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Summary In the Tai region of the Ivory Coast, mature forest is felled and burned and a crop of rice is grown; forest is then allowed to regenerate for 20 or more years before being cropped again. The top 10 cm of soil beneath a 21-year-old forest prior to felling contained 2000 viable seeds m−2 of mainly woody species of previous successional stages no longer represented in the vegetation. Seedling emergence was greater in full sunlight than under leaf canopy, especially for herbaceous species of open habitats. Burning destroyed almost half of the seeds, but overall germination of those that survived was advanced by about 2 weeks. Germination of some common pioneer species was enhanced by the fire. Provided that burning took place and the rice was planted immediately, vegetation arising from the seed bank did not present a problem. The density never exceeded 70 seedlings m−2 and little or no weeding was required. Species present at densities greater than 1 seedling 10 m−2 were all recorded in the seed bank. Resume Graines dans un sol forestier humide et leur relation avec le changement des methodes culturales en Cole d'Ivoire Dans la region Tai de Cote d'Ivoire, quand une foret atteint sa maturite, elle est abattue et brulee, puis une culture de riz est implantee; puis une foret est regeneree pour 20 ans ou plus avant d'etre de nouveau coupee. Les 10 premiers cm du sol sous une foret de 21 ans avant l'abattage contenaient 2000 graines viables m−2 des principale especes forestiers, des stades successifs anterieurs et plus representees dans la vegetation. La levee des plantules est plus elevee en pleine lumiere que sous un couvert de feuilles, specialement pour les varietes herbacees des habitats ouverts. Le brulage detruit environ la moitie des semences, mais en outre la germination de celles qui restent est avancee d'environ 2 semaines. La germination de certaines especes pionnieres communes est accrue par le feu. Pourvu que l'on brule et que le riz soit plante immediatement, la vegetation issue du stock grainier ne represente pas un probleme. La densite n'est jamais superieure a 70 plantules m−2 et il est soit inutile de desherber, soit tres facile de desherber. Les especes presentes a des densites superieures a une plantule pour 10 m2 sont toutes enregistrees dans le stock grainier. Zusammenfassung Samenvorrat im Boden bei wandernder Rodungskultur im tropischen Regenwald der Elfenbeinkuste Im Tai-Gebiet der Elfenbeinkuste wird nach dem Fallen und Abbrennen des Regenwalds Reis angebaut, bis sich der Wald fur 20 oder mehr Jahre bis zur nachsten Nutzung regenerieren kann. Die oberste 10-cm-Bodenschicht eines 21 Jahre alten Waldes enthielt vor der Rodung 2000 Samen m−2, uberwiegend Samen von Baumarten fruherer Sukzessionsstadien, die im akluellen Bestand nicht mehr vorhanden waren. Die Keimung war im vollen Licht besser als im Bestand, besonders bei krautigen Arten der Lichtungen. Durch das Abbrennen wurde etwa die Halfte der Samen vernichtet, aber die uberlebenden Samen keimten rund 2 Wochen fruher. Bei einigen Pionierarten war die Keimungsforderung durch das Abbrennen besonders deutlich. Wenn der Reis unmittelbar nach der Brandrodung gesetzt wurde, stellten die wildwachsenden Pflanzen kein Problem dar. Ihre Dichte uberschritt 70 Pflanzen m−2 nie, so dass sie uberhaupt nicht oder kaum gejatet werden mussten. Von allen Arten, die mit mehr als 0,1 Pflanzen m−2 auftraten, wurden im Boden Samen gefunden.

