Open Plots Research Articles

Seed predation and moisture limit germination of recalcitrant Dobera glabra (Salvadoraceae) seeds in the Afar rangelands, Ethiopia

We studied current recruitment failure of Dobera glabra, an important famine-food throughout the dryland parts of the Horn of Africa. The species has previously been found to have recalcitrant seeds, a strategy not common for plants in dryland areas. We experimentally tested (1) how germination capacity of D. glabra is affected by seed form, storage period and moisture under nursery conditions, and (2) how seed predation by vertebrate herbivore and seed exposure at germination site affect germination under field conditions in northern Afar rangelands, Ethiopia. D. glabra seeds that received either mulching or supplementary watering (3 days/week) had a higher germination success than controls. The seeds are probably desiccation sensitive since stored seeds had poor germination performance compared to fresh seeds. Seeds in the rangeland plots protected from herbivores had significantly higher germination success compared to open plots. Our findings demonstrate that seed predation and moisture limitation highly reduced the germinability of the recalcitrant D. glabra seeds, indicating that the species might have persisted due to past wetter periods and low herbivore density in dry environments.

Experimental warming had little effect on carbon-based secondary compounds, carbon and nitrogen in selected alpine plants and lichens

Global warming is expected to change plant defence through its influence on plant primary resources. Increased temperature (T) will increase photosynthesis, and thus carbon (C) availability, but may also increase soil mineralization and availability of nitrogen (N). More access to C and N is expected to mainly increase plant growth, and, according to hypotheses on resource based defence, this could lower plant concentrations of carbon-based secondary compounds (CBSCs). We used two already established warming experiment with open top chambers (OTCs) and control plots in alpine south-western Norway, one on a ridge (8 years’ treatment) and a one in a leeside (3 years’ treatment), to study the effects of warming on plant and lichen defensive compound concentrations. The study included five vascular plant and six lichen species. One vascular plant species had lower concentration of CBSCs under elevated T, while the others did not respond to the treatment. In lichens there were no effects of warming on CBSCs, but a tendency to reduced total C concentrations. However, there were effects of warming on nitrogen, as the concentration decreased inside OTCs for three species, while it increased for one lichen species. Lichens generally had higher CBSC and total C concentrations on the ridge than in the leeside, but no such pattern were seen for vascular plants. No elevated temperature effect on CBCSs is most probably a result of high constitutive defence under the limiting alpine conditions, suggesting that chemical defence is little subject to change under climate warming, at least on a short-term basis. We suggest that the driving forces of plant defence in the arctic-alpine should be tested individually under controlled conditions, and suggest that competition from other plants may be a greater threat under climate warming than increased herbivory or disease attacks.

Species Composition of Grasshoppers (Orthoptera) in open Plots and Farmlands in Calabar Metropolis, Southern Nigeria

The grasshoppers are strategic in the welfare of man and may constitute a major threat when its population is not checked. A study on the distribution of grasshoppers in open plots and farmlands was carried out within Calabar Metropolis between August to November, 2010. A total of 295 grasshoppers belonging to 11 species grouped under 3 families (Tettigoniidae, Acrididae and Pyrgomorphidae) were collected from 8 study locations. Grasshoppers were collected weekly from all study sites using sweep nets between 11 a.m. to 4 p.m. The collection was done using sweep nets between 11 a.m. to 4 p.m. when grasshoppers baked themselves under the sun. The percentage abundance of these species were Spathosterrium pygmaeum (16.27%), Tettigonia viridissima (11.86%), Catantops spissus (11.19%) Acridaturita sp. (10.17%), Gastrimargus acrididae (9.83%), Schistocerca nitens (9.49%), Tylopsis sp. (7.46%), Zonocerus variegatus (6.78%), Omocestus viridulus (6.10%), Scudderia mexicana (5.76%) and Zonocerus elegans (5.08%). Tettigonia viridissima and Acridaturita sp. were largely distributed as it occurred in 7 of 8 study sites while Scudderia mexicana was the least distributed, as it was reported in 3 sites only. The dominant grasshopper species in open plot was Spathosterrium pygmaeum (19%) in relative abundance and the least was Zonocerus variegatus (0.64%). Zonocerus variegatus was the dominant species in farmland (14%) in relative abundance and the least was Schistocerca nitens (4%). Chi-square test showed a high significant difference between the distribution of grasshoppers in open plots and farmlands (p < 0.05). Variations in grasshopper species composition were attributed to lizard predation and management practices such as grass cutting, fertilizer and pesticide applications. It was therefore concluded that species abundance and population of grasshoppers could be enhanced by minimizing human activities that interfere with land use.

