Showing papers in "Journal of Ecology in 1986"
3,721 citations
TL;DR: Beattie as discussed by the authors reviewed the natural history of ant-plant interactions, discussed the scientific evidence for the mutualistic nature of these relationships, and reached some conclusions about the ecological and evolutionary processes that mold them.
Abstract: Mutualistic interactions between ants and plants involve rewards offered by plants and services performed by ants in a mutually advantageous relationship. The rewards are principally food and/or nest sites, and ants in turn perform a number of services for plants: they disperse and plant seeds; they protect foliage, buds, and reproductive structures from enemies such as herbivores and seed predators; they fertilize plants with essential nutrients; and they may sometimes function as pollinators. In this book, initially published in 1985, Professor Beattie reviews the fascinating natural history of ant–plant interactions, discusses the scientific evidence for the mutualistic nature of these relationships, and reaches some conclusions about the ecological and evolutionary processes that mold them. This important work explores the natural history, experimental approach, and integration with contemporary evolutionary and ecological literature of the time will appeal to a wide variety of biologists.
749 citations
TL;DR: Two families of assumptions implicit in coevolutionary approaches to the interaction between vertebrate-dispersed plants and their seed vectors are argued to be to blame for their frequent predictive failure.
Abstract: Recent field studies of the interaction between vertebrate-dispersed plants and their seed vectors have often revealed patterns departing significantly from those predicted by earlier coevolutionary approaches. It is argued here that two families of assumptions implicit in these approaches account, in the case of plants at least, for their frequent predictive failure. These assumptions are that (1) the interaction between a plant and its vertebrate dispersal agents takes place in a world where they virtually are the only inhabitants; and (2) plant attributes relevant to the dispersal process effectively undergo measurable evolutionary change within a reasonable time frame in response to changing ecological conditions. It is shown that these two sets of assumptions are not generally supported by available evidence.
466 citations
TL;DR: In this article, a computer model was used to track the consequent changes in the carbon balance of nine wetland regions in the temperate zone of the United States and Europe.
Abstract: (1) Organic soil-wetlands, particularly those in the temperate zone, under natural conditions, are net carbon sinks and hence are important links in the global cycling of carbon dioxide and other atmospheric gases. Human alteration of wetlands has brought about shifts in the balance of carbon movement between the wetlands and the atmosphere. Because previous analyses have not fully considered these shifts, disturbance of carbon storage in organic soil-wetlands of the temperate zone has been analysed for the last two centuries and considered in relation to other sources of atmospheric CO2 from the biosphere. (2) Storage before recent disturbance is estimated as 57 to 83 Mt of carbon per year, over two-thirds of this in boreal peatlands. The total storage rate, lower than previous estimates, reflects accumulation rates of carbon of only 0.20 t ha-' yr-1 and less in the boreal zone where 90% of temperate organic soils are found. (3) Widespread drainage of organic soil-wetlands for agriculture has significantly altered the carbon balance. A computer model was used to track the consequent changes in the carbon balance of nine wetland regions. Drainage reduced or eliminated net carbon sinks, converting some wetlands into net carbon sources. Different regions thus can function as smaller carbon sinks, or as sources, depending on the extent of drainage. In either case a shift in carbon balance can be quantified. (4) The net carbon sink in Finland and the U.S.S.R. has been reduced by 21-33%, in Western European wetlands by nearly 50%, and in Central Europe the sink has been completely lost. Overall, by 1900 the temperate zone sink was reduced 28-38% by agricultural drainage alone. (5) By 1980 the total annual shift in carbon balance attributable to agricultural drainage was 63-85 Mt of carbon, 38% in Finland and U.S.S.R. wetlands, and 37% in Europe. Twenty-five percent of the shift occurred in North American wetlands south of the boreal zone. No apparent change occurred in boreal Canada and Alaskan wetlands. (6) Peat combustion for fuel released 32-39 Mt of carbon annually, nearly all in the U.S.S.R. A total of 590-700 Mt of carbon has been released from peat combustion since 1795, compared with a release of 4140-5600 Mt from agricultural drainage. (7) The aggregate shift in the carbon balance of temperate zone wetlands, when added to a far smaller shift from tropical wetlands, equalled 150-185 Mt of carbon in 1980 and 5711-6480 Mt since 1795. Despite occupying an area equivalent to only 2% of the world's tropical forest, the wetlands have experienced an annual shift in carbon balance 15-18% as great. Wetlands thus are seen on an area-specific basis to be concentrated sources of atmospheric CO2 which respond differently from those ecosystems assumed to have no net carbon exchange before disturbance.
