Article

Tree seed dispersal among forest fragments: II. Dispersal abilities and biogeographical controls

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Aim To investigate the medium to long‐distance dispersal abilities of temperate hardwood tree species and the ecological controls on dispersal, including distance to and connectivity with seed sources, seed source strength, and species dispersal mechanism and seed size. Location A fragmented forest system in the Long Point region, Southern Ontario. Methods Pine plantations were the `seed traps' in which seedlings of hardwood species were enumerated to indicate past dispersal events. The influence of distance to seed sources, dispersal mechanism and seed mass on the probability of dispersal to plantations were evaluated using logistic analysis. Regression analysis was used to determine the effect of seed source strength (mature tree abundance within 150 m of plantations) on seedling density in plantations. Connectivity was assessed by comparing the strength of correlations between seedling abundance in plantations and the abundance of mature trees around plantations in connected vs. unconnected source areas. Results Seedling presence in plantations decreased significantly with distance from the nearest potential seed source for species grouped according to dispersal mechanism. Probabilities of seedling presence were ≥0.8 at 25 m distances, decreasing to under 0.3 at 175 m distances. While twenty‐seven of twenty‐nine species were present in at least one plantation with a seed source within 25 m, only thirteen of twenty‐seven species occurred in plantations with a seed source ≥100 m away, and only nine of twenty‐four species in plantations ≥150 m from seed sources, indicating limited potentials for interfragment migration. Seed source strength was significantly related to seedling density in plantations for twelve of fifteen species tested, indicating the importance of species commonness to interfragment migration. Connectivity was not related to dispersal frequency in the system, but this finding applies to a relatively well‐connected system of forests and plantations and is expected to differ for systems with greater patch isolation. In addition to these general controls, dispersal was related to species dispersal mechanism. Seed size was negatively related to dispersal frequency, but only within the rodent dispersal spectra. Bird‐dispersed species appeared to have superior interfragment dispersal abilities, closely followed by lighter seeded rodent‐ and wind‐dispersed species. Large‐seeded rodent‐dispersed species ( Juglans spp., Quercus macrocarpa ) and species lacking well‐developed adaptations for dispersers were infrequent in plantations generally, and with the exception of Q. macrocarpa , were absent from plantations more than 50 m from seed sources. Species dispersal abilities were ranked according to dispersal mechanism and seed size such that: bird > lighter‐seeded rodent = wind > larger‐seeded rodent = unspecialized. Main conclusions Distance to seed sources appears to be a key determinant of patch colonization. Infrequent dispersal over distances of >100–150 m for most species in this system raises concerns about the abilities of tree species to be sustained in fragmented forests. For some species, distances of as little as 50 m appear to be isolating, and these, in particular, risk regional extinctions over time scales depending on their local population persistence. Artificial introductions may be needed to maintain fragmented tree populations, particularly for rare species and those with poor dispersal indicated in this study.

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... La présence de l'érable à sucre est attestée depuis c. 600 ans AA, ce qui suggère que pendant plus de 3000 ans, le peuplement du site T70 aurait pu être exempt d'érable à sucre alors que l'érable rouge était présent, indiquant un important décalage temporel entre l'établissement des deux espèces d'érable. Ce délai d'arrivée de l'érable à sucre pourrait témoigner de la dispersion limitée des graines (Hewitt and Kellman 2002;Kellman 2004) et/ou des contraintes édaphiques entravant l'établissement de l'espèce en forêt boréale (Collin et al. 2017;Solarik et al. 2020). ...
... La forme et la taille des graines peuvent avoir un effet sur la distance de dispersion d'une espèce et donc sur sa capacité à s'établir et à persister dans un nouvel habitat (Peroni 1994;Cain et al. 2000). Par exemple, Hewitt and Kellman (2002) suggèrent que les caractéristiques aérodynamiques des graines peuvent limiter la capacité de dispersion des samares d'érable, disséminées par le vent. Une distance limitée de la dispersion moyenne des graines et donc la dépendance à de rares événements de dissémination à longue distance (Nathan et al. 2002;Kellman 2004) pourraient expliquer le délai d'arrivé de l'érable à sucre au site T70. ...
... Bien que les changements climatiques prédisent une migration vers le nord, les capacités de déplacement des espèces tempérées pourraient être limitées par la distance moyenne de dispersion des graines, les rares événements de dispersion à longue distance (Hewitt and Kellman 2002;Kellman 2004) et/ou par les conditions édaphiques locales ou régionales (Lafleur et al. 2010) ce qui pourrait expliquer les délais de migration entre les espèces (Collin et al. 2017). Une modification des conditions édaphiques causée par le réchauffement du climat pourrait contribuer à faciliter l'établissement des espèces tempérées en forêt boréale. ...
... The establishment of the native forest species within pine plantations depends on both in situ land-use legacies as well as the distance to seed sources from remnant native forest fragments. In addition, other ecological factors intervene, such as internal spatial structure of plantation patches (Utsugi et al., 2006;Gómez-Aparicio et al., 2009;González-Moreno et al., 2011), vegetation type surrounding plantation patches (Hewitt and Kellman, 2002a;2002b;Zamora et al., 2010), availability of seed-dispersal vectors or abiotic factors González-Moreno et al., 2011). The arrival of off-site propagules through organisms acting as mobile links is of special importance to plantations, where the internal resources for ecological succession are impoverished (Bengtsson et al., 2003;Lundberg and Moberg, 2003;Gómez-Aparicio et al., 2009). ...
... On the other hand, the amount and diversity of seeds provided by a seed source depends on its size (natural forest patch size) and specific composition. The distance to the seed source affects the process of seed dispersal (Hewitt and Kellman, 2002a;2002b). Shorter distances to the natural vegetation patches boost the probability of propagules entering afforested stands González-Moreno et al., 2011). The degree of adjacency of the patches of natural vegetation also affects the amount of seeds that penetrate the pine plantations , so the greater the area of adjacency, the greater the entry of seeds, and therefore the greater the probability of new species establishing themselves in these plantations. ...
... Seed dispersal depends on the distance from the seed source (Hewitt and Kellman, 2002b). In pine plantations, the presence and abundance of species other than pines is determined, among others, by the distance to the seed source (González-Moreno et al., 2011). ...
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Forest plantations are an example of widespread land-use change shaping terrestrial ecosystems. They usually have high stand density, low tree diversity, and homogeneous structure. Their conversion into more natural forests, i.e. naturalization, to foment active regeneration, heterogeneous structure, high biodiversity levels, and high resilience to disturbances such as pests and fires, is urgently needed. More diverse and heterogeneous forest stands display greater resilience to global change, in addition to protecting the ecosystem services that mountainous pine-plantations provide.We present diveRpine (diveRsification of pine plantation), an interactive application designed to show how the species richness (and therefore resilience) varies in pine plantations based on the mountain landscape configuration, the internal structure of the stand, and the composition of the dispersal vectors. The aim of the application is double. On the one hand, it would provide a guidance tool for natural resource managers that aid in the naturalization of forest plantations to recover the multifunctionality of these ecosystems. On the other hand, this tool could be a valuable teaching resource in ecology and conservation classes, since it has great value to explore virtual scenarios and demonstrate the process of prioritization of the management actions. The user can simulate different combinations and analyze how they would affect the tree-species richness in a specific pine plantation stand. It also allows the user to visualize some of the complex ecological processes that underlie the diversification of pine plantations in Mediterranean mountain areas. This tool provides a valuable aid for decision making, for example helping managers to decide whether or not to intervene in a certain pine stand, by projecting the most probable ecological succession under a specific scenario. Our diveRpine concept combining scientific rigor with simplicity of presentation and interpretation is applicable in any restoration context.
... As shown by Johnson (1992, 1993), seed mass controls the terminal velocity of wind-dispersed diaspores, and thus is strongly negatively related to dispersal capacity. For animal dispersal, there is evidence that heavy-seeded species may achieve only limited distances of transport (Ranney and Johnson 1977;Darley-Hill and Johnson 1981;Hewitt and Kellman 2002b), though Thomson et al. (2011) found no relationship between dispersal and seed size. At the same time, for all vectors, seed mass is proportional to juvenile survivorship Johnson 1998, 2000;Moles and Westoby 2006), particularly in shady forest environments (Hewitt 1998;Bruun and Ten Brink 2008). ...
... To fill the knowledge gaps identified above, in this paper, we develop and test a full model of inter-fragment tree colonization in a southern Ontario hardwood forest for a large number of animal-and wind-dispersed tree species, varying dramatically in seed mass. To test and calibrate the model, we employ one of the few available, comprehensive empirical and experimental datasets on inter-fragment medium-to long-distance temperate tree dispersal and colonization (Hewitt and Kellman 2002a, 2002b. ...
... Granivory by squirrels and other larger vertebrates on nut-tree species was measured in a separate experiment on three species spanning a range of seed sizes and genera: J. nigra, C. cordiformis, F. grandifolia (Hewitt and Kellman 2004) and these results were used to estimate losses for all nut tree species according to taxonomic and seed mass similarity (see Table 1). Additional details of the study system, field and lab methodology may be found in Hewitt and Kellman (2002a, 2002b). ...
Article
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We developed a model of hardwood tree colonization in forest patches. We began with a basic model of species’ recruitment density calculated as a function of seed production and juvenile survivorship. Survivorship probability was expressed as a function of seed size, using seed-sowing data for a wide variety of species. To account for dispersal, we used an exponential distance-decay function based on empirical colonization data for species classified by dispersal mechanism and seed mass. The basic model reasonably predicted observed recruitment densities at or near forest edges, except for small seeded, wind-dispersed species with strong establishment constraints, for which it over-predicts. Our dispersal term yielded predictions that were not statistically different from observed colonization. However, species with large seeds and unspecialized dispersal mechanism appear to have distinct thresholds beyond which no dispersal occurs. Further research should better account for establishment constraints among small-seeded species, dispersal constraints among large-seeded species and unspecialized dispersers, and improve the dispersal functions to better reflect vectors such as birds. Nevertheless, the present model is adequate for the prediction of colonization probabilities in fragmented forests, requiring only an estimate of the abundance of source trees of a species and the mean inter-fragment distances.
... Dispersal is the primary mechanism through which species expand their distribution (Clark 1998;Broennimann et al. 2006;Corlett and Westcott 2013), but is often oversimplified in bioclimatic envelope models (Araújo and Peterson 2012). Recent reviews suggest most seeds are dispersed no further than 10-1500 m from the parent plant, with only a small number of seeds (<2-10%) dispersing beyond this distance (e.g., Hewitt and Kellman 2002;Kinlan and Gaines 2003;Corlett 2009). However, there have been relatively few quantitative assessments of actual seed dispersal distance (Vittoz and Engler 2007). ...
... Information is primarily inferred from seed characteristics, spatial patterns of seedlings, or seed rain observations. This information is typically measured in open fields or after forest harvest, but rarely measured in closed forest stands (Greene and Johnson 1995;Clark 1998; but see Hewitt and Kellman 2002). In the absence of quantitative estimates of seed dispersal distance for most species, seed dispersal vector is widely used as a proxy of dispersal ability (documented for 87% of North American trees in TRY, Table 2). ...
... While this may be because of the complexity of expressing dispersal ability through a simple index, or the generally low quality of existing trait information (Angert et al. 2011;Stahl et al. 2014), it is also likely to be caused by our poor understanding of the relative importance of the different traits in this process. Mechanisms apparently unrelated to traits, such as rare long-distance dispersal events (Clark et al. 2003), availability of suitable edaphic conditions (Beauregard and de Blois 2014), fragmentation of the landscape matrix (Hewitt and Kellman 2002), and even the availability and quality of spatial data on the physical environment, are also likely to affect migration-related predictions. ...
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The integration of functional traits into vulnerability assessments is a promising approach to quantitatively capture differences in species sensitivity and adaptive capacity to climate change, allowing the refinement of tree species distribution models. In response to a clear need to identify traits that are responsive to climate change and applicable in a management context, we review the state of knowledge of the main mechanisms, and their associated traits, that underpin the ability of boreal and temperate tree species to persist and (or) shift their distribution in a changing climate. We aimed to determine whether current knowledge is sufficiently mature and available to be used effectively in vulnerability assessments. Marshalling recent conceptual advances and assessing data availability, our ultimate objective is to guide modellers and practitioners in finding and selecting sets of traits that can be used to capture differences in species’ ability to persist and migrate. While the physiological mechanisms that determine sensitivity to climate change are relatively well understood (e.g., drought-induced cavitation), many associated traits have not been systematically documented for North American trees and differences in methodology preclude their widespread integration into vulnerability assessments (e.g., xylem recovery capacity). In contrast, traits traditionally associated with the ability to migrate and withstand fire are generally well documented, but new key traits are emerging in the context of climate change that have not been as well characterized (e.g., age of optimum seed production). More generally, lack of knowledge surrounding the extent and patterns in intraspecific trait variation, as well as co-variation and interaction among traits, limit our ability to use this approach to assess tree adaptive capacity. We conclude by outlining research needs and potential strategies for the development of trait-based knowledge applicable in large-scale modelling efforts, sketching out important aspects of trait data organization that should be part of a coordinated effort by the forest science community.
... Both seed sources have been found important in forest landscape recovery (Schlawin and Zahawi 2008;Kepfer-Rojas et al. 2014;Seidl et al. 2014;Kemp et al. 2016). Seed dispersal is a spatial and stochastic process which links the propagules from the seed sources to the disturbed landscapes using abiotic (e.g., wind, gravity) or biotic (e.g., mammal, bird) means (Willson 1993;Hewitt and Kellman 2002;Levin et al. 2003;González-Varo et al. 2017). ...
... Spatial configuration of seed sources (e.g., distance), parent tree abundance, and species life-history traits (e.g., age of reproductive maturity, number of seeds produced, seed dispersal mechanisms) are also important in forest landscape recovery (Turner et al. 1998;Hewitt and Kellman 2002;Kepfer-Rojas et al. 2014;Horáčková et al. 2016;Tautenhahn et al. 2016). Seed sources in close proximity can expedite the recovery rate (Kepfer-Rojas et al. 2014), whereas seed sources beyond a certain threshold have little effect on forest landscape recovery (Kepfer-Rojas et al. 2014;Kemp et al. 2016). ...
