Distribution and ecology of dictyostelid cellular slime molds in Great Smoky Mountains National Park

Great Smoky Mountains National Park encompasses an area of 2080 km2 in eastern Tennessee and western North Carolina between 35 degrees 28' and 35 degrees 47' N. Elevations are 270-2000 m above sea level, and the topography and vegetation are as diverse as any region of eastern North America. In 1998-2004 soil/litter samples for isolation of dictyostelid cellular slime molds were collected throughout the park. Collecting sites included examples of all major forest types along with the more common types of nonforest vegetation. More than 2300 clones of dictyostelids were recovered from 412 samples. These clones included representatives of 20 described species together with at least 10 species new to science. This total is higher than those reported for other temperate regions of the world. In general both numbers of species and numbers of clones/g of sample material decreased with increasing elevation and several species displayed a distinct preference for either the low or high end of the elevation gradient. The relatively high number of new species recovered from samples collected at high elevations is an important new finding for dictyostelid ecology and distribution.     

Recovery of pristine boreal forest floor community after selective removal of understorey, ground and humus layers

In boreal spruce forests that rarely experience extensive disturbances, fine-scale vegetation gaps are important for succession dynamics and species diversity. We examined the community implications of fine-scale gap disturbances by selective removal of vegetation layers in a pristine boreal spruce forest in Northern Finland. The aim was to investigate how the speed of recovery depends on the type of disturbance and the species growth form. We also wanted to know if there appeared changes in species composition after disturbance. Five different treatments were applied in the study: Control, removal of the ground layer (bryophytes and lichens), removal of the understorey layer (dwarf shrubs, herbs and graminoids), removal of both the ground and understorey layers, and complete removal of the vegetation and humus layers above the mineral soil. The vegetation recovery was monitored in terms of cover and species numbers over a 5-year period. Understorey layer cover, composed mainly of clonal dwarf shrubs, recovered completely in 4 years in treatments where the humus layer remained intact, whereas ground layer cover did not reach the control level in plots from where bryophytes and lichens were removed. Recovery was faster in terms of species number than species cover. Bryophytes, graminoids and dominant dwarf shrubs appeared in all disturbed plots quickly after disturbance. Seedlings of trees appeared exclusively in disturbed plots. Graminoids dominated after the removal of humus layer. The results indicate that the regeneration of forest floor after small gap disturbance occurs mainly by re-establishment of the dominant species. Although destruction of the humus layer leaves a long-lasting scar to the forest floor, exposing of mineral soil may enhance the sexual reproduction of dominant species and the colonization of weaker competitors.     

Seasonal fluctuations in butterflies and nectar resources in a semi-natural grassland near Mt. Fuji, central Japan

We investigated seasonal fluctuation patterns in species and individuals of adult butterflies and flowering plants providing nectar in a semi-natural grassland in central Japan. We considered their interrelationships and implications for conservation. The semi-natural grassland included different vegetation structures and management regimes, including: (1) firebreaks where the grass was mowed and removed, (2) plantation areas that were mowed, (3) unpaved roads with mowed banks, (4) abandoned grassland, (5) scattered scrub forest, and (6) the surrounding forest. The sites with management (e.g., firebreaks), plantations and banks of the unpaved road sustained a larger number of butterflies and flowers than sites without management, such as the abandoned grassland, scrub forest and surrounding forest. The number of butterflies increased in the firebreak in June and at all sites in August and September. The firebreak sustained flowers in the spring, and the plantation area and banks of the unpaved road sustained flowers primarily in August and September, which was correlated with the distribution of butterflies. The different treatments such as mowing or mowing with removal of grass induced different numbers of flowers of each species affecting the habitat of adult butterflies through a season. On the other hand, the shrub tree species composing the scrub forest were host plants for the larvae of certain butterfly species. Our results suggest that heterogeneous environments with different human management or different vegetation structure or both could support habitat for various butterfly species, depending on the season and the seral stage.     

Subsistence strategies of two "savanna" chimpanzee populations: the stable isotope evidence.