1. It is hypothesized that the recent intensification of agricultural practice in the coastal fringe of West Connemara, Ireland, has affected the vegetation of vulnerable ecosystems like lakes and wetlands. 2. Lakes and wetlands, arranged in three transects running inland from the coast, were studied to detect an assumed decrease in the effects of eutrophication as a result of a decrease in the intensity in land use. 3. The data obtained from the vegetation survey in 1988 were compared with those collected at the same sites in 1975. The data were subjected to various multivariate statistics to detect changes in species composition and relationships between these changes and environmental variables such as pH and orthophosphate concentration in the surface waters. 4. Changes in species composition are accompanied by changes in environmental factors; notably a marked increase in orthophosphate level indicating an anthropogenic origin for most of the observed changes in vegetation. 5. Changes in species composition have also been used to construct a transition matrix for sites between 1975 and 1988. This has served as a basis for a prognosis on the state of the vegetation at these sites circa 2000. Data have also been grouped to indicate lake-specific patterns in the changes. 6. The dynamics of all plant species have been established based on their frequency of disappearance from sites since 1975 and their rate of establishment in new sites in 1988. Special attention has been given to species from the red data list. It is concluded that over the past 13 years species diversity decreased in the whole area, and especially in coastal lakes. Red data list species appeared to be the more vulnerable ones.

Competition between weeds and groundnuts was studied in two field experiments in the inland Zanderij area of Suriname. The crop was kept weed-free or without weed control for increasing periods of time after planting. Observations made at the end of each period with or without weed control provided an analysis of the growth of a crop with weed control and of a crop without weed control. Uncontrolled weed growth was concentrated between the rows. Competition with weeds reduced ground cover and LAI of the crop. DM accumulation was affected, resulting in lower yields. Plant density and number of branches per plant were not influenced. Weed competition increased stem length and reduced the number of leaves and pods per plant. Timing of flowering was not influenced. Competition for nutrients was absent, but there was competition for light and water. About 15 weed-free days after planting were sufficient to prevent yield losses. Yield losses were due to a reduction in number of pods per plant. Competition should especially be prevented in the period when the number of pods per plant is established, i.e. around 35-60 days after planting. (Abstract retrieved from CAB Abstracts by CABI’s permission)

Two field experiments were carried out in the inland Zanderij area of Suriname to study competition between soyabeans and weeds. The crop was kept weed-free or without weed control for increasing periods of time after sowing. An analysis of the growth and development of a crop with weed control and of a crop without weed control was obtained by making observations at the end of each period of time with or without weed control. Uncontrolled weed growth concentrated mainly between the rows. Competition with weeds reduced ground cover and LAI of the crop, leading to a lower weight and yield. Plant density was not affected, but weed competition reduced the number of branches, inflorescences, and pods per plant. Timing of flowering was not influenced. Competition for water was inferred and competition for light seemed likely. Competition for nutrients was weak. Weeding in the period of pod initiation, i.e. around 45-70 days after sowing, appeared to be essential to avoid competition with weeds. A period of around 4 weed-free weeks after sowing was necessary to avoid yield reduction or too much weed growth at harvest. (Abstract retrieved from CAB Abstracts by CABI’s permission)

Summary: Resume: Zusammenfassung The effect of broadcast or band-placed application of fertilizer on the growth of weeds was studied at two locations on low-fertility acid soils in Suriname. Band placement of fertilizers considerably reduced weed growth compared to fertilizer-applied broadcast. With band-placed fertilizer the increased weed growth due to fertilizer application was concentrated on the fertilized bands. Weed growth was also stimulated in planter wheel-tracks. The spatial distribution of the weed growth is discussed in relation to the crops groundnut, sorghum and soybean, grown at the same location. Reponse des adventices au mode d'application des engrais sur des sols acides de faible fertilite au Surinam L'effet d'application d'engrais sur le rang ou en plein sur la croissance des mauvaises herbes a eteetudiee en deux lieux du Surinam sur sols acides pauvres. Le traitement sur le rang des engrais a considerablement reduit la croissance des adventices comparea l'application en plein. Avec l'application de l'engrais en ligne l'augmentation de croissance due a la fertilisation etait concentree sur les bandes fertilisees. La croissance des adventices etaient egalement stimulee dans les traces de roues de tracteurs. La distribution spatiale de la croissance des adventices est discutee en relations avec la distribution spatiale de la croissance des adventices trouve chez le sorgho, le soja, l'arachide cultives dans les memes lieux. Wirkung der Dungungsmethode auf die Verunkrautung ertragarmer, saurer Boden in Surinam An 2 Ortem mit ertragarmen, sauren Boden in Surinam wurde die Wirkung der Dungungs-methode auf das Wachstum von Unkrautern untersucht. Banddungung reduzierte das Unkrautwachstum im Vergleich zur breitwurfigen Dungung erheblich. Ein gefordertes Unkrautwachstum zeigte sich nur auf dem Dongungsband und auch auf den Fahrspuren. Die unterschiedliche Verunkrautung in Erdnus, Sorghum und Sojabohne wird diskutiert.

