Plant Cover Composition Research Articles

Analysis of ecofloristic diversity of the Poaceae family of forest biogeocenoses of the northern steppe Prydniprovya

It is difficult to overestimate the importance of cereals in the functioning of natural ecosystems and their use for human life. They often play the role of dominants and edifiers in the composition of plant cover, primarily herbaceous types of vegetation. But they also take part in the composition of forest phytocenoses of different natural zones. Within Ukraine, the Poaceae family includes 71 genera (of which only 4 are in culture) and 208 species (of which only 15 are in culture) [20]. The cereal flora of forest biogeocenoses of the analyzed area was studied in the end of the 19th century [1]. Since the studied forest complexes are located within the steppe zone with various conditions of watershed-beam and valley-terrace landscapes, they contain species of various ecomorphs: from xerophytes to hygrophytes (or even helophytes); from heliophytes to sciophytes, from oligotrophs to megatrophs. The flora of forest biogeocenoses of the northern steppe Prydniprovya region includes 73 species of vascular plants. The greatest species richness belongs to the flora of floodplain forests, which confirms the statement about the extraordinary biodiversity of floodplain landscapes [35]. Of the entire flora of forest biogeocenoses, hemicryptophytes (42 species) predominate among climamorphs, heliophytes (66 species) predominate among heliomorphs, mesotrophs (39 species) among trophomorphs, and mesophytes (45 species) among hygromorphs. Among the coenomorphs, the majority are forest-meadow (55 species) and ruderal-forest (18 species). The Roaceae family of the forest biogeocenoses of the northern steppe Prydniprovya region includes 6 rare species that are included in the regional red list of rare plants [29]. The ecomorphic analysis of the flora confirms the peculiarities of the physical and geographical conditions of different types of forests. Among the climamorphs, hemicryptophytes predominate in birachous and wall forests. The majority of heliophytes are characteristic of arenaceous forests, and sciophytes are characteristic of floodplain forests. Among trophomorphs, megatrophs predominate in birachous and walled forests, oligotrophs in arena forests. The largest number of hygrophytes is characteristic of floodplain forests, and xerophytes is characteristic of arena forests. The forest biogeocenoses of the northern steppe Prydniprovya are characterized by significant anthropogenic transformation of the vegetation cover. In the composition of the forest flora, there are only 16 purely ruderal (weedy) species, and 23 ruderal species in mixed ecomorphs. Among them, 16 are adventive ruderal species. The assessment of anthropogenic transformation of the plant cover using the hemerobium method shows that the majority of the hemerobium species belong to mesohemerobes – species that grow on the territories of landscapes with a medium degree of transformation. This indicates a moderate transformation of the forest biogeocenoses of the northern steppe Prydniprovya. Among all types of forests, the least transformed are floodplain, ravine and wall forests.

Rhizobial root nodules in aeolian sandstones on Madeira (Piedade Beds, Pleistocene) and their significance for palaeonvironmental and “originator” hypotheses

Numerous rhizoliths were observed in aeolian Pleistocene sediments (ca. 80 ka) on the Ponta da São Lourenço Peninsula on eastern Madeira. Surface of some rhizoliths locally exhibit bulbous swellings which were identified as rhizobial root nodules. Based on palaeoenvironmental analysis and a comparison with other rhizoliths in the Macaronesian region, the arborescent species of Morella faya, domestic to the Madeira Island, is suggested as the source taxon for the rhizoliths. Actinorhizal fungi of the genus Frankia are considered to be responsible for creating the nodules. Tree rhizoliths also document the changes in climate and plant cover composition on Madeira. Their origin dates to a rather humid period dominated by partly continuous arborescent vegetation.

Robustness to import declines of three types of European farming systems assessed with a dynamic nitrogen flow model

