Showing papers in "Journal of Ecology in 1989"

Effect of nurse plants on the microhabitat and growth of cacti.

Abstract: (1) Seedlings of the cactus Carnegiea gigantea at two sites in the Sonoran Desert were found only in sheltered microhabitats, 89% occurring under the canopy of Ambrosia deltoidea and Cercidium microphyllum. In contrast, 29% of the seedlings of Ferocactus acanthodes, which tolerates higher temperatures than C. gigantea, occurred in unsheltered microhabitats, where maximum soil surface temperatures reached 71?C. Most (70%) of the sheltered seedlings of F. acanthodes occurred under the canopy of the perennial bunchgrass Hilaria rigida. (2) Shading by nurse plants reduced the total daily photosynthetically active radiation (PAR) available for their associated seedlings. Near an equinox, a seedling of C. gigantea located at the centre of an A. deltoidea shrub received 77% less total daily PAR, which reduces its predicted net CO2 uptake by 90% compared with an unshaded seedling. Similarly, a seedling of F. acanthodes located at the centre of an H. rigida plant received 64% less total daily PAR and could fix 65% less CO2 than could an unshaded seedling. (3) H. rigida and F. acanthodes have overlapping shallow root systems (mean root depth of 0 08 m for H. rigida and 0 05 m for seedlings of F. acanthodes), which accentuates competition for water. A water uptake model, which closely predicted the soil water potential in the root zone of H. rigida, indicated that a seedling of F. acanthodes located at the centre of the bunchgrass took up 32% less water than did an exposed seedling. (4) Assuming that the effects of temperatures, PAR, and soil water on net CO2 uptake are multiplicative, the predicted net CO2 uptake of a seedling of F. acanthodes under the canopy of H. rigida was only 36% of that of an exposed seedling. However, areole production by seedlings of F. acanthodes located under the nurse plant was 68% of that measured in exposed areas. This discrepancy probably reflects the 60% higher soil nitrogen levels under H. rigida. (5) Therefore, nurse plants facilitate seedling establishment by reducing high temperatures near the soil surface and provide a microhabitat with a higher soil nitrogen level. However, shading and competition for water with the nurse plants markedly reduce seedling growth. The magnitude of the reduction depends on seedling size and location under the nurse plant.

Responses of mediterranean grassland plants to grazing and protection.

Abstract: The aim of the present study was to evaluate species and community responses to cattle grazing at different intensities and to protection from grazing, in mediterranean grasslands in Israel. The following questions are addressed in this paper: How consistent are species' responses to grazing intensity and protection? Can most species be characterized as either grazing-increasers or protection-increasers? Are responses to grazing associated with attributes such as plant form, life cycle, taxonomic affiliation, palatability?

The Design of Experiments: Statistical Principles for Practical Applications.

Abstract: The book reviews section generally accepts for review only those books whose content and level reflect the general editorial policy of Technometrics. Publishers are invited to send books for review to Eric R. Ziegel, Amoco Research Center, P.O. Box 3011, Naperville, IL 60566. Please include the price of the book. The opinions expressed in this section are those of the reviewers and do not necessary reflect those of the editorial staff or the sponsoring societies. Listed prices were provided by the publishers when the books were received by Technomerrics and may not be current.

The growth, distribution and neighbour relationships of trifolium repens in a permanent pasture. v. the coevolution of competitors

Abstract: (1) Ramets of Trifolium repens were sampled from sites dominated by Agrostis capillaris, Holcus lanatus and Loliumperenne within a permanent pasture. After multiplication of the ramets in a greenhouse, they were transplanted, or replanted, into each of the original sites in all nine combinations of site of origin and transplant site. In addition, the plots were treated in two ways: (i) only the native T. repens removed; (ii) both the native T. repens and the native dominant grass species removed. (2) The pasture population of T. repens was shown to have diverged into a number of subpopulations based on the identity of the grass neighbour. Each T. repens replant grew better in its site of origin than did transplants into that site. This was interpreted as evidence that population divergence is due to interspecific competition with the dominant grasses. (3) Evidence is presented which strongly infers that the observed population divergence has a genetic basis even though formal genetic analyses were not used. (4) The home-site advantage to T. repens disappears when the grasses are removed. Local site conditions clearly have an impact on T. repens growth, but the grasses are the major factor in determining home-site advantage. (5) These results are interpreted as evidence for the coevolution of competitors and are discussed in relation to current and past competition.

