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Seedling Dynamics (seedling + dynamics)

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Life Sciences	85%

Selected Abstracts

Seedling dynamics of shrubs in a fully closed temperate forest: greater than expected

ECOGRAPHY, Issue 5 2004
N. A. Laskurain
Shrub seedling emergences were studied in a beech-birch forest in the Basque Country (Spain). During four years (1998,2001) all emerging shrubs were tagged and regularly monitored in 198 1 m2 plots. Seedling emergence was intense during the entire study period and primarily occurred in early spring. Emerging seedlings mainly belonged to Hedera helix, Rubus gr. glandulosus and several heath species (including genera Erica, Calluna and Daboecia). In contrast, some dominant species components of the shrub layer (Vaccinium myrtillus and Lonicera periclymenum) showed no emergences. While small seeded species (heath species and Rubus) showed clear microsite preferences, avoiding litter for emergence, that was not the case of large seeded Hedera helix. Strict microsite requirements appear clearly associated with having seed bank, suggesting that this trait may allow these species to select favourable microenvironment prior to germination. Average life varied largely among the different taxa. It was very low for Rubus (7.4 months) and heath (4.9), and high for Hedera seedlings (23.1). Final survival was extremely low in the case of small-seeded species. Survival of Hedera seedlings was high, although their growth was very low, suggesting the existence of a conspicuous seedling bank. Our results clearly show that several shrubs species have dramatic seedling dynamics in full closed forest stands. Small seeded species preferentially emerge on bare surfaces in early spring from the soil seed banks. On the other hand, Hedera seedlings are able to emerge on litter and maintain a conspicuous seedling bank based on an efficient dispersal capability. [source]

Species-specific Seedling Responses to Hurricane Disturbance in a Puerto Rican Rain Forest1

BIOTROPICA, Issue 4 2003
Lawrence R. Walker
ABSTRACT Seedling dynamics were followed in a Puerto Rican forest for 20 months following a severe hurricane to study the interactive effects of hurricane debris, nutrients, and light on seedling diversity, density, growth, and mortality. Three treatments (debris removal, an unaltered control with hurricane debris, and chemical fertilization added to hurricane debris) altered levels of forest debris and soil nutrients. Canopy openness was measured twice using hemispherical photographs of the canopy. We examined the demographic responses of six common species to treatments over time. Seedling densities increased for all six species but the only significant treatment effects were increased densities of the pioneer tree Cecropia and the shrub Palicourea in the debris removal treatment. Seedling growth declined with declining light levels for four species but not for the pioneer tree Alchornea or the non-pioneer tree Dacryodes. Only Cecropia and the non-pioneer tree Chionanthus had treatment effects on growth. Mortality also differed among species and tended to be highest in the fertilized plots for all but Cecropia and Dacryodes. We found only some of the expected differences between pioneer and non-pioneer plants, as each species had a unique response to the patchy distributions of organic debris, nutrients, and light following the hurricane. High local species diversity was maintained through the individualistic responses of seedlings after a disturbance. RESUMEN Seguimos la dinámica de plántulas en un bosque en Puerto Rico durante 20 meses después del huracán Hugo para estudiar el efecto de la interacción de hojarasca de huracán, nutrientes, y luz sobre la diversidad de especies, la densidad, el crecimiento, y la mortalidad. Establecimos tres tratamientos (remoción de hojarasca, control con la hojarasca de huracán inalterada, y fertilizante químico añadido a la hojarasca del huracán) para alterar los niveles de hojarasca en el bosque y los nutrientes en el suelo. Medimos luz directa e indirecta dos veces usando fotografias hemisféricas del dosel. La diversidad y la uniformidad en la distribución de especies pero no la riqueza de especies fueron reducidas en presencia de fertilización. Durante el estudio examinamos respuestas demográficas de seis especies communes a los tratamientos. La densidad de plántulas aumentó para todas las seis especies pero el único efecto de tratamiento fue el aumento en la densidad del árbol pionero Cecropia y el arbusto Palicourea en el tratamiento de remoción de hojarasca. El crecimiento de plántulas disminuyó según los niveles de luz disminuyeron para cuatro de las especies pero no para el árbol pionero Alchornea o el árbol nopionero Dacryodes. Sólo el crecimiento de Cecropia y del árbol no-pionero Chionanthus fue affectado por los tratamientos. La mortalidad fue diferente entre las especies y tuvo una tendencia a ser mayor en las parcelas fertilizadas. Sólo encontramos algunas de las diferencias esperadas entre plantas pioneras y no-pioneras. Cada especie respondió de forma única a la distribución en parches de hojarasca, nutrientes, y luz luego del huracán. La aha diversidad local de especies se mantuvo a través de las respuestas individualizadas de las plántulas después de la perturbación. [source]

