bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spatial pattern and process in forest stands within the Virginia piedmont
Authors: Druckenbrod Daniel L. , Shugart Herman H. , Davies Ian 
Published: February 2009

Abstract. Question: Underlying ecological processes have often been inferred from the analysis of spatial patterns in ecosystems. Using an individual‐based model, we evaluate whether basic assumptions of species’life‐history, drought‐susceptibility, and shade tolerance generate dynamics that replicate patterns between and within forest stands.Location: Virginia piedmont, USA.Method: Model verification examines the transition in forest composition and stand structure between mesic, intermediate and xeric sites. At each site, tree location, diameter, and status were recorded in square plots ranging from 0.25 to 1.0 ha. Model validation examines the simulated spatial pattern of individual trees at scales of 1–25 m within each forest site using a univariate Ripley's K function.Results: 7512 live and dead trees were surveyed across all sites. All sites exhibit a consistent, significant shift in pattern for live trees by size, progressing from a clumped understorey (trees ± 0.1 m in diameter) to a uniform overstorey (trees > 0.25 m). Simulation results reflect not only the general shift in pattern of trees at appropriate scales within sites, but also the general transition in species composition and stand structure between sites.Conclusions: This shift has been observed in other forest ecosystems and interpreted as a result of competition; however, this hypothesis has seldom been evaluated using simulation models. These results support the hypothesis that forest pattern in the Virginia piedmont results from competition involving species’life‐history attributes driven by soil moisture availability between sites and light availability within sites.
Short‐term changes affecting regeneration of Fagus crenata after the simultaneous death of Sasa kurilensis
Authors: Abe M. , Miguchi H. , Honda A. , Makita A. , Nakashizuka T. 
Published: February 2009

Abstract. Question: The aim of the present study is to determine whether seed/seedling predation will increase and Fagus survival will decline with the recovery of the Sasa cover.Methods: We examined Fagus crenata regeneration for seven years in an old‐growth Fagus‐Sasa forest near Lake Towada, northern Japan, by examining the effects of simultaneous death of Sasa, tree canopy gap formation, mast seeding of Fagus and seed and seedling predation by rodents on the survival of Fagus seeds and current year seedlings. We established four types of sites differing in forest canopy (closed or gap) and Sasa status (dead or alive) following the simultaneous flowering and death of Sasa kurilensis (dwarf bamboo) in 1995.Results: Fallen Fagus seed was abundant in 1997 and 2000 (mast years). In sites with alive Sasa, survival from the first growing season was low due to high seed and seedling predation. In sites with dead Sasa, seed survival under the canopy was high for both mast years, but in gaps it varied between years. Seedling survival was highest in canopy gaps with dead Sasa (gap‐dead) in 1998, because of higher light levels and lower predation by rodents. However, seedling survival in these plots was low in 2001, apparently because rapid Sasa recovery favoured rodent predation. In both mast years, Sasa die‐back had significant positive effects on seed and seedling survival under closed canopies because the seedlings there were more successful in escaping predation.Conclusion: The change in successful sites for the early stage of regeneration of Fagus appears to reflect the combined effects of canopy gap, seed/seedling predation and revegetation of Sasa.
Recruitment limitation along disturbance gradients in river flood plains
Authors: van Eck W.H.J.M. , van de Steeg H.M. , Blom C.W.P.M. , de Kroon H. 
Published: February 2009

