Palmer amaranth (Amaranthus palmeri S. Watson) is the most problematic weed of cotton (Gossypium hirsutum L.)-cropping systems in the U.S. Southeast. Heavy reliance on herbicides has selected for resistance to multiple herbicide mechanisms of action. Effective management of this weed may require the integration of cultural practices that limit germination, establishment, and growth. Cover crops have been promoted as a cultural practice that targets these processes. We conducted a 2-yr study in Georgia, USA, to measure the effects of two annual cover crops (cereal rye [Secale cereale L.] and crimson clover [Trifolium incarnatum L.]), a perennial living mulch (‘Durana®’ white clover [Trifolium repens L.]), and a bare ground control on A. palmeri population dynamics. The study was conducted in the absence of herbicides. Growth stages were integrated into a basic demographic model to evaluate differences in population trajectories. Cereal rye and living mulch treatments suppressed weed seedling recruitment (seedlings seed−1) 19.2 and 13 times and 12 and 25 times more than the bare ground control, respectively. Low recruitment was correlated positively with low light transmission (photosynthetic active radiation: above canopy photosynthetically active radiation [PAR]/below cover crop PAR) at the soil surface. Low recruitment rates were also negatively correlated with high survival rates. Greater survival rates and reduced adult plant densities resulted in greater biomass (g plant−1) and fecundity (seeds plant−1) in cereal rye and living mulch treatments in both years. The annual rate of population change (seeds seed−1) was equivalent across all treatments in the first year but was greater in the living mulch treatment in the second year. Our results highlight the potential of annual cover crops and living mulches for suppressing A. palmeri seedling recruitment and would be valuable tools as part of an integrated weed management strategy.

Chinese tallowtree [Triadica sebifera (L.) Small] has reached unprecedented prevalence in coastal landscapes in the Gulf of Mexico, especially along edge habitat with low competition and abundant resource (e.g., light) availability. This study investigated the spatiotemporal patterns and mechanisms of T. sebifera spread along roadways and fire lines. Triadica sebifera individuals and landscape and community features were surveyed in equally spaced, spatially mapped plots. All T. sebifera individuals were felled to determine tree age and status (seed trees or non-seed bearing trees), and T. sebifera seed and seedling (≤2 yr old) densities and community and landscape features (over- and understory conditions, distance to seed trees) were measured. A zero-inflated negative binomial model was used to evaluate factors affecting T. sebifera seed dispersal and seedling recruitment contributing to the observed spatiotemporal patterns. Introduced into the Grand Bay National Wildlife Refuge around 30 yr ago, T. sebifera trees distribute in clustered patterns along roadways and fire lines and exhibit an exponential growth in density. High T. sebifera seed and seedling densities mainly occurred in sites that are ≤250 m from seed trees or have sparse overstory and high understory grass/herb coverage. With respect to the avian seed dispersal mechanism, the spatiotemporal patterns of T. sebifera spread along roadways and fire lines could be simply characterized by using landscape and community features that influence avian behaviors, including distance to seed trees, overstory tree density, and ground grass/herb coverage.

Scatter-hoarding by rodents is expected to benefit palm recruitment by allowing cached seeds to escape predation and to colonize new areas, but evidence that seedlings emerge from cached seeds is scarce. We aimed to assess to what extent seedling establishment of two palm species (Astrocaryum aculeatissimum and Attalea humilis) is favoured by seed caching by rodents in a large Atlantic Forest remnant. We mapped the location of conspecific seedlings within circular plots of 15-m radius around five adult individuals of each palm species, checking if seedlings established from dispersed (>2 m from parent palms) or non-dispersed seeds (0–2 m from parent palms), and from buried or unburied seeds. We found a total of 42 A. aculeatissimum seedlings and 16 A. humilis seedlings. Nearly all (98%) seedlings established from seeds dispersed away from parents (mainly located 10–15 m from parents), and 83% and 75% of seedlings of A. aculeatissimum and A. humilis, respectively, established from seeds buried in the soil. Results show that both palm species depend almost entirely on caching of seeds by rodents to establish seedlings. Our study suggests that checking for endocarps associated with established seedlings can accurately estimate the process behind seedling establishment, improving our understanding about the net outcome of seed caching for large-seeded palms.