CONTEXTAgriculture in Western Europe is predominantly input-intensive (fertilisers, water, fuel, pesticides) and relies on feed imports. As a result, it is dependent on oil, which may start to decline in production in the 2020s, thus exposing the agricultural sector to potential economic stress, including increased input prices and decreased farmer purchase capacities. Therefore, it is necessary to assess the capacity of European farming systems (FS) to maintain production levels despite a decline in oil production (i.e., robustness). OBJECTIVEWe aimed to model and compare the time variations in the animal- and crop-sourced production of three French FS under three scenarios of decreased availability of feed and synthetic fertiliser imports. METHODSWe developed a FS-scale dynamic model that considers nitrogen flows between livestock, plant, and soil compartments. Plant production is a function of soil mineral nitrogen levels, and livestock numbers depend on feed availability. The three FS are characterised by different crop-grassland-livestock balances: (i) field crop (Plateau Picard), (ii) intensive monogastric (Bretagne Centrale), and (iii) extensive ruminant (Bocage Bourbonnais). The three scenarios consist of different combinations of synthetic nitrogen fertilisers and feed import availability declines until 2050: a decrease in synthetic fertilisers only (Synth-), a decrease in feed imports (Feed-), and a decrease in both external inputs (Synth-Feed-). RESULTS AND CONCLUSIONSThe first two scenarios highlight the positive role of livestock effluents and permanent grasslands on the robustness of food production. In the Synth-Feed- scenario, the extensive ruminant FS exhibits robustness (no decline in food production) for 13 years, whereas the field crop FS exhibits robustness for 4 years. In contrast, the intensive monogastric FS shows decreased food production within the first year. The difference between the two crop-livestock FS can be explained by livestock density, herd composition but also plant cover composition. In the long term, all three FS show a decrease in food production between 45 and 60%. SIGNIFICANCEOur modelling work shed some light on the role of ruminants and permanent grasslands in making FS more robust to decreases in synthetic fertiliser and feed import availability, increasing the time without production decline after the beginning of the perturbation. For longer-time resilience, configurational changes are still necessary, however a greater robustness gives more time to implement them, therefore facilitating adaptation and transformation. Our model paves the way to the study of resilience of FS from the point of view of their crop-grassland-livestock configuration and their dependence on external inputs.

Regeneration of the rare meadow species Iris sibirica in a postcultural land

ABSTRACT Investigations aimed at assessing agricultural activity in Molinia meadow and subsequent land abandonment on the species composition of plant cover, habitat characteristics, as well as regeneration of the Iris sibirica population were conducted in the year 2018 in the Gielniów Hummock (Southern Poland, Central Europe). The observations were carried out on two meadow complexes 1) subjected to disturbance by removal of plant cover, four-year cultivation of Zea mays L. (called postcultural meadow) and 2) unmanaged from at least 15 years (called abandoned meadow). In the abandoned meadow, advanced secondary succession was observed, while in the postcultural meadow the regeneration of meadow species inter alia Iris sibirica was noticed. The population of the aforementioned taxon presumably regenerated thanks to seedling recruitment and subsequent vegetative growth of juvenile individuals. The abundance of the population Iris sibirica was greater in the postcultural meadow. The number of leaf rosettes was greater in the abandoned meadow. The number of previous and current-year generative stems, as well as the number and dimensions of capsules, were similar in both study sites. The lower height of the leaves and generative stems of Iris sibirica in the postcultural meadow might be caused by the low height of plant cover and the lack of necessity of competition for light with neighbouring species. The obtained results lead to the promising conclusion that populations of endangered species Iris sibirica might regenerate in habitat of postcultural meadow, if not strongly destroyed (e.g. habitat of short-lived cultivation of annual species without pesticides).

Evolution of soil organic carbon in a carbonaceous glacial till as an effect of crop and fertility management over 50 years in a field experiment

Changes in soil organic carbon (SOC) content depending on different factors are extensively investigated when the soil is in steady-state equilibrium between formation and decomposition of soil organic matter. However, studies of SOC formation and dynamics in initally organic matter free soil are rare. Evolution of soil organic carbon was studied in a field experiment established in 1964 on a carbonaceous glacial till soil with very low initial SOC content (1.28 g kg−1). The effects on SOC content changes of bare fallow, barley and different perennial fodder crops such as grasses, clover-grass mixture, galega, hybrid lucerne and a turfgrass mixture, with or without mineral N and PK fertilisation and manure, were studied. There were 19 treatments in total and most had unchanged plant cover composition throughout the experiment. During 1964–2014, SOC stock increased in all treatments, by 0.11 Mg ha−1 y−1 in bare fallow and by at most 0.50 Mg ha−1 y−1 in the treatment with hybrid lucerne and manure. Average SOC sequestration rate was 0.35 ± 0.11 Mg ha−1 y−1. SOC changes were highly correlated with estimated C inputs and were therefore higher in treatments with perennials than with an annual barley crop. C retention efficiency for total crop-derived C inputs and for organic amendments was 6.1% and 22%, respectively. Water-soluble C measured in 2014 increased linearly with SOC, indicating that the quality of recently formed SOC was not strongly affected by the treatments. However, water-soluble C as a fraction of SOC was significantly lower in treatments with legumes than in treatments with bare fallow or a barley or grass crop. These results demonstrate that the quantity and quality of C inputs were both main drivers for observed changes in SOC. However, C retention efficiency of C inputs was relatively low. This may be related to soil texture with high sand proportion, suggesting that SOC sequestration rates in light-textured soils may be lower than expected even in case of low initial SOC content.