Summary: To assess the potential contribution of growing highly competitive crops to control Cyperus esculentus in the Netherlands, the influence of silage maize, hemp, winter barley and silage winter rye on emergence, growth and reproduction of this weed was studied in two field experiments. Growth and reproduction of C. esculentus (determined both as tuber production per plant and density of the weed in the subseuent crop maize) was reduced by each crop, compared to plots in which no crop was grown. In hemp, hardly any tuber production was observed. By growing a green manure crop after harvest of the winter barley the tuber production of the weed was reduced to about 40% of that in winter barley followed by fallow. Decreasing the light regime in a greenhouse experiment in the same order as was observed in the crops winter barley, maize and hemp, caused a similar reduction of tuber production to that found in the field. Therefore, it is suggested that competition for light is the main factor explaining the observed crop effects on the population dynamics of the weed. It is concluded that growing competitive crops as hemp in rotation may effectively complement chemical control of C. esculentus. Resume: Pour mesurer la contribution potentielle de cultures fortement competitives pour lutter centre Cyperus esculentus aux Pays-Bas, l'influence du mais ensilage, du chanvre, de l'orge d'hiver, du seigle d'hiver sur la levee, la croissance et la reproduction de cette adventice a eteetudiee dans deux experimentations au champ. La croissance et la reproduction de C. esculentus (determinees a la fois par la production de tubercules par plante et la densite d'adventice dans la culture suivante de mais) ont ete reduites par chaque culture comparativement aux parcclles laissees sans culture. Dans le chauvre, une assez forte production de tubercules a ete observed. En semant un engrais vert apres la moisson de l'orge de l'hiver, on a reduit la production de tubercules de l'adventice de 40% par rapport a celle observee en orge d'hiver suivi par une jachere. Dans une experimentation de serre en regime de lumiere decroissante de la meme nature que celle qui est observee sous les couverts d'orge d'hiver, de mais et de chanvre a entraine une reduction de la production de tubercules similaire de celle observee en plein champ. De cela, on deduit que la competition pour la lumiere est le principal facteur expliquant les effets observes des cultures sur la dynamique des populations de l'adventice. On en conclut que l'introduction d'une culture competitive comme le chanvre dans la rotation peut completer efficacement la lutte chimique contre C. esculentus. Zusammenfassung: Um den moglichen Beitrag konkurrenzstarker Kulturen zur Bekampfung von Cyperus esculentus L. in den Niederlanden zu erfassen, wurde der Einflus von Mais, Hanf, Wintergerste und Roggen auf den Austrieb, den Wuchs und die Reproduktion dieses Unkrauts in 2 Feldver-suchen untersucht. Wuchs und Reproduktion, beide in Mais als Folgekultur mit der KnoUen-zahl pro Pflanze und der Wuchsdichte bestimmt, wurden— im Vergleich zu Parzellen ohne Einsaaten— durch alle Kulturen herabgesetzt; in Hanf wurde kaum eine Bildung neuer Knollen beobachtet. Bei Anbau von Grundungungspflanzen nach der Ernte der Wintergerste wurden nur etwa 40% so viele Knollen gebildet wie bei folgender Brache. In einem Gewachshausversuch mit zunehmender Beschattung bis zu der in Wintergerste, Mais und Hanf beobachteten ergab sich eine ahnliche Abnahme der Knollenbildung wie im Freiland. Deshalb wird angenommen, das die Konkur-renz um Licht der wichtigste Faktor fur die festgestellten Einflusse der Kulturen auf die Populationsdynamik dieser Unkrautart ist. Der Anbau konkurrenzstarker Kulturen wie z. B. Hanf in einer Fruchtfolge kann die chemische Bekampfung von Cyperus esculentus wirkungs-voll erganzen.