Twenty-two chimpanzee hair samples collected from night nests at two different "savanna" sites were analyzed for carbon and nitrogen stable isotope ratios represented as delta13C and delta15N values. The first at Ugalla, Tanzania is a miombo woodland with grass groundcover and small patches of forest. The second at Ishasha, Democratic Republic of the Congo is a habitat composed of riverine gallery forest, semideciduous thicket forest, wooded grassland, and grassland. Based on comparative data from other primates, Ugalla hair delta13C values suggest that the chimpanzees are feeding primarily in the woodland rather than in forest patches or on grassland foods (grasses or grammivorous fauna). Similar comparisons indicate that the Ishasha chimpanzees are feeding within the forests and not in more open areas. In addition, the Ugalla chimpanzees had delta15N values that indicate extensive ingestion of leguminous flowers, seeds, and/or leaves. The Ishasha samples show a range encompassing three trophic levels. Two samples with the most positive values may indicate a nursing signal or vertebrate-feeding. Three individuals with intermediate values are similar to those in omnivorous nonhuman primate species. The four individuals with the lowest values are very similar to those in herbivorous monkeys. Stable isotope ratios permit time-averaged and habitat-specific dietary comparisons among sites, even without habituation or detailed foraging observations.     

Humus bacteria of Norway spruce stands: plant growth promoting properties and birch, red fescue and alder colonizing capacity

We studied the potential of the humus layer of the Norway spruce stands to supply beneficial rhizobacteria to birch (Betula pendula), alder (Alnus incana) and fescue grass (Festuca rubra), representatives of pioneer vegetation after clear-cutting of the coniferous forest. Axenically grown seedlings of these species were inoculated with the acid spruce humus, pH 3.7-5.3. Actinorhizal propagules, capable of nodulating alder, were present in high density (10(3) g(-1)) in humus of long-term limed plots, whereas plots with nitrogen fertilization contained almost none (相似文献   

Regional differences in floristic change in South Swedish oak forests as related to soil chemistry and land use

Abstract. Changes of the ground layer vegetation between 1983 and 1993 were studied on permanent oak forest plots in Skåne and eastern Småland, two regions of South Sweden rich in oak but with different climatic conditions. 79 of the 123 more common species differed considerably in frequency between Skåne and Småland. The oak forests in Skåne contained more typical forest species, whereas the number of light-demanding grassland species was higher in Småland. Almost half of the more common species showed significant changes in frequency between 1983 and 1993. Several species of clearings and some light-demanding grassland species increased their frequency in Skåne. They were probably favoured by canopy thinning which occurred in 65 out of 95 permanent plots. Only two species decreased in frequency in Skåne, but 14 species showed a decrease in Småland. All were typical grassland species and their decline may be regarded as a long-term response to ceased grazing and tree canopy closure as almost no tree cutting occurred during the study period in Småland. Total species richness increased with management intensity in Skåne. This was due to decreasing species losses and increasing establishment of new species at intense management. A small general increase in species numbers was recorded in Småland. Species richness was more closely related to soil pH in Skåne than in Småland. The floristic variability between the oak forest plots was closely related to soil pH in both Skåne and Småland. We suggest that changes of light conditions as a result of changes in forest management are important for current secondary succession in South Swedish oak forests, whereas the general floristic pattern is to a large extent controlled by soil acidity.     

Effects of microenvironment on net photosynthetic rate and growth of four tropical species in the La Mesa watershed

Seedlings of four tree species (Bischofia javanica, Dracontomelon dao, Erythrina orientalis, and Pterocarpus indicus) were planted in flat and sloping grassland in plantation sites established in May 2002 in the La Mesa watershed, Philippines. Tree growth and net photosynthetic rate (P _N) were monitored. The height, diameter at the root collar, and P _N of the four species grown in the sloping grass site were larger than those of seedlings grown in the flat grass site. In addition, soil moisture contents in the sloping grass site were higher than those of the flat grass site. Growth of the four species was probably strongly associated with microenvironments (e.g. air temperature) in both tested sites.     

Floristic composition, environmental variation and species distribution patterns in burned grassland in southern Brazil.

