Copyright 2010 Peter Martin Rhind Plant Formations in the Mascarenean BioProvince
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- Bu səhifədəki naviqasiya:
- Mascarenean Pandanus Upland Wet Woodland (Mauritius)
- Mascarenean Stillingia-Croton Upland Wet Woodland (Mauritius)
- Mascarenean Elaeodendron-Calvaria Forest (Rodriguez)
- Copyright © 2010 Peter Martin Rhind
- Mascarenean Philippia Upland Heath (Mauritius)
- Mascarenean Sideroxylon Upland Thicket (Mauritius)
- Copyright © 2010 Peter Martin Rhind Mascarenean Lowland Thickets (Mauritius)
- Mascarenean Lowland Forest (Mauritius)
- Mascarenean Savannah (Rodriguez)
| Copyright © 2010 Peter Martin Rhind
Forest dominated by several, mainly endemic canopy trees such as Canarium
(Monimiaceae) is considered to be the main upland climax community of Mauritius. These reach heights of between 18-21m and Sapotaceae is the dominant plant family. However, these forests are now confined to small, isolated blocks in parts of the Black River Gorge, Belombre, Grand Bassin and Kanaka on the southeastern plateau, Crown Lands, Osterlog and Grand Fonds on the Midland Mountains. In addition to the canopy, three other distinct strata can be distinguished. At between 8-18m there is a sub-canopy of smaller trees in which Euphorbiaceae, Flacourtiaceae and Myrtaceae are well represented but no particular family or species dominates. Again many of the characteristic species are endemic and include Antirrhoea verticillata (Rubiaceae), Conopharygia mauritiana (Apocynaceae), Erythrospermum mauritianum (Flacourtiaceae), Eugenia cotinifolia (Myrtaceae), Fernelia buxifolia (Rubiaceae), Homalium paniculatum (Samydaceae), Molinaea arborea (Sapindaceae), Psiloxylon mauritianum (Lythraceae) and Securinega durissima (Euphorbiaceae).
Under the dense shade cast by this closed second stratum, a more open stratum of under- trees and shrubs occurs reaching heights of between 2-8m. Many of the species are characterized by large leathery leaves and in this zone and Rubiaceae is the dominant family. In fact, when young trees of high strata are removed from this under storey the endemic Chasalia capitata (Rubiaceae) may represent up to 90% of the individuals. Nevertheless, there are many other species found at this level, most of which are endemic such as Bertiera zaluzania, Coffea mauritiana, Psathura terniflora (Rubiaceae), Colea mauritiana (Bignoniaceae), Claoxylon linostachys, Phyllanthus phillreifolius (Euphorbiaceae), Memocylon cordatum (Melastomataceae), Molinaea macrantha (Sapindaceae) and Tambourissa amplifolia (Monimiacaea). The final stratum is mainly composed of small shrubs but usually dominated by two species of the Mascarene endemic genus Psathura (Rubiaceae). These are Psathura borbonica and P. myrtifolia and typically form low flat-topped bushes reaching heights of no more than about 2 m. This is one of the most distinguishing features of these upland forests. Other small shrubs include the endemic Acalpha colorata (Euphorbiaceae). Another unusual feature of these forests is the tangle of large surface roots produced by some of the taller trees. These sometimes cover an area three to four times greater than the spreading canopy of the tree. Taproots are unable to develop owing to the very hard lava and thin soil, and so these surface roots seem to be an adaptation to withstand the onslaught of violent, cyclonic winds, although other species, especially in the Sapotaceae, achieve this through the production of buttresses. The ground layer, owing to the low light intensities, tends to be very sparse, and nearly all of the flowering plants belong to the families Orchidaceae, Piperaceae and Urticaceae. Endemic species are again in the majority and include Pilea atroviridis (Urticaceae), Peperomia elliptica (Piperaceae), and orchids such as Amphorchis calcarata, Arnottia mauritiana and Phajus tetragonus (Orchidaceae). Orchids, together with bryophytes and Pteridophytes, also form most of the epiphytic flora. Among the endemic epiphytic orchids are Beclardia macrostachya, Jumellea recurva and Polystachya
Copyright © 2010 Peter Martin Rhind
This forest type is confined to the eastern extremities of the southwestern plateau of Mauritius where rainfall exceeds 4445mm per annum. This area is also frequently shrouded in clouds and mist. The forest canopy rarely exceeds 15 m and there is little evidence of stratification. Several endemic species form the main canopy trees including Conopharyngia mauritiana (Apocynaceae), Eugenia cotinifolia (Myrtaceae), Moliniaea arborea (Sapindaceae), Nuxia verticillata (Loganiaceae), Psiloxylon mauritianum (Lythraceae) and Tambourissa sieberi (Monimiaceae). In some places an extremely thick, slightly sinister, canopy of woody lianas has developed some 4-6m above ground level composed principally of the two endemic species Roussea simplex (Brexiaceae) and Toddalia aculeata (Rutaceae). This can cause such dense shade that virtually all terrestral and epiphytic species are excluded from these zones. The smaller trees and shrubs typically include several endemic members of the Rubiaceae (Chassalia grandifolia,
(Nyctaginaceae). Ferns, particularly species with large fronds up to a metre in length, such as Diplazium sylvaticum and Lonchitis pubescens, dominate the ground flora, and there are also many epiphytic filmy ferns. But as expected mosses and hepatics are the most conspicuous life forms at this levels and every available space on the trunks and lower branches of woody species is crowded with a great variety of species. One of the most common hepatic is the endemic Plagiochila mauritiana, which festoons many branches with its light green, feathery fronds. Other common bryophytes include the endemic Jaegerina excurrens together with Aerobryopsis subpiligera, Anoectangium borbonense and Pleurozia gigantea.
