bluuebunny/crossref_metadata_2025 huggingface dataset:
Seed bank dynamics and tree‐fall gaps in a northwestern Mexican Quercus‐Pinus forest
Authors: Arriaga Laura , Mercado Carmen
Published: February 2009

Questions: How does the seed bank respond to different types of tree‐fall gaps and seasonal variations? How does the soil seed bank influence recovery of the standing vegetation in the mature forest and tree‐fall gaps?

Location: 1800 — 2020 m a.s.l., Quercus‐Pinus forest, Baja California Sur, Mexico.

Methods: Seed size, species composition and germination were estimated under different environmental conditions during dry and rainy seasons: a mature forest plot and gaps created by dead standing trees, snapped‐of f trees and uprooted trees. The soil seed bank was investigated using direct propagule emergence under laboratory conditions, from soil cores obtained during both seasons.

Results: 21 species, 20 genera and 14 families constitute the seed bank of this forest community. Fabaceae, Asteraceae, Euphorbiaceae and Lamiaceae were the most frequently represented families in the seed bank. Floristic composition and species richness varied according to the different modes of tree death. Species composition of seed banks and standing vegetation had very low similarity coefficients and were statistically different. Seed bank sizes varied between 164 and 362 ind.m‐2 in the mature forest plot for the dry and rainy seasons, respectively, while soil seed bank sizes for gaps ranged between 23–208 ind.m‐2 forthe dry season and between 81–282 ind.m‐2 for the rainy season.

Conclusions: Seed bank sizes and germination response were always higher in the rainy season under all the environmental conditions analysed. Results suggest that timing responses to gap formation of the soil seed bank could be more delayed in this temperate forest than expected.
Recruitment limitation in secondary forests dominated by an exotic tree
Authors: Lichstein Jeremy W. , Grau H. Ricardo , Aragón Roxana
Published: February 2009

Question: What factors limit woody plant recruitment in a mosaic landscape where former agricultural lands are dominated by the invasive tree Ligustrum lucidum (Oleaceae)?

Location: Subtropical northwestern Argentina.

Methods: In secondary forest patches, we measured (1) tree, shrub and liana abundance in different size classes; (2) seed rain of Ligustrum and two native trees and (3) topographic, soil and light variables. We used spatial autoregressive models to test for effects of Ligustrum dominance and environment on native plant abundance in each size class. We used multiple regression on resemblance matrices to quantify the relative importance of spatial (e.g. dispersal) and environmental effects on native species composition.

Results: Native tree abundance in the smallest size class was unrelated to Ligustrum canopy dominance, while native tree abundance in larger size classes and native liana abundance were negatively correlated with Ligustrum dominance. Native species composition was both environmentally and spatially structured, suggesting that some species are dispersal limited. Seed rain was spatially correlated with conspecific basal area for one of two native species, but not for Ligustrum.

Conclusions: Native tree recruitment appears to be limited primarily by sapling mortality in patches dominated by the invasive Ligustrum. Ligustrum does not appear to be dispersal limited in our study area and is likely to continue spreading. Invaded patches may persist for hundreds of years.
Distribution and abundance of trees in floodplain forests of the Wisconsin River: Environmental influences at different scales
Authors: Turner Monica G. , Gergel Sarah E. , Dixon Mark D. , Miller James R.
Published: February 2009

Questions: 1. How do physiography, flooding regime, landscape pattern, land‐cover history, and local soil conditions influence the presence, community structure and abundance of overstorey trees? 2. Can broad‐scale factors explain variation in the floodplain forest community, or are locally measured soil conditions necessary?

Location: Floodplain of the lower 370 km of the Wisconsin River, Wisconsin, USA.

Methods: Floodplain forest was sampled in 10 m × 20 m plots [n= 405) during summers of 1999 and 2000 in six 12‐ to 15‐km reaches.

Results: Species observed most frequently were Fraxinus pennsylvanica, Acer saccharinum and Ulmus americana. Physiography (e.g. geographic province) and indicators of flooding regime (e.g. relative elevation and distance from main channel) were consistently important in predicting occurrence, community composition, and abundance of trees. Correspondence analysis revealed that flood‐tolerant and intolerant species segregated along the primary axis, and late‐successional species segregated from flood‐tolerant species along the secondary axis. Current landscape configuration only influenced species presence or abundance in forests that developed during recent decades. Land‐cover history was important for tree species presence and for the abundance of late‐successional species. Comparison of statistical models developed with and without soils data suggested that broad‐scale factors such as geographic province generally performed well.

Conclusions: Physiography and indicators of flood regime are particularly useful for explaining floodplain forest structure and composition in floodplains with a relatively high proportion of natural cover types.
Effects of fire severity in a north Patagonian subalpine forest
Authors: Kitzberger Thomas , Raffaele Estela , Heinemann Karin , Mazzarino María Julia
Published: February 2009

Abstract. Question: What is the relative importance of fire‐induced canopy mortality, soil burning and post‐fire herbivory on tree seedling performance?