396 citations
393 citations
TL;DR: Nitrogen mineralization did not increase in the crown-fall zone of treefall gaps, although the possibility of a short-lived increase immediately after treefall could not be ruled out and low nutrient availability in the root-throw zone could select for colonizing species distinct from those establishing in other zones of tree fall gaps.
Abstract: SUMMARY (1) Nitrogen availability (net nitrogen mineralization) was extremely high in a lowland rainforest on volcanic soil at La Selva, Costa Rica, averaging 50-80 ug g-1 month-' (822 kg ha-' year-'). Available phosphorus concentrations were relatively low (25 ugg-1). (2) Nitrogen mineralization did not increase in the crown-fall zone of treefall gaps, although the possibility of a short-lived increase immediately after treefall could not be ruled out. Phosphorus concentrations increased slightly but not significantly (to 3.3 ,ug g-1). (3) The root-throw zone of treefall gaps had significantly lower nitrogen mineralization and phosphorus concentrations than the crown-fall zone or the zone along the fallen trunk. Low nutrient availability in the root-throw zone could select for colonizing species distinct from those establishing in other zones of treefall gaps.
314 citations
TL;DR: Field experiments showed that seedlings from larger seeds were favoured over those from smaller seeds during the early stages of growth in a drier, more disturbed, site, and Seed size had no effect on relative survival in a forest habitat.
Abstract: (1) The effects of different environmental conditions on the growth and physiological performance of seedlings derived from different seed sizes were studied in the perennial herb Desmodium paniculatum. (2) The differences in seed weight are due to differences in the amounts of reserve substances. Seedlings from larger seeds produce longer roots than those from smaller seeds and are able to emerge from greater depths of soil. (3) Seed size is positively correlated with cotyledon area and weight, leaf area, root weight and overall seedling dry weight. Seedlings from different-sized seeds have similar relative growth rates and patterns of dry-matter allocation and do not show a differential response to shading. Seedlings from larger seeds respond to nutrient addition to a greater extent than those from smaller seeds. The contribution of epigeal cotyledons to the early growth of seedlings seems to depend more on their storage capacity than on their photosynthetic capacity. (4) Overall carbon gain and water-uptake capacity are proportional to seedling size. With reduced water availability, the advantage of seedlings from large and small seeds depends on whether they are grown singly or in competition. (4) Field experiments showed that seedlings from larger seeds were favoured over those from smaller seeds during the early stages of growth in a drier, more disturbed, site. Seed size had no effect on relative survival in a forest habitat. (6) Variation in seed size, within the range of that produced by a single plant, results in seedlings differing significantly in size and physiological characteristics. Seedlings from larger seeds may have an advantage over those from smaller seeds if both types are grown in competition.
281 citations
TL;DR: The transport of pollen from donor flowers by bumble bees was measured by examining deposition on stigmata of sequences of recipient flowers, and pollen carryover in E. grandiflorum was similar in carryover, but Linaria vulgaris showed much higher carryover.