Predation risk indirectly enhances survival of seaweed recruits but not intraspecific competition in an intermediate herbivore species

Summary 1. Non‐consumptive predator effects are an important driver in predator–prey interactions. While indirect effects of predation risk shape interspecific species interactions, e.g. in fuelling trophic cascades, knowledge about non‐consumptive predator effects on intraspecific interactions among intimidated prey is scarce. 2. In laboratory experiments, we tested whether predation by male and female green crabs (Carcinus maenas) is stronger on small than on larger specimens of the periwinkle Littorina littorea, an important herbivore species in intertidal habitats of the temperate zone. Moreover, we asked whether size‐specific differences in predation‐induced mortality reflect as a stronger effect of predation risk (caused by nearby consuming crabs) on the foraging behaviour of more threatened periwinkles and ultimately on the recruitment success of the brown seaweed Fucus serratus. Furthermore, predator activity and prey abundance was measured in the field and the efficacy of predation risk on the survival of seaweed recruits was assessed in three field experiments with two different set‐ups (open plots and crab exclosures). 3. Male crabs consumed smaller periwinkles more often than larger conspecifics, while females refused periwinkles as food. In summer, 80–90% of periwinkles in the field attained a size at which crab predation was minimal in laboratory assays. The observed up to 15‐fold decrease in the consumption of seaweed recruits by periwinkles in the presence of nearby consuming crabs in laboratory assays was, however, independent of the size of periwinkles. Predation risk effects from the laboratory were only confirmed in field experiments using crab exclosures but not with open plots, suggesting an artefact due to trespassing by wild crabs in the open plot set‐up. 4. Synthesis. Predation risk may not change intraspecific competition for food in L. littorea. Yet, risk effects on foraging behaviour of periwinkles that experience a low threat of real predation indicate that non‐consumptive predator effects may affect prey population dynamics more strongly than consumptive predator effects. Thus predation risk effects may be indirectly beneficial for the survival of basal species like perennial seaweeds, as experimental evidence from field and laboratory experiments indicates.

Strategies for Restoring Native Riparian Understory Plants Along the Sacramento River: Timing, Shade, Non-Native Control, and Planting Method

Prairie L. Moore, Karen D. Holl, and David M. Wood doi: http://dx.doi.org/10.15447/sfews.2014v9iss2art1 Restorationists commonly plant overstory and understory species simultaneously at the outset of restoration, but a mature forest canopy may be necessary to facilitate survival of light-intolerant understory species. We conducted two experiments in riparian forest restoration sites along the Sacramento River to determine whether: (1) introducing understory species is more successful at the beginning of restoration or after the canopy has developed; (2) canopy cover directly (via reduced light) or indirectly (by reducing non-native competition) facilitates survival of native understory species; and (3) seeding or planting seedlings of understory species is most effective. Seven native understory species were introduced as both seeds and seedlings into an experiment that manipulated canopy cover (open or canopy) and non-native grass competition (control or grass-specific herbicide). We conducted another experiment using shade cloth to directly test the effect of different light levels on seedling survival and growth of three species. Both experiments showed that four species (Aristolochia californica, Carex barbarae, Clematis ligusticifolia, and Vitis californica) had higher survival under low-light conditions (canopy or shade cloth). In contrast, three species (Artemisia douglasiana, Euthamia occidentalis and Rubus californica) had similar survival across open and canopy conditions. Cover of unplanted understory vegetation (mostly non-native) was much lower under the canopy than in open plots treated with grass-specific herbicide. Establishment from seed was generally low and highly variable. Our results suggest that to restore understory species in riparian forests in north–central California: light-intolerant understory species should be planted after canopy closure; canopy cover is more effective than grass-specific herbicide at reducing non-native understory cover; and planting seedlings is more successful than direct seeding.