Растительность и растительное вещество плоскобугристых торфяников

The aim of the study was to reveal peculiarities and regularities in plant material stock and production as dependent on the plant cover composition, soil characteristics and microrelief of the flat palsa mires in the northern taiga zone in West Siberia. The hollow-lake complexes on permafrost peatlands were chosen as the study sites. The work was carried out in 2013-2017. Plant material structure with differentiation between living and dead belowground organs was investigated and net primary production evaluated. Net primary production was found to range 3.0-4.5 t/ha per year depending on plant species composition of the phytocenosis studied. The production averaged 4.0 t/ha per year with phytomass stock averaging 14.8 t/ha, whereas in dried lake sites the net primary production reached 8.5 t/ha per year with phytomass stock estimated as 18.0 t/ha. On flat palsa sites the ratio of the aboveground shrub production to their belowground production was 1:4, while in hollow sites the belowground organs of sedges and cotton grasses accounted for most of the production, with the ratio of the above- to the belowground production estimated as 1:6. Belowground production share in the total production was found to be maximal (70%) in mesotrophic hollows mainly due to the major sedges and cotton grasses. The total primary production was estimated as 4.1 t/ha per year on flat palsa sites, 3.0 t/ha per year in oligotrophic hollows and reached a maximum of 8.5 t/ha per year in dried lake sites. Thus the average plant material stocks, both above- and belowground, seemed to be rather constant from year to year, and their estimates agreed well with those reported for mires in Canada, Sweden and Finland. Phytomass stocks and production in flat palsa mires in the northern taiga of the West Siberia were shown to depend on soil mineral nutrition and water availability in the root-inhabited layer. Only in oligotrophic hollows mosses were found to dominate in production, while the latter on the palsa sites was dominated by lichens, displaying great species diversity, significantly exceeding that of other plants. The other factors being equal, in hollow sites phytomass stocks and yearly production increased with increased nutrient availability, being decreased on palsa sites due to the permafrost layer. Analysis of phytomass production in northern taiga mires allows concluding that soil characteristics play important role in phytomass production, which was found to be rather low overall. Phytomass stock and production on palsa sites are limited by shallow thawing depths, which effect is exacerbated by drying and warming of the upper soil layer in summer, altogether resulting in unfavourble environment for root growth and development.

Post-Fire Recovery in Coastal Sage Scrub: Seed Rain and Community Trajectory.

Disturbance is a primary mechanism structuring ecological communities. However, human activity has the potential to alter the frequency and intensity of natural disturbance regimes, with subsequent effects on ecosystem processes. In Southern California, human development has led to increased fire frequency close to urban areas that can form a positive feedback with invasive plant spread. Understanding how abiotic and biotic factors structure post-fire plant communities is a critical component of post-fire management and restoration. In this study we considered a variety of mechanisms affecting post-fire vegetation recovery in Riversidean sage scrub. Comparing recently burned plots to unburned plots, we found that burning significantly reduced species richness and percent cover of exotic vegetation the first two years following a 100-hectare wildfire. Seed rain was higher in burned plots, with more native forb seeds, while unburned plots had more exotic grass seeds. Moreover, there were significant correlations between seed rain composition and plant cover composition the year prior and the year after. Collectively, this case study suggests that fire can alter community composition, but there was not compelling evidence of a vegetation-type conversion. Instead, the changes in the community composition were temporary and convergence in community composition was apparent within two years post-fire.