Abstract: (1) The transport of pollen from donor flowers by bumble bees was measured by examining deposition on stigmata of sequences of recipient flowers. The rate of decay of grain deposition was estimated as a measure of pollen carryover. (2) Bombus bifarius was a much less effective pollinator of Erythronium grandiflorum than was the larger Bombus occidentalis. (3) The numbers of pollen grains deposited by bumble bees on the stigmata of Erythronium americanum vary greatly from flower to flower. (4) The time spent by a bee on a flower is positively related to the nectar concentration and volume. (5) Flowers with large volumes of nectar receive more pollen grains per visit than those with small volumes, presumably because the visits are longer. The results are insufficient to show a parallel increase in deposition with nectar concentration. (6) Measures of pollen carryover are presented. Most deposition of grains from a particular donor flower occurs on the first several recipient flowers subsequently visited by the bee, but a few grains travel much farther. (7) Pollen carryover in E. grandiflorum is reduced by bee grooming. (8) The negative effect of grooming on carryover is increased when the recipient flowers have undehisced anthers. (9) Erythronium americanum and E. grandiflorum were similar in carryover, but Linaria vulgaris showed much higher carryover. The reasons for this are discussed.
281 citations
TL;DR: The relationship between above-ground biomass of Spartina alterniflora and sediment oxidation status (Eh), available ammonium concentration and interstitial salinity was investigated at twenty-one sites in a New England salt marsh as discussed by the authors.
Abstract: (1) The relationship between above-ground biomass of Spartina alterniflora and sediment oxidation status (Eh), available ammonium concentration and interstitial salinity was investigated at twenty-one sites in a New England salt marsh. Sediment Eh gave the best prediction of above-ground biomass. The relationship between sediment oxidation and above-ground production existed between years and marshes. (2) Measurements in nitrogen-fertilized areas indicate that increasing plant production leads to more oxidized sediments. (3) Sediment oxidation in vegetated sediments occurs via air entry, which was found to cause a rapid and significant rise in sediment oxidation potential. Air enters the sediment in response to water removal from the sediment by evapotranspiration in short grass zones and evapotranspiration and drainage on creek banks. (4) The available data on the environmental controls of Spartina growth are used to construct a model consisting of a variety of feedbacks between plant production, available nitrogen, interstitial salinity and sediment oxidation state mediated primarily through the rates and pathways of interstitial water exchange.
TL;DR: Spatial patterns of the mortality of tropical trees were investigated using maps of four species on an 80 x 80-m site of primary rainforest in Costa Rica, and the adults of these three species were significantly more uniformly distributed than expected from the random mortality of their extant juveniles.
Abstract: (1) Spatial patterns of the mortality of tropical trees were investigated using maps of four species on an 80 x 80-m site of primary rainforest in Costa Rica. Using new statistical methodology, designed specifically for complete maps of individuals, models of clustering or uniformity were fitted to different size classes, and the relative uniformity of the different size classes compared. The data for the extant juveniles were then used to predict what the extant adult spatial distribution would be given random mortality of the juveniles. The actual adult distribution was compared to this hypothetical distribution to see if they were more or less uniform than predicted. (2) For three of the four species, the spatial models which fit the adults were more uniform than the models which fit the juveniles. The adults of these three species were significantly more uniformly distributed than expected from the random mortality of their extant juveniles. The fourth species had adults with a similar distribution to randomly thinned extant juveniles. (3) Post-germination survival leads toward a uniform distribution. During the lifespan of three of the four species, repulsion occurs between individuals. At small scales, clumping, when present, may be more the result of patchy dispersal of seeds or seedling germination than the patchy survival of germinated individuals.
TL;DR: Emission factors of Atmospheric Elements (J. M. Pacyna et al. as mentioned in this paper ) measured and measured trace element emissions from Particulate Control Devices (PCDs).
