Variability in exchange of CO2 across 12 northern peatland and tundra sites

Many wetland ecosystems such as peatlands and wet tundra hold large amounts of organic carbon (C) in their soils, and are thus important in the terrestrial C cycle. We have synthesized data on the carbon dioxide (CO₂) exchange obtained from eddy covariance measurements from 12 wetland sites, covering 1–7 years at each site, across Europe and North America, ranging from ombrotrophic and minerotrophic peatlands to wet tundra ecosystems, spanning temperate to arctic climate zones. The average summertime net ecosystem exchange of CO₂ (NEE) was highly variable between sites. However, all sites with complete annual datasets, seven in total, acted as annual net sinks for atmospheric CO₂. To evaluate the influence of gross primary production (GPP) and ecosystem respiration (R_eco) on NEE, we first removed the artificial correlation emanating from the method of partitioning NEE into GPP and R_eco. After this correction neither R_eco (P= 0.162) nor GPP (P= 0.110) correlated significantly with NEE on an annual basis. Spatial variation in annual and summertime R_eco was associated with growing season period, air temperature, growing degree days, normalized difference vegetation index and vapour pressure deficit. GPP showed weaker correlations with environmental variables as compared with R_eco, the exception being leaf area index (LAI), which correlated with both GPP and NEE, but not with R_eco. Length of growing season period was found to be the most important variable describing the spatial variation in summertime GPP and R_eco; global warming will thus cause these components to increase. Annual GPP and NEE correlated significantly with LAI and pH, thus, in order to predict wetland C exchange, differences in ecosystem structure such as leaf area and biomass as well as nutritional status must be taken into account.     

Birds in willow short-rotation coppice compared to other arable crops in central England and a review of bird census data from energy crops in the UK

We present the results of spring and winter surveys of birds using 22 willow short-rotation coppice (SRC) fields and 22 paired arable or grassland controls over a 5 year period in central and northern England. The study sites were linked to the first commercial wood-fuelled electricity plant in Yorkshire and were managed commercially. We use the findings of this study, in the context of other work on birds in energy crops, to suggest how birds may be affected by commercial cropping of SRC or energy grasses on UK farmland. For willow SRC, most existing farmland species were not completely displaced by SRC cropping. Even farmland specialists such as Skylark Alauda arvensis used cut SRC fields. Some species characteristic of scrub and wood-type habitats were attracted onto farmland by SRC. Birds were more abundant in hedgerows next to SRC than in those adjoining arable or grass. The interior of large SRC plots contained fewer birds than the edge-zone (< 50 m). In winter, the same resident species occured in SRC as the summer, plus winter migrants such as Snipe Gallinago gallinago and Fieldfare Turdus pilaris . Overall, more individuals and species were recorded in and around SRC than equivalent arable or grassland throughout the year. Yellow Wagtail Motacilla flava and certain locally occurring farmland specialists may be displaced by SRC plantations. Equivalent census data for energy grasses in the UK are not available. The impact of large regional energy crop developments on birds is not known. We do not know if species commonly recorded in these crops survive and breed well so population effects are unknown. However SRC crops are often weedy and insect rich and hence have potential as foraging habitats in summer and winter. The scope for agri-environment schemes to include energy crops is discussed.     

A new species of Arctotis (Compositae, Arctotideae) from kommetjie grassland in Eastern Cape Province, South Africa

Arctotis debensis R.J.McKenzie, a new species from the Albany Centre of Floristic Endemism, South Africa, is described and illustrated. It grows almost exclusively in grassland on kommetjies, a distinctive landform of depressions and mounds associated with giant earthworms, in a restricted area west of King William's Town, Eastern Cape Province. It is the first plant taxon reported to be endemic or near-endemic to this unusual habitat. The new species appears to have been collected rarely and previous collections examined have remained undetermined to species level. The new species is distinguished from closely allied species by the combination of its usually larger dimensions in all parts, prostrate habit, coriaceous leaves that are green, scabrous, and eglandular on the adaxial surface and densely lanate on the abaxial surface, and involucral-bract morphology.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 151 , 581–588.     

A HEXAPOD FROM THE EARLY DEVONIAN WINDYFIELD CHERT, RHYNIE, SCOTLAND

Abstract: New diagnostic morphological features discovered following a re‐examination and further preparation of the holotype of Leverhulmia mariae Anderson and Trewin from the Early Devonian (Pragian) Windyfield chert are described and discussed here. The discovery of anterior (thoracic?) leg appendages with attached pretarsal elements comprising a fixed median unguis, a pair of articulated lateral ungues and possible unguitractor plate has allowed us to reclassify this enigmatic fossil as Hexapoda incertae sedis. We interpret the holotype as part of an abdomen bearing at least five pairs of segmented leglets. The condition of the ungues on the anterior appendages is strongly reminiscent of Archaeognatha and Zygentoma (= Thysanura s.s.), and the segmented leglets on the abdomen show similarities with certain fossil ‘apterygotes’ known from the Carboniferous. Leverhulmia is the third hexapod species found in the cherts at Rhynie, the other forms being the collembolan Rhyniella praecursor Hirst and Maulik, and the pterygote insect Rhyniognatha hirsti Tillyard. Showing closer affinities with Archaeognatha and Zygentoma, Leverhulmia may well represent the earliest fossil apterous insect known to date.     

