Effects of accumulations of sediments and drift algae on recruitment of sessile organisms associated with oyster reefs

Increases in sediment and drift algae accumulations have caused degradation of coastal lagoons worldwide. It is well known that these factors are stressors of seagrass beds, sediment fauna and coral reefs. However, little is known about the impacts on temperate hard-bottom assemblages within soft-bottom lagoons. To test if accumulations of sediment and drift algae (stress) affected recruitment of sessile oyster reef organisms, we constructed cages in Hog Island Bay, Virginia that trapped drifting macroalgae (≈ 2.7 kg WW m²) and facilitated sedimentation (≈ 7 mm per 2-3 month). The stress treatments and unstressed controls were placed in front, between, and behind reefs (position) to represent wave exposed (≈ 0.3 m, windy conditions), current exposed (≈ 0.2 m s^− 1, peak tide) and protected (≈ 0 m, 0.0 m s^− 1) habitats. The percentage cover of recruited taxa onto bricks was mapped 4 times during a 1-year period. There were strong significant effects of stress on the total assemblage, plant (but not animal) richness, total plant and animal cover, and cover of the most common taxa. Unstressed bricks had high plant richness, high animal and plant cover, and high cover of the oyster Crassostrea virginica, the alien algae Gracilaria vermiculophylla and Codium fragile, the alga Agardhiella subulata, and high to medium cover of the opportunistic algae Ulva curvata and Enteromorpha spp. In comparison, sediment-stressed bricks had low plant richness, low animal and plant cover, and low cover of C. virginica, G. vermiculophylla, C. fragile, A. subulata, U. curvata and Enteromorpha spp. Similarly, algae-stressed bricks also had low cover of animals, C. virginica, G. vermiculophylla, C. fragile, and A. subulata, but intermediate plant richness and plant cover and high cover of U. curvata and Enteromorpha spp. Although reef position caused significant multivariate results, this factor was clearly less important than the stress factor. Our study shows that accumulations of sediments and drift algae have an adverse impact on sessile temperate reef organisms, reducing richness and abundance, but favoring a few small opportunistic taxa. As the reef-generating oysters themselves performed poorly under these stressors, the long-term impact of the causes of these stressors, eutrophication and urbanization, is likely to be diminished reefs with cascading adverse effects on sessile reef organisms.     

Seedbed filter controls post-fire succession

Using black spruce (Picea mariana)-Kalmia angustifolia dominated communities of eastern Canada we tested the hypothesis that habitat filter pre-empts biotic filter as a community structuring force in early post-fire succession leading to Kalmia dominated heath. We considered post-fire seedbed as an abiotic (habitat) filter and post-fire aboveground biomass of dominant plants as a biotic filter. First we surveyed and categorized post-fire seedbed types and tested the seedbed filter by a black spruce seeding experiment in 155 small plots (30×30 cm²) on nine sites burned between 1 and 38 years previously. We then quantified black spruce seedling establishment in a competition removal and nitrogen addition experiment in twenty four 3×3 m² plots on four sites burned 7, 24, 23 and 29 years previously. We also conducted a vegetation survey in 200 plots (1×1 m²) on 20 sites along a 1- to 76-year post-fire chronosequence. Only about 10% post-fire seedbed with little or no residual organic matter was suitable for black spruce regeneration. On the rest of the seedbeds made up of charred humus and lichen substrates Kalmia grew profusely by sprouting from sub-surface fire survived components. Removal of aboveground competition and addition of nitrogen did not help black spruce seedling establishment. Kalmia dominated the chronosequence with 50–90% cover until 60 years after fire. Black spruce cover was insignificant during the first 20 years followed by a slow increase surpassing Kalmia cover around 60 years. Herbaceous cover was initially high followed by a decline coinciding with high Kalmia cover and then increased again with decreased Kalmia cover. Lichen cover followed a similar trend. We interpret this post-fire vegetation assembly as a seedbed controlled phenomenon where seedbed limitation filters out the pre-fire dominant, black spruce, in favour of vegetatively regenerating Kalmia turning coniferous forest into Kalmia heath during the first four decades of secondary succession.     

