Fire,grazing history,lichen abundance,and winter distribution of caribou in Alaska's taiga

In the early 1990s the Nelchina Caribou (Rangifer tarandus) Herd (NCH) began a dramatic shift to its current winter range, migrating at least an additional 100 km beyond its historic range. We evaluated the impacts of fire and grazing history on lichen abundance and subsequent use and distribution by the NCH. Historic (prior to 1990) and current (2002) winter ranges of the NCH had similar vascular vegetation, lichen cover (P = 0.491), and fire histories (P = 0.535), but the former range had significantly less forage lichen biomass as a result of grazing by caribou. Biomass of forage lichens was twice as great overall (P = 0.031) and 4 times greater in caribou selected sites on the current range than in the historic range, greatly increasing availability to caribou. Caribou on the current range selected for stands with >20% lichen cover (P < 0.001), greater than 1,250 kg/ha (P < 0.001) forage lichen biomass and stands older than 80 yr postfire (P < 0.001). After fires, forage lichen cover and biomass seldom recovered sufficiently to attract caribou grazing until after ≥60 yr, and, as a group, primary forage lichen species did not reach maximum abundance until 180 yr postfire. Recovery following overgrazing can occur much more quickly because lichen cover, albeit mostly fragments, and organic substrates remain present. Our results provide benchmarks for wildlife managers assessing condition of caribou winter range and predicting effects of fires on lichen abundance and caribou distribution. Of our measurements of cover and biomass by species, densities and heights of trees, elevation, slope and aspect, only percentage cover by Cladonia amaurocraea, Cladina rangiferina, Flavocetraria cuculata, and lowbush cranberry (Vaccinium vitis-idaea) were necessary for predicting caribou use of winter range. © 2011 The Wildlife Society     

Remote sensing reveals long-term effects of caribou on tundra vegetation

Declining use and abandonment of traditional ranges by migratory caribou (Rangifer tarandus) have often been related to density-dependent depletion of summer forage. The Pen Islands caribou herd (R. t. caribou), Ontario and Manitoba, Canada, numbered in the thousands on its traditional summer tundra range during the 1980s, but then declined in that region. We postulated that increased caribou abundance over three decades negatively affected phytomass, given that under the exploitation ecosystem hypothesis (EEH), grazers limit the amount of primary production if few predators are present. We tested this prediction using the Normalized Difference Vegetation Index (NDVI), as a proxy for phytomass available to caribou. We lagged caribou abundance in the explanatory model by the number of years (4–7) between peak caribou abundance and minimum NDVI. NDVI was negatively related to caribou abundance lagged by 6 years, and growing degree days explained much of the annual variation in NDVI. Precipitation was not an important predictor in the model. Our study is the first to apply NDVI to support the EEH for caribou. We propose that this method could be used over broad scales to shed light on limiting factors for migratory caribou across the circumpolar North.     

Relative effects of nutrient enrichment and grazing on epiphyte-macrophyte (Zostera marina L.) dynamics

The independent and interactive effects of nutrient concentration and epiphyte grazers on epiphyte biomass and macrophyte growth and production were examined in Zostera marina L. (eelgrass) microcosms. Experiments were conducted during early summer, late summer, fall, and spring in a greenhouse on the York River estuary of Chesapeake Bay. Nutrient treatments consisted of ambient or enriched (3× ambient) concentrations of inorganic nitrogen (ammonium nitrate) and phosphate. Grazer treatments consisted of the presence or absence of field densities of isopods, amphipods, and gastropods. epiphyte biomass increased with both grazer removal and nutrient enrichment during summer and spring experiments. The effect of grazers was stronger than that of nutrients. There was little epiphyte response to treatment during the fall, a result possibly of high ambient nutrient concentrations and low grazing pressure. Under low grazer densities of early summer, macrophyte production (g m^–2 d^–1) was reduced by grazer removal and nutrient enrichment independently. Under high grazer densities of late summer, macrophyte production was reduced by enrichment only with grazers absent. During spring and fall there were no macrophyte responses to treatment. The relative influence of epiphytes on macrophyte production may have been related to seasonally changing water temperature and macrophyte requirements for light and inorganic carbon.     

