bluuebunny/crossref_metadata_2025 huggingface dataset:
Causal analysis of the invasion of broad‐leaved forest by bamboo in Japan
Authors: Okutomi Kiyoshi , Shinoda Shigeyuki , Fukuda Hiroko
Published: May 2006

Abstract. In southwestern Tokyo the area covered by bamboo forest has expanded by a factor of 2.7 over the last 26 years. This has mainly been due to bamboo (Phyllostachyspubescens) invading secondary broad‐leaved forests, probably after these were abandoned. In the first stage, bamboo sprouts develop from rhizomes at the periphery of the broad‐leaved forest and then grow very quickly into young culms. In the next phase culm density increases annually, while the existing broad‐leaved trees gradually lose their vitality and die. Finally, the broad‐leaved forest is completely replaced by bamboo forest. The competitive ability of bamboo, based on its morphological and growth features, is suggested as the causal factor for the invasion: (1) bamboo can invade a neighboring broad‐leaved forest by its vigorous rhizomes; (2) young bamboo culms can break through the canopy of broad‐leaved trees; (3) bamboo quickly forms a crown in or above the canopy of the broad‐leaved forest; (4) bamboo is very tolerant of strong wind and heavy snow accumulation; (5) bamboo culms, being very pliable during strong wind mechanically damage neighbouring broad‐leaved trees.
Production and rain use efficiency in short‐grass steppe: grazing history, defoliation and water resource
Authors: Varnamkhasti A.S. , Milchunas D.G. , Lauenroth W.K. , Goetz H.
Published: May 2006

Abstract. Grassland in the semiarid shortgrass steppe, subjected to 50 years of heavy, light, and no grazing intensity, was clipped to simulate the natural pattern and intensities of defoliation by cattle or not clipped. A level of water resource treatment was superimposed upon the grazing and clipping treatments. Half of the plots were supplemented with additional water to simulate a wet year and half were not supplemented in a year of average precipitation. All three treatments interactively determined above‐ground production. Water treatment had the largest overall effect on above‐ground production. Current‐year defoliation had no direct significant effect on production, but mediated differences between both longterm grazing and watering treatments. Long‐term ungrazed compared to grazed grassland was capable of responding to high amounts of precipitation, but was also most affected by low amounts of precipitation and, therefore, displayed greater variability in above‐ground production and rain use efficiency. Only in the year of average precipitation, defoliation increased rain use efficiency in long‐term lightly, but not heavily, grazed treatment. This suggests a water conservation mechanism of defoliation that is reduced with heavy grazing.
Constrained indicator species analysis (COINSPAN): an extension of TWINSPAN
Authors: Carleton T.J. , Stitt R.H. , Nieppola J.
Published: May 2006

Abstract. A new vegetation classification method, COnstrained‐INdicator‐SPecies‐ANalysis (COINSPAN) is introduced as an elaboration of Two‐Way‐INdicator‐SPecies‐ANalysis (TWINSPAN). Instead of operating on the bisection of a primary Correspondence Analysis ordination axis, at each level of division, COINSPAN bisects a primary Canonical Correspondence Analysis axis. The associated computer program, of the same name, performs both analyses as options. COINSPAN is applied to a simple model data set, with two constraining gradients, and to a pine forest vegetation survey in order to illustrate the functioning and utility of the method.
Interspecific variation in tree seedling establishment in canopy gaps in relation to tree density
Authors: Reader R.J. , Bonser S.P , Duralia T.E. , Bricker B.D.
Published: May 2006

Abstract. We tested whether interspecific variation in tree seedling establishment in canopy gaps was significantly related to interspecific variation in tree density, for seven deciduous forest tree species (Quercus alba, Hamamelis virginiana, Acer rubrum, Sassafras albidum, Quercus rubra, Prunus serotina, Ostrya virginiana). For each species, seedling establishment was calculated as the difference in seedling density before experimental gap creation versus three years after gap creation. In each of the six experimentally‐created gap types (33 % or 66 % removal of tree basal area from 0.01‐ha, 0.05‐ha or 0.20‐ha patches), differences in seedling establishment among species were significantly related to differences in their density in the tree canopy. A regression model with loge tree density as the independent variable accounted for between 93 % and 98 % of interspecific variation in seedling establishment.