Summary: Resume: Zusammenfassung The effect of nitrogen, phosphorus and potassium on the growth of weeds was studied at two locations on low-fertility acid soils in Suriname. Nitrogen stimulated the growth of weeds in terms of ground-cover and weight on a loamy sand of comparatively low fertility, as well as on a sandy loam of higher fertility. Phosphorus ultimately only stimulated ground-cover development and growth on the sandy loam, and interacted positively with nitrogen on that soil. Potassium had no effect on weed weight, but at both locations the number of plants increased with application of K. Differences in the amount of weed growth between the two locations were related to differences in the composition of the weed flora. On the sandy loam with application of 50 kg N, 50 kg P and 40 kg K ha−1, nutrient uptake by the weeds was 72 kg N, 10 kg P and 121 kg K ha− over a period of 35 days. Reponse des adventices a l'application d'azote, phosphore et potassium sur des sols pauvres acides au Surinam En deux lieux du Surinam avec des sols pauvres acides, l'effet de l'azote, du phosphore et du potassium sur la croissance des adventices a eteetudie. L'azote a stimule la croissance des adventices en terme de couverture du sol et de poids sur un sable limoneux relativement pauvre aussi bien que sur un limon sableux de plus grande fertilite. Le phosphore a finalement seulement stimule le developpement et la croissance sur le limon sableux et il y a eu une interaction positive avec l'azote. Le potassium n'a pas eu d'effet sur le poids des adventices, mais dans les deux situations le nombre de plantes a augmente avec l'application de K. Les differences dans la quantite de mauvaises herbes entre les deux situations etaient liees aux differences dans la composition de la flore adventice. Sur le limon sableux avec une application de 50 kg d'azote, 50 kg de phosphore et 40 kg de potasse a l'hectare, l'absorption par les adventices a ete en 35 jours de 72 kg N, 10 kg P et 121 kg K a l'hectare. Wirkung einer Stickstoff-, Phosphor- und Kaliumdungung auf die Verunkrautung ertragarmer, saurer Boden in Surinam An 2 Orten mit ertragarmen, sauren Boden in Surinam wurde die Wirkung einer Stickstoff-, Phosphor- und Kaliumdungung auf das Wachstum von Unkrautern untersucht. Stickstoff forderte das Wachstum von Unkrautern (Bodendeckung, Biomasse) sowohl auf einem verhaltnismasig ertragarmen lehmigen Sand als auch auf einem ertragreicheren sandigen Lehm. Phosphor forderte letzten Endes Deckungsgrad und Wachstum nur auf dem sandigen Lehm und wirkte da positiv mit Stickstoff zusammen. Kalium hatte keine Wirkung auf die Biomasse, aber an beiden Orten fuhrte es zu einer groseren Pflanzendichte. Die Wachstumsunterschiede an den beiden Orten hingen von der Zusammensetzung der Unkrautflora ab. Auf dem sandigen Lehm betrug bei 50 kg N, 50 kg P und 40 kg K ha−1 die Nahrstoffaufnahme der Unkrauter 72 kg N, 10 kg P und 121 kg K ha−1 innerhalb 35 Tagen.

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SUMMARY In eight experiments the competition between sun and shade plants was studied in different light environments. In higher light intensities the competitive ability of sun species was definitely greater. In lower light intensities, competitive ability did not differ basically between sun and shade species, but seemed mainly to depend on the weight of the plant at the start of the expiment. It is concluded that the competitive ability of sun and shade plants does indeed correlate positively with the light intensity of their natural habitats. The effect of the red/far-red ratio on competitive ability cannot be predicted from the experiments, but it is probable that when competing, sun species will be disadvantaged by a low red/far-red ratio.

