Isolde Ullmann

The vegetation of roadside verges with respect to environmental gradients in southern New Zealand

. A survey of the vegetation of roadside verges was made across the southern part of the South Island of New Zealand. Samples were taken at 10-km intervals along selected roads providing a climatic range from the suboceanic conditions of the east coast into semi-arid Central Otago, and from Central Otago through the Southern Alps to the hyper-oceanic areas of high rainfall on the west Coast. The variation in the floristic composition is associated mainly with variation in rainfall, continentality, altitude, soil acidity, soil organic matter, and presence of forest. Sites in the arable and pastoral regions on the eastern side of the Southern Alps support a herbaceous vegetation consisting mostly of exotic species of European origin, with a few native grasses scattered through the drier and less fertile sites. A greater proportion of native species is found at higher altitudes. Roadside vegetation in the area of high rainfall to the west is characterized by indigenous ferns and woody species, although vegetation adjacent to cleared areas is more similar to that on roadsides adjacent to farmland on the east coast. The pattern of distribution of both native and exotic species is strongly related to altitudinal and climatic gradients, and the environmental responses of the exotic species are similar to those recorded in Europe. This suggests a colonization of all available sites by the exotic species, despite the relatively short time since their introduction to New Zealand, rather than an incomplete invasion.

Mikroklima, Wassergehalt und Photosynthese von Flechten in der küstennahen Nebelzone der Namib-Wüste: Messungen während der herbstlichen Witterungsperiode

Summary The coastal fog zone of the Namib Desert (Namibia, Southwest Africa) where there are hardly any higher plants, is known for its rich lichen vegetation. The functional mechanisms that allow existence of these lichens under the special conditions of the “fog desert” are investigated. The study is part of our general efforts to analyse the ecological basis of the photosynthetic production of lichen-dominated habitats in order to explain physiological factors underlying the success of the lichens. During the fall, in April 1988, microclimate, water relations, and photosynthesis of 10 characteristic species were studied in their natural environment in one of the lichen fields north of Swakopmund. Time courses of CO 2 exchange and water content were used to estimate the daily primary production and provide information about light dependence of CO 2 -assimilation of well-hydrated thalli, and about their light (LKP) and moisture compensation point (FKP). Fog is the most important source of water for these lichens. However, dew condensation without fog also results in high degrees of hydration. Maximal water contents of more than 150% of dry weight of the thalli are reached. Soon after sunrise, the hydrated lichens show a steep increase in the rate of net photosynthesis which initially is determined by the increase of photosynthetically active radiation. Subsequently, the lichens lose water, and metabolic activity is then limited by their hydration. Typically, photosynthesis of the drying lichens ceases 2 to 4 hours after sunrise and the water content of the thalli drops below 10%. In addition to hydration through liquid water, water vapor uptake in air of high humidity alone can reactivate the photosynthetic apparatus of the lichens. This may result in a second, smaller peak in CO 2 uptake at late afternoon. This general diurnal pattern of photosynthetic activity is modified according to the actual weather conditions. There occurred one day during the measuring period where no CO 2 was gained. The characteristics of a species, especially its growth form, determine maximal rate of photosynthesis and the ability of the lichen to make use of the available moisture. The multibranched fruticose species (e.g., Teloschistes capensis, Alectoria spec., Ramalina lacera ) reach higher rates of net photosynthesis than the more compact foliose lichens (e.g., Xanthomaculina convoluta, X. hottentotta, Xanthoparmelia walteri ), both their maximal apparent quantum use efficiency (initial slope of the light response curve) and their maximal photosynthetic rates at light saturation being greater. Light saturation of the whole thalli in their natural position takes place between 583 ( Xanthomaculina hottentotta ) and 1856 μE m −2 S −1 (Ramalina lacera) photosynthetically active radiation. LKP varies between 16.3 (Caloplaca elegantissima) and 31.5 μE m −2 S −1 (Xanthomaculina hottentotta) , FKP after desiccation in the morning lies between 15.0 (Santessonia hereroensis) and 25.6% (Ramalina lacera) water content relative to dry weight of the thallus. Caloplaca elegantissima , the only crustose species studied which grows on stone pebbles, is characterized by medium rates of photosynthesis when related to dry weight or carbon content of the thallus and by high rates when related to chlorophyll content. Its LKP is very low. In the most productive species Teloschistes capensis , the maximal daily carbon gain during the daylight period amounts to about 0.25% of the thallus carbon content. This is ten times the relative carbon gain of the Xanthomaculina species under the same microc1imatic conditions. The results show that primary production of the cushion forming, fruticose growth form of the lichens is superior in the habitat with heavy fog formation near the coast. This accords with the fact that Teloschistes capensis is the dominant species in these lichen fields. Continuation of the work will be extended over other seasons of the year and will concentrate further on the analysis of the different growth forms as adaptations to the extreme environment. Field investigations will be complemented by measurements of the factor dependency of CO 2 exchange under controlled conditions in the laboratory.