Location: Subalpine Nothofagus pumilio forests at Challhuaco valley (41°13'S, 71°19'W), Nahuel Huapi National Park, Argentina.

Methods: We fenced and transplanted soils of three burning severities along a fire severity gradient produced by a fire in 1996. Over two growing seasons we monitored soil water, direct incoming solar radiation, seedling survival, final seedling total biomass and root/shoot ratio. Additionally, we assessed severity‐related changes in soil properties.

Results: Incoming radiation (an indicator of the amount of canopy cover left by the fire) was the primary factor influencing spring and summer top soil water availability, first and second‐year seedling survival and seedling growth. While seedling survival and soil water content were negatively affected by increased radiation, seedling final biomass was highest in very open microsites. Burned soils showed lower water holding capacity and soil carbon; however these changes did not affect topsoil water, and, contrary to expectation, there was a slight tendency toward higher seedling survival on more heavily burned soils. Herbivory significantly reduced seedling survival, but only under high‐radiation conditions. While the effect of radiation on final seedling biomass was not affected by herbivory, R/S ratios were significantly reduced by herbivory in high radiation micro sites.

Conclusions: Despite inducing faster aerial growth, increased radiation and herbivory in severely burned sites may effectively prevent post‐fire regeneration in north Patagonian subalpine forest where seed sources are not limiting.
Determinants of community organization of a South African mesic grassland
Authors: Fynn Richard W.S. , O'Connor Timothy G.
Published: February 2009

Abstract.Question:What is the long‐term influence of nutrient availability, productivity and soil pH on grassland community organization?

Location:Ukulinga research farm, KwaZulu‐Natal, South Africa.

Methods:The influence of fertilization on soil pH, nitrogen (N) and phosphorus (P) on variation in plant traits, community composition and species richness were examined in a 50‐year grassland fertilization experiment.

Results:Averaged over 30 years, above‐ground net primary production (ANPP) was 337, 428 and 518 g.m‐2in sites not fertilized, fertilized with N, and fertilized with N plus P respectively. ANPP depended directly on N‐fertilization but not on P‐fertilization or liming, and responded positively to the interaction of N (first limiting nutrient) and P (second limiting nutrient). Short narrow‐leaved grass species —Themeda triandra, Tristachya leucothrixandSetaria nigrirostris— dominated sites of lowest ANPP where N was limiting (unfertilized, P‐fertilized or limed sites). A tall narrow‐leaved species,Eragrostis curvula, dominated sites of intermediate ANPP where P was limiting (N‐fertilized sites). By contrast, a tall broad‐leaved species,Panicum maximum, dominated the most productive sites where neither N nor P were limiting (N‐ and P‐fertilized sites). Certain species responded to liming and type of N‐fertilizer apparently because of their effects on soil pH. N‐fertilization reduced the density of herbaceous dicots (forbs) from 14 (unfertilized) to two (high N, no P, no lime) and five species per m2(high N, no P, limed). This effect was attributed to increased ANPP and a decrease in soil pH from 4.6 (KCl) in unfertilized sites to 3.49 (high N, no lime) and 4.65 (high N and lime). Soil acidification had no effect on grass species richness but influenced the abundance of certain species.

Conclusions:Grassland community organization is determined not only by the influence of N availability, but also by the hierarchical interaction of N and P availability, in part through their compounded effect on ANPP, and by individualistic species responses to soil pH.
Oscillating vegetation dynamics in a wet heathland
Authors: Urban Katharina E.
Published: February 2009

Abstract. Question: The significance of disturbances caused by periodical inundation was investigated with respect to its effects on vegetation dynamics, species richness and fluctuations, and to the relevance of certain plant properties.

Location and Method: At a sod‐cut stand within nutrient‐poor inland sand dunes, permanent plots along a transect were surveyed over a period of up to nine years after sod cutting.

Results: In contrast to never inundated plots, periodically inundated plots were characterized by low vegetation cover and by high numbers of species belonging to many different communities, each of them with a low cover. Periodical inundations favoured the presence of pioneers, species tolerant of disturbances, species adapted to wet conditions and stoloni‐ferous species. Furthermore, annual fluctuations of species within each plot were higher and most species occurred only sporadically.

Discussion: A comprehensive model is presented describing the relevant processes identified in the littoral zone. Changing water tables result in the creation of gaps. The re‐colonization of these gaps follows mainly from vegetative regeneration and less to the dispersion of diaspores. Highest species numbers in the zone of moderate disturbances result from a high rate of re‐colonization in spite of local extinctions following each disturbance event. It is suggested that colonization abilities are among the most important features for species occurrence at a site rich in disturbances (more important than competitive abilities and more important than a slow rate of displacement). For nature conservation such sites are very important, because they allow (rare) pioneer species to survive for longer periods of time.
The role of the seed bank, seed rain and the timing of disturbance in gap regeneration
Authors: Pakeman R.J. , Small J.L.
Published: February 2009

Abstract. Question: Does the degree and timing of disturbance contribute significantly to the pattern and process of regeneration in plant communities as a consequence of the availability and number of species of propagules present?