Factors Affecting Harp Seal (Pagophilus groenlandicus) Strandings in the Northwest Atlantic

The effects of climate change on high latitude regions are becoming increasingly evident, particularly in the rapid decline of sea ice cover in the Arctic. Many high latitude species dependent on sea ice are being forced to adapt to changing habitats. Harp seals (Pagophilus groenlandicus) are an indicator species for changing high-latitude ecosystems. This study analyzed multiple factors including ice cover, demographics, and genetic diversity, which could affect harp seal stranding rates along the eastern coast of the United States. Ice cover assessments were conducted for the month of February in the Gulf of St. Lawrence whelping region from 1991–2010 using remote sensing data, and harp seal stranding data were collected over the same time period. Genetic diversity, which may affect how quickly species can adapt to changing climates, was assessed using ten microsatellite markers to determine mean d ² in a subset of stranded and by-caught (presumably healthy) seals sampled along the northeast U.S. coast. Our study found a strong negative correlation (R ² = 0.49) between ice cover in the Gulf of St. Lawrence and yearling harp seal strandings, but found no relationship between sea ice conditions and adult strandings. Our analysis revealed that male seals stranded more frequently than females during the study period and that this relationship was strongest during light ice years. In contrast, we found no significant difference in mean d ² between stranded and by-caught harp seals. The results demonstrate that sea ice cover and demographic factors have a greater influence on harp seal stranding rates than genetic diversity, with only a little of the variance in mean d ² among stranded seals explained by ice cover. Any changes in these factors could have major implications for harp seals, and these findings should be considered in the development of future management plans for the Arctic that incorporate climate variability.     

Effect of a Terminated Cover Crop and Aldicarb on Cotton Yield and Meloidogyne incognita Population Density

Terminated small grain cover crops are valuable in light textured soils to reduce wind and rain erosion and for protection of young cotton seedlings. A three-year study was conducted to determine the impact of terminated small grain winter cover crops, which are hosts for Meloidogyne incognita, on cotton yield, root galling and nematode midseason population density. The small plot test consisted of the cover treatment as the main plots (winter fallow, oats, rye and wheat) and rate of aldicarb applied in-furrow at-plant (0, 0.59 and 0.84 kg a.i./ha) as subplots in a split-plot design with eight replications, arranged in a randomized complete block design. Roots of 10 cotton plants per plot were examined at approximately 35 days after planting. Root galling was affected by aldicarb rate (9.1, 3.8 and 3.4 galls/root system for 0, 0.59 and 0.84 kg aldicarb/ha), but not by cover crop. Soil samples were collected in mid-July and assayed for nematodes. The winter fallow plots had a lower density of M. incognita second-stage juveniles (J2) (transformed to Log₁₀ (J2 + 1)/500 cm³ soil) than any of the cover crops (0.88, 1.58, 1.67 and 1.75 Log₁₀(J2 + 1)/500 cm³ soil for winter fallow, oats, rye and wheat, respectively). There were also fewer M. incognita eggs at midseason in the winter fallow (3,512, 7,953, 8,262 and 11,392 eggs/500 cm³ soil for winter fallow, oats, rye and wheat, respectively). Yield (kg lint per ha) was increased by application of aldicarb (1,544, 1,710 and 1,697 for 0, 0.59 and 0.84 kg aldicarb/ha), but not by any cover crop treatments. These results were consistent over three years. The soil temperature at 15 cm depth, from when soils reached 18°C to termination of the grass cover crop, averaged 9,588, 7,274 and 1,639 centigrade hours (with a minimum threshold of 10°C), in 2005, 2006 and 2007, respectively. Under these conditions, potential reproduction of M. incognita on the cover crop did not result in a yield penalty.     