Seedling dynamics of shrubs in a fully closed temperate forest: greater than expected

Reciprocal distribution of two congeneric trees, Betula platyphylla var. japonica and Betula maximowicziana, in a landscape dominated by anthropogenic disturbances in northeastern Japan

JOURNAL OF BIOGEOGRAPHY, Issue 12 2005
Katsuhiro Osumi
Abstract Aim, Information has been compiled on disturbance regimes and the life-history characteristics of Betula platyphylla var. japonica (Miq.) Hara and B. maximowicziana Regel to investigate the impact of humans on the present distribution patterns of these two congeneric tree species. Location, The study area is in the central region of the northern Kitakami Mountain Range, located in the northeast of Honshu Island, Japan. Methods, First, the present distributions of B. maximowicziana and B. platyphylla var. japonica were mapped at the landscape scale. To examine the factors affecting the distribution patterns, topographic features and past land use were taken into account. Second, life-history traits of both species were clarified at various growth stages either by fieldwork or through a literature search. Previous studies have provided some information on seed production, seed dispersal, seedling dynamics, sprouting, and growth. In the present study, field observations and experiments were conducted regarding seed-bank formation, size and age at reproduction, and the life span of canopy trees. Results,Betula platyphylla var. japonica and B. maximowicziana were spatially segregated in the studied landscape (14,000 ha). The distribution of each species was correlated more strongly with land use at the beginning of the twentieth century than with site environmental factors such as altitude or slope angle. Betula platyphylla var. japonica was distributed more frequently on former grasslands, whereas B. maximowicziana was almost exclusively limited to past old-growth forests. As typical pioneers, the two species showed similar life-history traits but differed in several critical points. Betula platyphylla var. japonica has a vigorous sprouting ability, which might increase its resistance to burning and logging, whereas B. maximowicziana forms a persistent seed bank in the soil, indicating an advantage in regenerating in disturbances found in forest communities. Other critical differences were detected in age-related characteristics such as minimum age of reproduction and life span. Main conclusions, The earlier reproductive maturity and the shorter life span of B. platyphylla var. japonica indicate a shorter population cycle than that for B. maximowicziana. The latter would be excluded from grasslands that were burned frequently, as a result of the longer time span before initial reproduction and its poor sprouting ability. In contrast, B. platyphylla var. japonica would be excluded from old-growth forests, where disturbance was infrequent, owing to its shorter life span and lack of a persistent seed bank. [source]

Conspecific plant,soil feedbacks reduce survivorship and growth of tropical tree seedlings

