SEED DENSITY, COVER, PREDATION AND THE DISTRIBUTION OF BIRDS IN A BEECH WOOD IN SOUTHERN SWEDEN

The distribution of six species of birds within a beech wood was analysed in two winters when beech seeds were abundant. All species were concentrated in patches where seed density was high in one winter, but only two showed a similar distribution in the second winter. The distribution of the other four species, three tits Parus spp. and the Nuthatch Sitta europaea, was positively correlated with low cover. Cover was inversely correlated with seed density. Bird predators were recorded many times during the second winter but not at all during the first winter. It is suggested that predator avoidance was more important than food density for some species in the second winter. The relationships between bird density and both food and cover were sigmoid in shape. The proportion of the seed crop consumed by the birds was estimated at about 4.5%, which was probably more than the amount consumed by mammals. The Woodpigeon Columba palumbus (which took 44% of the total seeds consumed by birds) and the Brambling Fringilla montifringilla (33%) were the most important seed consumers among the birds.     

An interactive effect of simultaneous death of dwarf bamboo, canopy gap, and predatory rodents on beech regeneration

To clarify the interactive effect of the simultaneous death of dwarf bamboo (Sasa kurilensis), forest canopy gap formation, and seed predators on beech (Fagus crenata) regeneration, we analyzed beech demography from seed fall until the end of the first growing season of seedlings in an old-growth forest near Lake Towada, northern Japan. The simultaneous death of S. kurilensis took place in 1995. We established four types of sampling site differing in forest canopy conditions (closed or gap) and Sasa status (dead or alive). Beech seed survival and emergence ratio were both highest in gaps with dead Sasa (gap-dead), because rate of predation was lowest. Seedling survival during the first growing season was also highest in the gap-dead treatment, because of less predation and less damping off. As a result, even though density of seed fall was lowest in the gap-dead treatment, the living seedling density there was highest at the end of the first growing season. Predation, which caused the greatest mortality during the seed and seedling stages, was significantly lower at both sites in gaps and sites with dead Sasa. This was probably due to changes in the behavior of rodents in response to the structure of the forest canopy and undergrowth. Both the death of Sasa and canopy gap formation allowed seedlings to avoid damping off because of the high light availability. The indirect effect of the simultaneous death of Sasa and canopy gap formation in reducing predation contributed more to beech regeneration than their direct effect in increasing light for the seedlings.     

Effects of snow accumulation on survival of beech (Fagus crenata) seed

The escape of beech seeds from seed predators and winter desiccation due to snow accumulation was studied by comparing two sites in Japan: one site that experiences much snow and another site that experiences less snow cover. At the site with greater snow cover, about 70% of the beech seeds escaped seed predation by rodents during winter and about 70% of surviving seeds germinated successfully in spring. At the site with less snow cover, however, all of the beech seeds were eaten by rodents, and all seeds that were protected from feeding were killed by winter desiccation. We confirmed that snow prevents beech seeds from predation by rodents because it conceals their sight and scent. These effects are one of the main reasons why beeches in snowy areas regenerate constantly and those in less snowy areas do not.     

Effects of snow cover on the social and foraging behavior of the great tit Parus major

In the Joetsu region of central Honshu, Japan, snow lies on the ground 2–3 m deep from January to February every year. To test the effects of snow cover on the social and foraging behaviors of the great tit (Parus major Linnaeus) in the region, the following parameters were compared between the pre-snowy period (November and December) and the snowy period (January and February) at the individual level: population size, monospecific flock size and the stability of its membership, home range size, attendance rate with mixed-species flocks, and foraging height. Great tits lived alone or in pairs, but often joined mixed-species flocks. Throughout the study period, individuals exhibited strong site fidelity, which resulted in a stable population size. Neither the size of a monospecific flock nor its membership was affected by snow cover. The home range expanded when birds joined mixed-species flocks during both periods. Birds more frequently joined mixed-species flocks during the snowy period, and the size of mixed-species flocks was significantly larger than during the pre-snowy period. During the snowy period, birds shifted their foraging position from the ground to the upper parts of trees. They also used the upper parts of trees when they joined mixed-species flocks. These results suggest that the intraspecific sociality of great tits is relatively insensitive to snow cover, but that the home range size and foraging positions are affected by joining mixed-species flocks, rather than by snow cover.     

