Gerhard Wiegleb

A study of habitat conditions of the macrophytic vegetation in selected river systems in western Lower Saxony (Federal Republic of Germany)

Abstract In connection with a phytosociological survey of running water macrophytes in Lower Saxony, ecological investigations were carried out in selected river systems. Within these systems, 43 sampling sites were studied. The vegetation of the sampling sites was classified by means of cluster analysis into 7 groups, 3 of which occurred on the diluvial plains and 2 in the coastal marsh area only. Forty-one parameters were measured 3–7 times covering 2 vegetation periods. In the first instance, the structure of the data was carefully studied by bivariate correlation analysis and factor analysis. A high number of significant correlations was detected, which indicates difficulties in ecological interpretation. Temporal variation of the parameters measured was also studied, and they were classified into 3 groups according to stability. For a study of the relationships between the vegetation and the ecological parameters, the data set was split into 5 subsets (physical data, water chemical data, interstitial water chemical data, sediment characteristics, and a mixed set of simple field data). The relationships of each subset to the vegetation was studied separately using cluster analysis. The mixed data set FIELD showed the highest degree of similarity to the vegetation clustering. Analysis of variance was carried out in order to find out which variables differ most among the vegetation types. The best differentiation qualities were shown by some physical and water chemical parameters (oxygen content, turbitity, current velocity, acidity, calcium). This result can only be interpreted ecologically in connection with the intercorrelations observed. The ecological behaviour of some species of medium frequency was also studied in detail by means of analysis of variance. The means of all parameters for occurrence and non-occurrence were compared. In the case of Ranunculus peltatus Schrank, Myriophyllum alterniflorum DC and Elodea canadensis Michx., several differentiation variables could be detected. Finally, the zonation of two rivers was studied in detail by comparing the vegetation sequence with important physical and chemical parameters. The interaction between these parameter groups is clearly shown. Physical parameters like current velocity are responsible for the basic zonation, whilst chemical parameters can modify the zones to a large extent. The necessity for a comprehensive approach to such types of data sets, including profound structural data analysis, is stressed in the discussion. The special problem of relating phytosociological and ecological data is discussed. The methods used are explained and possible objections are noted. The difficulties of using the habitat ecological results for bioindication purposes are outlined. Spatial autocorrelation, vegetation dynamics, interactive processes between the system parameters and the genetic variability of species have to be considered as the main problems in this special application. Nevertheless, the study produced some results which indicated the significance of physical, chemical and sediment parameters for macrophyte growth in the type of waters under investigation, and suggested subject areas for future research.

Ten years of vegetation dynamics in two rivulets in Lower Saxony (FRG)

The vegetation dynamics in six permanent plots in two lowland rivulets of the Federal Republic of Germany are analyzed. The year-to-year change in species cover is displayed by means of tables. In each site there are core species (both hydrophytes and helophytes) which have been able to successfully reproduce within the sampling plots over the total observation period. There are also transient hydrophytes which regularly become washed in from the upper course, and transient helophytes growing permanently into the river from the banks. A numerical analysis of the performance of the 12 most frequent and abundant hydrophytes in relation to various independent variables was carried out using canonical correspondence analysis. There is no directional temporal variation within the vegetation data set. The hydrochemical variables were almost constant within the observation period. Rainfall in summer has some influence via discharge and turbidity. Most of the variance in the data set is explained by the position of the sites along the rivers. Most of the residual variance can be explained by a binary disturbance variable. The processes observed can mostly be explained from life history characteristics of the dominant species, particularySparganium emersum, Ranunculus peltatus andPotamogeton natans. The spatial scale of the study site was relatively adequate. A smaller size would have produced noisy data (suggesting erratic change), while a greater size would have produced no change at all. The adequate temporal scale for observation is the comparison of the yearly maxima because of the seasonality of most of the species. An exact prediction of dominance and species composition of the following year is impossible.

Explanation and prediction in vegetation science

A definition of vegetation science is given, spanning 6 levels of integration and stressing the interrelations among them. The problems of realism are discussed. The selection of levels is related to the adequate correspondence between conceptualization and research aims. Pattern and process are introduced as the central concepts of vegetation science. The perception of reality is dependent on the spatial and temporal scale chosen. The concept of noise is discussed in relation to stochasticity and randomness of events. Traces of essentialism are found both in classification of communities and habitat ecology. Classification is important, particularly the coexistence of alternative classification approaches. Organicism as a basis of vegetation research is rejected because the organismic view is inadequate on higher integration levels. The concept of function is redefined in a non-teleologic way. Present vegetation ecological research is inductivistic. One possible alternative to inductivism is falsificationism. The major domain of this approach is hypothesis testing, which will become more important. Progress can only be reached by a maximum degree of communication among scientific individuals. Predictive ecology is partly based on historic explanation, partly on complementary approaches. Characters of vegetation worthwhile to be predicted are listed and the necessary requirements for vegetation science to become predictive are discussed. A major requirement is the development of succession and life-history theory. A further elaboration of the individualistic concept will be a main task of vegetation science in the near future.

