Seed dispersal and seedling emergence in an old field community in central New York (USA)

Summary Seed dispersal and seedling emergence of common taxa growing in a Solidago-dominated old field in central New York (USA) were monitored from May 1982 to June 1984. Over 3.5x10⁴ seeds per m² were captured on seed traps in each of the two years, with peaks occuring in July (due to Hieracium) and in November (due to Solidago). About 4.0x10³ seedling/m² emerged beneath the intact community in each of the two years. Although seedlings emerged predominantly in the early spring, a secondary peak occurred in September and October when many seedlings of introduced grasses appeared. Two additional aspects of the reproductive biology of the major taxa were related to the seasonal timing of seed dispersal: As the date of peak seed dispersal (among taxa) became progressively later in the season, (1) the duration of dispersal increased from about one week to about one-half year, and (2) the delay between the peak of seed dispersal and the peak of seedling emergence increased from a few days to about one-half year.     

Timing and spatial patterning of seed dispersal and redistribution in a South American warm desert

We measured newly-produced seeds entering the soil (Potential Seed Bank) to assess the timing and spatial patterning of Phase I dispersal in the central Monte desert, Argentina. Rates of forb- (6.13 mg m^-2 d^-1) and shrub-seed input (48.9 mg m^-2 d^-1) were maximum in early summer. The rate of grass-seed input, instead, was similar in early and late summer (7 to 8 mg m^-2 d^-1). About 90% of forb- and shrub-seed mass entered the habitat through protected (i.e., under canopy) areas, whereas 70% of grass-seed mass did so through exposed areas. Adult plant location and the uneven impact of wind on shrub, forb and grass seeds may explain such patterns.We also compared the Potential Seed Bank with the soil seed bank in the following spring (Realized Seed Bank). Seeds that form transient banks in other ecosystems (e.g., shrub seeds of the genus Larrea, or perennial grass seeds like those of Pappophorum and Trichloris) prevailed in the Potential Seed Bank. Some annual forb seeds, instead, appeared to form a more persistent seed bank, and prevailed in the Realized Seed Bank (e.g., Chenopodium). Horizontal redistribution did not affect the spatial patterning of forb and shrub seeds, but produced a more homogeneous distribution of grass seeds in the habitat. The impact of wind could explain the redistribution pattern of grass seeds. Finally, we found almost 80% of total seeds in the top 2 cm of soil. The smallest grass and forb seeds (Sporobolus and Descurainia) as well as some medium-sized and large forb seeds (e.g., Glandularia, Sphaeralcea, Phacelia) were able to reach deeper soil layers in the central Monte desert.     

SPATIAL PATTERNS OF SEED DISPERSAL AND POSTDISPERSAL SEED PREDATION OF CRYPTANTHA FLAVA (BORAGINACEAE)

I examined the spatial patterns of seed dispersal and postdispersal seed predation of the semidesert perennial Cryptantha flava (A. Nels.) Payson (Boraginaceae) at two sites in north-eastern Utah. Most flowers mature only one seed (nutlet) which is permanently retained within a pubescent calyx. The calyx and enclosed seed abscise from the plant as a unit. These dispersal units are effectively dispersed by wind as evidenced by the highly directional seed shadows and the long distances some of them travel (up to 31.3 m). Potential seed predators at the sites include five species of rodents, of which Peromyscus maniculatus is the most common, and two species of ants, Pogonomyrmex occidentalis and an undescribed species of Conomyrma. There were no strong spatial patterns of postdispersal seed predation. More seeds were removed from dishes placed at the bases of fruiting adults than from dishes ≥ 1.0 m away in one of three experiments. More seeds were removed from under shrubs or clumps of grass than in the open in one of four experiments. After 3–4 days, there was a consistent tendency for more seed removal from high density (75 seeds per .25 m²) quadrats than from low density (75 seeds per 6.25 m²) quadrats, but the difference was not always significant. There was a similar nonsignificant difference between high- and low-density quadrats exposed for 21 days. The pubescent calyx greatly discourages seed predation by ants, and probably also reduces predation by rodents. In addition, by increasing the surface area of the dispersal unit, the calyx may facilitate dispersal by wind.     