Abstract: Emission Factors of Atmospheric Elements (J. M. Pacyna). Atmospheric Trace Elements from Natural and Anthorpogenic Sources (J. M. Pacyna). Sampling and Measurement of Trace Element Emissions from Particulate Control Devices (A.D. Shendrikar & D. S. Emsor). Smelting Operations and Trace Metals in Air and Precipitation in the Sudbury Basin, (W. H. Chan & M. A. Lusis). Emissions and Air Quality Relationships for Atmospheric Trace Metals (G. R. Cass & G. R. McRae). Quantitative Source Attribution of Metals in the Air Using Receptor Models (P. K. Hopke). Trace Metals in the Atmosphere of Rural and Remote Areas (G. B. Wiersma and C. I. Davidson). Trace Metals in the Arctic Aerosol (N. Z. Heidam). Chemical Elements as Tracers of Pollutant Transport to a Rural Area (L. Husain). Chemical Speciation and Reaction Pathways of Metals in the Atomspere, (R. M. Harrison). Characterization of Trace Metal Compounds in the Atmosphere in Terms of Density (A. Sugimae). The Sizes of Airborne Trace Metal-Containing Particles (C. I. Davidson & J. F. Osborn). Metal Solubility in Atmospheric Deposition (D. F. Gatz & L.-C. Chu). Impact of Atmospheric Inputs on the Hydrospheric Trace Metal Cycle (W. Salomons). Atmospheric Toxic Metals and Metalloids in the Snow and Ice Layers Deposited in Greenland and Antarctica from Prehistoric Times to Present (C. F. Boutron). Monitoring the Atmospheric Depostion of Metals by Use of Bog Vegetation and Peat Profiles (W. A. Glooschenko). Mercury Vapor in the Atmosphere: Three Case Studies on Emission, Deposition, and Plant Uptake (S. E.. Lindberg). Biogeochemical Cycling of Organic Lead Compunds (W. R. A. De Jonghe & F. C. Adams). Airbone Lead in the Environment in France (J. Servant).
TL;DR: Measurements of growth and photosynthesis, and carbon-gain simulations suggest that light conditions along gap edges and within small gaps are ideal for these species.
Abstract: (1) The consequences of light variation for daily carbon gain in three understorey palm species are described. Detailed measurements of photosynthetic photon flux density (PPFD) were made in closed-canopy understorey, gap-edge and gap-centre sites to determine the range of light conditions. Based on these results and the responses of seedlings grown in full shade, computer simulations were used to compute total daily leaf carbon gain. (2) Median daily total PPFD in gap-edge habitats was 1-1.5 mol m-2, compared with 0.26-0-33 mol m-2 in adjacent understorey sites. Median daily PPFD in the gap centre increased with gap size. In the understorey, more than 80% of averages calculated for 5-min periods were below 10 ,umol m-2 S-1, whereas most readings in the centre of a 150-M2 gap were between 50-100 ,umol m-2 s-1 and along the gap edge 20-50 ,umol m-2 s(3) For Asterogyne martiana and Geonoma cuneata, two dwarf species, median daily total PPFD did not increase from ground level to 1-5 m. Fifty per cent of all PPFD measurements below 1-5 m were between 0 -18-0-39 mol m-2. At crown heights above 1.5 m, median daily total PPFD increased to 0.51 mol m-2. Within clones of G. congesta, daily total PPFD increased significantly with crown height; median PPFD incident on crowns 3-5-4-0 m tall was five times greater than PPFD at heights below 1.4 m. (4) On sunny days, the proportion of daily total PPFD contributed by sunflecks ranged from 10% to 78%. The relative proportion of daily PPFD contributed by sunflecks increased as the PPFD of background diffuse radiation decreased. (5) Photosynthesis of seedlings grown in full shade did not differ significantly among the three species. Light compensation points of full-shade-grown plants were between 3-4 ,umol m-2 s-1, and light-saturated photosynthetic rates measured as CO2 uptake were between 3 and 4 ,umol m-2 s-1. Light saturation occurred between 200 and 400,umol m-2 s(6) Carbon gain simulations of full-shade-grown seedlings indicate that a positive carbon gain over 24 h occurs at PPFD greater than 0.20 mol m-2. When most of the total daily PPFD was in the form of diffuse radiation, total daily carbon gain was linearly related to total daily PPFD. Daily carbon gain was not a simple function of daily total PPFD when sunflecks contributed more than 50% of the total quantum flux. On days with sunny periods, the proportion of total daily carbon gain during sunflecks ranged from 15% to 60%. (7) Seedlings of the three species grown in the gap edge had higher rates of leaf production, were taller and had larger leaves than seedlings grown in a closed-canopy understorey site. Measurements of growth and photosynthesis, and carbon-gain simulations suggest that light conditions along gap edges and within small gaps are ideal for these species.