Soil Microbial Biomass And Activity In A Cork Oak Savanna

Cork oak savannas are composed by a sparse tree canopy (30-70 trees/ha) and a grassland understory predominantly composed of C3 annuals that survive the hot and dry Mediterranean summers as seeds in the soil. Microbial communities can be more or less efficient at converting organic substrates into microbial biomass carbon depending on the quantity and quality of organic matter inputs. The cork oak savannas have two distinct types of plant litter that can affect soil microbial biomass and activity differently: herbaceous litter and the more recalcitrant woody plant litter resulting from the trees. Spatial variability of soil microbial biomass and activity due to the tree-grassland component of cork oak savannas were evaluated in order to better understand the soil carbon dynamics of these systems.To quantify changes in soil microbial biomass and activity, measurements were performed in a Cork oak savanna in Southern Portugal. At this site 8 plots were randomly established under mature cork oak trees and paired with 8 open grassland plots. During one year soil cores (0-10 cm) were monthly collected at each site for measuring soil microbial biomass C and other eco-physiology parameters. Soil microbial biomass carbon (Cmic) and nitrogen (Nmic) were always higher under the tree canopy than in the open grasslands. Organic carbon (Corg) was also higher under the tree canopies. The Cmic/Corg ratio relates to the microbial activity and its potential to mineralize organic substances. The Cmic/Corg ratio was lower under the tree canopies than in the open grasslands. Less microbial biomass was supported per unit of Corg. Basal activity was always higher under the canopy than in the open grassland.Trees scattered in the savanna function as islands inducing larger soil microbial communities and higher basal activity under the canopies. Lower Cmic/Corg ratio under the tree canopies suggests a more recalcitrant nature of the litter and a decrease in relative availability of organic matter under the trees.

Soil Microbial Biomass And Activity In A Cork Oak Savanna

AbstractCork oak savannas are composed by a sparse tree canopy (30-70 trees/ha) and a grassland understory predominantly composed of C3 annuals that survive the hot and dry Mediterranean summers as seeds in the soil. Microbial communities can be more or less efficient at converting organic substrates into microbial biomass carbon depending on the quantity and quality of organic matter inputs. The cork oak savannas have two distinct types of plant litter that can affect soil microbial biomass and activity differently: herbaceous litter and the more recalcitrant woody plant litter resulting from the trees. Spatial variability of soil microbial biomass and activity due to the tree-grassland component of cork oak savannas were evaluated in order to better understand the soil carbon dynamics of these systems.To quantify changes in soil microbial biomass and activity, measurements were performed in a Cork oak savanna in Southern Portugal. At this site 8 plots were randomly established under mature cork oak trees and paired with 8 open grassland plots. During one year soil cores (0-10 cm) were monthly collected at each site for measuring soil microbial biomass C and other eco-physiology parameters. Results/Conclusion Soil microbial biomass carbon (Cmic) and nitrogen (Nmic) were always higher under the tree canopy than in the open grasslands. Organic carbon (Corg) was also higher under the tree canopies. The Cmic/Corg ratio relates to the microbial activity and its potential to mineralize organic substances. The Cmic/Corg ratio was lower under the tree canopies than in the open grasslands. Less microbial biomass was supported per unit of Corg. Basal activity was always higher under the canopy than in the open grassland.Trees scattered in the savanna function as islands inducing larger soil microbial communities and higher basal activity under the canopies. Lower Cmic/Corg ratio under the tree canopies suggests a more recalcitrant nature of the litter and a decrease in relative availability of organic matter under the trees.