Effects of urbanization on Song Sparrow (Melospiza melodia) population connectivity

Urbanization may affect genetic differentiation among animal populations because it converts native vegetation to novel land cover types that can affect population connectivity. The effect of land cover change on genetic differentiation may vary among taxa; mobile birds may be least affected. Regardless, genetic differentiation between populations should be best predicted by measures of distance that incorporate the effect of land cover on movement. We studied the relationship between land cover and genetic differentiation in Song Sparrows (Melospiza melodia) at eighteen sites in the Seattle metropolitan region. We generated a series of hypothetical “resistance surfaces” based on land cover and development age, calculated “resistance distances” between pairs of sampling sites, and related them to pairwise genetic differentiation. Genetic differentiation was best described by a multiple regression model where resistance to gene flow (1) linearly increased with age of development and (2) was greater in high- and medium-density urbanization than in native forest land cover types (R ² = 0.15; p = 0.003). The single variable with the highest correlation with genetic differentiation was derived from a linear relationship between development age and resistance (R ² = 0.08; p = 0.007). Our results thus suggested that urban development reduced population connectivity for Song Sparrows. However, the relation of development age to genetic differentiation suggested that equilibrium was not yet reached. Hence, the effects of lost connectivity will increase. Our understanding of the landscape genetics of this recently anthropogenically modified landscape benefited from considering population history.     

Changes in litter decomposition and soil organic carbon in a reforested tropical deciduous cover (India)

Soil organic carbon (SOC) up to 1 m depth originates from contemporary vegetation cover dating from past millennia. Deforestation and reforestation with economically important species is influencing soil carbon sequestration. An attempt has been made in this study to evaluate the impact of vegetation cover change (due to replacement of natural heterogeneous cover by teak and bamboo) on SOC using carbon isotopes (δ¹³C, ¹⁴C) in a tropical system (India). A litter decomposition study was carried out to understand the impact of differences in vegetation characteristics (specifically of leaves) on decomposition. Both experiments were carried out to look at the impact of changes in vegetation characteristics (specifically of leaves) on litter decomposition, and how these influence near term litter decomposition rates (k values) and long-term SOC content of the soil system beneath. Leaves of teak, bamboo and eight other species were selected for this study. The proportion of structural carbohydrates (lignin and cellulose) in leaves significantly (at 5 % level) influenced k values. The SOC and carbon isotope data collected in this study indicate that C₃ vegetation cover in the study area could be contemporary and dominant for the past few centuries. This can be extended up to ~2,200 years from the recorded ¹⁴C values of teak cover. The study confirms that k values of leaf litter influence SOC present beneath the vegetation cover at the decadal/century time scale.     

Land cover change effects on soil chemical and biological properties after planting Mongolian pine (Pinus sylvestris var. mongolica) in sandy lands in Keerqin, northeastern China

We compared soil moisture content, pH, total organic carbon (C _org), total nitrogen (TN), total phosphorus (TP) and inorganic N (NH₄ ⁺–N, NO₃ ^?–N) concentrations, soil potential C and N mineralization rates, soil microbial biomass C (C _mic), soil metabolic quotient (qCO₂), soil microbial quotient (C _mic/C _org) and soil enzyme (urease and invertase) activities in semiarid sandy soils under three types of land cover: grassland, Mongolian pine (Pinus sylvestris var. mongolica) plantation, and elm (Ulmus punila)–grass savanna in southeastern Keerqin, in northeast China. Soil C _org, TN and TP concentrations (0–10, 10–20, 20–40 and 40–60 cm) were lower while soil C/N and C/P ratios were higher in the plantation than in grassland and savanna. The effects of land cover change on NH₄ ⁺–N and NO₃ ^?–N concentrations, soil potential nitrification and C mineralization rates in the surface soil (0–10 cm) were dependent on sampling season; but soil potential N mineralization rates were not affected by land cover type and sampling season. The effects of land cover change on C _mic and qCO₂ of surface soil were not significant; but C _mic/C _org were significantly affected by land cover change and sampling season. We also found that land cover change, sampling season and land cover type?×?sampling season interaction significantly influenced soil enzyme (urease and invertase) activities. Usually soil enzyme activities were lower in the pine plantations than in grassland and savanna. Our results suggest that land cover change markedly influenced soil chemical and biological properties in sandy soils in the semiarid region, and these effects vary with sampling season.     

