High Seedling Research Articles

Predicting pine weevil risk: Effects of site, planting spot and seedling level factors on weevil feeding and mortality of Norway spruce seedlings

Several insecticides used against large pine weevil (Hylobius abietis (L.)) feeding have been prohibited due to environmental and health issues. Thus, there is a need to find other protection methods. We investigated whether spot mounding without insecticide protection could ensure high seedling survival in boreal conditions. In addition, we predicted pine weevil feeding and mortality by site, planting spot and seedling level factors. A generalized linear mixed model (GLMM) was used for predicting feeding pressure. Multivariate GLMM was used for modelling the effects of feeding pressure on lambda-cyhalothrin insecticide-sprayed and unsprayed seedlings. We planted Norway spruce (Picea abies (L.) Karst.) container seedlings for two different years in central Finland. Seedlings were planted with and without insecticide treatment in spot mounds. Untreated seedlings were also planted in unprepared humus to predict pine weevil feeding pressure. Pine weevil feeding pressure was explained only by the age of the clear cuts: feeding pressure was high in fresh clear cuts and decreased if there was one growing season between the clear cut and the planting. On average, 8% of unsprayed seedlings planted in mounds died within two years after planting, while 2% of sprayed seedlings died. Under high feeding pressure, mortality probability of an unsprayed seedling planted in a mound was less than 0.1 only when the seedling was surrounded by mineral soil and the stem base diameter of seedlings was at least 4mm. In mounds covered by mineral soil, especially if it was medium coarse, soil was splashed on the stem base and thereby protected seedlings from pine weevil feeding. Under lower feeding pressure, also thinner seedlings survived without insecticide treatment if mounds were covered by mineral soil. Thus, if Norway spruce seedlings are planted without insecticide treatment, they should have a relatively thick stem and need to be planted in mounds covered with mineral soil.

Effect of Trichoderma and fungicide on seedling establishment and yield performance of dry direct seeded boro rice

Poor seedling establishment and seedling mortality is the major barrier to optimum stand establishment in dry direct seeded boro rice. Experiments were carried out at the Agronomy Field Laboratory, Bangladesh Agricultural University (BAU), Mymensingh, Bangladesh during January to June 2013 to study the effect of Trichoderma and fungicide application on seedling establishment and yield performance of dry direct seeded Boro rice. The experiment comprised ten treatment combinations of Trichoderma and fungicides viz. seed treatment with Trichoderma (M1), seed treatment with Trichoderma+spraying of Thiovit (M2), seed treatment with Trichoderma + spraying of Propiconazole (M3), seed treatment with Trichoderma + spraying of Thiovit and Propiconazole (M4), spraying of Thiovit (M5), spraying of Propiconazole (M6), seed treatment with Thiovit + spraying of Propiconazole (M7), seed treatment with Propiconazole + spraying of Thiovit (M8), spraying of mixture of Thiovit and Propiconazole (M9), and control (no fungicide or Trichoderma ) (M10).The experiments used Randomized Complete Block Design (RCBD) with three replications. Experiment revealed that seed treatment with Trichoderma harzianum followed by spraying of Thiovit gave the highest yield of rice. The study concludes that Trichoderma and then application of sulphur fungicide at 20 days after sowing could be practiced for ensuring high seedling establishment and yield of rice under dry direct seeded system in boro season.J. Bangladesh Agril. Univ. 14(1): 37-42, June 2016

Janzen-Connell patterns are not the result of Janzen-Connell process: Oak recruitment in temperate forests