Plant canopies: their growth, form and function.

Abstract: List of contributors Preface 1. The description and measurement of plant canopy structure G. S. Campbell and J. M. Norman 2. Absorption of radiation by canopies and stand growth G. Russell 3. Turbulent transfer in plant canopy M. R. Raupach 4. Regional interactions between canopies and the atmosphere K. G. McNaughton 5. Modelling the effects of nitrogen on canopy development and crop growth H. Van Keulen 6. Canopies as populations J. L. Harper 7. Diurnal leaf movements and productivity in canopies J. R. Ehleringer and I. N. Forseth 8. Modules, models and meristems in plant architecture J. R. Porter 9. Synthesis of canopy processes J. M. Norman Index.

Seed banks, fire season, safe sites and seedling recruitment in five co-occurring Banksia species

Abstract: Quantity of seed stored in the canopy of 5 co-occurring Banksia species varied by nearly 2 orders of magnitude. The 3 species which resprout vegetatively after fire, produced less seeds and retained smaller seed banks than 2 non-sprouting species. Contiguous patches of scrub-heath were burned in spring and autumn. The spring fire was cooler, and both sets of seed released subsequently did not germinate until the following (common) winter. Rate of seed release was higher after the autumn fire. The non-sprouting species released more seeds after each fire and yielded more seedlings per parent than the resprouting species. Percentage (field) germination of the non-sprouters was not consistently different from that of the resprouters. Seeds exposed on the soil surface during summer soon lost viability compared with buried seeds. The large number of seedlings established up to 8 months after the spring fire resulted from many seeds escaping exposure by dispersal into litter-covered "safe' sites. Although litter microsites covered only 30% of the ground surface after the spring burn, they accounted for 80% of seedlings both before and after the summer drought. Litter microsites covered only 14% of the autumn-burned site but accounted for 60% of seedlings before summer and 40% after summer, suggesting density-dependent thinning of seedlings. The autumn-burned site supported more than twice the density of seedlings than the spring-burned site by the end of the 1st winter. Summer mortality of seedlings was 32% in the spring-burned site and 65% in the autumn-burned site, equalizing the seedling:parent ratio at both sites. Net recruitment of 1-yr-old seedlings varied from 0 for 2 resprouters to >100 per parent for a non-sprouter.

Root morphology and aerenchyma formation as indicators for the flood-tolerance of Rumex species

Abstract: (1) Rumex species are zoned along a gradient of elevation in the river ecosystem in The Netherlands. (2) Plants of R. thyrsiflorus, R. acetosa, R. obtusifolius, R. crispus, R. conglomeratus and R. maritimus were flooded to identify and quantify any relevant adaptive features and to test whether their distribution might be caused by a differential response to flooding in the growing season. (3) Most Rumex species have a tap-root from which the laterals originate. As a response to flooding, new laterals are formed. (4) The number, place of origin, growth direction and formation rate of new laterals differed between the species. (5) The number and formation rate of new roots were associated with the elevational distribution of the species: as a response to flooding, low-elevation species formed more new roots, and faster, than high-elevation species. (6) The high-elevation species had root porosity values lower than 10%; the intermediateand low-elevation species had values higher than 10%. (7) Schizogenous aerenchyma was constitutively formed by the low-elevation and floodtolerant R. maritimus, and not by the high-elevation and flood-intolerant species R. thyrsiflorus. In the intermediate-elevation species R. crispus it was induced in stagnant hypoxic solution cultures. (8) The results indicate that aerenchyma formation is closely connected with the growth rate of new roots. It appears that development of aerenchyma in the new roots is the main determinant in the flood-tolerance of Rumex species.

