Showing papers in "Plant Ecology in 1985"

Coexistence of plant species with similar niches

Abstract: In the context of a simple mathematical model, we derive several mechanisms whereby plant species can coexist in a community without differing in their trophic niches (their relations with habitats, resources and exploiters). The model is based on the dynamics of species turnover in microsites, and incorporates localized competition, non-uniform seed dispersal and aspects of spatiotemporal environmental heterogeneity. These factors, which are not included in most standard competition models, allow stable coexistence of trophically equivalent species due to: (a) Differences in life-history ‘strategy’. (b) Input of seeds from nearby habitats (spatial Mass Effect). (c) Differences in demographic responses to environmental fluctuations (temporal Mass Effect). (d) Turnover in species composition between different habitat patches.

North American vegetation patterns observed with the NOAA-7 advanced very high resolution radiometer

Abstract: Spectral vegetation index measurements derived from remotely sensed observations show great promise as a means to improve knowledge of land vegetation patterns. The daily, global observations acquired by the advanced very high resolution radiometer, a sensor on the current series of U.S. National Oceanic and Atmospheric Administration meteorological satellites, may be particularly well suited for global studies of vegetation. Preliminary results from analysis of North American observations, extending from April to November 1982, show that the vegetation index patterns observed correspond to the known seasonality of North American natural and cultivated vegetation. Integration of the observations over the growing season produced measurements that are related to net primary productivity patterns of the major North American natural vegetation formations. Regions of intense cultivation were observed as anomalous areas in the integrated growing season measurements. Significant information on seasonality, annual extent and interannual variability of vegetation photosynthetic activity at continental and global scales can be derived from these satellite observations.

Coastal fore-dune zonation and succession in various parts of the world

Abstract: A table is presented of the most important species of the fore-dune complex in various parts of the world, representing all continents. The complex is divided into six zones or habitat types, which have proved to be widely applicable for this purpose. The zones are briefly described in terms of floristics, geomorphology, ecology (sand movement, salinity, organic matter) and climate. A major division is indicated between tropical (including subtropical) and temperate (including cold) regions. The former are subdivided into those with humid and those with arid climates, the latter into those with cool to warm-temperate and those with boreal to subarctic climates. The highest, most extensive and most complicated dune areas occur in those regions where the effects of disturbance by wind and fixation by plant growth are about equally strong. A number of species show the ‘retraction phenomenon’: a shift from a certain zone towards a more sheltered zone in an area with more harsh conditions (e.g. a shorter vegetation period). The filling of empty niches by introduced species (e.g. in connection with the scarcity of native tidemark species in temperate Australia) is also quite common. Most communities are rich in (sub)cosmopolitan species.

Ecophysiological adaptations of coastal halophytes from foredunes and salt marshes

Abstract: Ecophysiological strategies of coastal halophytes from foredunes and salt marshes are discussed. A comparison is made of the factors that limit growth in salt marshes and sand dunes. In salt marshes, zonation and succession are primarily governed by variation in soil salinity, which strongly depends on inundation with seawater. Results are described of experiments which aim at separating salinity and inundation effects on growth, osmotic and mineral relations in a comparison of salt-marsh halophytes. The growth response of plants cannot simply be correlated (and causally explained) with the concentration of Na, Cl, and K in the tissues. Also, the compatible osmotic solutes proline and methylated quaternary ammonium compounds may accumulate both in species with a positive response to increased salinity and in species with a growth reduction under seawater inundation. More likely inadequate adaptation of the plants water potential with these components is partly the cause of retarded growth. Disfunctioning of the plant in this respect may be at three levels: (a) total water potential of the plant, (b) (loss) of turgor pressure potential; (c) regulation at the cellular level.