According to the Janzen-Connell hypothesis, seedling mortality is greater close to conspecific (or closely related) adult trees because of higher enemy pressure, ultimately increasing local tree-species diversity. However, this pattern (i.e. a decline of seedling performance close to conspecific or closely related adults) could also result from other processes: (1) heterospecific adults might positively affect seedlings; (2) conspecific (or closely related) adults might negatively affect seedlings by causing a deterioration of the microenvironment. We tested these hypotheses, accounting also for sizes of adults. We planted oak-seedlings in a temperate forest, characterized their adult neighbourhoods, measured 26 microenvironmental conditions, seedling mortality during one year, budburst and leaf herbivory. We detected Janzen-Connell-like patterns (frequent lack of budburst close to conspecific adults; high seedling mortality close to closely related adults) that were consistent with the Janzen-Connell process. However, these patterns were either counteracted by non-Janzen-Connell processes such as a favourable microenvironment or were weak with little explained variance. We detected Janzen-Connell-like patterns that were not consistent with the Janzen-Connell process: proximity to heterospecific adults per se decreased leaf herbivory partly due to microenvironmental effects, such that a lower leaf herbivory decreased seedling mortality. Overall, the spatial pattern of tree recruitment may resemble that predicted by Janzen-Connell but result from different processes: notably heterospecific adults creating refuges from enemies, facilitating the establishment of oaks below non-oaks without hindering their establishment below oaks.

Effects of anthropogenic disturbances on natural regeneration and population structure of gum arabic tree (Acacia senegal) in the woodlands of Lake Baringo ecosystem, Kenya

Despite the ecological and economic importance of Acacia senegal, little is known about the effects of anthropogenic disturbances on its natural regeneration patterns and population structure. We investigated the effects of these factors within the Lake Baringo woodland ecosystem. Data was collected from 60 plots of 20 m × 20 m systematically distributed in four A. senegal-dominated populations within the Lake Baringo woodland. Sample populations spanned a degradation gradient measured by a population disturbance index (PDI). Trees were measured for diameter at breast height (DBH) and categorized by growth stages: seedling, sapling and adult tree. Higher seedling and sapling densities were recorded in lightly than heavily disturbed populations, but only sapling density was significantly different between the two disturbance levels (P = 0.02). Lightly disturbed populations revealed a reversed J-shape size-class distribution (SCD) indicative of stable structure unlike the heavily disturbed populations. The quotient and permutation indices indicated unstable populations with episodic recruitment and mortality. Our study reveals that natural regeneration and population structure of A. senegal were affected majorly by selective harvesting and heavy browsing. Suitable management strategies to control livestock grazing and illegal tree harvesting within the woodland is required to promote conservation of the species genetic resources

Vertebrate herbivores are the main cause of seedling mortality in a logged African rainforest—implications for forest restoration

AbstractHigh seedling mortality can limit tropical forest regeneration after disturbance, such as selective logging. However, causes of seedling mortality are often poorly understood although this information is critical for designing appropriate restoration methods. We studied seedling mortality in a rainforest in Uganda where natural recovery has failed after selective logging carried out 40 years earlier and the sites are dominated by herbaceous vegetation. We established an experiment where seeds of 12 indigenous tree species were sown into different‐sized logging gaps in order to capture factors that cause early seedling mortality. We examined whether seedling mortality was influenced by vegetation cover (VC), vertebrate herbivores (VHs), gap size, or forest compartment and recorded causes of mortality. We found that seedling mortality was in general high but showed high tree species‐specific variation (ranging from 19 to 92% six months after emergence). VHs, particularly rodents, were the most important cause of mortality. Rotting caused mortality particularly in smaller gaps, but elephant trampling, drying, being washed away by rain and falling debris were only minor mortality causes. Dense VC was not a considerable barrier to seedling survival, but by providing shelter for rodents, it indirectly increased seedling herbivory. Our results show that high seedling mortality on logged sites can limit forest regeneration and rodents in particular can be a significant factor causing high seedling mortality.