The impact of cattle and goats grazing on vegetation in oak stands of varying coppicing age

The effects of cattle and goats grazing on oak shoot growth and herbaceous vegetation in three oak forest stands with different coppicing age (1, 4 and 7 yrs after the clear cutting) were investigated. In April 1997, an experimental area was chosen with three forest stands, which were clear cut in 1996 (CL1996), 1993 (CL1993), and 1990 (CL1990). All stands were grazed by cattle and goats after they were clear cut. In each forest stand, five 10m×10m paired plots were located, which represented grazed and protected patches. Herbage biomass within protected and grazed plots was measured four times each year (spring: May–June, summer: July–August, autumn: September–October, and winter: November–December). Behavioural observations on grazing animals were conducted in the same periods. In both protected and open plots the height and basal diameter of all oak shoots on 5 preselected stumps were measured at the end of five growing periods from 1997 to 2001. All forest stands carried a similar amount of available herbage (averaged over forest stands and growing season, 2614kg/ha). Grazing animals removed on average 1057kg/ha throughout the growing period. Cattle mainly consumed herbage (97% of bites) while goats consumed a mixture of oak browse (41% bites), herbaceous species (34% bites), and other woody species browse (25% bites). The height, diameter and volume of oak shoots were affected by grazing. The three forest stands had similar shoot heights in the protected plots in 2001 after 5 years of grazing protection. The volume of oak shoots of the grazed plots were 146.7cm3 for CL1996, 232.9cm3 for CL1993, and 239.1cm3 for CL1990 in 2001 (i.e. 5, 8, and 11 years grazing after the clear cuttings, respectively). The protected plots carried greater volumes of oak shoots, CL1996: 496.0cm3 (few months grazing before protection), CL1993: 690.0cm3 (4 years grazing before protection), and CL1990: 344.0cm3 (7 years grazing before protection). In conclusion, almost half of the herbaceous vegetation was removed through grazing but it had no positive effect on the growth rate of oak shoots. It seems that goats, which selected almost half of their diet from oak shoots, are responsible for that relative negative growth of shoots. However, cattle grazed only herbs and may therefore control herbaceous vegetation.

Viruses Infecting Tomato in València, Spain: Occurrence, Distribution and Effect of Seed Origin

AbstractViral diseases are a serious limitation to the tomato crop in the region of València, Spain. A survey of tomato viruses in open field cultivation plots was made in the three provinces of this region. A total of 228 plots classified according to the origin of the seed (farmer seed plots or commercial seed plots) were surveyed, from which 1300 individual plants were sampled and tested for Cucumber mosaic virus (CMV), Pepino mosaic virus (PepMV), Parietaria mottle virus (PMoV), Potato virus Y (PVY), Tomato mosaic virus (ToMV), Tomato spotted wilt virus (TSWV) and for the tomato yellow leaf curl disease (TYLCD). Virus infection was detected in 58.9% of the plants sampled and in 86.0% of the plots surveyed. All these viruses were detected, and the most prevalent were ToMV and PVY (34.1% and 27.1% of infected plants, respectively), but PMoV and TYLCD were the less prevalent (1.2% and 1.3% of infected plants, respectively). Differences among provinces and seed origin were found for most of the viruses studied. In particular, both ToMV and PVY had a higher level of infection in plants from farmer seed plots than in commercial seed plots, which accounts for the higher percentage of virus‐infected plants in the former (64.2%) when compared to the latter (49.1%). Single and multiple infections were found in 42.38% and 16.54% of the samples, respectively. The most common multiple infection was of ToMV, PVY or both. These results show that the percentage of infected plants and plots in open field cultivation is very high in this region and the origin of the seed is an important factor in the incidence of virus infection. In this respect, preventive measures, including virus‐free seed, resistant cultivars and improved cultural practices, could reduce the incidence of virus infection.