Secondary successional patterns in a sagebrush (Artemisia tridentata) community as they relate to soil disturbance and soil biological activity

Abstract: The relationship between secondary succession, soil disturbance, and soil biological activity were studied on a sagebrush community (Artemisia tridentata) in the Piceance Basin of northwestern Colorado, U.S.A. Four levels of disturbance were imposed. I: the vegetation was mechanically removed and as much topsoil as possible was left; 2: the vegetation was mechanically removed and the topsoil scarified to a depth of 30 cm; 3: topsoil and subsoil were removed to a depth of 1 m, mixed and replaced; 4: topsoil and subsoil were removed to a depth of 2 m and replaced in a reverse order. Plant species composition, dehydrogenase and phosphatase enzymatic activity, mycorrhizae infection potentials, and percent organic matter were the variables measured. Treatment 4 drastically altered the pattern of vegetation succession. Treatments 2, 3, and 4 started with Salsola iberica as the dominant species but six years later, 3 and to lesser extent 2 changed in the direction of the species composition of 1, dominated by perennial grasses and perennial forbs. Treatment 4 developed a shrub dominated community. The rate of succession was not decreased by the increased levels of disturbance. Both dehydrogenase enzyme activity and mycorrhizae infection potential (MIP) increased with the change from Salsola iberica to a vegetation dominated by either perennial grasses and forbs or shrubs. The intensity of disturbance in 2, 3, and 4 reduced drastically dehydrogenase activity and MIP, but in six years they recovered to levels comparable to 1. Phosphatase enzyme activity and organic matter were unrelated to species composition but related to treatment and time elapsed. In both cases a significant decrease was observed throughout the six-year period.

Salinity and seed germination patterns in coastal plants

Abstract: The seed germination behaviour of a number of coastal species suggests that they can be separated into three categories, whose response to salinity shows some correlation with habitat. All but two germinated well in fresh water. After immersion for several days in ½, full, and 1 ½ strength seawater all recover at least partly. Dune species are more adversely affected by salinity than those from shingle, driftline or salt marsh. Several species, mostly from salt marsh, exhibit ‘salt stimulation’. The final germination on transfer to fresh water of these species is greater the higher the salinity during pretreatment.

The impact of grazing on plant communities, plant populations and soil conditions on salt marshes

Abstract: Grazing an abandoned salt marsh causes retrogressive succession, since mid salt-marsh communities change into lower salt-marsh communities. Grazing and mowing are compared in detail. Both management practices enhance species diversity in an abandoned salt marsh. This can be attributed to the removal of litter. The finding that lower salt-marsh species appear more with grazing than with mowing or abandoning is not related to a higher soil salinity as compared to mowing or abandoning, but probably to locally baring of the soil by grazing animals. Only species of pioneer or unstable environments seem to have a persistent seed bank, for other species seed dispersal seems to be a limiting factor for their establishment.

The effect of cattle and sheep grazing on salt-marsh vegetation at Skallingen, Denmark

Abstract: The aggregated effect of cattle and sheep grazing on Puccinellion maritimae and other salt-marsh vegetation has been studied together with changes in species composition, the percentage cover of each species, total cover and the percentage of bare ground, six years after grazing had been prevented by construction of experimental exclosures. The results of these experiments are discussed in relation to the natural development of the vegetation that occurred in a permanent plot in the ungrazed part of the salt marsh. Six years without grazing caused a marked increase in total cover and a dramatic reduction in the amount of bare ground. The species composition of the Puccinellia maritima community did not change during these six years, but all species increased in cover. Whereas Artemisia maritima migrated into the Festuca rubra community and only two species Festuca and Halimione portulacoides, increased in cover, all other species showed reduced cover and Salicornia europaea disappeared from the plot after six years without grazing. During the same period of time, three species, Salicornia europaea, Suaeda maritima, and Glaux maritima, disappeared from the plot in the ungrazed marsh as a result of natural development. During thirty-five years the vegetation originally dominated by Puccinellia maritima and Salicornia europaea has changed into a community dominated by Halimione portulacoides, whereas the grazed salt marsh is still dominated by Puccinellia maritima and Salicornia europaea.

Vegetation succession on the dunes near Oostvoorne, The Netherlands; a comparison of the vegetation in 1959 and 1980