Our results provide empirical support for models of tree dynamics in gaps that assume seedling establishment depends on canopy tree density.
What constitutes evidence of community structure? A reply to van der Maarel, Noest & Palmer
Authors: Wilson J. Bastow , Peet Robert K. , Sykes Martin T.
Published: May 2006

Abstract. Van der Maarel et al. (1995) — hereafter VNP — criticize our analyses of Öland limestone grassland. They have four general objections, addressed below.

1. VNP attribute our significant results to randomness (‘volatility’); however, significant deviation from randomness cannot be explained by randomness. VNP's conclusion of volatility derives from results that are inconsistent with ours. Their ecological interpretation assumes spatial and temporal near‐constancy in the vegetation; we demonstrate that these assumptions are not correct.

2. We discussed physical limitations to plant module packing. VNP give estimated module sizes. We appreciate this information, though data on actual module sizes and overlap patterns would be required before the real module packing effects could be determined. If module packing were really the main cause of deficits of variance in richness, the effect would not fluctuate between sites and years, as VNP admit it does.

3. The shape of the richness frequency distribution is a potentially interesting additional form of analysis, albeit one that we had chosen not to include in our analysis. However, it is surprising that VNP dismiss analysis of richness variance, but then interpret a more subtle aspect of the richness distribution — the skewness. VNP's redefinition of the terms‘Niche facilitation’for a deficit of low richness values, and ‘Niche limitation’ for a deficit of high values, leads them to misrepresent our arguments. They are mistaken in suggesting that niche limitation will necessarily lead to a skewed curve: they do not allow for the fact that the species frequencies, on which the null model is based already, incorporate effects of species interactions.‘Niche facilitation’, as defined by VNP, would lead to a variance excess, not a deficit as they assume.

4. VNP's criticism of a priori guild classifications had already been met by our use of the intrinsic guild approach. Guild analyses offer the best way forward.

VNP use principally the methodology of 1987. There have been a number of methodological advances since that time. We used these advances in our original paper specifically to circumvent the kinds of problems that they identify. We agree with VNP that it would be very useful to explore the mechanisms behind assembly rules with experiments, but the logical first step is to identify potential assembly rules, as we have been attempting to do. We conclude that, whilst VNP make some interesting observations, none of their criticisms invalidate our results or conclusions. Our original approach stands as the best known approach, we believe, for searching for community structure in such data, and we reaffirm the validity of our ecological conclusions.
Recolonization of cleared riverine macrophyte patches: importance of the border effect
Authors: Barrat‐Segretain M.H. , Amoros C.
Published: May 2006

Abstract. Recolonization of two experimentally cleared 9 m2‐patches by macrophytes in a former channel of the Rhône River, France, was investigated from May to July 1994. Two patterns of recolonization were recognized: (1) Groenlandia densa, Luronium natans and Potamogeton natans invaded the bare areas by propagation from the adjacent vegetation (border effect); (2) Potamogeton pusillus colonized the disturbed areas at random, apparently independently from the position of nearby clumps. An intermediate recolonization pattern was shown by Callitriche platycarpa, Elodea canadensis, Hippuris vulgaris, Ranunculus circinatus and Sparganium emersum. Species recolonization patterns and associated strategies were related to species traits, particularly vegetative and sexual reproduction.
Effects of stand composition on fire hazard in mixed‐wood Canadian boreal forest
Authors: Hély C. , Bergeron Y. , Flannigan M.D.
Published: May 2006

Abstract. Surface fuels were examined in 48 stands of the Canadian mixed‐wood boreal forest. Tree canopy was characterized with the point‐centred quadrant method and stands were characterized as deciduous, mixed‐deciduous, mixed‐coniferous or coniferous according to the percentage of conifer basal area. Woody debris loadings were measured with the line intersect method and the litter, duff, shrub loads and depths or heights were sampled with various quadrats. No significant difference was found among stand types for total woody debris load, large basal diameter shrub loads and load or depth of litter and duff. However, conifer stands had significantly heavier loads of small diameter elements (twigs and shrubs) and conifer pieces were more numerous within these stands than in deciduous stands. The BEHAVE prediction system was used to evaluate the impact of these differences on the potential of fire ignition in situations where topography and weather were constant. The qualitative and quantitative changes in fuels, resulting from species replacement and fast decay rates, influence fire hazard. Simulations of fire behaviour showed that in the mixed‐wood boreal forest fires were less intense and spread more slowly in deciduous stands than in mixed or coniferous stands. Moreover, spring fires were more intense than summer fires, and differences between seasons increased with the increase of deciduous basal area.
Two decades of change in the ground vegetation of a mixed deciduous forest in an agricultural landscape
Authors: Lameire Simon; , Hermy Martin , Honnay Olivier
Published: May 2006