Summary Weed species in arable ecosystems are adapted to the conditions produced by agricultural management. In order to give preventive and curative guidelines to weed management one needs to predict the composition of the weed vegetation after certain (soil) cultivation measures. Dormancy mechanisms of seeds in the seedbank and the environmental conditions in the furrow before and after cultivation are usually such that the vegetation composition is heterogeneous. Multivariate analyses enable us to describe and classify weed vegetation and to analyse its relationship to environmental factors. Resume Analyses multivariances en malherbologie Les especes d'adventices dans les ecosystemes cultives sont adaptees aux conditions creees par les conditions culturales. Afin de donner des conseils preventifs et curatifs de desherbage, on a besoin de prevoir la composition de la flore apres certaines facons culturales (/sol). Les mecanismes de dormance des semences du stock grainier et les conditions environnementales dans le sillon avant et apres le travail du sol sont tels que normalement on a des population vegetatives heterogenes. Les analyses multivariances nous permettent de decrire et classifier les populations d'adventices et d'analyser leur relation avec les facteurs de l'environnement. Zusammenfassung Multivariate Analyse in der Unkrautforschung Die Unkrautarten in anbaufahigen Oekosystemen sind den Bedingungen angepasst, die jeweils durch die Anbaumethoden hervorgerufen werden. Um fur ein Unkrautmanagement praventive und kurative Richtlinien zu geben, ist es notwendig, die Zusammensetzung der nach bestimmten (Boden) Bearbeitungsmassnahmen auftretenden Unkrautflora vorherzusagen. Die Vegetationszu-sammensetzung ist gewohnlich heterogen wegen der Dormanzmechanismen des Samenvorrats im Boden und der Umweltbedingungen in der Furche vor und nach Bestellung des Bodens. Eine multivariate Analyse ermoglicht uns die Unkrautvegetation zu beschreiben und zu klassi-fizieren als auch ihre Beziehung zu Umweltfaktoren zu analysieren.

SUMMARY Bush bean seedlings were grown at 16 and 25°C and two light intensities. At 25°C the relative growth rate (RGR) was twice that of 16°C and plant development took half the time. This suggests a linear proportionality between relative growth rate and temperature in this range because the minimum temperature for growth and development is about 8°C for bush beans. This relation implies that the relative growth rate has a specific maximum which depends on temperature. Slow extension growth induced by low temperature leads to a high level of carbohydrate reserves under conditions of high light intensity. This explains why at 16°C the dry matter content of seedling leaves rises gradually whereas it remains practically constant at 25°C. This also explains why leaf area per unit leaf dry weight drops at 16°C (fig. 2) so that leaf area ratio (LAR) decreases after reaching a maximum (fig. 1). This, however, does not lead to a drop in relative growth rate which suggests that a compensation through a higher net assimilation rate (NAR) occurs. At 25°C the decline of RGR in low light intensity is relatively strong, probably because of a high respiration level. Light intensity and temperature have little influence on the specific weight of leaves (fig. 4). Furthermore leaf area per unit fresh leaf weight appears to be proportional to the inverse of leaf thickness (fig. 5). These findings suggest that inner leaf structure maintains a certain homogeneity independent of outward conditions. Cotyledons are exhausted by the young seedling at a constant rate which is higher in high temperatures and low light intensities.