Snow Duration Effects on Density of the Alpine Endemic Plant Packera franciscana

Packera franciscana (Greene) W.A. Weber and Á. Löve (Asteraceae) (San Francisco Peaks ragwort) is an alpine-zone endemic of the San Francisco Peaks in northern Arizona. Previous studies have shown that P. franciscana is patchily distributed in alpine-zone talus habitats. The purpose of this study was to describe the relationship between snow duration and P. franciscana abundance. We established trailside transects through P. franciscana habitat along the Weatherford Trail to estimate the abundance of P. franciscana ramets. Snow-free and snowbed sample segments were chosen based on a 17 May 2013 snow photograph taken from within the Inner Basin of the San Francisco Peaks caldera. The section of the Weatherford Trail under snow on 17 May 2013 had a 5-year arithmetic mean of 1.53 ramets ⋅ m-2 (SE 0.37)—much less dense than the snow-free section which had a 5-year arithmetic mean of 7.17 ramets ⋅ m-2 (SE 1.09). The steep upper portion of talus slopes is known to move downslope faster than mid- and lower slope portions due to gravitational processes working on surface particle size, slope angle, and frost heave/needle ice during moist periods. Needle ice is known to uproot seedlings in other species. Active talus shift may inhibit P. franciscana colonization and growth on upper talus slopes via high seedling mortality in the snowbed zone during spring snowmelt.

English

The aim of this work was to evaluate commercially available substrates and levels of potassium on the development of passion fruit seedlings in protected conditions. The experiment was conducted at the city of Presidente Prudente, Sao Paulo within the period from April to September of 2010. The treatments were made with three different substrates (Bioplant®, Coconut fiber and Vivatto®) and four levels of potassium (0, 150, 300 and 600 mg-1 of K dm-³), arranged in a 3 × 4 factorial design with five repetitions. The following parameters were analyzed 120 days after seedlings transplanting: Plant height, number of leaves, length of root, dry matter of shoot, root, total matter and chlorophyll content. The dose of 600 mg dm-3 of K provided the highest seedling height, 85.83 cm independent of the substrate. The commercial substrates Bioplant® and Coconut fiber with a dose of 150 mg dm-3 of K influenced the maximum accumulation of total dry matter of seedlings. However, Vivatto® substrate provided the highest accumulation of total dry matter with application dose of 600 mg dm-3 of K. Mineral potassium fertilization in the substrate Bioplant® and Coconut fiber with a dose of 150 mg dm-3 reduced the length of passion fruit’s roots. Key words: Passiflora edulis Sims., mineral nutrition, protected cultivation.

Notice of Release of 'Trailhead II basin wildrye

‘Trailhead II’ basin wildrye ( Leymus cinereus (Scribn. & Merr.) A. Love [Poaceae]) is a tetraploid basin wildrye release for use in re-vegetation efforts on rangelands of western North America. Trailhead II is the result of 2 cycles of recurrent selection within the basin wildrye cultivar ‘Trailhead’ for rapid seedling emergence from deep seeding. Trailhead II is genetically distinct from Trailhead. Additionally, in comparisons between Trailhead II and Trailhead, Trailhead II possessed higher total emergence and more rapid emergence from deep seeding (7.6 cm [3 in]) and exhibited higher seedling establishment at 3 of 5 field sites where it was evaluated in Nevada, Utah, and Wyoming. The release of Trailhead II basin wildrye improves this native germplasm to enhance the success of conservation and re-vegetation plantings in the Intermountain West and Northern Great Plains areas of the US and Canada.

Growth indices and grain yield attributes in six maize cultivars representing two era of maize breeding in Nigeria