Sulphide as a soil phytotoxin: differential responses in two marsh species

Abstract: A glasshouse experiment was set up to investigate if sulphide addition affects the growth of this species. A comparative study using Panicum hemitomon Schult., which dominates the freshwater marshes of Louisiana, was conducted to determine whether wetland species that grow in mineral-poor, low-sulphide environments are more susceptible to sulphide additions

Vegetation patterns in spring-fed calcareous fens: calcite precipitation and constraints on fertility

Abstract: This report considers the chemistry, vegetation composition and productivity of several spring-fed sites where both «short-fen» and «taller-fen» occurred in juxtaposition. This vegetation pattern was apparently related to water movement in the fens as the short-fen vegetation mostly occupied the main seepage tracks whilst the taller-fen flanked these

Regeneration and Establishment Strategies of Emergent Macrophytes

Abstract: The questions are; Are the traits possessed by juveniles (seed/seedlings) of an assemblage of twenty-five emergent macrophyte species independent of the traits possessed by adults of these species? What are the patterns of covariation among twenty morphological traits of these species of widely different taxonomy? Is there any predictable relationships between these traits and the environments in which the species occur?

Models of Nature: Ecology, Conservation and Cultural Revolution in Soviet Russia.

Abstract: \"Models of Nature \"studies the early and turbulent years of the Soviet conservation movement from the October Revolution to the mid-1930s Lenin s rule to the rise of Stalin. This new edition includes an afterword by the author that reflects upon the study's impact and discusses advances in the field since the book was first published.\

Species interactions in a successional grassland. i. seed rain and seedling recruitment

Abstract: SUMMARY (1) Seed rain and recruitment for the five most abundant species of grasses were quantified in a California coastal grassland undergoing succession after release from sheep grazing. (2) Species distributions were very patchy, and four patch types accounted for about 950/o of total cover. Three patch types ('perennial patches') were dominated, respectively, by one of three species of perennial grasses, Anthoxanthum odoratum, Holcus lanatus or Deschampsia holciformis. The fourth type ('annual patches') was dominated by annual grasses, including the most abundant annual Vulpia bromoides, the perennial grass Rytidosperma pilosum and forbs. (3) Dispersal limited the seed rain to the species dominating the local vegetation. Species not present in patches contributed little to the seed rain and nothing to recruitment in the interiors of those patches. (4) Species differed significantly in the densities of their seed rain in the patches they dominated, ranging from 2300 m-2 for R. pilosum to 82 300 m-2 for H. lanatus. The density of seed rain was patchy on all spatial scales examined (from cm to km), but was not significantly correlated with densities of recruits on any scale for the perennial species. However, V. bromoides recruitment correlated positively with the density of its seed rain on small spatial scales (up to 1 mi2) in annual patches. The poor relationship between seed rain and recruitment for the perennials probably reflects the over-riding importance of adult interference as an influence on seedling establishment in the perennial vegetation. (5) A. odoratum had relatively high recruitment (30 m-2) in the patches it dominated. Other perennials had very low recruitment in their own stands (less than 5 m-2). V. bromoides had the highest recruitment (904 m-2) in annual patches. (6) The seed bank contribution to recruitment was estimated using seed exclosures. Only those species abundant in the seed rain and in the local vegetation recruited inside the seed exclosures, i.e. there was no evidence of a persistent, functional seed bank of other species. The seed bank could account for no more than 30/o of V. bromoides recruitment in annual patches. However, establishment in the seed exclosures overestimated recruitment from the seed bank for A. odoratum and possibly for other perennial species (7) The implications of the results for population dynamics and succession are discussed.

Species interactions in a successional grassland. iii. effects of canopy gaps, gopher mounds and grazing on colonization