Macroalgal herbivory on recovering versus degrading coral reefs

Macroalgal-feeding fishes are considered to be a key functional group on coral reefs due to their role in preventing phase shifts from coral to macroalgal dominance, and potentially reversing the shift should it occur. However, assessments of macroalgal herbivory using bioassay experiments are primarily from systems with relatively high coral cover. This raises the question of whether continued functionality can be ensured in degraded systems. It is clearly important to determine whether the species that remove macroalgae on coral-dominated reefs will still be present and performing significant algal removal on macroalgal-dominated reefs. We compared the identity and effectiveness of macroalgal-feeding fishes on reefs in two conditions post-disturbance—those regenerating with high live coral cover (20–46 %) and those degrading with high macroalgal cover (57–82 %). Using filmed Sargassum bioassays, we found significantly different Sargassum biomass loss between the two conditions; mean assay weight loss due to herbivory was 27.9 ± 4.9 % on coral-dominated reefs and 2.2 ± 1.1 % on reefs with high macroalgal cover. However, once standardised for the availability of macroalgae on the reefs, the rates of removal were similar between the two reef conditions (4.8 ± 4.1 g m^?2 h^?1 on coral-dominated and 5.3 ± 2.1 g m^?2 h^?1 on macroalgal-dominated reefs). Interestingly, the Sargassum-assay consumer assemblages differed between reef conditions; nominally grazing herbivores, Siganus puelloides and Chlorurus sordidus, and the browser, Siganus sutor, dominated feeding on high coral cover reefs, whereas browsing herbivores, Naso elegans, Naso unicornis, and Leptoscarus vaigiensis, prevailed on macroalgal-dominated reefs. It appeared that macroalgal density in the surrounding habitat had a strong influence on the species driving the process of macroalgal removal. This suggests that although the function of macroalgal removal may continue, the species responsible may change with context, differing between systems that are regenerating versus degrading.     

Influence of Seeding Ratio,Planting Date,and Termination Date on Rye-Hairy Vetch Cover Crop Mixture Performance under Organic Management

Cover crop benefits include nitrogen accumulation and retention, weed suppression, organic matter maintenance, and reduced erosion. Organic farmers need region-specific information on winter cover crop performance to effectively integrate cover crops into their crop rotations. Our research objective was to compare cover crop seeding mixtures, planting dates, and termination dates on performance of rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth) monocultures and mixtures in the maritime Pacific Northwest USA. The study included four seed mixtures (100% hairy vetch, 25% rye-75% hairy vetch, 50% rye-50% hairy vetch, and 100% rye by seed weight), two planting dates, and two termination dates, using a split-split plot design with four replications over six years. Measurements included winter ground cover; stand composition; cover crop biomass, N concentration, and N uptake; and June soil NO₃ ^--N. Rye planted in mid-September and terminated in late April averaged 5.1 Mg ha^-1 biomass, whereas mixtures averaged 4.1 Mg ha^-1 and hairy vetch 2.3 Mg ha^-1. Delaying planting by 2.5 weeks reduced average winter ground cover by 65%, biomass by 50%, and cover crop N accumulation by 40%. Similar reductions in biomass and N accumulation occurred for late March termination, compared with late April termination. Mixtures had less annual biomass variability than rye. Mixtures accumulated 103 kg ha^-1 N and had mean C:N ratio <17:1 when planted in mid-September and terminated in late April. June soil NO₃ ^--N (0 to 30 cm depth) averaged 62 kg ha^-1 for rye, 97 kg ha^-1 for the mixtures, and 119 kg ha^-1 for hairy vetch. Weeds comprised less of the mixtures biomass (20% weeds by weight at termination) compared with the monocultures (29%). Cover crop mixtures provided a balance between biomass accumulation and N concentration, more consistent biomass over the six-year study, and were more effective at reducing winter weeds compared with monocultures.     

