Stephen Waite

The persistence of calcareous grassland species in the soil seed bank under developing and established scrub

The relationships between the composition of the soil seed bank, the field layer vegetation, and the scrub canopy were investigated along a 69 m transect, grading from incipient woodland, through scrub, into intensively rabbit-grazed calcareous grassland. The results are used to assess the persistence of species associated with open calcareous grassland in the seed bank under developing scrub. Scrub age, composition and density, changed along the transect from the woodland to open grassland. A total of 35 forb and grass species were found in the field layer. The pattern evident in the scrub layer was also reflected in the herbaceous vegetation. The field layer in the most closed portion of the transect, where the scrub was oldest, was dominated by shade-tolerant species normally associated with woodland habitats. The abundance of these species decreased along the transect as the scrub age declined, and the field layer became increasingly dominated by species typical of open grassland. A total of 47 species germinated from the seed bank. Few species were recorded in the seed bank along the entire length of the transect. Overall, the seed bank was dominated by Hypericum perforatum and Centaurium erythraea, which accounted for 38.2% and 28.6% of emerging seedlings respectively. As with a number of similar studies, the composition of the seed bank had a low correspondence with the composition of the field layer vegetation. The results also emphasise that the composition of the seed bank can be viewed as an ‘ecological palimpsest’, with germinable seed of species from each stage of the old-field succession occurring in the soil. The seed bank is an important component in the re-vegetation of an area after disturbance such as scrub removal. This study supports the findings of previous research in showing that relatively few characteristic calcareous grassland species form persistent seed banks. The soil seed bank would therefore appear to be of limited value in the restoration of such grassland following scrub removal.

Response of floodplain grassland plant communities to altered water regimes

Floodplain grasslands are often composed of a mosaic of plant communities controlled by hydrological regime. This article examines the sensitivity of floodplain grassland plant communities to water regime using reciprocal transplantation of an inundation grassland and a flood-meadow within an English floodplain. Experimental treatments comprised control, transplanted and lifted plots; the last treatment, in order to elucidate any disturbance effects of transplantation. Plant community response was analysed using species abundance and their ecological traits. Results from both communities showed substantial annual variations related to hydrology, including significant species changes, but generally, vegetation seemed to be responding to drier conditions following a major flood event. This ‘drying’ trend was characterised by increased species diversity, a greater abundance of competitive species and fewer typical wetland plants. Transplanted community composition increasingly resembled receptor sites and transplant effects were most pronounced the first year after treatment for both vegetation types. Differential responses to water regime were detected for the two plant communities. The inundation grassland community was particularly dynamic with a composition that rapidly reflected drying conditions following the major flood, but transplantation into a drier flood-meadow site prompted little additional change. The flood-meadow community appeared more resistant to post-inundation drying, but was sensitive to increased wetness caused by transplantation into inundation grassland, which significantly reduced six species while none were significantly favoured. The effects of disturbance caused by lifting the transplants were limited in both communities, although five species showed significant annual fluctuations. The study shows that small alterations in water regime can prompt rapid vegetation changes and significant plant species responses in floodplain grasslands, with effects probably magnified through competitive interactions. The dynamic properties of floodplain vegetation demonstrated by this study suggest that its classification, management and monitoring are challenging and ideally should be based on long-term studies.

Field evidence of plastic growth responses to habitat heterogeneity in the clonal herbRanunculus repens

Stolon internode lengths were measured on plants of the clonal herbRanunculus repens growing in a hay meadow which was subject to disturbance by mole (Talpa europaea) activity. Within the site three habitat types were recognized: closed grassland, the open ground of fresh molehills and the grass-molehill boundary. The lengths of stolon internodes ofR. repens differed significantly in each of the three habitats. The shortest internodes occurred on stolons on the open molchills. The longest occurred in the closed grassland habitat. The type of habitat in which parent ramets were rooted did not significantly influence the length of internodes on their daughter stolons. The length of a stolon internode was determined by its immediate surrounding habitat type. Consecutive internode lengths on a given stolon showed considerable plasticity, shortening significantly as stolons spread onto molehills from surrounding habitats, and increasing significantly as stolons advanced from a molehill into the surrounding closed grassland habitat. These results are consistent with the proposition that under favorable conditions (on the molehills, where resources are expected to be more abundant, and competition absent) internode lengths shorten and the plant forages intensively, whereas under conditions of low resource availability (in the closed grassland, where competition occurs) internode lengths increase, allowingR. repens to forage extensively. Such morphological plasticity may promote more efficient exploitation of resource-rich sites and more rapid vacation of resource-poor sites.