Consequences of frugivore diversity for seed dispersal, seedling establishment and the spatial pattern of seedlings and trees

Many plants depend on frugivorous animals for the dispersal of their seeds. However, it is only poorly known whether regional differences in frugivore diversity have consequences for seed dispersal, seedling establishment, and the spatial distribution of seedlings and trees. This comparative study of seed dispersal investigated the consequences of regional differences in frugivore diversity for two tree species of the genus Commiphora. C. harveyi was studied in South Africa where avian frugivore diversity is high, C. guillaumini was studied in Madagascar where the avian frugivore community is depauperate. At both study sites, the percentages of handled and dispersed seeds in Commiphora trees were quantified by fruit traps, and visitation rates, seed handling rates and dispersal rates were quantified for each animal species for two consecutive years. Seedlings were mapped and the spatial distribution of trees quantified. At both study sites, fruits were mainly eaten by birds. The total percentage of dispersed seeds in South Africa was significantly higher than in Madagascar (70.8% vs. 7.9%) because there was a lack of effective dispersers that swallowed seeds in Madagascar. Seed dispersal benefit, i.e. the increase in the probability of becoming established as a seedling away from parent trees due to dispersal was much higher in Madagascar (80 times higher probability) compared to South Africa (6 times higher). Corresponding with the different dispersal percentages, seedlings in South Africa were found at relatively large distances from the nearest Commiphora tree (median distance=21.0 m), whereas in Madagascar seedlings were found mostly under and close to the nearest Commiphora tree (median distance=0.9 m). Finally, Commiphora trees in the Malagasy study site were clumped, but were more randomly distributed in the South African study site. These results suggest that regional differences in frugivore diversity and behaviour strongly affect seed dispersal of trees, seedling establishment and the spatial distribution of seedlings and trees.     

Harvester ant response to spatial and temporal heterogeneity in seed availability: pattern in the process of granivory

The influence of temporal and spatial heterogeneity in seed availability on the foraging behaviour of the harvester ant Messor arenarius was studied in an arid shrubland in the Negev Desert, Israel. The study investigated the implications of behavioural responses to heterogeneity in seed availability for the seed predation process and the potential for feedback effects on vegetation. Vegetation and seed rain were monitored across two landscape patch types (shrub patches and inter-shrub patches) in 1997. Shrub patches were shown to have higher plant and seed-rain density than inter-shrub patches. Patch use and seed selection by M. arenarius foragers were monitored through the spring, summer and autumn of 1997. After a pulse of seed production in the spring, the ants exhibited very narrow diet breadth, specialising on a single annual grass species, Stipa capensis. At this time, ants were foraging and collecting seeds mainly from inter-shrub patches. In the summer, diet breadth broadened and use of shrub patches increased, although the rate of seed collection per unit area was approximately equal in the two patch types. The increase in the use of shrub patches was due to colony-level selection of foraging areas with relatively high shrub cover and an increase in the use of shrub patches by individual foragers. In the autumn, a pulse of seed production by the shrub species Atractylis serratuloides and Noaea mucronata led to a reduction in diet breadth as foragers specialised on these species. During this period, foragers exhibited a large increase in the proportion of time spent in shrub patches and in the proportion of food items collected from shrub patches. The seasonal patterns in foraging behaviour showed linked changes in seed selection and patch use resulting in important differences in the seed predation process between the two landscape patch types. For much of the study period, there was higher seed predation pressure on the inter-shrub patches, which were of relatively low productivity compared with the shrub patches. This suggests that the seed predation process may help maintain the spatial heterogeneity in the density of ephemeral plants in the landscape.     

