed mainly of ferns (Lindsaea, Schizaea, Nephrolepsis, Adiantum, Asplenium) and orchids (Calanthe, Sarcochilus). Poaceae (Oplismenus) and Cyperaceae (Carex) are relatively rare. The shrubby undergrowth often includes many palms, species of the genera Pandanus and Psychotria, and many species with a monocaulous habit (Araliaceae, Euphorbiaceae, Acropogon, Tapeinosperma) often with very large leaves (Listea ripidion, Meryta, Didymochiton, Symplocos, Ficus). The lianas and hemiepiphytes are not very abundant (Freycinetia especially, Lamiaceae, Apocynaceae).
The floristic composition of these forests varies according to the nature of the soil, the altitude and the geographical situation. Several species occur in a particular massif, notably in the great massif of the South. Among the most common species are Agathis lanceolata, Araucaria spp., Calophyllum caledonicum, Archidendropsis granulosa, Montrouziera cauliflora, various Cryptocarya, Kermadecia, Planchonella, Pycnandra, Sloanea and Syzygium. Many of these large trees, Montrouziera, Calophyllum, Archidendropsis and Kermadecia are not specific to the ultramafic domain.
Some species, by their abundance (Arillastrum gummiferum, Agathis ovata), by their ability to form monospecific stands (Nothofagus) or by their particular habit (Araucaria), make some formation distinctive, and are representative of forests on ultramafic soils.
Arillastrum forests have been largely destroyed by fire and logging; only isolated and often degraded patches remain today. This forest must have once occupied a large part of the south of the island, as is evident from many white trunks of dead trees that dominate some postfire maquis with Gymnostoma deplancheanum on indurated Ferritic Ferralsols or with Cyperaceae and Pteridium esculentum on eroded Ferralsols. A few individuals have been able to escape fire here and there.

Agathis ovata formation
This community only occurs in the south of the island, covering small areas in patches. It appears on flats situated above the slopes, between 500 and 900 m of altitude, rarely lower, on gravelly or indurated Ferritic Ferralsol, often covered by typical rainforests. It is a low forest with a tree layer made up mainly of Agathis ovata, a small, stocky tree with an umbelliform habit that hardly exceeds 15 to 20 m in height. The variously dense shrub layer, between 8 and 15 m high, includes heliophilous species (Gymnostoma deplancheanum, Dacrydium araucarioides), and hemisciaphilous or sciaphilous palms and Pandanus. Epiphytes (orchids, ferns and lycophytes) are well represented; lianas are few.
Although they never had the importance of the Arillastrum forests, these forests must have had a more significant extension in the south of the island. They probably occupied the areas above 500 m left free by Arillastrum, a more thermophilic species. Currently, the forest stands with Agathis ovata are less extensive than the open stands with Agathis ovata dominating the postfire maquis.

Nothofagus formation
The species of Nothofagus found in New Caledonia are all found in ultramafic areas, and most do not deviate from this. These species form monospecific groups occupying the bottoms of talwegs at altitudes generally higher than 650 m, but in the more humid Southern Massif, the stands go down to 200 m. Nothofagus stands are often embedded in "normal" forest. The bluish-grey colour of the foliage stands out, and the monospecificity of the tree layer differentiate them from the rest of the forest.

Araucaria formation
Araucaria is ubiquitous in the New Caledonian vegetation (14 species): they are found in both forest and maquis and play a predominant role on ultramafic rocks. Except for three species, A columnaris, A. schmidii and A. montana, all New Caledonian Araucaria are almost restricted to the ultramafic domain. Several species are primarily maquis species (A. goroensis, A. rulei, A. montana, A. bernieri). Still, all of them, without exception, can be found in forests, and some (A. biramulata, A. laubenfelsii, A. subulata) are primarily forest species.
Araucarias are often scattered throughout the forest, which is a very classical type (e.g. the Rivière Bleue forest in the south). Sometimes, however, a high concentration of Araucaria, generally monospecific, is found on ridges or steep slopes, where the forests are relatively low, creating a very particular formation: the undergrowth becomes more luminous and hemisciophilous species appear. There are many intermediate communities between these Araucaria forests and the maquis dominated by the same species. They include stages of regressive evolution resulting from the effect of repeated fires, or stages of progressive evolution towards taller and denser maquis in the absence of fire.