JOURNAL OF ECOLOGY, Issue 2 2010
Sarah McCarthy-Neumann
Summary 1.,The Janzen,Connell (J,C) Model proposes that host-specific enemies maintain high tree species diversity by reducing seedling performance near conspecific adults and promoting replacement by heterospecific seedlings. Support for this model often comes from decreased performance for a species at near versus far distances from conspecific adults. However, the relative success of conspecific versus heterospecific seedlings recruiting under a given tree species is a critical, but untested, component of the J,C Model. 2.,In a shade-house experiment, we tested plant,soil feedbacks as a J,C mechanism in six tropical tree species. We assessed effects of conspecific versus heterospecific cultured soil extracts on seedling performance for each species, and we compared performance of conspecific versus heterospecific seedlings grown with soil extract cultured by a particular tree species. Additionally, we tested whether soil microbes were creating these plant,soil feedbacks and whether low light increased species vulnerability to pathogens. 3.,Among 30 potential comparisons of survival and mass for seedlings grown in conspecific versus heterospecific soil extracts, survival decreased in seven and increased in two, whereas mass decreased in 13 and increased in 1. To integrate survival and growth, we also examined seedling performance [(mean total mass × mean survival time)/(days of experiment)], which was lower in 16 and higher in 2 of 30 comparisons between seedlings grown with soil extract cultured by conspecific versus heterospecific individuals. Based on performance within a soil extract, conspecific seedlings were disadvantaged in 15 and favoured in 7 of 30 cases relative to heterospecific seedlings. 4.,Species pairwise interactions of soil modification and seedling performance occurred regardless of sterilization, suggesting chemical mediation. Microbes lacked host-specificity and reduced performance regardless of extract source and irradiance. 5.,Synthesis. These results, along with parallel research in temperate forests, suggest that plant,soil feedbacks are an important component of seedling dynamics in both ecosystems. However, negative conspecific feedbacks were more prevalent in tropical than temperate species. Thus, negative plant,soil feedbacks appear to facilitate species coexistence via negative distance-dependent processes in tropical but not temperate forests, but the feedbacks were mediated through chemical effects rather than through natural enemies as expected under the J,C Model. [source]

Abiotic and biotic drivers of seedling survival in a hurricane-impacted tropical forest

JOURNAL OF ECOLOGY, Issue 6 2009
Liza S. Comita
Summary 1. ,Many forests experience periodic, large-scale disturbances, such as hurricanes and cyclones, which open the forest canopy, causing dramatic changes in understorey light conditions and seedling densities. Thus, in hurricane-impacted forests, large variations in abiotic and biotic conditions likely shape seedling dynamics, which in turn will contribute to patterns of forest recovery. 2. ,We monitored 13 836 seedlings of 82 tree and shrub species over 10 years following Hurricane Georges in 1998 in a subtropical, montane forest in Puerto Rico. We quantified changes in the biotic and abiotic environment of the understorey and linked seedling dynamics to changes in canopy openness and seedling density, and to spatial variation in soil type, topography and tree density. 3. ,Canopy openness was highest when first measured after Hurricane Georges and dropped significantly within c. 3 years, while seedling densities remained high for c. 5 years post-hurricane. When all species and census intervals were analysed together, generalized linear mixed effects models revealed that canopy openness, seedling and adult tree densities were significant drivers of seedling survival. 4. ,The relative importance of abiotic and biotic factors changed over time. Separate analyses for each census interval revealed that canopy openness was a significant predictor of survival only for the first census interval, with lower survival at the highest levels of canopy openness. The effect of conspecific seedling density was significant in all intervals except the first, and soil type only in the final census interval. 5. ,When grouping species into life-history guilds based on adult tree susceptibility to hurricane damage, we found clear differences among guilds in the effects of biotic and abiotic factors on seedling survival. Seedlings of hurricane-susceptible and intermediate guilds were more strongly influenced by canopy openness, while seedlings of the hurricane-resistant group were less affected by conspecific seedling density. Individual species-level analyses for 12 common species, however, showed considerable variation among species within guilds. 6. ,Synthesis. Our results suggest that hurricanes shape species composition by altering understorey conditions that differentially influence the success of seedlings. Thus, predicted increases in the intensity and frequency of hurricanes in the Caribbean will likely alter seedling dynamics and ultimately the species composition in hurricane-impacted forests. [source]