Characterization of the canopy structure of Dutch grasslands

In order to characterize the canopy structure of different grassland types 50 stands, representing 15 syntaxonomically distinct types, were examined by harvesting the standing crop during the main flowering period. The types differ in water and nutrient conditions and vary largely in aboveground phytomass (0.5–23 t·ha^?1) and Leaf Area Index (0.4–21: bifacial). Living aboveground phytomass and canopy structure are almost entirely determined by phanerogams. The graminoids generally dominate over the forbs. Variation in aboveground phytomass is related to foliage characteristics such as Aboveground Leaf Area Ratio, Specific Foliage Weight and Leaf Area Development. A PCA with these canopy variables and the variables canopy height, phytomass density and the phytomass ratios stem-leaf-inflorescence shows a clear arrangement related to aboveground phytomass and LAI. The grassland stands can be divided into four groups of different productivity levels for which various combinations of canopy variables are characteristic. Leaf size and leaf inclination are also used for characterization of the different grasslands. Ordinations with these variables by means of PCA and CCA resemble partly to those computed with the canopy variables of aboveground phytomass and LAI. Small leaf sizes are characteristic for low productive grasslands, while the largest leaves occur in high productive grasslands, although they mostly do not belong to the species contributing most strongly to the phytomass of the stand. The leaf inclinations erect and erecto-patent are most common in each grassland. Horizontal leaf areas occur less frequent, but they are relatively well presented in some high productive grasslands. Ranges in leaf size vary more than ranges in leaf inclination do for this series of grasslands. However, leaf size and leaf inclination are useful variables for characterization of grassland canopies in a hierarchical way, where phytomass and leaf area are the first criteria for such a characterization.     

Population structure of the threatened perennial Serratula tinctoria in relation to vegetation and management

Question: How does vegetation and management affect the population stage structure of Serratula tinctoria, a species indicative of highly endangered and species‐rich flood‐plain meadows? Are different management regimes suitable to support viable populations of S. tinctoria? Location: Flood‐plain of the northern Upper Rhine, Germany. Methods: We analysed the population structure of S. tinctoria at 24 meadow sites which differed in vegetation and management. In this comparative study the investigated meadows were either (1) late mown in September; (2) early mown in June or (3) mown in June and then grazed by sheep. Results: The structure of the surrounding vegetation had a clear effect on the population structure of S. tinctoria. The percentage of bare soil, as well as the cover of bryophytes, were positively related, whereas the Ellenberg N‐value of the established vegetation was negatively related to the density and proportion of seedlings. Generally, we found only slight differences between the population structure of S. tinctoria in early and late mown meadows. Both management regimes had high densities of seedlings. In contrast, the meadow pastures supported significantly lower densities of seedlings and generative adults but relatively high densities of juveniles and vegetative adults, indicating a greater importance of clonal propagation under grazing pressure. Conclusions: Our results clearly showed that viable populations of S. tinctoria may occur in all of the studied management regimes. Although S. tinctoria was considered to be highly sensitive to early mowing, our findings suggest a facilitation of the species at more nutrient‐rich sites by mowing in June, which is also a benefit for the integration of management in farming systems.     

Seed bank diversity in mesic grasslands in relation to vegetation type,management and site conditions