Influence Of &lt;i&gt;Phytolyma lata&lt;/i&gt; (Homoptera: Psyllidae) On Seedling Growth Of &lt;i&gt;Milicia excelsa&lt;/i&gt;

Milicia excelsa (Iroko) is a valuable timber species occurring naturally in the humid forests of Africa. The high quality and great demand of wood obtained from M. excelsa has resulted in its overexploitation. Attempts at establishing large scale plantations to ensure sustained production have been hampered by the gall forming psyllid Phytolyma lata. In spite of the economic importance of P. lata little research has been conducted on the impact of the psyllid on the establishment of M. excelsa plantations. The effect of P. lata on growth, dry matter accumulation and allocation of M. excelsa seedlings is assessed in this study. Seedling growth in infested plots was significantly reduced. Plants infested had lower height, stem diameter and biomass growth. Mean yield losses of stem, branches, and leaves of infested plants were 68.9%, 48.3% and 64% respectively of matched uninfested plants. Infested plants also had smaller, fewer and highly chlorotic leaves. There were no significant differences (P > 0.05) in yield, specific leaf area, leaf area ratio and leaf weight ratio of plants growing in the open screen house and open plot without screening (infested plots) even though irradiance incident in the open screen house was 70% of that in the open plot without screening. It is concluded that P. lata infestation has significant effect on growth and biomass accumulation in the early development of Iroko and that such information would improve integrated pest management (IPM) programme for P. lata. Secondly, biomass allocation of M. excelsa seedlings is not significantly different probably at irradiances greater than 70% ambient full sun.Keywords: Milicia excelsa, Phytolyma lata, seedling growth, pest infestation, biomass

Influence of fallen coarse woody debris on the diversity and community structure of forest-floor spiders (Arachnida: Araneae)

Purely observational studies have documented differences in the abundance and diversity of several litter-dwelling arthropods between sites adjacent to, and far from, CWD, which suggests that reduction of fallen coarse woody debris (CWD) in temperate forests by traditional forestry practices may affect the litter arthropod community. As few field experiments have directly tested the impact of CWD on arthropods inhabiting the litter at different distances from CWD, we removed CWD from replicated open plots on the floor of a second-growth deciduous forest in order to reveal the causal connection between CWD and litter-dwelling spiders, often the most diverse and abundant predators among the litter macrofauna of temperate forests. We also documented the impact of the CWD manipulation on spider prey and several other major macroarthropod groups. Before removing CWD (∅ = 14.3 ± 0.7 cm), we measured response variables as a function of distance (0.5–1.5 m) from CWD in both removal and control plots. In agreement with results of previous research that solely utilized this observational approach in temperate forests, volume and dry mass of litter, spider diversity, overall spider density, and densities of 8 of 16 major spider genera were higher adjacent to CWD before experimental manipulations. Removing CWD reduced the amount of litter and the density of spiders in litter close to where the CWD had been. Removing CWD also altered spider community structure, which had differed between litter sites adjacent to, and far from, CWD prior to the experimental removal of CWD. The patterns, though, were not completely congruent, as some of the taxa affected by the manipulation had not differed between sites prior to the removal of CWD, and vice-versa. Our findings suggest that complex interactions among structural, biotic and microclimatic factors underlie the observed responses to CWD removal by spiders and other arthropods in the litter layer. We also conclude that drawing inferences solely from observational studies is not a reliable approach for predicting the impact of changes in the amount of CWD on arthropods of forest-floor leaf litter. Further field experiments manipulating different volumes of CWD are needed in order to determine the minimum amount of CWD that should be kept on the forest floor of managed forests in order to maintain densities and diversities of major leaf-litter arthropods.