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Context The rate and trajectory of forest landscape recovery after a volcanic eruption rely largely on available seed sources and patterns of seed dispersal. However, quantifying the importance of various seed sources has not been attempted. Objectives We demonstrate a forest landscape modeling framework for spatiotemporal reconstruction of post-volcanic-eruption forest landscape. We quantify the effects of remnant seed sources on post-eruption forest landscape recovery at tree species level in Changbai Mountain, China. Methods We used a factorial experiment of modeled scenarios with/without remnant seed sources and/or matrix seed sources. We applied the modeling framework to reconstruct the post-eruption forest landscape from 1710 to 2010. Results Remnant seed sources’ contribution to basal area and density was minimum before year 1810 and 1770, and increased to maximum at 1940 (51%) and 1840 (79%), respectively. Remnant seed sources contributed > 40% to stand age from 1740 to 1870. Remnant seed sources’ contribution to species area was minimum at 1760 for all species, while it increased to > 40% at 2010 for some late-successional species. Conclusions Remnant seed sources have relatively small effects in the early stage of post-volcanic-eruption forest landscape recovery. This is different from what has been reported of other disturbances such as wind and fire. Remnant seed sources facilitate late-successional species recovery, advance forest succession, and increase stand age. These findings coincide with reports of other types of disturbances. Spatiotemporal historic landscape reconstruction provides a platform to simulate seed dispersal and quantify the roles of remnant seed sources on post-disturbance landscape recovery.
... The species found in the quadrats were identified with the help of standard text materials (Floras of Chhattisgarh & Madhya Pradesh, Handbook of Weeds of Chhattisgarh, flora/ encyclopedia ;Hooker 1875;Pullaiah 2006;Singh et al. 2010). Raunkiaer's frequency class (Raunkiaer 1934) analysis was used to assess the rarity or commonness of the tree species (Hewit and Kellman 2002). ...
... As per Raunkier frequency law, the herbaceous vegetation was heterogeneous in nature as most of the cases, class C, D and E, were absent. This may be attributed towards biotic interference as well as floral poverty (Hewit and Kellman 2002;Kumar et al. 2017;Khan et al. 2019b). ...
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Adjoining areas of urban environment has undergone rapid alteration in structure, composition and ecological changes, which makes them a dynamic entity. During the present investigation, herbaceous vegetation were studied in east, west, north and south directions of Ambikapur township at various seasons during March 2017 to April 2018. A total of 18 species representing 11 families were recorded at various directions of Ambikapur township in different seasons. Asteraceae was the predominant family in the study area. Highest species counts were recorded during summer season. Among the herbaceous vegetation, more than two-thirds of the herb species were exotic in nature, revealing the anthropogenic role towards loss of indigenous species. Highest species density was recorded in north direction (152,000 herb/ha during rainy, 104,000 herb/ha in winter and 184,000 herb/ha in summer) and lowest in south direction (90,000 herb/ha during rainy, 72,000 herb/ha in winter and 88,000 herb/ha in summer) in all seasons. Higher Shannon diversity (2.71 in rainy, 2.69 in winter and 3.07 in summer) and richness (0.67 in rainy, 0.52 in winter and 0.66 in summer after west direction) were recorded in the north direction. Total biomass, C storage and CO2 mitigation were found to be highest towards north direction in all seasons. Argemone mexicana, Cassia tora, Ocimum tenuiflorum and Sida acuata are the most suitable species in terms of C storage, CO2 mitigation under urban setup. Beside, some weed species also reflected significant potential. CO2 mitigation by herb species can act as complimentary system towards climate cane adaptation beside other vegetal layers. Such studies are also very much effective towards development of greenery in an urban setup leading to climate mitigation process.
... Radius used in the final models were those that for different size classes showed values close to the significance level of the variable within the model. When the contribution of the different radius was similar, values closest to the distances in which dispersion processes begin to be limiting (i.e., 150-300 m according to Hewitt and Kellman, 2002) were prioritized. Similarly, we plotted "t" values representing the contribution of the distance to the nearest native forest patch against patch size (area). ...
... The native forest cover in a 300 m radius surrounding the sampling units was a better predictor of seedling richness than measures based on the distance to the nearest patch of native forest. It has been observed that in the studied area (Vespa et al., 2014) as well as in other forests (Carlo et al., 2013;Hewitt and Kellman, 2002), only a very small proportion of seeds is dispersed further than 300 m. Igarashi et al. (2016) found that the species richness in a cedar plantation in Japan was correlated with the proportion of native forest within a radius of 300 m for seedlings (plants similar in size to those here called seedlings), and within a radius of 100 m for saplings (plants similar in size to those here called saplings). ...
Article
The interest in the conservation of biodiversity in productive ecosystems has increased considerably in recent years due to the continuing loss of natural vegetation. The effect of forest plantations on biodiversity is currently a relevant research topic since they are expanding worldwide. Native understory vegetation may maintain ecosystem processes and increase the availability of habitats, food and other resources for different animal groups. Native tree regeneration in plantations is affected by the planted species, stand age and density, and silvicultural practices, among others. Despite that some general trends have been identified, results from different studies are not always comparable, partially because not all sources of variation were considered simultaneously, the size of plants is different between studies, no different classes of plant sizes are compared, or the local flora determines specific responses to landscape and stand variables. In this work, we analyzed the relationship between native tree density, species richness and species composition in the understory of forest plantations and stand characteristics including stand age and density, canopy openness, proximity to native forests remnants and pre-planting land use history. The study was conducted in monoculture plantations of Pinus taeda in Misiones Province, Northeastern Argentina. In 35 stands, we estimated plant density and species richness for three plant size classes: seedlings (>50 cm height and <1 cm in diameter at breast height (DBH)), saplings (1–5 cm DBH) and small trees (5–10 cm DBH). Our results are in agreement with general trends previously reported in the study area and worldwide. We found that native trees in the plantations showed a strongly size-dependent response to stand and landscape variables. The composition and richness of the seedlings were primarily dependent on the native forest cover at a landscape scale while the species composition, richness, and density of saplings and small trees were mainly affected by stand age and density. Our results showed that the management of pine plantations should maintain the rotation for more than 20 years, a basal area below 30 m²·ha⁻¹ and a 25–30% of native forest cover at the landscape scale to increase the richness and density of the native trees in loblolly pine plantations of the Atlantic Forest.
... Th is relationship between Tilia populations and shell-midden-infl uenced soils has been demonstrated on back-barrier islands along the coasts of North Carolina, South Carolina, and Georgia ( Whitaker et al., 2004 ;Pigott, 2012 ). Given the limited ability of Tilia to disperse by seed ( Johnson, 1988 ;Hewitt and Kellman, 2002 ) and the large expanses of salt marsh and tidal creeks that separate the islands, it is possible that small Tilia populations on these islands have been isolated from each other for the last 2400 yr due to sea-level rise ( Napolitano, 2012 ). ...
... Rackham (1986) reported that T. cordata growing in ancient woodlands in Suff olk, England, failed to colonize adjacent secondary woodlands that were established in the 1600s. Similarly, Hewitt and Kellman (2002) found that T. americana growing in a mature hardwood forest in southern Ontario failed to colonize adjacent pine plantations beyond 25 m. Th e seed bracts are considered to function in wind dispersal of the fruits. ...
Article
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PREMISE OF THE STUDY: Sprouting in woody plant species allows for the long-term persistence of small, isolated populations experiencing changing environments and can preserve genetic diversity in these populations despite the infrequent recruitment of sexually produced individuals. We examined demographic data collected over a 10-yr period for Tilia americana var. caroliniana populations in the context of genetic structure as an empirical case study of this concept. METHODS: Two back-barrier islands on the Georgia coast of the United States were completely censused for T ilia americana var. caroliniana. Recruitment, growth, and mortality of all stems were tracked over 10 yr. All genets were genotyped using eight nuclear microsatellite loci to assess population genetic structure among sampled stems and among populations in the region. KEY RESULTS: The two island populations differed in their ability to establish seedlings despite having similar patterns in flowering frequency. Seedling mortality was high throughout the 10 yr, and cycling of ramets within genets was common. Long-term recruitment in this system appears to be primarily a result of vegetative growth via basal sprouts. Genetic structure was limited, both between islands and among populations in the region. CONCLUSIONS: Long-lived woody species that persist by vegetative reproduction may unexpectedly influence regional forest responses to climate change, particularly on the trailing edge of a species’ distribution.
... Most studies of pollen and seed dispersal follow one of three methodologies: ecological observation, genetic analysis, and dispersal modeling. Ecological observation studies have included using pollen and seed traps (Wright, 1952;Wang et al., 1960;Nathan et al., 2000;Hewitt and Kellman, 2002), tracking dispersed items (Iida, 1996;Pons and Pausas, 2007), and observation of dispersers and offspring (Johnson, 1988;Lindgren et al., 1995;Gomez, 2003). Genetic analysis studies of dispersal use the relationships between individuals to develop estimates of dispersal curves and distances for pollen and seeds (Shen et al., 1981;Dow and Ashley, 1998;Streiff et al., 1999;Gonzalez-Martinez et al., 2002;Grace et al., 2004;Austerlitz et al., 2007). ...
... Wright, 1953, Iida, 1996and Vander Wall, 2003 or evidence of object movement, such as pollination due to the transport of pollen grains (Lindgren et al., 1995). These types of studies typically describe dispersal through the development of dispersal curves (Wright, 1952(Wright, , 1953Wang et al., 1960;Johnson, 1988;Nathan et al., 2000), or distance-based descriptions of movement (Lindgren et al., 1995;Iida, 1996;Hewitt and Kellman, 2002;Vander Wall, 2003;Pons and Pausas, 2007). The dispersal curves provide a quantification of the dispersed objects along a distance axis (with the height of the curve representing the amount of dispersant transported a certain distance from the point of origin, while the studies with distance-based descriptions typically only provide an average distance of dispersal and observed dispersal distance limits). ...
Article
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The Modifiable Areal Unit Problem (MAUP) is a famous issue in spatial analysis that states the output of a spatial analysis is influenced by the spatial extent of the units used in the analysis. This study demonstrates that the MAUP is accompanied with another intractable spatial issue in spatial modeling; the Modifiable Conceptual Unit Problem (MCUP). The MCUP states that the conceptualization of spatial processes impacts the output of spatial analysis and occurs when a model with one spatial dimension is applied to a spatial model with more than one spatial dimension. This study demonstrates the MCUP by developing three conceptual models of dispersal and showing how they produce different results even when given the same initial dispersal curves and areal units. Three conceptual models of dispersal (sum of curve points model, area of distance range model, and the volume of distance range model) are described and applied to a grid landscape with a single point of dispersal and a grid landscape with multiple points of dispersal. A Geographic Information System (GIS) is used to evaluate how the models differ in their distribution of pollen or seeds across the landscapes. The three models of dispersal are each valid conceptualizations of the dispersal process, but when given the same dispersal curve parameters, they produce different distributions of dispersed items across grid landscapes. The sum of curve points model is the least complicated model because it only uses a few points from the defined dispersal curve. The area of distance range model uses the entire dispersal curve, but is based on a single dimension of space and thus conceptually abstracted from the grid landscape. The volume of distance range model uses the two spatial dimensions present in the grid landscape and thus is the most conceptually sound model of the three. The underlying conceptualization of the dispersal process can impact the results of dispersal models. Applying dispersal curves with one spatial dimension to grids with two spatial dimensions makes inherent assumptions about the conceptualization of dispersal. This study highlights the necessity of researchers to declare their conceptual models of dispersal when applying modeled dispersal curves to grid landscapes.
... Wind-dispersed seeds generally have limited dispersal capacity inversely related to seed size, while animal-dispersed seeds do not show a clear relationship with propagule mass. Small animals tend to avoid recent clearings, restricting the dispersal range of relatively large walnut fruits by rodents to within 50 m seed trees (Hewitt and Kellman 2002). In contrast, birch species (Betula spp.) produce small seeds that can travel long distances, aided by wind movement along the snow surface (Houle 1998). ...
Chapter
Stand regeneration after harvesting is driven by complex interactions between ecological factors and extrinsic elements (seed/propagule availability, soil characteristics, light, water and nutrient levels, species autecology, plant–plant interactions, predation, browsing, etc.). By modifying stand composition and structure and affecting the soil, harvesting interacts with these factors to influence regeneration establishment. These interactions can be illustrated by examining natural regeneration in three contrasting forest ecosystems. Conifer-dominated boreal stands are typically harvested using clear-cutting approaches that mimic large natural disturbances. Natural regeneration is dependent on the presence of advance regeneration (mainly of layer origin) or germination of seeds on exposed mineral soil. The cold climate, thick organic horizon, and ericaceous vegetation act as filters of regeneration establishment. In contrast, broadleaf-dominated stands of temperate ecosystems are often harvested through single-tree selection or gaps. Regeneration established prior to cutting (often of relatively shade-tolerant species) then takes advantage of increased light availability. Seed predation, browsing, and competition by tolerant or intolerant competing species affect regeneration success of many desirable intermediate-tolerant species. Finally, natural regeneration of Mediterranean forests after harvest is rather variable and highly dependent on microsite characteristics and the climatic conditions following treatments. In these ecosystems, conferring seedling protection from drought by the use of shelterwood or partial cuttings is commonly needed for successful regeneration establishment.
... To assess the most appropriate management strategies for natural regeneration, we need to identify the composition and con guration of landscapes that enable or obstruct frugivore seed dispersal into open areas [33][34][35][36]. Recent evidence highlights the correlation between landscape forest cover and forest regeneration [37]. ...