Questions: 1. Do different management types (i.e. hay meadow, silage meadow, meadow‐pasture, pasture) have different impact on the size and composition of the seed bank of mesic grassland (Arrhenatheretalia)? 2. How strong is the effect of management on the seed bank in relation to above‐ground vegetation, edaphic factors and land‐use history? 3. Are there differences in C‐S‐R plant strategy types and seed longevity under different management regimes? Location: Lahn‐Dill Highlands in central‐western Germany. Methods: Above‐ground vegetation and the soil seed bank of 63 plots (at 21 sites) in mesic grasslands were studied. Differences between management types in quantitative seed bank traits and functional characteristics were tested by ANOVA. The impact of management, above‐ground vegetation, site conditions and land‐use history on seed bank composition were analysed by partial CCA. Results: Management had no significant impact on species richness and density of the seed bank but significantly influenced their floristic composition and functional characteristics. CCA revealed that even after adjustment for soil chemical parameters and above‐ground vegetation management still had significant impact on seed bank composition. ANOVA revealed that silage meadows contained higher proportions of R‐strategy compared to hay meadows. In contrast, in hay meadows and meadow‐pastures proportions of S‐strategy were higher than in silage meadows. Conclusions: The type of grassland management has little impact on quantitative seed bank traits. Management types with a high degree of disturbance lead to an increase of species following a ruderal strategy in the seed bank. Irrespective of management type only a limited proportion of characteristic grassland species is likely to re‐establish from the seed bank after disappearance from above‐ground vegetation.     

南方山地人工草地群落结构组建及其与环境因子的关系

采用CCA排序技术,定量分离了刈割和放牧下环境、空间、生物和随机因素对亚热带山地人工草地群落结构组建的贡献,分析了不同管理制度下的群落．环境关系．放牧和刈割条件下,与环境因素有关的群落结构变化分别为27．4％、25．9％(其中环境因素独立作用分别为18．9％、19．8％),空间因素解释的变化分别为32．5％、24．2％,生物及随机因素造成的变化分别为48％、56％．说明放牧削弱了生物学过程(主要是物种相互作用和种子扩散)对群落结构组建的作用,增强了空间因素的影响．空间因素主要是通过与环境因素耦合(改变直接环境的空间分布)对群落结构组建起作用、刈割条件下,群落结构和物种多度沿环境变化呈梯度分布．放牧条件下,环境因素与群落、物种的关系比较复杂,不同干扰程度的群落小斑块向不同方向演替．     

Phytosociology and ecology of old hay meadows in Hordaland,western Norway in relation to management

Well-drained mown hay meadows in Hordaland, western Norway, were investigated. The hay meadows are either managed in a traditional or in a semi-traditional way. Traditional management in the area involves little or no use of manure or fertilizer, mowing once or twice a year with a first cut later than June 23, clearing in spring and intensive grazing for short periods in spring and autumn. Semi-traditional management involves use of small to medium quantities of commercial fertilizer, often in addition to manure. Grazing may be irregular, light or lacking.Eight units of hay meadow vegetation are described, all assigned to the class Molinio-Arrhenatheretea, order Arrhenatheretalia; four units to the Atlantic alliance Cardaminion pratensis, association Cardamino pratensis-Conopodietum majoris (with three subassociations); one unit to the alliance Arrhenatherion elatioris, three units are provisionally grouped as Galium uliginosum-Knautia arvensis meadows.Continuous management of these meadows has resulted in characteristic species compositions, which vary along a west-east climatic gradient, and are related to the amount of commercial fertilizer used and the natural mineral-content of the soil.These hay meadows seem to be best maintained by continuing the traditional management regime. Grazing in spring and in autumn reduces fast growing dominants and creates openings for new seedlings of annuals and biennials. A late first cut allows for ripening of the seeds and creates openings for light for the species of the lower field layer. A list of species characteristic of traditionally managed permanent hay meadows is presented, and possible effects of present changes in management on the species composition of the meadows are discussed.The amount of organic matter in the topsoil is small in most stands. The pH values are between 4.0 and 5.6. The highest values were recorded in soil where little or no commercial fertilizer is used, and where the subsoil is naturally rich in minerals. A tendency to Mg impoverishment in the best fertilized stands is demonstrated. Species-rich stands on Ca-rich soils are poor in P.The expected changes in vegetation, future use, and conservation of permanent hay meadows in Hordaland are discussed.     