Location: Acid grassland at 230 m a.s.l., eastern Scotland, UK.

Methods : Plots were surface disturbed or had their soil profile inverted at monthly intervals at 12 dates during a year. Seed bank and seed rain were assessed at each treatment time. The effect of disturbance intensity and timing on the regenerating vegetation was assessed.

Results: Removing the seed bank significantly slowed regeneration, as it contributed 43 % of developing cover after one year where it was present.

At an individual seed level, seed in the seed rain had a much higher likelihood of contributing to the regenerating vegetation than a seed in the seed bank. Some species showed a reliance on the seed bank for regeneration, and hence there was a significant difference in the vegetation that developed between plots with the seed bank intact and those where it was removed. Winter disturbed plots (little seed rain) had slower rates of re‐vegetation than summer disturbed plots. Timing had little effect on species composition, though a significantly higher cover of perennial forb species developed on the winter disturbed plots.

Conclusion: Removing the contribution of the seed bank had a greater effect on the composition of regenerating vegetation than the effect of seasonal variation on the seed rain.
Contrasting impacts of a native and an invasive exotic shrub on flood‐plain succession
Authors: Bellingham Peter J. , Peltzer Duane A. , Walker Lawrence R.
Published: February 2009

Abstract. Question: How do Coriaria arborea, an N‐fixing native shrub, and Buddleja davidii, a non‐N‐fixing exotic shrub, affect N:P stoichiometry in plants and soils during early stages of primary succession on a flood‐plain?

Location: Kowhai River Valley, northeast South Island, New Zealand.

Methods: We measured soil and foliar nutrient concentrations, light levels, plant community composition and the above‐ground biomass of Coriaria and Buddleja in four successional stages: open, young, vigorous and mature.

Results: Coriaria occurred at low density but dominated above‐ground biomass by the vigorous stage. Buddleja occurred at 5.3 ± 1.0 stems/m2 in the young stage and reached a maximum biomass of 520–535 g.m‐2 during the young and vigorous stages. Mineral soil N increased with above‐ground Coriaria biomass (r2= 0.45), but did not vary with Buddleja biomass. In contrast, soil P increased with Buddleja biomass (r2= 0.35), but not with Coriaria biomass. In early successional stages, 70–80% of the species present were exotic, but this declined to about 15% by the mature stage. Exotic plant species richness declined with increasing Coriaria biomass, but no other measures of diversity varied with either Coriaria or Buddleja biomass.

Conclusion: These results demonstrate that Buddleja dominates early succession and accumulates P whereas Coriaria dominates later succession and accumulates N. A key ecosystem effect of the invasive exotic Buddleja is alteration of soil N:P stoichiometry.
BOOK REVIEWS
Authors: Fargione Joseph E.
Published: February 2009

Abstract. Canham, C.D., Cole, J.J. & Lauenroth, W.K. 2003. Models in ecosystem science. 476 pp. Princeton University Press, Princeton, NJ, USA. ISBN 0‐691‐09289‐3 (paperback). Price: USD $35.00.
Epiphytic macrolichen communities along regional gradients in northern Norway
Authors: Werth S. , Tømmervik H. , Elvebakk A.
Published: February 2009

Abstract.Question:What are the relative influences of human impact, macroclimate, geographic location and habitat related environmental differences on species composition of boreal epiphytic macrolichen communities?

Location:Troms county in northern Norway.

Methods:Detrended Correspondence Analysis revealed the main gradient structure in lists of epiphytic macrolichen species from deciduous forests. By Canonical Correspondence Analysis with variance partitioning, the relative amount of variance in macrolichen species composition attributable to human impact, macroclimate, spatial context and environmental differences was quantified.

Results:There was no significant effect of human impact on species composition of epiphytic macrolichens of deciduous forests. Macroclimate was the most important factor determining epiphytic macrolichen communities, which were also strongly influenced by ecological differences such as forest stand properties.

Conclusions:Epiphytic macrolichen communities are determined by a macroclimatic gradient from the coastline to the interior of central north Norway. In marked contrast, the species composition of epiphytic macrolichen communities seems to be unaffected by human impact in the study area, where air pollution was marginal.
Prediction of plant cover from seed bank analysis in a semi‐arid plant community on gypsum
Authors: Olano J.M. , Caballero I. , Loidi J. , Escudero A.
Published: February 2009

Abstract. Question: Does the seed bank filter annual plant composition and determine cover at the species level?

Location: 510 m a.s.l., central Spain.

Methods: Seven transects and 136 quadrats were established in a semi‐arid gypsum system. Seed bank samples were collected in each quadrat in September. The community was sampled the following April. For each quadrat we measured slope, microslope, landform, elevation, perennial cover and crust cover. Seed bank was estimated using the direct emergence method in glasshouse. Relationship among seed bank and annual community was assessed by Mantel correlations. Above‐ground cover for the five most abundant species was modelled with GLMs.