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Forest restoration is fundamental to overcoming biodiversity crises and climate change. However, restoration success remains challenging. In tropical forests, animals can improve forest recovery as they disperse > 70% of tree species. Until now, representing animals in restoration and climate change policies remains challenging because we lack a quantitative assessment of their contribution to forest and carbon recovery. Here, we used individual-based models to assess frugivore-mediated seed rain in open areas along a fragmentation gradient. Movements of large birds were limited in landscapes with > 40% forest cover, although small birds continued to disperse seeds. Large birds disperse seeds from late-successional species with higher carbon-storage potential. Therefore, their restricted movement reduced by 35% the potential carbon that can be absorbed. Maintaining forest cover > 40% is essential to optimize animals' contribution to restoration success. In contrast, active restoration (e.g., planting trees) is required in fragmented landscapes to achieve carbon and biodiversity targets.
... Such factors are positively correlated with the disperser community abundance and composition (Bael et al. 2013;Falcão et al. 2018), and many authors suggest the benefits for seed rain and seedling recruitment (Chazdon et al. 2009;Tambosi et al. 2014). Accordingly, assuring connectivity between reference habitats and restoration sites would be essential as the lack of propagules could impede restoration of taxonomic and functional diversity (Hewitt & Kellman 2002;Ib añez et al. 2014). In this line, as expected, our analysis also revealed that "highly degraded" sites often showed "unsuccessful" restoration for all biome types, as duration and severity of the disturbance reduce propagule availability and create competitive environmental conditions for regeneration (Martínez-Ramos et al. 2016). ...
Article
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Animal‐mediated seed dispersal is envisaged as a key process to promote forest restoration success. Yet, we lack a comprehensive knowledge of the contribution of intrinsic and extrinsic factors which directly and indirectly influence this process and, ultimately, restoration outcomes. Here, we reviewed 157 articles to identify the most relevant intrinsic (e.g., plant and animal species traits) and extrinsic (e.g., connectivity) factors which mediate the seed dispersal process. We analyzed the contribution of such factors to restoration success, as identified in the reviewed articles, globally and for tropical and temperate biomes. Generally, our analysis revealed that the main factors affecting restoration success were the extrinsic ones (i.e., connectivity, type of restoration conducted, forest protection and disturbance degree), while the ability of animals to achieve long distance dispersal was the main intrinsic factor. Differences among biomes were observed for extrinsic factors, specifically for restoration approach, as more intense efforts seem to be needed for successful restoration in tropical systems (i.e., reconstructive restoration), whereas assisted restoration (e.g., perch placements) was mostly enough for temperate ones. Within intrinsic factors, rodent frugivory and “large‐sized” seeds were related to unsuccessful restoration in tropical forests, while frugivory by carnivores and “small‐sized” seeds favored restoration in temperate ones, and the main constraint to success in this biome was ungulate frugivory. Our results highlight the importance of distinguishing between intrinsic and extrinsic factors mediating animal seed dispersal in forest restoration in different biomes. Furthermore, this paper will help to promote adequate measures when planning restoration actions. This article is protected by copyright. All rights reserved.
... Quantitative community characteristics such as frequency, density, abundance and importance value index (IVI) of each plant species were determined, following Misra (1968) and A/F value (Whiteford, 1949). The resultant frequency values were classified into frequency classes following Raunkiaer, 1934 frequency class analysis, such as: class A (1%-20%), class B (21%-40%), class C (41%-60%), class D (61%-80%) and class E (81%-100%) (Hewit and Kellman, 2002). ...
... Whit ford' s index = Abundance( A)/ Frequency( F) if A/F ratio:< 0.025 :Regular distribution; 0.025 -0.05 :Random distribution, > 0.05 :Contagious or clumped distribution Raunkiaer frequency class analysis was performed to examine the rarity or commonness of the tree species 12 . In this classification, the percentage frequency of the species was classified as A, B, C, D, and E, where A represents rare (0-20%), B represents low frequency (20-40%), C represents intermediate frequency (40-60%), D represents moderately high frequency (60-80%),and E represents high frequency or common (80-100%) (See table 3). ...
... Our results showed different abundances of oak juveniles between sites, with higher abundances at the southern sites (CA) (Table 4; Figure 2). It is known that the distance to the source and the structure of the seed source influenced the propagule input into new habitats [79][80][81]. In our study sites, all the abandoned croplands are surrounded by native forests. ...
Article
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Land abandonment is a major global change driver in the Mediterranean region, where anthropic activity has played an important role in shaping landscape configuration. Understanding the woodland expansion towards abandoned croplands is critical to develop effective management strategies. In this study, we analyze the colonization pattern of abandoned croplands by Quercus pyrenaica in the Sierra Nevada mountain range (southern Spain). We aimed to assess differences among populations within the rear edge of the Q. pyrenaica distribution. For this purpose, we characterized (i) the colonization pattern of Q. pyrenaica, (ii) the structure of the seed source (surrounding forests), and (iii) the abundance of the main seed disperser (Eurasian jay, Garrulus glandarius). The study was conducted in five abandoned croplands located in two representative populations of Q. pyrenaica located on contrasting slopes. Vegetation plots within three habitat types (mature forest, edge-forest and abandoned cropland) were established to compute the abundance of oak juveniles. The abundance of European jay was determined using data of bird censuses (covering 7 years). Our results indicate that a natural recolonization of abandoned croplands by Q. pyrenaica is occurring in the rear edge of the distribution of this oak species. Oak juvenile abundance varied between study sites. Neither the surrounding-forest structure nor the abundance of jays varied significantly between study sites. The differences in the recolonization patterns seem to be related to differences in the previous- and post-abandonment management.
... Study about the different ecological parameters of vegetation highlights the present environmental conditions of the soil environment. Modifications of the abiotic issues can contribute to spontaneous shifts in community composition (Hewit and Kellman 2002). Streblus asper and Senna siamea reflected the highest IVI value in the present study. ...
Article
Mining activities cause substantial decimation of environment and biological diversity. Plant populations are disrupted by the operation of coal mining. The present study deals with the ecological assessment of tree species and physicochemical properties of soil in the Dhandardihi coal mining area of Raniganj Coal Field (RCF), West Bengal, India. For this purpose, three coal mine generated wasteland were randomly selected from the Dhandardihi coal mining area. A sum of 23 different tree species belonging to 22 genera and 16 different families were recorded. Most of the tree species showed rare or lower frequency class. Shannon diversity index was varied from 2.224 to 2.572. The findings of the Canonical Correspondence Analysis (CCA) indicated that the available nitrogen and phosphate content of the soil were the factor which heavily impacted the composition of tree species in the study area. The study indicated that Streblus asper and Senna siamea can be recommended for effective eco-restoration of the concerned sites due to cosmopolitan distribution, high regeneration potential with stable population structure. The findings could be used as an impactful means for predicting the suitability of specific species to revegetate mined regions. Even further, the findings suggest adverse effects of the mining operations on the area’s vegetation. Those actions really need to be monitored regularly along with suitable policies should be framed in terms of eco-restoration of mined wastelands based on indigenous vegetation.
... Distance from seed source is a major determinant of regeneration success for all tree species (Clark et al., 1999;Nathan & Muller-Landau, 2000), and was shown to predominate over competition from tree seedlings or neighbouring vegetation in mixed forests in north-eastern France (Dassot and Collet, 2015). Long distances from potential seed sources reduce seedling density according to patterns that may differ among tree species (Clark et al., 1998;Hewitt & Kellman, 2002;Rozman et al., 2015). The dissemination strategies of oak, beech and hornbeam differ (Vittoz and Engler, 2007): beech and oak are barochorous, whereas hornbeam is anemochorous and usually disseminates over longer distances (Vittoz and Engler, 2007). ...
Article
Oak (Quercus petraea (Matt.) Liebl. and Quercus robur L. grouped), European beech (Fagus sylvatica L.) and hornbeam (Carpinus betulus L.) are three major species of western and central European forests. When conditions are suitable for the three species, silvicultural management often favours oak because of its greater economic interest. Forest managers know that beech and hornbeam are strong competitors for oak during the regeneration phase, but the conditions that influence the relative success of the regeneration of the three species growing in mixture are still poorly characterised. The natural regeneration of the three species 20 years after canopy openings was studied based on 108 study sites established in 2001 in French forests impacted by the windstorms Lothar and Martin in 1999. In spring and summer 2018 and 2019, all saplings over 0.1 m in height were counted, species were identified and diameter at breast height (DBH) was measured for all saplings over 1.30 m. The height of the saplings with the highest and median DBH in each plot was recorded for each species. Mixed models were used to analyse the combined effects of former stand type, distance from the edge of the gap and soil conditions on species presence, sapling abundance, DBH and height. The modelling approach highlighted the preponderant role of the initial seed rain on the presence and sapling density of the three species compared to interspecific competition or distance from the edge. The two latter factors had a secondary effect on sapling DBH and height. Beech and hornbeam saplings were more abundant than oak saplings regardless of soil conditions (on average, 3097, 3063 and 344 saplings ha
... Distance to seed source is a major determinant of regeneration success, for all tree species (Clark et al., 1999;Nathan & Muller-Landau, 2000), and has been shown to predominate over competition from tree seedlings or neighbouring vegetation in mixed forests of north-eastern France (Dassot and Collet 2015). Large distance from potential seed sources reduces seedling density, according to patterns that may differ among tree species (Clark et al., 1998;Hewitt & Kellman, 2002;Rozman et al., 2015). The dissemination strategies of oak, beech and hornbeam differ (Vittoz & Engler, 2007): beech and oak are barochory while hornbeam is anemochore and usually disseminates over longer distances (Vittoz & Engler, 2007). ...
Thesis
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In a context where the disturbances could be more severe and/or more frequent, the choice of silvicultural management to be implemented following disturbances comes up against the lack of knowledge of the spontaneous dynamics of regeneration obtained in the context of climate change. From permanent plots installed in France following the storms of 1999, the objective of this study is to analyse the medium-term vegetation dynamics observed within forest gaps, to identify its main determinants and assess the interaction between disturbances and adaptation of plant communities to climate change. The natural tree regeneration, obtained in the post-storm gaps, seems to be sufficient in terms of density and species diversity. Most sites have in average more than 2000 stems ha-1 and 4.4 species present in the stratum greater than 2 m. The few concerning situations have been identified from the young stages of regeneration and have common characteristics: they are old coniferous stands on acidic soil where competing vegetation has been able to develop, inducing regeneration blocking. In these contexts, a silvicultural intervention would have been desirable to promote regeneration. À specific study of the natural regeneration of three major European hardwood species was carried out: oak, hornbeam and beech. We have highlighted a decline in the abundance of oak over time, in favour of the two most competitive species of beech and hornbeam. Oak is still present on 22% of the sites 19 years after the canopy was opened despite its low density. It also shows growth equivalent or even superior to that of hornbeam and beech, suggesting different development strategies between the three species. Nevertheless, in view of the observed dynamics of the oak, without intervention to promote its regeneration, its future seems uncertain in the coming decades. Finally, our study revealed a greater thermophilisation of the plant communities present in forests that have had an open canopy compared to those in undisturbed forests. By stimulating thermophilisation, disturbance thus plays a major ecological role in the adaptation of plant communities to climate change. The importance of large-scale disturbances should therefore not be underestimated, especially in a future climate context where they are likely to intensify.
... Trampling and grazing by livestock may decrease seedling survival (Jansen and Robertson, 2001). Moreover, increased isolation of plant populations within fragmented landscapes will inhibit effective seed and pollen dispersal and thus gene flow among populations and may increase local extinction risk (Hewitt and Kellman, 2002) (see also section 1.2). ...
Thesis
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Worldwide, biodiversity is under pressure from anthropogenic environmental change. In concert, environmental change and modifications of dispersal pathways induce immense and rapid alterations to the geographic distributions of species including range retractions, expansions, shifts, and the invasion into novel regions. Here, rare or declining species vs. invasive species represent the opposite ends of a gradient of demographic success. This habilitation thesis assembles conceptual and empirical research on five phenomena that shape the eco-evolutionary dynamics of natural plant populations under global change: 1) anthropogenic alterations of biotic and abiotic environments, 2) demographic and genetic bottlenecks 3) inbreeding depression and inbreeding x environment interactions, 4) interspecific hybridization between previously isolated taxa, 5) and ultimately altered evolutionary trajectories. In summary, the research assembled in this thesis contributes to a more general understanding of the important role of eco-evolutionary processes for the demographic success and thus management implications of declining and invasive species.
... Whit ford' s index = Abundance( A)/ Frequency( F) if A/F ratio:< 0.025 :Regular distribution; 0.025 -0.05 :Random distribution, > 0.05 :Contagious or clumped distribution Raunkiaer frequency class analysis was performed to examine the rarity or commonness of the tree species 12 . In this classification, the percentage frequency of the species was classified as A, B, C, D, and E, where A represents rare (0-20%), B represents low frequency (20-40%), C represents intermediate frequency (40-60%), D represents moderately high frequency (60-80%),and E represents high frequency or common (80-100%) (See table 3). ...
Article
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The present study is conducted to produce an account of the inventory of plant species, phytosociological characteristics and determination of species diversity of vegetation of Gunjan Ecological Park pit lake, West Bengal, India. Pit lakes are large water body and are generated from abandoned open mines. These pit lakes are not only large water reservoirs but also have rich floral biodiversity which could play a great role in socioeconomic aspect. The vegetation of these pit lakes are also important for rehabilitation. Our principle objective of this paper is to inventory of the embankment and aquatic vegetation and determine the phytosociology and phytoclimate of the study area. Five different sites were randomly taken in various directions of the study area. A total of 50 quadrats were laid down in various directions of the study area to quantify vegetation. During our investigation, we found hundred different embankment tree species representing 41 families and 14 aquatic species of 13 families in the study site. The growth patterns, life form, life span, phytosociology and phytoclimate analysis of plant communities of the study area could reflects the ecological restoration of this region.