Vertical structure of wet grasslands under grazed and non‐grazed conditions in Tierra del Fuego

Abstract. We studied the vertical structure of wet grazed grasslands in Tierra del Fuego (southern Argentina). A point quadrat method was developed using a fine needle graduated in cm. The vertical and horizontal frequency of species and organs was quantified in samples collected from non‐grazed and grazed plots in the field. There was vertical stratification in both types of samples, but only in the first eight cm above the ground in grazed samples, with a dominance of Caltha sagittata. In non‐grazed samples graminoids grew taller than forbs and their inflorescences were an important element of the canopy structure. In both treatments, vertical species diversity was maximum in the lower part of the canopy, although diversity was significantly higher in grazed pots. In grazed samples, Caltha sagittata was the dominant species in 46% of samples and its leaves occupied 35% of the upper canopy. In the non‐grazed samples, Hordeum pubiflorum and Festuca magellanica were dominant in 63% of the samples, with H. pubiflorum leaves occupying 55% of the upper canopy. Comparing species by pairs, significant differences in vertical position were maintained in non‐grazed versus grazed pots. It is concluded that vertical stratification occurs even in the shortest communities. In this community, forb species grew close to the ground in the grazed areas, while forbs grew in the gaps and grasses above them in the non‐grazed areas. The main differences were in the relative dominance of forb and grass species and the presence of inflorescences.     

Leaf dynamics of seedlings of rain forest species in relation to canopy gaps

Summary Leaf dynamics of eight tropical rain forest species seedlings was studied in three environments: the shaded forest understorey, a small gap of ±50 m², and a large gap of ±500 m². Leaf production rate and leaf loss rate were enhanced in gaps, and a large gap resulted in larger increases than a small gap. For most species net leaf gain rate was larger in gaps, although this rate was not always largest in the large gap. Leaf loss decreased, and leaf survival percentages increased with increasing shade tolerance of species, indicating a slower leaf turnover for more shade tolerant species. Leaf area growth rate was only partly determined by net leaf gain rate. Ontogenetic effects on leaf size were also important, especially in the large gap. Species which possessed leaves with high specific leaf weight (SLW) showed lower leaf loss rates and higher leaf survival percentages than species with low SLW leaves. Leaf life span seemed to be related to leafcost per unit area. The relation of specific patterns in leaf production and leaf loss to the regeneration mode of the species is briefly discussed.     

Grazing effects upon plant community structure in subhumid grasslands of Argentina

Changes in plant community structure are identified as a result of grazing in grasslands of the flooding pampa which evolved under supposedly light grazing conditions. The effect of excluding grazing upon total leaf area index was an increase of 30%. The largest response was observed in the distribution of leaves in the canopy. In the grazed areas, most of the green material was concentrated in the 0–5 cm layer while in the ungrazed treatments the largest portion of the leaf area was in the 10–30 cm layer. Grazing exclusion resulted in a small change in total basal area but a larger change in its distribution, from many small tussocks to less numerous large ones. The effect of grazing upon leaf area and basal area was accounted for by changes in vigor as well as by changes in species composition. The major effect of excluding grazing upon species composition was the disappearance of some native planophile species and most of the exotics. The species composition of grazed areas of both communities was very similar while there were large differences between the ungrazed areas and between the grazed and ungrazed areas of the same community. It is suggested that there is a group of species which responds to the coarse-grained ‘signal’ of grazing and its presence can cause dissimilar communities to converge under grazing conditions. The other group of species responded to the fine-grained ‘signal’ of the environmental conditions associated with topography.     

Community structure in montane grasslands of central Argentina in relation to land use

Abstract. We compared the responses of natural montane grasslands in central Argentina to two land-use patterns: cultivation - high intensity, low frequency, and short history of disturbance - and livestock raising - low intensity, high frequency and long history of disturbance. We analysed species composition, richness, and architectural traits in seven neighbouring sites under different land use. There were sharp floristic discontinuities between post-agricultural stages, whereas only minor shifts occurred among different grazing situations. Unlike cultivation, grazing did not produce significant differences in species richness and allowed very slight invasion by exotics. In post-cultivation situations, architectural differences were accounted for by species composition. In the case of different grazing intensities, they were mainly explained by morphological differences among populations of the same dominants. In view of the historical information and current ideas, we suggest that the differential responses to both land uses can be explained not only by the different frequencies and intensities of disturbance they represent, but also by their contrasting histories in the area. Accordingly, herbivory by ungulates should not be considered as a disturbance in these montane grasslands.     