Results: Seed bank density was the best predictor for annual community cover; perennial cover and landform were also included in the model. Species composition between September seed bank and April annual community cover was also highly related according to the Mantel test. This relationship was constant, even when the effect due to other abiotic (landform, microslope) or biotic (perennial cover, crust cover) parameters were partialled out. Microslope, elevation and seed bank density were the best parameters to predict spring cover of the five most abundant species.

Conclusions: Above‐ground and below‐ground community compartments are strongly related in terms of abundance and species composition. This relationship is filtered by several environmental factors (e.g. perennial cover, landform, microslope) that exert a strong control at community and individual levels. Our results support the hypothesis that annual community performance is affected by seed bank pattern.
On hierarchical diversity decomposition
Authors: Ricotta Carlo
Published: February 2009

Abstract. Question: According to Whittaker's proposal, ecologists have traditionally viewed β‐diversity as the ratio between γ‐diversity and average α‐diversity. More recently, an alternative way of partitioning diversity has been ‘rediscovered’for which β‐diversity is obtained as the difference between γ‐diversity and average α‐diversity. This additive way of partitioning diversity has rapidly become a very popular framework for hierarchical diversity decomposition at various spatial scales. The question for this study is: Can we highlight any relation between these two ways of partitioning diversity, or do these methods really capture different facets of spatial turnover in species composition?

Methods: First the properties that a diversity measure should possess for enabling additive decomposition into α‐, β‐, and γ‐components are reviewed. Next, attention is drawn to the relationships between additive and multiplicative diversity decomposition.

Results: It is shown that the additive model is closely related to its multiplicative counterpart through a simple logarithmic transformation.

Conclusions: Contrary to the current assumption, both methods for partitioning diversity are not as different as they appear. Hence, the supposed superiority of additive diversity partition over multiplicative diversity decomposition is largely unjustified.
Tempo and mode of vegetation dynamics over 50 years in a New Zealand alpine cushion / tussock community
Authors: Mark Alan F. , Wilson J. Bastow
Published: February 2009

Abstract. Question: What are the tempo and mode of long‐term succession and of demographic processes in an alpine community, especially: tenacity, transition patterns, predictions, growth of individual cushion plants, cyclic succession, spatial patterns? Location: A low‐alpine mixed cushion /turf /snow‐tussock / shrub community in southeastern New Zealand.

Methods: The distribution of seven plant cover‐types was recorded at 1024 fixed points in an 8 m × 8 m plot at approximately decade intervals for 50 years. The diameters of eight Donatia novae‐zelandiae cushions were monitored.

Results: The process was essentially first‐order Markovian. There was a change in transition frequencies about 1980. The tenacity of the two major cover types — cushion and turf — was high, but that of cushion decreased about 1980 as some of its area was taken over by turf. The original informal prediction of 1955 that the cushion/turf would increase proved to be correct, probably because of paludification of the site. A prediction of 1987 made from observed transitions that cushion would dominate over turf has proved untrue because of a change in the transition probabilities in the 1980s, of unknown cause. There is a ten‐fold range in diameter growth rates among the eight cushions measured, but the mean rate of 5.3 mm.a‐1 is similar to that reported from other alpine and arctic sites. As cushions aged, turf colonized their centres, and in two cases new cushions colonized into this turf: consistent with cyclic succession. The pattern of transitions was compatible with a general interpretation of cyclic succession, but not definitive.

Conclusions: Change is slow in this alpine community, and tenacity high. The change in transition frequencies about 1980, the invasion of individual cushions, and the decrease in spatial autocorrelation all suggest that cushions established on the site as a result of the clearance of woody vegetation after 1400 AD. Paludification may be causing some loss of tussock grass. A tendency for the cushions to break up, and the shallow peat accumulated below them, may indicate that they are the first generation of cushions on the site. Though these cushions are breaking up, other cushions are establishing, and cushions will continue to be an important part of the vegetation dynamics which may be part of a cyclic succession.
Spatial pattern and neighbour effects onHelianthemum squamatumseedlings in a Mediterranean gypsum community
Authors: Escudero Adrián , Romão Roberto L. , de la Cruz Marcelino , Maestre Fernando T.
Published: February 2009

Question:

Do, in a semi‐arid gypsum environment, neighbours condition the spatial patterns of emergence, survival and height ofHelianthemum squamatumseedlings?

Location:

Vicinity of Chinchón, province of Madrid, Spain (40°11′N, 3° 35′W, 550 m a.s.l.)

Methods:

We evaluated the effects of neighbours on the survival and growth of naturally emergingHelianthemumseedlings in a semi‐arid area during a two‐year period. We followed a two‐fold approach based on the use of neighbour models for seedling survival and growth and spatial point pattern analyses for seedling emergence, taking into account the germination date.

Results:

Seedlings appeared clumped in the vicinity of matureHelianthemumindividuals. The neighbour models fitted showed that interactions with neighbours were extremely important for the survival and growth ofHelianthemumseedlings. These models also suggest that the effects of neighbours on these variables vary with changes in spatial scale and in the abiotic conditions. Some species exerted negative or positive effects onHelianthemumseedlings only at certain spatial scales, and others exerted negative or positive effects at earlier stages of seedling development, but none later andvice versa.