Patterns of Seed Dispersal and Dispersal Failure in a Hawaiian Dry Forest Having Only Introduced Birds

Dry forests are among the most endangered natural communities in the Hawaiian Islands. Most have been reduced to isolated trees and small forest fragments in which native tree species reproduce poorly. The replacement of native birds by introduced generalists may be contributing to dry forest decline through modification of seed dispersal patterns. To document seed dispersal by introduced birds, we conducted foraging observations on fleshy-fruited trees and measured seed rain under trees and in adjacent open areas for 1 year in a dry forest dominated by native trees. Although trees covered only 15.2 percent of the study area, 96.9 percent of the bird-dispersed seeds were deposited beneath them. The Japanese white-eye (Zosterops japonicus) was the principal dispersal agent. Among bird-dispersed seeds, those of the invasive tree Bocconia frutescens accounted for 75 percent of all seeds collected beneath trees (14.8 seeds/m²/yr) and the invasive shrub Lantana camara accounted for 17 percent. Although nearly 60 percent of the reserve's native woody species possess fleshy fruits, introduced birds rarely disperse their seeds. Native trees accounted for <8 percent of all bird-dispersed seeds and are consequently experiencing dispersal failure by falling directly under parent trees. Smaller-seeded non-native plants, in contrast, may be benefiting from dispersal by introduced birds. Current dispersal patterns suggest that these readily disseminated non-native plants may eventually replace the remaining native flora.     

氮磷添加对内蒙古温带草原植物功能群氮含量的影响

植物功能群氮含量既是理解氮沉降对生物多样性影响的关键指标,也是生产力过程模型模拟的重要参数,极易受氮素可利用性的影响和磷元素的限制。基于内蒙古温带草原4年氮磷添加试验(N10、N40、P5、P10及其交互,数字代表添加剂量,单位为g m^-2 a^-1),分析氮磷添加对植物群落及三种植物功能群(禾本科、灌木和杂类草)氮含量的影响。结果表明:(1)氮添加显著增加了群落及各功能群的氮含量,同一处理水平下禾本科(N10)和灌木(N10和N40)的氮含量显著高于杂类草,同一功能群不同氮添加剂量间无显著差异;(2)磷添加对群落和三种功能群的氮含量无显著影响;(3)与单独氮添加相比,氮磷同时添加显著增加了群落、禾本科和杂类草氮含量,且高剂量氮磷添加的促进作用更大;(4)与单独氮添加相比,氮磷同时添加显著增加群落和三种功能群磷含量而降低氮磷比,相同处理水平下禾本科和杂类草磷含量增加幅度最大。本研究将为草原生态系统管理和应对全球变化提供科学依据。     

In vitro Growth and Shoot Multiplication of Achras zapota in a Controlled Carbon Dioxide Environment

The culture vessels with multiplying shoots of Achras zapota L. on Schenk and Hildebrandt (SH) medium containing 8.88 M 6-benzylaminopurine (BAP) with or without sucrose were kept under varied CO₂ concentrations ranging from 0.6 to 40.0 g m^–3 using different concentrations of sodium bicarbonate (NaHCO₃), sodium carbonate (Na₂CO₃), potassium bicarbonate (KHCO₃), and potassium carbonate (K₂CO₃) in small acrylic chambers. Complete absence of carbon source caused death of shoots within 20 d. Under elevated concentrations of CO₂ (10.0 and 40.0 g m^–3) the shoots grew photoautotrophically on sucrose-free medium. The growth of cultures was better at 40.0 g (CO₂) m^–3 than on 3.0 % sucrose under ambient air of growth room. However, the best response was obtained at 10.0 g (CO₂) m^–3 and 3.0 % sucrose where maximum number of shoots, shoot length, fresh and dry mass, total number of leaves and leaf area was observed.     

Dispersal and seed limitation affect diversity and productivity of montane grasslands

So far, seed limitation as a local process, and dispersal limitation as a regional process have been largely neglected in biodiversity–ecosystem functioning research. However, these processes can influence both local plant species diversity and ecosystem processes, such as biomass production. We added seeds of 60 species from the regional species pool to grassland communities at 20 montane grassland sites in Germany. In these sites, plant species diversity ranged from 10 to 34 species m⁻² and, before manipulation, diversity was not related to aboveground biomass, which ranged from 108 to 687 g m⁻². One year after seed addition, local plant species richness had increased on average by six species m⁻² (29%) compared with control plots, and this increase was highest in grasslands with intermediate productivity. The increased diversity after adding seeds was associated with an average increase of aboveground biomass of 36 g m⁻² (14.8%) compared with control plots. Thus, our results demonstrate that a positive relationship between changes in species richness and productivity, as previously reported from experimental plant communities, also holds for natural grassland ecosystems. Our results show that local plant communities are dispersal limited and a hump‐shaped model appears to be the limiting outline of the natural diversity–productivity relationship. Hence, the effects of dispersal on local diversity can substantially affect the functioning of natural ecosystems.     