... Whit ford' s index = Abundance( A)/ Frequency( F) if A/F ratio:< 0.025 :Regular distribution; 0.025 -0.05 :Random distribution, > 0.05 :Contagious or clumped distribution Raunkiaer frequency class analysis was performed to examine the rarity or commonness of the tree species 12 . In this classification, the percentage frequency of the species was classified as A, B, C, D, and E, where A represents rare (0-20%), B represents low frequency (20-40%), C represents intermediate frequency (40-60%), D represents moderately high frequency (60-80%),and E represents high frequency or common (80-100%) (See table 3). ...
Article
Full-text available
The present study is conducted to produce an account of the inventory of plant species, phytosociological characteristics and determination of species diversity of vegetation of Gunjan Ecological Park pit lake, West Bengal, India. Pit lakes are large water body and are generated from abandoned open mines. These pit lakes are not only large water reservoirs but also have rich floral biodiversity which could play a great role in socioeconomic aspect. The vegetation of these pit lakes are also important for rehabilitation. Our principle objective of this paper is to inventory of the embankment and aquatic vegetation and determine the phytosociology and phytoclimate of the study area. Five different sites were randomly taken in various directions of the study area. A total of 50 quadrats were laid down in various directions of the study area to quantify vegetation. During our investigation, we found hundred different embankment tree species representing 41 families and 14 aquatic species of 13 families in the study site. The growth patterns, life form, life span, phytosociology and phytoclimate analysis of plant communities of the study area could reflects the ecological restoration of this region.
... Quantitative community characteristics such as frequency, density, abundance and importance value index (IVI) of each plant species were determined, following Misra (1968) and A/F value (Whiteford, 1949). The resultant frequency values were classified into frequency classes following Raunkiaer, 1934 frequency class analysis, such as: class A (1%-20%), class B (21%-40%), class C (41%-60%), class D (61%-80%) and class E (81%-100%) (Hewit and Kellman, 2002). ...
... (a) good, if seedlings > saplings > adult; (b) fair, if seedlings > saplings ≤ adults; (c) poor, if a species survives in only sapling stage, but not as seedlings (though saplings may be less, more or equal to adults); (d) none, if a species is absent both in sapling and seedling stages, but present in adults; and (e) new, if a species has no adults, but only saplings and/or seedlings. Raunkiaer's (1934) frequency class analysis was used to assess the rarity or commonness of the tree species (Hewit & Kellman 2002). In this classification, the percentage frequency of the species was classified as A, B, C, D, and E, where A represents rare (0-20%), B represents low frequency (20-40%), C represents intermediate frequency (40-60%), D represents moderately high frequency (60-80%), and E represents high frequency or common (80-100%). ...
... Furthermore, the importance of island area in regulating the occurrence and abundance of species as well as their interactions has been observed (Connor and McCoy 1979). A study based on logistic analysis confirmed that the distance to the mainland pool could be the critical determinant of plant dispersal and species composition rather than the characteristics of the propagules (Hewitt and Kellman 2002). Thus, the plant richness was found to be inversely related to the isolation of an island from the nearest mainland pool (Moody 2000). ...
Article
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The plant–disperser relationship and its key predictors in Indian tropical archipelagos are understudied. East of the Indian mainland (the Eastern coast, EC) are the Andaman and Nicobar Islands (AN, about 1221 km away at the shortest distance), which exhibit a great plant diversity, with 848 unique species. West of the Indian mainland (the Western Ghats, WG) are another group of islands, the Lakshadweep Islands (LD, about 320 km away at the shortest distance), which exhibit less diversity (102 unique species) than do the AN. We compared these two mainland–island pairs (EC–AN, WG–LD), which exhibit different insular isolation conditions, to understand the plant dispersal mechanisms and their determining predictors (plant richness, geographic area, perimeter, elevation, and shortest distance). We found epizoochory (adherence to an animal surface), ornithochory (birds), and hydrochory (water) to be the dominant dispersers of both the pairs. Additionally, the plant dispersal in the WG–LD pair is predominantly driven by anemochory (wind), possibly denoting the effects of the northeasterly trade winds. The major role of biotic dispersers in the EC–AN pair may be explained as resulting from plant dispersal to more remote islands through biotic dispersers being more rapid and efficient. The plant commonality was found to be positively correlated with the plant richness, geographic area, and perimeter; whereas it was negatively correlated with the shortest distance and elevation of the selected mainland–island pairs. Both linear (R² = 0.85) and non-linear (R² = 0.95) regression with maximum accuracy found island plant richness, geographic area, and shortest distance to the nearest mainland pool to be the determinants in explaining plant-dispersal mechanisms. These predictors are important to maintain the habitat suitability and connectivity and thereby support more newly dispersed plants. The plant–disperser relationship (epizoochory, ornithochory, anemochory, and hydrochory) and the key predictors (plant richness, geographic area, and shortest distance) found in this study could be useful for conservation, planning, and monitoring of biodiversity.
... A considerable number of scientific studies have shown that a very large set of variables affects forest regeneration. We list some examples of such variables, non-exhaustively: air temperature [23,24]; moisture [25]; light [26][27][28][29]; aspect [30]; nurse-effect of shrubs or trees [30][31][32]; animal mediated seed dispersal [33,34]; grazing and browsing [23,35]; proximity to seed source [36]; disturbance regimes like those emerging from fire patterns [12,37]; soil nutrients [26,27]; soil organic layer depth [11,38]; soil texture [11]. Modelling forest regeneration is thus challenging, as a vast set of variables is known to possibly affect it. ...
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Persistence of native forests is a global concern. We aimed at unveiling the main factors affecting tree recruitment in Portuguese native forests, modelling sapling data collected during the 5th Portuguese Forest Inventory, for five main Quercus taxa. Zero-inflated count data models allowed us to examine simultaneously (i) the absence of tree recruitment and (ii) the density of tree recruitment. Using Akaike weights, we obtained importance values for 15 relevant explanatory variables. Results showed that seed availability and climatic variables were determinant to understand regional absence of regeneration for all taxa. Seed availability was also an important driver of sapling density, except for Quercus suber. Other variables impacted on regeneration density: grazing hindered Q. suber regeneration; regeneration of Q. rotundifolia and Q. suber was lower in flat areas; recurrent fire hampered the regeneration of Q. robur and Q. pyrenaica; Q. broteroi and Q. pyrenaica showed depressed regeneration in regions where forest plantations abound, while Q. robur and Q. suber seemed selectively protected. We conclude that caution is warranted when analysing pooled data for Quercus spp. regeneration, as different variables affected Quercus taxa differently. Finally, we suggest dedicated management actions to enhance the establishment of new native forests.
... Projected environmental suitability is more strongly correlated with demographic performance than geographic position in several other species, as well (Pironon et al., 2017). (Hewitt & Kellman, 2002). The current distributional boundary of A. utahensis may result from a lag in colonization following glacial retreat, a condition thought to be common in European and North American species (Normand et al., 2011;Qian & Ricklefs, 2007;Svenning, Normand, & Skov, 2008). ...
Article
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A central goal of ecology is understanding the determinants of species’ distributions. “Metapopulation” models for the existence of distributional boundaries predict that species’ geographic ranges arise from the landscape‐scale deterioration of habitat suitability towards the range edge (i.e., niche mechanisms), which simultaneously hinders demographic performance and limits dispersal to suitable habitat beyond the edge (i.e., dispersal limitation). However, few studies have examined both of these mechanisms for the same species by examining abundance and comprehensive measures of demographic performance across the distribution and beyond its boundary. We tested the predictions of metapopulation models for range limits by contrasting abundance, demographic performance, and population growth (λ) of the perennial forb Astragalus utahensis in central and northern range edge populations. We tested for dispersal limitation by transplanting individuals at and beyond the northern range boundary and monitoring their demographic performance. Astragalus abundance and stochastic λ decreased from the range centre to the northern range edge, with stochastic λ falling to or below replacement in range edge populations. However, transplants at some sites beyond the northern range edge survived and reproduced at levels similar to transplants within the range. Thus, in addition to deteriorating conditions at the range edge, dispersal limitation appears to contribute to limiting A. utahensis’ northern distribution. Synthesis. Our results support metapopulation models for range limits by suggesting that decreased demographic performance constrains the viability of range edge populations while contributing to dispersal limitation of Astragalus utahensis’ distribution. Thus, the tandem action of niche and dispersal processes appears to play an important role in constraining this species’ northern latitudinal range.
... Cervids 2002, Terborgh et al. 2008. This process provides the means for most plants to escape of increased seedling mortality under conspecific plants (Janzen 1970, Howe and Smallwood 1982, Schupp 1988, Hammond DS 1998, reduces the effects of inbreeding depression Hardy 2004, Bizoux et al. 2009) and allows the colonization of new habitats (Hewitt andKellman 2002, Brunet 2007). In this context, seed dispersal influences the spatial distribution, regeneration, demography, and genetic structure of plants (Howe and Smallwood 1982, Nathan and Muller-Landau 2000, Herrera 2002, Dennis and Westcott 2006. ...
... Projected environmental suitability is more strongly correlated with demographic performance than geographic position in several other species, as well (Pironon et al., 2017). (Hewitt & Kellman, 2002). The current distributional boundary of A. utahensis may result from a lag in colonization following glacial retreat, a condition thought to be common in European and North American species (Normand et al., 2011;Qian & Ricklefs, 2007;Svenning, Normand, & Skov, 2008). ...
Article
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A central focus of ecology is to understand the conditions under which biotic interactions affect species’ abundance and distribution. Classic and recent studies have shown that biotic interactions can strongly impact local or regional patterns of species abundance, but two fundamental questions remain largely unaddressed for non‐competitive biotic interactions. First, do the effects of these interactions on population performance change predictably with environmental context? Second, to what extent do population‐scale effects contribute to limiting species’ geographic distributions? To address these questions, we experimentally assessed the extent to which pollen limitation and insect seed predators affected the fecundity and projected population growth rate (λ) of the native forb Astragalus utahensis . We studied populations at the centre and northern edge of the latitudinal range of A. utahensis that occur across a gradient in abiotic harshness characterized primarily by declining mean annual precipitation. Supplementing pollen and suppressing pre‐dispersal seed predators increased seed production similarly within A. utahensis populations at the centre and northern edge of the range. Integral projection population models revealed that relaxing these checks on seed production tended to increase λ in most populations, regardless of their location within the range. Synthesis . Our results suggest that pollen limitation and insect herbivores limit population growth in A. utahensis similarly across the centre‐to‐north portion of its latitudinal distribution. However, because A. utahensis population growth barely reaches the level of replacement at the northern range edge, the reduction in λ resulting from these interactions may contribute to limiting expansion at the northern edge of A. utahensis ’ latitudinal range.
... The species found in the quadrats were identified with the help of standard text materials (Regional floras of Chhattisgarh & Madhya Pradesh, Handbook of Weeds of Chhattisgarh, flora/ encyclopedia; Hooker's 1875;Pullaiah 2006;Singh et al. 2010). Raunkiaer (1934) frequency class analysis was used to assess the rarity or commonness of the tree species (Hewit and Kellman 2002). In this classification, the percentage frequency of the species was classified as A, B, C, D, and E, where A represents rare (0-20%), B represents low frequency (20-40%), C represents intermediate frequency (40-60%), D represents moderately high frequency (60-80%), and E represents high frequency or common (80-100%). ...
Article
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Phytosociological study in and around reclaimed coal mine site is an essential requirement for judging restoration impact on a disturbed site. Various studies have been aimed towards assessing the impact of different restoration practices on coal mine wastelands.Plantation scheme in a scientific way is the most suitable approach in this context. During the present investigation, an effort have been made to assess the vegetation dynamics through structure, composition, diversity, and forest floor biomass analysis in and around Bishrampur collieries, Sarguja division, northern Chhattisgarh,India. We have tried to develop strategies for eco-restoration and habitat management of the concerned study sites. Four sites were randomly selected in different directions of the study area. We classified the vegetation community of the study sites into various strata on the basis of height. Two hundred forty quadrats were laid down in various directions of the study area to quantify vegetation under different strata. During our investigation , we found eight different tree species representing four families in the different study sites.The density of the various tree species ranged between 40 and 160 individuals ha−1. The density of sapling,seedling, shrub, and herb ranged between 740 and 1620;2000 and 600 0; 1200 and 20 00; and 484,000 and 612,000 individuals ha−1, respectively, in different directions. The diversity indices of the tree reflected highest Shannon index value of 1.91. Simpsons index ranged between 0.28 and 0.50, species richness ranged between 0.27 and 0.61, equitability up to 1.44, and Beta diversity ranged between 2.00 and 4.00. Total forest floor biomass ranged between 4.20 and 5.65 t/ha among the study sites. Highest forest floor biomass occurred in the south direction and lowest at east direction. Total forest floor biomass declined by 6.19% in west, 13.10%in north, and 25.66% in east direction, respectively. The mining activities resulted significant damage to natural vegetation and its dynamics. The study indicated that Acacia mangium, Cassia siamea, and Dalbergia sissoo can be recommended for effective eco-restoration of the concerned sites due to cosmopolitan distribution, high regeneration potential, as well as existence in the form of various girth classes with stable population structure.
... Seed production by plants is positively correlated to various measures of individual size and for tree species it is proportional to leaf mass, or basal area (Calogeropoulos et al., 2003;Greene and Johnson, 1994;Hewitt and Kellman, 2002b). In this study, stem volume per hectare was used as a measure of seed production capacity because this measure was available in the kNN-data. ...
Article
The seed ecology and regeneration management of birch species in Fennoscandia has been quite thoroughly investigated through decades of forestry research. Nonetheless, there are few methods for precise predictions of spontaneous natural regeneration. In this study a first framework of a model is presented that combines possible seed supply with seed emergence and seedling survival based on GIS data and the results of past experiments. The birch seed supply was calculated by combining spatial data on standing birch volume with birch seed dispersal distributions. The establishment on a site was further estimated based on the effect parameters of soil moisture conditions and soil scarification. This model shows a reduced variance compared to general means of seed supply and partly explains the variation between sites with the same soil scarification treatments. Even though additional management and ecological variables should be incorporated to increase the model’s predictive ability, it could already be of use in practical forestry.