Distribution,density and impact of invasive plants in Lake Nakuru National Park,Kenya

Invasive plants have invaded swathes of grasslands in Lake Nakuru National Park thus necessitating the Park management to institute measures to control them. Despite this, information on the status and impact of invasive plants in these grasslands is lacking. Six grassland types were identified and assigned random numbers. Five study sites were then randomly selected from each grassland type. The Point‐Centre Quarter method was used to determine the distribution and density of seven major invasive plants, whilst their impact was assessed by comparing biomass and crude protein content of important forage grasses in invaded and noninvaded grasslands. Results show that the distribution of invasive plants did not differ among the grasslands (F_{5, 30} = 1.47, P = 0.229) but their densities differed among the plants (F_{6, 30} = 20.99, P < 0.001). The mean biomass in invaded and noninvaded grasslands (22 g m^?2 versus 37.2 g m^?2) was significantly different (t‐test, P < 0.05), while crude protein content of grasses in invaded (7.73, % DM) and noninvaded (9.3, % DM) patches was not significantly different (t‐test; P > 0.05). Our results suggest that invasive plants lower grass production and hence might reduce food availability to grazers.     

Percentage of Fecal Moss in Arctic Ungulates as an Indicator of Wintering Area Quality

Abstract: I investigated local and regional differences in percent moss in the feces of muskoxen (Ovibos moschatus) and reindeer or caribou (Rangifer tarandus) in northwestern Alaska, USA, and related fecal moss to forage availability, snow conditions, animal density, and terrain ruggedness on wintering areas. Reindeer are a partially domesticated form of Rangifer tarandus originating from Europe and Asia and differ physiologically and ecologically from caribou. Percent moss in feces of muskoxen differed locally among individual wintering areas. Because of the large local variation in moss content of muskox feces, regional differences between the 2 study areas were difficult to resolve. Percent of moss in the feces of reindeer–caribou did not differ between wintering areas within the same study area but did differ between study areas. On muskox wintering areas, fecal moss correlated negatively with graminoid cover and snow hardness and positively with moss cover and muskox density, but fecal moss did not correlate with snow depth or terrain ruggedness. On reindeer–caribou wintering areas, fecal moss correlated positively with moss availability but not with lichen cover or snow depth or hardness. Because muskox groups in Alaska are isolated from each other in winter, even groups wintering on neighboring hills may face different foraging availability and might, therefore, exhibit differences in growth or productivity. Reindeer–caribou are more mobile than muskoxen in winter, and fecal samples may not be representative of vegetative and snow conditions at the wintering area where I collected them. I conclude that managers can use fecal moss as an indicator of overgrazed ranges, severe snow conditions, or crowded conditions on muskox wintering areas, but that the association between fecal moss and range conditions has to be drawn with caution for the more mobile reindeer–caribou.     

Extensive Predator Space Use Can Limit the Efficacy of a Control Program

ABSTRACT Reduced to small isolated groups by anthropogenic habitat losses or habitat modifications, populations of many endangered species are sensitive to additive sources of mortality, such as predation. Predator control is often one of the first measures considered when predators threaten survival of a population. Unfortunately, predator ecology is often overlooked because relevant data are difficult to obtain. For example, the endangered Gaspésie caribou (Rangifer tarandus caribou) has benefited from 2 periods of predator control that targeted black bears (Ursus americanus) and coyotes (Canis latrans) in an attempt to reduce predation on caribou calves. Despite a high trapping effort, the number of predators removed has remained stable over time. To assess impact of predator movements on efficacy of a control program, we studied space use of 24 black bears and 16 coyotes over 3 years in and around the Gaspésie Conservation Park, Quebec, Canada, using Global Positioning System radiocollars. Annual home ranges of black bears averaged 260 km² and 10 individuals frequented area used by caribou. Annual home ranges of resident coyotes averaged 121 km², whereas dispersing coyotes covered >2,600 km². Coyotes were generally located at lower altitudes than caribou. However, because coyotes undertook long-distance excursions, they overlapped areas used by caribou. Simulations based on observed patterns showed that 314 bears and 102 coyotes potentially shared part of their home range with areas used by female caribou during the calving period. Despite low densities of both predator species, extensive movement and use of nonexclusive territories seem to allow predators to rapidly occupy removal areas, demonstrating the need for recurrent predator removals. Our results underscore the necessity of considering complementary and alternative solutions to predator control to assure long-term protection of endangered species.     