Abstract: SUMMARY (1) In a perennial grassland undergoing succession after the removal of domestic grazers, three natural processes could disrupt the canopy, and thus affect colonization. These are: canopy gap formation due to the death of individual bunchgrasses; soil disturbance by gophers; and grazing by native animals. (2) Species' abilities to colonize canopy gaps and gopher mounds were assessed in the field, with seed introduction experiments, for the five most cover-dominant grass species: Anthoxanthum odoratum, Holcus lanatus, Deschampsia holciformis, Rytidosperma pilosum (all perennial bunchgrasses) and Vulpia bromoides (an annual grass). (3) The effects of native grazers on colonization by the most abundant species, Anthoxanthum, were assessed, using grazer exclosures and seed introductions in annualdominated vegetation, where grazing activity was highest. (4) Colonization success was quantified as total leaf area, number of survivors and seed production, in sites where seeds of the colonist either fell naturally, or were introduced at natural densities. (5) The formation of canopy gaps by the death of individual bunchgrasses and soil disturbances by gophers strongly affected colonization success. The best colonizers were Anthoxanthum and Holcus, whose colonization success was increased 6-2500-fold by canopy gap formation, and 10-200-fold by the formation of gopher mounds. Few, small seedlings of Deschampsia and Rytidosperma survived in canopy gaps or on gopher mounds. Unlike Anthoxanthum and Holcus, Deschampsia and Rytidosperma did not reproduce in gaps or on mounds over a two-year period. (6) Vulpia colonists had higher seed production on mounds than the four perennials. Vulpia also colonized canopy gaps, but was excluded by perennial vegetation in the second year of growth in the gaps. (7) In annual-dominated vegetation, neither aboveground biomass nor colonization by Anthoxanthum was affected by excluding grazers. However, exclusion of grazers led to an increase in the cover of forbs after two years. Clipping aboveground vegetation allowed Rytidosperma to achieve dominance in sites where, under undisturbed conditions, it existed only as a suppressed understorey. All other perennials were negatively affected by clipping. (8) The species with the highest natural densities of seed rain also had the greatest perseed colonization success, even though negative density-dependent effects must have been

Ecological studies on Gunung Silam, a small ultrabasic mountain in Sabah, Malaysia. II: Some forest processes

Abstract: SUMMARY (1) The rates of several processes in the rain forests, at a range of altitudes, on an ultrabasic mountain, Gunung Silam, Malaysia, were investigated. In spite of the unusual soil chemistry, none of these processes occurred at an exceptionally low rate. (2) Herbivory (judged from the percentage area missing from large numbers of leaf samples of several species) in four plots was: 7 6% (330 m), 6 8% (610 m), 6 9% (790 m) and 7 1% (870 m). (3) Annual mortality of trees (?, 10 cm d.b.h.) was estimated over twelve or thirteen years in ten plots. This was (i): 0 025 (280 m), 0 012 (330 m), 0015 (410 m), 0 011 (480 m), 0 008 (540 m), 0 011 (610 m), 0 008 (700 m), 0 008 (790 m), 0 010 (790 m) and 0 016 (870 m). (4) Median diameter increment of tree boles was estimated over twelve or thirteen years in six plots. This was (mm year- ): 1 56 (280 m), 1 13 (330 m), 1 31 (480 m), 0 93 (610 m), 0 91 (790 m) and 0-77 (870 m). (5) Small litter fall was estimated from twenty 0 25 m2 litter traps in each of six plots over twelve months. It was (t ha-' year-'): 6 51 (280 m), 7 37 (330 m), 5 22 (480 m), 5 60 (610 m), 5 53 (790 m) and 4 80 (870 m). There was no correlation between small litter fall and median diameter increment. (6) Chemical analyses of the small litter fall showed a number of important features, including an excess of calcium concentrations over magnesium concentrations and relatively high concentrations of nickel. (7) Chemical analyses were made of the leaves of a large number of species in four plots. These suggested that the tree species rooted in ultrabasic soil have an ability to grow at low foliar nutrient concentrations and that they are able to concentrate calcium relative to magnesium. A comparison with the results of the litter-fall analyses suggested that there may be an excretion of nickel into the senescing leaves. (8) Shorea tenuiramulosa (Dipterocarpaceae) appeared to accumulate nickel and had up to 1 -0 mg'- nickel in its leaf dry matter. An unidentified Eugenia species (Myrtaceae) had 13-7 mg g' foliar manganese.

Lake development and limnological response to prehistoric and historic land-use in diss, norfolk, u.k.