Anatomy of leaves of submerged and emergent forms of Littorella uniflora (L.) Ascherson

Abstract Littorella uniflora (L.) Ascherson is able to grow successfully both under submerged and emergent conditions. After emergence, the submerged leaves die within a short time and aerial leaves are formed within a few days. The general architecture of both leaf forms is the same. The epidermis is thin and does not contain chloroplasts. The mesophyll is disintegrated into many lacunae; the cells are large and have large vacuoles. Chloroplasts are of the granal type with plastoglobuli and starch granules. The leaf has three vascular bundles, one large bundle and two smaller ones located in the upper mesophyll tissues, forming a kind of triangle with the central bundle. The xylem is well developed and shows spiral tracheids. As a consequence of greater lacunar space, the diameter of the submerged leaf is about two or three times larger, as compared with the aeriel leaf. The submerged leaf seems to be distended. The epidermis of the submerged leaves, the central vascular bundle is in direct contact stomata of the Helleborus type. In submerged leaves, the central vascular bundle is in direct contact with the surrounding water. The same observation was made in aerial leaves after submersion, whereas in normal aerial leaves the central bundle is closed.

Spider colonization of former brown coal mining areas — time or structure dependent?

Colonization of former mining areas by a highly mobile arthropod group, spiders (Arachnida), is studied based on a comparative analysis of four mining areas of different age and habitat structure including adjacent undisturbed areas. Species number was lowest in sparsely vegetated sites, and highest in dense vegetation regardless of age. Species number may exceed that of undisturbed adjacent sites after 70 years. Similarity among the sites ranges from 26 to 75% (Sorensen index). A DCA ordination of sites revealed a grouping into three relatively distinct clusters, one including the vegetation free sites, the second the sparsely vegetated short grass sites, and the third both the plant species rich, mature, short grass sites and the tall grass stands. Environmental variables were related to the species composition by means of CCA. However, most of these relations proved to be spurious being either not significant or if so, showing a low contribution to variance explanation. The influence of scale parameters such as area size and distance (when analysing all data, data from mining areas only, or data from one mining area separately) becomes visible in all analyses. A detailed analysis including age as an independent variable shows that age has some influence on the structure of the whole data set including undisturbed sites, but not within the subset of the mining areas. Using data from one mining area only it is shown that the influence of age and spatial autocorrelation effects cannot be properly distinguished on the larger scales. A more detailed account on the known autecology of the species encountered showed that biological spectra of the communities remain similar in the course of development. Initial colonization occurs very rapidly during the first years after dumping. The most decisive aspect of population establishment is the structure of the vegetation, as expressed by height or volume amenable for colonization. Despite some developmental trends such as increase in species number clearly separated successional stages cannot be distinguished.

A phytosociological study of the macrophytic vegetation of running waters in western Lower Saxony (Federal Republic of Germany).

A survey was carried out of the macrophytic vegetation in running waters of Western Lower Saxony. Three hundred and eighty-two phytosociological relevees were classified by common table work to 30 vegetation types of different phytosociological validity. The vegetation types are described and floristically characterized. Most of them belong to the complex Sparganium emersum community, which is characterized by the dominant occurrence of the nymphaeid species Sparganium emersum Rehm., Nuphar lutea (L.) Sm., Sagittaria sagittifolia L. and Potamogeton natans L., but magnopotamid-, parvopotamid-, batrachiid- and pleustophyte-dominated communities also occur. Similarity between the different vegetation types was checked by multivariate techniques, one classification technique (minimum variance clustering) and one ordination technique (principal components analysis). Additionally, syndynamical relations between the types were studied by observing the vegetation changes of 46 sample points within 2 years. The relations between different vegetation types are shown by combination of the different approaches. Finally, some more general statements are made regarding the handling of such data sets, as well as the consequences of the results for the classification of macrophytic vegetation in Central European rivers.