... Rackham (1986) reported that T. cordata growing in ancient woodlands in Suff olk, England, failed to colonize adjacent secondary woodlands that were established in the 1600s. Similarly, Hewitt and Kellman (2002) found that T. americana growing in a mature hardwood forest in southern Ontario failed to colonize adjacent pine plantations beyond 25 m. Th e seed bracts are considered to function in wind dispersal of the fruits. ...
... Few data exist, however, on the use of forest succession elements for management purposes. Remnants of adult individuals and groups of native species, primarily broadleaves (e.g., oak, beech and ma-ple) and/or conifers (such as fir), admixed in pure secondary coniferous stands, can be found both in Europe (Karlsson 2001, Ganz 2004, Kunstler et al. 2004, Stimm & Knoke 2004, Dobrovolný & Tesar 2010a, 2010b and in other parts of the world (Hewitt & Kellman 2002a, 2002b. Their potential for spontaneous reproduction differs depending on climatic, site and stand conditions, as well as the silvicultural strategy. ...
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The conversion of Norway spruce monocultures to mixed forest is a long-term and costly process, and little information is available on the silvicultural use of spontaneous regeneration of native tree species to such purposes. In this context, we focused on the natural expansion of European beech in pure Norway spruce stands currently occurring in central Europe. The study was conducted in three secondary spruce stands with single adult (seed) beech trees growing on acidic sites of the fir-beech vegetation zone in the Bohemian-Moravian Highlands (Czech Republic). The regeneration strategy of beech and spruce (in terms of density and height increment) was studied under different light regimes (expressed using the indirect site factor – ISF) on the forest edge (9.7-41.2% ISF) and within gaps in the forest interior (10.7-20.8% ISF). Beech showed a broad light adaptability, being present under the spruce canopy with high density, depending on the distance from beech seed trees. Sparse beech saplings were found at a distance of more than 100 m from adult beech trees; however, abundant beech regeneration was found up to a distance of 25 m. Contrastingly, the density and growth in height of the spruce regeneration was strongly affected by light conditions. Spruce reached a density higher than beech in the understory where ISF > 17% (i.e., up to a distance of 45 m from the stand edge or within gaps no smaller than 400 m2), and competed with beech in terms of height growth where ISF > 20% (i.e., at the very stand edges). Knowledge of the spatial pattern and the light strategy of both species provided useful information to support the conversion of spruce monocultural stands to mixed spruce-beech forests.
... Studies relating seed arrival (inferred from the occurrence of dispersed seeds) with the characteristics of the neighborhood around deposition sites have revealed significant effects of habitat cover or patch isolation on dispersal (e.g. Hewitt & Kellman 2002;Koh, Reineking, Park, & Lee 2015) as well as different effects of habitat features depending on, for example, the seed dispersal syndrome (e.g. McEuen & Curran 2004;Cramer, Mesquita, & Williamson 2007;Carlo & Tewksbury 2014). ...
Article
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Seed dispersal enables plants to reach favorable sites for population renewal or expansion far from conspecifics. However, the ability of plants to respond to habitat heterogeneity at large spatial scale is strongly mediated by seed dispersal vectors, e.g. animals, which usually restrict seed deposition to sites with specific environmental conditions, and at short distances from source plants. This spatial constraint, together with the technical difficulties of following the movement of seeds in the wild, makes the estimation of plant response to large-scale heterogeneity a challenge. Here, we applied an isotope-based technique to track bird-mediated seed dispersal of two co-occurring tree species in eight replicated landscapes in the Cantabrian Range (N Spain): the hawthorn Crataegus monogyna and the holly Ilex aquifolium. These species bear very similar fruits, partially overlap in the timing of fruit production, and their seeds are dispersed by the same species of frugivorous birds. Thus we expected that landscape structure, as represented by the amount of forest cover in the landscape, would affect the large-scale seed dispersal of neighboring individuals of C. monogyna and I. aquifolium in a similar fashion. Contrary to our expectation though, the effects of forest cover on the dispersal patterns of co-occurring hawthorn and holly were opposite: high forest cover in the landscape decreased large-scale dispersal for hawthorn, but enhanced it for holly. Our results suggest that small differences in the traits of plant and frugivore species, such as phenology patterns, can interact with the distribution of adult plants to generate strong differences in the response to landscape structure through seed dispersal, even for neighboring trees belonging to different species.
... The dispersal capacity of seeds moved by the wind is generally inversely proportional to seed size; for animal dispersal of seeds, there is no clear relationship with propagule mass. Further, small animals will tend to avoid recent clearings; for example, the relatively big (>1 g) fruits of walnut (Juglans) are generally dispersed by rodents no farther than 50 m from the seed tree (Hewitt and Kellman 2002), because these caching animals tend to avoid open spaces. On the other hand, birch species (Betula spp.) produce small (around 1 mg) seeds that can travel large distances as they are blown by the wind along the surface of the snow (Houle 1998). ...
Chapter
This comprehensive handbook provides a unique resource covering all aspects of forest ecology from a global perspective. It covers both natural and managed forests, from boreal, temperate, sub-tropical and tropical regions of the world. The book is divided into seven parts. In this chapter, we summarize the fundamental concepts related to natural forest regeneration dynamics after harvesting. We explore how harvesting disturbs the ecosystem and how it affects and interacts with stand characteristics, soil and environmental properties to influence regeneration success. We then exemplify these concepts by examining the impacts of harvesting and its interaction with key ecosystem properties on natural forest regeneration of three contrasting ecosystems, namely the boreal forest, the temperate deciduous forest, and the dry Mediterranean ecosystems.
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Forest restoration is fundamental to overcoming biodiversity crises and climate change. In tropical forests, animals can improve forest recovery as they disperse >70% of tree species. However, representing animals in restoration and climate change policies remains challenging because a quantitative assessment of their contribution to forest and carbon recovery is lacking. Here we used individual-based models to assess frugivore-mediated seed rain in open areas along a fragmentation gradient. Movements of large birds were limited in landscapes with <40% forest cover, although small birds continued to disperse seeds. Large birds disperse seeds of late-successional species with higher carbon storage potential. Their restricted movement therefore reduced potential biomass in future forests by 38%. Maintaining forest cover >40% is essential to optimizing animals’ contribution to restoration success. Active restoration (for example, planting trees) is required in more fragmented landscapes to achieve carbon and biodiversity targets.
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Climber species tend to provide various important ecosystem services within the habitat condition. Very little study was conducted on climber diversity, biomass, carbon (C) stock, and CO2 mitigation under urban setup. To address this research gap, the present study was conducted to evaluate the phytosociological attributes, diversity, climbing mode, host specificity, and their potential role in combating climate change. The study was carried out across the four directions of Ambikapur in various seasons using a random sampling method. Results revealed 11 species of climbers representing 9 families across the various study sites in different seasons. Most of the climber species were found to be herbaceous vine and woody wine in nature followed by the higher representation of stem twiner as climbing mode. Variation in species diversity across the study sites revealed higher value toward the west direction as reflected by the beta diversity value. Further, species richness and diversity were mostly reported from the east and north direction. The higher biomass, C stock, and mitigation value were recorded for the south direction in various seasons. Species such as Ampelocissus latifolia, Cuscuta reflexa, Cryptolepis buchanani, Ipomoea quamoclit, Mucuna pruriens, and Thladiantha cordifolia reflected higher biomass accumulation followed by C stock and greater CO2 mitigation potential among the observed climber species across various sites in various seasons. The present study highlights the importance of climber species under the urban ecosystem as a potential alternative for regulating the urban ambient environment followed by mitigation of changing climate.
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Seed long-distance dispersal (LDD) is essential to explain plant migration. However, few studies have addressed the magnitude and frequency of LDD events given the difficulty of measuring them in situ. Computational simulation offers an alternative to the in situ methods. In this study we proposed a simulation model of seed dispersal for two anemochoric conifers, which includes wind patterns, seed and tree traits. We proposed and measured 18 dispersal traits for Abies religiosa and Pinus hartwegii and analyzed variation between traits and species through a principal component analysis. We used the Weather Research and Forecasting (WRF) atmospheric simulation model to obtain wind speed and direction data at the study zone (Iztaccihuatl volcano, central Mexico). We performed linear regression models to simulated seed dispersal events considering horizontal wind speed, seed traits and seed release height, and using a mechanistic model, we integrated vertical wind speed and wind direction. Seeds of both species presented similar morphology but were sorted into two groups. The relationship between wing size and seed weight may be a key element to dispersal, as it influences the interaction of the seed with the wind. Although we expected that P. hartwegii, seed traits and higher distribution would promote more and longer LDD events, A. religiosa presented more and longer LDD. The maximum dispersal distance was 105 m for A. religiosa and 64 m for P. hartwegii. Both species showed differences in dispersal capacity, which may be related to their seed traits. The frequency of LDD events indicates that a low proportion of seeds would travel more than 20 m away from the parent tree. This suggests that, under migration scenarios, new trees movement up would take place gradually.
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Urban expansion has been one of the main factors contributing to the reduction and fragmentation of tropical forests, and such urban green areas are crucial for conserving and maintaining local and regional biodiversity. This study assessed different aspects of the seed rain (seed size, seed density, dispersal syndromes, ecological groups) in two urban Atlantic Forest fragments (Jardim Botânico – 11 ha / Mata do Curado – 106 ha) in Recife, northeastern Brazil. We expected that i) the connectivity and large size would reduce the floristic homogenization in Mata do Curado, ii) the continuous human presence would increase the abundance of non-shaded tolerant species, and iii) in the Jardim Botânico the absence of connectivity and small size would reduce the abundance of shade-tolerant species (large seeds). A total of 50 fruit traps were maintained for 12 months at each site, and visits were performed fortnightly to collect seeds. The collected seeds were quantified, measured (length and width), and categorized into dispersal syndromes (zoochoric, anemochoric, autochoric) and ecological groups (shade and non-shade tolerant). 4,621 seeds were collected in the traps across the study period (Jardim Botânico: 1,778, 7 spp. / Mata do Curado: 2,843, 8 spp. plus 18 morphotypes). Overall, large seeds (15.1 mm - 30 mm) were more abundant in the Jardim Botânico. Zoochoric seeds were longer in length and width in the Mata do Curado. As expected, connectivity and size appeared to contribute to the decrease of floristic homogenization, and human presence increased the abundance of non-shade tolerant seeds in the Mata do Curado. In contrast, albeit small and isolated, the Jardim Botânico demonstrated a higher abundance of shade-tolerant seeds. Our results reinforce the urgency of preserving urban forests to conserve regional biodiversity.
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Understanding the effects ofClimateclimate changeClimate change and human activities on fragile mountain ecosystems is necessary to successfully managing these environments under future climateClimate scenarios (e.g., global warming, enhanced aridity). This can be done through the study of paleoecological records, which can provide long paleoenvironmental databases containing information on how ecosystems reacted toClimateclimate changeClimate change and human disturbances before the historical record. These studies can be particularly interesting when focusing on especially warm and/or dry past climatic phases. Biotic (pollen, charcoal) and abiotic (physical, geochemistry) analyses from wetland sediment records from the Sierra NevadaSierra Nevada, southern SpainSpainrecordSouthern spain changes in vegetation, fire historyHistory and lake sedimentation since ~11,700 years (cal yr BP). This multiproxy paleoecological study indicates that maxima in temperatureTemperature and humidity occurred in the area in the Early and Middle HoloceneHolocene, with a peak in precipitationPrecipitation between ~10,500 and 7000 cal yr BP. This is deduced by maxima in water runoff, the highest abundance of tree species and algae and high total organic carbon values recorded in the alpine wetland’s sedimentary records of the Sierra NevadaSierra Nevada during that time period. In the last 7000 cal yr BP, and especially after a transition period between ~7000 and 5000 cal yr BP, a progressive aridification process took place, indicated by the decrease in tree species and the increase in xerophytic herbs in this region and a reduction in water runoff evidenced by the decrease in detritic input in the wetland sedimentary records. An increasing trend inSaharan dustSaharan dust depositionSaharan dust deposition in the Sierra NevadaSierra Nevada wetlands is also recorded through inorganic geochemical proxies, probably due to a coetaneous loss of vegetation cover in North Africa. The process of progressive aridification during the Middle and Late HoloceneHolocene was interrupted by millennial-scale climatic oscillations and several periods of relative humid/droughty conditions and warm/cold periods have been identified in different temperatureTemperatureand/or precipitationPrecipitation proxies. Enhanced human impactHuman impact has been observed in the Sierra NevadaSierra Nevada in the last ~3000 cal yr BP through the increase in fires, grazing, cultivation, atmospheric pollution as well as reforestation by Pinus and the massive cultivation of Olea at lower altitudes.
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Question Which plant community characteristics most consistently vary with prior land use? Location Oak Openings Preserve, Ohio, USA. Methods In 2020, we measured plant communities on 22 sites encompassing three prior land uses: 1) contemporary Quercus forests continuously forested since before the 1930s; 2) former agricultural lands, under cultivation in the 1930s and abandoned 70-80 years before our study and that were unburned; and 3) former agricultural lands also abandoned 70-80 years earlier and that were burned in 2013 prescribed fires. Among the three land uses, we compared 12 plant community variables, categorized into four groups characterizing different sets of community properties (structure, diversity, composition, and conservation values). Results A multivariate combination of the 12 community variables differed among all three land uses, each of the four categories of variables differed between at least two land uses, and 8 of 12 individual variables differed between at least two land uses. Community structure displayed a gradient of decreasing tree canopy and understory plant cover and increasing lichen-moss cover from continuously forested to unburned and burned formerly cultivated sites. Understory plant species richness did not vary with land use, but species diversity was higher on cultivated sites, irrespective of fire history. While all three land uses now contain Quercus tree overstories, each land use exhibited unique understory species composition. Only formerly cultivated sites contained state-listed endangered species. Cultivated sites had a lower proportion of native species cover than did continuously forested sites, but native species still comprised over 90% of the plant cover on cultivated sites. Compared with continuous forests, the soil organic layer (O horizon) was 5× thinner and loss-on-ignition in the 0-15 cm mineral soil 49% (unburned) and 66% (burned) lower on previously cultivated sites. Conclusions Community characteristics varied in their sensitivity to land use history, with species composition among the most sensitive to prior land use. A dense sapling layer of Acer rubrum forming in long-unburned Quercus forests across much of eastern North America was absent in our study on formerly cultivated sites, possibly due to dry, infertile soil. From a restoration and conservation standpoint of the study region’s pre-settlement, frequently burned and open savannas and woodlands, previously cultivated sites may be easier to keep open via prescribed fire. Moreover, perhaps precisely because much of the flora historically developed in open savannas and woodlands which previously cultivated sites on the contemporary landscape most closely mimicked, previously cultivated sites presently contain higher species diversity and more conservation-priority species than do continuously forested sites.