Recent historical land use change on the South Downs, United Kingdom

There is considerable interest in the fragmentation and loss of natural and semi-natural habitats, but few studies have examined the dynamics and mechanisms of change. A temporal analysis of landscape change on the South Downs in Sussex, UK, provides a clear description of the process of change over the 20 years 1971–1991. Transition probabilities were calculated from digital interpretations of an aerial photography time series of West Sussex. The analysis enabled quantitative comparison of landscape mosaics within different landscape ecoregions and under different management regimes to be made. Past changes in land use have produced a fragmented downland landscape. The key land conversion sequences identified show a substantial transition towards arable production, often at the expense of the internationally and nationally important unimproved grassland systems. A geographical information system facilitated greater understanding of the environmental and topographical characteristics of land converted to arable and other uses, and highlighted areas for protection and potential restoration. The patterns of land-use conversion observed in the study provide a landscape-scale planning tool for assessing the potential impact of agri-environmental policies, plans, and programmes in semi-natural grassland habitats.

A Spatial Analysis of Serotine Bat (Eptesicus serotinus) Roost Location and Landscape Structure: A Case Study in Sussex, UK

Roost location is a key factor affecting the survival and fitness of British bats. It has been suggested that a knowledge and understanding of the factors which may influence the selection of roost location are fundamental to conservation efforts. Our study aims to investigate the relationship between Eptesicus serotinus roost location and landscape structure. The study is based in the Sussex region of South East England. The landscape characteristics of 97 roosts locations were compared against 100 random control locations. Habitat analysis was carried out at three distance bands and included an analysis of roost density. The results indicate that E. serotinus is selective in locating roosts. The study demonstrates that there are significant differences between the landscape composition surrounding roost sites and the wider landscape. In particular, E. serotinus roost sites are found to be located in areas with a significantly higher cover of arable land and improved grassland. Kernel density analysis was successfully used as an additional method to the direct comparison of roost neighbourhood composition. Density analysis identified the location and characteristics of possible centres of E. serotinus activity. It is anticipated that the findings will enable the needs of bats to be considered in future landscape conservation initiatives and development policies.

The Radiate Capitulum Morph of Senecio Vulgaris L. Within Sussex: The Use of GIS in Establishing Origins

The geographical distribution of the radiate morph of Groundsel (Senecio vulgaris), Senecio vulgaris var. hibernicus was examined in the county of Sussex in southeast England using records from 1980 and 2000. In addition the geographical distribution of Oxford Ragwort (Senecio squalidus) was also investigated for the same area. The spatial distribution of S. squalidus was strongly correlated with the past and present railway network, as is that of S. vulgaris var. hibernicus.

Der Einsatz von Biotechnologien bei der Behandlung von Organischen Schadstoffen

Toxische organische Verbindungen, die Produkte unserer modernen Gesellschaft, werden zunehmend als extreme Bedrohungen der Selbstregulierungsfahigkeit der Biosphare angesehen. Die komplexen, in Kapitel 5 beschriebenen Kreislaufe des organischen Materials, die die uns bekannte bewohnbare Umwelt herausgebildet und aufrechterhalten haben, werden anscheinend zunehmend uberlastet. Ein wachsendes offentliches und politisches Bewustsein uber diese Probleme hat zu der Erkenntnis gefuhrt, das ein groser Bedarf dafur besteht, Umweltverschmutzungen zu verhindern bzw. zu rehabilitieren.