Two bromeliad species with contrasting functional traits partition the understory space in a South American xerophytic forest: correlative evidence of environmental control and limited dispersal

We examined the spatial distribution of two bromeliad species with contrasting functional traits in the understory of a xerophytic South American Chaco forest. Aechmea distichantha is a facultative terrestrial species with well-developed phytotelma and short rhizomes, whereas Bromelia serra is a strictly terrestrial species with soil-exploring roots and long rhizomes. Both bromeliads develop colonies on relatively elevated patches in Schinopsis balansae forests. We evaluated the roles of environmental controls, limited dispersal, and interspecific competition as drivers of the different distribution of these bromeliads. We mapped the overstory, understory and topography of 16 forest plots with bromeliads (400 m² each, subdivided in 100 4-m² subplots). We sampled soil characteristics on sectors dominated by each bromeliad species. We used structural equation modeling to assess direct and indirect associations of each bromeliad species cover with environmental conditions, abundance of conspecifics in the vicinity, and local abundance of the other species. A. distichantha cover increased on elevated subplots with high tree/shrub basal area, whereas B. serra cover showed the opposite pattern. In addition, A. distichantha cover was negatively associated with B. serra cover, but not vice versa, and cover of both species increased with the abundance of nearby conspecifics, suggesting that limited vegetative dispersal partly accounted for their distribution. Sectors dominated by A. distichantha had lower soil bulk density and higher organic matter content than those dominated by B. serra. According to our model, influences of competition and limited vegetative dispersal reinforce the association between distribution of these bromeliads and environmental heterogeneity of the forest understory.     

Habitat use,density, and conservation status of the white-browed guan (Penelope jacucaca Spix, 1825)

The white-browed guan (Cracidae: Penelope jacucaca) is an endemic bird species to the Caatinga, the largest centre of dry forest in South America. This taxon was considered Vulnerable by the International Union for Conservation of Nature (IUCN) due to continued habitat loss within its distribution and intense hunting pressure that contributed to population declines. However, information on population aspects and habitat use by P. jacucaca, which is fundamental for monitoring its conservation status, is not available. We studied habitat use (analysed in a Generalized Linear Model) and population density (estimated by distance sampling) in a specific area in Northeast Brazil. Using species distribution modelling (SDM), forest cover loss data (performed in the MaxEnt program) and quantitative information about hunting, more rigorous estimates of the distribution limits, available habitat, and population declines of P. jacucaca were generated. Based on the IUCN criteria, we applied analysed data to reassess the conservation status of the white-browed guan. Local density was estimated at 13.1 individuals/km² and the estimated number of individuals removed per year due to hunting was 121.7 in the forest cover area (110.46 km²) of the Serra de Santa Catarina. Consequently, the annual removal rate of hunted individuals in the study area corresponds to approximately 11% of the population. The habitat use analysis pointed to a strong positive association with seasonally dry deciduous forest (SDDF) vegetation and with arboreal vegetation. The SDM indicated a potential distribution (climatically favourable) area of 675,823 km², and forest cover and loss calculations indicated a total of 81,307 km² of available suitable habitat in 2013. Therefore, comparing these results to the IUCN criteria, we recommend that P. jacucaca remain in the Vulnerable category.     

Effects of wave exposure on population and reproductive phenology of an algal turf, Gelidium pusillum (Gelidales,Rhodophyta), Songkhla,Thailand

The effect of wave exposure on the population and reproductive phenology of the common red alga, Gelidium pusillum (Stackhouse) Le Jolis, was investigated between July 2003 and June 2004, at Suan Song Tha Le, Songkla Province, Thailand. Lengths of thalli, percentage cover, percentage of reproductive fronds and the number of reproductive structures were examined monthly in relation to different degrees of wave exposure (sheltered vs. exposed), temperature, rainfall, day length and tidal cycles. Frond length and percentage cover of G. pusillum were different among sites and seasons. Shorter fronds were found on the exposed shore which had a greater percentage cover. Fronds bleached and died off during the summer months (April and May), which resulted in shorter fronds and reduced percentage cover in June. The thalli reproduced throughout the year, with a predominance of tetrasporophytes. The highest percentage of tetrasporic fronds was 33% in February 2004 and 13% of cystocarpic fronds in April 2004, but male gametophytic fronds were never observed. Rainfall showed a strongly negative influence on reproduction since no reproductive fronds were observed during the rainy season (R² = 0.49, P = 0.01). The dominance of G. pusillum at this study site and throughout elsewhere in turf habitats might be a function of persistent vegetative growth, densely clumped, and the ability to reproduce almost throughout the entire year.     