TL;DR: Algae as ecological indicators, Algae as ecology indicators, and algae as ecological indicator .
Abstract: Algae as ecological indicators , Algae as ecological indicators , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی
TL;DR: It is concluded that most previous studies have taken far too few soil samples and buried seeds of Danthonia and, to a lesser extent, of Agrostis were significantly clumped.
Abstract: (1) Density of germinable seeds has been determined in each of 128 blocks of surface soil each 7 cm x 7 cm, together forming a 112 cm x 56 cm rectangle, taken from an acidic grassland on Dartmoor, Devon. (2) Agrostis capillaris and Danthonia decumbens were the major species in the seed bank. Agrostis was also common in the vegetation but Danthonia was absent. Festuca ovina was frequent in the vegetation but absent from the seed bank. (3) Buried seeds of Danthonia and, to a lesser extent, of Agrostis were significantly clumped. The implications of this for the practical sampling of seed banks are discussed and it is concluded that most previous studies have taken far too few soil samples. Possible reasons for the clumping of Agrostis and Danthonia are discussed.
TL;DR: The rate of increase in leaf weight per unit of surface area was relatively constant among the three species compared, and it is speculated that this variable may serve as a useful characterization of canopies at particular sites.
Abstract: SUMMARY (1) The structural properties of the canopy of a mature stand of oak-hickory (mixed species, uneven-aged, deciduous) forest in eastern Tennessee, U.S.A., were measured along randomly-located vertical transects by a variety of techniques. (2) The overall distribution of the leaf-inclination angles was plagiophile although the leaf-angle distributions in canopy strata below the zone where crowns meet to close the canopy (15-17 m above the floor) were planophile. The woody-biomass inclination-angle distribution was erectophile. The mean, area-weighted, leaf-inclination angle for the whole canopy was 330 to the horizontal; however, substantial differences existed among the major canopy strata. In the overstorey above the zone of closure, it was 380; in the overstorey below crown closure, it was 200; and in the sub-canopy, 100. (3) The greatest leaf-area density was in the overstorey canopy where the (one-sided) leaf-area index (L) was over 3.5. The lower canopy strata contributed slightly over one additional unit, yielding a total L of about 4.9 for the stand. The silhouette-area index of woody biomass was about 0.6. Thus, the total plant-area index of this forest was about 5.5. (4) The mean area of individual leaves increased from the forest floor to midcanopy and decreased in the upper canopy. Generally, the mean dry weight of leaves increased with height, although some decline was observed in the uppermost portion of the canopy. The increase with height in mean leaf dry weight per unit of surface area was much more uniform than that of mean leaf dry weight. Because the rate of increase in leaf weight per unit of surface area was relatively constant among the three species compared, we speculate that this variable may serve as a useful characterization of canopies at particular sites.
TL;DR: In a population of Desmodium paniculatum, increase in temperature during the growth of the plants, reduces nutrient and water availability, and shortening of the photoperiod decreases the mean seed weight, while a 50% reduction in total leaf area during seed development increasesmean seed weight of plants grown at high temperatures.