High-altitude rainforests
Forests at high altitudes ( Figure 4B) are most commonly found above 1000 m on eroded and highly desatured Ferritic Ferralsols. Climatically, they occupy areas swept by clouds, receiving rainfall exceeding 3500 mm per year, subject to fairly wide temperature variations and, in the cool season, to low temperatures with minima very close to 0°C.
These are low forests (8 to 15 m) formed by shrubs with twisted trunks covered with numerous epiphytes (ferns, lycophytes, mosses, orchids). Many species have relatively small and sclerophyllous leaves (Metrosideros, Xylosma, Cunonia and all gymnosperms) or hairy leaves (Hibbertia baudouinii, Apiopetalum velutinum). The flora is diverse and original: gymnosperms are numerous and abundant (Acmopyle pancheri, Callitris neocaledonica, Dacrydium lycopodioides, Retrophyllum comptonii) as well as representatives of endemic families (Phelline) and ancient lineages (Ascarina, Nemuaron, Zygogynum). In the south of the island, particularly in the Humboldt region, these forests are often dominated by numerous Araucaria humboldtensis, a small and strictly montane tree.

Lichens, bryophytes and Hymenophyllaceae formation
The intensification of some characteristics of this formation creates an original community: the forest with lichens, bryophytes and Hymenophyllaceae. It is a low forest, not exceeding 6 to 10 m in height, whose upper layer is mainly composed of Metrosideros brevistylis (Myrtaceae). The seed plant flora is impoverished in favour of a very varied cryptogamic flora, the trees and the ground being covered with Hymenophyllaceae, bryophytes and lichens. The lower shrub layer consists of a small number of often bushy and sclerophyllous species (Cunonia pulchella, Pterophylla dichotoma, Quintinia media, Dracophyllum verticillatum). The hemiepiphytes of the genus Freycinetia (Pandanaceae) are very abundant and contribute, with the tangled stilt roots of Metrosideros and the large number of epiphytes ferns, orchids, and Astelia neocaledonica, in making the undergrowth look dense and inextricable. The soil in these forests is an humic accumulation soil or ranker made up of a single, thick (greater than 1 m) and spongy horizon of organic matter resting directly on a lightly weathered bedrock (Latham 1975a).
The conditions that lead to the installation of this forest are still poorly understood. However, the geological sublayer, which influences the nature of the soil, could play a significant role. Indeed, the forest with bryophyte lichens and Hymenophyllaceae is not found, at least in its typical form, outside the mining massifs. The microclimatic conditions (stagnation of cloud masses) can also be considered together with the particular biological conditions created by the abundance of the gregarious species Metrosideros brevistylis. The tangled stilt roots of this tree, between which organic matter accumulates, constitute a favourable environment for the development of epiphytes and semi-epiphytes. It is also possible that its leaves, rich in essential oils, like those of many Myrtaceae, lead to the formation of unique humus, with a strong selective effect on the flora.

The maquis
The maquis occupies 60 to 90% of the ultramafic terrain, extending from sea level to the highest peaks of the ultramafic massifs (1600 m). It thus accommodates very variable rainfall conditions, ranging from less than 900 mm of rain per year at the base of the Taom Massif to more than 4 m on several summits of the Southern Massif. It is an evergreen sclerophyllous formation with bushy or ligno-herbaceous vegetation and a dense cyperaceous layer, forming an assemblage of great physiognomic and structural variety and numerous transitional forms with the forest.
The term maquis, applied to all non-forest formations on ultramafic rocks, is of local use and results from its resemblance to the Mediterranean maquis and garrigue in France, macchia in Italy and Corsica, matorral in Spain, xerovuni in Greece, and which are also comparable to the Californian chaparral, the espinal of Chile, the fynbos of the Cape region, and the mallee broombush of South Australia. However, whereas these latter formations have both a physiognomic and bioclimatic homology with the typical Mediterranean maquis (as noted by Schnell (1977) for the fynbos and by Specht (1969) for the mallee broombush), the similarity with the New Caledonian maquis is purely physiognomic and, in some cases, appears to be very loose. The term maquis is also used in New Caledonia to designate the low shrubby to bushy plant formations on siliceous soils in the north of the island. In the UNESCO (1973) international vegetation classification, the Caledonian maquis are characterised by the evergreen Fruticeae and the evergreen bushes or thickets with sclerophyllous leaves.