In regularly burned grassland on Morro Santana, Porto Alegre, RS, Brazil, we investigated differences in the floristic composition and their relation to soil properties, aspect and distance from the forest border. In 48 plots of 0.75 m2, we identified a total of 201 species from a local species pool of approximately 450 to 500 species. Most species occurred in low frequencies, showing clumpy distribution patterns in the studied area. Multivariate analysis showed that plots close to the forest edge clearly differed from plots in the open grassland concerning composition and structure. Plots exposed to the north differed from plots on the top of the hill both in the composition of species as well as in soil variables, mainly due to shallower soil in the former. No strong relation between soil properties and variation in vegetation composition could be detected at a finer scale. The studied grassland, as all grassland vegetation in southern Brazil, is very rich in species compared to other grassland formations worldwide. However, this high biodiversity and conservational value of Campos vegetation in general has so far not been recognized properly. Disturbance is essential to maintain this open vegetation type and its species richness. Fire should be considered as a management option in the absence of grazing.     

Ecology of Lantana camara: An invasive plant species in Amurum Forest Reserve,Jos Plateau,Central Nigeria

Lantana camara (Lantana) is an invasive species of South American origin, and it is visibly widespread in Amurum Forest Reserve (AFR) Jos-Plateau, central Nigeria. Presently, there is no baseline study on Lantana and its spread despite its conspicuous presence within AFR. This is the first study to investigate its abundance and interactions with native fauna and flora in AFR. Established study plots were used to estimate its relative abundance in three habitat types (gallery forest, savannah woodland and rocky outcrops) and to investigate its effect on plants. An experiment using cowpea-tested allelopathic effects of Lantana and focal observation/beating tray method was used to collect data on vertebrate and invertebrate species utilising/interacting with Lantana. Lantana is widespread within AFR occupying 77% of plots with the gallery forest habitat having the highest abundance compared with the savannah woodland and rocky outcrop. Plots with Lantana had fewer woody plant species than plots without Lantana. Tests on soil samples from the reserve for basic properties revealed that Lantana-infested sites had relatively poor soils compared with non-Lantana-infested sites. Birds and insects in AFR utilise Lantana and are probably responsible for its spread. Control measures are necessary to limit its spread and mitigate its likely negative effect on plant species.     

Plant Functional Types of Woody Species Related to Fire Disturbance in Forest–Grassland Ecotones

The study of plant functional types (PFTs) has been widely emphasized when analysing plant community changes in relation to variations in climate and disturbance regime. In this study, we search for PFTs of woody species near forest–grassland boundaries in South Brazil where, due to climate, forests tend to expand over grassland but are being restricted by frequent fires. We aimed at answering the questions: (i) which plant functional types of forest woody species can establish in adjacent grassland subject to fire disturbance and (ii) which plant functional types of forest and grassland woody species are related to short-term community dynamics in frequently burned grassland. Traits were assessed in woody plants in 156 plots (6.75 m²) arranged in 12 transects across forest–grassland boundaries with different fire history in their grassland part. The analysis used a recursive algorithm to search for traits and PFTs maximally associated to spatial distance from forest limit in one analysis, and elapsed time since last fire in another. As a result, nine PFTs of forest woody species were identified that best described community patterns associated to distance from forest. Resprouting ability characterized forest plants able to colonize grasslands. PFT diversity was higher in border plots than inside forest or grassland. Four PFTs of forest and grassland woody species best described woody species community patterns in the grassland associated to elapsed time since fire. Taller individuals of single-stemmed shrubs predominated in late post-fire recovery (3–4 years), while shorter multi-stemmed shrubs in recently burned areas (3 months to 1 year). PFTs of forest trees occurred in border plots or, as established adults, in grassland, remaining unaffected by fire. We conclude that easily measurable structural plant traits, such as those used in our study, are sufficient to evaluate post-fire community dynamics. Forest PFTs in burned grassland are restricted to those with resprouting ability to survive recurrent fire events. Establishment success is highest on protected sites with lesser or low-intensity fire.     