Changes in survivorship, behavior, and morphology in native soft‐shell clams induced by invasive green crab predators

AbstractMany studies on invasive species show reduced native densities, but few studies measure trait‐mediated effects as mechanisms for changes in native growth rates and population dynamics. Where native prey face invasive predators, mechanisms for phenotypic change include selective predation, or induced behavioral or morphological plasticity. Invasive green crabs, Carcinus maenas, have contributed to declines in native soft‐shell clams, Mya arenaria, in coastal New England, USA. We tested the hypothesis that clam ability to detect chemical cues from predators or damaged conspecifics would induce greater burrowing depth as a refuge from invasive crabs, and greater burrowing would require increased siphon growth. To determine how crab predation affected clam survivorship and phenotypic traits in the field, clams in exclosure, open, and crab enclosure plots were compared. Crab predation reduced clam density, and surviving clams were deeper and larger, with longer siphons. To determine whether the mechanism for these results was selective predation or induced plasticity, phenotypes were compared between clams exposed to chemical cues from crab predation and clams exposed to seawater in laboratory and field experiments. In response to crab predation cues, clams burrowed deeper, with longer siphons and greater siphon mass. Overall, crab predation removed clams with shorter siphons at shallow depths, and crab predation cues induced greater burrowing depths and longer siphons. Longer siphons and greater siphon mass of deeper clams suggests clams may allocate energy to siphon growth in response to crabs. By determining native behavior and morphological changes in response to an invasive predator, this study adds to our understanding of mechanisms for invasive impacts and illustrates the utility of measuring trait‐mediated effects to investigate predator–prey dynamics.

Effects of an Exotic Plant Invasion on Native Understory Plants in a Tropical Dry Forest

The dry forests of southern India, which are endangered tropical ecosystems and among the world's most important tiger (Panthera tigris) habitats, are extensively invaded by exotic plants. Yet, experimental studies exploring the impacts of these invasions on native plants in these forests are scarce. Consequently, little is known about associated implications for the long-term conservation of tigers and other biodiversity in these habitats. I studied the impacts of the exotic plant Lantana camara on understory vegetation in a dry-forest tiger habitat in southern India. I compared the richness, composition, and abundance of tree seedlings, herbs, and shrubs and the abundance of grass among plots in which Lantana was cleared or left standing. These plots were distributed across two blocks-livestock free and livestock grazed. Removal of Lantana had an immediate positive effect on herb-shrub richness in the livestock-free block, but had no effect on that of tree seedlings in either livestock block. Tree-seedling and herb-shrub composition differed significantly between Lantana treatment and livestock block, and Lantana removal significantly decreased survival of tree seedlings. Nevertheless, the absence of trees, in any stage between seedling and adult, indicates that Lantana may stall tree regeneration. Lantana removal decreased the abundance of all understory strata, probably because forage plants beneath Lantana are less accessible to herbivores, and plants in Lantana-free open plots experienced greater herbivory. Reduced access to forage in invaded habitats could negatively affect ungulate populations and ultimately compromise the ability of these forests to sustain prey-dependent large carnivores. Additional research focused on understanding and mitigating threats posed by exotic plants may be crucial to the long-term protection of these forests as viable tiger habitats.

Root distribution of under-planted European beech (Fagus sylvatica L.) below the canopy of a mature Norway spruce stand as a function of light

Aboveground and belowground biomass of 15-year-old under-planted European beech seedlings (Fagus sylvatica L.) in Norway spruce stand were studied along a light gradient in three plots, in the northern part of Slovenia. Differences in soil water content, aboveground and fine root biomass distribution were confirmed between studied plots. Light had significant effect on the total biomass, root-shoot ratio (0.388 ± 0.076 under canopy, 0.549 ± 0.042 in the edge, 0.656 ± 0.047 in the open), specific root length (SRL) of fine beech roots (561.9 ± 42.2 under canopy, 664.3 ± 51.2 in the edge, 618.2 ± 72.8 in the open) and specific leaf area in beech, indicating morphological adjustment to shade. However, SRL of beech fine roots indicated no change between plots. The correlation between total aboveground and root biomass and light below the mature stand canopy was higher in the case of diffuse light intensity. Most fine roots of spruce were concentrated in the top (0–20 cm) soil layer. Beech fine roots under canopy and edge conditions were also concentrated in top (0–20 cm) soil layer and exhibited shift downwards to deeper soil horizons in open plot. Root proportion between beech and spruce changed with light toward beech with increasing light intensity for both fine and coarse roots.