Summary A two-species model was used to summarize results of four experiments with two component mixtures of barley (Hordeum vulgare L.), peas (Pisum sativum L.), Chenopodium album L. and Sinapis alba L. grown in pots in greenhouses. The results, covering a wide range of plant densities both in mixtures and pure stands, showed that the model was not always able to describe the relationship between the yield of a species and the densities of itself and its companion species. The deviations from the model were in all instances greatest for the least competitive species. The model that quantifies competition and niche differentiation appeared to be too general because competition between species was not independent of the wide plant density ranges used here. The results are discussed in relation to possible improvements of the model and an analogy between the principles of assessing crop weed competition and the assessment of the relative potency of herbicides in bioassay studies is put forward. Resume Estimation de la competition entre cultures el adventices Un modele a especes a ete utilise pour resumer les resultats des essais conduits avec des melanges a deux composantes d'orge (Hordeum vulgare L.) de pois (Pisum sativum L.) de Chenopodium album L. et de Sinapis alba L. cultives en pots sous serre. Les resultats, couvrant un large eventail de densites de plantes a la fois en melange ou seules, montrent que le modele ne permet pas toujours de decrire la relation entre le rendement d'une espece et les densites de celle-ci et des especes l'accompagnant. Les differences avec le modele etaient dans tous les cas plus importantes pour l'espece la moins competitive. Le modele qui quantifie la competition et la differentiation des sites apparait etre trop general car la competition interespeces n'est pas independante de l'eventail tres large des densites de plantes utilise ici. Les resultats sont discutes en relation avec des ameliorations possibles du modele et une analogie entre les principes d'une estimation de la competition culture/adventice et l'estimation du potentiel relatif des herbicides dans les essais biologiques est prevue. Zusammenfassung Bestimmung der Konkurrenz zwischen Kultur-pflanzen und Unkrautern Fur die Zusammenfassung der Ergebnisse von Konkurrenzversuchen mit jeweils zwei Partnern wurde ein 2-Arten-Modell verwendet; die Versuche mit Gerste (Hordeum vulgare L.), Erbse (Pisum sativum L.), Weisem Gansefus (Chenopodium album L.) und Weisem Senf (Sinapis alba L.) wurden im Gewachshaus in Topfen mit unterschiedlicher Pflanzendichte, sowohl in den Misch- als auch in den Reinbestanden, durchgefuhrt. Mit dem Modell lies sich die Beziehung zwischen dem Ertrag und der Dichte der einzelnen Arten und ihrer Konkurrenzpartner nicht immer beschreiben, wobei die grosten Abweichungen fur die konkurrenzschwacheren Arten auftraten. Mit dem Modell lassen sich die Konkurrenz- und Nischendifferenzierung beschreiben, doch erwies es sich als zu allgemein, weil die Konkurrenz von den hier gewahlten weiten Dichlebereichen nicht unabhangig war. Die Ergebnisse wurden in Hinblick auf eine Weiterentwicklung des Modells diskutiert, und es wurde auf eine Analogie zwischen den Prinzipien der Bestimmung der Kulturpflanzen/Unkraut-Kon-kurrenz und der Bestimmung der relativen Wirksamkeit von Herbiziden in Biotests hingewiesen.

SUMMARY In three experiments the effects of light intensity and nutrient supply (nitrate or phosphate) and their combined effects on the growth and morphogenesis of two shade-tolerant plant species and a non-tolerant species were studied. Nutrient supply was limited by placing the plants on a standard nutrient solution for a limited period each day and placing them on a nitrogen-free or phosphate-free solution for the rest of the day. The effects of light intensity and nitrate supply on growth and morphogenesis showed a marked interaction: low nitrate supply caused a much greater decrease in the relative growth rate under high light intensity, because of much larger changes in the dry matter ditribution; the net assimilation rate was only slightly affected by nitrate supply. The effects of light intensity and phosphate supply on the dry matter distribution and the net assimilation rate both showed interaction, but the effects on the relative growth rate were independent. Low phosphate supply caused greater changes in the dry matter distribution under high light intensity and a greater decrease in the net assimilation rate under low light intensity; the relative growth rate decreased to the same extent under both high and low light intensities. The experimental data were compared with the balanced quantitative model for root/shoot ratios proposed by Thornley (1972). The results were very satisfactory, but it was concluded that the model must be used in its exact form and that the use of approximations cannot be allowed.