Several endemic species of Pandanus, such as P. carmichaelii, P. microcarpus, P. palustris, P. pyramidalis and P. vandermeerschii (Pandanaceae) are the characteristic species of certain upland marshy woodlands. They display numerous aerial roots including stilt-like structures and many pneumatophores. Associated species include Aphloia
endemic Gaertnera psychotriodes (Rubiaceae).
This type of woodland is confined to a small area near Les Mares in the southwestern region of the upland plateau, and only develops on the highly aluminous grey clay overlying unweathered ferruginous lava. The dominant species are both endemic. Stillingia lineata (Euphorbiaceae) is a small tree rarely exceeding 3 m in height, while Croton fothergillaefolius (Euphorbiaceae) is a small shrub reaching about 1 m. The ground flora frequently consists of tussocks of the endemic, peat forming Carpa costularioides (family?) and the two bog mosses Sphagnum cymbifolium and S. tumidulum.
The only remnant of native forest on Rodriguez seems to be confined to the upper region of the Cascade Victoire. In addition to a semi-open canopy a lower stratum can also be distinguished. The canopy, which reaches about 15 m in height, is dominated by the two endemic species Elaeodendron orientale (Celastraceae) and Calvaria galeata (Sapotaceae). Most other characteristic canopy species are also endemic including
(Combretaceae), and the palm Dictyosperma aureum (Arecaceae). At heights ranging from about 2-10m the second stratum is much more closed and again mainly composed of endemic species comprising various small trees and shrubs. These include Dombeya Copyright © 2010 Peter Martin Rhind
Hibiscus liliiflorus (Malvaceae), Pittospermum senecia (Pittosporaceae), Quivisia laciniata (Meliaceae), Scyphochamys revoluta (Rubiaceae) and Securinega durissima (Euphorbiaceae). The proportion of endemic species found in this stratum is quite high amounting to about 53%, but in general these forests are less diverse than their upland counterparts on Mauritius. The ground layer is mainly composed of herbaceous species such as Peperomia reticulata and the endemic Pilea balfourii (Urticaceae) and various ferns, but there is a complete absence of ground orchids on Rodriguez. Climbers and lianas are mainly represented by Scutia commersonii, Tanulepis sphenophylla and the endemic Asparagus recemosus, A. umbellatus (Liliaceae) and Toddalia aculeata (Rutaceae). In contrast to the ground layer, the epiphytic flora includes a number of orchids such as Bulbophyllum incurvum, Listrotachys aphrodite and the endemic
and bryophytes, although Trichomanes cuspidatum the endemic Selaginella rodriguesiana (Selaginaceae) and several bryophytes are commonly found at the base of trees.
This community, dominated by the endemic tree heather Philippia abietina (Ericaceae), is one of the most striking communities of the uplands, and closely resembles the Philippia heaths of Madagascar and East Africa. It is now confined to a small area of the southwestern part of the upland plateau, where humidity levels remain high throughout the year. In many places soil is virtually absent and for plants to gain anchorage their roots often have to penetrate the joints between frozen lava streams. The shrub layer is dominated by the endemic Helichrysum yuccaefolium (Asteraceae) and Phylica mauritiana (Rhamnaceae), while other endemic but less common shrubs include Olea lancea (Oleaceae), Psiadia trinervia (Asteraceae) and Siderxylon puberulum (Sapotaceae). The ground between shrubs is frequently devoid of vegetation consisting of lava fragments and scoria, but in other places the lichens Cladonia rangiferina and C. rangiformis from large grey cushions up to 30 cm across. Another important pioneer of bare lava is the endemic moss Campylopus introflexus var. mauritius. The epiphytic flora mainly consists of mosses, including the endemic Schotheimia fornicata, and lichens, while other less common epiphytes include the endemic orchid Bulbophyllum nutan (Orchidaceae) and the curious fern Polypodium serrulatum with its very small linear fronds.