Abstract: The vegetation of a 150 ha coastal dune area in the SW Netherlands was carefully analyzed and mapped at a scale of 1:2500 in 1959 and 1980. About 600 releves were treated numerically. 127 vegetation types were distinguished, the overlap in community composition between the two years was very small. An intermediate level between this community level and the level of the structural-physiognomic formation was adopted. 56 so-called subformations, in which floristic and structural characters are combined, have been recognized and the overlap was then considerably larger, at least in number of types. Ordination results suggest that in each subset: grasslands, dune slacks, woodlands + scrubs, the first axis reflects floristic differentiation along with progression. The ordination of the entire material shows moisture as the main factor underlying the first axis, zonation as the second and nutrient status as the third factor. Change in vegetation was detected through a network overlay with 2 300 points for each of which the transition between 1959 and 1980 was scored. The pattern of change between 1959 and 1980 is apparently multiple pathway in type. This would be one of the few examples of such a pattern to be established on the medium term level of change, which is considered as succession sensu strictu. On an areal basis the change in vegetation is extremely large; even on the subformation level only 15% of the area was found to be unchanged, and on the community level only 4%. The overall trend is progression with a strong increase in the area of tall scrubs and woodlands. Retrogression also occurs, partly as a result of disturbances such as fire, partly due to local death of a dominant woody species. This latter phenomenon is interpreted against the background of the starting point of the succession; a sudden release of the inner dune area from overgrazing by cattle and a subsequent rapid dune development (outer dunes) on the beach in front of the inner dunes. Both species and community diversity increased, which is related to both differentiation under progression and to retrogression.

A study on long-term salt-marsh succession using permanent plots

Abstract: Succession of plant communities on a salt marsh at the Boschplaat, Terschelling (The Netherlands) is described on the basis of releves from permanent plots in three transects, covering a period of almost 30 years. All releves were clustered, using a hierarchical fusion technique. Succession has been quantified in terms of transitions between clusters over time in all plots. Analysis of the results showed four clearly distinct successional trends, each restricted to a particular altitudinal zone of the salt marsh. Between zones there were only few interconnections. This implies that zonation does not represent succession, at least not on the time scale of this study. It is suggested that initial differences between zones in the processes that change the abiotic environment, form the basis of vegetation zonation at the Boschplaat.

Population biology of salt marsh and sand dune annuals

Abstract: Annuals represent a significant component of the vegetation of coastal salt marshes and sand dunes. From many points of view, the two habitats might appear to have little in common. Yet both are characterized by episodes of low water potential, marked spatial and temporal heterogeneity and a zonation which, within certain limits, reflects successional change.

Phenological characteristics of the tree layer of Kumaun Himalayan forests

Abstract: The phenology of tree components of natural forests occurring between 350 and 2150 m in Kumaun Himalaya is descibed. All forests had more evergreen than deciduous taxa. The degree of evergreenness increased with increasing elevation and decreasing summer dryness. For most species (including all dominants) concentrated leafdrop and simultaneous leafing occurred during the warm-dry period of the year. About half of the species showed multiple leafing. All species had a sharp flowering peak in April. Wet-season flowering was rare. Most of the species flowered synchronously. In the sal- (Shorea robusta) and pine (Pinus roxburghii) forests a single peak of fruit maturation occurred in summer, while in other forests there also was a secondary peak in autumn.

Clump spacing in a desert dwarf shrub community

Abstract: A Monte Carlo method based on Ripley's K function-a cumulative function related to the number of plants encountered at different distances from other plants-is used to test the null hypothesis of random distribution of shrub clumps in a desert dwarf shrub community in Namaqualand, South Africa, where Psilocaulon arenosum is the dominant shrub. The method takes into account the apparent regularity of pattern caused by the finite size (up to 2 m diameter) of the clumps. It is shown that the clump centres are significantly aggregated (compared to random expectation) at distances on the order of 1 m. Such aggregation is expected, as a simple result of regeneration near to seed sources, if the time between catastrophic droughts is short in relation to the time required for development of a non-aggregated or regular pattern determined by moisture competition. No significant regulatiry was detected at distances of 3 m or less. One subplot showed regularity above 3 m, but this pattern was not shown by the other subplot and may not be a competition effect. These results support a hypothesis of aggregation caused by regeneration pattern decaying slowly toward randomness as larger individuals compete.