Abstract. Question: Along river floodplains lower distribution limits of plant species seem largely determined by their tolerance to rarely occurring floods in the growing season. Such distribution patterns remain fixed for many years suggesting additional effects of winter floods at lower positions. Our objective was to investigate the direct and indirect effects of winter floods on colonization of floodplains in a series of field experiments.Location: River Rhine, The Netherlands.Methods: We measured the direct effects of winter floods on seedling survival and seed removal and survival at low and high floodplain elevation. Indirect effects of winter flooding through changes in the soil were investigated by measuring seedling emergence on soil transplants that were exchanged between high and low floodplain elevation. To investigate indirect effects of floods on the germination environment through changes in the vegetation structure, we measured the effects of vegetation removal on recruitment of sown species.Results: Recruitment was seed limited at both floodplain elevations. An additional effect of vegetation removal on seedling emergence was also observed. Soil types from both zones did not differently affect seedling emergence. Seeds were not removed from the soil surface by a single winter flood. Moreover, seeds remained viable in the soil for at least two years, while the experimental plots were flooded several times during the experimental period. During one of those floods a thick sand layer was deposited at the low zone and subsequently no seedlings were observed anymore.Conclusions: Colonization of low floodplain zones in years between subsequent summer floods is prevented by seed limitation while the direct effects of winter floods are limited except for irregularly occurring sand depositions.
Dynamic tree aggregation patterns in a species‐poor temperate woodland disturbed by fire
Authors: Davis Mark A. , Curran Claudia , Tietmeyer Andrea , Miller Andy 
Published: February 2009

Abstract. Question: How does fire affect the aggregation patterns of trees in a species‐poor oak woodland?Location: East‐central Minnesota, USA.Methods: More than 10 000 trees with DBH > 2 cm (comprising more than 11 000 stems) were monitored in a 16‐ha grid on an annual basis from 1995‐ 2001 in a species‐poor temperate woodland. Different portions of the grid experienced different frequencies of controlled burns. Aggregation indices were calculated for individual species and individual size classes within species. A community‐wide aggregation index was also calculated for different burn units. Spatial data were managed, and many of the aggregation indices calculated using a GIS ArcInfo™ (ESRI).Results: Fire initially increased clumping, although repeated fires reduced it, a finding that suggests a corollary to the intermediate‐disturbance hypothesis, the corollary stating that intermediate levels of disturbance are expected to maximize community‐wide patterns of aggregation. Analyses also showed that all species are aggregated at small scales, that the degree of aggregation of a stem type (species or size) declines with distance from individual stems, that the degree of aggregation of large stems is usually less than that of small stems, and that rare species are more aggregated than common species. Findings from this study are consistent with those from similar studies in other temperate and tropical forests, woodlands, and savannas.Conclusion: The spatial patterns of trees in this woodland are dynamic, continually changing in response to the relative strengths of the often opposing forces of competition, which tends to reduce clumping, and disturbance, which, at low and intermediate frequencies, tends to increase it.
Mycorrhiza and seedling establishment in a subarctic meadow: Effects of fertilization and defoliation
Authors: Pietikäinen A. , Kytöviita M.‐M. , Vuoti U. 
Published: February 2009

Abstract. Question: How does changing resource availability induced by fertilization and defoliation affect seedling establishment and mycorrhizal symbiosis in a subarctic meadow?Location: 610 m a.s.l., Kilpisjärvi (69°03’N, 20°50’E), Finland.Methods: A short‐term full‐factorial experiment was established, with fertilization and defoliation of natural established vegetation as treatments. Seeds of two perennial herbs Solidago virgaurea and Gnaphalium norvegicum were sown in natural vegetation and their germination and growth followed. At the final harvest we measured the response in terms of arbuscular mycorrhizal (AM) colonization, biomass and nitrogen concentration of the seedlings and the established vegetation.Results: Germination rate was negatively affected by defoliation in the unfertilized plots. The shoot biomass of S. virgaurea seedlings was reduced by the defoliation and fertilization treatments, but not affected by their interaction. In G. norvegicum, the germination rate and the seedling shoot biomass were negatively correlated with moss biomass in the plots. In the established plants the arbuscular colonization rate was low and defoliation and fertilization treatments either increased or did not affect the colonization by AM fungi. In the seedlings, the colonization rate by AM fungi was high, but it was not affected by treatments. Both seedlings and established plants were colonized by dark septate fungi.Conclusions: Reduction of plant biomass by herbivores can have different effects on seedling growth in areas of high and low soil nutrient availability. The weak response of AM colonization to defoliation and fertilization suggests that AM symbiosis is not affected by altering plant resource availability under the conditions employed in this study.
Safe sites for tree regeneration in wooded pastures: A case of associational resistance?
Authors: Smit Christian , Béguin Daniel , Buttler Alexandre , Müller‐Schärer Heinz 
Published: February 2009