A study on floristic structure and dynamics of communities with Potamogeton alpinus Balbis in water bodies of the northern part of the Federal Republic of Germany

Abstract A total of 129 releves with Potamogeton alpinus Balbis from sites in Lower Saxony were classified by table work into 18 structurally and floristically defined vegetation types. Additionally, 52 releves from sites in Schleswig-Holstein were classified into 14 vegetation types with 5 singular cases left. Potamogeton alpinus was found to be present in a large number of species groups. The separate classification of the two data sets resulted in a different vegetation typification even though the study areas are geographically adjacent and similar with respect to ecological characteristics of the waters colonized. For the observation of vegetation dynamics, 65 of the sites were surveyed repeatedly, at least both in 1981 and 1984. Some of the sites were studied more intensively for up to 9 years. The occurrence in time of P. alpinus is very constant in some places, but unstable in others. The behaviour of P. alpinus was compared with the behaviour of the community as a whole. A high degree of independence between population changes in P. alpinus and changes in the composition and structure of the community was observed. The species behave individualistically.

Ecological restoration as precaution and not as restitutional compensation

Ecological restoration has become a major issue in environmental management. To overcome the backward orientation of the restoration concept (focusing on reference states and natural ecosystems) the introduction of a precautionary principle is proposed. The principle has been developed for decision-making under high uncertainty about the probability and severity of an environmental damage. Meanwhile, it has been accepted in many countries of the world as a guiding principle for environmental legislation. Likewise it is the basis for international conventions aiming at the conservation of biodiversity. Nevertheless, biodiversity is still neglected in large reclamation projects. Several links between precaution and restoration are described. Restoration can be used to prevent future damage. Otherwise restoration is plagued by uncertainty about the outcome of the measures and may have negative effects or even fail. An analysis of common evaluation methods of restoration projects shows that most approaches focus on comparison of restoration results with a reference state, and are thus useless in a precautionary context. Other methods (e.g. comparing restored with unrestored sites) require data gathered by long-term observation (monitoring) of socio-economically defined desired states (Leitbild). Two large-scale restoration projects are analyzed, coastal land reclamation in Korea and open cast mining reclamation in Germany. Both projects had or have honorific aims and are legally admissible. However, they violate both international law based on precaution and simple rules of prudence or wise use. Costly post hoc ‘restoration’ measures are the usual consequence.

The influence of different CO2 concentrations in the light and the dark on diurnal malate rhythm and phosphoenolpyruvate carboxylase activities in leaves of Littorella uniflora (L.) Aschers.

Abstract In short-term experiments, Littorella uniflora (L.) Aschers. was exposed to a sequence of different CO2 supply situations. A direct relationship between CO2 supply and Crassulacean acid metabolism (CAM) activity was shown. The results were confirmed by control experiments applying different constant CO2 supply situations for a period of 20 days. A diurnal difference in malate concentrations of ∼ 25 μmol g−1 wwt was found when the CO2 concentration was ∼ 22 μmol l−1 (=air equilibrium) in the light phase and ∼ 60 μmol l−1 in the dark phase. The diurnal change in malate concentration increased to ∼ 45 μmol g−1 wwt when the CO2 concentration was increased in the dark phase to ∼ 1.4 mmol l−1. With high CO2 supply (∼ 1.4 mmol l−1) in the light, diurnal changes in malate concentration ceased immediately. Phosphoenolpyruvate carboxylase (PEPC) activity was found to be dependent on CO2 concentration. It decreased with increasing CO2 supply, regardless of whether the CO2 concentration was increased in the dark or in the light phase. In spite of this effect, decreasing PEPC activities did not induce a switch off of diurnal malate rhythm. So far, no decisive role of in vitro PEPC activity in the modulation of CAM has been found.

Ecological Orientors: Pattern and Process of Succession in Relation to Ecological Orientors

A theoretical analysis reveals that the concept of “succession” is generally applied both to community and ecosystem phenomena, which must be kept strictly apart. “Succession” is also applied to phenomena which we call “dynamics”, “change” and “development”. Additionally, any satisfactory theory on the temporal behavior of ecological systems must account for both succession and its logical counterpart, constancy. Furthermore, it is shown that the community level is difficult to distinguish from both the population and the ecosystem level. Important community characteristics which enable us to delimit the community from other observation levels can be drawn from the analysis of semiautonomous behavior of hierarchically ordered levels. A list of aspects relating to semi-autonomy distinguishing the community both from the ecosystem and the population is presented. The confusion relating to key concepts of spatial and temporal relations in ecological systems is outlined. Different terminologies are necessary to speak about observational and theoretical entities. “Pattern” and “process” are adequate terms of an observational terminology, while “structure” and “function” are terms of theoretical reasoning. Also, discreteness or continuity of phenomena must be described in different terms. The term “process” accounts for continuous phenomena, while the term “event” is necessary to describe discrete ones.