The influence of vegetation on erosion and accretion in salt marshes of the Oosterschelde, The Netherlands

Abstract: The total root strength of two plant species (Spartina anglica and Limonium vulgare) is related to salt marsh cliff erosion in the Krabbenkreek (Oosterschelde). A ranking order in cliff stability is predicted on the basis of these root strength calculations. It turns out that the S. anglica root system is more effective in reducing lateral cliff erosion than the root system of L. vulgare. Also the establishment of S. anglica by germination of seeds is studied in relation to the erosion/ deposition rates at an accretion site in the Krabbenkreek. The percentage of seeds washed away depends on the mobility of the superficial sediment which increases with decreasing height above N.A.P. (Dutch Ordnance Level). Above 0.90 m + N.A.P. a germination of 20% is measured, but seedlings survive the winter period only in the zone where a patchy vegetation already exists. It is concluded that generative spread of S. anglica in the Krabbenkreek is not very likely under the present hydrodynamic conditions.

Sulphide tolerance in coastal halophytes

Abstract: The effect of sulphide on the growth of several species of salt-marsh plants was investigated. Relative growth rates were significantly reduced in two upper-marsh species, Festuca rubra and Atriplex patula, and in the lower-marsh species Puccinellia maritima. However the growth of Salicornia europaea, a species frequently associated with sulphide-containing sediments, was unaffected. In a separate experiment the wide ranging halophyte Aster tripolium, also appeared to be tolerant of sulphide at a concentration frequently encountered in salt marshes. Sulphide pretreatment inhibited the activity of two metallo-enzymes, polyphenol oxidase and external phosphatase, in plants from the upper marsh, but had no effect on enzymes from P. maritima or S. europaea. The rate of respiration by root tissue was significantly reduced in all of the species investigated but whereas the uptake of 86rubidium was markedly inhibited in the other three species, uptake by S. europaea showed a significant stimulation. Similarly, whereas sulphide-grown plants of F. rubra, A. patula and P. maritima had a considerably reduced tissue iron content, the total iron concentration in S. europaea tissues was comparable to that of the controls. When the sulphide-tolerant species A. tripolium was grown in sulphide-containing media there was no significant effect on the tissue concentration of any of the elements investigated. These results are discussed in relation to possible mechanisms of sulphide toxicity and resistance.

Vegetation succession on the dunes near Oostvoorne the Netherlands since 1934, interpreted from air photographs and vegetation maps

Abstract: The vegetation succession on the dunes near Oostvoorne, The Netherlands has been followed by means of a novel combination of repeated large-scale vegetation mapping and air photograph interpretation. Vegetation units have been discerned on the formation level because these could be distinguished fairly easily on the photographs and because the rates of change are appropriate to the time interval chosen. Nineteen formations were distinguished. Five 1:6250 maps were constructed, reflecting the formation pattern in 1934, 1943, 1959, 1972 and 1980. An overlay with 2736 grid points at 25 m field distance was used to quantify changes in the formation pattern.

Xeric Mediterranean-type shrubland associations of Alta and Baja California and the community/continuum debate

Abstract: A survey of the xeric shrublands of Pacific coastal North America from San Francisco to El Rosario (Mexico), including the inner Channel Islands, was conducted using 99 sample sites of 0.063 ha size. TWINSPAN classification and DECORAN A ordination confirmed the existence of two plant formations, distinguishable physiognomically: coastal sage scrub and coastal succulent scrub. Within coastal sage scrub, four floristic associations were recognized: Diablan, Venturan, Riversidian and Diegan. Within coastal succulent scrub, two floristic associations were defined: Martirian and Vizcainan. These associations occur in distinct geographical regions following the coastline, with the Riversidian association occurring in the basin inland from Venturan and Diegan regions. Their locations are strongly correlated with differences in evapotranspirative stress regimes. The Channel Island sites show affinities to several of the mainland associations. The Venturan association can be further subdivided floristically into two subassociations, dominated by Salvia mellifera and S. leucophylla respectively. These subassociations which are coextensive geographically at a regional scale, typically do not intermingle at a local scale but often meet along sharp boundaries in the landscape. The dominant species segregate by moisture preference, S. mellifera preferring coarser-texture soils and more southerly aspects thanS. leucophylla. Richness and equitability of these sites are depressed relative to other xeric shrubland sites, reflecting the fact that the two subassociations partition the Venturan flora into substantially non-overlapping subsets of species. This segregation of associates between the two Salvia dominance types strongly suggests biotic influence of the dominants on subordinate species, perhaps mediated by allelopathy. This biotic interaction, leading to relatively strong floristic subassociations segregating independently in the landscape, would provide an example of the holistic community structure referred to by Clements and his followers, embedded within a larger pattern of continuity in species distributions.