Predictions of weed emergence can be used by practitioners to schedule POST weed management operations. Common sunflower seed from Kansas was used at six Midwestern U.S. sites to examine the variability that 16 climates had on common sunflower emergence. Nonlinear mixed effects models, using a flexible sigmoidal Weibull function that included thermal time, hydrothermal time, and a modified hydrothermal time (with accumulation starting from January 1 of each year), were developed to describe the emergence data. An iterative method was used to select an optimal base temperature (Tb) and base and ceiling soil matric potentials (ψb and ψc) that resulted in a best-fit regional model. The most parsimonious model, based on Akaike's information criterion (AIC), resulted when Tb = 4.4 C, and ψb = −20000 kPa. Deviations among model fits for individual site years indicated a negative relationship (r = −0.75; P < 0.001) between the duration of seedling emergence and growing degree days (Tb = 10 C) from October (fall planting) to March. Thus, seeds exposed to warmer conditions from fall burial to spring emergence had longer emergence periods.

Several studies were conducted to evaluate the effects of different tillage systems on the vertical seed distribution, seedling recruitment pattern, and persistence of the rigid ryegrass seed bank. Experiments were conducted in South Australia at two locations (Roseworthy Campus and Minlaton, a site on the Yorke Peninsula) in 2003 and 2005. The distribution of surface seeds through the soil profile was associated with the level of soil disturbance. The low–soil-disturbance tillage systems left more seed on the soil surface, whereas the high–soil-disturbance systems buried most of the seeds. The seedling recruitment of rigid ryegrass was lower under the low–soil-disturbance tillage systems than under the high–soil-disturbance tillage systems at both locations. The seedling recruitment was two- to fourfold greater under minimum tillage than under no-till. Not only was the seedling recruitment lower under the low–soil-disturbance tillage systems, biomass accumulation by rigid ryegrass seedlings was also lower under these systems. The carryover of residual viable seeds from one season to the next was similar between the tillage systems. However, seed decay under no-till (48 to 60%) was much greater than under minimum tillage (12 to 39%).

Relationships among weed seed rain, soil seedbank, and seedling recruitment in no-tillage systems were studied from July 1993 to May 1996. Multiple regression analysis indicated that seedling recruitment of only six of the 25 weed species present was correlated with seed rain samples from the previous autumn, spring soil seedbank samples, or a combination of the two. However, seedling recruitment of the dominant annual grasses (yellow foxtail, giant foxtail, and fall panicum in Field 1–1994, Field 2–1995, and Field 3–1996, respectively) was related to seedbank populations or a combination of seedbank and seed rain densities. These grasses accounted for at least 32% of the emerged seedlings, 12 to 78% of the seedbank, and 16 to 77% of the seed rain. Seedling recruitment of large crabgrass and two broadleaf species, Virginia copperleaf and wild carrot, also were described by seedbank densities or a combination of seedbank and seed rain densities. However, both the broadleaf species were minor components of the cropping system, representing ≤ 4% of all seedlings. In each year, the sum of all weeds in the seedbank exceeded 1,300 seeds m−2 (0 to 10 cm deep). The fraction of the total seedbank that emerged each year ranged from 3 to 17%, but there was great variability among species. The aforementioned dominant grasses ranged in emergence from 3 to 25% of their seedbanks. Emergence of other species ranged from a low of 1% for common lambsquarters up to 41% for large crabgrass. Prediction of seedling recruitment from seed rain or seedbank densities was variable; however, combining both components improved the fit of regression describing seedling recruitment.