Diversity and activity of methanotrophs in landfill cover soils with and without landfill gas recovery systems

Aerobic CH₄ oxidation plays an important role in mitigating CH₄ release from landfills to the atmosphere. Therefore, in this study, oxidation activity and community of methanotrophs were investigated in a subtropical landfill. Among the three sites investigated, the highest CH₄ concentration was detected in the landfill cover soil of the site (A) without a landfill gas (LFG) recovery system, although the refuse in the site had been deposited for a longer time (∼14–15 years) compared to the other two sites (∼6–11 years) where a LFG recovery system was applied. In April and September, the higher CH₄ flux was detected in site A with 72.4 and 51.7 g m⁻² d⁻¹, respectively, compared to the other sites. The abundance of methanotrophs assessed by quantification of pmoA varied with location and season. A linear relationship was observed between the abundance of methanotrophs and CH₄ concentrations in the landfill cover soils (R = 0.827, P < 0.001). The key factors influencing the methanotrophic diversity in the landfill cover soils were pH, the water content and the CH₄ concentration in the soil, of which pH was the most important factor. Type I methanotrophs, including Methylococcus, Methylosarcina, Methylomicrobium and Methylobacter, and type II methanotrophs (Methylocystis) were all detected in the landfill cover soils, with Methylocystis and Methylosarcina being the dominant genera. Methylocystis was abundant in the slightly acidic landfill cover soil, especially in September, and represented more than 89% of the total terminal-restriction fragment abundance. These findings indicated that the LFG recovery system, as well as physical and chemical parameters, affected the diversity and activity of methanotrophs in landfill cover soils.     

Culturable psychrotolerant methanotrophic bacteria in landfill cover soil

Methanotrophs closely related to psychrotolerant members of the genera Methylobacter and Methylocella were identified in cultures enriched at 10°C from landfill cover soil samples collected in the period from April to November. Mesophilic methanotrophs of the genera Methylobacter and Methylosinus were found in cultures enriched at 20°C from the same cover soil samples. A thermotolerant methanotroph related to Methylocaldum gracile was identified in the culture enriched at 40°C from a sample collected in May (the temperature of the cover soil was 11.5–12.5°C). In addition to methanotrophs, methylobacteria of the genera Methylotenera and Methylovorus and members of the genera Verrucomicrobium, Pseudomonas, Pseudoxanthomonas, Dokdonella, Candidatus Protochlamydia, and Thiorhodospira were also identified in the enrichment cultures. A methanotroph closely related to the psychrotolerant species Methylobacter tundripaludum (98% sequence identity of 16S rRNA genes with the type strain SV96^T) was isolated in pure culture. The introduction of a mixture of the methanotrophic enrichments, grown at 15°C, into the landfill cover soil resulted in a decrease in methane emission from the landfill surface in autumn (October, November). The inoculum used was demonstrated to contain methanotrophs closely related to Methylobacter tundripaludum SV96.     

Post-fire regeneration patterns in the eastern Iberian Peninsula

Post-fire regeneration patterns (plant cover and richness) in the Valencia region (eastern Iberian Peninsula) are studied by analysing data from two different samplings after two periods of large fires (1991 and 1994). Emphasis is given to comparing different environmental conditions (thermo-Mediterranean vs. meso-Mediterranean; south facing vs. north facing slopes) and different bedrock types (limestone vs. marls). Results suggest that the highest post-fire cover and species richness is reached in thermo-Mediterranean conditions on limestone, and the main species are the resprouters Quercus coccifera and Brachypodium retusum. North-facing sites have higher plant cover than south-facing ones, and most life forms (trees, shrubs, grasses) have higher cover in these sites. Species richness is higher on north-facing sites than on the south-facing ones at the small scale (1 to 200 m²), but differences were not significant at the highest scale studied (1 000 m²). Plant species richness with increasing sampling area follows the classical log-log relationship; however, when species are segregated by life forms (woody species and herbs), different species-area relationships were found.     