Osmotic adaption in Australian mangroves

Abstract: Young and old leaves of twenty-three mangrove species from northern Queensland (Australia) were investigated for their mineral ion and organic solute content. With a few exceptions, the Na+ and the Cl− concentrations calculated on the basis of plant water (p.w.) were close to that of seawater and showed little age-induced changes. In some species, especially in Ceriops tagal, SO 4 2− accumulated with increasing leaf age. The most widely distributed organic solutes were pinitol and mannitol, which were stored up to 280 mM plant water. A negative correlation between pinitol and SO 4 2− was found in the case of Ceriops tagal. Other compatible solutes known for halophytes, such as proline and methylated quaternary ammonium compounds (MQAC), were present only in a few mangrove species. Proline occurred in two Xylocarpus species, while MQAC were accumulated by Avicennia eucalyptifolia, A. marina, Acanthus ilicifolius, Heritiera littoralis and Hibiscus tiliaceus. In all other species, low molecular weight carbohydrates (LMWC) were the main organic solutes.

The physiological ecology of strandline plants

Abstract: Factors which affect the vegetation of strandlines on sandy shores were investigated with particular attention to the growth of four annual species Atriplex glabriuscula, Atriplex laciniata, Cakile maritima and Salsola kali which are widely distributed around the coasts of North-West Europe. The response of these species to increases in salinity and sand accretion are reported from laboratory experiments. Field observations were also made of photosynthesis and the availability of, and the response to, nitrogen. The results are used to discuss the adaptation of these plants to growth on strandlines in an attempt to explain their restriction to this habitat.

Vegetation of the Santa Catalina Mountains: community types and dynamics

Abstract: This paper interprets plant community dynamics within three major vegetation regions - the Sonoran desert, the Encinal and coniferous forest - which extend from 700 m to the summit (2 766 m) on the south slope of the Santa Catalina Mts., Arizona. On the bajada, Larrea tridentata and disturbed desert scrub communities have been degraded by overgrazing and Carnegiea gigantea reproduction is failing on many sites. In the Spinose, suffrutescent desert scrub on protected lower mountain slopes Carnegiea is reproducing but mature populations are periodically decimated by freezing temperatures. In the desert grassland, graminoids or Agave schottii dominate, the former favored by fire, the latter by fire protection. In the Encinal above 1 220 m an open oak woodland dominated by Quercus oblongifolia is transitional to the pine, oak woodland where fire and drought result in several community segregates. A relict Cupressus arizonica forest is restricted to certain canyons. Above the Encinal (2 100 m) a Pinus ponderosa-Q. hypoleucoides forest is replaced by a less xeric P. ponderosa forest. In the latter a dense pine understory develops with fire protection and savanna-like pine stands are favored by fire. At higher elevations a mature Pseudotsuga menziesii, Abies concolor forest dominates the north-facing slopes where fire plays a significant factor in its perpetuation. An even-aged subalpine Abies lasiocarpa stand on the north slope below the summit suggests post-fire origin. In the Pinaleno Mts. to the northeast, mixed conifer and spruce, fir forests complete the vegetation gradient typical of these southwest mountain ranges. Here fire and windthrows interact in maintaining a mosaic of pure or mixed even or uneven-aged stands.

Phytomass structure of natural plant communities on spodosols in southern Venezuela: the Bana woodland