Conclusions:

We suggest that the observed patterns are mainly influenced by small‐scale modifications in soil conditions and microclimate created by neighbours, which change in time and space.
Disturbance history of a European old‐growth mixed‐species forest—A spatial dendro‐ecological analysis
Authors: Splechtna Bernhard E. , Gratzer Georg , Black Bryan A.
Published: February 2009

Question:

We were interested if and how variation in frequency and/or size of disturbances affect the dynamics of a montane old‐growth forest in Central Europe.

Location:

The forest, co‐dominated by Fagus sylvatica, Picea abies and Abies alba, is located in Lower Austria and represents one of the few sizable virgin forests in Central Europe.

Methods:

We extracted cores from 100 trees using systematic grid sampling (grid cell size 10 m × 10 m) on each of four 1‐ha plots distributed across the old‐growth remnant of 300 ha. We inferred disturbance events from rapid early growth and release events. For defining release criteria, we applied the boundary line method. We investigated the spatial structure of current age and gap distributions and past disturbance events in grid cells, using a pair density statistic.

Results:

The disturbance histories indicate decades with peaks and also extended periods without disturbance. Some peaks occurred synchronously at three of the four plots (1910s, 1930s, 1960s and 1980s). Peaks and gaps in the disturbance chronologies widely agreed with peaks and gaps in the age distributions. Most disturbance events during single decades showed a random spatial distribution.

Conclusions:

There is considerable variation in disturbance frequency and/or severity over time. Most disturbance events will rather thin the stand than clear larger areas at once. Following scattered disturbance two pathways occur: (1) gap expansion leading to creation of larger gaps, and (2) gap closure by lateral encroachment or by subcanopy trees growing into the canopy.
Is seed dormancy under environmental control or bound to plant traits?
Authors: Jurado Enrique , Flores Joel
Published: February 2009

Questions:

Is dormancy selected as a means by which a seed defers germination until suitable environmental conditions occur? Are plant species in frost‐free and drought‐free environments less likely to have some form of dormancy than species from environments with frost and/or drought? Are there any relationships between dormancy and three important plant traits: seed size, plant longevity, and growth form?

Methods:

Data from the literature including 3164 species were compiled. We quantified the relationship between dormancy and seed size (1795 species), plant longevity (183 species), and growth form (3164 species).

Results:

Plant species of environments with frost and/or drought were more likely to possess some form of seed dormancy (morphological, physiological, morphophysiological, or physical) than species in more benign environments. Seeds exhibiting some form of dormancy were lighter in weight and generally more prevalent among herbaceous species. Woody plants had a larger proportion of non‐dormant seeds. There was a broad overlap in seed size between species with dormant and non‐dormant seeds. We also found no significant relationship between seed dormancy and plant longevity.
Spatial relationships between tree species and gap characteristics in broad‐leaved deciduous woodland
Authors: Koukoulas Sotirios , Blackburn George Alan
Published: February 2009

Questions:

1. What are the spatial patterns of all trees, individual tree species, trees within particular height classes, all gaps and gaps with specific properties across the study site in broad‐leaved deciduous forest at a range of scales? 2. Are patterns of the above features spatially associated? 3. Are these patterns indicative of gap creation mechanisms and phases of regeneration?

Location:

Frame Wood, New Forest, UK.

Methods:

Ripley'sK‐function analysis was applied to spatial information derived from airborne remotely sensed imagery to characterize the patterns of trees and gaps and to test for spatial interactions between these patterns. The patterns of trees and gaps with specific physical and spatial properties were analysed.

Results:

The pattern of all tree species combined was random for most scales;Quercus roburfollowed the same random pattern, whileFagus sylvaticaandBetula pendulawere clustered over most spatial scales. Large gaps (> 250 m2) and larger trees (> 17.5 m) were randomly distributed, while smaller gaps and smaller trees were clustered. Significant spatial relationships were demonstrated between the patterns of different tree species and between trees within different size classes, as well as between the patterns of trees and gaps with specific properties.

Conclusions:

Small gap patterns and field evidence indicated that progressive gap enlargement is the most likely creation mechanism for large gaps (> 250 m2). Clustered patterns of younger individuals were indicative of patches of past regeneration. As a complement to field‐based data, data derived from remotely sensed imagery provides spatially comprehensive information with which to further investigate woodland stand/community processes and gap dynamics.
Book Reviews
Authors: Jonsson Bengt Gunnar
Published: February 2009

Feldmeyer‐Christe, E., Ghosh, S., Wildi, O., Zimmermann, N.E. & Podani, J. (eds.) 2004. Modern approaches in vegetation monitoring. 143 pp. Akadémiai Kiadó, Budapest, Hungary. ISBN 963‐05‐8183‐3 (hardcover). Price: EUR 70.‐.
Is there limiting similarity in the phenology of fleshy fruits?
Authors: Burns K.C.
Published: February 2009

Question:

Is there evidence for limiting similarity in the timing of fruit production by a bird‐dispersed plant community? Is the rate of fruit removal in each plant species inversely related to fruit availability in other species? Can simple measurements of fruit phenologies (i.e. temporal changes in fruit availability) obscure important fruit attributes that influence their removal by birds?