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Habitat fragmentation and isolation are considered important causes of biodiversity loss in cultural landscapes. To counter the negative effects of fragmentation such as reduced connectivity and increased risks of population extinction due to stochastic processes and genetic erosion, it has been proposed to establish linear ecological corridors to facilitate dispersal between isolated habitat patches. We summarise the current knowledge on the potential benefits and limitations of corridors for reducing the negative effects of habitat fragmentation on plant populations. We address the opportunities and problems that are associated with linear corridors and advocate the use of semi-open corridors as an alternative that might overcome some shortcomings of conventional corridors for plants. Observational and experimental studies have found that various types of linear corridors can increase plant dispersal. Other linear structures such as paths, roads and railways and streams may also function to a certain extent as corridors, although mostly for widespread species. Because plants are highly dependent on external agents such as animals or wind to reach new habitats, the effectivity of corridors is strongly influenced by their structural features and suitability for animal dispersers. However, many plant species can only use corridors for long-distance dispersal if they can also use them as stepping stone habitats where they can establish, grow, reproduce and then disperse further. This dispersal critically depends on suitable light conditions and disturbance regimes, and on a sufficient width of a corridor to reduce edge effects. Thus, hedgerows appear to be suitable corridors for some forest species but are too narrow for forest specialists from the interior of woodlands. Corridors do not only have positive effects but may also facilitate the spread of invasive species. Moreover, a potentially underestimated negative effect of linear corridors is that they may actually create new dispersal barriers when they intersect other habitats. For example, linear woodland corridors that intersect grasslands may successfully connect patches of woodland but simultaneously form strong barriers for grassland species and increase the fragmentation of their populations. As an alternative to linear corridors, we recommend “semi-open corridors” that simultaneously connect patches of both open habitats and woodlands and promote the dispersal of species of both types of habitat. This idea is based on the various types of semi-open landscapes in Europe that have been formed by grazing with livestock, resulting in a mosaic of open habitats, groups of trees or shrubs and small woodland patches and are characterised by a high diversity of environmental conditions on a small scale. Wide corridors of such semi-open habitats may avoid the strong edge and barrier effects associated with linear corridors and provide suitable stepping stone habitats for species with different habitat requirements.
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The Chora and Joyalbhanga area is famous for coal mining under Raniganj Coal Field (RCF), West Bengal. These two sites have also known for dense forest. Mining operation has seriously harmed the vegetation and the overall ecosystem of these areas. During the current investigation, 22 species from 15 families were reported at the two sampling locations. Highest and lowest total density values were recorded for and in Chora whereas, and in Joyalbhanga. Pongamia pinnata Streblus asper Azadirachta indica Aegle marmelos Streblus asper and were the two dominant tree species in Chora and Joyalbhanga respectively in terms of IVI (34.39 and 38.13 respectively) Aegle marmelos though in both the wasteland herb and shrub species were more dominant tree species. Agglomerative hierarchical clustering (AHC) analysis indicates the relationship among all species in the study area. It was apparent from the study that clumped type of distribution in both the study sites were prevalent. The phytosociological lists additionally showed the impact of mining activity on the vegetation structure of the mining areas. The study suggested that and , , , and Streblus asper Aegle marmelos Croton bonplandianus Setaria glauca Clerodendrum infortunatum Tephrosia purpuria could be utilized in reclamation process due to their high frequency and higher regeneration capability. The study highlighted the fact that the resulting vegetation assessment might be used as a relevant means of predicting the appropriateness of specific species to revegetate the mined locations.
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An overarching conclusion in the literature is that soil seed banks rarely contain many restoration‐target species and are often liabilities rather than assets to restoration. Our objective was to evaluate composition and spatial variation of seed banks and their potential contributions to restoration, including restoration‐target species such as rare species and those characterizing historical habitats. On 64 sites in a Midwestern U.S.A. oak savanna landscape, we sampled soil seed banks in seven habitat types (restored oak savannas, oak woodlands, and mesic prairies; unmanaged upland oak and mesic forests; and unmanaged and managed pine plantations). The germinable seed bank was exceptionally rich in restoration‐target species. In total for the 64 sites, seedlings of 127 species emerged from seed bank samples. Of the 101 native species, 56 were restoration‐target species, an unusually high number among seed bank studies. Restoration‐target species in seed banks included 13 threatened or endangered species, in addition to 43 other specialist species associated with high‐quality native habitats or on a floral list thought to characterize historical ecosystems. When analyzed across the 64‐site gradient, seed banks differed among the seven habitat types and varied with historical (1939) land use, recent management activities that restored open‐structured habitats, and biophysical gradients of tree density, soil drainage, and soil texture. While not all restoration‐target species were detected in the seed bank, the unusually high‐quality seed bank is a potential asset to restoration and was partly structured along environmental gradients across the landscape. This article is protected by copyright. All rights reserved.
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Mode of seed dispersal is an important trait for understanding geographical distributions, population dynamics, and community composition of plant species. However, data of dispersal modes are scarce for Chinese plant species. Previous studies have shown that growth form, plant height, fruit type, and seed mass have strong correlations with seed dispersal modes, thus predictions using modelling could be an alternative to gain this information. We collected information on growth forms, plant height, fruit types, seed mass, and dispersal modes from 360 kinds of Chinese angiosperm plants, and built a neural network model (NNET), decision tree (TREE), Fisher linear discriminant model (LDA), and support vector machine model (SVM) to predict seed syndromes from these four traits. For each model, an 80% sample (288 species) was randomly drawn from dataset as the training sample, with remaining 20% of data was used as a test sample. Results showed that all four models achieved rather good predictions, and the average total correctness rate for the NNET, TREE, LDA, and SVM was 78.90%, 77.09%, 77.81%, 78.14%, respectively. The neural network model had the highest correctness rates for different dispersal modes, i.e., zoochory (81.32%), autochory (74.90%), and anemochory (81.45%). This paper establishes the basis for the prediction of seed dispersal modes.
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Native vegetation development in forestry plantations may depend on seed dispersal, seed predation and seed germination. These processes may depend on distance to native forest fragments and presence of understory. In this study we evaluated the effect of distance to native forests on seed rain and seed predation and the effect of presence of understory on seed rain, post-dispersal predation and germination in Pinus radiata plantations of Chile. We installed seed traps, Petri dishes with Quillaja saponaria seeds and sowed seeds of this species at different distances to native forest fragments, in plantations with and without understory. The total number of seeds and species richness in the seed rain was negatively correlated to distance to native forests, although only in plantations with understory. The total number of seeds did not vary between plantations with and without understory, but the species richness in the seed rain was higher in the one with understory. Seed predation was not related to distance to native forests, neither was the presence of understory and germination higher in plantations with understory. These results suggest that regeneration of native woody species in plantations is negatively affected by distance to native forest and positively affected by the presence of understory. Thus, forestry management should consider dispersal distances and preservation of understory in plantations in order to improve the biodiversity conservation in forest landscapes.
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The paper presents spatial analysis of sea buckthorn (Hippophae rhamnoides L.) dispersion on outer dumping ground of Belchatow lignite mine. Sea buckthorn very effectively spreads on Outer dumping ground by means of ornitochory creating new specimens even 250 meter from seed source. In open areas a single sea buckthorn colony increases its radius about I m per year, effectively competing with lower vegetation. Huge dispersal abilities of this species could be used during dumping grounds reclamation in the process of directed succession. Due to symbiosis with nitrogen-fixing actinomycete sea buckthorn can fix atmospheric nitrogen which is especially useful on soil-less substrata. Due to high light demands this species is not able to compete with higher trees. In long run sea buckthorn colonies change substratum and retreat leaving space for trees, then it can be seen as succession facilitator.
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Landscape ecology has rapidly established itself as an interdisciplinary research field worldwide in the past few decades. However, diversification in perspectives and approaches has apparently caused some concerns with the “identity” of the field in recent years. For example, Wiens (1999) stated that “landscape ecology continues to suffer from something of an identity crisis,” while Moss (1999) warned that landscape ecology's “healthy, youthful development will be cut off before it matures if it does not recognize and develop its own distinctive core and focus.” As landscape ecologists, we feel that we should not be particularly worried about the identity or the fate of the field. Its identity is to some extent self-defining through the activities that people calling themselves landscape ecologists undertake, and its fate will be determined by its utility and its ability to provide techniques, approaches, and applications which help tackle the complex environmental management challenges facing humanity. However, we do think that, after two decades of rapid developments in both theory and practice, landscape ecology can benefit from a forward-looking introspection.
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We studied the effects of habitat fragmentation on the movements of cotton rats (Sigmodon hispidus), deer mice (Peromyscus maniculatus), and prairie voles (Microtus ochrogaster) living in a fragmented landscape using 7.7 yr (1984-1992) of mark-recapture data. The study area included three kinds of 0.5-ha blocks: single large patches (5000 m(2)), clusters of medium patches (288 m(2)), and clusters of small patches (32 m(2)). We tested three predictions regarding animal movements. First, animals should move longer distances as fragmentation increases. Second, the proportion of animals moving will decrease as fragmentation increases. Third, species will show more movement from putative sources to putative sinks. In support of our first two predictions, all species (except male cotton rats) moved farther, and lower proportions of animals moved, as fragmentation increased. In testing our third prediction, we found no trends, for all species, between patch size and the net number of animals a block either imported or exported, indicating source-sink dynamics were probably not occurring on our study site. Furthermore, animals of all species (except female deer mice) switched more frequently to blocks of larger patches. For prairie voles in the spring and deer mice in the summer, relative abundances among blocks predicted from a Markov matrix model of switching probabilities showed high congruence with the actual abundances, indicating movement and abundances were related. In both cotton rats and prairie voles but not in deer mice, more juveniles and nonreproductive animals switched between blocks than did adults or reproductive animals. Deer mice switched more frequently than did either cotton rats or prairie voles; the latter species switched in similar frequencies. We discuss the implications of our data for modeling and conservation.
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Eurasian red squirrels Sciurus vulgaris in fragmented woodlands had a similar spacing pattern as in large woodlands: females had intrasexual exclusive core-areas, while core-areas of males overlapped extensively with core-areas of other males and with core-areas of females. However, in fragmented woodlands, home ranges (site B) and core-areas (both study sites) were smaller than in large deciduous woodlands. Hence, space use and home range size in habitat fragments are strongly influenced by size and structure of the woodlots and, in case of small woodland patches, by the presence of connecting treerows. Juveniles had very small home ranges prior to dispersal, but home range size increased after the dispersal period. In area B only within-population dispersal was observed, while in area K some juveniles moved to another, nearby, population. Only 20% of weaned juveniles settled near the natal home range.
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The shape of a red cedar seed shadow was determined by counting the number of bird-deposited seeds along a 290-m-long fenceline, situated in an open pasture in SW Virginia. The seed shadow described a negative exponential relationship of density with increasing distance from the fruit source located along the border of the pasture. This seed shadow was similar in shape to seed shadows determined by various other means for endozoochorously generated seed shadows reported in the literature.
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The understory flora of successional forest in the Delaware/Pennsylvania Piedmont zone (USA) is species poor relative to old regrowth stands in the region. Impoverishment may reflect (a) limitations on dispersal of potential colonists, or (b) the unsuitability of successional stands for establishment. To examine the importance of dispersal, herb and shrub distributions were surveyed in successional stands of varying age and spatial arrangement. In successional stands contiguous with species-rich old-regrowth forest, understory species richness declined with distance into the successional stands, implying contagion across the old-regrowth ecotone. Individual species showed evidence of contagion in 67% of site x species combinations. Mean rates of migration ranged from to measurable movement (e.g., Carex laxiflora, Cimicifuga racemosa) to >2 m/yr in some species (e.g., Galium aparine, Potentilla canadensis). Significant differences in rate of migration were observed among seed dispersal modes: ingested > adhesive @? wind @> ants @> none. By contrast, there were no significant differences in rate between clonal and exclusively sexual species. In stands disjunct from old regrowth, the understory was species poor relative to old-regrowth forest due to a lack of species dispersed by ants and spores and those with no obvious dispersal vector. Understory species richness was greater in older disjunct stands and in stands closer to potential sources of propagules than in young and isolated stands, trends that were also noted in distributions of individual species. These results suggest that accessibility to colonists plays an important role in determining understory composition of successional stands. Medium- and long-range migration appears to be an issue of seed and spore dispersal rather than vegetative propagation. The extremely low migration rates of some species threaten their continued existence in the second-growth forest landscape.
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Introduction to the Logistic Regression Model Multiple Logistic Regression Interpretation of the Fitted Logistic Regression Model Model-Building Strategies and Methods for Logistic Regression Assessing the Fit of the Model Application of Logistic Regression with Different Sampling Models Logistic Regression for Matched Case-Control Studies Special Topics References Index.