Grazer control of nutrient availability in the periphyton

Summary Benthic algal assemblages are regulated by both abiotic (e.g., nutrient) and biotic (e.g., grazing) constraint. The objective of this study was to determine how changes in these two factors affected the structure of an algal assemblage in an ephemeral stream. Coverslips were incubated for 21 days in enclosures containing one of three nutrient environments (ambient, phosphorus-enriched, or phosphorus and nitrogen enriched) and one of four densities of the snail Gonibasis (0, 40, 80, or 120 snails/m²) and examined directly to enumerate the algal assemblage. The effect of grazing on algal biomass was dependent on the nutrient environment. An overstory of diatoms was susceptible to removal by grazing and was not strongly affected by nutrient enrichment. An understory of Stigeoclonium was more resistant to grazing and responded strongly to nutrient enrichment only in the presence of grazers. Snail grazers may mediate nutrient availability to the understory indirectly by removing overlying cells or by direct excretion of nutrients. Multiple interactions occur between benthic herbivores and algae, and, as shown here, some of them are positive and involve modifications of the nutrient environment.     

Invading white-tailed deer change wolf–caribou dynamics in northeastern Alberta

Human-caused habitat change has been implicated in current woodland caribou (Rangifer tarandus caribou) population declines across North America. Increased early seral habitat associated with industrial footprint can result in an increase in ungulate densities and subsequently those of their predator, wolves (Canis lupus). Higher wolf densities can result in increased encounters between wolves and caribou and consequently higher caribou mortality. We contrasted changes in moose (Alces alces) and deer (Odocoileus spp.) densities and assessed their effects on wolf–caribou dynamics in northeastern Alberta, Canada, pre (1994–1997) versus post (2005–2009) major industrial expansion in the region. Observable white-tailed deer (O. virginianus) increased 17.5-fold but moose remained unchanged. Wolf numbers also increased from approximately 6–11.5/1,000 km². Coincident with these changes, spatial overlap between wolf pack territories and caribou range was high relative to the mid-1990s. The high number of wolf locations in caribou range suggests that forays were not merely exploratory, but rather represented hunting forays and denning locations. Scat analysis indicated that wolf consumption of moose declined substantively during this time period, whereas use of deer increased markedly and deer replaced moose as the primary prey of wolves. Caribou increased 10-fold in the diet of wolves and caribou population trends in the region changed from stable to declining. Wolf use of beaver (Castor canadensis) increased since the mid-1990s. We suggest that recent declines in woodland caribou populations in the southerly extent of their range have occurred because high deer densities resulted in a numeric response by wolves and consequently higher incidental predation on caribou. Our results indicate that management actions to conserve caribou must now include deer in primary prey and wolf reduction programs. © 2010 The Wildlife Society     

Response of zooplankton to nutrient enrichment and fish in shallow lakes: a pan-European mesocosm experiment

1. Responses of zooplankton to nutrient enrichment and fish predation were studied in 1998 and 1999 by carrying out parallel mesocosm experiments in six lakes across Europe. 2. Zooplankton community structure, biomass and responses to nutrient and fish manipulation showed geographical and year‐to‐year differences. Fish had a greater influence than nutrients in regulating zooplankton biomass and especially the relative abundances of different functional groups of zooplankton. When fish reduced the biomass of large crustaceans, there was a complementary increase in the biomasses of smaller crustacean species and rotifers. 3. High abundance of submerged macrophytes provided refuge for zooplankton against fish predation but this refuge effect differed notably in magnitude among sites. 4. Large crustacean grazers (Daphnia, Diaphanosoma, Sida and Simocephalus) were crucial in controlling algal biomass, while smaller crustacean grazers and rotifers were of minor importance. Large grazers were able to control phytoplankton biomass even under hypereutrophic conditions (up to 1600 μg TP L^?1) when grazer biomass was high (>80–90 μg dry mass L^?1) or accounted for >30% of the grazer community. 5. The littoral zooplankton community was less resistant to change following nutrient enrichment in southern Spain, at high temperatures (close to 30 °C), than at lower temperatures (17–23 °C) characterising the other sites. This lower resistance was because of a greater importance of nutrients than zooplankton in controlling algal biomass. 6. Apart from the reduced role of large crustacean grazers at the lowest latitude, no consistent geographical patterns were observed in the responses of zooplankton communities to nutrient and fish manipulation.     