Effect of hyperaccumulating plant cover composition and rhizosphere-associated bacteria on the efficiency of nickel extraction from soil

Most plant species selected as appropriate candidates for phytoextraction have been studied as monocultures. However, alternative cropping patterns which include rhizosphere microbial communities can significantly influence the extraction of metals, as well as soil protection and quality. Therefore, the objective of this work was to study the effect of species-rich vegetation cover, which consisted of three hyperaccumulator plant species, on the efficiency of nickel extraction from a naturally mineralized ultramafic soil. An experiment was set up with three hyperaccumulator species (Leptoplax emarginata, Noccaea tymphaea and Alyssum murale). Plants were cultivated separately (monospecific cover), or in combination (multispecies cover) in mesocosms under controlled conditions, on a nickel-rich ultramafic soil. Plants were grown for 92 days in controlled conditions. Each plant produced more biomass when grown in multispecies cover than alone. Noccaea and Alyssum showed the highest shoot Ni concentrations but Alyssum had by far the lowest shoot biomass. So, in this soil, Noccaea and Leptoplax have greater potential for hyperaccumulation than Alyssum. The amount of nickel accumulated in total biomass of Noccaea alone and of the multispecies cover was higher than that accumulated in either the monospecies Leptoplaxor Alyssum. Furthermore, the highest values of microbial biomass were obtained with the multispecies cover and a consistent production of auxin compounds by bacterial communities was measured, which emphasized the role of rhizosphere bacteria. The bacterial genetic structure also depended on the plant covers. A combination of the three species (multispecies cover), could be a good strategy for phytoremediation.

Soil organic matter in restored rangelands following cessation of rainfed cropping in a mountainous semi-arid landscape

Agricultural abandonment is known to influence plant cover composition and C inputs into the soil with a consequence for changes in soil organic matter (SOM) storage and dynamics in rangeland ecosystems. This study was conducted on a chronosequence of high altitude rangelands (1) cultivated with rainfed wheat (CR0), (2) abandoned for 4 (AR4), 12 (AR12) and 45 (AR45) years and (3) uncultivated (reference) rangelands (UR) with three replicates in Zagros Mountains, Central Iran. We studied the changes in the concentrations and stocks of bulk soil organic carbon (OC), total N, particulate organic C (POC) and N (PON), dissolved organic C (DOC), microbial biomass C (MBC), and potentially mineralizable C (Min-C) at 0–0.15 and 0.15–0.3 m soil depths. Results showed that the concentrations and stocks of OC, N, and labile fractions increased with the abandonment of agriculture at both soil sampling depths. After 4–45 years of agricultural abandonment, soil OC and N stocks increased logarithmically by 3.8–46 % and 2.8–32 % in the whole 0–0.3 m, respectively. Although, the stocks of labile fractions decreased slightly 4 years after agricultural abandonment, there were considerable increases (logarithmic) in these fractions after 12–45 years of abandonment (POC, 65–148 %; PON, 68–147 %; DOC, 76–139 %; MBC, 24–62 %). The study shows that rangelands abandoned for 45 years contained lower soil OC and N concentrations and stocks compared to uncultivated rangelands, reflecting 45 years of abandonment would not be sufficient for SOM to attain the level of uncultivated rangelands. The present study provided evidence that the rate of increases in POC and DOC stocks was greater than that of OC and MBC stocks, demonstrating POC and DOC fractions of total SOM pool may be suitable and sensitive indicators for detecting the effects of agricultural abandonment on soil OC changes and storage in these restored semi-arid rangelands. Soil bulk density decreased, while the mean weight diameter (MWD) and aggregate ratio as measures of aggregate stability increased considerably within the abandoned rangelands with increasing time of abandonment. Results from a multivariate analysis suggested that soil variables such as bulk density, OC, TN, DOC, POC, PON, MBC, MWD and metabolic quotient (qCO2) were successful in separating land uses. In brief, the abandonment of agricultural activities in previously cultivated high altitude rangelands can potentially lead to an increase of total and labile SOM and also sequestration of C in these semi-arid rangelands.