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A stochastic simulation model of extinction in nature reserves is presented. The model yields clear guidelines for minimizing the probability of stochastic extinction in reserves. Simulation time is crucial to how the risk of extinction changes with fragmentation. For short to moderate time spans the probability of extinction increases exponentially with the degree of fragmentation. When the time span considered is long enough relative to the size of the reserve, the relationship is sigmoidal. With increasing time span or decreasing reserve size the curve gets steeper. Eventually only the sheer incline and ensuing plateau of a truncated sigmoidal curve remains. Consistently, a species is more likely to survive in a continuous tract of natural habitat than in one that is subdivided into isolated parcels. Migration can greatly reduce the extinction probability of species in fragmented reserves. -from Author
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The input of bird-disseminated seeds into four old fields of different structural complexity was examined. Seed input was greatest along the edges of fields. Significantly more seeds were found in a 13 year old field that had structurally complex vegetation, than in a 3-year-old field with a single layer of vegetation. The lower input into the latter field was a function of both low fruit availability and low structural complexity of the field. Similarly, more seeds were found in a 2-year-old field which had artificial structures, simulating saplings, placed in it than in an adjacent control field of the same age. The shape of the structures was not a significant factor in the input of seeds. Timing of seed deposition was correlated with fruit ripening times, relative nutritional value of the fruit and the movements of frugivorous birds. The input of bird-disseminated seeds into fields appears to be directly related to the structural complexity of the vegetation. Woody plants increase the structural complexity of the old fields and serve as recruitment foci for bird-disseminated seeds. Thus, seed deposition by birds influences vegetation pattern, and conversely, the presence of recruitment foci in the vegetation may influence bird dispersal patterns of bird-disseminated seeds.
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This chapter is not merely a recapitulation, but mainly an application serving to discover again a line in evolutionary processes, aided by special data. As a non-taxonomist, I hope not to commit too many sins in proposing thoughts connected with systematics and that Dr. J. F. Veldkamp (Leyden), who sometimes advised me, may forgive them.
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During the Holocene boreal and temperate tree species advanced into deglaciated regions of North America at rates averaging 100-400 m per year. The mechanisms are examined by which shade-tolerant, long-lived and generally slow-growing late-successional tree species (beech Fagus grandifolia and hemlock Tsuga canadensis) were able to extend their ranges rapidly and to invade forest communities. -from Author
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This book had its origin when, about five years ago, an ecologist (MacArthur) and a taxonomist and zoogeographer (Wilson) began a dialogue about common interests in biogeography. The ideas and the language of the two specialties seemed initially so different as to cast doubt on the usefulness of the endeavor. But we had faith in the ultimate unity of population biology, and this book is the result. Now we both call ourselves biogeographers and are unable to see any real distinction between biogeography and ecology.
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The purpose of this study was to gain information on how squirrels respond to nuts buried on prairie-forest ecotones as a means of understanding how squirrels influence the invasions of prairies by nut-bearing trees. Of the three common species of nut-bearing riparian forest trees studied, seedlings of black walnut, Juglans nigra, the species whose nuts are most highly preferred by fox squirrels, Sciurus niger, tended to occur farthest from the forest edge onto the prairie. Squirrels removed walnuts buried in the woods in direct proportion to the density of the nuts buried, rather than in proportion to the distance the nuts were located from a conspecific nut-bearing tree. In contrast, when walnuts were experimentally buried at extremely high densities in prairies next to woods during a good mast year, squirrels removed those nuts more quickly that were nearer to the forest and did not remove nuts buried farther than 9 m from the edge of the canopy. Because walnut seedlings were observed at much greater distances from the forest edge, we speculate that squirrels may bury nuts on open prairies at considerable distances from forest cover in poor mast years, when the benefit of fewer nuts lost to other squirrels outweighs the added risk of predation in the prairie.
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Gray and fox squirrels show similar preferences for various types of natural foods. Their preferences are based on a combination of two factors; the speed with which they can ingest food energy and the digestibility of the food eaten. The two species of squirrels have essentially the same ability to digest their natural foods. However, five species of nuts differ in their digestibility, ranging in percentage of energy assimilated from about 78% for white oak to 95% in shagbark hickory. The squirrels' efficiency in digesting the kernels of different species of nuts is correlated with the lipid content of the kernels. The niche differences between gray and fox squirrels are not based on food preference or feeding efficiency. Instead, they are probably related to differences in foraging behavior and predator escape behavior which adapt fox squirrels to open forests and forest edges and gray squirrels to dense forests. The annual activity pattern of gray and fox squirrels make the hard-shelled nuts of hickory and walnut the most efficient food in fall and spring and acorns the most efficient food in winter. This change in the relative efficiency of foods results in the squirrels acting as dispersing agents for the seeds of both oaks and hickories in mixed stands of trees.
Article
Typical seed caches made in the fall of the year by white-footed mice (Peromyscus leucopus) and red-backed voles (Clethrionomys gapperi) contained 20-30 pine seeds, buried beneath the litter of pine needles and in contact with mineral soil. Many caches were revisited by the mice and their contents destroyed before winter. Most caches not decimated in the fall were invaded the following spring. However, some of them escaped complete destruction and their unconsumed seeds germinated and produced seedlings. Although mice make their caches in micro-environments highly favorable to germination, their subsequent feedings on the stored seeds, both before snowfall and before and during the spring germination period, greatly deplete the number of potential germinants. Therefore, the contribution to forest regeneration of seeds stored by these small forest mammals is probably of minor significance except when bumper seed crops are produced and large numbers of caches are created. Under these circumstances, stored seeds may be of sufficient quantity to exceed food requirements of the mice. If pirating by other animals is low, then a surplus of seeds is left to help regenerate the forest.
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Is there necessarily a trade-off between seed size (mass) and dispersal capacity for wind-dispersed diaspores? Within three families (Pinaceae, Aceraceae, and Leguminosae) with asymmetric samaras, shape is maintained (isometry) despite size change. Consequently, within these three families, equilibrium descent velocity is proportional to samara mass raised to the 1/6 power and, necessarily, larger samaras are more poorly dispersed.
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The major objective of this study was to evaluate the influence of contrasting landscape corridors on population dispersal behavior of feral house mice (Mus musculus). Eight 0.1-ha enclosures were divided into two linear systems of four enclosures each. The two end enclosures of each system were planted in oats (Avena sativa). Two 1-m wide corridors connected the end enclosures. Corridors in one system consisted of strips of unmowed vegetation; corridors in the other system consisted of strips of unmowed vegetation plus a split-rail fence. Trials were conducted in early summer, late summer, autumn and winter. Significantly more mice dispersed in the corridors containing the split-rail fence during late summer and autumn, whereas equal numbers dispersed in both corridors in early summer and winter. Significantly more adult males dispersed than did adult females. Population density was not responsible for differences in dispersal rates observed between the two systems. Results suggest that both the vegetative and man-made corridor components influence the dispersal of small mammals within an agricultural landscape.
Article
Twenty-sevem secondary woods, 32-51 years old, occurring on a limestone hill near Krakow, Poland, were investigated. Twenty-five woods were Scot's pine woods; twelve of them were planted. They differ in area, shape and isolation from the primary woods. 195 species of vascular plants were found in the secondary woods, including fifty-nine small shrub and herb woodland species (out of the seventy woodland species growing in the nearby primary woodlands). Only thirteen woodland species occurred in more than a half of the secondary woods. Statistical analysis included ten independent variables (area, age, shape, distance to primary woodlands, cover of tree and shrub layer, and others) and two dummy variables. The results of a stepwise multiple regression analysis show that the number of all species depends only on area. The number of woodland species is significantly dependent on distance from the source of diaspores, area, shape, age and type of soil. The number of conifer woodland species is independent of wood age, which affects the number of broadleaf woodland species. A close relationship was found between the type of dispersal of woodland species and their distribution in secondary woods. Hovering and flying anemochores and endozoochores are the best colonizers, the worst are heavy anemochores, myrmecochores and barochores. The slow rate of the secondary succession in the study woods is due to poor colonizing ability of many woodland species as well as to the effect of the xeric conditions on the establishment and growth of seedlings.
Article
In both ancient and recent woods the number of species increased with area, probably because of a correlated increase in habitat diversity. The number of species present in part of an ancient wood was not significantly different from the number present in whole ancient woods of equivalent area. The number of species present in recently reduced ancient woods was not significantly different from the number present in ancient woods which were reduced to their present size long ago. Ancient woods were significantly richer than isolated recent woods. Recent woods which have had a physical contact with an ancient wood were significantly richer in species than isolated recent woods, and significantly poorer than ancient woods. The number of species present in recent woods did not increase with age. This was tested in woods originating between 1600 and 1947. Number of species present in recent woods was influenced by habitat diversity. Previous land use influenced which species were present, not how many. Although ancient woods comprised only 25% of all sites (43% by area), 62 of the 174 species recorded had >50% of their localities in ancient woods (= ancient woodland species) and 43 species had <33% of their localities in ancient woods (= recent woodland species). Recent woodland species tended to inhabit disturbed parts of ancient woods; ancient woodland species tended to inhabit undisturbed parts. -from Authors
Article
(1) Trapping, observation and road mortality studies indicated that small forest mammals (e.g. Tamias striatus, Sciurus carolinensis, and Peromyscus leucopus-Rodentia) were reluctant to venture on to road surfaces where the distance between forest margins exceeded 20 m. (2) Wider roads were crossed almost exclusively by medium-sized mammals such as Marmota monax, Erethizon dorsatum (Rodentia), Procyon lotor and Mephitis mephitis (Carnivora). (3) Road mortality increased with increasing road improvement for medium-sized mammals and was highest when traffic density was high and young were emerging. (4) A four-lane divided highway may be as effective a barrier to the dispersal of small forest mammals as a body of fresh water twice as wide.
Article
Black cherry occupies a key position in the dynamics of oak (Quercus spp.) forests in southern Wisconsin. Its relative importance in sapling and small-tree sizes averaged over 50%, and in some stands it was the only species in these strata. Age analysis of 854 cores showed that 58% of all black cherry stems were established between 1931 and 1941. The appearance of large amounts of black cherry in the 1930 decade was the result of drought and livestock-feed shortages. The latter were especially severe in 1934 and 1936 and resulted in large-scale disturbance of forests through grazing and possibly extensive cutting of forests for foliage. The presence of a strong shrub component exerted a major influence on the dynamics of the oak forest. An inverse relationship existed between overstory tree basal area and the importance of shrubs. Although density and cover of tree seedlings were independent of tree basal area and shrub cover, seedling numbers were insufficient for adequate restocking of most stands. In clear-cut forests the shrub layer was extensive, and regrowth of trees was largely confined to stump sprouts. Shrubs in disturbed forests averaged 38,635 stems/acre, 4,535 square inches basal area/acre, and 145.8% cover. In undisturbed forests, shrub competition (average 16,231 stems/acre, 1,036 square inches basal area/acre, and 51.4% cover) largely precluded seedling establishment by tree species, and maximum basal area levels in these forests were not maintained. Growth and survival of black cherry in the understory depended on the complex interaction of environmental factors. Tree overstory basal area and soil available water were the most significant factors controlling its vigor. Suppressed stems of cherry were as old as 60 years. Growth patterns in stem cores showed that stems responded to release after 39 years of suppression. The capacity of black cherry to develop basal sprouts and the occurrence of light intensities greater than 1,200 ft-c in the understory greatly aided its survival in this stratum. The important role of black cherry in the dynamics of the oak forests was based on opportunistic characteristics including widespread dispersal, delayed germination of seeds, and flexible seedbed requirements. Forest conditions, such as the isolation of forests as woodlots, pioneer environmental conditions, and widespread disturbance, predisposed invasion by opportunistic species. Dynamic processes were characterized by general rather than gradient compositional changes. Patterns of replacement were not orderly and predictable, but irregular as a result of chance dispersal and local catastrophe. Although not uncommon in oak forests in the northeastern United States, invasion by Acer saccharum is not occurring in southern Wisconsin. Succession to Acer-Tilia is confined to specific sites. The overall existing pattern is one of increasing diversity typical of many pioneer communities in an early phase of colonization.
Article
Wind is the only important agent of dispersal of E. regnans F. Muell. seed and most seed is disseminated in the direction of the locally prevailing winds. Seed-trapping studies over several years have shown that dissemination is poor from the edge of a dense forest, but much better from isolated trees. The degree to which the local winds are deflected and obstructed is obviously important. It is concluded that adequate coverage of self-sown seed cannot be expected on completely felled areas which are more than two or three chains wide. Adequate distribution of seed from isolated trees probably depends more on amount of available seed than on efficiency of dissemination.
Article
The native Hawaiian flora is analyzed by genera for probable method of arrival of ancestral immigrants, and these data are listed in detail and discussed. Fruit and seed morphology are used as evidence for mode of dispersal interpreted in the light of known dispersal methods. Modes of arrival on the Hawaiian islands are computed as percentages, and similar percentages are presented for angiosperms of other Pacific oceanic islands and archipelagos. These data show that ecology of recipient island is much more important than distance in determining modes of successful transport. On high islands, internal transport by birds is of prime importance, and decreases only slightly with increased distance. On atolls, oceanic drift is of overwhelming importance. Adherence to feathers by barbed or bristly seeds or fruits is of maximum importance on dry volcanic islands. Transport of seeds by air flotation decreases sharply with distance, and thus is responsible for only a few genera on the Hawaiian Islands. To account for floras of oceanic islands, no factors not currently operative seem necessary. Shore birds are cited as a particularly likely vector for transport of fleshy-fruited plant species. Reasons are given for absence of South Pacific drift species in the North Pacific. The great similarity between floras and faunas of the Pacific oceanic islands and those of Mascarene oceanic islands derives from the fact that islands in both the Pacific and Indian oceans have been populated by those groups from Indo-Malaysia capable of long-distance dispersal. The implications of the present data for inter-continental and intracontinental dispersal are discussed, and the implications for hypotheses of continental drift are explored.