Reducing Competitive Suppression of a Rare Annual Forb by Restoring Native California Perennial Grasslands

Populations of the rare annual forb Amsinckia grandiflora may be declining because of competitive suppression by exotic annual grasses, and may perform better in a matrix of native perennial bunchgrasses. We conducted a field competition experiment in which Amsinckia seedlings were transplanted into forty 0.64‐m² experimental plots of exotic annual grassland or restored perennial grassland. The perennial grassland plots were restored using mature 3 cm‐diameter plants of the native perennial bunchgrass Poa secunda planted in three densities. The exotic annual grassland plots were established in four densities through manual removal of existing plants. Both grass types reduced soil water potential with increasing biomass, but this reduction was not significantly different between grass types. Both grass types significantly reduced the production of Amsinckia inflorescences. At low and intermediate densities (dry biomass per unit area of 20–80 g/m²), the exotic annual grasses reduced Amsinckia inflorescence number to a greater extent than did Poa, although at high densities (>90 g/m²) both grass types reduced the number of Amsinckia inflorescences to the same extent. The response of Amsinckia inflorescence number to Poa biomass was linear, whereas the same response to the annual grass biomass is logarithmic, and appeared to be related to graminoid cover. This may be because of the different growth forms exhibited by the two grass types. Results of this research suggest that restored native perennial grasslands at intermediate densities have a high habitat value for the potential establishment of the native annual A. grandiflora.     

Termite mounds differ in their importance for herbivores across savanna types,seasons and spatial scales

Herbivores do not forage uniformly across landscapes, but select for patches of higher nutrition and lower predation risk. Macrotermes mounds contain higher concentrations of soil nutrients and support grasses of higher nutritional value than the surrounding savanna matrix, attracting mammalian grazers that preferentially forage on termite mound vegetation. However, little is known about the spatial extent of such termite influence on grazing patterns and how it might differ in time and space. We measured grazing intensity in three African savanna types differing in rainfall and foliar nutrients and predicted that the functional importance of mounds for grazing herbivores would increase as the difference in foliar nutrient levels between mound and savanna matrix grasses increases and the mounds become more attractive. We expected this to occur in nutrient‐poor areas and during the dry season when savanna matrix grass nutrient levels are lower. Tuft use and grass N and P content were measured along transects away from termite mounds, enabling calculation of the spatial extent of termite influence on mammalian grazing. Using termite mound densities estimated from airborne light detection and ranging (LiDAR), we further upscaled field‐based results to determine the percentage of the landscape influenced by termite activity. Grasses in close proximity to termite mounds were preferentially grazed at all sites and in both seasons, but the strength of mound influence varied between savanna types and seasons. In the wet season, mounds had a relatively larger effect on grazers at the landscape scale in the nutrient‐poor, wetter savanna, whereas in the dry season the pattern was reversed with more of the landscape influenced at the nutrient‐rich, driest site. Our results reveal that termite mounds enhance the value of savanna landscapes for herbivores, but that their functional importance varies across savanna types and seasons.     

放牧对若尔盖高原湿地CH4排放的影响

湿地是大气甲烷(CH_4)的主要排放源,而有关放牧对湿地CH_4排放的影响特征仍未得到足够的报道。因此,通过静态箱法,研究了放牧对四川省若尔盖高原湿地CH_4排放的影响,CH_4气体通过快速温室气体分析仪测量。结果表明:放牧样地和围栏内样地生长季CH_4排放量为(31.32±19.57)g/m~2和(30.31±23.46)g/m~2,它们之间无差异显著;但是集中放牧期间(7—9月),放牧样地(21.01±12.35)g/m~2较围栏内样地显著增加了CH_4排放量为54.3%。2014年生长季期间通过刈割植物模拟放牧表明两种刈割强度CH_4排放量为(5.01±5.37)g/m~2和(4.69±5.99)g/m~2,较未刈割样地(1.15±1.89)g/m~2增加了335.9%和308.0%,其原因可能是放牧或者刈割减少地表植物生物量,降低植物高度,缩短了CH_4排放的路径距离。该结果可为我国高原湿地保护与管理决策提供基础数据支撑。     

Abundance and daytime vertical distribution of planktonic fish larvae in an oligotrophic South Island lake