Abstract: SUMMARY (1) The history of Diss Mere, Norfolk, U.K. was reconstructed by diatom and pigment analysis of a sediment core, with emphasis on the influence of changing vegetation and land-use on lake history. (2) The lake was mildly nutrient-rich (mesotrophic) early in its history. (3) The lower part of the core shows large variations in diatom concentrations and distinct lithological changes, including broad bands of silt and short sections of laminated sediments, which suggest fluctuating lake levels in the early Holocene. (4) Increased concentrations of the blue-green algal pigment oxcillaxanthin indicate the expansion of Oscillatoria about 6000 years B.P., probably in response to increased stabilization of the water column. (5) The subsequent preservation of over 3 m of laminated sediments in the midHolocene and extremely high pigment concentrations indicate a long period of moderate water levels and seasonal hypolimnetic oxygen depletion. (6) Increased pigment concentrations and percentages of diatom taxa characteristic of moderately enriched lakes correlate with pollen evidence of Neolithic and Bronze Age forest disturbance. (7) The termination of the laminated sediments and a transition from a Cyclotelladominated diatom assemblage to one dominated by Stephanodiscus spp. correlate with pollen evidence of widespread deforestation. Thus rapid and sustained eutrophication of the mere probably resulted from increased nutrient inputs caused by forest clearance. (8) The mere remained eutrophic throughout the remainder of its history, and subsequent shifts in the diatom community indicate limnological responses to agricultural practices associated with Cannabis cultivation and later to the growth of a town around the mere.

Genet and ramet demography of Oenocarpus mapora spp. mapora, a clonal palm of Panamanian tropical moist forest

Abstract: This study analyses the demography of a clonal plant species explicitly at the genet level. The tropical palm Oenocarpus mapora ssp. mapora produces vegetative ramets that root and are capable of independent survival; its growth from results in clones (genets) that are readily distinguishable as clumps in the field. The importance of clonal growth to the dynamics of the population of genetic individuals is evaluated and the influence of the clonal habit upon the demographic variation among O. mapora populations growing in heterogeneous forest habitats is examined

Modelling the population dynamics of an annual plant Sorghum intrans in the wet-dry tropics

Abstract: The major aim of this paper is to investigate what factors are responsible for determining the abundance of Sorghum intrans F. Muell. ex Benth. in the wet-dry tropics of northern Australia. The role of both density-dependent and density-independent processes are examined. In addition, we specifically investigate how variation in weather conditions from year to year, local variations in edaphic conditions, fire and ant predation can be expected to affect plant density. In doing so we provide an example of how a theoretical and an empirical approach together may be used to examine the various influences that affect the population dynamics of a plant

Changes over twenty-one years in the kolombangara rain forests

Abstract: The results of the first 6.6 years of study have shown that the distribution and population structure of the twelve common big tree species reflect past disturbance history. The question addressed in this paper is whether over the total 21.3 years the forests are in equilibrium or not, that is to say, has the amount of disturbance (monitored as canopy structure) been sufficient up to November 1985, to maintain the populations as they were at July 1964

Seasonal variation in flowering intensity and pollination limitation of fruit set in four co-occurring Banksia species

Abstract: Patterns of flowering, levels of fruit set and pollination limitation of fruit set were examined over four years in a group of four co-occurring Banksia species (Proteaceae) in south-eastern Australia

Acidification of lakes in Galloway, south west Scotland: a diatom and pollen study of the post-glacial history of the Round Loch of Glenhead.

Abstract: SUMMARY (1) Potential acidification by chemical weathering, soil leaching and organic matter accumulation in the catchment of the Round Loch of Glenhead is evaluated using diatom and pollen analysis of a radiocarbon dated sediment core. The Round Loch is situated on granite bedrock and is likely to have been sensitive to acidification throughout the postglacial period. (2) About 9000 years B.P. the open habitats of the late and early post-glacial were replaced by birch/hazel woodland, then oak/elm/pine woodland, and oak/hazel/alder woodland by about 5400 years B.P. After 5700 years B.P., blanket mires increasingly replaced woodland. The present vegetation on the blanket peat is a Molinia/Calluna heathland. (3) The lake was acid in the late-glacial period (pH 5 3-5 7). No evidence of long-term acidification in the early post-glacial period was found, and from 9000-4150 years B.P. the pH of the loch was probably between 5 3 and 5 6. In the mid post-glacial no indication of lake acidification that might be associated with peat development in the catchment was identified, and from 4100 years B.P. there is evidence that a slight increase in pH or nutrient availability or both occurred. (4) Despite a clear change from mineral to acid organic soils in the catchment in the mid post-glacial, feedback mechanisms operated to maintain a lake with pH stable at 5 and above for most of the post-glacial period. With the introduction of strong acid anions associated with acid deposition after A.D. 1800 the pH fell to its present value of 4 7.