A number of herbacious sun and shade plants were grown at different light levels to investigate their adaptations in morphology and growth to light intensity. All species examined respond to low light intensity strongly, but very much the same. It is concluded that shade tolerance is not based on different adaptations in morphology or growth rate

SUMMARY The relationship between the distribution of plant communities occurring on river dikes and the inundation by river water is described. The distribution of many species is restricted to the non-flooded upper part of the dike slope, while their lowest distribution limit coincides with the highest water-level for the growing season for the year preceding the recording of the vegetation. The phytosociological elements show the same distribution pattern in all five transects studied and can be clearly ordered by means of detrended correspondence analysis as well as by their relative inundation values: —hardly flooded: Koelerio–Corynephoretea, Festuco–Brometea and Mesobromion. —slightly flooded: Arrhenatheretum and Trifolion medii. —flooded: Arrhenatherion, Molinio–Arrhenatheretea, Artemisietea, Lolio-Cynosuretum and arable weeds. —considerably flooded: Ranunculo–Alopecuretum, Bidentetalia, Molinietalia, Phragmitetea and Lolio–Plantaginetum. Typical ‘fluviatile’ plant communities are strongly declining on river dikes. (Re) Introduction of these communities by means of special construction measures (e.g. the application of suitable soil) and special management practices is only possible above 2–2.30 m below ‘normative water level‘.

SUMMARY The life history of two populations of Plantago lanceolata L. from two different habitats is described, using standard demographical techniques. The first habitat is an open dune grassland on poor sandy substratum and grazed as a commonage for centuries. The vegetation occasionally suffers from drought. The second habitat is a closed hay meadow on organic substratum that is permanently waterlogged and mown once a year in July. The plantains in the dry site form small flat rosettes with many leaves and side rosettes. Small seeds are produced from many globular inflorescences on short ascending stalks late in the season (known as subvar. sphaerostachya f. minor). The plain-tains in the wet site form few tall erect leaves and no side rosettes. Big seeds are produced from few long inflorescences on long stalks in the early season (known as subvar. latifolia). Seeds from the dry population show innate dormancy that shifts the main germination period of this population towards spring. The seeds require light and high temperatures for germination and form an appreciable seedbank. Seeds from the wet population show little dormancy and germinate readily in autumn at low temperatures and light intensities without forming a seedbank. Juveniles and adults share more or less equal risks in the dry site. Rosettes are short-lived and can flower in the second season even at small sizes. Seeds are produced at considerable costs. Juveniles are clearly more at risk in the wet site, where it takes several years to first flowering. Adults are long-lived and flower repeatedly, producing seeds at low costs. The results are discussed in connection with theoretical predictions from current life history theories.

SUMMARY In a secondary succession series in grasslands, which is induced by a drastic change in management regime, the annual hemi-parasite Rhinanthus angustifolius* appears, builds up a population (phase I) and becomes temporarily abundant (phase II) whereupon the population decreases to a low level (phase III), but with considerable fluctuations. Different vegetational succession stages (corresponding to the three phases of population development) were found in closely adjacent lots which had been managed for different periods of time. In this paper results of four years demographic work on Rhinanthus angustifolius in these three succession stages are analysed. The shown differences in population phases cannot be explained by selection or density dependent behaviour of the plants. The biggest loss factor in the population is in the seed stage in all phases. No clear correlation exists between seed production and number of seedlings the following year. Seedling survival on average is high in phase I but can also be quite high in the other phases. Seed capsule production early in phase I is much higher than in phase II and III, and no difference in seed capsule production occurs between phase II and III. Predation of the seeds in the seed capsules is highest in phase II and can reach 30%. When the seeds are shed seed predation is high just after the shedding, but much seeds disappear in spring when germination begins. Differences between the phases are clear but the year to year fluctuations are of the same order of magnitude or even greater. The spatial distribution of a colonizing population of Rhinanthus angustifolius was mapped for 4 years, numbers increase continuously despite the yearly fluctuations. Local environmental conditions are mainly responsible for differences in densities of Rhinanthus angustifolius between the succession stages. Fluctuations in numbers are caused by climatological factors and local conditions (e.g. species composition and microclimate).