Regeneration growth of the invasive clonal forb Rorippa austriaca (Brassicaceae) in relation to fertilization and interspecific competition

A special type of clonal growth, spread by lateral roots, ishypothesized to be a favourable trait of invasive, opportunistic plant speciesof disturbed habitats. We tested this hypothesis for the invasive forbRorippa austriaca (Brassicaceae). Regenerationfrom root fragments, subsequent vegetative spread and allocation patterns inrelation to varied nutrient supply and intensity and pattern of interspecificcompetition were analyzed in container experiments. Regeneration success fromroot fragments was 100% and clonal spread was rapid but vegetativeperformance was strongly reduced under unfertilized conditions and,particularly, when interspecific competition was present. While the ratio ofabove- to belowground bio-mass did not differ considerably betweentreatments, R. austriaca allocated a high amount ofresources to belowground growth resulting in low aboveground but highbelowground biomass at harvest time relative to the matrix vegetation.Differences in shoot number or biomass between simulated gaps and denselyvegetated quadrants in the containers were (relatively) weak.Reproductive effort was less reduced under low resource levels, and the clonesdid not set seed at all, irrespective of the treatment. Our results show thatclonal growth by lateral roots and plasticity in clonal growth patterns inR. austriaca promote both exploitation of gaps andnutrient-rich microsites and resistance to competitors. Such plasticity,combined with its ability to regenerate from widely-dispersed rootfragments, contribute to the ability of the species to invade and persistwithindisturbed and spatially heterogeneous habitats.

LATERAL DIFFERENTIATION AND THE ROLE OF EXOTIC SPECIES IN ROADSIDE VEGETATION IN SOUTHERN NEW ZEALAND

Summary Roadside vegetation was surveyed across the southern part of the South Island, New Zealand. Samples were taken at 10 km intervals along 750 km of selected roads that provided a climatic gradient from semi-arid to hyperoceanic conditions and which crossed both, areas of farmland, where the native vegetation has been replaced by an anthropogenic plant cover consisting almost entirely of introduced species, and areas of managed native tussock grassland and native forest. Contiguous plots, placed in four zones parallel to the road, were used to examine any lateral differentiation of vegetation. Variation in floristic composition in all four zones was associated with variation in rainfall, continentality, altitude, and the presence of forest. In all sites there was a distinct change in species composition from the outer verge to the inner roadside. The vegetation of the zone nearest to the road showed weaker correlation with altitude and stronger correlation with continentality, a marked increase in short-lived exotic species, and a greater proportion of the more continental and weedy vegetation types than the vegetation of the outermost verge. This supports the hypothesis of anthropogenic continentality of road-shoulders. The most frequent species on the road-shoulders are those exotic species that transgress climatic barriers in their native continents. This suggests that, globally, the range of such species is liable to expand, particularly in the habitat-complex provided by roadsides.

Phenological shifts of the alien colonizer Bunias orientalis: image-based analysis of temporal niche separation.

. Phenological development of the colonizer Bunias orientalis L. was investigated in permanent plots in herbaceous vegetation, using photography and image analysis. In all habitats but one, B. orientalis showed a two-phased rosette growth behaviour, with a first peak cover reached in spring, roughly coinciding with an early peak cover of the matrix vegetation, and a second autumn growth flush occurring in a phase of reduced matrix vegetation cover. This seasonally bimodal growth pattern of B. orientalis appears to partly compensate for its competitive inferiority in crowded herbaceous vegetation. Small or overshadowed individuals of this species particularly profit from higher above-ground performance or release from overlap in autumn. The significance of temporal niche separation for survival and growth of B. orientalis individuals varies with habitat conditions, being most apparent in occasionally disturbed habitats with a relatively low frequency of gap formation. Despite some limitations, image analysis proved to be useful for phenological investigations within herbaceous plant stands.