The vertical distribution of common bully (Gobiomorphus cotidianus) and koaro (Galaxias brevipinnis) larvae in the limnetic zone of Lake Coleridge were determined using a high-frequency (200 KHz) echosounder. Planktonic bully larvae first appeared in appreciable numbers in January. By February, they formed a scattering layer between depths of 12 to 24 m during the day, where they achieved a maximum density of 0.59 fish m^-3. Larger (> 18mm) fish migrated to the littoral zone and densities declined to < 0.01 fish m^-3 by July, when remaining larval fish occupied greater daytime depths. Their vertical distribution during the day appeared to be influenced mainly by light levels and water temperatures. Larvae grew more slowly (0.12 mm d^-1) than in more productive North Island lakes, and were also present in lower densities for a more restricted period of time. Koaro larvae first appeared in November and December and were found in low numbers (< 0.01 fish m^-3) in summer at depths of 10 to 26 m. Salmonid production in the limnetic zone is probably limited by the small size and relative scarcity of forage fish present.     

Waterfowl feces as a source of nutrients to a prairie wetland: responses of microinvertebrates to experimental additions

We tested the hypothesis that inorganic nutrients released fromwaterfowl feces would stimulate primary production, therebyaffecting microinvertebrate grazers, by making controlledadditions of waterfowl feces to fishless wetland enclosures andmeasuring the response of planktonic and phytophilouscladocerans, copepods, and rotifers. Feces were added in twopulses, four weeks apart, to duplicate enclosures at a ‘high’level (115 g m⁻² wet feces), simulating the total P load(1.6 g m⁻²) applied in an earlier fertilizationexperiment, and a ‘low’ level (11.5 g m⁻²). Density ofmicrocrustacean grazers in the water column increased inresponse to both feces additions, although the response wasmore noticeable after the second feces addition. After eachaddition, cladocerans (predominantly Ceriodaphnia dubia)and copepodites in the water column (and associated withperiphyton on acrylic rods in the water column) were mostabundant in enclosures with high loading. In contrast, densityof microcrustacean grazers associated with macrophytes(predominantly Chydorus spp. and copepodites) increasedin response to the second feces addition only.Microinvertebrate density increased only slightly with lowfeces loading. Community composition showed similar changesover the season in all enclosures, and differences in relativeabundance were not attributable to treatment effects. Given thesmall effects produced by nutrient additions that greatlyexceed natural loadings, nutrients leaching from waterfowlfeces do not appear to have a significant impact on the foodwebof this wetland. This revised version was published online in July 2006 with corrections to the Cover Date.     

Abundance and dispersion of the invasive Mediterranean annual, Centaurea melitensis in its native and non-native ranges

In general, invasive plants are assumed to behave more aggressively in their invasive ranges than in their native range, and studies of the mechanisms of invasion often assume these differences. However, comparisons of abundances between native and invasive ranges are rarely carried out. We compared density and dispersion of the invasive plant, Centaurea melitensis (Asteraceae) in its native range and two invasive ranges of similar mediterranean-climate type. The objective was to quantify the differences in its abundance among three distant regions. We surveyed six sites in the native range (Spain) and in each of two invaded ranges (California and central Chile) for population density, relative dominance and spatial distribution of Centaurea. Centaurea occurred at higher densities in invasive sites than in native ones, with a median of 100 plants per m² and 70 plants per m² in California and Chile, respectively, compared to only 4 plants per m² in Spain. Centaurea was more dominant in both invasive ranges than in the native range. Centaurea density and relative dominance were highly variable within regions. Plants in Spain were randomly dispersed, while those in both invasive ranges were more aggregated. Annual precipitation and mean annual temperature were the best predictors of Centaurea density. In California sites, density was negatively correlated with soil nutrients. The presence of at least one high-density population with near total dominance in Spain suggests that there might be ecological mechanisms for invasiveness in Centuarea that are not unique to invaded ranges.     