Abstract: Bana, or Low Amazon Caatinga is an evergreen sclerophyllous woodland. It occurs on bleached quartz sands in the lowlands of SW Venezuela, where it occupies relatively small ‘islands’ amidst Tall Amazon Caatinga which is exclusively developed on tropaquods. There is an outer vegetation belt about 20 m in width in which trees over 10 m in height occur (Tall Bana); its structure and floristic composition resemble Tall Amazon Caatinga. Low Bana (maximum tree height usually below 5 m) follows next. The central part is occupied by Open Bana in which even lower trees are very widely spaced. Destructive phytomass sampling was carried out for chemical analyses in seven plots along a 150 m line across the zonation. The total dry matter of living plants including roots of Tall Bana (30–32 kg/m2) compares rather well with 41 kg/m2 in Tall Amazon Caatinga. This is only 9–14 kg/m2 in Low Bana, and 4–6 kg/m2 in Open Bana. The average root % of total phytomass increases from 41% in Tall Bana to 63% in Low Bana, and is 88% in Open Bana. Average total dry dead above-ground phytomass (including standing trees and stumps) declines from 1 kg/m2 in Tall Bana to 0.2 kg/m2 in Open Bana. An accumulation of dead matter in Low and Open Bana, relative to the above-ground phytomass of living plants, is noted and this contrasts with the general absence of raw humus in the soil. Eighty-two species of woody plants (dbh≥1 cm) were recorded on the total plot area (640 m2); 90% of the species are also known to occur in Tall Amazon Caatinga. The species number declines from 59 in Tall Bana to 18 in Open Bana. Mesophylls sensu strictu dominate in Tall Bana, while notophylls are dominant in Low and Open Bana. Herbaceous species are less numerous: most of them belong to the Araceae, Bromeliaceae, Orchidaceae, Droseraceae, Eriocaulaceae and Xyridaceae.

Development of mangrove habitats along ria shorelines in north and northwestern tropical Australia

Abstract: Along ria shorelines mangrove assemblages are closely related to habitat types and there is a recurring pattern in their distribution that is linked to the origin and history of the geomorphic units. The coastal geomorphology is related to ancestral landforms developed prior to the post-glacial transgression, as well as to tidal levels, aspect, modern shore-forming processes, and types of hinterland/tidal flat contacts. These historical and process patterns develop distinct geomorphic units which dictate the distribution of habitats and their mangrove assemblages. Mangrove assemblages are classified according to their habitat: main tidal flat, hinterland fringe, alluvial fan, spit/chenier, tidal creek bank, tidal creek shoal and rocky shore. Within a given habitat there are various physico-chemical gradients which are instrumental in developing zonation within the assemblages. The variety of internal zones within an assemblage is related to the richness of species within the regional species pool which in turn is related to climate.

Vegetation and succession on the Krakatau Islands, Indonesia

Abstract: An analysis of the vegetation of four islands of the Krakatau group (Rakata Besar, Rakata Kecil, Sertung and Anak Krakatau), Indonesia, was conducted based on our two expeditions of 1982 in centennial commemoration of the great explosion in 1883. Pioneer communities on lava flow, ash fields, beaches, cliffs and on a scoriaceous slope were quite different from each other. Forest communities were grouped into nine types using Morisita's index of similarity, Cλ(W). Two new forest types which have never been described from Krakatau were identified: Timonius compressicaulis forest and Dysoxylum caulostachyum forest. Successional relations among these community types and the Neonauclea calycina forest were discussed from the viewpoint of seed morphology, dispersal, and the development of juvenile generations in the three types of forest. Dysoxylum forest is the most advanced forest community on the Krakatau Islands. The climax forest is supposed to be a tropical monsoon forest similar to that of the volcanic island Panaitan. A successional scheme is proposed. The invasion times of three forest dominants on the three old islands of Krakatau are compared and it is concluded that the difference in vegetation between these islands, the two Rakatas and Sertung, is determined by the earlier invasion of species which could then extend their cover and build up a forest thus preventing later invaders to establish. We are greatly indebted to Dr Fred Hehuwat, Director of the National Institute of Geology and Mining in Bandung, Mr Peter E. Hehanussa, Chief manager for soil and water resource development in the National Institute of Geology and Mining, Dr Soenartono Adisoemarto, Head of the Museum Zoologicum Bogoriense, Dr Kusuwata Kartawinata, Head of the Herbarium Bogoriense, National Institute of Biology, for their kind cooper-ation and use of their facilities. We also thank the staff of the Indonesian Institute of Sciences for their invaluable help in the field and Dr P. J. Grubb who kindly commented on the manu script. The identification of flowering plants was carried out by T. Partomihardjo, who compared samples with specimens in the Herbarium Bogoriense. The identification was counterchecked by Dr M. Hotta, Associate Professor at the Yoshida College, Kyoto University. Dr C. G. G. J. van Steenis taught us a correct name of a species of Bignoniaceae. Pteridophytes were identified by Dr S. Mitsuda, Dept. of Botany, Faculty of Science, Kyoto University, and bryophytes by Dr T. Seki, Dept. of Botany, Faculty of Science, Hiroshima University.