Stickstoff und Phosphor in der Umwelt

Stickstoff und Phosphor liegen auf der Erde zum grosten Teil in Formen vor, die der Lebewelt nicht ohne weiteres zuganglich sind. Stickstoff tritt hauptsachlich in molekularer Form als N2 in der Atmosphare auf, wahrend der Nachschub des Phosphors in den Gesteinen und Boden der Erde fixiert ist. Nachschub und Umweltkreislaufe der verfugbaren Formen dieser Nahrstoffelemente hangen im wesentlichen von der biologischen Zersetzung der N- und P-enthaltenden Verbindungen ab, die sich in der Lebewelt angesammelt haben. Wegen der Bedeutung der Zersetzung laufen die Kreislaufe von in der lebenden Biomasse angesammelten Elementen nicht unabhangig voneinander ab. Umsetzung und Zersetzung von Biomasse schwanken zwischen den einzelnen Lebensraumen stark und hangen von Grose und Aktivitat der jeweiligen Mikroben- und Pilzgemeinschaften ab. In feuchtwarmen oxidierenden Umgebungen laufen Zersetzung und Freisetzung von Nahrstoffen schnell ab. In tropischen Regenwaldern betragt die Verweilzeit von Kohlenstoff in der Laubstreu nur etwa 3 Monate, in gemasigten Waldern hingegen 4–16 Jahre, und in borealen Systemen kann sie sogar uber 100 Jahre betragen (Recklefs, 1990). Die bakterielle Zersetzung wird haufig durch die Verfugbarkeit von Stickstoff begrenzt. Das durchschnittliche C: N-Verhaltnis in bakterieller Biomasse betragt etwa 10:1, d. h. fur 11 g mikrobieller Biomasse wird 1 g N benotigt. Dieser Wert kann als Mas fur den Bedarf der Mikroben an diesen beiden Elementen gelten. Typische Pflanzenmaterialien weisen C:N-Verhaltnisse von 40–80:1 auf und damit ein Defizit an N, weshalb eine rasche Zersetzung von Pflanzenmaterialien von der Verfugbarkeit externer N-Quellen abhangt. Uberreste von Tieren, deren C:N-Verhaltnis dem der sie abbauenden Organismen ahnlich ist, werden rasch abgebaut (Swift et al, 1979; Begon et al, 1990). Die Zersetzung tierischer Biomasse wird auch durch das Fehlen nicht leicht aufzubrechender Polymere wie Lignin und Zellulose erleichtert, sowie durch die Tatsache, das dabei ein groser Teil der Biomasse anfanglich in flussiger Form vorliegt. Das C:N-Verhaltnis ist mit einem Wert um 10 erstaunlich konstant, obwohl der Wert in wassergesattigten oder sauren Boden, in denen die Zersetzung behindert wird, bis auf 17 steigen kann. Begon etaL (1990) bemerkten, das das System der Bodenabbauer ausergewohnlich stabil ist und wiesen darauf hin, dao im allgemeinen bei einer Zugabe von Material mit weniger als 1,2–1,3 % N zu Boden alle verfugbaren Ammoniumionen adsorbiert werden, wahrend bei Materialien mit mehr als 1,8 % N Ammoniumionen zunehmend freigesetzt werden.

Biologische Behandlung von Metallen und Radionukliden

Lebende Organismen benotigen bestimmte Elemente fur ihr Wachstum und zur Aufrechterhaltung ihrer physikalischen Struktur, der Stoffwechselaktivitaten und der Fortpflanzungsfahigkeit. Sie haben geeignete Mechanismen zur Aufnahme der fur den Stoffwechsel wesentlichen Elemente ausgebildet. Bei bestimmten Gelegenheiten konnen toxische Metalle aufgenommen werden, die zu physiologischem Schaden fur den Organismus und sogar zu seinem Tod fuhren konnen. Selbst die in geringen Mengen oder Spuren fur die normalen Zellfunktionen benotigten Metallelemente konnen behindernde oder toxische Auswirkungen zeigen, wenn sie in ubermasiger Konzentration vorhanden sind (Kap. 13). Viele Organismen haben Entgiftungsmechanismen entwickelt, um den schadlichen Auswirkungen der Metalle zu entgehen. Bei Mikroorganismen haben sich dafur verschiedene Resistenzmechanismen herausgebildet, darunter z. B. Umbildungen der toxischen Metalle, die dazu fuhren, das das Metall in einer anderen physikalischen und/oder chemischen Form freigesetzt wird, wie dies bei einer Metallalkylierung stattfindet. Einige der von Organismen katalysierten Verfahren zur Aufnahme und Umbildung von Metallen konnen auch zur Behandlung metallhaltiger Abfalle eingesetzt werden.

Umwelt und Umweltverschmutzung

Holgate (1979) definierte Umweltverschmutzung als „durch den Menschen verursachte Einbringung von Stoffen oder Energie in die Umwelt, die das menschliche Leben gefahrden, lebende Ressourcen schadigen und okologische Schaden auslosen konnen, sowie die Behinderung legitimer Nutzungen der Umwelt“. Die Schadstoffe sind verschiedenartigster Natur und umfassen u. a. bestimmte Metalle, ein breites Band verschiedener organischer Verbindungen und einige Gase. Die Bedeutung, die einem bestimmten Schadstoff beigemessen wird, hangt ublicher weise von seiner angenommenen Giftigkeit fur den Menschen ab. Die Europaische Union (EU) fast die Verbindungen mit der hochsten Giftigkeit in einer „Schwarzen Liste“ zusammen und die weniger giftigen in einer „Grauen Liste“. In vergleichbarer Weise erfast die US-amerikanische Umweltbehorde (EPA) 129 Chemikalien in seiner Liste der Prioritatsschadstoffe (Tabelle 1.1). Die Verbindungen der „Schwarzen Liste“ der EU und die Prioritatsschadstoffe der EPA sind meist nicht nur stark toxisch sondern auch sehr bestandig und neigen zur Bioakkumulation (Kap. 2). Bei dem Stoff oder dem Schadstoff kann es sich um eine synthetische Verbindung handeln oder um ein in der Natur vorkommendes Element oder eine Verbindung, deren Konzentration durch menschliche Aktivitaten auf eine Hohe gebracht wird, die entweder toxisch wirkt oder die Okologie eines Gebietes nachhaltig storen kann.