Geographical variation in the early regeneration process of Siebold's Beech (Fagus crenata BLUME) in Japan

The causes and timing of seed death in early regeneration process of Siebold's beech (Fagus crenata Blume) was studied at 15 sites along a snowfall gradient in Japan, in order to clarify why the seedling density of the species has geographic difference remarkably. Seed production did not significantly differ along the snowfall gradient. Pre-dispersal seed mortality by insect damage was higher at sites with light snowfall than at sites with heavy snowfall, but this only seemed to be a minor factor influencing the population. A large proportion of the viable nuts that fall in autumn ware killed in winter before germination. Winter mortality was much higher at sites with thin snow cover than that at sites with thick snow cover, and this factor was strongly correlated with the geographic variation of seedling regeneration probability. There was little seed mortality by winter desiccation. The main factor contributing to the geographic difference seemed to be a seed predation by rodents in winter. Deep snow cover may reduce the success of rodents finding seeds in winter. Thus the observed relationship between snowpack depth and early mortality may be due to an indirect effect through the process of seed predation.p>     

Seed production and outbreaks of non-cyclic rodent populations in deciduous forests

Summary In a 10-year study period, outbreaks of the bank vole, Clethrionomys glareolus, Schreber only occurred in years following huge seed production of European beech, Fagus sylvatica. Intensive winter reprodution preceded the outbreaks, in contrast to a normal breeding season from April through September. No winter reproduction occurred in nearby populations from habitats without mast production. During the winter, the average weight of C. glareolus remained high in the mast forests and the age structure resembled that of a summer breeding population. Despite excess energy requirements of winter breeding, survival rates were similar to that of non-breeding winter populations. In mast years, rodent consumption in the beech forest was estimated as 1.0–10.3% of endosperm production available to postdispersal seed predators. Between mast years rodent consumption made up 30–100% of endosperm production available. Mast years occurred at irregular intervals and seed production seems to be synchronized between individual trees over large areas and induced by climatic events. These phenomena lead to seed predator satiation.     

Seed-caching responses to substrate and rock cover by two <Emphasis Type="Italic">Peromyscus</Emphasis> species: implications for pinyon pine establishment

We examined whether pinyon mice (Peromyscus truei) and brush mice (P. boylii) could act as directed dispersal agents of pinyon pine (Pinus edulis) through differential responses to soil particle size and rock cover. In field experiments, we allowed mice to either cache pinyon seeds or recover artificially cached seeds (pilfer) from quadrats containing large- or small-particle soils. Both species placed most (70%) seed caches in small-particle soil. Pilfering was the same from both particle sizes in the first year, while more seeds were pilfered from large-particle soils in the second year. In separate experiments, rock cover interacted with soil particle size, with both species placing over 50% of their caches in small-particle soil with rock cover. Overall, we found greater seed-caching in small-particle soils near rocks, with equal or lower pilfering from small-particle soils, suggesting more seeds would survive in small-particle soils near rock cover. Three lines of evidence supported the hypothesis that mice could act as directed dispersers by moving pinyon seeds to beneficial microsites for germination and establishment. First, in greenhouse experiments, pinyon seed germination was 4 times greater in small-particle soil cores than in large-particle soil cores. Second, soils near rocks had significantly higher water content than areas of open soil at the driest time of the year, a critical factor for seedling survival in the arid southwestern USA. Third, 75% of juvenile pinyon trees were growing in small-particle soils, and 45% were growing near rock nurses.     

Mechanical properties of spruce and beech wood grown in elevated CO2

Biomechanical responses of stems of 6- to 7-year-old spruce [Picea abies (L.) Karst.] and beech (Fagus sylvatica L) trees were studied after 4 years of growth in elevated atmospheric CO₂ in combination with a nitrogen treatment and on two different soil types. At the end of the treatment, stems were harvested and tested in fresh and air-dried status. Bending characteristics of juvenile wood (modulus of elasticity, termed rigidity) were determined by bending tests. Fracture characteristics (termed toughness) were determined by stroke-pendulum tests. From the base disk of each stem densitometric data were obtained. In spruce, wood produced under elevated CO₂ was tougher on both soil types; enhanced N deposition made wood less rigid only on acidic soils. In contrast, beech wood samples showed no significant reaction to CO₂ but were significantly tougher under high nitrogen depositions on acidic soil. Effects on wood density of both CO₂ and N treatments were not significant, but wood density was higher on acidic soil and so were rigidity and toughness (soil effect). Different genotypes of spruce and beech reacted significantly differently to the treatments. Some genotypes reacted strongly to CO₂ or N, whereas others did not react or showed interactions between CO₂ and N. This underlines the importance of genetic diversity in tree communities.     