Abstract: SUMMARY (1) In a population of Desmodium paniculatum seed weight varies by a factor of about four. Increase in temperature during the growth of the plants, reduces nutrient and water availability, and shortening of the photoperiod decreases the mean seed weight. A 50% reduction (to mimic grazing loss) in total leaf area during seed development increases mean seed weight of plants grown at high temperatures. (2) Seed size varies significantly among individual plants, but there is no correlation between mean seed weight per plant and total numbers of seeds produced per plant. Within a plant, seed size may vary by as much as a factor of two if grown under highnutrient supply, but this variability is significantly reduced if plants are grown with limited nutrients. Part of the within-plant variability is due to the production of fruits with a variable number of seeds and to the position of the seed within a fruit. Seedlings from different positions within the fruit have different probabilities of survival. (3) In plants grown with low (but not with high) nutrients, parental seed sizes are positively correlated with offspring seed sizes. Seed size may thus affect the subsequent generation.
TL;DR: It is suggested that the control of relative abundance in chalk grassland involves steady-state relationships: (i) between species with taller (and more widely-spreading) and shorter individuals and (ii) between Species with longer- and shorter-lived individuals.
Abstract: SUMMARY (1) A study of the relative abundance of perennial species in chalk grassland in southern England revealed great constancy (P < 0.001) in rank order: (a) across any one site (twenty stands of 0-48 m2 in an area of 3480 m2), (b) from year to year (1980-82) and (c) between two sites 150 km apart. Comparison of these records with transformed data from phytosociological accounts in the literature provides evidence of high constancy of rank order over much larger areas and longer periods. Ancient chalk grassland is thus an ideal community for investigation of the mechanisms determining the relative abundance of species. (2) Two experiments were carried out to determine the extent to which the order of relative abundance may be explained by short-term (1-2 years) ability to interfere with growth of plants of other species in the vegetative phase. (3) In an outdoor pot experiment, fourteen dicotyledons were grown in monocultures and in mixtures with one or two standard species (a grass and a dicotyledon). After 18 weeks there was a significant positive correlation between interference ability in the experiment and mean relative abundance in the field. Essentially, the same results were found after 70 weeks. (4) In a field experiment, six dicotyledons were grown in monocultures, and in all possible mixtures of two species, in plots on an area of chalk grassland cleared of turf. After 62 weeks, the order in interference effects paralleled the order of relative abundance in the grassland. There was also a positive correlation between interference ability and the mean height of rosette leaves of each species. This suggests the importance of aboveground interference. (5) After 115 weeks, and for 3 years afterwards, additional elements of the perennial life-history became important in determining performance in the plots, especially longevity of adult individuals, degree of lateral spread and the frequency of establishment of seedlings. (6) We suggest that the control of relative abundance in chalk grassland involves steady-state relationships: (i) between species with taller (and more widely-spreading) and shorter individuals and (ii) between species with longer- and shorter-lived individuals.
TL;DR: The effects of seed size on reproductive performance were studied in plants of Desmodium paniculatum grown singly and in competition and plants derived from larger seeds, when grown in competition with those from smaller seeds showed a higher total reproductive yield.
Abstract: (1) The effects of seed size on reproductive performance were studied in plants of Desmodium paniculatum grown singly and in competition. (2) For plants grown singly, seed size had no effect on the date of flowering or on the weight of seeds produced, but plants from smaller seeds produced more seeds than those from larger seeds. Growth at high densities delayed flowering and reduced seed number without affecting seed weight. Plants derived from smaller seeds flowered later than those derived from larger seeds. (3) If grown in pure stands, plants from smaller seeds attained a higher dry weight at maturity than those from larger seeds. Initial seed size had no effect on sizes or numbers of seeds produced. (4) Plants derived from larger seeds, when grown in competition with those from smaller seeds, showed a higher total reproductive yield.
TL;DR: Changes in species composition, live standing crop and plant litter have been measured in a salt marsh at La Perouse Bay, Manitoba in the presence of a grazer and when the grazer is excluded.