Abstract. Question: Are tree saplings in wooded pastures spatially associated with specific nurse structures or plants that facilitate tree sapling survival?Location: Wooded pastures in the Jura Mountains, Switzerland.Methods: In two sites, 73 km apart, we sampled 294 plots of 4 m2, systematically distributed on 1 ha. We recorded number and height of all established Picea abies saplings (> 1 a of age and up to 40 cm in height), and visually estimated cover of rocks, shrubs, tree stumps, overhanging tree branches and unpalatable plant species.Results: Despite differences in site characteristics, we found overall positive effects of cover of unpalatable plants, rocky outcrops and tree stumps on the density of Picea saplings. Plots with tree stumps and higher cover of rocky outcrops and unpalatable plants were more likely to contain Picea saplings.Conclusions: Unpalatable plants, rocky outcrops and tree stumps seem to form safe sites for Picea saplings in this grazed system, improving their establishment and survival. Our findings support the idea that associational resistance drives the dynamics of wooded pastures, but experimental evidence for this hypothesis is still required.
Long‐term changes in semi‐arid vegetation: Invasion of an exotic perennial grass has larger effects than rainfall variability
Authors: Clarke Peter J. , Latz Peter K. , Albrecht David E. 
Published: February 2009

Abstract. Questions: This paper examines the long‐term change in the herbaceous layer of semi‐arid vegetation since grazing ceased. We asked whether (1) there were differences in the temporal trends of abundance among growth forms of plants; (2) season of rainfall affected the growth form response; (3) the presence of an invasive species influenced the abundance and species richness of native plants relative to non‐invaded plots, and (4) abundance of native plants and/or species richness was related to the time it took for an invasive species to invade a plot.Location: Alice Springs, Central Australia.Methods: Long‐term changes in the semi‐arid vegetation of Central Australia were measured over 28 years (1976–2004) to partition the effects of rainfall and an invasive perennial grass. The relative abundance (biomass) of all species was assessed 25 times in each of 24 plots (8 m × 1 m) across two sites that traversed floodplains and adjacent foot slopes. Photo‐points, starting in 1972, were also used to provide a broader overview of a landscape that had been intensively grazed by cattle and rabbits prior to the 1970s. Species’abundance data were amalgamated into growth forms to examine their relationship with environmental variation in space and time. Environmental variables included season and amount of rainfall, fire history, soil variability and the colonization of the plots by the exotic perennial grass Cenchrus ciliaris (Buffel grass).Results: Constrained ordination showed that season of rainfall and landscape variables relating to soil depth strongly influenced vegetation composition when Cenchrus was used as a covariate. When Cenchrus was included in constrained ordination, it was strongly related to the decline of all native growth forms over time. Univariate comparisons of non‐invaded vs impacted plots over time revealed unequivocal evidence that Cenchrus had caused the decline of all native growth form groups and species richness. They also revealed a contrasting response of native plants to season of rainfall, with a strong response of native grasses to summer rainfall and forbs to winter rainfall. In the presence of Cenchrus these responses were strongly attenuated.Discussion: Pronounced changes in the composition of vegetation were interpreted as a response to removal of grazing pressure, fluctuations in rainfall and, most importantly, invasion of an exotic grass. Declines in herbaceous species abundance and richness in the presence of Cenchrus appear to be directly related to competition for resources. Indirect effects may also be causing the declines of some woody species from changed fire regimes as a result of increased fuel loads. We predict that Cenchrus will begin to alter landscape level processes as a result of the direct and indirect effects of Cenchrus on the demography of native plants when there is a switch from resource limited (rainfall) establishment of native plants to seed limited recruitment.
Multi‐scale patterns and bush encroachment in an arid savanna with a shallow soil layer
Authors: Wiegand Kerstin , Ward David , Saltz David 
Published: February 2009