Carbon and water relations of juvenile Quercus species in tall‐grass prairie

Abstract. In ecosystems where environments are extreme, such as deserts, adult plant species may facilitate the establishment and growth of seedlings and juveniles. Because high temperatures and evaporative demand characterize tall‐grass prairies of the central United States (relative to forests), we predicted that the grassland‐forest ecotone, by minimizing temperature extremes and moderating water stress, may function to facilitate the expansion of Quercus species into undisturbed tall‐grass prairie. We assessed the carbon and water relations of juvenile Quercus macrocarpa and Q. muhlenbergii, the dominant tree species in gallery forests of northeast Kansas, in ecotone and prairie sites. To evaluate the potentially competitive effects of neighboring herbaceous biomass on these oaks, juveniles (< 0.5 m tall) of both species also were subjected to either: (1) removal of surrounding above‐ground herbaceous biomass, or (2) control (prairie community intact) treatments. Herbaceous biomass removal had no significant effect on gas exchange or water relations in these oak species in either the prairie or the ecotone environment. Although the ecotone did alleviate some environmental extremes, photosynthetic rates and stomatal conductance were ca. 20 % higher (p < 0.05) in both oaks in prairie sites vs. the ecotone. Moreover, although leaf temperatures on average were higher in oaks in the prairie, high leaf temperatures in the ecotone had a greater negative effect on photosynthesis. These data suggest that the grassland‐forest ecotone did not facilitate the growth of Quercus juveniles expanding into this grassland. Moreover, the carbon and water relations of juvenile oaks in the prairie appeared to be unaffected by the presence of the dominant C₄ grasses.     

人工埋藏植物种子对鼠类采食下辽东栎坚果存活及萌发率的影响

辽东栎林（Q. liaotungensis)是北京东灵山地区典型地带植被。过去研究表明,鼠类对辽东栎更新有很大影响。本研究主要调查3个问题：（1）采食辽东栎坚果的鼠类种类;（2）将坚果埋藏于土中能否减少鼠类对坚果的采食,并提高出苗率？（3）地表植被是否影响辽东栎的出苗率？1996年9月在北京东灵山地区山地选取5个类型的样地37块,每样地在地表放置10粒坚果,检查地表种子消失率。使用木板夹来调查采食坚果的鼠类种类,诱饵分别为坚果和花生米。于1997年10月,选取5块样地,间隔25 m,每样地在1m²范围内埋50粒坚果,深度5 cm,次年5月调查出苗情况。研究结果表明,大林姬鼠、社鼠和黑线姬鼠为取食坚果的主要种类,取食比例与其丰富度有关。370粒坚果放在地表后,1d、10d、20d的消失率分别达15.1%、78.1%、和 100%。250粒坚果埋入土层后,出苗率达11.2%,苗平均高度为7.8cm,出苗率与地表植被盖度有一定负相关。本研究认为,人工埋藏植物种子可以减少鼠类捕食坚果,并能增加其出苗率。     

The seed bank in an estonian calcareous grassland: Comparison of different successional stages

Seed bank species-composition and seed-density were determined in a successional calcareous (alvar) grassland in western Estonia. Three similar study areas were chosen to compare two different successional stages: open alvar grassland and overgrown areas with young pine forest 30 to 40 years old. In both successional stages, the centre and the edge of a relatively uniform stand were examined. Fifteen soil samples (7 cm in diameter, 5 cm deep) were taken from each of twelve sampling sites. The seedling emergence method was used to estimate seeds in the soil samples. A total of 69 species were detected in the seed bank, of which 18 did not occur in the vegetation. Eighty-nine taxa were recorded in the vegetation and of these 38 were not detected in the seed bank. Fifty-one species occurred both in the seed bank and in the vegetation. The three most abundant taxa in the seed bank wereCarex tomentosa, Linum catharticum andPlantago media, which together made up 49% of the seedlings recorded. Differences in the species compositions of seed bank samples from grassland and forest sites were negligible, although the species richness per area of the above-ground vegetation was significantly higher in the open grassland. The only species tending to be lost from forest site vegetation but still occurring in the forest soil seed bank wereArenaria serpylifolia, Cerastium fontanum andLinum catharticum. About half of all the emerged species from all samples belonged to the transient or short-term persistent seed bank. In the grassland sites there were more species which belonged to the transient seed bank than in the forest sites, where the seed bank contained more short-term persistent type seeds. The seed density was significantly higher in forest sites and lower in grassland sites, which may be explained by the better germination conditions in well-illuminated communities. On the basis of the current study it might be assumed that the soil seed banks of overgrown alvar grasslands which include young pine forests can play a certain role in grassland restoration management.     