Tagesgänge von Transpiration und stomatärer Leitfähigkeit Sahelischer und Saharischer Akazien in der Trockenzeit)

Summary The genus Acacia is one of the most important genera in the arborescent flora of the dry savannas and the contracted desert vegetation of Africa. In general the deciduous African Acacias bear leaves during the moist season, but they display a vegetative behaviour unusual amongst raingreen plants. Even in desert areas, new leaves are produced weeks to months before the onset of the rainfall. Typically these leaves experience extreme evaporative conditions in their environment as well as high temperature stress. Although it is known that the leaves may be killed by the high temperature, there is only initial information on the ecophysiological performance of the leaves in less severe stress situations. In the present investigations, therefore, water relations and stomatal reactions of native Acacias were examined under natural conditions at the height of the dry season in the Sahelian zone and in the Southern Sahara. Daily time course measurements of leaf diffusion conductance, transpiration rate under porometer conditions, leaf temperature and leaf microclimate were obtained from the leaves of 8 Acacia species growing in various landscape units in the region of Niamey (Sahel) and at Indoudou in the Kori Teloua north of Agadez (Sahara). Incident light intensity above the plant canopy and at individual leaves, relative humidity in the measurement cuvette, leaf diffusion resistance, transpiration rate into the cuvette, leaf temperature and air temperature in the measurement cuvette were obtained directly from a Li-1600 steady state porometer. The water potential of leaves of the experimental plants were determined with a pressure chamber of the Scholander type. The measuring period in late March and the first half of April 1983 was characterized by high temperatures and extreme low relative humidity of the air. Deciduous Acacias had been reported as species with high transpiration rates in comparison to succulent halophytes or small woody plants growing in the same habitats. This behaviour was confirmed by comparative measurements on Acacias, palms and an epiphytic hemiparasite (Figs. 5, 6). There was no species-specific differentiation evident in the behaviour of the investigated Acacia species. However, there was a correlation between types of patterns of stomatal performance and leaf age. For mature leaves the daily time course of leaf diffusion conductance was characterized by a steep increase after sunrise, a pronounced peak in the early morning and a continuous decrease during the day. Typically this decrease was interrupted by a minor peak in the afternoon associated with an intermittant rise of relative humidity (Figs. 6, 7). The diurnal course of transpiration rates for these leaves was dome shaped with a maximum about noon, due to the rapid increase of air temperature and the decrease of relative humidity in the late morning. Senescent leaves which had experienced the full range of the dry season exhibited a midday depression of stomatal conductance and leaf water loss (Fig. 8). Newly produced leaves had high conductance from early morning to the late afternoon (Figs. 5, 9, 10). Daily maximal leaf diffusion conductance was not associated with leaf age, but with predawn water potential of the plants. A correlation between high daily maximal leaf diffusion conductance and high transpiration rates was as evident within a population of a single species in a restricted area (Fig. 11) as in a comparison of all species investigated (Fig. 12). In spite of the accentuated drought in spring 1983 a general response of the Acacias to “dry season conditions”, i.e. to high temperatures and high atmospheric evaporative demand could not be detected. It seems that the complex root system with a central tap root and wide spreading lateral roots enables a great number of individual Acacia plants to adopt at least in part a phreatophytic lifeform. A response to individual plant water supply rather than control of water use in response to seasonal rainfall or change in air humidity would seem advantageous. Abundant water supply in the root zone leads to unrestricted gas exchange in spite of the dry season, as observed for the Acacias rooting in the ground water table of the Kori Teloua (e.g. Fig. 11 a) or the Niger valley (Fig. 7). Since the rainfall during the period 1980—1982 had (slightly) exceeded the average amount, an influence of the immediate drought on the response of the leaves was apparent only in individuals with low water supply. The shrubs of A. ehrenbergiana growing in a run-off line and in a sandy depression in the granitic foothills in the Kori Teloua, for example, did show a clear decrease in maximal stomatal conductance and a restriction of water loss. Along with differences due to the individual habitats there was still a variation in the individual plant behaviour (Fig. 11 b, c). One can expect a more uniform performance of the plants rooting outside the ground water channels after a few years with poor rainfall. There are indications that vegetative cycles of deciduous Acacias are dominated as well by local environmental changes (Ross 1966). To develop a better idea of ecophysiological adaptation of Acacias to semi-arid and arid conditions and of the seasonal responses of these phreatophytic types of plants we need, therefore, longterm studies including climatologic and phenologic observations.