How important is the relationship between Protea humiflora (Proteaceae) and its non-flying mammal pollinators?

The interaction between Protea humiflora and its non-flying mammal pollinators was investigated with the aim of quantifying the relationship for both the plants and mammals involved. We manipulated flower density by inflorescence removal and determined the effect upon mammal captures, and excluded mammals to determine their effect upon seed set. Of three mammal species captured frequently, the smallest, Acomys subspinosus (18dž SD g, Rodentia: Muridae), demonstrated the strongest relationship with P. humiflora. Breeding coincided with flowering, and pollen constituted 33.5ᆯ.5% by volume (max 80%, n=19) of winter scats. Acomys captures on control grids were twice those on inflorescence-removal grids during flowering. Aethomys namaquensis (51ᆢ g, Rodentia: Muridae) included flower products in its diet (pollen comprising 3.2dž.9% of winter scats, n=73), but captures were not affected by inflorescence removal. Aethomys is a seasonal breeder and juveniles entered the population 2 months after flowering. Elephantulus edwardii, although an insectivore (48lj g, Macroscelidea: Macroscelididae), carried more pollen grains on its nose than the rodents, acquired while foraging in inflorescences for insects. Pollen comprised 3.1LJ.4% (n=23) of winter scats. From the plant perspective, seed set was significantly reduced in caged inflorescences and in those >20 cm above the ground, presumably due to limited accessibility by terrestrial animals. We conclude that small mammals are responsible for around half (56%) of the effective seed set in P. humiflora.     

Behavioural responses to changing landscapes: flock structure and anti-predator strategies of tits wintering in fragmented forests

We analysed the effects of forest fragmentation on the flock structure of insectivorous forest passerines (Parus, Aegithalos, Certhia, Regulus, etc.), and on the anti‐predator behaviour and energy management of blue tits in these flocks. We surveyed flocks in Central Spain during two winters. Flocks in fragments comprised fewer individuals and species than flocks in unfragmented forests. The most abundant species in forest flocks (blue tit, Parus caeruleus, and firecrest, Regulus ignicapillus) were also the most abundant in fragments, while the rarest species in the area never occurred in small woodlots. We investigated how fragmentation and related changes in flock structure affect anti‐predator behaviour of blue tits, a widely distributed species in the area. In fragments but not in forests, blue tits increased scanning rates with decreasing flock size. Vigilance was relaxed when great tits, Parus major, were abundant as flock mates, suggesting that the absence of this dominant species in fragments could intensify anti‐predator behaviour of blue tits. Blue tits enhanced anti‐predator behaviour in the second winter parallel to an increase in the abundance of raptors. This behavioural change was stronger in fragments, where blue tits foraged deeper in the canopy and increased scanning and hopping rates. Under increased predation risk, birds are expected to reduce body mass to improve predator avoidance. On average, blue tits weighed similar in fragments and forests the second winter. However, they accumulated fat along the day in fragments only, and adjusted body mass to body size more closely in that habitat type. This suggests that blue tits perceived fragments as unpredictable habitats where fattening would help avoid starvation, but also as dangerous sites where overweight would further increase the risk of predation. In summary, our results support that fragmentation affects individual behaviour of blue tits, and show the potential of behavioural approaches to unravel how different species face the advancing fragmentation of their habitats.     