Growth parameters such as seedling germination attributes, crop growth rate (CGR), relative growth rate (RGR), net assimilation rate (NAR) and leaf area ratio (LAR) as well as yield parameters were investigated in six maize cultivars representing two era of maize breeding in Nigeria during the 2005 late and 2006 early cropping seasons. Differences between maize breeding era were significant for seedling emergence (E %) and emergence index (EI) while genotypes within a particular breeding era (G/E) differed significantly for E% and emergence rate index (ERI). Seasonal (S) variation in seedling parameters was also significant for E % and ERI with a 15% higher seedling emergence in 2006 early season. CGR in the genotypes in breeding era 1 was higher by seven percent (7%) during vegetative growth phase but lower by 14% at flowering phase compared to genotypes in breeding era 2. NAR on the other hand was consistently higher in varieties developed in 1970’s by 15.2 and 13.8% compared to varieties developed in 1990’s. Regardless of the breeding era, varieties with higher values for LAR at flowering (except var. TZPB-SR) were higher yielding than those with lower LAR. Overall, varieties developed in era 2 were superior to those developed in era 1 for E% and also had six percent (6%) higher values for LAR at vegetative growth phase than those developed in era 1 but decreased by two percent (2%) at flowering phase. E% in the genotypes ranged from 48.56 in ACR 9943 DMRSR to 79.33 in ACR99TZL COMP4 DMRSR, while EI and ERI ranged from 0.86 and 0.010 in TZB-SR to 0.96 and 0.014 in ACR 97 TZL COMP1-W. Grain yield was significantly higher in 2006 early cropping season by 0.3t/ha -1 translating to 14.78% than in late season and it ranged from 1.64t/ha -1 in TZPB-SR (era 1) to 2.94t/ha -1 in ACR99TZLCOMP4DMRSR (era 2). Var. ACR99TZL COMP4DMRSR with the lowest values for CGR, RGR and NAR at vegetative phase had the highest grain yield (2.94t/ha -1 ) indicating that genotypic superiority for grain yield is not particularly related to differences in any of these traits but rather dependent on the inherent genetic potential of the varieties themselves. Keywords: Zea mays L., Growth indices, Maize breeding era, Grain yield

Study on antioxidation system in high yield hybrid rice Langyoupeijiu seedlings under dry raising conditions

Compared with Shanyou 63, the characters of antioxidation system in a new developed rice hybrid Liangyoupeijiu seedlings under dry raising conditions was studied. The results showed that activities of SOD, POD and CAT in Liangyoupeijiu seedlings under dry raising conditions were higher than those of seedlings under water raising conditions. In terms of MDA content and producing rate of O 2 —· in seedling, there were not notable differences between dry and water raising conditions. Proline content was accumulated more in seedlings under dry raising conditions than seedlings under water raising conditions. Which enhanced ability of rice at repelling dry, at the same time, made material bases for dominance growthing in field. The study suggested Liangyoupeijiu displayed its potentiality of light energy inversion better under the high activity of antioxidation system, which was one of the physiologic bases on high yield. And study suggested it was good that the time raising seedling was thirty days or can’t get good seedling.

Influence of temperature on seed germination in papaya under subtropical conditions of India

The effect of temperature on germination and days taken for germination was evaluated in Carica papaya cvs., ‘Pune selection-3’ and ‘Pusa Dwarf’. The highest average seed germination per cent was observed in the month of July (96.8 and 93.0 %), followed by August (94 and 88.5 %), whereas the lowest average seed germination was observed in the month of January (44.2 and 36.8 %) in ‘Pune selection-3’ and ‘Pusa Dwarf’, respectively. Minimum number of days (5.17 and 6.33) was observed for germination in the month of July, whereas the maximum number of days (29.5 and 31) was taken in the month of January in both the cultivars, respectively. The average highest germination and seedling height was observed at temperature 29.8 °C and 29.5 °C during July and August, respectively, whereas the lowest was observed at temperature 14 °C and 15.9 °C during January and December, respectively. The optimum time for nursery sowing was July to August for autumn season crop under subtropical conditions of India.

Influence of Environmental Factors on Seed Germination and Emergence of Asia Minor Bluegrass (Polypogon fugax)

Asia minor bluegrass (AmB) is a major weed impacting rapeseed production in Dongting Lake District, China. Growth chamber experiments were conducted to determine the influence of environmental factors on germination and emergence of AmB. The optimum constant temperature for germination was around 20 C. Seeds showed germination percentages above 60% under 22/15 and 24/19 C day/night temperature regimes. Seeds could germinate in the dark, but light exposure significantly enhanced the germination percentage. More than 50% of seeds germinated over a pH range between 4 and 10. Seeds were highly sensitive to osmotic stress, and germination was completely inhibited at an osmotic potential of −0.4 MPa, indicating that it was favored by a moist environment. Increasing salinity reduced germination of AmB seeds from 58% at 0 mM to 13% at 80 mM NaCl. The highest seedling emergence (62%) was observed when seeds were placed on the soil surface, and no seedlings emerged from seeds placed at a depth of 5 cm. This work shows that the climate and soil conditions in Dongting Lake District are suitable for AmB seed germination and that no-till fields, where seeds remain on the soil surface, promote the successful establishment of the weed.