Humus cover and its fabric depending on pedo-ecological conditions and land use: an Estonian approach to classification of humus forms

The fabric of humus cover (HC) may be very variegated, depending on local pedo-ecological conditions (origin and composition of deposits, topography, moisture regime, soil climate, plant cover composition). This multiplicity can be expressed by the HC types (or humus forms). On natural areas, where the HC is formed as a result of long-term equilibrated mutual influences of soil cover and plant cover, the fabric and properties of the HC may be used as an ecological indicator in the evaluation of the functioning character and intensity of the soil-plant system (or also the whole ecosystem). In Estonia, besides natural areas, the classifications of HCs are also elaborated for arable areas. Regardless of the profound changes in the fabric of the HC occurring with land-use change (from natural land to arable and vice versa), certain inherited properties are sustained in newly formed HCs. In this paper the fabric and properties (thickness, carbon and nitrogen stocks) of the main HC types (19 in total) are analysed and ecological aspects of HC formation are explained. Data on tree layer taxation, agro-chemical parameters of the soil cover, and ground vegetation productivity are presented with the HC types used as the ecological background. The relationships of soil cover with soil and forest site type are analysed against the background of soil matrix tables and ordination net of forest sites, respectively. Comparative analysis of the Estonian HC classification with the European Reference Base for humus forms (ERB) showed a relatively good correspondence of the Estonian classification of HC types with ERB's humus forms.

This ped is my ped: Visual separation and near infrared spectra allow determination of the origins of soil macroaggregates

Summary Macroaggregation is a highly dynamic attribute of soils that is claimed to have a significant impact on their ability to store C and conserve nutrients. A major obstacle to the description and modelling of macroaggregate dynamics, and of the associated processes, is an almost complete ignorance of the real origin of the different types of aggregates found in soils, their turnover times and positions in the soil matrix. We present here a general methodological approach in which the origin of aggregates separated according to visual criteria could be determined by comparing their specific organic matter signatures assessed by Near Infrared Spectrometry (NIRS) to signatures of biogenic structures produced by soil ecosystem engineers (invertebrates and roots) living in the same soil. Macroaggregates and other soil components were separated visually from samples taken at 61 locations regularly distributed across a watershed in Nicaragua and representing crops, pastures, forests, coffee plantations and fallows. Coinertia analyses among soil macroinvertebrate communities and the matrix of soil morphological variables showed highly significant relationships. In Amazonian forest patches and pastures from the state of Para in Brazil, 75 different types of biogenic structures were collected at the soil surface and on tree trunks, and analysed by the NIRS spectral method. Significant differences among the different types of structures allowed grouping according to their broad phylogenetic origin with large interspecifc differences. In a field experiment conducted at the same site, soils previously under pastures were planted in 16 possible combinations of four plant species, in a fully randomized design replicated three times in different sites. Surface casts of the earthworm species Andiodrilus pachoensis and soil macroaggregates separated by our visual technique had significantly different spectral signatures depending on the location of the plot and the composition of plant cover. However, the comparison of NIRS signatures of soil macroaggregates and casts suggested that Andiodrilus pachoensis was not responsible for the production of the biogenic aggregates that comprised a large proportion on the soil volume in this soil.

Of Lions, Herders and Conservationists: Brief Notes on the Gir Forest National Park in Gujarat (Western India)