Seed dispersal and germination patternsin a rare Mediterranean island endemic (Anchusa crispa Viv., Boraginaceae)

We analyse and discuss patterns of seed dispersal and germination of a rare endemic plant species, Anchusa crispa Viv. (Boraginaceae) from Corsica and Sardinia. This coastal plant inhabits dunes and back-dunes, and currently numbers only a few thousand individuals which generally occur in isolated populations. This study included experiments conducted in the field in Corsica and also under controlled conditions in the laboratory. Short-distance dispersal of A. crispa is performed by ants, both by myrmecochory and dyszoochory. The invasion of an exotic species of ant, Linepithema humile, could locally modify the dispersal system and possibly the population dynamics of A. crispa. Long-distance dispersal may occur by water transport since seeds can germinate after at least 1 week of immersion in seawater and readily float on the surface. Burial of seeds is favourable for germination, percentage germination being maximised at a depth of 1–2 cm below the soil surface. A. crispa has a seed bank of about ten viable seeds per m², which may contribute to the survival of this species which exists in small populations with a short life span. Due to its seed dispersal and germination patterns, the conservation of this species will necessitate that human disturbance, which can destabilise the surface of the sand is prevented and that new populations are introduced to favourable sites.     

DIRECT AND INDIRECT ESTIMATES OF NEIGHBORHOOD AND EFFECTIVE POPULATION SIZE IN A TROPICAL PALM,ASTROCARYUM MEXICANUM

To estimate the relative importance of genetic drift, the effective population size ???(N_e) can be used. Here we present estimates of the effective population size and related measures in Astrocaryum mexicanum, a tropical palm from Los Tuxtlas rain forest, Veracruz, Mexico. Seed and pollen dispersal were measured. Seeds are primarily dispersed by gravity and secondarily dispersed by small mammals. Mean primary and secondary dispersal distances for seeds were found to be small (0.78 m and 2.35 m, respectively). A. mexicanum is beetle pollinated and pollen movements were measured by different methods: a) using fluorescent dyes, b) as the minimum distance between active female and male inflorescences, and c) using rare allozyme alleles as genetic markers. All three estimates of pollen dispersal were similar, with a mean of approximately 20 m. Using the seed and pollen dispersal data, the genetic neighborhood area (A) was estimated to be 2,551 m². To obtain the effective population size, three different overlapping generation methods were used to estimate an effective density with demographic data from six permanent plots. The effective density ranged from 0.040 to 0.351 individuals per m². The product of effective density and neighborhood area yields a direct estimate of the neighborhood effective population size (N_b). N_b ranged from 102 to 895 individuals. Indirect estimates of population size and migration rate (Nm) were obtained using F_st for five different allozymic loci for both adults and seeds. We obtained a range of Nm from 1.2 to 19.7 in adults and a range of Nm from 4.0 to 82.6 for seeds. We discuss possible causes of the smaller indirect estimates of Nm relative to the direct and compare our estimates with values from other plant populations. Gene dispersal distances, neighborhood size, and effective population size in A. mexicanum are relatively high, suggesting that natural selection, rather than genetic drift, may play a dominant role in patterning the genetic variation in this tropical palm.     

Dispersal of ornithochorous seeds from forest edges in central Florida

Dispersal of ornithochorous seeds from isolated forests in the phosphate mining region of central Florida, U.S.A., were studied for two seasons (July to November) to determine patterns of dispersal. Three separate studies included (1) dispersal directly from forest edges to early successional herbs; (2) standardized perches (2 m high post with a crossbeam); and (3) snags (dead trees, 11.3±2.8 m high, 21.4±23.3 stem branches). Perch availability was more important than distance in predicting seed types and quantities of bird-dispersed seeds. The greatest concentration of bird-dispersed seeds were found under standard perches (255±249 seeds/m²/fall) followed by snags (147±85 seeds/m²/fall) and early successional vegetation (3.0±4.1 seeds/m²/fall). Seed quantities dispersed to snags were positively correlated with the number of stem branches on snags. Seeds beneath standard perches were significantly lighter and less diverse than those found beneath snags. This difference is attributed to the larger percentage of forest or later successional species found beneath snags (73%) as compared to the standard perches (15%). Perches and vegetative structural development should facilitate ecological succession by increasing the quantity, quality and diversity of seed deposition.     

