Epiphytic succession on tree trunks in a mixed oak-cedar forest,Kumaun Himalaya

The epiphytes present at about breast height on trunks of different size were studied for three major tree species in a seasonally wet forest at 2050 m altitude in the Kumaun Himalaya: Cedrus deodora, Quercus floribunda and Q. leucotrichophora. The total biomass and species number per unit trunk area, were found to increase with trunk size. It was supposed that the results indicated a succession in the type of epiphytic cover from young trunks to older trunks.The amount of loose material (plant remains and soil) per unit area of trunk increased with increasing girth. The C:N ratio in this material was initially very high on the oaks (129–197) and declined with increasing trunk size (to 73–78); the ratio was constant across girth classes in the cedar (86–87).Bryophytes produced most biomass on most trunks; next to them were lichens on the smallest trunks, and flowering plants on the largest. The number of species of epiphytes was similar on all three host species. The results are discussed in relation to contemporary ideas on diversity and strategies.Nomenclature follows: Ganguli (1972, 1977 & 1980); Kashyap (1929); Nayar (1970); Osmaston (1927).Financial support from the Council of Scientific and Industrial Research, Delhi and University Grants Commission, New Delhi is gratefully acknowledged.     

Restoration of Natural and Semi-Natural Wetland Systems in Central Europe: Progress and Predictability of Developments

After almost 40 years of experience in wetland restoration in Central Europe in which vegetation changes have been monitored by means of permanent plots or vegetation maps, some light can be shed on the intrinsic dynamics of such ecosystems, showing the limits of restoration and constraints in its manipulation. Sometimes such constraints in the restoration process can be identified, mostly being constraints in nutrient availability or in the water regime, but unexpected changes can also be the result of intrinsic species fluctuations or invasive species. Unexpected vegetation developments are sometimes undesired, can be very persistent and may indicate that environmental conditions are not suitable for target communities. Unexpected developments also illustrate the limits in restoration ecology. Very often the restoration process simply proceeds along successional pathways we did not anticipate. Theories about such alternative pathways can be explored using prediction models, such as cellular automata, which can handle the results of biomonitoring very efficiently. Biomonitoring during 40 years, however, has also shown that a certain amount of unpredictability has to be taken for granted, both in natural wetlands and in areas under restoration.     

Competition under high and low nutrient levels among three grassland species occupying different positions in a successional sequence

To clarify the role of seasonal change, competitive response and nutrient availability in the competitive asymmetry of grassland species a competition experiment was conducted on Holcus lanatus , Anthoxanthum odoratum and Festuca ovina , which represent a successional sequence of decreasing nutrient availability. Seven harvests were taken over two growing seasons. At each harvest the dry weight of plant parts, dead leaves, leaf area and plant height were measured. Three key traits that determine the successional status of the species were studied: specific leaf area, specific shoot height, and dead leaf fraction.
The response of these traits to competition appeared to be limited and insufficient to change the competitive relations in the experiment. However, all three traits showed marked seasonal changes which resulted in superior growth and survival in winter of the species adapted to nutrient-poor environments. The findings support the theory that competitive asymmetry increases at higher nutrient levels. It is postulated that the directionality of light makes it possible for the dominant species to monopolize this resource more easily than nutrients.     

Plant Demography and Habitat: A Comparative Approach

Abstract Progress in plant demography will depend upon being able to synthesize a large body of data and this requires a means of comparing populations between sites and species. We have employed a comparative technique using elasticity analysis of stage-projection matrices to partition the contributions of fecundity (F), survival (L) and growth (G) to the finite rate of increase λ. Ordination of populations of 77 perennial herbs and trees in G-L-F space has shown that species segregate in this triangular space according to their life history and habitat. In the present paper we use the correspondence between demographic parameters and habitat revealed by this method to predict how succession and a variety of environmental factors such as grazing and fire are likely to alter the demography of populations and ultimately to change the composition of communities.     

Seasonal pattern of ammonium (methylamine) uptake by phytoplankton in an oligotrophic lake

Our primary objective was to determine if a relationship existed between seasonal change in phytoplankton and high affinity for (K _m) or uptake rates (V _maX) of ammonium which might explain seasonal phytoplankton succession in oligotrophic ecosystems. We measured ammonium uptake using [¹⁴C]-methylamine and estimatedK _m andV _max using Hanes Plots at 2-week intervals during 6 months of thermal stratification in Mountain lake, Virginia (37° 22 N, 80° 32 W). Community composition, nutrient levels, and other variables were determined in all uptake experiments. A second objective was to determine if ammonium was preferentially utilized over nitrate and to characterize further the ammonium transport system.V _max increased steadily from May until the end of July, each increase coinciding with major changes in the phytoplankton community. Cryptophyceans dominated in May, chlorophyceans in June and July, and cyanophyceans from the end of July to late October. With cyanophycean dominance,V _max declined until chlorophyceans reestablished dominance in late October. By contrast,K _m values increased from May to the end of July, but thereafter showed no correlation. Acetylene reduction experiments showed no nitrogen fixation during late summer and fall when blue-green algae were present. Preference for ammonium was implied also by negative nitrate reductase assays. Overall, the coincidence ofV _max andK _m values for [¹⁴C]-methylamine uptake and changing phytoplankton community structure suggests the possibility that successive algal communities may be changing as a result of specific species differences in ammonium affinity and uptake rates.     