Germination response of perennial wall rocket to temperature, light, osmotic potential, and depth of burial emergence was evaluated under controlled environmental conditions. The effect of seed burial depth on seedling recruitment in the field was also investigated at Roseworthy, South Australia. Under optimal conditions (30 C, light/dark) germination of perennial wall rocket was rapid, with 90% of seeds germinating within 48 h of imbibition. Germination was reduced (20%) at lower, suboptimal temperatures (10 to 20 C) when seeds of perennial wall rocket were exposed to light. Germination declined with increasing osmotic potential and was completely inhibited at osmotic potentials of −1.5 MPa. Perennial wall rocket emergence was greatest from seeds placed on the soil surface, but some seedlings (< 10%) emerged from a depth of 0.5 to 2 cm. Under both field and growth-cabinet conditions, the greatest seedling emergence of perennial wall rocket occurred from seed present on the soil surface; however, the level of absolute recruitment from the seed bank was much lower (< 5%). Information gained from this study will further improve our understanding of the germination behavior of perennial wall rocket and contribute to developing sustainable strategies for its control.

Twenty-day cohorts of corn poppy were grown in the presence or absence of barley, and seedling survival, biomass accumulation and allocation, plant reproduction, and seed dormancy were measured. Seedling survivorship and biomass accumulation differed strongly among cohorts and were influenced by crop competition. In the absence of crop competition, plants from the first three cohorts (emerging October to January) had 900% higher biomass and 160% more seeds per plant than later cohorts (emerging January to April). Crop competition reduced cohort fitness; for example, in 2003 to 2004, corn poppy biomass was reduced 57 to 96%, and seed production 77 to 97%. Seeds collected from plants that had emerged in spring were less dormant, and thus, germination and emergence of these seeds were higher (25% higher and 200 to 600% higher, respectively) than those for seeds collected from other cohorts. Environmental factors at the time of seed formation may be responsible for the observed differences in dormancy. Cohort-dependent emergence, growth, reproduction, and dormancy have relevant implications for corn poppy management and demography in agricultural systems in northeastern Spain. The dormant seeds produced by autumn to winter cohorts will be the main contributors to the seed bank and weed population shift in subsequent generations. For efficient corn poppy management, the control of cohorts emerging before or with the crop in a cereal field is essential.

The effects of spring tillage sequence on summer annual weed populations were evaluated over two cycles of a 3-yr crop rotation of snap beans, sweet corn, and winter wheat. Continuous no-till (N) planting of vegetable crops each spring (NNNN) reduced summer annual weed density 63 to 86% compared to that of continuous conventional tillage (CCCC), depending upon site and herbicide level. Hairy nightshade populations were reduced by 88 to 96% when spring tillage was eliminated from the crop rotation. The effects of the NNNN spring tillage sequence on weed density were similar at two sites even though the crop rotations at the two sites began with different crops. The rotational tillage sequence of NCNC at the East site, in a crop rotation that began with corn, reduced summer annual weed density by 46 to 51% compared to that of continuous conventional tillage and planting (CCCC) at low and medium herbicide rates, respectively. In contrast, the tillage sequence of CNCN in the same crop rotation and at the same site increased weed density by 80% compared to that of CCCC at a low herbicide rate. The effects of the NCNC and CNCN rotational tillage sequences on weed density were reversed at the West site, and was probably caused by pairing sweet corn with conventional tillage rather than no tillage. The reduction in summer annual weed density caused by reduced spring tillage frequency did not significantly increase crop yields.

Manipulation of cropping systems to improve weed management requires a better understanding of how crop- and soil-related factors affect weed life cycles. Our objective was to assess the impacts of timing of primary tillage and use of legume green manure on giant foxtail demography and soil properties. We measured giant foxtail seed survival and dormancy, seedling emergence and survival, and fecundity, in addition to soil phytotoxicity, chemical properties affecting soil fertility and soil water, in the transition between the wheat and corn phases of a wheat–corn–soybean crop sequence. Postdispersal predation of giant foxtail seeds was measured in all three phases of the crop sequence. Wheat was grown either as a sole crop (W) or underseeded with red clover (R), and residues from this phase were rototilled either in the fall (FT) or in spring (ST). There were strong interactions between Red clover and Tillage timing in their effects on giant foxtail recruitment and fecundity in corn. Giant foxtail seedling emergence was 30% lower, and time to 50% emergence was more than 1 wk later, in the ST/R treatment than in the ST/W, FT/W, and FT/R treatments, which did not differ. However, fecundity of giant foxtail was 200% greater in the ST/R treatment than in the other three treatments because of suppressed early corn growth. The net effect of the ST/R treatment on giant foxtail demography in corn was to greatly increase inputs to the seedbank compared with the ST/W, FT/W, and FT/R treatments. Giant foxtail demography in the wheat phase was also affected by Red clover. There was a 200% increase in daily rates of postdispersal seed predation in the wheat phase of the R treatment compared with the W treatment. High-seed predation in the wheat phase and low fecundity in the corn phase of the FT/R treatment suggest that population growth rate of giant foxtail will be lower in this treatment than in the other treatments. The degree of soil phytotoxicity from red clover residues, the changes in the amount of interference from the corn crop early in the growing season, and the differential suitability of crop residues in the different rotations as habitat for seed predators all contributed to changes in giant foxtail demography. Understanding the effects of cropping system characteristics on entire weed life cycles will facilitate the design of integrated suites of complementary weed management tactics.