Verbreitung, Standortcharakter und infraspezifische Gliederung bei Molopospermum peloponnesiacum (L.) K och ( Apiaceae) .

Summary Molopospermum peloponnesiacum (L.) K och , an orophytic forb with a limited distribution in the montane and subalpine zone of the Pyrenees, the Massif Central and the southern Alps, is the only species of the taxonomically isolated genus. The plants are easily recognized by their strong odour, a feature which was used by B auhin to characterize the species. Previous analysis of the volatile oils of Molopospermum p. did not result in new information about the systematic placement of the genus, however, comparative analysis of the volatile oils of different stands showed phytochemical variability corresponding to at least 2 chemotypes. This led to the hypothesis of infraspecific differentiation in the morphologically uniform species. In order to check this hypothesis the volatile oils of plants from different stands in the whole range of the area of distribution of Molopospermum p. were analysed. The phytochemical analysis was combined with analysis of habitat characteristics and phytosociological performance of Molopospermum p. to obtain information about the mode of possible differentiation. Molopospermum peloponnesiacum shows an uniform ecological and phytosociological behaviour in its whole area of distribution, whereas phytochemically 2 well defined types occur. In the composition of the volatile oils these types are the same as the previously described chemotypes. The 2 types are geographically separated: the area of distribution of the “Apiole-Type” includes the Pyrenees, the Massif Central (Cevennes), and the Alpes Maritimes. The “Terpene-Aldehyde-Ester-Type” of the South Alps covers the area from Switzerland to Yugoslavia. Intermediates between the 2 types were not found. There is a strict correlation in the differentiation of the volatile oils and of the flower pigmentation. The plants of the western Apiole-Type have yellow petals; those of the eastern Terpene-Aldehyde-Ester-Type white ones. The pattern of the infraspecific differentiation of Molopospermum p. is comparable with the differentiation patterns observed on generic and specific levels in various plant families inhabiting the European high mountains. In the southern Alps, it corresponds to the phytogeographic division between the Alpes Maritimes and the South Alps. On the basis of parallels in the differentiation of the taxa of Molopospermum p. and in taxonomically related and unrelated genera it is concluded that the 2 taxa of Molopospermum peloponnesiacum are well delimited and consequently they are defined herein as subspecies; ssp. peloponnesiacum corresponds to the western Apiole-Type, ssp. bauhinii to the eastern Terpene-Aldehyde-Ester-Type.

Verbreitung, Standortswahl und Gesellschaftsanschluß thermophiler staudiger Umbelliferen (Laserpitium, Peucedanum) in den spanischen Pyrenäen

Summary Stands of umbelliferous forbs in the Spanish Pyrenees were investigated in connection with studies of thermophilic forest fringe communities (phytosociological class Trifolio-Geranietea). The distribution of the different genera proved to be correlated with altitudinal zonation. The similarity of an umbelliferous forb community in the Pyrenees to a plant association known in Central Europe is linked to similar climatic conditions that occur within the range of this particular community. Laserpitium latifolium is distributed in the region of montane beechforest. Natural habitats of this species are mostly rocky crevices in gorges or along steep hills; more frequently Laserpitium latifolium stands occur in successional habitats. On the basis of their floristic composition and their habitat preferences these anthropogenous Laserpitium latifolium communities should be regarded as a western variation of a lpic forb fringe communities. The Peucedanum stands are restricted to the submediterranean Quercus pubescens-region and are not equivalent to Central European plant associations. They show clear relations to (sub)mediterra nean semiruderal and ruderal xerothermic plant communities. As a result of a comparison of the thermophilic forb fringe communities in Europo thrco major groups of communities emerge: a) species-rich thermophil ic or mesophilic communities in lowland Central Europe; b) North European and montane communities, combining thermophilic and mesophilic characters; c) semiruderal communities under drier climatic conditions especially in Southern and Southeastern Europe. The existence of ecologically and floristically well-defined “border communities” adds emphasis to the legitimacy of the Trifolio-Geranietea as a Central European vegetation unit.