Abstract: SUMMARY (1) Changes in species composition, live standing crop and plant litter have been measured in a salt marsh at La Perouse Bay, Manitoba in the presence of a grazer (the lesser snow goose, Anser caerulescens caerulescens) and when the grazer is excluded. (2) The composition of vegetation in exclosures (5 m x 5 m) changed rapidly. After five years sixteen species of higher plants were present in the oldest exclosure compared with six species in an adjacent (control) grazed area. Dicotyledons, such as Potentilla egedii and Plantago maritima, increased in frequency in the absence of grazing, and Carex subspathacea replaced Puccinellia phryganodes as the dominant graminoid. (3) New species, which appeared in the exclosure, were present in ungrazed areas elsewhere in the marsh. However, the frequency of these species in the exclosures was different from that in ungrazed areas. (4) The grazer is a generalist in its selection of forage species. The removal of geese leads to extensive clonal growth of species, such as Potentilla egedii, which are unable to tolerate heavy grazing and trampling, unlike Carex and Puccinellia. (5) Within a season the standing crop of vegetation was highest in exclosures erected one or two years previously. Litter accumulated in exclosures. The ratio of maximum standing crop to litter fell from >4: 1 to <2: 1 as communities aged in the absence of grazing. (6) Cessation of grazing leads to rapid changes in the structure and composition of the community. The vegetation within an exclosure was poorly grazed when the fence was removed after two years.
TL;DR: The combination of approaches enabled several features of organic matter and nutrient dynamics in the forest floor, which would not be apparent using any of the methods in isolation, to be deduced.
Abstract: SUMMARY (1) The dynamics of organic matter and nutrient elements in the forest floor of Pinus contorta spp. latifolia (lodgepole pine) forests in Wyoming, U.S.A., were investigated by combining three related measurements: leaching of the forest floor; long-term decay of leaf litter; and steady-state residence times in the forest floor. (2) Elemental fluxes (g m-2 yr-1) resulting from leaching by spring snowmelt were: Ca = 135, Mg = 0.30, K = 0*65, N = 0-46, P = 0.022 and C = 8.3. Over 95% of the N flux was in organic forms. (3) Most of the organic compounds were acidic, and anions of these organic acids were the principal mobile species accompanying cation flux; smaller, but important, contributions were S04 and HCO3. The chemical nature of the dissolved organic compounds changed as snowmelt proceeded, with polyphenolics and carbohydrates (leached from fresh litter) being important in the early stages, and polymeric acid compounds (fulvic and humic acids) dominating in the later stages. (4) About 35% of the original mass of leaf litter remained after 84-96 months. Potassium and magnesium were lost rapidly from leaf litter, whereas there was temporary immobilization of Ca. Nitrogen accumulated in decaying leaves for 72 months, reaching 180% of the original content before net mineralization and release occurred. Relatively small changes in P content of leaf litter were noted during the decay process. The loss of soluble organic constituents (polyphenols, carbohydrates, lipids) was more rapid than for solid residues (holocellulose, lignin). (5) The combination of approaches enabled several features of organic matter and nutrient dynamics in the forest floor, which would not be apparent using any of the methods in isolation, to be deduced: (i) about 30% of annual C release from the forest floor resulted from leaching of organic compounds; (ii) over 20% of the leaching flux for Ca and Mg was attributed to release from 01 litter, compared with less than 10% for K; (iii) high amounts of organic-N leaching from forest-floor layers, combined with rapid accumulation in 0- to 8-year-old litter, indicated rapid translocation of N from subsurface layers to 01 litter via heterotrophs; and (iv) leaching of polyphenols from the forest floor was 50% lower than the apparent loss from 01 litter, suggesting chemical transformation and changes in solubility of these compounds during litter decay. An association of this phenomenon with protein accumulation observed in the 02 horizon is postulated.