Introduction Conflicts between pastoral nomads and protectionists and the various attempts undertaken in recent years to solve these have been widely described and analysed for East Africa. The claim that grazing by nomadic herds leads to competition between domesticated and wild ungulates over fodder, the extraction of forest produce and the felling of trees has more often than hot led to the expulsion of pastoral peoples from `protected areas' and/or to their resettlement elsewhere. Understandably enough, where large carnivores pose a threat to pastoral herds and their owners, herders try to reduce the number of these predators. In South Asia, as in other parts of file world, such conflicts between protectionists and pastoralists (Rao and Casmir forthcoming) have taken place when protected areas have been created. In this paper I shall briefly examine one such natural reserve in South Asia, where conflicts between transhumants, mainly sheep herders, and local government forest departments (e.g. Kavoori 1996) are on the increase. I focus on the situation of the Maldhari, buffalo and cow-breeding herders of the Gir forest in the state of Gujarat in an arid region of western India. The Maldhari are confronted by a dual problem: their expulsion from their forest pasture lands and the growing number of attacks from the Asiatic lion, for whose protection a sanctuary and the Gir Forest National Park within it were established (see Map 1). The Gir Forest Protected Area In the 1970s various wildlife organisations rightly decided to protect the last extant population of the Asiatic lion (Panthera leo persica) by creating a sanctuary. In 1893 only eighteen animals of this subspecies, which was commonly found from northern Greece through most parts of western and central Asia, were found to survive. Thanks to the strict protection given to it, first by the local royalty (i.e. the Nawab of Junagadh) (1) and then by the Gujarat Forest Department, its population rose to about 200 in 1938 (Rangarajan 2001: 417) and then to 284 by 1990, with a density of one animal per 5-7 [km.sup.2] (Saberwal et al. 1994: 503, see. also Dasgupta 1999). Located in the western part of the Indian state of Gujarat and covering a total forest area of 1,882.64 [km.sup.2] (Choudhary 2000: 2,662, Saberwal et al. 1994), the Gir Protected Area was created in 1965. Including a sanctuary of 1,153 [km.sup.2], it comprised various reserved forests which had been notified since 1882. This sanctuary was expanded in 1974, and in 1975 the Gir National Park of 259 [km.sup.2], was constituted in the middle of the sanctuary (see Figure 1). The terrain is rugged, hilly (at altitudes between 152 and 530 meters above sea level) and paleotropical, with dry deciduous and thorn forest as well as shrub land and some wetland biomes. There are eighty-one common tree species, dominated in some parts by teak (Tectona grandis), forty-eight species of herbs and shrubs, and fifteen species of grasses (Rodgers and Pawar 1988, in Narayan 1996: 214). Due mainly to past incidents of logging, grazing and fire, many parts of the forest have changed their original composition of plant cover, and today thorny and poisonous plants dominate in many parts (for details see Narayan 1996: 213-14). [FIGURE 1 OMITTED] The last `Working plan for the Gir Forest' was formulated in 1975 and was applicable from 1976 to 1985. The central objectives of the management of the protected area were (cited in Narayan 1996: 220-21): 1. Conservation of the Gir habitat and improvement of its quality. 2. Conservation of the lion and all other wildlife. 3. Minimising human interference and removal of ecological imbalance. 4. Improving its aesthetic and recreational value for tourism. 5. Consistent with the above, meeting local demands for timber, firewood and grass to the extent possible. 6. Initiating research and education in wildlife management. …

Plant succession in perennial grass strips and effects on the diversity of leafhoppers (Homoptera, Auchenorrhyncha)

The biodiversity of agroecosystems may be enhanced by increasing species richness and structural diversity of vegetation by creating perennial strips. Aims of the study were (1) to describe the plant succession of perennial strips in northern conditions; (2) to clarify the difference in insect fauna between cereal fields and perennial strips; (3) to determine the effect of succession on leafhoppers in perennial strips; and (4) to compare the leafhopper fauna of perennial strips with that of other uncultivated biotopes. Three perennial grass strips (12 m wide, 420 m long) were sown in the middle of cereal fields (15 ha) in 1991 with a seed mixture of timothy ( Phleum pratense), meadow fescue ( Festuca pratensis), red clover ( Trifolium pratense) and white clover ( Trifolium repens). The perennial strips were not mown or renewed after the establishment. In 1992 and 1993 barley and in 1994 spring wheat were grown in the surrounding fields. The composition of plant cover in the grass strips changed over four seasons. The total number of plant species decreased from 23 species in 1992 to 10 in 1995. The change resulted from the dramatic decrease of annual weeds after the first year. Furthermore, the total plant cover declined slightly. The cover of P. pratense increased, whereas that of T. pratense and T. repens decreased. The plant species typical of early succession were annual weeds including Tripleurospermum inodorum and Thlaspi arvense. In the last year, perennial weeds such as Cirsium arvense and Elymus repens became common. Leafhopper abundance and species number were higher in perennial grass strips than in cereal fields. Furthermore, the species composition varied between habitats. Year-to-year fluctuations in leafhopper catches were large. Leafhopper abundance and diversity (Shannon index) were highest in 1993 when 192 sweep net samples contained a total 4680 specimens belonging to 37 species. The plant species richness of the grass strips did not correlate with the abundance and species richness of leafhoppers, which seemed to be more dependent on other factors. Although the plant species number in grass strips decreased clearly during succession, changes in species richness of leafhoppers were not so great. Factors affecting the leafhopper community are discussed.

Studies on the succession of vegetation on some islands and sand banks in the nile near Khartoum, Sudan

The main Nile near Khartoum contains a number of islands which differ in age, degree of soil stabilization, height in relation to flood-water mark and in the amount and composition of plant cover. These islands were studied with a view to understanding the sequence of colonization and succession.