Intraspecific interactions shift from competitive to facilitative across a low to high disturbance gradient in a salt marsh

Disturbances are ubiquitous among salt marshes, and disturbances such as litter removal may form stressful environmental conditions. The stress-gradient hypothesis (SGH) predicts that the relative importance of facilitation and competition between species will vary inversely to each other across abiotic stress gradients. However, how intraspecific interactions vary across disturbance levels, and whether they follow the SGH has not been investigated. To test the SGH with intraspecific interactions within Suaeda salsa individuals, we assessed individual survival in established fully mapped salt marsh plots with two treatments, disturbed, litter removal and control, undisturbed plots. Recently developed spatial statistics were applied to distinguish between random processes, intraspecific facilitation, scramble competition, and contest competition underlying the spatial patterns at different spatial scales, growth stages, and disturbance levels. We found evidence that intraspecific interactions among S. salsa individuals across disturbance levels tended to support the SGH, but this support depended on time and space. Intraspecific interactions were more likely to show positive density dependence in disturbed plots, particularly at the seedling period and when individuals were separated by < 9 cm. However, positive density dependence was not detected in undisturbed plots. The protective effects of litter on seedlings, which were lost in undisturbed sites, may have been at least partly simulated at high seedling densities. Mortality in disturbed sites was not random, and facilitation had a more important influence than competition on population dynamics in high disturbance sites. However, the influence of competition on population dynamics, specifically scramble competition was also clearly important.

Effects of Eucalyptus litter and roots on the establishment of native tree species in Eucalyptus plantations in South China

Transforming plantation monocultures into sustainable, mixed-species forests that contain native species is an important goal in South China. The establishment of native species in Eucalyptus plantations is generally considered difficult, however, because of the potential allelopathic effects of Eucalyptus. In this study, a field trial with completely randomized block was conducted to determine the degree to which Eucalyptus litter and Eucalyptus roots limit the establishment of native trees in Eucalyptus plantations. Growth of seedlings of four native tree species (Schima superba, Michelia macclurei, Cinnamomum burmannii, Cinnamomum camphora) that were tested was inhibited by Eucalyptus roots. Seedling emergence was less sensitive than subsequent seedling growth to inhibition by Eucalyptus roots. In contrast, litter enhanced the emergence and growth of seedlings of most of the tested species (Castanopsis chinensis, Elaeocarpus sylvestris, S. superba, Liquidambar formosana, C. burmannii, and C. camphora), suggesting that retaining litter on the forest floor may promote the establishment and growth of native tree species in Eucalyptus plantations. We propose the following strategies for establishing native tree species in Eucalyptus plantations: (1) direct sowing of the native tree species C. chinensis, Castanea henryi, Erythrophleum fordii, and C. camphora; (2) transplanting of E. sylvestris, S. superba, and Tsoongiodendron odorum, which had low germination rates but high seedling establishment rates; and (3) the exclusion of Eucalyptus roots via inter-row trenching to enhance the establishment of S. superba, L. formosana, C. burmannii, and C. camphora.

Genetic Variation and Correlation among Seedling and Mature Plant Traits of Soybean Evaluated in Acid Sand Culture and on Acid/Neutral Soil Fields of Nigeria