On the density dependence of replacement-series competition experiments

Abstract: The sensitivity of replacement-series experiments to variations in density was investigated in Agropyron repens, Phleum pratense and Poa pratensis collected from a hayfield in south-eastern Ontario (...) The results suggested that interpretations from replacement-series experiments are not sensitive to variations in density per se, but to the extent to which the supply of resources exceeds the demands made on them. This may be controlled for by choosing a mixture density (N) such that each component yield (at density N/2) would be at constant final yield if in a monoculture at that density

Seed size and number in Rubus chamaemorus: between-habitat variation, and effects of defoliation and supplemental pollination

Abstract: This study examines the within- and between-population variation in components of yield in R. chamaemorus. Specifically, it addresses the following questions: are there any consistent differences in seed size or total allocation to seeds between populations of open and shaded habitats? Is seed size negatively correlated with yield components like seed number, number of seeds per unit leaf mass, or number of seeds per unit rhizome mass? How do supplemental pollination and defoliation affect seed number and size?

Historical Records of Climate-Related Growth in Cassiope Tetragona from the Arctic

Abstract: (1) Shoots of the circumpolar species Cassiope tetragona were collected on brief visits to three remote arctic and subarctic sites, two in Svalbard and one in Swedish Lapland. The shoots were subsequently analysed by measuring leaf lengths in strict sequence along individual shoots. (2) This evergreen species retained up to 232 leaves per shoot. Leaf lengths, plotted against leaf position on the shoots, revealed two trends: (i) more or less regular waves caused by the alternation of short spring and autumn leaves with long summer leaves, and (ii) an ontogenetic trend represented by a general increase in leaf length with increasing distance between the point of origin of the leaf and the origin of the shoot. (3) The seasonal trend of leaf length was used to delimit annual complements of leaves, of which up to twenty persisted. The number of leaves was counted for each year and the ontogenetic trend of leaf length was removed by statistical methods so that leaf length indices could be calculated and relative lengths compared, both between years within populations and between populations. Three indices of leaf length were derived: maximum, minimum and the total of all leaf length indices for each year. (4) Correlation analysis between the four measures of annual leaf performance showed several similarities between the two Svalbard populations, a few between the low altitude population from Svalbard and that from Swedish Lapland and none between the higher altitude Svalbard population and that from Swedish Lapland. (5) Correlation analysis between annual leaf performance and mean monthly temperature and monthly total precipitation showed that July temperatures and precipitation during May were particularly important for leaf development in the Svalbard populations. July temperatures represent mid-summer conditions during a very short growing season in Svalbard, whereas May is normally the driest month in this region of generally low precipitation. Ambient temperature is usually sub-zero for most of May and precipitation as snow is probably important in protecting the sensitive shoot apices of C. tetragona which lack true buds. (6) In Swedish Lapland, the number of leaves per year was correlated with summer temperatures but only negatively with precipitation which was greater at the Swedish site than in Svalbard. At the Swedish site, therefore, the protection of leaf primordia from frost is probably greater than in Svalbard because of a more persistent snow cover. (7) Correlations between the number of leaves per year and leaf length indices in the previous year, together with correlations between leaf performance and weather conditions in the previous year, were often significant. In general, the same weather variables were correlated with leaf performance as in the within-year comparisons. (8) The correlations between the number of leaves per year and the other measures of leaf performance and weather in the previous year were particularly strong in the Svalbard populations. This demonstrates the preformation of an annual leaf complement by the High Arctic Svalbard populations. This may be an important mechanism to buffer

The seed regeneration dynamics of an emergent salt marsh

Abstract: La dynamique de la phase de regeneration des graines est etudiee pour plusieurs especes d'halophytes d'un marais sale. Pour chacune des especes, le nombre de graines produites, la viabilite des graines, le nombre de graines dans le sol, la germination et la viabilite des plantules sont observes.