Measuring and modelling anthropogenic secondary seed dispersal along roadverges for feral oilseed rape

Seed dispersal of feral crop plants along roadverges is likely to be influenced by numerous anthropogenic vectors in the agroecosystem. Within the context of introducing genetically modified (GM) cultivars, long-distance dispersal of feral seeds associated with the growth of GM feral populations (via a selective advantage due to transgene expression) could make these populations become invasive. Their expansion could then favour the spread of transgenes and modify the composition of roadverge plant communities. Because quantitative data on anthropogenic seed dispersal along roadverges were few, we estimated effective secondary dispersal for oilseed rape, the seeds of which are not adapted to dispersal by wind or biotic agents. A seed deposition experiment showed that secondary dispersal did not systematically occur along roadverges, was correlated with traffic intensity and was local. Low traffic intensity and anthropogenic disturbances (covering of seeds by mown grasses and burial by farming machinery) prevented dispersal on three of the experimental sites. Along a road with higher traffic, secondary dispersal occurred (d_max=21.5 m), probably induced by wind turbulence behind vehicles. The best-fitting dispersal kernel was a mixture of two components: 20% of seeds dispersing over a few metres on average and 80% remaining in the original place. Expansion rates of feral populations of GM herbicide-tolerant oilseed rape were computed using an invasion model and this kernel. They were low (1–4 m yr⁻¹) when only ballistic and/or secondary dispersal were included but higher (4–20 m yr⁻¹) when theoretically rare events of long-distance dispersal by verge mowers were added. This study suggests that secondary seed dispersal is unlikely to have a significant impact on the spread of GM feral oilseed rape populations in highly disturbed and dynamic habitats such as roadverges. Detecting long-distance dispersal events induced by other vectors (e.g. mowers) would require integrative approaches based on genetic and spatial data.     

Reducing Competitive Suppression of a Rare Annual Forb by Restoring Native California Perennial Grasslands

Populations of the rare annual forb Amsinckia grandiflora may be declining because of competitive suppression by exotic annual grasses, and may perform better in a matrix of native perennial bunchgrasses. We conducted a field competition experiment in which Amsinckia seedlings were transplanted into forty 0.64‐m² experimental plots of exotic annual grassland or restored perennial grassland. The perennial grassland plots were restored using mature 3 cm‐diameter plants of the native perennial bunchgrass Poa secunda planted in three densities. The exotic annual grassland plots were established in four densities through manual removal of existing plants. Both grass types reduced soil water potential with increasing biomass, but this reduction was not significantly different between grass types. Both grass types significantly reduced the production of Amsinckia inflorescences. At low and intermediate densities (dry biomass per unit area of 20–80 g/m²), the exotic annual grasses reduced Amsinckia inflorescence number to a greater extent than did Poa, although at high densities (>90 g/m²) both grass types reduced the number of Amsinckia inflorescences to the same extent. The response of Amsinckia inflorescence number to Poa biomass was linear, whereas the same response to the annual grass biomass is logarithmic, and appeared to be related to graminoid cover. This may be because of the different growth forms exhibited by the two grass types. Results of this research suggest that restored native perennial grasslands at intermediate densities have a high habitat value for the potential establishment of the native annual A. grandiflora.     

Dispersión Primaria de Semillas por Primates y Dispersión Secundaria por Escarabajos Coprófagos en Tikal,Guatemala1

We linked primary dispersal by spider monkeys (Ateles geoffroyi) and howler monkeys (Alouatta pigra) to post‐dispersal seed fate by studying the effects of dung type and defecation pattern on secondary seed dispersal by dung beetles. First, we described the defecation patterns for both primate species. Howler monkeys generally defecated in groups (88% of observed defecations), with each individual producing on average 31 g of dung, resulting in a large area of the forest floor (31 m²) covered by large amounts of dung (clumped spatial pattern). Spider monkeys generally (96% of observed defecations) defecated individually, each individual producing an average of 11 g of dung, resulting in a small area of the forest floor (2 m²) covered by small amounts of dung (scattered spatial pattern). Secondly, we captured dung beetles using as bait the dung of both primate species, to detect differences in the assemblages of these secondary seed dispersers attracted to the dung of both primates. More individual dung beetles, but not more species, were attracted to howler monkey dung than to spider monkey dung. Finally, we assessed experimentally (using plastic beads as seed mimics) how dung type (Ateles vs. Alouatta) and defecation pattern (scattered vs. clumped) affect secondary seed dispersal by dung beetles. We found that post‐dispersal seed fate was affected by dung type, with more seeds being buried when present in howler monkey dung, than in spider monkey dung, but was not affected by defecation pattern. It is important to consider post‐dispersal processes, such as secondary seed dispersal by dung beetles, when comparing species of primary dispersers.     