&lt;p&gt;Experiments in acid sand culture, acid and neutral soil fields were carried out in 2003 with the objective of studying genetic variability and correlation among seedling and mature plant traits with a view of guiding breeders on appropriate selection options in breeding for aluminium/acid stress tolerant soybean in Nigeria. Genotypic variance was high for all the sand culture traits (root dry weight, shoot dry weight and relative root surface area), leading to the high heritability estimates of 77.85% to 83.72%. Genetic advance as a percentage of the mean (GA) was very high (85.51%-155.84%) for the sand culture traits. As expected, a better performance in terms of grain yield and yield components was observed for the neutral soil field compared to the acid soil field. However, higher heritability estimates were observed for the field traits measured on the acid soil field compared to the neutral soil field. Heritability estimates for the days to flowering and plant height were high (66.44%-79.63%) compared to the moderate heritability (47.42%-58.89%) observed for the number of pods/plant and grain yield on both soils. Conversely, the GA for days to flowering and plant height was lower (12.08%-26.49%) compared to the values (27.27%-41.56%) observed for number of pods/plant and grain yield on both fields. Higher genotypic and phenotypic coefficients of variation (GCV and PCV) were observed for the sand culture traits compared to the field traits. On the acid and neutral soil fields GCV and PCV values were lower for the days to flowering and plant height compared to the values observed for the number of pods/plant and grain yield, with highly significant correlation between/within the sand culture traits and the field traits. These results indicate that selection of soybean genotypes with high seedling root dry weight and relative root surface area in acid sand culture at 450 μM Al&lt;sup&gt;3+&lt;/sup&gt; will enhance progress in the selection of high yielding acid tolerant tropically adapted genotypes of soybean on acid soils of Nigeria.&lt;/p&gt;

Soursop seedlings: biomasses and biometric relations in different farming environments and substrates – Part II

ABSTRACT The quality of seedling is critical to obtain vigorous plants in the field. The present study aimed to assess biomasses and biometric relations of soursop seedlings. We used different substrates in protected environments. The experiment was performed at the Universidade Estadual do Mato Grosso do Sul (UFMS) (State University of Mato Grosso do Sul). Five farming environments were developed in greenhouses: one covered with low-density polyethylene film (LDPE), another with with polyethylene and heat-reflective cloth under film under 50% shading in aluminized color, monofilament cloth under 50% shading in black, thermo-reflective cloth under 50% shading in aluminized color, and an environment covered with bacuri coconut straw. Substrates were made of manure, humus, cassava branches and vermiculite at different proportions. Each of them varying from 25%, 33.3%, 50% and 75% in mixture combination. Each environment was considered an experiment. A completely randomized design was adopted and later a joint analysis of them. Agricultural greenhouse covered with LDPE and thermo-reflective cloths under 50% of shading, proportionated seedlings with greater biomass. Substrates containing manure are the most suitable for soursop seedlings. High percentages of earthworm humus produce low quality soursop seedlings. Soursop seedlings had a Dickson’s quality index around 0.335. The greenhouse covered only with LDPE film did not produce high quality seedlings.

Effects of Different Root Restriction Media on Root Activity and Seedling Quality and Early Growth Parameters of Runner Plantlets of Strawberry After Transplanting

The present study aimed to determine the influence of various root restriction media on seedling quality and early growth of strawberry after transplanting. The root activity of the seedlings, measured 20 days after fixation, was considerably higher (0.096, 0.090, and 0.063 mg·g-1·h-1 at 420, 450, and 480 nm, respectively) in expanded rice hull (ERH) treatment than in the sandy loam and loamy sand treatments. The volumetric water content (VWC) of the root media tested across 3 irrigation regimes (15 d, 30 d, 45 d) in the nursery field was highest in sandy loam (65.0–66.8%), followed by 59.4–61.3% in loamy sand and 38.6–45.3% in ERH. When growth parameters of runner plantlets were compared, ERH treatment was found to result in the highest crown thickness and fresh weights of root and above-ground parts. This had a favorable influence on above-ground tissue growth after transplanting to plastic house soil. As mentioned above, ERH treatment resulted in the highest seedling quality and early growth after transplanting. The results of this study would serve as useful on-site data for the production of high-quality strawberry seedlings.