TL;DR: Acorus calamus, Alisma plantago-aquatica, Bidens cernua, B. vulgata, Cyperus aristatus, Lythrum salicaria, Polygonum punctatum, Sagittaria latifolia, Scirpus americanus, Typha angustifolia
Abstract: Acorus calamus, Alisma plantago-aquatica, Bidens cernua, B. vulgata, Cyperus aristatus, Lythrum salicaria, Polygonum punctatum, Sagittaria latifolia, Scirpus americanus, Typha angustifolia
TL;DR: A study of the gradual destruction of Uganda's extensive forest is presented in this paper, where the author traces the process and analyzes its causes from the first introduction of agriculture to the appropriation of national forest reserves by private individuals in the Amin years.
Abstract: A study of the gradual destruction of Uganda's extensive forest. The author traces the process and analyzes its causes from the first introduction of agriculture to the appropriation of national forest reserves by private individuals in the Amin years. He documents the developments that have turned Karamoja from a well-wooded land into one of the world's most disastrous famine areas, and reduced the forest cover and wildlife habitat to a mere fraction of its former extent.
TL;DR: Seasonal patterns of carbohydrate, lipid, cellulose, hemicellulose and lignin were examined in plants of major tundra growth forms: deciduous shrub, evergreen shrubs, decidulent forb, tussock graminoid, moss and lichen to suggest characteristics of the plant material exert primary control over patterns of food choice by these generalist herbivores.
Abstract: SUMMARY (1) The seasonal patterns of carbohydrate, lipid, cellulose, hemicellulose and lignin were examined in plants of major tundra growth forms: deciduous shrub, evergreen shrub, deciduous forb, tussock graminoid, moss and lichen. (2) Stems of deciduous shrubs (Salix pulchra and Betula nana) and forb (Rubus chamaemorus) showed well-developed over-winter carbohydrate storage, with concentrations increasing in autumn and declining in spring, coincident with initiation of leaf and root growth. The evergreen shrub (Ledum palustre) showed little seasonal fluctuation in carbohydrates of stems and old leaves. The graminoid (Eriophorum vaginatum), which had an intermediate amount of over-wintering green leaf biomass, showed seasonal carbohydrate fluctuations in stems intermediate between those of evergreen and deciduous shrubs. Among mosses, Aulacomnium spp. showed greater seasonal fluctuation in carbohydrate concentration of brown material than did Polytrichum! Pogonatum spp. The chemical procedure designed and used here for vascular plants gave ambiguous results for lichens. (3) Ether-extractable lipid in stems of Salix, Rubus and Eriophorum was low and showed no consistent seasonal pattern among different categories of stems, suggesting that it was not a major over-winter energy store in these species. Stems of Betula had higher lipid contents than did other deciduous species, but lipid declined from mid-summer to autumn and was therefore unlikely to be a major over-winter energy store. Lipid showed little seasonal fluctuation in Ledum. In brown tissue of mosses it declined in summer and increased in autumn. (4) Cellulose content generally increased with age in leaves and stems of most species, reflecting its structural role. (5) Hemicellulose content was higher in graminoids than in other growth forms and fluctuated substantially through the growing season in a pattern suggesting that it acts as an energy store. The large 'hemicellulose' fraction of lichens probably included particular lichen polysaccharides. (6) Of the plants examined, mosses had the highest concentrations of lignin-like materials, and Eriophorum and lichens were lowest in lignin. Lignin content was similar in stems of all dicotyledonous species examined and bore no clear relation to woodiness. (7) Chemical composition of all study species was compared with the preferences for them of herbivores studied at the same site. Preferences of each of eight generalist herbivores (vertebrate and invertebrate) for the study species correlated positively with nitrogen, phosphorus and potassium and negatively with lipid and cellulose contents. The similarity of preference ranking among generalist herbivores suggests that characteristics of the plant material (rather than animal digestive physiology) exert primary control over patterns of food choice by these generalist herbivores. Preference ranking of Lemmus (brown lemming), a specialist on graminoids and mosses, correlated postively with fibre and negatively with mineral nutrient contents.