Location:

Vancouver Island, British Columbia, Canada.

Methods:

Periods of fruit availability were measured in ten woody angiosperm species for two years. In the second year, the fate of individual fruits was quantified to disentangle dates of fruit maturation, removal and mortality from measurements of availability.

Results:

Null model analyses of fruit availability distributions showed no evidence for limiting similarity. However, fruit removal rates of most plant species were correlated with their relative abundance in the community, indicating fruits were removed more rapidly when other fruits were less abundant. Species with similar periods of fruit availability often had different dates of fruit maturation, rates of fruit removal and fruit persistence times, indicating fruit availability measurements can obscure important bird‐fruit interactions.

Conclusions:

Competition for dispersers appears to occur. However, it has not resulted in limiting similarity in fruit availability distributions. A likely explanation for this discrepancy is that fruit availability distributions often confound several important fruit attributes that can independently influence fruit removal by birds.
Effects of fire severity and initial tree composition on understorey vegetation dynamics in a boreal landscape inferred from chronosequence and paleoecological data
Authors: Lecomte Nicolas , Simard Martin , Bergeron Yves , Larouche Alayn , Asnong Hans , Richard Pierre J.H.
Published: February 2009

Question and Location:

How does soil burn severity and early post‐fire tree composition affect long‐term understorey vegetation dynamics in the coniferous forests of eastern Canada?

Method:

Vegetation dynamics were assessed using paleoecological methods and a chronosequence analysis of extant stands. The relation between environmental factors and succession was evaluated using ordination techniques on the chronosequence data. Understorey succession was studied by regression analysis on the chronosequence data and through within‐site Markovian transition probabilities between successive 1‐cm layers of plant macroremains from soil organic matter profiles.

Results:

Initial tree composition (Picea mariana and Pinus banksiana) had little effect on understorey composition. Soil burn severity (measured as the thickness of the residual forest floor humus) significantly affected temporal changes in understorey species. Following fires of high severity, stands underwent a gradual paludification with a net increase in Sphagnum and ericaceous shrubs (Ledum groenlandicum), and a decrease in feathermosses. Paludification was accelerated after low severity fires, which led to the dominance of Sphagnum less than 200 years after fire, and of L. groenlandicum shortly after fire. In situ paleo‐ecological work confirmed results obtained with the chronosequence analysis.

Conclusions:

One vegetation gradient related to time after disturbance is insufficient to account for the full complexity of long‐term changes in understorey composition following fire. Current forestry practices that protect the forest floor humus may induce a premature paludification.
Vegetation change shows generic features of non‐linear dynamics
Authors: Gassmann Fritz , Klötzli Frank , Walther Gian‐Reto
Published: February 2009

Question:

In non‐linear physical, or chemical, systems dynamic instability limits predictability and external fluctuations cause interesting, and sometimes counter intuitive, effects. We ask how these generic properties of complex systems are seen in vegetation change.

Methods:

An interacting particle system is used to simulate possible developments of a plant community that was observed for 30 years on a test area in the Lüneburger Heide (Germany). We investigate simulated trajectories for five plant types over several decades. The internal updating rule, simulating the interactions between the five plant types, is completely deterministic, the only sources of stochasticity being the initial conditions and the external climatic variations.

Results:

Though the results of our simulation model share many aspects with those of stochastic models with probabilistic transition matrices, the solution manifold of our non‐linear model goes beyond the possibilities of stochastic models. Among many stable developments, chaotic trajectories were also found. Climatic fluctuations increased the frequency of certain plant types. These properties of vegetation dynamics match the long‐term field observations. They reflect generic features of complex systems.

Conclusions:

The presented non‐linear model can provide insights into the dynamics of vegetation change, even though the mechanisms observed in the real world are modelled only in a rather general way. The rich behavioural repertoire, resulting from deterministic internal dynamics, can simulate observed properties that are beyond the possibilities of models with probabilistic internal dynamics.
Similarity between seed bank and vegetation in a semi‐arid annual plant community: The role of productivity and grazing
Authors: Osem Yagil , Perevolotsky Avi , Kigel Jaime
Published: February 2009

Question:

Large variation in the similarity between seed bank and standing vegetation generally occurs along environmental gradients. We asked: 1. How is seed bank‐vegetation similarity in Mediterranean semi‐arid annual plant communities related to variation in primary productivity; 2. How is this productivity‐similarity relationship affected by exclusion from grazing.

Location:

Mediterranean, semi‐arid rangeland in the Northern Negev desert, Israel.

Methods:

Density of seeds and plants, and species composition of the seed bank and vegetation were compared in grazed and ungrazed subplots, in four neighbouring topographic sites differing in productivity. Seed bank samples were collected in autumn, just before the rainy season, and vegetation samples in the following spring, at peak above‐ground biomass, when net primary productivity was assessed.