Patterns of light and nitrogen distribution in relation to whole canopy carbon gain in C3 and C4 mono- and dicotyledonous species

An analytical model was used to describe the optimal nitrogen distribution. From this model, it was hypothesized that the non-uniformity of the nitrogen distribution increases with the canopy extinction rate for light and the total amount of free nitrogen in the canopy, and that it is independent of the slope of the relation between light saturated photosynthesis (P_m) and leaf nitrogen content (n_L). These hypotheses were tested experimentally for plants with inherently different architectures and different photosynthetic modes. A garden experiment was carried out with a C₃ monocot [rice, Oryza sativa (L.)], a C₃ dicot [soybean, Glycine max (L.) Merr] a C₄ monocot [sorghum, Sorghum bicolor (L.) Moensch] and a C₄ dicot [amarantus, Amaranthus cruentus (L.)]. Leaf photosynthetic characteristics as well as light and nitrogen distribution in the canopies of dense stands of these species were measured. The dicot stands were found to have higher extinction coefficients for light than the monocot stands. Dicots also had more non-uniform N distribution patterns. The main difference between the C₃ and C₄ species was that the C₄ species were found to have a greater slope value of the leaf-level P_m—n_L relation. Patterns of N distribution were similar in stands of the C₃ and C₄ species. In general, these experimental results were in accordance with the model predictions, in that the pattern of nitrogen allocation in the canopy is mainly determined by the extinction coefficient for light and the total amount of free nitrogen.     

A new life table of leaves ofPhaseolus vulgris L. in relation to their position within the canopy and plant density

In order to demonstrate in detail the relationship between the longevity and productivity of leaves within a canopy, a new life table approach, the ‘bioeconomic life table’, was applied to the leaves of kidney bean plants (Phaseolus vulgaris L.) in relation to planting density and their position within the canopy. The net photosynthetic rate for upper leaves under full daylight tended to decline gradually due to leaf senescence from about 20 days after leaf emergence, and for the lower leaves the decrease was very rapid due to both shading and senescence about 10 days after emergence. Analysis of the survivorship curves and daily surplus production of leaves suggested that the lower and middle leaves, especially the latter, survived without surplus production of dry matter after they had reached mean longevity, and while the upper leaves at high density had a much shorter mean longevity, they had very large values of daily surplus production throughout the survival period. For the total foliage, the summed value of accumulated surplus production during the survival period was about five times as large as the summed value of the dry weight of the dead leaves, regardless of planting density. The daily rate of canopy leaf respiration was almost proportional to that of canopy gross photosynthesis for the various leaf area indices of the canopy, so that there was no optimum leaf area index that maximized canopy daily surplus production.     

Architecture of Ulex europaeus: Changes in the vertical distribution of organs in relation to plant height and season

Abstract. This paper is concerned with the vertical distribution of photosynthetic, woody, reproductive and dead organs of Ulex europaeus, the dominant pyrophytic species in most of the shrublands of Galicia (NW Spain). Frequency and weight data for the above‐mentioned organs were collected each season for individual plants up to 150 cm tall, in order to quantitatively characterize the vertical organ distribution in this species. The study also deals with regression equations that would allow the prediction of phytomass from easier measurements. Frequency values were recorded using a grid of quadrats situated on the plant's vertical axis, and clipping each individual into vertical layers of 6 cm to obtain phytomass values. The abundance and location of photosynthetic, woody and dead organs varies in the three height classes studied, both regarding frequency and phytomass. A marked decrease in the ratio between photosynthetic and total phytomass is also observed as plant height increases. Significant seasonal differences were recorded only for reproductive organs. A good fit was obtained for several regression equations; total phytomass can be predicted from the largest diameter of the shrub, or organ phytomass from total weight.     