Abstract.Question:Bush encroachment (i.e. an increase in density of woody plants often unpalatable to domestic livestock) is a serious problem in many savannas and threatens the livelihood of many pastoralists. Can we derive a better understanding of the factors causing bush encroachment by investigating the scale dependency of patterns and processes in savannas?Location:An arid savanna in the Khomas Hochland, Namibia.Methods:Patterns of bush, grass, and soil nutrient distribution were surveyed on several scales along a rainfall gradient, with emphasis on intraspecific interactions within the dominant woody species,Acacia reficiens.Results:Savannas can be interpreted as patch‐dynamic systems where landscapes are composed of many patches (a few ha in size) in different states of transition between grassy and woody dominance.Conclusions:In arid savannas, this patchiness is driven both by rainfall that is highly variable in space and time and by inter‐tree competition. Within the paradigm of patch‐dynamic savannas, bush encroachment is part of a cyclical succession between open savanna and woody dominance. The conversion from a patch of open savanna to a bush‐encroached area is initiated by the spatial and temporal overlap of several (localized) rainfall events sufficient forAcaciagermination and establishment. With time, growth and self‐thinning will transform the bush‐encroached area into a matureAcaciastand and eventually into open savanna again. Patchiness is sustained due to the local rarity (and patchiness) of rainfall sufficient for germination of woody plants as well as by plant‐soil interactions.
Long‐term dynamics of the long‐lived conifer Libocedrus bidwillii after a volcanic eruption 2000 years ago
Authors: Ogden J. , Fordham R.A. , Horrocks M. , Pilkington S. , Serra R.G. 
Published: February 2009

Abstract. Question: Following a volcanic eruption of ca. 232 AD, known as the Taupo eruption, the emergent conifer Libocedrus bidwillii expanded on Mt. Hauhungatahi, upwards above the current tree‐line, and downwards into the mixed montane forest. We ask: (1) if current age‐structures at different altitudes support the patterns predicted by the temporal stand replacement model, with cohort senescence and progressively depleting recruitment at ca. 600 year intervals (average cohort age) since the eruption: and (2) if the case history of the population sheds light on the persistence of mixed conifer‐hardwood forests in general.Location: Mt. Hauhungatahi, Tongariro National Park, New Zealand.Methods: The species composition and structure of seven stands covering the altitudinal range of Libocedrus bidwillii, were quantified. Libocedrus trees were cored, and regression equations used to predict ages. Cohorts were identified.Results: Libocedrus densities and basal areas, and the abundance of seedlings and saplings, peaked at different altitudes. At the species’lower limits there has been no recruitment for ca. 550 years, and the angiosperm Weinmannia racemosa has gained dominance. In the tree line and sub‐alpine forest stands, a low level of continuous regeneration has been boosted by periodic cohort recruitment following exogenous disturbances.Conclusions: In the montane zone, the Libocedrus age structure, and its replacement by Weinmannia, are consistent with a model of depleting cohorts separated by ca. 600 years since the Taupo eruption. At higher altitudes more frequent disturbances and reduced competition have allowed Libocedrus persistence. Comparison with other studies suggests long‐term relationships between gymnosperms and angiosperms are mediated by the scale and frequency of disturbance.
Simulated distribution of vegetation types in response to climate change on the Tibetan Plateau
Authors: Song Minghua , Zhou Caiping , Ouyang Hua 
Published: February 2009