Seed Availability as a Limiting Factor in Forest Recovery Processes in Costa Rica

Abandoned pastures and secondary forests are increasingly prominent features of tropical landscapes. Forest regrowth on abandoned pastures is generally slow and virtually limited to regeneration from seeds from external sources, since agricultural activities alter site conditions. We hypothesize that seed availability is a major limiting factor in forest recovery on abandoned pastures. This hypothesis was tested by studying the seed bank, seed rain, and seed predation in a small pasture (1 ha) situated in a forest‐pasture mosaic in northwestern Costa Rica. The tree seed density in the pasture seed bank was much lower (21/m²) than the density in the seed bank of a neighboring secondary forest (402/m²). Within a period of five weeks, 23 tree seeds entered the pasture by seed rain. This number is low compared to densities found in closed forests but higher than densities reported in other studies where virtually no seeds were found beyond 20 m from the forest edge. Possibly the small size of the pasture with seed sources nearby and the small‐scale landscape mosaic enhance seed dispersal. Predation limits the seed density in pastures, with 42% of the woody species consumed by predators. The low seed density in the seed bank, and hampered recruitment combined with significant losses, pose severe restrictions to forest recovery on abandoned pastures. Moderate land use, and small sized clearings with seed sources nearby may increase the pace of recovery. Nevertheless, forest establishment may still take a considerable time. Thus, enlarging the available pool of species may be a worthwhile management strategy.     

Endophytic fungi alter foraging and dispersal by desert seed-harvesting ants

Endophytic fungi are thought to interact mutualistically with host plants by producing alkaloid metabolites that deter herbivory. Since such fungi are transmitted via seed in some grasses, the presence of endophytes may also protect plants from seed predators. We conducted seed choice experiments for two dominant seed harvesting ants, Pogonomyrmex rugosus in the Sonoran desert and Pogonomyrmex occidentalis at a higher elevation, riparian zone in Arizona, USA. Non-infected fescue (Festuca arundinacea) seeds and seeds infected with the endophytic fungus, Acremonium coenophialum, were presented to ant colonies in three different populations. Infected seeds were harvested less frequently than non-infected seed for the two populations of Pogonomyrmex rugosus but not for the population of Pogonomyrmex occidentalis. We also a conducted seed dispersal experiment for one population of Pogonomyrmex rugosus. Of the seeds that were harvested, most of the colonies discarded more infected seeds into refuse piles than expected by chance. Seeds discarded into refuse piles have greater germination success than surrounding areas. The most important interaction of endophytes and grasses may be deterrence of seed predation and enhancing the probability of germinating in favorable sites, since these processes directly increase plant fitness.     

Seed dispersal of alien and native plants by vertebrate herbivores

Seed dispersal is crucial for the success and spread of alien plants. Herbivores often establish a dual relationship with plants: antagonist, through herbivory, and mutualist, through seed dispersal. By consuming plants, herbivores may disperse large amounts of seeds, and can facilitate the spread of alien plants. However, seed dispersal of alien plants by herbivores has been largely uninvestigated. I studied factors associated with dispersal of alien and native seeds by the three most important vertebrate herbivores in SW Australia: emus (Dromaius novaehollandia), western grey kangaroos (Macropus fuliginosus) and European rabbits (Oryctolagus cuniculus). Overall frequencies of alien and native seeds dispersed by these herbivores were determined by differences among them in (1) the plant groups they predominantly disperse, that differed in frequencies of aliens versus natives, and (2) the predominant dispersal of aliens or natives within those plant groups. Emus and kangaroos (natives) tended to disperse predominantly alien seeds within plant groups (defined by life forms, dispersal syndromes, and diaspore size), whereas rabbits (alien) tended to disperse predominantly natives. This agrees with the hypothesis that herbivores will use predominantly plants that have evolved in different areas, because of less effective defences against new enemies. Overall frequencies were consistent with this pattern in kangaroos and rabbits, but not in emus. Kangaroos dispersed mostly plant groups that were mainly aliens (herbaceous species and small and medium sized dispersal units and seeds), which together with their predominant use of aliens over natives within groups resulted in the highest overall frequency of alien seeds (73%). Rabbits were similar to kangaroos in the type of plants dispersed, but their predominant use of natives over aliens within groups contributed to an overall predominance of native seeds in their pellets (88%). Emus dispersed mostly plant groups that were mainly natives (e.g. woody species with big diaspores), resulting in low overall frequency of alien seeds (11%), despite their predominant use of aliens over natives within plant groups. Thus, the within-groups trend pointed to a facilitative role of native herbivores of plant invasions through seed dispersal, but was obscured by the different use by herbivores of plant groups with different frequency of aliens.     