Ecosystem recovery: heathland response to a reduction in nitrogen deposition

Atmospheric deposition of nitrogen is responsible for widespread changes in the structure and function of sensitive seminatural ecosystems. The proposed reduction in emissions of nitrogenous pollutants in Europe under the Gothenburg Protocol raises the question of whether affected ecosystems have the potential to recover to their previous condition and, if so, over what timescale. Since 1998, we have monitored the response of a lowland heathland in southern England following the cessation of a long‐term nitrogen addition experiment, and subsequent management, assessing changes in vegetation growth and chemistry, soil chemistry and the soil microbial community. Persistent effects of earlier nutrient loading on Calluna growth and phenology, and on the abundance of lichens, were apparent up to 8 years after nitrogen additions ceased, indicating the potential for long‐term effects of modest nutrient loading (up to 15.4 kg N ha^?1 yr^?1, over 7 years) on heathland ecosystems. The size and activity of the soil microbial community was elevated in former N‐treated plots, 6–8 years after additions ceased, suggesting a prolonged effect on the rate of nutrient cycling. Although habitat management in 1998 reduced nitrogen stores in plant biomass, effects on belowground nitrogen stores were small. Although some parameters (e.g. soil pH) recover pretreatment levels relatively rapidly, others (e.g. vegetation cover and microbial activity) respond much more slowly, indicating that the ecological effects of even small increases in nitrogen deposition will persist for many years after deposition inputs are reduced. Indeed, calculations suggest that the additional soil nitrogen storage associated with 7 years of experimental nitrogen inputs could sustain the observed effects on plant growth and phenology for several decades. Carry over effects on plant phenology and sensitivity to drought suggest that the persistence of vegetation responses to nitrogen deposition should be integrated into long‐term assessments of the impact of global climate change on sensitive ecosystems.     

Centennial‐scale changes to the aquatic vegetation structure of a shallow eutrophic lake and implications for restoration

1. We investigate long‐term (>200 years) changes to the composition and spatial structure of macrophyte communities in a shallow, eutrophic lake (Barton Broad, eastern England) and consider the implications for lake restoration. 2. Historical macrophyte data were assembled from a variety of sources: existing plant databases, museum herbaria, journal articles, old photographs and eyewitness accounts. Additionally, two types of sediment core sample were analysed for plant macro‐remains and pollen; bulk basal samples from multiple core sites analysed to provide information on ‘pre‐disturbance’ macrophyte communities and two whole cores analysed to determine historical change. 3. Prior to the late 1800s, macrophyte communities were diverse and included a multilayered mosaic of short‐stature submerged taxa and taller submerged and floating‐leaved species. With the progression of eutrophication after around 1900, the former community was displaced by the latter. Diversity was maintained, however, since an encroaching Schoenoplectus–nymphaeid swamp generated extensive patches of low‐energy habitat affording refugia for several macrophytes otherwise unable to withstand the hydraulic forces associated with open water conditions. When this swamp vegetation disappeared in the 1950s, many of the ‘dependent’ aquatic macrophytes also declined leaving behind a sparse, species‐poor community (as today) resilient to both eutrophication and turbulent open waters. 4. The combination of historical and palaeolimnological data sources offers considerable benefits for reconstructing past changes to the aquatic vegetation of lakes and for setting restoration goals. In this respect, our study suggests that successful restoration might often be better judged by reinstatement of the characteristic structure of plant communities than the fine detail of species lists; when nutrients are low and the structure is right, the right species will follow.     

Low tide distribution of wintering waders and shelduck on the Severn Estuary in relation to the proposed tidal barrage

Waders and shelduck were counted at low tide on 162 sectors comprising 85% of the intertidal area (21 467 ha) of the Severn Estuary on 12 occasions during winter 1987/88. On average, 50% of birds present at low tide utilized just 13 sectors (12% of the area); 90% of birds occurred on only 56 sectors, leaving large expanses of intertidal sand virtually devoid of birdlife. Dunlin, the numerically dominant species, occurred widely on the middle and outer estuary, whereas shelduck predominantly occurred on the outer estuary and redshank around many tributary river mouths. Curlew, the most ubiquitous species, was the only one concentrated on the inner estuary. Severe gales in both late December and mid-January concentrated all main species within fewer sectors, probably by the short-term removal of surface sediment from substantial areas. It is estimated that the proposed tidal barrage would eliminate intertidal areas accounting for between c. 40% (for shelduck and curlew) and 80% (for redshank) of current total low tide usage by the internationally important populations present.