The different types of maquis
There are three main maquis types in mining areas: -The shrubby maquis ( Figure 4C) is a thicket of variable density with a sparse cyperaceous layer, consisting mainly of low Cyperaceae (Fimbristylis, Scleria) and a shrubby layer consisting of branching nano and micro-phanerophytes. It is found at the base of the massifs on eroded Magnesic Cambisols close to Magnesic Leptosols.
-The bushy maquis ( Figure 4D) is a very bushy thicket with practically no herbaceous layer and a shrub layer made up of groups of highly branched shrubs. It develops on gravelly or indurated Ferritic Ferralsols plateaus from 200 m of altitude.
-The ligno-herbaceous maquis ( Figure 4E) is characterised by a highly developed cyperaceous herbaceous layer of large Cyperaceae (Chamaedendron, Lepidosperma, Schoenus, Tetraria) and a shrubby layer that is variously bushy and discontinuous. It grows on slopes or piedmont situations at various altitudes on Ferritic Ferralsols truncated by erosion or modified by colluvial inputs. The wetland maquis-like formations of the south of the island ( Figure 4F), developing on hydromorphic colluvial and alluvial soils, can be linked to this type of maquis.

Maquis variations and evolution
The numerous maquis physiognomic and structural variations are often linked to edaphic and altitudinal conditions. Some of these variations result in the presence of particular species: gregarious species (case of maquis with Gymnostoma, Acacia spirorbis, Tristaniopsis guillainii), or arborescent species (case of maquis dominated by a loose layer of Araucaria or Agathis ovata). Others are characterised by changes in the height of the shrub layer or the density of shrub or herbaceous layers. All these variations make it possible to distinguish for each type of maquis (shrubby, bushy, ligno-herbaceous) a series of intermediate stages between practically bare soil and forest, without, however, in many cases, allowing to predict their evolution (regression, stability, or succession).
The pioneer vegetation groups that re-establish after fires are generally characterised by a very open structure, revealing large patches of bare soil vulnerable to erosion. On desaturated Ferritic Ferralsol, there may also be an invasion by the bracken fern, Pteridium esculentum, resulting in a moorland-like formation. Any destruction of the maquis by fire, whether partial or almost total, even repeated, does not lead to its replacement by secondary vegetation of a completely different type. The vegetation that reappears is always at least related to the previous one, if not identical.
Fires certainly largely explain the extent and current physiognomic configuration of the maquis on ultramafic rocks. Indeed, secondary maquis is most often found after the destruction by fire of preexisting maquis or forests.
In contrast to the pioneer maquis, there are taller and more closed maquis which correspond to different successional stages from maquis to forest. However, certain tall and closed maquis hardly evolve on human time scale, at least in the current climatic conditions and thus constitute fixed stages which can be qualified as "maquis paraforestier".

Biological characteristics of the maquis
If the maquis on ultramafic rocks is deprived of a proper structural and physiognomic identity, biological and floristic characteristics contribute to its unity. The floristic attributes are studied in Jaffré (2023b). Here, we examine the different biological forms represented and the characteristics of the foliage, the root systems and the development of the species.

