Vegetation succession on the dunes near Oostvoorne,The Netherlands,since 1934, interpreted from air photographs and vegetation maps

The vegetation succession on the dunes near Oostvoorne, The Netherlands has been followed by means of a novel combination of repeated large-scale vegetation mapping and air photograph interpretation. Vegetation units have been discerned on the formation level because these could be distinguished fairly easily on the photographs and because the rates of change are appropriate to the time interval chosen. Nineteen formations were distinguished. Five 1:6250 maps were constructed, reflecting the formation pattern in 1934, 1943, 1959, 1972 and 1980. An overlay with 2736 grid points at 25 m field distance was used to quantify changes in the formation pattern.The results suggest a pronounced multiple pathway succession with nevertheless three principal trajectories of succession from pioneer to woodland vegetation. The outer dunes, which have originated since 1910, are distinct in successional characteristics from the inner dunes, which already existed but were released from heavy grazing pressure in 1910. The rate of change in the outer dunes was high in the beginning and is slowly decreasing eversince. In the inner dunes it went the other way around. Through visual extrapolation the likely formation patterns in 1910 and in 2000 were estimated.Transition frequencies proved highly variable for most formations. Moreover, strong spatial dependence was found. Limitations in the use of Markov models in cases of long-term succession in heterogeneous environments are discussed.Nomenclature follows the same sources as in van der Maarel et al. (1984).Field work carried out 1980–1981 when the authors were at the Division of Geobotany, University of Nijmegen. We thank Jos Rijntjes, Nijmegen, for his cooperation in the field. Vegetation maps were prepared and calculations performed at Uppsala. We thank the Foundation Het Zuid-Hollands Landschap, Rotterdam, for providing facilities and a grant for fieldwork as well as additional means to reproduce the vegetation maps. Two reviewers gave useful comments.     

The influence of food plant dispersion on caterpillar searching success

Abstract. 1. Collards (Brassica oleracea L.) grown in clumps were more difficult for unstarved, early instar cabbage white caterpillars (Pieris rapae L.) to find than collards spaced at regular intervals, although total plant densities were identical.
2. Early instar, unstarved larvae are less mobile than later instar larvae (our data) or starved larvae (Jones' 1977 data).
3. Starved larvae and late instar larvae tend to find plants more readily than do unstarved or younger larvae.
4. We contend that larval mobility governs the success of searching caterpillars and their sensitivity to variations in plant dispersion.
5. Our results show that the dispersion of targets can influence searching success even though target density is constant. This means that the degree of clumping in host plants is capable of influencing their availability to herbivores.     

鄱阳湖水生植被

本文列出了鄱阳湖98种水生维管束植物的名录,叙述了水生植被的分布。鄱阳湖水生植被面积为2262平方公里,占全湖总面积的80．8％。湖中植被呈不规则环带状分布,并可划分为湿生、挺水、浮叶和沉水4个植物带,9个主要植物群丛。并研究了鄱阳湖水生植被的演变及发展趋势和湖水位的季节性变化对植被的影响。     

鄱阳湖水生维管束植物生物量及其合理开发利用的初步建议

用4种不同的计算方法测定了鄱阳湖水生维管束植物的生物量。根据22个断面,199个采集点,398个样方的测定结果,得出鄱阳湖水生维管束植物的年生产量为431.76万吨(湿重),即相当于5.44×10~(-15)焦耳(能量)。其中,马来眼子菜、苦草和黑藻等3种合计约占总生物量的71.46%。全湖可供草食性鱼类食用的水生维管束植物约占总量的86.9%。文中还对4个植物带和9个群丛生物量的分布规律进行了讨论。提出了人工增殖草食性鱼类,调整湖中植被组成,保护和种植水生经济植物等合理开发利用鄱阳湖水生植物资源的初步建议。     

Modelling Mediterranean pasture dynamies

Pasture vegetation in an open woodland of Quercus rotundifolia subjected to periodic ploughing was sampled in spring during 8 consecutive years. The frequency of herbaceous species was recorded in a total of 69 permanent plots located on 5 adjacent sites with similar lithology, slope and orientation but differing in age since previous ploughing.Vegetation dynamics expressed as trajectories of permanent plots in a non-metric multidimensional scaling space has been modelled in terms of evironmental variables. By fitting a generalized linear model, the dynamics are shown to be related to years since last ploughing, geographical location of plots, total annual rainfall and November rainfall. Meteorological patterns of the sampling period are also described.Abbreviations GLM = Generalized Linear Model - NMDS = Non-metric Multi-Dimensional Scaling - UPGMA = Unweighted Pair-Group Method using Arithmetic Averages     

Buried seed populations on the volcano Mt. Usu,northern Japan,ten years after the 1977–78 eruptions

In 1987, a study on buried seed populations was conducted in the crater basin of Mt. Usu, a volcano located in northern Japan, where the vegetation had beeen almost completely destroyed by eruptions in 1977 and 1978. The former vegetation had consisted of grassland and broad-leaved forest. In the areas formerly occupied by this grassland and forest, 2128.0 and 1985.3 seeds per square meter, respectively, were extracted from 12 blocks of the former topsoil using a floattion method. This revealed that many seeds were still viable even after ten years of burial under thick volcanic deposits. The seeds were distributed more in sandy soil than in rocky soil of the former topsoil. Twenty-five species, most of which favored grassland, were detected in both the former grassland and forest. From comparison of α-and β-diversities between the grassland and forest, the structure of the buried seed population was considered likely to have been more diverse in the forest than in the grassland. The determinants of composition of the buried seed populations were discussed with reference to the former vegetation and soil characteristics.     

Climate and vegetation in China II. Distribution of main vegetation types and thermal climate

The authors examined relationships between Kira's warmth index (WI) and four other important thermal indices: the sums of daily mean temperatures above 5°C and 10°C, Thornthwaite's potential evapotranspiration (PE) and Holdridge's annual biotemperature. The thermal records of 671 meteorological stations evenly located all over China were used to make these comparisons. Close correlations were found within the four relationships, and accordingly WI was used to analyse the thermal distributions of the main vegetation types. Vegetation types around the 671 stations were read from a vegetation map with a scale of 1/4000000. Vegetation types at 269 stations corresponded to the natural or seminatural vegetation, and 29 vegetation types were distinguished by arranging the 269 data into the same or similar types. The geographical distribution of these 29 types and the corresponding main climatic features were described. The relations between WI and distribution of these vegetation types were discussed in detail. As a result, WI values (°C month) corresponding to the vegetation zones could be summarized as follows: (1) arctic or alpine vegetation zone: 0–15; (2) boreal or subalpine vegetation zone: 15-(50–55); (3) cool-temperate vegetation zone: (50–55)–(80–90); (4) warm-temperate vegetation zone: (80–90)–(170–180). These values almost coincided with Kira's values. Chinese postgraduate student in Japan sent by the Chinese Government.     

Plant growth in relation to a rain incident in Wadi Agag,South Egypt

Plant growth in the extremely arid southern part of the Eastern Desert of Egypt is supported by the torrential moisture stored in the subsurface layers of wadi-fill deposits. The space-time stratification of the soil moisture and corresponding adaptive stratification of root systems lead to the niche separation of the species. The survivorship of all studied plants except Zilla spinosa, has a low mortality at early and middle life, but a rapid change to high mortality at a later stage. Zilla spinosa shows the high juvenile and low adult mortality which related significantly to the population density.