Variation in primary dormancy among populations of black nightshade and hairy nightshade collected on two dates was investigated. In addition, emergence characteristics of both species were studied during 2 yr with several populations and soil disturbance regimes. Results revealed a variation in the level of primary dormancy among populations and collection dates in black nightshade. However, fresh seeds of hairy nightshade showed no or negligible germinability, indicating a deeper level of dormancy. Emergence was higher in black nightshade than in hairy nightshade in both years, but with significant differences among populations. In addition, various categories regarding the soil temperature requirements for seedling emergence were found within seed batches. This enables the species to extend their emergence timing and therefore escape from climatic extremes or weed control operations. This information can be used to improve weed management strategies by timing weed control measures to larger seedling flushes.

In western Canada, little is known about the seedbank ecology of volunteer canola. Therefore, integrated recommendations for the management of this weed are limited. In this study, we investigated the seedbank persistence and seedling recruitment of two spring canola genotype groups with different secondary seed dormancy potentials under contrasting tillage systems. The study was conducted at two locations with different soils in the Mixed Moist Grassland ecoregion of Saskatchewan. A single cohort seedbank was established in 1999 and was followed for 3 yr in successive wheat crops. In a separate laboratory study, the six canola genotypes examined were classified as those with high and those with medium potentials for the development of secondary seed dormancy (HD and MD, respectively). After one, two, and three winters, maximum persistence of 44, 1.4, and 0.2% of the original seedbank was observed among the treatments, respectively. In 2001, HD canola genotypes tended to exhibit 6- to 12-fold greater persistence than MD canola genotypes, indicating lower seedbank mortality in HD canola. Seedling recruitment of HD canola also was higher than MD canola when differences were observed between these genotype groups. Therefore, long-term seedbank persistence of canola can be reduced by growing genotypes with low inherent potential for the development of secondary seed dormancy. The proportion of persisting seeds tended to be higher under conventional tillage than under zero tillage because of lower seedbank mortality, but no clear distinction in seedbank persistence in terms of absolute time could be made between these two tillage systems. Volunteer canola seedling recruitment followed the pattern of a typical summer-annual weed, where seedling emergence was observed only during May and June.

South-East Asian tropical rain forests experience sporadic, but profuse, seed production after general flowering, leading to the synchronous emergence of various seedlings and subsequent seedling dynamics, which play a crucial role in determining species distribution and coexistence. We examined the relative importance of both biotic (initial height, conspecific seedling density) and abiotic (canopy openness, per cent sand, soil water content) drivers using survival data for 1842 seedlings of 12 dipterocarp species for 1.5 y following mast fruiting in an old-growth Bornean tropical rain forest. More than 30% of all dipterocarp seedlings survived 1.5 y after mast fruiting. When all species were analysed together, we found that initial seedling height, canopy openness and conspecific seedling density affected dipterocarp seedling survival. Negative density dependence indicated that predators were not satiated, but dipterocarp seedlings rather suffered from host-specific natural enemies or intraspecific competition. Species-level analyses of seven dipterocarp species showed large variation in response to biotic and abiotic factors. These results suggest that interspecific differences in the relative importance of biotic and abiotic effects on seedling survival might contribute to species coexistence.