Comparative Evaluation of Metal Phytoremediation Potential of Trees,Grasses, and Flowering Plants from Tannery-Wastewater-Contaminated Soil in Relation with Physicochemical Properties

This study reports a comparative account of metal accumulation in the trees, grasses, and flowering plants from agricultural fields contaminated with tannery wastewater. Soil physico-chemical properties along the pollution gradient and soil depth were analyzed. Monitoring and assessment of the plants growing on contaminated sites revealed that the accumulation of Cr in the aboveground part of the trees ranged from 1.87 to 34.44 μg g^?1 dw with maximum concentration in Dendro-calamus strictus (34.44 μg g^?1 dw). Chrysanthemum coronarium and Tagetes erecta showed better accumulation of Cr than other flowering plants. Separate field experiments were conducted on the contaminated area. The shoots of Vetiveria zizanoides (532 mg 4 m^?2) and Cymbopogan winterianus (535.46 mg 4 m^?2) have shown almost similar removal potential of Cr, with maximum removal potential in the roots of C. winterianus (1206.43 mg 4 m^?2). Seasonal flowering plants (i.e., C. coronarium) have shown better accumulation of Cr than T. erecta. The results indicate that the plants of V. zizanoides, C. coronarium, and C. winterianus are suitable for phytoremediation of contaminated sites and trees can successfully be used for phytostabilization.     

Seed and microsite limitation in a late-successional old field: the effects of water, adults, litter, and small mammals on seeds and seedlings

Many plant communities are recruitment limited, which may occur because there are either too few seeds to fill available microsites, too few available microsites, or both. In a recruitment-limited, Minnesota, USA old field, we tested among these alternatives in a three-phase study. In phase 1, we estimated the production of late-successional forb and C4 grass seeds. In phase 2, we experimentally modified field establishment conditions with rainfall amendment, adult plant thinning, litter reduction, and small mammal exclusion. We then measured recruitment. On average, of the nearly 2,600 seeds produced m^?2, only 164 seeds m^?2 were present and living after overwintering, as measured by field and greenhouse germination. Furthermore, on average, only 9 of those 164 seeds m^?2 germinated in the field, even under the relaxed establishment conditions of our four experimental treatments. Although adults of C4 grasses dominate the field, surprisingly few C4 grass seedlings germinated. To understand why, in phase 3, we added seed of the three dominant C4 grasses into the same plots the following year. Their ability to recruit into control plots compared with treated plots was relatively lower than for the ambiently recruited forbs from phase 2, suggesting that the competitively dominant C4 grasses have greater difficulty establishing in the extant community. Of the seeds that did germinate in the field in phases 2 and 3, all four experimental treatments significantly improved at least one stage of establishment, with the rainfall amendment having the greatest overall effect across species. In total, our results suggest that seed limitation was exacerbated by microsite limitation via multiple mechanisms.     

Density Studies on Lupins. II. Components of Seed Yield

Components of seed yield of cv. Ultra (Lupinus albus L.) andcv. Unicrop (L. angustifolius L.) were measured when grown atthree densities. The low density (10 plants m^–2) Unicropyield (34 g seed per plant) was 1.8 times that of Ultra as ithad more branches, pods and seeds per pod. Ultra seeds (310mg per seed) were heavier than Unicrop seeds (180 mg). The branchingpattern of Ultra was less dependent on plant density, henceat 93 plants m^–2 it gave a higher per plant yield (7.4vs 6.4 g) than Unicrop at lower densities (83 plants m^–2).Density had most influence on pod formation and only small effectson seeds per pod and seed weight. Yield components on the main-steminflorescence were influenced less by density than componentson branch inflorescences. Later formed, higher order generationsof inflorescences were most affected by increased inter- andintra-plant competition. Pod numbers on the main-stem were similarfor both species. Pods formed at higher flower nodes in Unicrop,but the lower flower nodes were less fertile than those in Ultra.Node position of flowers had no influence on seed set in main-stemUnicrop pods, but pods from higher nodes in Ultra formed fewerseeds. Seed weights in Unicrop were similar among main-stemnodes but in Ultra seed weights tended to increase at highernodes. Lupinus spp, lupins, seed yield, planting density