Thicket in which the endemic Sideroxylon bojerianum (Sapotaceae) dominates is regarded as a sub climax to high forest. It has a highly complex floristic composition and the vertical structure includes three distinct strata. In addition to Sideroxylon bojerianum the canopy, which ranges from 8-10m, also commonly includes the endemic Sideroxylon puberulum. Beneath this is a dense closed specie-rich stratum, which ranges in height from 2-6m, and includes several endemics such as Antidesma longifolium (Euphorbiaceae), Doratoxylon
is a sparsely populated stratum of small shrubs, including the endemic Acalypha colorata (Euphorbiaceae), and a few herbaceous species like Carex brunnea, Oplismenus histellus and Selaginella deliquescens. In contrast the epiphytic flora is comparatively rich comprising several small endemic orchids such as Angraecum multiflorum, A. parvulum and A. ramosum (Orchidaceae). In fact, Angraecum parvulum is virtually found on every tree. Other than the ubiquitous Hymenophyllum and Trichomanes epiphytic ferns are uncommon but may include Blechnum attenuatum, Polypodium phymatodes and Stenochlaena pollicinia.
Copyright © 2010 Peter Martin Rhind
These lowland thickets comprise many species, mostly endemic, that are confined to the lowlands. The few remaining remnants occur on the lower spurs of the mountain ranges near Port Louis, in the Black River district and on recent unweathered lava near Flacq. Typical dominants include endemic species such as Clerodendron heterophyllum (Verbenaceae), Conopharyngia persicariaefolia (Apocynaceae), Dombeya populnea (Sterculiaceae), Eugenia mespiloides (Mrytaceae), Lomatophyllum macrum (Liliaceae), Monarrhenus saliicifolius (Asteraceae), Pouzolzia laevigata (Urticaceae), Senecio appendiculatus and Vernonia populifolia (Asteraceae). However, some of these species are now very rare and many of these indigenous thickets have been invaded by exotic species.
Unlike the uplands, there is a pronounced dry season in the lowlands between May and November. Consequently these forests are markedly different from their upland counterparts in both composition and structure. They are less species rich and the number of woody plants per 25 sq. m diminishes from an average of 60 in the upland climax forest to no more than about 20 in the lowland forest. The canopy, which reaches heights of up to 15m, is closed but with the decreased density of trees much more light can penetrate to the forest floor than in upland forests. The stratification is also less discernable. However, only remnants of these native forest remain, but what can be gleaned from these suggests that most of the dominant trees were endemic species such as Diospyros tesselaria (Ebenaceae), Elaeodendron orientale (Celastraceae), Foetidia mauritiana (Foetidiaceae), Poupartia pubescens (Anacardiaceae) and Stadtmannia sideroxylon (Sapindaceae), although most of these are now very rare. Other endemic trees not necessarily confined to these forests include Protium obtusifolium (Burseraceae) and Ochna mauritiana (Ochnaceae). Probably resulting from the increased light level the shrub layer is well developed with species such as the two endemics Pittosporum senacia (Pittosporaceae) and Quivisia ovata (Meliaceae). At ground level there are fewer ferns than in the upland forests together with other floristic differences. The most conspicuous species is the gregarious Nephrolepis biserrata; while other common species include Asplenium rhizophorum and A. viviparum. Bryophytes are also few in number and mainly represented by Frullania affinis, Rhacopilum praelongon and the two endemic species Hymenostomum ayresii and Sematophyllum schimperi.
Savannah type vegetation is confined to the drier eastern coast of Rodriguez. Prior to the influx of exotic grasses, the main savannah grassland species were native grasses such as Cymbopogon excavatus and Vetiveria arguta. The scattered trees mainly comprise the endemic, drought resistant screw-pine Pandanus heterocarpus (Pandanaceae) and the two endemic palms Latania verschaffeltii and Mascarena verschaffeltii (Arecaceae). Other occasional trees include Gastonia custispungia (Araliaceae) and Mathurina penduliflora (Turneraceae). Among the typical herbaceous species is the cushion forming composite
the strong southeast trade winds. Shrubs such as Carissa xylopicron, Premna serratifolia and the endemic Fernalia buxifolia (family?) also assume a cushion forming habit seldom growing more than about half a metre high.
Further information required. Copyright © 2010 Peter Martin Rhind
References
Baker, J. G. 1999. Flora of Mauritius and the Seychelles. (reprint of 1877 edition). Asian Educational Services, India.
Balgooy, Van. M. M. J. 1969. A study of the diversity of island floras. Blumea, 17: 139-178. Wiehe, P. O. 1949. The vegetation of Rodrigues Island. The Mauritius Institute Bulletin, 2: 280-304.
Renvoize, S. A. 1979. The origins of Indian Ocean Island floras. In: Plants and Islands. Ed. D. Bramwell. Academic Press.
Vaughan, R. E. 1937. Studies on the vegetation of Mauritius. I. A preliminary survey of the plant communities. Journal of Ecology, 25: 289-343.
Vaughan, R. E. 1941. Studies on the vegetation of Mauritius. III. The structure and development of the upland climax forest. Journal of Ecology, 29: 127-160.
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