Abstract. Questions: What is the relationship between alpine vegetation patterns and climate? And how do alpine vegetation patterns respond to climate changes?Location: Tibetan Plateau, southwestern China. The total area is 2500000 km2 with an average altitude over 4000 m.Methods: The geographic distribution of vegetation types on the Tibetan Plateau was simulated based on climatology using a small set of plant functional types (PFTs) embedded in the biogeochemistry‐biography model BIOME4. The paleoclimate for the early Holocene was used to explore the possibility of simulating past vegetation patterns. Changes in vegetation patterns were simulated assuming continuous exponential increase in atmospheric CO concentration, based on a transient ocean‐atmosphere simulation including sulfate aerosol effects during the 21st century.Results: Forest, shrub steppe, alpine steppe and alpine meadow extended while no desert vegetation developed under the warmer and humid climate of the early Holocene. In the future climate scenario, the simulated tree line is farther north in most sectors than at present. There are also major northward shifts of alpine meadows and a reduction in shrub‐dominated montane steppe. The boundary between montane desert and alpine desert will be farther to the south than today. The area of alpine desert would decrease, that of montane desert would increase.Conclusions: The outline of changes in vegetation distribution was captured with the simulation. Increased CO2 concentration would potentially lead to big changes in alpine ecosystems.
Variation in leaf traits through seasons and N‐availability levels and its consequences for ranking grassland species
Authors: Al Haj Khaled Raouda , Duru Michel , Theau Jean Pierre , Plantureux Sylvain , Cruz Pablo 
Published: February 2009

AbstractQuestion:Are leaf dry matter content, specific leaf area and leaf life span relevant plant traits to discriminate the fertility gradient in species‐rich natural grasslands? In other words, is species ranking conserved when nitrogen availability or growing periods change?Location:Toulouse Research Centre, France; 150 m a.s.l.Methods:Fifteen grasses and nine dicotyledons were sown in pure stands in a random block design with three replicates. Each species was cultivated at two levels of nitrogen supply, limiting and non‐limiting for growth, with three replications per nitrogen level. Leaf traits were measured across both levels of nitrogen supply and growing periods over the year.Results:Leaf dry matter content values separated the species into three life‐form classes (grasses, rosette forbs and upright forbs, P < 0.001). This was not the case for specific leaf area and leaf life span. The three leaf traits were variable across growing periods and nitrogen levels, but the ranking of species was conserved over N‐levels and growth periods. Furthermore leaf dry matter content was always less variable than the other leaf traits.Conclusion:We conclude that leaf dry matter content measured only on grasses could be used as an indicator to describe the N‐richness of the habitat where native herbaceous vegetation develops.
Biomass production, N:P ratio and nutrient limitation in a Caucasian alpine tundra plant community
Authors: Soudzilovskaia N.A. , Onipchenko V.G. , Cornelissen J.H.C. , Aerts R. 
Published: February 2009

AbstractQuestions:1. To what extent is biomass production of a Caucasian alpine tundra plant community limited by soil nitrogen and/ or phosphorus? 2. Can the foliar N:P ratio predict the nutrient limitation pattern of alpine vascular plant communities?Location:Lichen‐rich tundra on Mt. Malaya Khatipara in the NW Caucasus, Russia (43°27’N, 41°42’E; alt. 2800 m a.s.l.).Methods:We conducted a 4–year fertilization experiment (N, P, N+P, lime additions and irrigation) on the alpine tundra in the northwestern Caucasus, Russia. We determined responses of biomass, tissue nutrient concentrations and nutrient pools of the above‐ground component of the plant community.Results:Total plant community biomass did not respond to fertilization. However, lichen biomass strongly decreased in response to the N‐ and N+P treatments, whereas vascular plant biomass increased in response to the N‐ and even more to the N+P treatment, but not to P or lime addition or irrigation. P‐concentrations in vascular plant species were very low, but their biomass production was not principally P‐limited, suggesting adaptation to low soil P‐availability. The N‐limitation of vascular plant biomass production in the community, which in lowlands usually occurs at N:P ratios below 16, could not be predicted from the mean foliar N:P mass ratio in the control (N:P = 29).Conclusions:This Caucasian alpine plant community is an example of N‐ and P‐co‐limitation of vascular plant biomass production, with N being the principal and P the secondary limiting nutrient. Critical N:P ratios as determined for lowland communities are not applicable here.