This study tested whether the reduction in the number of large-bodied seed dispersers is correlated with shifts in the taxonomic and functional (e.g. dispersal mode and seed size) traits of the seeding communities within small fragments of semi-deciduous forest, southern Mexico. In five fragments (2.3–640 ha) and one continuous forest site we sampled tree and seedling species in 40 (20 × 20 m) and 120 (3 × 3 m) plots respectively, and recorded the incidence (presence/absence) of the disperser fauna (three common large-birds and >500-g mammals). Tree and seedling species were categorized according to dispersal mode, seed size and whether they originated from local (i.e. from dropped) or immigrant (i.e. from actively dispersed) seeds. Fragment size negatively correlated with number of species of medium to large vertebrate seed-dispersers and number of seedlings of large-seeded species, but had no influence on functional traits of the adult-tree community. Between 41% and 61% of all seedlings were considered as immigrants and the proportion of immigrant seedlings of large-seeded tree species was negatively correlated with forest size. The results suggest that biased defaunation in small forest fragments may seriously reduce recruitment of large-seeded tree species (>1.4 cm length) dispersed by vertebrates, negatively affecting successional trajectories of small forest fragments.

Damage to Hawaiian Acacia koa forest by Hurricane Iniki was assessed by comparison with our previous measures of stand structure and leaf area index (LAI) at sites along a precipitation/elevation gradient on western Kauai. Reductions in LAI ranged from 29 to 80% and were correlated with pre-hurricane LAI and canopy height. The canopy damage resulted in a large pulse of litter, ranging from 4 to 19 t ha-1 across our study sites. In the first year post-hurricane, LAI recovery and relative increase in stand basal area were negatively correlated with the fraction of canopy LAI lost. The two major overstorey species, A. koa and Metrosiderous polymorpha, were damaged less than the sub-canopy species, Dodonaea viscosa and Psidium guajava. Although D. viscosa and P. guajava were both severely damaged in the hurricane, the alien species P. guajava had much higher survival than the native D. viscosa, both as adults and as seedlings. However, seedling density of P. guajava was limited by low recruitment. At these sites, there was no drastic change in species composition following hurricane disturbance, and forest structure and productivity had recovered to a great degree within 2 y.

Diversity is positively correlated with water availability at global, continental and regional scales. With the objective of better understanding the mechanisms that drive these relationships, we investigated the degree to which variation in water availability affects the performance (recruitment, growth and survival) of juvenile trees. Precipitation was supplemented throughout two dry seasons in a seasonal moist forest in south-eastern Peru. Supplementing precipitation by 160 mm mo−1, we increased soil moisture by 17%. To generate seedling communities of known species composition, we sowed 3840 seeds of 12 species. We monitored the fates of the 554 seedlings recruited from the sown seeds, as well as 1856 older non-sown seedlings (10 cm ≤ height < 50 cm), and 2353 saplings (> 1 m tall). Watering significantly enhanced young seedling growth and survival, increasing stem density and diversity. Watering diminished the recruitment of species associated with upland forests, but increased the survival of both upland- and lowland-associated species. Though supplemental watering increased the growth of older seedlings, their density and diversity were unaffected. Sapling performance was insensitive to watering. We infer that variation in dry-season water availability may affect seedling community structure by differentially affecting recruitment and increasing overall survival. These results suggest that differential seedling recruitment and survival may contribute to the observed relationships between water availability, habitat associations and patterns of tree species richness.

A close relationship has been reported between seed size and many different plant traits such as seedling size, relative growth rate, seedling survival, distance of dispersion, colonization and density of seeds in the soil (Coomes & Grubb 2003, Jurado & Westoby 1992, Lahoreau et al. 2006, Saverimuttu & Westoby 1996, Souza & Valio 2001). Although the association of seed size and shade tolerance is unclear (Westoby et al. 1996) some authors have suggested that a larger-seeded species is better able to tolerate low light availability (Foster 1986, Foster & Janson 1985, Leishman & Westoby 1994) by producing a vigorous seedling with a higher ability to withstand predation (Armstrong & Westoby 1993, Foster 1986) and delaying the beginning of carbon fixation so as to increase survival under a canopy and under leaf litter.