Sawgrass Seedling Responses to Transplanting and Nutrient Additions

Understanding Cladium jamaicense (sawgrass) seedling establishment is an important component of an Everglades restoration program because the degree of sawgrass recovery and concurrent Typha domingensis (cattail) decline will be used to evaluate restoration success. To understand sawgrass recovery at locations with increased soil nutrients, we tested the effects of transplanting sawgrass seedlings to pots at different densities and investigated how nutrient additions affect seedling growth. Survivorship of seedlings transplanted into moist commercial potting soil at three densities ranged from 61% to 95%. After 6 months, maximum survivorship (90%) occurred at medium densities (2–4 seedlings per pot 16 cm in diameter). Nutrient additions, totaling 6.5 N g/m², 9.8 P g/m², 6.5 g/m², were applied approximately 4 months after seedlings were transplanted. The biomass of the plants receiving nutrient additions (pulsed) was significantly higher (by over 30%) than plants with no nutrient addition (control). Photosynthetic rates for nutrient-enriched plants (measured 6-weeks after the nutrient additions) were significantly greater (by 32–45%) than for control plants. Instantaneous leaf water use efficiency increased significantly (by more than 20%) in pulsed plants. The results suggest that preventing root damage is crucial for the success of trans planted sawgrass seedlings and that nutrient additions enhanced seedling growth.     

Space use and social association in a gregarious ungulate: Testing the conspecific attraction and resource dispersion hypotheses

Animals use a variety of proximate cues to assess habitat quality when resources vary spatiotemporally. Two nonmutually exclusive strategies to assess habitat quality involve either direct assessment of landscape features or observation of social cues from conspecifics as a form of information transfer about forage resources. The conspecific attraction hypothesis proposes that individual space use is dependent on the distribution of conspecifics rather than the location of resource patches, whereas the resource dispersion hypothesis proposes that individual space use and social association are driven by the abundance and distribution of resources. We tested the conspecific attraction and the resource dispersion hypotheses as two nonmutually exclusive hypotheses explaining social association and of adult female caribou (Rangifer tarandus). We used location data from GPS collars to estimate interannual site fidelity and networks representing home range overlap and social associations among individual caribou. We found that home range overlap and social associations were correlated with resource distribution in summer and conspecific attraction in winter. In summer, when resources were distributed relatively homogeneously, interannual site fidelity was high and home range overlap and social associations were low. Conversely, in winter when resources were distributed relatively heterogeneously, interannual site fidelity was low and home range overlap and social associations were high. As access to resources changes across seasons, caribou appear to alter social behavior and space use. In summer, caribou may use cues associated with the distribution of forage, and in winter caribou may use cues from conspecifics to access forage. Our results have broad implications for our understanding of caribou socioecology, suggesting that caribou use season‐specific strategies to locate forage. Caribou populations continue to decline globally, and our finding that conspecific attraction is likely related to access to forage suggests that further fragmentation of caribou habitat could limit social association among caribou, particularly in winter when access to resources may be limited.     

Potential functional redundancy and resource facilitation between tadpoles and insect grazers in tropical headwater streams

1. We quantified production and consumption of stream‐dwelling tadpoles and insect grazers in a headwater stream in the Panamanian uplands for 2 years to assess their effects on basal resources and energy fluxes. At the onset of our study, this region had healthy, diverse amphibian populations, but a catastrophic disease‐driven decline began in September 2004, which greatly reduced amphibian populations. 2. Insect grazer production was 348 mg ash‐free dry mass (AFDM) m^?2 year^?1 during the first year of the study and increased slightly to 402 mg AFDM m^?2 year^?1 during the second year. 3. Prior to amphibian declines, resource consumption by grazers (tadpoles and insects) was estimated at 2.9 g AFDM m^?2 year^?1 of algal primary production, which was nearly twice the estimated amount available. Insect grazers alone accounted for c. 81% of total primary consumption. During the initial stages of the declines, consumption remained at c. 2.9 g AFDM m^?2 year^?1, but only 35% of the available resource was being consumed and insect grazers accounted for c. 94% of total consumption. 4. Production and resource consumption of some insect grazers increased during the second year, as tadpoles declined, indicating a potential for functional redundancy in this system. However, other insect grazer taxa declined or did not respond to tadpole losses, suggesting a potential for facilitation between tadpoles and some insects; differential responses among taxa resulted in the lack of a response by insect grazers as a whole. 5. Our results suggest that before massive population declines, tadpoles exerted strong top‐down control on algal production and interacted in a variety of ways with other primary consumers. 6. As amphibian populations continue to decline around the globe, changes in the structure and function of freshwater habitats should be expected. Although our study was focused on tropical headwater streams, our results suggest that these losses of consumer diversity could influence other aquatic systems as well and may even reach to adjacent terrestrial environments.     