Diet shift of lentic dragonfly larvae in response to reduced terrestrial prey subsidies

AbstractInputs of terrestrial plant detritus and nutrients play an important role in aquatic food webs, but the importance of terrestrial prey inputs in determining aquatic predator distribution and abundance has been appreciated only recently. I examined the numerical, biomass, and diet responses of a common predator, dragonfly larvae, to experimental reduction of terrestrial arthropod input into ponds. I distributed paired enclosures (n = 7), one with a screen between the land and water (reduced subsidy) and one without a screen (ambient subsidy), near the shoreline of 2 small fishless ponds and sampled each month during the growing season in the southern Appalachian Mountains, Virginia (USA). Screens between water and land reduced the number of terrestrial arthropods that fell into screened enclosures relative to the number that fell into unscreened enclosures and open reference plots by 36%. The δ13C isotopic signatures of dragonfly larvae shifted towards those of aquatic prey in reduced-subsidy enc...

The impact of indigenous ungulate herbivory over five years (2004–2008) on the vegetation of the Little Karoo, South Africa

This study investigated the impact of rainfall and herbivory by indigenous herbivores over five years (2004–2008) on the vegetation of the Sanbona Wildlife Reserve (SWR), a 54 000 ha privately owned conservation area in the Little Karoo. Changes in floristic composition, species richness, aerial plant cover and grazing capacity were determined using drop-point surveys in fenced and open (i.e. grazed) plots in four dominant vegetation types. Annual and seasonal rainfall totals, herbivore stocking rate and herbivore utilisation patterns were also measured. Ordination analyses showed that fenced plots did not develop a fundamentally different successional trajectory from open plots over time. There were also no significant differences in species richness, plant cover and grazing capacity between fenced and open plots in all vegetation types. This lack of indigenous herbivore impact is ascribed to the relatively low stocking rates that were maintained on SWR during most of the study period. Species richness, plant cover and grazing capacity also did not differ significantly between years in all vegetation types except for the highly disturbed Old Land sites. The existing monitoring programme provides a useful tool for assessing the impact of indigenous herbivores and should be supported at local and provincial levels.

The introduced clam Ensis americanus in the Wadden Sea: field experiment on impact of bird predation and tidal level on survival and growth

In the Danish Wadden Sea the intertidal distribution of the introduced bivalve Ensis americanus (syn. E. directus) is restricted to a narrow zone around the mean low water level. To test the possible impact of birds and submersion time on dynamics and distribution of the clams, adult specimens of E. americanus collected near the low water line were transplanted to two intertidal sites and established in open and net-covered experimental plots for 9 weeks (autumn 2001). The lowest survival of clams was registered at the low-shore-site (LSS) in plots open to bird predators, suggesting that birds such as Common Eider (Somateria mollissima) or Oystercatcher (Haematopus ostralegus) may control the abundance of E. americanus at the lower tidal levels. For clams showing increment in shell length during the study period, the shell growth rates were highest at the LSS and lowest in the open plots at the high-shore-site (HSS). Differences in immersion time and thus food supply may explain this pattern. Body mass index (BMI) of the clams showed basically the same pattern as the survivorship: lowest BMI in open plots at the LSS and highest in the covered plots at this site. Clams from the HSS were intermediate in their BMI. Disturbance by birds in the open plots at the LSS may explain the low BMI. In conclusion birds may be an important factor controlling abundance of E. americanus in the lower intertidal zone.