PK additions modify the effects of N dose and form on species composition, species litter chemistry and peat chemistry in a Scottish peatland

Wet N deposition comprises oxidised (nitrate) and reduced (ammonium) N forms in proportions that vary spatially with source and topography. Field evidence of long-term N form effects on semi-natural ecosystems and how these are modified by phosphorus and potassium availability are lacking. This study describes cover changes for some key peatland species and litter chemistry from Sphagnum capillifolium, Calluna and Eriophorum vaginatum, and peat in response to 9 years of N treatment. Ammonium and nitrate as NH₄Cl or NaNO₃ were provided to replicate plots in rainwater spray at +8 (low) or +56 (high) kg N ha^?1 year, with and without PK via an automated system coupled to site meteorological conditions. Reduced N caused greater N accumulation in all key species than oxidised N, especially at higher doses, but cover declined more, though not significantly so, with oxidised than reduced N at the high N dose. Overall the detrimental effects of high N on Sphagnum and Calluna cover were significant but small. By comparison PK inclusion with 56 kg N ha^?1 year as oxidised N, not reduced N, had devastating effects on cover, causing both S. capillifolium and Calluna to decrease 3–5-fold, facilitating invasion and expansion of nitrophiles, non-characteristic bog plants e.g. Epilobium angustifolium, Epilobium palustre, Juncus effusus, Digitalis purpurea and Dryopteris dilatata. N form appears to be significant for peatlands because of its effects on pH. The significance of changes in plant cover for peat chemistry and decomposition for biogeochemistry is discussed.     

西南高山地区净生态系统生产力时空动态

西南高山地区生态系统类型丰富、地形复杂,是响应全球气候变化的重点区域,对全球气候变化具有重要的指示作用.应用生态系统模型(Carbon Exchange between Vegetation,Soil,and the Atmosphere,CEVSA)模型估算了1954-2010年西南高山地区净生态系统生产力(NEP)的时空变化,分析了其对气候变化的响应.结果表明:(1)1954-2010年西南高山地区NEP平均为29.7gC·m-2·a-1,其中低海拔地区常绿针叶林和常绿阔叶林NEP较高,而高海拔地区的草地覆盖类型NEP较低.(2)西南高山地区NEP总量的变动范围为-8.36-29.4Tg C/a,平均每年吸收碳15.4Tg C;NEP年际下降趋势显著(P＜0.05),平均每年减少0.187Tg C,下降显著的区域占研究地区总面积的35.2％ (P＜0.05),其中草地(-0.526 g C·m-2·a-2,P＜0.01)和常绿针叶林(-0.691g C·m-2·a-2,P＜0.01)下降趋势极为显著.(3)年NEP总量的年际变化与年平均温度呈负相关(r=-0.454,P＜0.01),与年降水量呈正相关(r=0.708,P＜0.01),与温度显著负相关的区域占60.3％ (P＜0.05),与降水显著正相关的区域占52.1％(P＜0.05),其中草地和常绿针叶林均与温度极显著负相关(r=-0.603,P＜0.01;r=-0.485,P＜0.01),而与降水量极显著正相关(r=0.554,P＜0.01; r=0.749,P＜0.01).(4)西南高山地区是明显的碳汇区,但是由于土壤异养呼吸(HR,heterotrophic respiration)的增长速度大于净初级生产力(NPP,net primary production)的增长速度,最近20a有部分地区开始由碳汇转为碳源.     