Element storage in native, agri-, and silvicultural ecosystems of the Brazilian savanna

The expanding agriculture in the Brazilian savanna, the Cerrado, changes C and nutrient storages of the savanna ecosystems thereby affecting the global C budget and the sustainability of the local land use. We examined the biomass and the C, N, P, and S storages in above- and belowground biomass, in the organic layer, and in the top 2 m of the mineral soil (Anionic Acrustoxes) of three replicate plots of each of native Cerrado, Pinus caribaea Morelet plantations, productive and degraded Bracchiaria decumbens Stapf. pastures, and of conventional and no-tillage soybean cultivation. Aboveground biomass – in the cropping systems shortly before harvest – decreased in the order, Pinus (15 kg m^–2) > Cerrado (2.3) > conventional tillage (1.9) > no tillage (1.5) > productive pasture (0.64) > degraded pasture (0.37) and belowground biomass in the order, Pinus (9.1) > Cerrado (3.0) > productive pasture (2.2) > degraded pasture (1.5) > conventional tillage (0.60) > no tillage (0.41). The aboveground biomass contained 1.1 (degraded pasture) to 19% (Pinus) of the total C storage, 0.3 (productive pasture, degraded pasture) to 3.5% of the total N storage, 0.3 (degraded pasture) to 2.1% (no tillage, conventional tillage) of the total P storage, and 0.3 (degraded pasture) to 3.7% (Pinus) of the total S storage of the ecosystems. Total C storage in the ecosystems was significantly larger in the Pinus stands (36 kg m^–2) than in all other systems; differences among Cerrado (20), degraded pasture (19), productive pasture (20), no tillage (19), and conventional tillage (19) were small and not significant. All land-use systems had larger N (Pinus, 1.5; degraded pasture, 1.3; productive pasture, 1.4; no tillage, 1.4; conventional tillage, 1.4 kg m^–2) and S storage (PI, 28; degraded pasture, 33; productive pasture, 34; no tillage, 36; conventional tillage, 38 g m^–2) than the Cerrado (N, 1.2 kg; S, 26 g m^–2). The P storages varied between 17 and 29 g m^–2 and were not significantly different among the studied ecosystems. The N and S accumulations in the 12–20-year-old land-use systems were larger than the cumulative known fertilizer inputs indicating that there were unknown inputs possibly including the exploration of the deeper subsoil by deep-reaching roots and transfer of nutrients to the topsoil. Our results indicate that afforestation with Pinus trees has the potential to sequester large amounts of C while pasture degradation, no tillage, and conventional tillage tended to result in small C losses. Land use resulted in a marked accumulation of N and S relative to the Cerrado.     

Foraging geese,vegetation loss and soil degradation in an Arctic salt marsh

Abstract. The North American mid‐continent population of Lesser snow geese (Chen caerulescens caerulescens L.) has increased by ca. 7% per year, largely as a result of geese feeding on agricultural crops in winter and on migration. We describe the long‐term effects of increasing numbers of geese at an arctic breeding ground (La Pérouse Bay, Manitoba) on intertidal salt‐marsh vegetation. Between 1985 and 1999 goose grubbing caused considerable loss of graminoid vegetation along transects in intertidal marshes. Loss of vegetation led to bare sediment with a plant cover of less than 2%. Changes in vegetation could not be described by simple linear, geometric or exponential functions; most losses occurred between 1988 and 1990 and losses were staggered in time between individual transects, some of which had all vegetation removed. Between 1979 and 1999 the standing crop in July in remaining intact heavily‐grazed swards of Puccinellia phry‐ganodes and Carex subspathacea fell from 40–60 g m^‐2 to 20–30 g m^‐2. Intense grazing on remaining patches of sward has restricted growth of these clonal forage plants and hypersalinity of bare sediments has precluded re‐establishment of vegetation. Between 1989 and 1993 numbers of faecal droppings in grazed plots reached maximum values of 15–22 droppings m^‐2 wk^‐1. Since then peak values have remained at less than 13 droppings m^‐2 wk^‐1. The loss of vegetation and changes in soil conditions have resulted in the establishment of an alternative stable state (hypersaline bare sediment).