Contributions of forage competition, harvest, and climate fluctuation to changes in population growth of northern white-tailed deer

Recently there has been considerable interest in determining the relative roles of endogenous (density-dependent) and exogenous (density-independent) factors in driving the population dynamics of free-ranging ungulates. We used time-series analysis to estimate the relative contributions of density-dependent forage competition, climatic fluctuation, and harvesting on the population dynamics of white-tailed deer (Odocoileus virginianus) in Nova Scotia, Canada, from 1983 to 2000. A model incorporating the population density 2 years previous, an interaction term for the harvest of females and population density 2 years previous, and the total snowfall during the previous 2 winters explained 80% of the variation in inter-annual population growth rate. Natality of adult females was negatively related to deer density during the present winter, whereas that of yearlings may have been correlated with the snowfall of three winters previous. Natality of fawns was related to deer density and total snowfall during the previous winter. Coyotes (Canis latrans) prey extensively on deer fawns in northeastern North America and the annual harvest of snowshoe hares (Lepus americanus), the major alternate prey of coyotes, explained 48% of the inter-annual variation in fawn recruitment. The proportions of fawn, yearling, and adult deer suffering from severe malnutrition during late winter were all correlated with deer density during the present winter. We conclude that the limiting effects of winter weather on over-winter survival of deer may be cumulative over two consecutive winters. During the late 1980s, density dependence and winter severity acted in concert to effect substantial declines in deer population growth both by effecting winter losses directly and by exacerbating predation by coyotes. During this period liberal harvesting did not relieve density-dependent forage competition and probably accelerated the decline.     

Distance and non-randomness of seed dispersal by the dwarf cassowary Casuarius bennetti

To determine the sources of dispersed seeds I inserted unique tags in fallen Aglaia aff flavida seeds before dwarf cassowaries (Casuanus bennetti) ate the fruits containing the seeds Thirty naturally-dispersed, marked seeds were re-located in cassowary droppings m a 400 ha study area The distribution of seed dispersal distances did not differ significantly from a normal distribution with a mean dispersal distance of 388 m, SD= 196 8 Mean distance of dispersed seeds to nearest mature conspecific tree was 170 m, SD= 108 4, dispersed seeds usually landed closer to other conspecifics than their parent The estimated distribution of all seeds (including many undispersed seeds) was leptokurtic, creating high densities near source trees (>0 035 seeds m^-2 within 100 m of bole) that quickly tapered off (<0 002 seeds m^-2 > 100 m from the bole), any density dependent effects are liable to be manifest only near parent trees
Cassowary movement patterns and resting behavior caused non-random dispersal of seeds Seeds were preferentially moved to level sites uphill from their source trees along routes that did not cross.steep terrain Undispersed seeds generally landed downhill from source trees This population of Aglaia would probably contract downhill into smaller, fragmented populations m the absence of cassowary-mediated dispersal     

The greater seedling high-light tolerance of <Emphasis Type="Italic">Quercus robur</Emphasis> over <Emphasis Type="Italic">Fagus sylvatica </Emphasis>is linked to a greater physiological plasticity

The responses of Quercus robur (oak) and Fagus sylvatica (beech) seedlings to four different light environments (full, 50%, 40% and 15% sunlight) and to a rapid increase in irradiance were explored during the summer, after 2 years of growth in a forest nursery at Nancy (France). Significant differences between the two species were found for most variables. Phenotypic plasticity for morphological variables (root-shoot ratio, leaf size, leaf weight ratio) was higher in beech than in oak, while the reverse was true for anatomical (stomatal density, epidermis thickness, exchange surface area of the palisade parenchyma) and physiological (maximum photosynthetic rate, stomatal conductance, Rubisco activity) variables. Predawn photochemical efficiency (F_v/F_m) was higher in oak than in beech in all light environments except in 15% sunlight. F_v/F_m was significantly lower in 100% sunlight than in the other light environments in beech but not in oak. Maximum photosynthetic rates (A_max) increased with increasing light availability in the two species but they were always higher in oak than in beech. Oak exhibited higher Rubisco activity than beech in full sunlight. The transfer of shade-adapted seedlings to the open caused a decrease of F_v/F_m, which was larger for beech than for oak. Transferred oak but not beech plants recovered gradually to the control F_v/F_m values. The decreased chlorophyll content and the increased non-photochemical quenching observed in high-light beech seedlings were not enough to avoid photoinhibition. The results suggest that a greater tolerance of strong irradiance is linked to an enhanced physiological plasticity (variables related to photosynthesis), while shade tolerance relies on an enhanced plasticity in light-harvesting variables (crown morphology and chlorophyll content).     