The seed-bank dynamics of Ambrosia artemisiifolia (Asteraceae), an annual invasive plant introduced from North America to Europe, were studied in nine French populations developing in field crops, set-asides or wastelands. The vertical distribution of seeds was studied in two different depth sections (0–5 cm and 5–20 cm), and the spatial horizontal pattern of distribution was analysed for two selected field-crop and set-aside populations. The proportions of dormant, non-dormant and dead seeds, as well as the changes in seed-bank dormancy over time, were evaluated. Natural seedling recruitment and its variation under different disturbance treatments in competitive set-asides were also studied. From 536 ± 194 to 4477 ± 717 seeds m− 2 were found in the living seed bank (0–20 cm). The majority of seeds in field crops was found in the lower soil layer, whereas the opposite pattern was observed in set-asides and wastelands. Dormant seed proportions were low (0–18%) before natural germination, but then regularly increased. The seed bank of A. artemisiifolia was spatially aggregated irrespective of the extent of soil disturbance. On average, 23 ± 12 to 292 ± 62 seedlings m− 2 were recorded, with densities lower in set-asides than in field crops and wastelands. Seedling densities were not correlated to upper seed densities except for two field crops. Soil disturbance and the removal of vegetation had positive effects on seedling recruitment in set-asides. Seed-bank dynamics appear to be crucial in the invasive success of A. artemisiifolia, and this knowledge will provide insights for the management of the species.

Seeds of two grass (Arrhenatherum elatius and Festuca rubra), two herb (Plantago lanceolata and Rumex acetosa) and two legume (Lotus corniculatus and Trifolium repens) species were sown in summer 1995 at four densities (no seed, 1000, 10 000 and 50 000 seeds m−2) into an established rabbit-grazed grassland given factorial combinations of rabbit fencing (with and without fences) and soil disturbance (with and without cultivation). On plots where no seeds were sown, only the species with persistent seed banks (P. lanceolata, L. corniculatus and T. repens) showed enhanced seedling emergence in response to disturbance. In disturbed soil, seedling densities of all species increased with increasing density of sown seeds, the effects of which were still evident for plant cover 2 years after seed sowing. In undisturbed vegetation, A. elatius, F. rubra, P. lanceolata and R. acetosa showed increased seedling densities following seed sowing; but in each case, there was an upper asymptote to seedling recruitment, presumably due to microsite limitation. Rabbit grazing reduced seedling densities, with this reduction being more pronounced with disturbance than without. However, the effect of rabbit grazing did not persist for some species; seedling mortality of R. acetosa, P. lanceolata, L. corniculatus and T. repens was higher on plots without rabbit grazing, so that plant densities of these species in summer 1996 and plant cover in summer 1997 were greater on grazed plots. The results indicate interactions between soil disturbance, propagule availability and herbivory, rather than disturbance alone, will play an important role in controlling seedling recruitment and species habitat distributions in grasslands.

The Hellshire Hills are an extensive area of tropical dry forest over limestone, located on the south coast of Jamaica. Despite being a protected area, they are subject to encroachment and clearance by charcoal burners, leaving a relatively pristine core within more disturbed areas of forest. Future management requires a consideration of the forest's resilience to such disturbance, and this study reports on seedling dynamics before and after different intensities of disturbance. The study was conducted within twelve 225-m2 plots comprising four blocks and three treatments. The treatments were removal of all trees (≥ 2 cm dbh), removal of 50% of stems (> 5 cm) and an uncut control plot. Seedling dynamics were monitored before and 3, 8, 13 and 20 mo after the application of treatments. The study indicates that regeneration by seed was not severely affected by this small-scale disturbance. However, the density of some species was affected by the environmental conditions created by partial and clear cutting, and seasonal effects were more pronounced after disturbance. Biomass recovery by seedlings was negligible in comparison with coppice regrowth which clearly offers considerable resilience to disturbance in this dry forest where successful regeneration by seed is highly susceptible to rainfall seasonality. This will likely affect long-term species diversity if the present rate of clearance continues.