A comparative study of aboveground biomass of three Mediterranean species in a post-fire succession

The aboveground biomass of three woody species (Cistus albidus, Quercus coccifera and Pinus halepensis) in two early successional stages (3- and 10-year old) of a post-fire Mediterranean ecosystem was investigated. Among these three species, which belong to the successional series of holm oak (Quercus ilex), C. albidus and Q. coccifera are two dominant shrub species in the garrigue ecosystem and P. halepensis is a pioneer tree species widely represented in the Mediterranean area. The results obtained showed that in monospecific stands, C. albidus and Q. coccifera had a high recovery potential. In the 3-year-old stands, the cover of P. halepensis was only 19.8% for a total biomass of 0.75 ± 0.21 t ha^–1, while the plant cover of C. albidus and Q. coccifera was, respectively, 26% and 85.5% and biomass was 4.72 ± 1.09 and 11.5 ± 0.16 t ha^–1. Only 10 years after fire, the plant cover of C. albidus and Q. coccifera was, respectively, 55% and 100% and total biomass 13.2 ± 1.7 and 35.8 ± 4.7 t ha^–1. The greatest increase in biomass was noted for P. halepensis (29.7 t ha^–1). If mean annual biomass increments are considered, it appears that there was a significant decrease with the stand age for the two shrub species although the tree species showed an increase in productivity. These differing patterns in biomass and productivity of shrub and tree species with stand age provide information on biomass accumulation rates of pioneer species in a Mediterranean succession and their importance in the vegetation dynamics.     

Forest cover and heterogeneous pastures shape the diversity of predatory rove beetles in tropical riparian habitats

In tropical landscapes, forest remnants have been reduced to narrow strips of vegetation along rivers and streams surrounded by agricultural land that affects biodiversity, depending on the habitat and landscape characteristics. To assess the effect of riparian forest loss on the diversity of Staphylininae predatory rove beetles, we considered two habitat conditions (river sites with riparian vegetation and sites with heterogeneous pastures) within two micro-basin types (with >70% and <40% forest cover) in a tropical montane cloud forest landscape, Mexico. Beetles were collected using baited pitfall traps during the rainy season of 2014. No differences were found between micro-basin types and, although species richness (⁰D) was similar between habitat conditions, when the diversity of common (¹D) and dominant (²D) species was considered, sites with heterogeneous pastures were almost twice as diverse as those with riparian vegetation. All diversity measurements were greater in sites with heterogeneous pastures of either micro-basin type. Air temperature and canopy cover were the environmental variables that best explained the variation in beetle species composition. The greatest environmental differences related to species composition were detected between habitat conditions and were more evident in sites with heterogeneous pastures and low forest cover in the surroundings. The results suggest that replacing riparian vegetation with heterogeneous pastures, within micro-basins that lost between 30% and 60% of their forest cover, does not significantly reduce the diversity of predatory rove beetle but rather modifies the beetle composition. Effective formulation of management strategies to mitigate the impact of land use modification therefore requires an understanding of the interaction between vegetation remnants and landscape characteristics.     

Effect of vegetation on alpha cellulose decomposition in littoral lake sediments

The effect of vegetation cover on the decomposition of organic matter (alpha cellulose) was studied at three sediment depths (5, 15 and 25 cm) in the littoral area of a small Lake Kiruvere (Estonia). The experiment was carried out in two adjacent sites, with and without vegetation, using the litter bag method. At all sediment depths decomposition was faster at the site covered with vegetation, and was highest at 5 cm sediment depth (decomposition rate k = 0.0037 day⁻¹) and lower at 15 and 25 cm depths (k = 0.0014 day⁻¹ and k = 0.0013 day⁻¹). Higher decomposition rates coincided with higher root mass in the sediment. Decomposition rates were similar at all sediment depths in the site without a vegetation cover (k = 0.0007-0.0009 day⁻¹). The presence of a vegetation cover also affected temperatures in sediments. Temperatures were several degrees higher at all sediment depths in the area with vegetation cover, than in the area without. Mean sediment temperature differences between the two experiment areas were 1.4 °C at 5 cm sediment depth, 2.5 °C at 15 cm depth and 3.1 °C at 25 cm depth. Higher decomposition rates in the site covered with vegetation can be explained by oxygen dispersion from young roots in the higher sediment layers and by higher sediment temperatures due to the internal gas flow enhancing the microbial activity in the lower sediment layers.