Spatial analysis of density dependent pattern in coniferous forest stands

Abstract: An investigation of spatial pattern in relatively sparse Pinus ponderosa-P. Jeffreyi stands showed that a simple Poisson model of random distribution described the pattern at 5 to 50 m scales in the denser stands examined when allowance is made for inhibition between nearest neighbors. There is evidence for a clumped distribution in large quadrats for the sparsest stands, which concurs with prior work where a mixed Poisson model was fit to the data. The technique used was innovative in that it involved digitally recording tree locations from high resolution aerial photos, which allowed for the automatic application of several statistical techniques in order to determine how pattern varies with plot density and scale. Point locations were recorded for six 11.3 ha plots in three density regions of a 340 ha study area in northeastern California, USA. The inter-event distance distribution, and one- and two-dimensional power spectra were calculated, and variable quadrat analysis was performed for the data sets. The second order and spectral analyses showed no evidence of a distinctive clumped pattern at any scale, and all analyses showed that the pattern was regular at the scale of the average inter-plant distance in the denser stands. For the sparser stands, the counts in large quadrats did not fit a Poisson distribution, but were better fit by a mixed Poisson model describing aggregated pattern.

Dynamics of Nothofagus-dominated rainforest on mainland Australia and lowland Tasmania*

Abstract: Cool temperate rainforest in Australia is commonly dominated by Nothofagus species. In Victoria and Tasmania, Nothofagus cunninghamii dominates old rainforest on optimal sites and is able to regenerate continuously. Size structure analysis of the major lowland tree species in this forest suggest that no major changes in species composition or dominance are occurring. This contrasts with the status of Nothofagus in lowland rainforest in New Zealand and rainforest below about 1000 m a.s.l. in south-central Chile. N. cunninghamii is a relatively light-demanding species, and is maintaining its dominance by seedling regeneration in canopy gaps created by the death of old individuals. The dynamics of the cool temperate rainforest in northern New South Wales are more complex. These forests are dominated by Nothofagus moorei, and size structure analysis indicates that persistence of this species within the rainforest is dependent on vegetative regeneration. On some sites this rainforest is being actively invaded by warm temperate and sub-tropical elements from lower altitudes. In these areas N. moorei in unable to regenerate beneath the canopy.

Stress metabolites and their role in coastal plants

Abstract: The stress metabolites proline, glycine betaine and sorbitol were accumulated in the leaves of some angiosperms from sand dunes and shingle. Chloride, where it was measured, was not accumulated to high concentrations in leaves suggesting that these soils are not saline. Sand dunes and shingle soils have low water-holding capacity, so it is possible that solute accumulation was a response to drought which could be of adaptive significance. In sand dunes low water availability could be associated with increased leaf temperatures because of reduced transpiration rates and high soil temperatures. The role of stress metabolites in heat tolerance was considered. Proline, betaine, sorbitol and mannitol increased the heat stability of glutamine synthetase (GS) and glutamate: oxaloacetate aminotransferase from Ammophila arenaria. For GS the effect increased with solute concentration. The polyols were more effective at high temperatures. The heat stability of GS from the moss Tortula ruraliformis and the brown alga Fucus vesiculosus was increased by mannitol. The effect of the solutes was independent of plant species and type of enzyme. It is suggested that the accumulation of solutes may have ecological importance in protecting sand-dune plants from heat damage during periods of drought.

Adaptation in perennial coastal plants — with particular reference to heritable variation in Puccinellia maritima and Ammophila arenaria

Abstract: Perennial species invading the early stages of primary successions face constant, and often rapid, change in their biotic and abiotic environment. The relative abilities of different species to adapt to this change is reflected in the zonation patterns which characterize coastal vegetation. Variation in those species with wide ecological amplitudes, particularly in populations near the boundary of the realized niche, is likely to be particularly revealing.

Population differentiation in the life-history characteristics of salt-marsh annuals

Abstract: Coastal salt marshes are heterogeneous spatially but predictable temporally. Genetic differentiation between populations on different parts of a marsh in response to this combination of circumstances has been well documented in several perennial species; differentiation has been evident in certain features of the life cycle that contribute to overall fitness.