Variations in resistance to canopy disturbances and their interactions with the spatial structure of major species in a cool‐temperate forest

Question: How does typhoon‐related disturbance (more specifically, disturbance in the understorey due to tree‐fall and branch‐fall) affect different species mortality rates in a vertically well‐structured forest community? Location: Cool‐temperate, old‐growth forest in the Daisen Forest Reserve, Japan. Methods: We investigated the canopy dynamics and mortality rate trends of trees ≥5 cm diameter at breast height in a 4‐ha study plot, and analysed the effects of tree diameter and spatial structure on the mortality risks for major tree species in the understorey. Results: Significant differences were found in the mortality rates and proportions of injured dead stems between census periods, which were more pronounced in the understorey than in the canopy. Acer micranthum, which showed increased mortality during typhoon disturbance periods, had a clumped distribution. In contrast, Acer japonicum and Viburnum furcatum, which showed similar mortality rates between census periods, had a loosely clumped spatial distribution and a negative association with canopy trees, respectively. In the understorey stems of Acanthopanax sciadophylloides and Fagus crenata, whose spatial distribution patterns depended on canopy gaps, significant increases in mortality rates were observed only during severe typhoon‐related disturbance periods. Conclusions: The sensitivity of trees to typhoon‐related canopy disturbance is more pronounced in the lower layers of vertically structured forest communities. Differences in mortality patterns generated through the combined effects of spatial variation in disturbance regime and species‐specific spatial distribution patterns (spatial aggregation, association with canopy trees, and canopy gap dependency) contribute to the co‐existence of understorey species in forest communities that are subject to typhoon‐related disturbance.     

Adjustment of foliage structure and function to a canopy light gradient in two co-existing deciduous trees. Variability in leaf inclination angles in relation to petiole morphology

 Foliar inclination angles, petiole morphology and dry matter partitioning between assimilative and support biomass were studied in shade-intolerant Populus tremula L. and shade-tolerant Tilia cordata Mill. along a natural light gradient across the canopy. The leaves of sub-canopy species T. cordata were on average exposed to lower irradiances, and they were also more horizontal with greater blade inclination angles (ϕ_B, defined as the angle between the leaf fall-line and the horizon; ϕ_B was positive for the leaves inclined upwards, and negative for the leaves inclined downwards) than those in P. tremula. Seasonal average daily integrated quantum flux density (Q _int, mol m^–2 day^–1) and ϕ_B were not related in T. cordata, and only a weak negative effect of Q _int on ϕ_B was detected in P. tremula. Nevertheless, when both species were pooled, there was a strong negative relationship between Q _int and ϕ_B, implying that the leaves became progressively vertical with increasing height in the canopy. Interspecific differences in foliage inclination were mainly related to petiole morphology, in particular to petiole length, rather than to contrasting biomass investment patterns between assimilative and support tissues within the leaf. It was suggested that more horizontal leaves, resulting from the species-specific structure of petioles, partly explain the superior performance of shade-tolerant T. cordata in the understory and the sub-canopy. Received: 13 November 1997 / Accepted: 6 March 1998     

Rose leaf structure in relation to different stages of micropropagation

Summary The Mme Isaac Pereire rose was investigated in an attempt to establish how micropropagated roses might best be weaned into normal growth conditions. Leaves of in vitro grown plants, weaned plants and the stock plant were studied, using light microscopy and different scanning and transmission electron microscopical techniques. Features that varied in the different growing conditions were leaf size and thickness, amount of wax, thickness of cuticle and external epidermal cell wall, number and aperture of the stomata, size of the epidermal cells, number of layers of the palisade cells, and size of the chloroplasts in the mesophyll. The rose in the present study had wax on the in vitro cultured plants; this wax was of similar ultrastructural appearance to that of the stock plant, even though in smaller quantities. Weaned plants had an intermediate amount of wax. The cuticle was thin, ranging from 0.04 m on plants growing in vitro to 0.3-0.6 m on weaned plants and stock plants. Stomata were always wide-open on leaves taken from cultures with a relative humidity of 100%. After four weeks in a humidity lowered to 85% stomata had closed.Abbreviations BAP 6-benzyl-aminopurine - CPD critical point drier - CTEM conventional transmission electron microscopy - NAA a-naphthaleneacetic acid - psi pounds per square inch - SEM scanning electron microscopy - TEM transmission electron microscopy     