Reversing borealization as a means to restore biodiversity in Central-European mountainforests – an example from the Krkonoše Mountains, Czech Republic

Forestry in the Central-European mountains is confronted with a severe forest decline, which is attributed to the combined effects of 'borealization', brought about by large scale continued spruce (mainly Picea abies) monocultures, and atmospheric deposition. Borealization is defined as enhanced soil acidification and litter accumulation, retarded nutrient cycling and changed forest climate in such planted coniferous forest ecosystems. An additional effect of borealization is a major decline in biodiversity of the stands. Based on a comparative study of Norway spruce and European beech stands in the Krkonoe National Park (Czech Republic), it is concluded that traditional management should be abandoned and that management should instead focus on regeneration towards broad-leaved or mixed forest stands, to enhance the stability of forest ecosystems and their biodiversity, and to reverse borealization in lower montane zones. Available surveys of forest typology were evaluated for their suitability in regeneration management and were found to be unsuitable, since they reflect the effects of borealization rather than true site conditions. The two main pioneer tree species, birch (Betula pendula) and mountain ash (Sorbus aucuparia), were found to improve soil conditions and reverse borealization. Furthermore, trends in natural vegetation and soil development in declined forests and clear-cuts, and their relevance for forest restoration management were studied, focusing on borealization and plant species diversity. It is concluded that this natural development offers very good possibilities for a more passive, low-cost restoration management.     

Field responses to added organic matter, arbuscular mycorrhizal fungi, and fertilizer in reclamation of taconite iron ore tailing

A three season study was conducted to determine the effect of added composted yard waste, arbuscular mycorrhizal (AM) fungi, and fertilizer on plant cover, standing crop biomass, species composition, AM fungal infectivity and spore density in coarse taconite iron ore tailing plots seeded with a mixture of native prairie grasses. Plant cover and biomass, percent seeded species, mycorrhizal infectivity and spore density were greatly increased by additions of composted yard waste. After three seasons, total plant cover was also greater in plots with added fertilizer. Third season plant cover was also greater in plots amended with the higher rate (44.8 Mg ha^{–1) of compost than the moderate rate (22.4 Mg ha-1}). Field inoculation with AM fungi also increased plant cover during the second season and infectivity during the first two seasons. Seeded native species, consisting mostly of the cover species Elymus canadensis, dominated plot vegetation during the second and third seasons. Dispersal of AM fungal propagules into nonmycorrhizal plots occurred rapidly and increased infectivity in compost-amended plots during the third season. In plots with less than 10% plant cover, AM fungal infectivity of inoculated plots was greatly reduced after the second season. The high level of plant cover and the trend of increasing proportion of mycorrhizal-dependent warm-season grasses, along with increases in infectivity, forecast the establishment of a sustainable native grass community that will meet reclamation goals.     

Seed rain,seedling establishment and clonal growth strategies on a glacier foreland

Abstract. Seed production, composition of the seed rain, germination, and seedling mortality, as well as vegetative growth characteristics of common pioneer plant species were studied on the foreland of the retreating Morteratsch glacier in the Swiss Alps. The frequency of diaspores trapped in different successional stages was related to their dispersal mode and was highly skewed towards a few species. Plenty of diaspores well adapted for dispersal by wind are a precondition for the most important pioneer species. Seeds from all pioneer species investigated had a good germination success, provided that the moisture content of the soil was high enough. However, requirement for seedling establishment differed among sites of increasing terrain age and among species. Only specialized pioneers such as Cerastium pedunulatum, Linaria alpina, Oxyria digyna and Saxifraga aizoides tolerate the cold and moist conditions near the glacier. However, these species are restricted to early successional stages. Seedlings of Epilobium fleischeri are affected not only by the cold and moist conditions near the glacier but also by moderately dry conditions on older sites. Availability of safe sites becomes crucial for most species with increasing age of sites and with drier conditions. Most species playing a dominant role during early succession and persisting during later successional stages have a distinctive ability to spread clonally and have a growth form with more or less widely spaced ramets: Achillea moschata. Cerastium pedunculatum. Epilobium fleischeri and Hieraium staticifolium. The growth strategy and demography of the clonal E. fleischeri is presented as an example. The life cycle of this species is characterized in succession by (1) the colonization of safe sites by small seeds adapted for wind dispersal, (2) horizontal spread by clonal growth, and (3) the persistence through phenotypic morphological plasticity in later successional stages. Seedling establishment and clonal growth are thus complementary mechanisms in plant succession on recently deglaciated terrain.     

Stand Biomass and Tree Mortality from Permanent Forest Plots on Krakatau,Indonesia, 1989–19951

Forest closure on the three original Krakatau Islands (Panjang, Rakata, and Sertung) took place ca 1930, about 50 yr after the apparent sterilization of the islands due to volcanic eruptions. Two permanent forest plots were established on each of these islands in 1989. A full enumeration of these plots, of two additional Rakata plots, and of two “mainland”plots from the Ujung Kulon National Park, West Java, was undertaken in 1992. These data provide the first estimates of aboveground biomass from Krakatau. The values reported for Krakatau are below the local West Javan figures, with considerable variation occurring within the islands. In 1992, the fourth Krakatau island, Anak Krakatau, began an eruption sequence which continued through the study period, depositing ash on the study sites of Panjang and Sertung. A further partial survey of these plots in 1994–1995 revealed a significant increase in mortality since the volcanic activity recommenced, with an increase in deaths of larger stems. Although Rakata has not been influenced directly by volcanism, three sites surveyed on Rakata in 1994–1995 have experienced increased tree mortality, in two cases as a consequence of storm damage and in particular, of lightning strikes. Stand dynamics on Krakatau thus appear to be strongly influenced by episodic environmental disturbance with varying degrees of dependence on the volcanic activity of Anak Krakatau.