Secondary Succession in Two South-eastern Ontario Old-fields

Secondary succession was documented throughout a long-term study of two abandoned hay fields in south-eastern Ontario. In one field (Field 1), eighteen plots (measuring 100 m²) were established. Nine of these plots were ploughed to bare ground and nine remained in their original abandoned state. A third set of nine plots were established in a second field (Field 2), which had been abandoned 5 years earlier. Detailed surveys of the plant flora were conducted twice yearly, insect sweep data were collected bi-monthly, from 1976 – 1988, 1995 and 1998. Soil and climate data were collected and community patterns analyzed against these variables and field treatment (ploughing). While the vegetation in all plots began predominantly as a grass mixture, only a few exhibited the typical secondary succession pathway for this region. The remaining plots persist at various stages of succession, with some still in the early stages. Succession stage, as quantified by a succession ratio, varied across these plots largely by soil moisture, and to a lesser degree by field treatment (ploughing). When grouped by soil moisture, wet plots had lower ratios (characterized by later species and trees), than dry plots (characterized by early or grass species). Species richness was highest in plots that were wet, regardless of field treatment. Partial CC analysis using CANOCO of plant species versus field treatment, soil moisture and insect outbreak determined their contribution to the plant variation observed. It is generally accepted that plots over time, regardless of initial composition, will converge to become similar. Convergence of our plots, grouped according to soil moisture, did not occur. Analyses of insect outbreaks against changes in the succession ratio over time provide some evidence that herbivory can influence the likelihood of plots to converge.     

Factors Limiting the Survival of Native Tree Seedlings Used in Conservation Efforts at the Edges of Forest Fragments in Upland Madagascar

We tested four reforestation techniques in tropical forest fragments that were damaged by fire in upland Madagascar. We conducted a full‐factorial experiment on the survival of transplanted seedlings of five native tree species in grassland plots adjacent to the forest fragments in the Ambohitantely Forest Reserve. The species studied were Dodonaea madagascariensis, Filicium decipiens, Olea lancea, Podocarpus madagascariensis, and Rhus taratana. A total of 480 seedlings were planted; 207 survived the 15 months of the experiment. The factors examined were distance of the reforestation plots from the forest, mixing of forest soil into the plots, application of chemical fertilizers, experimental shading of plots, and the cover of naturally establishing shrubs. Both increasing the distance of plots from the forest edge and adding chemical fertilizers significantly reduced the survival of all seedlings. The surprising negative effects of fertilization may be partly due to increased competition from naturally establishing shrubs that are adapted to exploit high nitrogen levels. Mixing soil from the forest areas into the plots did not change seedling survival. Shading reduced the survival of D. madagascariensis seedlings and did not increase the survival of any species. These findings suggest that the success of reforestation projects can be increased by planting seedlings close to the existing forest fragments. Reforestation of similar tropical forests is likely to be more successful if efforts are focused on expanding the size of existing fragments of tropical forest, rather than on establishing new fragments in grassland openings.     

Influence of tree species composition on soil and soil solution properties in two mixed spruce-beech stands with contrasting history in Southern Germany

The properties of the soil and soil solution of two mixed spruce-beech forests in Southern Germany were investigated in order to identify non-additive effects of tree species compared to the monocultures. At five subplots in each of the two monocultures and at 10 subplots in each of the two mixed stands humus morphology, topsoil acidity as well as nitrate and sulphate concentrations in seepage water below the rooting zone were measured. At the Höglwald site, an 8×8 m sampling grid was also installed. Tree species composition within a 10 m circle surrounding each sampling point was correlated with the soil properties and the soil solution properties using the method of breakpoint estimation as well as a linear and a cubic model. At both sites, thickness and acidity of the forest floor as well as sulphate and nitrate concentrations in seepage water were significantly higher in the spruce monocultures than in the beech monocultures. Non-linear patterns in the correlation between both the thickness and the acidity of the forest floor and tree species composition occurred at both sites. In addition, nitrate concentration in the seepage water showed a non-linear correlation pattern at the Höglwald site. The correlation patterns were site specific and depended on stand history. While the influence of spruce at the Höglwald site was greater than expected from spruce monocultures, the opposite was found at the Schongau site. Interaction effects on nitrate concentration were absent at the Schongau site. Interaction effects on sulphate concentrations were absent at both sites. Current knowledge about the complex processes and patterns in mixed species stands is still limited. At least for certain properties, mixed species stands cannot be treated as a summation of the corresponding monocultures.     