SNOWMIP2: An Evaluation of Forest Snow Process Simulations

The Northern Hemisphere has large areas that are forested and seasonally snow covered. Compared with open areas, forest canopies strongly influence interactions between the atmosphere and snow on the ground by sheltering the snow from wind and solar radiation and by intercepting falling snow; these influences have important consequences for the meteorology, hydrology, and ecology of forests. Many of the land surface models used in meteorological and hydrological forecasting now include representations of canopy snow processes, but these have not been widely tested in comparison with observations. Phase 2 of the Snow Model Intercomparison Project (SnowMIP2) was therefore designed as an intercomparison of surface mass and energy balance simulations for snow in forested areas. Model forcing and calibration data for sites with paired forested and open plots were supplied to modeling groups. Participants in 11 countries contributed output from 33 models, and the results are published here for sites in Canada, the United States, and Switzerland. On average, the models perform fairly well in simulating snow accumulation and ablation, although there is a wide intermodal spread and a tendency to underestimate differences in snow mass between open and forested areas. Most models capture the large differences in surface albedos and temperatures between forest canopies and open snow well. There is, however, a strong tendency for models to underestimate soil temperature under snow, particularly for forest sites, and this would have large consequences for simulations of runoff and biological processes in the soil.

Influence of fine woody debris on spider diversity and community structure in forest leaf litter

Exploitation of forests for biofuel results in variable amounts of fine woody debris (FWD) being left on the forest floor. Such practices have the potential to affect the diversity and taxonomic composition of litter-dwelling organisms. The ability to predict the consequences of harvesting biofuel will be strengthened by knowledge of how variation in FWD affects litter organisms in non-harvested forests. A field experiment with three treatments [Control (no manipulation), FWD Removal, and FWD Addition] was carried out in replicated open plots in an unexploited forest in order to determine how the amount of fallen FWD affects the abundance, diversity and community composition of spiders, selected because of their importance as predators in the leaf-litter food web. Manipulation of FWD started in August, and by the following July total spider density in the FWD Addition treatment was 1.6× that of FWD Removal plots. Spider density in FWD Removal plots was 30% lower than the Control treatment, with no statistically significant difference between Control and FWD Addition. Manipulating FWD had no statistically significant effects on standard indices of spider diversity. However, multivariate community-level analyses revealed statistically significant differences in spider community structure between the FWD Removal and FWD Addition treatments. Two dominant genera of web builders contributed the most to this effect of manipulating FWD. Our results, and the findings of studies of woody debris in younger forests, suggest that the relatively small effects of FWD in our field experiment may reflect the age of the forest, with effects on the fauna likely being larger in forests younger than the one we studied.

Atmospheric Deposition and Heavy Metal Contamination in an Organic Farming System in a Seasonally Dry Tropical Region of India

Increased consciousness about agricultural sustainability and health risks associated with agrochemicals has lead organic farming to be a globally emerging alternative farm practice. We report the effect of atmospheric deposition on soil quality and heavy metal contamination of agricultural produce under an organic farming system using wheat and corn as test crops. Data obtained in the open field (OFO) were compared with a plastic-covered glass-house-grown system (OFG). The results showed that depositions of Cd, Cu, Ni, Pb, and Zn increased with time. Soil porosity, water holding capacity, microbial biomass carbon (Cmic), substrate-induced respiration (SIR), alkaline phosphatase, and FDAase activity decreased, whereas the bulk density and contents of Cd, Cu, Ni, Pb, and Zn increased over time in open plots receiving atmospheric deposition. Concentrations of metals in grains in OFO crops exceeded the safe limits of Indian standards and were three to sixfold higher than those recorded in OFG plots. These results indicate that atmospheric deposition of heavy metals can have a destabilizing effect on soil fertility in organic farming and can greatly increase the dietary intake of toxic metals. This may have long–term implications for human health as well as for agricultural sustainability. The data presented here have particular concern for developing countries, where unprecedented urban–industrial growth and consequently increased input fluxes of heavy metals will continue for decades to come.