The study of vocal communication of wild mandrills in Cameroon in relation to their social structure

The vocal repertoire of the mandrill (Mandrillus sphinx), a forest living baboon, is described, and their vocal communication analyzed quantitatively. Although the vocal repertoire of mandrills corresponds well to that of savanna living baboons,Papio, some characteristics differed, such as the development of long-distance calls and differentiation of vocalizations between age-sex classes. Vocal communication within a group was closely related to changes in the spatial distribution of group members, and the two most common vocalizations, crowing and 2PG, appear to function as contact calls. Based on the wide dispersion of food trees, a group of mandrills divided into several feeding groups (subgroups). The two types of contact call were given in different and in some senses complementary contexts, and helped to facilitate and maintain group integration. According to their acoustic structure, these calls are long distance calls. Influenced by the high-level of attenuation of vocalization on the forest floor, the mandrill has developed them as contact calls, instead of using the contact “grunt,” which is common to the savanna living baboons. Comparing the patterns of vocal exchanges of mandrills with those of gelada and hamadryas baboons which have a multi-levelled society, the social structure of the mandrill is discussed. From the analysis of the spatial distribution of vocal emission, a number of clusters of vocalizations were obtained. These clusters correspond to subgroups. The frequent female-female and female-male vocal exchange between subgroups of mandrills suggest that the relationships between subgroups are less closed than between the one-male units of gelada and hamadryas baboons. Furthermore some of these clusters include more than two vocalizing adult males, while in other clusters there are no vocalizing adult males. Thus, the social structure of mandrills is suggested to be multi-male rather than a multilevelled type. The absence of contact calls specific for short distance and the functional replacement of the grunting of all group members by persistent emission of a loud call (2PG) by usually just one adult male suggests that the social structure of mandrills is not exactly equivalent to that of the multimale troop of savanna living baboons. Usually the use of 2PG is monopolized by one adult male travelling in the rear part of the group. Such monopolization of 2PG emission and the pattern of 2PG-2PG or 2PG-roar exchanges by adult males in some cases indicate the existence of strong dominance relationships among adult males, and especially the existence of a leader male within a multi-male group of mandrills.     

Growth,cell volume,and fine structure of Porphyra umbilicalis in relation to osmotic tolerance

Porphyra umbilicalis, a marine red alga occurring in the intertidal zone of the cold North Sea, tolerates a wide range of osmotic conditions from 0.2 x to 6 x artificial seawater medium ASP₁₂. In cells osmotically adapted for two weeks, photosynthesis and respiration are progressively inhibited in media more concentrated than 2 x. In both hypo- and hyperosmotic stress ranges, the most striking fine structural change is the development of vacuoles. In comparison to 1 x medium, where vacuoles are virtually lacking, the vacuolar part of the protoplasm increases 6-fold in 0.2 x and 10-fold in 3.5 x medium, respectively. However, at extreme hyperosmotic stress (6 x medium) the vacuolar part is extremely small. The largest cell volumes are found in 0.2 x and 3.5 x media, the smallest one in 6 x medium. In the osmotically regulated range (0.2–3.5 x medium), the regulated parameter is the volume of the protoplasm without the vacuolar system. It is suggested that at hyperosmotic stress the vacuoles may serve as osmotically active compartment, probably by accumulation of inorganic ions. The intracellular content of Floridean starch granules decreases with increasing osmotic pressure, possibly indicating the significance of soluble organic constituents as osmotically active solutes.Member of the Arbeitsgemeinschaft für Elektronenmikroskople un der Ticrärztlichen Hochschule Hannover