Results:

Quantitative and qualitative similarities between seed bank and the vegetation (Sørensen index values) varied between 0.14–0.61 and 0.40–0.68. Quantitative similarity and productivity were positively and linearly related within the low productivity range (up to 160 g.m‐2), in both grazed and ungrazed subplots. In contrast, at higher productivity levels (up to 500 g.m‐2), similarity decreased slightly with productivity in the ungrazed subplots, but no trend occurred in the grazed subplots. At low productivity, grazing did not affect similarity, while at higher productivity grazing prevented the reduction in similarity with increasing productivity.

Conclusion:

seed bank—vegetation similarity, with and without grazing, is positively related to productivity up to a threshold range, above which soil resource availability is no longer the factor limiting plant density. Above this range grazing prevents a reduction in similarity with increasing productivity, by diminishing vegetation cover and litter accumulation that constrain germination, seedling emergence and plant survival.
Successional replacement mediated by frequency and severity of wind and snow disturbances in a Picea‐Abies forest
Authors: Nishimura Takashi B.
Published: February 2009

Question:

How do wind and snow disturbances affect the successional replacement of Picea glehnii by Abies sachalinensis in a sub‐alpine coniferous forest?

Location:

Cool temperate, northern Japan.

Methods:

Tree demography (growth, mortality and recruitment rates) was determined by repeated measurements of stem diameter and height, and multiple censuses in four Picea‐Abies stands undergoing succession. Above‐ground stand bio‐mass, residence time and tree growth trajectories of the component species were estimated to examine successional changes in structure and dynamics. Individual based simulations were used to examine the effects of disturbances that slowed down succession. Multiple regression analyses were used to determine the relative importance of disturbance frequency and intensity on species composition during succession.

Results:

Above‐ground biomass was larger in P. glehnii than in A. sachalinensis stands, whereas residence time, a proxy of productivity, was much shorter for A. sachalinensis than for P. glehnii populations. During successional replacement, both species increased in initial growth rate and decreased in size‐dependency of growth in canopy gaps. These plastic growth responses were more prominent in P. glehnii than in A. sachalinensis. Disturbance frequency was the most important predictor of species composition in the simulations, and windstorms were more important than snowfall in terms of disturbance intensity.

Conclusions:

The frequency of natural disturbances does not have the potential to initiate stand dynamics but it does, however, slow down succession. When disturbance is locally frequent because of the direction and pitch of the topography, early‐successional P. glehnii stands may persist for thousands of years.
Determinants and spatial modeling of tree β‐diversity in a tropical forest landscape in Panama
Authors: Chust Guillem , Chave Jérôme , Condit Richard , Aguilar Salomon , Lao Suzanne , Pérez Rolando
Published: February 2009

Questions:

The objectives of this study were to clarify the extent to which environmental factors and geographical distance account for tropical floristic composition, and propose a methodology for delimiting the boundaries of floristic types based on species similarity.

Location:

The Panama Canal watershed.

Methods:

To assess which factors (climate, topography, geology and geographical distance) account for floristic composition, we performed Mantel tests on distance matrices and partitioned variation in species composition using canonical analysis. We used a permutation‐based regression model computed on distance matrices and a hierarchical clustering of the tree composition to construct a predictive map of forest types of the Panama Canal Watershed.

Results:

We found that spatial variation alone explained 22–27% of species variation, while the fraction of species variation explained by environmental variables was smaller (10–12%); 13–19% of the variation was accounted for by the joint effect of environmental variation and geographic distance. The similarity‐based map emphasizes the principal division in tree flora between the drier Pacific side and the wetter Caribbean slopes.

Conclusions:

The distribution of Panamanian tree species appears to be primarily determined by dispersal limitation, then by environmental heterogeneity. ‘Environmental segregation’processes do play an important role. Maps of broad‐scale vegetation patterns based on thorough tree inventories can be used in conservation planning in the tropics.
Species responses to experimentally induced habitat changes in a Corynephorus grassland
Authors: Hasse Thilo , Daniëls Fred J.A.
Published: February 2009

Question:

To which extent do external ecological factors effect Corynephorus grassland vegetation?

Location:

Central Netherlands.

Methods:

We implemented different treatments (sand deposition, litter deposition, nitrogen input, mechanical disturbance, control) in permanent plots representing different successional phases in Corynephorus grassland. Plots were recorded just before the treatments and during the subsequent two years. Vegetation changes were analysed by Redundancy Analysis for repeated measurements and Correspondence Analysis, changes in single species abundances by ANOVA.

Results:

Species composition hardly changed during the observation period. Several single species abundances showed significant responses to different treatments, most often decrements as direct effects of cover, removal, or dieback. However, Corynephorus canescens and Polytrichum piliferum benefited from sand deposition, the exotic moss Campylopus introflexus from litter deposition. In the colonization phase Polytrichum, Campylopus and Cladonia diversa increased irrespective treatment. Therophytes such as Spergula morisonii showed the strongest negative response to drought, grasses (e.g. Corynephorus canescens) and bryophytes (e.g. Polytrichumpiliferum) were less susceptible. Most lichens did not respond at all.