冀西北高原植被生产力与退耕对策

依据冀西北高原的气候与土壤条件,进行了区域内不同类型农田农林草现实生产力状况的比较研究．结果表明,就不同植被而言,不论是草甸栗钙土还是砂质栗钙土,农田和草地与林地相比具有明显的生物产量优势,而农田和人工草地之间的生物产量差异相对较小．就不同农田类型而言,草甸栗钙土植被生产力明显高于砂质栗钙土．在明确不同植被现实生产力间差异的基础上,提出了要首先实施砂质栗钙土农田的退耕,退耕地只能还草,不能还林,退耕后必须进行植被生产结构的战略性调整等兼顾保护生态环境与发展农村经济的退耕对策．     

Restoring riparian meadows currently dominated by Artemisia using alternative state concepts ‐ the establishment component

Abstract. We evaluated the potential for restoring riparian grass and sedge meadows currently dominated by Artemisia tridentata var. tridentata with an experiment in which we burned sites with low, intermediate, and high water tables, i.e., dry, intermediate, and wet sites. To define the alternative states and thresholds for these ecosystems, we examined burning and water table effects on both abiotic variables and establishment of grasses adapted to relatively high (Poa se‐cunda ssp. juncifolia), intermediate (Leymus triticoides), or low (L. cinereus) water tables. Wet sites had lower soil temperatures and higher soil water contents than dry sites. Burning increased soil temperatures on all sites. Undershrub microsites on control plots had the lowest temperatures, while former undershrub microsites on burn plots had the highest temperatures. Surface soil water was low on burn plots early in the growing season due to desiccation, but higher at deeper depths after active plant growth began. Emergence was generally greater on wet sites, but survival was microsite‐ and species‐specific. Undershrub microsites on control plots facilitated emergence and first‐year survival, but seedlings that survived initially harsh conditions on burn plots had similar numbers alive at the end. In general, favorable environments and establishment of species adapted to mesic conditions indicate that wet sites represent an alternative state of the naturally occurring dry meadow ecosystem type, and can be restored to grass and sedge meadows. Harsh environments and lack of establishment of species adapted to mesic conditions indicate that dry sites have crossed a threshold and may represent a new ecosystem type. Understory vegetation and seed banks on dry sites have been depleted, and restoration will require burning and reseeding with species adapted to more xeric conditions.     

Shrub persistence and increased grass mortality in response to drought in dryland systems

Droughts in the southwest United States have led to major forest and grassland die‐off events in recent decades, suggesting plant community and ecosystem shifts are imminent as native perennial grass populations are replaced by shrub‐ and invasive plant‐dominated systems. These patterns are similar to those observed in arid and semiarid systems around the globe, but our ability to predict which species will experience increased drought‐induced mortality in response to climate change remains limited. We investigated meteorological drought‐induced mortality of nine dominant plant species in the Colorado Plateau Desert by experimentally imposing a year‐round 35% precipitation reduction for eight continuous years. We distributed experimental plots across numerous plant, soil, and parent material types, resulting in 40 distinct sites across a 4,500 km² region of the Colorado Plateau Desert. For all 8 years, we tracked c. 400 individual plants and evaluated mortality responses to treatments within and across species, and through time. We also examined the influence of abiotic and biotic site factors in driving mortality responses. Overall, high mortality trends were driven by dominant grass species, including Achnatherum hymenoides, Pleuraphis jamesii, and Sporobolus cryptandrus. Responses varied widely from year to year and dominant shrub species were generally resistant to meteorological drought, likely due to their ability to access deeper soil water. Importantly, mortality increased in the presence of invasive species regardless of treatment, and native plant die‐off occurred even under ambient conditions, suggesting that recent climate changes are already negatively impacting dominant species in these systems. Results from this long‐term drought experiment suggest major shifts in community composition and, as a result, ecosystem function. Patterns also show that, across multiple soil and plant community types, native perennial grass species may be replaced by shrubs and invasive annuals in the Colorado Plateau Desert.