The biological forms in the maquis
To classify the species, we used the major subdivisions of Raunkier, which have already been applied to the vegetation of New Caledonia by Virot (1956). The application of this classification to the maquis species of a mining massif, the Koniambo Massif, of which we made a detailed floristic inventory , resulted in the following count: 79 % of phanerophytes mainly including nano and microphanerophytes with a maximum of species between 30 cm and 2.50 m high, 8 % of hemicryptophytes mainly represented by Cyperaceae, 6.50 % of mainly woody chamaephytes, 6.50 % of geophytes, especially ferns, and less than 1 % of therophytes mainly represented by Paramollugo digyna. The predominance of phanerophytes contradicts the results of several authors, such as Proctor and Woodell (1975) for serpentine outcrops in other regions of the world, showing a predominance of hemicryptophytes (Table 1). However, this comparison was for serpentine vegetation in temperate zones where phanerophytes are not as abundant as in tropical zones. Phanerophytes are very numerous in the maquis flora; but are sometimes dwarf form (nano and microphanerophytes) of species, which, in better conditions of fertility and humidity, can reach 10 to 15 m

Foliage characteristics
The vast majority of the maquis species have sclerophyllous leaves with a coriaceous consistency ( Figure 5A) a varnished appearance and a thick cuticle, which justifies the name of "sclerophyllous maquis" often used to designate these formations. The tiny leaves or leptophylls (blade surface less than 25 mm 2 ) are not very frequent ( Figure 5B) They are found in several Myrtaceae (Myrtastrum rufopunctatum, Metrosideros tetrasticha, Cloezia aquarum, three species of Sannantha), in two Ericaceae (Styphelia floribunda and Cyathopsis albicans), and one Loganiaceae (Geniostoma imbricatum). Most species have small leaves that can be classified between nanophylls and microphylls (leaf blade area approximately between 25 and 2000 mm 2 ); many have hairy leaves. The species with narrow leaves (stenophyllous) are well represented. Many shrubs have leaves with oil glands (Myrtaceae, Rutaceae). Generally speaking, the foliage is sparse, and many species ( Figure 5C) have leaves arranged in pseudowhorl at the end of the branches (Xanthostemon, Melaleuca, Myodocarpus, Dracophyllum, Boronia).
In these diversity of leaf features, Virot (1956) saw xeromorphic condition that he linked to supposedly unfavourable water supplies. However, these features are found in all types of maquis, including those best supplied with water, and we find it difficult to agree with him when he qualifies all the maquis on ultramafic rocks as xerophilous sclerophyllous maquis. At most, we recognise a preadaptation to drought in the sclerophyllous and xeromorphic structures of the plants of the most drought-exposed maquis.
Among the foliage characteristics of maquis on ultramafic rocks, we can also mention a red colouration of young leaves ( Figure 5D) in many genera species (Pancheria, Styphelia, Metrosideros, Xanthostemon). Similar characteristics were noted by Rune (1953) for the vegetation of serpentinite outcrops in Scandinavia.

Characteristics of the root systems
The examination of many soil profiles revealed that most of the maquis species are characterised by highly developed superficial root systems. Even the species with a large tape-root also have lateral plagiotropic systems with significant development (case of Araucaria). We found that the length of these roots is sometimes 4 to 5 times greater than the height of the aerial part of the plant (Montrouziera sphaeroidea, Grevillea exul, Tristaniopsis guillainii).

Developmental characteristics
Growth -The species of the maquis generally have very slow growth. This character remains when they are planted on fertile soils. Although their growth rate accelerates noticeably on fertile soils, it is still much lower than plants not related to mining maquis.
Reproduction -Flowerings, with a dominance of bright red, bright yellow and white hues, are very abundant, but for many species, the fruiting aborts or is destroyed by insects before reaching maturity. When germination does occur, the seedlings grow very slowly and mortality rate are high during the driest periods. Also, usually, young plants are rare in the maquis.

Conclusions
The ultramafic rocks' vegetation is a very diversified group, with, on the one hand, forested formations that physiognomically only differ from the other New Caledonian forests by certain communities, and, on the other hand, very specific low formations or maquis. New Caledonian maquis display great physiognomic and structural diversity, but their biological unity is undeniable: sclerophyllous formations with weak growth dynamic.
Although very often degraded, maquis are very original vegetation units. They mostly appear relatively stable on a human scale. They are paraclimacic formations in perfect balance with the edaphic conditions resulting from soil degradation after the destruction of the vegetation cover. Some maquis are undoubtedly evolving towards dense forests. In contrast, those located in the driest areas would evolve very slowly towards closed shrubby formations, relatively dense but low, of which one still finds relict fragments on certain massifs that can be qualified of climacic maquis.