Post‐dispersal seed depletion by rodents in marginal populations of yew (Taxus baccata): consequences at geographical and local scales

Post‐dispersal seed predation is a crucial phenomenon for plant recruitment, and its incidence can be hypothesized to increase in ecologically and geographically marginal populations of threatened species, such as yew (Taxus baccata). Here we examine the among‐ and within‐population patterns of seed consumption by rodents and evaluate to what extent they are linked to marginality in Mediterranean low‐density yew stands. Among populations we tested: (i) whether the rates of seed predation found in our marginal sites were consistently higher than in populations from core regions; (ii) within populations we evaluated whether rodents preferred microhabitats with greater seed availability (beneath female yew trees) or with lower predation risk (shrubs) in two seeding seasons (fall–winter 2005 and 2006). Predation rates were extremely high (92.5%) and they were well above values reported for core populations (65.4%), to the extent that rodents almost completely depleted the experimental seeds in all populations and years. Our expectation of lower predation rates with decreasing vegetation cover was also confirmed for all years and populations, suggesting that rodent foraging was risk‐sensitive. This microhabitat effect outweighed the effect of seed availability under female yew trees, implying also that rodents selectively consumed the most valuable seeds in terms of their recruitment prospects. Overall, our results suggest that the mechanisms underlying seed depletion and its demographic consequences are linked to the effects of reduced yew performance in ecologically marginal habitats.     

Ficus seed shadows in a Bornean rain forest

Due to their copious seed production and numerous dispersers, rain forest fig trees have been assumed to produce extensive and dense seed shadows. To test this idea, patterns of seed dispersal of two species of large hemiepiphytic fig tree were measured in a Bornean rain forest. The sample included four Ficus stupenda and three F. subtecta trees with crop sizes ranging from 2,000 to 40,000 figs (400,000 to 13,000,000 seeds). Seed rain out to a distance of 60 m from each study tree was quantified using arrays of seed traps deployed in the understory. These trees showed a strongly leptokurtic pattern of dispersal, as expected, but all individuals had measurable seed rain at 60 m, ranging from 0.2 to 5.0 seeds/m². A regression of In-transformed seed rain density against distance gave a significant fit to all seven trees' dispersal patterns, indicating that the data could be fitted to the negative exponential distribution most commonly fitted to seed shadows. However, for six of seven trees, an improved fit was obtained for regressions in which distance was also In-transformed. This transformation corresponds to an inverse power distribution, indicating that for vertebrate-dispersed Ficus seeds, the tail of the seed rain distribution does not drop off as rapidly as in the exponential distribution typically associated with wind dispersed seed shadows. Over 50% of the seed crop was estimated to fall below each fig tree's crown. Up to 22% of the seed crop was dispersed beyond the crown edge, but within 60 m of the tree. Estimates of the maximum numbers of seeds which could have been transported beyond 60 m were 45% for the two largest crops of figs, but were under 24% for the trees with smaller crops. Seed traps positioned where they had an upper canopy layer above them were associated with higher probabilities of being hit by seeds, suggesting that vertebrate dispersal agents are likely to perch or travel through forest layers at the same level as the fig crown and could concentrate seeds in such areas to some degree. The probability of a safe site at 60 m from the fig tree being hit by seeds is calculated to be on the order of 0.01 per fruiting episode. Fig trees do not appear to saturate safe sites with seeds despite their large seed crops. If we in addition consider the rarity of quality establishment sites and post-dispersal factors reducing successful seedling establishment, hemiepiphytic fig trees appear to face severe obstacles to seedling recruitment.     