Conclusions:

The experiment confirms the high stability of Corynephorus grassland vegetation. Most vegetation changes are in accordance with the hypothetical series of successional phases. In contrast, changes in abundance of single species express considerable dynamics within the vegetation. Species responses also depend on extreme weather conditions as well as on the successional phase of the grassland vegetation and therefore on the competition situation.
Estimating epiphytic macrolichen biomass from topography, stand structure and lichen community data
Authors: Berryman Shanti , McCune Bruce
Published: February 2009

Question/Location:

We modelled lichen epiphyte biomass in relation to topography, stand structure, and lichen community composition in the central Cascades of western Oregon.

Methods:

Sampling was stratified by stand structure. Epiphyte biomass was estimated based on lichen litter for three functional groups: cyanolichens, forage lichens, and matrix lichens. Regression models for estimating lichen biomass (log10kg.ha‐1) were developed based on three pools of predictors, each pool demanding different levels of effort to obtain the data. First, we created models from topographic predictors that are easily extracted from GIS data. We then developed models based on both topographic and stand‐structure variables. Finally, we developed models using topography, stand structure, and lichen community data.

Results/Conclusions:

Lichen biomass changed with elevation, cyanolichen biomass highest at low elevations (470–950 m) and forage lichen biomass highest at higher elevations (950–1470 m). Lichen biomass was lowest in even‐aged young stands and highest in mature stands with remnant trees and in old‐growth. Stands with remnant trees had more lichen biomass than even‐aged stands.

Models with the greatest explanatory power were: cyanolichen biomass predicted as a function of elevation, stand age index, the sum of Lobaria oregana and L. pulmonaria abundance, and cyanolichen species richness (R2= 0.85); forage lichen biomass predicted as a function of stand age index and, Alectoria sarmentosa abundance (R2= 0.55); and matrix lichen biomass predicted as a function of stand age index and matrix lichen abundance (R2= 0.58). These models are useful tools for understanding and predicting the distribution of epiphytic macrolichen biomass at a landscape scale.
Forest lichen communities and environment—How consistent are relationships across scales?
Authors: Will‐Wolf Susan , Geiser Linda H. , Neitlich Peter , Reis Anne H.
Published: February 2009

Question:

How consistent are relationships of forest lichen community composition with environmental variables across geographic scales within region and across regions?

Location:

Northwestern continental USA and east central continental USA.

Method:

Four macrolichen data sets were compiled using identical plot sample protocol: species abundance estimated in 0.4‐ha permanent plots on a systematic grid, as part of government (USDA‐FS) forest inventory programs. One data set in each region represented a large area; the other represented part of the large area. We used global NMS ordination of plots based on species abundance to extract major axes of variation in community composition. Correlations of species, guilds, and environmental variables with ordination axes were compared between geographic scales for the two regions.

Results:

Primary axes of community variation at larger scales were correlated with climate variables and related geographic variables such as latitude and elevation, and with pollution. Forest vegetation variables such as stand age and tree species composition became more important at small scales. Community variation unexplained by macro‐environment variables also became more important at small scales. Of several hundred species tested, ten lichen species showed consistent behaviour between scales within region (one also across regions) and are thus potential general indicators of ecological conditions in forests. Of six lichen guilds tested, several show strong patterns not consistently related to environmental conditions

Conclusions:

Interpretation of lichen species and community composition as indicating particular environmental conditions is context‐dependent in most cases. Observed relationships should not be generalized beyond the geographic and ecological scale of observation.
Plant characteristics are poor predictors of microsite colonization during the first two years of primary succession
Authors: Walker Lawrence R. , Bellingham Peter J. , Peltzer Duane A.
Published: February 2009

Questions:Do plant characteristics predict microsite colonization in severe habitats dominated by abiotic factors? Specifically, does colonization of microsites differ among shrubs, forbs and grasses or between wind‐ and water‐dispersed plants, non‐native and native plants, or N‐fixing and non‐N‐fixing plants?

Location:Kowhai River floodplain, Kaikoura, South Island, New Zealand.

Methods:Five microsite characteristics were measured for > 1000 individuals representing 27 colonizing plant species on a two‐year old surface of a primary succession on a New Zealand floodplain. The microsite characteristics included surface contour (convex, concave, or flat), the position of the plant (e.g., upstream, downstream) relative to the closest rock with > 20 cm maximum dimension, the distance to that same rock, the depth of the base of the stem below the surface of a plane resting on the adjacent microrelief, and soil particle size (gravel, pebbles or sand).

Results:All plants preferred concave microsites near large rocks relative to systematically placed null points. We found no clear preferences for microhabitats by dispersal mode, native vs. non‐native status, or plants with or without nitrogen‐fixing symbionts, but grasses preferentially colonized fine soil particles. Highly variable responses among species contributed to these results. Better predictability of microsite preference was obtained for individual species than forplants grouped by characteristics.

ConclusionsOur results suggest that in severe habitats with strong abiotic filters and low microsite availability, such as found in early primary succession, coarse categories of species characteristics are poor predictors of colonization success.