ACCESS TO IMPROVED HYBRID SEEDS IN GHANA: IMPLICATIONS FOR ESTABLISHMENT AND REHABILITATION OF COCOA FARMS

SUMMARYPoor access to improved seeds in West and Central Africa has compromised crop yields and productivity as most farmers source the bulk of their seeds from informal channels. The use of farmer produced seeds has mostly resulted in high seedling mortality thereby presenting challenges to cocoa rehabilitation programmes across the sub region. With the aid of a mobile data collection system (MDCS), the first of its kind to enhance accuracy of survey results in an improved seed supply system through brokerage and linkages among diverse actors, this study assesses Ghanaian farmers’ access to improved hybrid cocoa seeds and provides evidence on the socio-cultural factors that affect field performance of such planting materials. Results show that farmers value a seed brokerage system (SBS), which is facilitated through group bulk purchase, timely acquisition and delivery of seeds. The study also revealed that farm size, land use type and gender have significant effect on survival rate of transplanted hybrid cocoa seedlings over two dry seasons. Regardless of the rehabilitation process, mean survival rate was high (79%) although an 11% (p &lt; 0.000) difference occurred between gender with men recording a higher rate. The majority of farmers prefer cultivating cocoa on forest and fallow lands, implying continues degradation of forest areas. There is therefore an urgent need for a change of mind set, to advocate for land recycling to spare forest areas to thrive.

Overwintering seeds as reservoirs for seedling pathogens of wetland plant species

AbstractSeed germination and seedling establishment are central to the distribution and abundance of plant species in wetlands. While fungal and oomycete pathogens are known to affect seed viability and emergence, relatively little is known about which fungi and oomycetes are associated with seeds in the soil or how these species affect seeds and seedlings. We characterized the fungi and oomycetes associated with overwintering seeds in wetlands and determined their potential to influence seed germination and subsequent seedling mortality. Fungi and oomycetes did not affect seed germination, despite the isolation of high frequencies of known seed and seedling pathogens in the fungal genera Alternaria, Peyronellaea, Epicoccum, and Fusarium. However, many of the most frequently isolated fungal species from overwintering seeds were highly virulent to seedlings. While both native and nonnative plant species were tested, we did not observe consistent differences in either seed germination or seedling susceptibility based on the invasive status of plants tested, contrary to what we expected given several established hypotheses for invasive success. The high seedling virulence of fungi from overwintering seeds coupled with the differential abundance of some of the more pathogenic fungi among seeds of different plant species, led us to the conclusion that the fungal pathogens that colonize seeds in the seed bank over winter are likely to strongly impact subsequent seedling establishment in wetlands the following spring despite not reducing overwintering seed germination in the seed bank or differently effecting invasive plant species.

Establishment of invasive plant species in canopy gaps on Robinson Crusoe Island

To design preventive and management measures it is crucial to identify the mechanisms that facilitate an invasion process. We evaluated how microsites affect establishment success of the alien small tree Aristotelia chilensis, the alien climber Rubus ulmifolius, and endemic tree species on Robinson Crusoe Island forest. Seedling and sapling densities were estimated in 65 canopy gaps in two forest stands (PEY and Villagra) along a canopy forest-gap gradient, and in three microsites (mound, pit, and trunk) of canopy gap-maker trees. Two statistical models were applied to evaluate the effects of the position in the gap (center, edge, and close forest) and substrate microsites in relation to topographic and structural variables on invasive and endemic species establishment. The density of invasive species was higher in the center of canopy gaps and forest edges than under forest canopy. Invasive plants were present in 86.5 % (n = 32 gaps in PEY) and 89.8 % (n = 25 forest gaps) in Villagra. A higher seedling and sapling density of endemic rather than invasive species was found in canopy-gap center and gap edges. However, trunks, mounds, and pits were dominated by invasive species. We found different responses in seedlings, saplings, and juvenile stages in relation to the explanatory variables studied and between the two stands. The decomposition state of gap-maker trees, which was used as a proxy of gap age, was the only variable that showed the same tendency in the two forest stands and for both invasive and endemic seedlings. In this case, we found that the densities of invasive and endemic seedlings were lower in older gaps, but sapling densities were higher in older gaps. Based on the results we cannot conclude a general pattern of seedling, sapling, and juvenile establishment in forest gaps for either invasive species, but in some gaps the invasion seems to start in trunks, mounds, and pits. We recommend focusing invasive species control on mounds and pits in some forest stands; and in general, we recommend controlling invasive saplings, more than seedlings or juveniles.