Seed and seedling demography of invasive and native trees of subtropical Pacific islands

Abstract. Bischofia javanica is an invasive tree of the Bonin Islands in the western Pacific, Japan. This species has aggressive growth, competitively replacing native trees in the natural forest of the islands. The aim of this study was to examine seed and seedling factors which might confer an advantage to the establishment of Bischofia over native trees. During a 5‐yr period we compared the demographic parameters of early life history of Bischofia and Elaeocarpus photiniae‐folius, a native canopy dominant, in actively invaded forests. Predation of Elaeocarpus seeds by in troduced rodents was much higher before (27.9–32.9%) and after (41.3–100%) dispersal of seeds than that of B. javanica. Most Elaeocarpus seeds lost viability ca. 6 mo after burial in forest soil while some seeds of Bischofia remained viable for more than 2 yr. Seedling survival in the first 2 yr was much higher in Bischofia (16%) than in Elaeocarpus (1.3%). The high persistence of Bischofia in the shade, coupled to its rapid acclimation to high light levels, is an unusual combination because in forest tree species there is generally a trade‐off between seedling survival in the shade and response to canopy opening. Compared with a native canopy dominant, greater seed longevity, lower seed predation by introduced rodents, longer fruiting periods and the ability to form seedling banks under closed canopy appear to have contributed to the invasive success of Bischofia on the Bonin Islands.     

The effects of elevated CO2 on seed production and seedling recruitment in a sheep-grazed pasture

Seed production and seedling recruitment were measured over 2 years under ambient (360 ppm) and elevated (475 ppm) atmospheric CO₂ in a free air carbon dioxide enrichment (FACE) experiment, carried out in a sheep-grazed pasture on dry, sandy soil in New Zealand. In both years elevated CO₂ led to more dispersed seeds of the grasses Anthoxanthum odoratum, Lolium perenne and Poa pratensis, the legumes Trifolium repens and T. subterraneum and the herbs Hypochaeris radicata and Leontodon saxatilis. The increased seed dispersal in A. odoratum, H. radicata, Leontodon saxatilis and T. repens reflected both more inflorescences per unit area and more seeds per inflorescence under elevated CO₂. The increased seed dispersal in Lolium perenne, P. pratensis and T. subterraneum was due solely to more inflorescences per unit area. The number of seedlings that emerged and survived to at least 7 months of age was increased by elevated CO₂ for H. radicata, Leontodon saxatilis, T. repens and T. subterraneum in both years and for A. odoratum and Lolium perenne in the first year. For species where increased seedling recruitment was noted, there was a significant positive correlation between seed production in summer and seedling emergence in the following autumn and winter, and sowing 200 extra seeds per species m^-2 resulted in more seedlings compared to unsown controls. Elevated CO₂ did not affect seedling survival in any species. There was no measurable effect of elevated CO₂ on canopy and soil surface conditions or soil moisture at the time of seedling emergence. The results suggest the dominant effect of elevated CO₂ on seedling recruitment in this pasture was an indirect one, reflecting effects on the number of seeds produced. The biomass of H. radicata, Leontodon saxatilis, T. repens and T. subterraneum in the above-ground vegetation was greater under elevated than ambient CO₂. However, the size of individual seedlings and mature plants of these four species was unaffected by elevated CO₂. The results indicate an important way elevated CO₂ influenced plant species composition in this pasture was through changes in the pattern of seedling recruitment.     

Chlorophyll fluorescence and photosynthetic response to light in 1-year-old needles during spring and early summer in <Emphasis Type="Italic">Pinus leucodermis</Emphasis>

Ten-year-old trees from four Italian populations of Pinus leucodermis (populations A, B, C and D), which were collected from different sites at different altitudes, were grown near Florence, Italy. Needle CO₂ gas exchange and chlorophyll fluorescence response to increasing light intensities were evaluated; gas exchange and chlorophyll fluorescence variation between April and July were also monitored. Populations A, B and C showed a similar photosynthetic response to increasing photosynthetic photon flux density (PPFD) intensities, while at various light intensities population D, which originated from the highest altitude, showed the highest photosynthetic rates. In this population photosynthesis was saturated at PPFDs higher than 900 µmol m^-2s^-1 and a slow decrease of effective photosystem II quantum yield and F'_V/F'_M in response to increasing PPFDs were found. The same trees also showed a faster recovery in photosynthesis from limitations induced by winter temperatures than the other three populations. This work showed that photosynthetic response to light in population D was different from the other populations; trees from this population were probably naturally selected to prevent photoinhibition due to excess light.