Article
A generalized birth–and–death process serves as a simple, flexible model for computing the expected persistence time of a small population in a random world. We may reparametrize the model in ways that allow explicit incorporation of density dependence, random differences in events experienced by different individuals, and random environmental variation experienced by all individuals in concert. This model seems to capture the important features of real population dynamics for purposes of computing the mean persistence time, even though the underlying mechanisms presumed in the mathematics of the model are decidedly unrealistic. The lack of isomorphism between birth and death rates, as they feature in the model, and vital rates of real biological populations can lead to extremely misleading results, if the classic formulation, rather than the reparametrization is applied without due circumspection. Using the reparametrized model, we find that environmental variation poses a greater problem for population persistence than does individual variation. In particular, with purely individual variation, the expected persistence time increases approximately with the power of the ceiling on population size; but with purely environmental variation, the expected persistence time increases somewhat less than linearly with the size of the population ceiling. The birth–and–death process model can also be applied to calculating the persistence time of a population on an ensemble of reserves which are linked by natural migration or by deliberate reintroduction programs. Results of this model, for an idealized ensemble, show that multiple independent reserves with a sufficient recolonization rate (natural or otherwise) will confer a longer persistence time than a single reserve with the same total carrying capacity, but in the absence of recolonization, the system of smaller separate reserves confers a shorter persistence time than the single large reserve.
Book
From the reviews of the First Edition."An interesting, useful, and well-written book on logistic regression models . . . Hosmer and Lemeshow have used very little mathematics, have presented difficult concepts heuristically and through illustrative examples, and have included references."—Choice"Well written, clearly organized, and comprehensive . . . the authors carefully walk the reader through the estimation of interpretation of coefficients from a wide variety of logistic regression models . . . their careful explication of the quantitative re-expression of coefficients from these various models is excellent."—Contemporary Sociology"An extremely well-written book that will certainly prove an invaluable acquisition to the practicing statistician who finds other literature on analysis of discrete data hard to follow or heavily theoretical."—The StatisticianIn this revised and updated edition of their popular book, David Hosmer and Stanley Lemeshow continue to provide an amazingly accessible introduction to the logistic regression model while incorporating advances of the last decade, including a variety of software packages for the analysis of data sets. Hosmer and Lemeshow extend the discussion from biostatistics and epidemiology to cutting-edge applications in data mining and machine learning, guiding readers step-by-step through the use of modeling techniques for dichotomous data in diverse fields. Ample new topics and expanded discussions of existing material are accompanied by a wealth of real-world examples-with extensive data sets available over the Internet.
Article
The study of seed dispersal between the widely separated forest patches (forest islands) of the eastern Great Plains can contribute to understanding effects of deforestation in the more complex forest island landscapes of the eastern United States. In the East, there is growing concern that the dissection of regional forests and the creation of small forest islands surrounded by non-forest uses (e.g., agriculture) may be affecting plant species richness and developmental patterns of vegetation (Levenson 1976), as has already been noted in the tropics (Gomezpompa et al. 1972). Curtis (1956) showed that the presettlement forest area in a portion of Green County, Wisconsin had been reduced by 70% as of 1882,90% by 1902,95% by 1935, and more than 96% by 1950. The effect of distance in altering seed exchange between forest islands has not been directly tested. However, the use of forest islands as study sites has provided some clues about the effects of distance (isolation) on dispersal and forest composition. Scanlan (1975), Tramer and Suhrweir (1975), and Levenson (1976) all noted that the species richness of forest stands in Minnesota, Ohio, and Wisconsin, respectively, was inversely proportional to the degree of isolation from neighboring stands. It is not clearly understood whether the characteristics of deforested landscapes preferentially reduce the abundance of species with certain dispersal characteristics (e.g., heavy animal-dispersed and heavy wind-dispersed seeds).
Article
Insular systems tend to exhibit nonrandom patterns of species composition in which smaller species assemblages contain subsets of those found on richer ones. The fact that such {open_quotes}nested{close_quotes} patterns of species composition have usually been observed in systems where species number is correlated with island size has led to the hypothesis that differences among species in the effect of island size on the probability of extinction represent the main mechanism producing nested patterns of species composition. This study tested the hypothesis that differences among species in dispersal ability may interact with geographic isolation to produce nested subsets of species composition. This hypothesis was tested in a system of woody plants inhabiting artificial islands that were created by the filling of the Clarks Hill Reservoir, Georgia, USA. All of the studied islands had been logged prior to their separation from the mainland and their species number 34 yr later was found to be negatively correlated with distance to the closest mainland. The results of the present analysis indicated that (1) species occupancy of the whole island system was highly nested, (2) nestedness occurred with respect to geographic isolation but not with respect to island size, (3) only a small portion of the overall species included in the study contributed to the observed nestedness, and (4) the degree to which individual species contributed to the observed nested was correlated with their dispersal properties, with wind-dispersed species showing no evidence for nestedness and species lacking adaptations for long-range dispersal showing the strongest patterns of nestedness. These results indicate that isolation effects may interact with species-specific dispersal properties to produce nested subsets of species composition. 27 refs., 2 figs., 3 tabs.
Article
I tested a sexual recruitment model that couples equations for seed production, dispersal, and juvenile survivorship using 10 sets of recent strip cuts in Quebec and New Brunswick. The model states that seed production is dependent on basal area and inversely proportional to seed mass, while juvenile survival is directly proportional to seed mass. In consequence, the seed mass effects should (roughly) cancel out, and fecundity should be primarily a function of basal area. Further, the model predicts that species evenness should be more or less the same following strip-cutting. As expected from the model, the single best predictor (r(2) = 0.53) of recruitment density was the basal area density (area/area) of the source trees, and all cuts were well stocked. There was a stronger tendency toward a post-harvest increase in species evenness than was expected. Ninety percent of all stems were recruited by the fourth growing season.
Article
Histories of changing land use and vegetation of a 380-ha forested area in central Massachusetts (Prospect Hill tract of the Harvard Forest) were reconstructed to investigate the environmental controls over land ownership patterns, agricultural practice and logging activity, and the vegetation response to these land-use factors. Forest clearance and agricultural expansion parallel trends for central New England: increasing rates of deforestation through the late 18th century led to a peak in 1820-80 when more than 80% of the land was open. Reforestation on abandoned fields commenced in 1850 and increased progressively through the early 20th century. Ownership patterns varied temporally in turnover rate and size of individual holdings. twenty-five lots comprising the study area were sold an average of 13 times in the period 1730-1910. Land use in the mid 1800s, formed an intricate pattern best explained by soil drainage and proximity to farmhouses and town roads. This land-use pattern controlled the reforestation process. Regionally, the distribution of modern and pre-settlement forest types match well despite structural changes and the loss of some tree species. At a landscape scale, modern forest characteristics are strongly controlled by land use. Long-term forest trends in the 20th century include a decrease in the importance of Pinus strobus due to logging and the 1938 hurricane, a gradual decline in early successional hardwoods and increase in later successional species. -from Author
Article
In September 1981, many thousands of green Fagus grandifolia nuts were dispersed by Cyanocitta cristata from a woodlot in SE Wisconsin and cached in their former breeding territories. Dispersal distances ranged up to 4km. Jays dispersed an average of 7 nuts per trip, with a range of 3-14. During dispersal trips, jays routinely followed wooded fencerows. This practice allowed for escape from avian predators whose migration coincided with the dispersal period. Jays selected the best nuts for dispersal, because all nuts recovered from jays were sound and most germinated in the laboratory. Only 11% of nuts on seed trees were sound. Dispersal by blue jays may be the primary means by which beech seeds are dispersed to patches of forest without beech trees and which are isolated by human and land uses or by different nutural habitats.-Authors
Article
Natural areas are continuously disappearing. Surviving patches resemble islands in terms of limited area, isolation and distance from each other.Road construction and agricultural activities contribute to habitat isolation. Field studies suggest that roads represent barriers and cut off the gene flow by dividing animal populations into fractions on either side of the road.Several mobility diagrams show significant isolation effects of roads on populations of forest-dwelling mice (Apodemus flavicollis) and carabid beetles.Small habitat islands tend to hold more animal species than expected according to the island biogeographic theory. The ratio is highest in small isolates, indicating continuous movement of individual animals from surrounding agricultural areas resulting in unstable species composition.
Article
(1) White-footed mice (Peromyscus leucopus) and chipmunks (Tamias striatus) moved between a beech-maple wood and connecting fencerows four times as often as they moved between traplines within the wood. They seldom moved between the wood and adjacent perennial grass fields or across the fields. (2) Birds seldom flew directly across open fields between woods. More species of birds moved more frequently between the wood and fencerows than between any other habitats. Wood-nesting birds moved more frequently from well-vegetated fencerows into fields to forage than from an equal length of wood border. Poorly developed fencerow vegetation restricted foraging by wood-nesters into fields. None of tree species diversity, line intercept measures, dendrograms, or foliage height diversity satisfactorily distinguished among the vegetation structure of different fencerows. (3) The results indicate that fencerows connect the wood to the surrounding agricultural mosaic and concentrate the activity of small mammals and birds into a habitat corridor that may relieve the isolating effect of farmland surrounding the wood.
Article
. It is suggested that many plant species often thought of as wind dispersed may in fact be largely dispersed by animals, mostly birds, at larger spatial and temporal scales. This possibility is illustrated by using data on Holocene tree migrations in Europe. It is suggested that exploratory movements, often by young birds, may play an important role in such dispersal rather than the classic return migrations of birds. In the case of European trees there could have been active selection for rapid migrations occurring even in the glacial refugia sites in the mountains of southern Europe. Plant migration rates, and hence the ability to deal with climatic change, may have been lower before the evolution of a diverse avifanua. It is suggested that for many ‘wind dispersed’ seeds the wind dispersal mechanism is adapted to local dispersal (over distances of a few canopy diameters) and larger scale dispersion is due to birds.
Article
Long-distance seed dispersal figures prominently in most plant conservation biology arguments, yet we possess little more than anecdotes concerning the relationship among deposition (seeds/m2), source strength (seeds/m2), and distance. In this paper we derive two simple models for long-distance deposition. The models are tested at the scale of 100–1600 m from the source and found to be within 5-fold of the observed deposition. There is no discernable decline in deposition for the range 300–1600 m. While we hesitate to extend model predictions to greater distances, both the models and the empirical results allow us to assert that rare wind-dispersed species in woodlots (dispersal distance around 1 km) are effectively isolated from one another at the temporal scale of 1000 years. Key words: plant conservation biology, wind dispersal of seeds, metapopulations.
Article
A model of seed dispersal from vegetation islands of variable sizes is presented. The model is developed using an exponential decay of seeds from individual plants, the quantity of seeds produced by each plant and the density of trees within the island. The quantity of seeds dispersed to a given distance from the island is a function of the seed contribution of each plant at their respective distances from this distance. An example using a species of pine (Pinus palustris, Mill.) indicates that a vegetation island of two hectares disperses as many seeds away from the island's edge as larger islands. Many small to intermediate size islands should be more effective at revegetating adjacent land than a few large islands for the same size area left in islands. © 1986.
Article
Aim In fragmented landscapes, the survival of plant populations may depend on sufficient rates of migration between fragments with which to counteract local extinctions. Empirical information on the plant migration process is limited because of the difficulties of directly measuring the rare medium to long‐distance dispersal events involved. The potential for hardwood tree species' seedlings growing in conifer plantations to offer `a posteriori' measures of intermediate to long‐distance dispersal events was evaluated. Location Fragmented eastern deciduous forest in a rural, agricultural landscape, Southern Ontario. Methods To indicate the degree to which plantations `sample' incoming seed, seedling populations were enumerated in plantations and their species composition and abundances compared with those of mature trees, the presumed seed sources, in the surrounding landscape (to 150 m distance). To further quantify the degree to which hardwood seedling populations in plantations represent seed input, seeds of twelve hardwood species were sown in pine plantations and their emergence and early seedling survival monitored for 2 years. A subset of four of these species was planted in hardwood woodlots and their survival compared with survival in plantations to indicate how well seedlings in plantations reflect colonization in deciduous forest fragments. Results Hardwood seedling populations in plantations comprised the majority of tree species present in the surrounding landscape. Species' seedling abundances were significantly related to tree abundances around plantations. These findings indicate that most hardwood species can establish in plantations and do so in approximate proportion to the amount of seed supplied. All species produced first year seedlings in plantations, but rates of seedling survival were variable, ranging from under 5 to over 40% per species. Large‐seeded species had significantly greater seedling survival than smaller‐seeded species, suggesting that seed size—survivorship relationships could be used to adjust seedling frequencies to measure seed rain. Mean light levels photosynthetically active radiation (PAR) were significantly higher in plantations than in hardwood woodlots, yet rates of early seedling establishment were comparable between plantations and woodlots for four experimentally sown species. Main conclusions Hardwood seedlings in plantations appear to provide reasonable, although conservative, measures of dispersal to forest fragments, albeit with certain qualifications including adjustments for species' establishment abilities.
Article
Seed dispersal is important both to plant fitness and to plant population structure. We suggest that the tail of the seed dispersal curve is at least as important biologically as the modal portion of the curve, and we present a relatively simple, four-parameter model, based on diffusion principles, for the tail of the seed distribution. This model includes two types of qualitative behavior: algebraic tails (which tend to be longer and have greater reach) and exponential tails (which are shorter and have less reach). We have selected 68 data sets from the literature, each giving a seed shadow that could be categorized statistically as (1) exponential, (2) algebraic, (3) neither, or (4) both models fit adequately. Algebraic shapes for seed-shadow tails were common in this sample, and tail behavior was not generally specific to a particular dispersal mode. This result may suggest that algebraic tails are generally favored by selection and can be achieved by several means, but limitations of existing data sets and of statistical methodology preclude final judgement. Smaller complete samples of seed distances would provide a better basis for the analysis of tails than do the present form of data sets (consisting of counts of seeds in discrete distance categories).
Article
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, 11.32.8 m high, 21.423.3 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 (255249 seeds/m2/fall) followed by snags (14785 seeds/m2/fall) and early successional vegetation (3.04.1 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.