Abstract. A vegetation survey of semi‐permanent plots was performed in 1977–1980 and in 1997–1998 to study the floristic changes in a mixed deciduous forest situated in a region of intensive livestock breeding. Our aim was to test the hypothesis of allogenic succession in the forest ground vegetation caused by the emissions of the surrounding agricultural activities. During the last 20 years, a significant increase of nitrogen indicators and a decline of moisture indicators were observed. Results were consistent at the community, the plot and the species level. Nitrogen deposition and the lowering of the groundwater table are suggested as the driving forces behind the changes. The results are discussed in the context of current ecological theory concerning resource competition and community diversity.
Correlation between richness per unit area and the species pool cannot be used to demonstrate the species pool effect
Authors: Herben Tomáš
Published: May 2006

Abstract. Significant correlation between the size of the species pool and richness per unit area is usually taken as a demonstration of the effect of the species pool on the species richness per unit area. This is not logically necessary. It has to be emphasized that such a correlation cannot be interpreted as a demonstration of the effect of species pool on the species richness per unit area. More generally, correlation cannot be used to demonstrate a one‐directional effect of one variable upon another, since several types of (functional) relationships could produce correlations between such variables; the same caution has to be taken when analysing the species pool vs. richness per unit area correlation.

In this paper, a simple Monte Carlo simulation model is used to demonstrate that (1) statistical processes acting only at the local scale (such as competitive exclusion) can generate exactly the same correlation that has been used to infer the effect of the species pool on richness per unit area; (2) this correlation would be deemed significant even if the mathematical dependency between species pool and richness per unit area is taken into account; and (3) the strength of this relation depends on beta diversity within the contiguous area used to determine the species pool.
Early succession on plots with the upper soil horizon removed
Authors: Lepš Jan , Michálek Jaroslav , Rauch Ota , Uhlík Petr
Published: May 2006

Abstract. Succession was studied on plots with the upper soil horizon removed in an area affected by acidic air pollution in the Krušné Hory Mts., Czech Republic. 10 permanent 1‐m2 plots were marked and vegetation recorded annually using a grid of 100 subplots from 1989 to 1995. Constrained ordination analyses showed that soil texture is the most important environmental factor influencing the course of succession. Its effect on species composition increases with successional age of the plant community. On fine‐grained soils species‐poor communities dominated by grasses (Calamagrostis villosa, Deschampsiaflexuosa) and on coarse‐grained soils species‐rich communities dominated by heather (Calluna vulgaris) developed. Succession proceeded from communities where species composition was determined by diaspore availability towards communities where species composition depended on environmental conditions. Successional communities after 10 yr are more dependent on soil characteristics and consequently environmental determination increases over the course of succession and causes the communities to diverge.
BOOK REVIEWS
Authors: Baskin Jerry M.
Published: May 2006

Bolen, E. G. 1998. Ecology of North America. xv + 448 pp. John Wiley & Sons, Inc., New York. ISBN 0–471–13156 (hardback). Price: USD 79.95.
Plant communities of New Brunswick in relation to environmental variation
Authors: Roberts Mark R. , Wuest Lawrence J.
Published: May 2006

Abstract. The objective of this study was to quantitatively describe vegetation‐environment relationships at a regional scale within the Province of New Brunswick, Canada, using vegetation and environment data from 3947 provincial forestry sample plots. The major plant community types in the province were identified using cluster analysis. Relationships of these communities to climate, topography and soil variables were analyzed by Canonical Correspondence Analysis (CCA), using both a reduced data set consisting of cluster likelihood scores × sample plots and an unreduced species × sample plots data matrix. The vegetation types and major axes of environmental variation were mapped to examine the geographic distributions of these factors within the province. Eight communities were identified and described in terms of enhanced/reduced species (significantly higher or lower frequencies of occurrence in a specific community type relative to all plots) and common species (species in the community type with the highest frequencies of occurrence). The canonical axes explained 25 % of the variation in the vegetation cluster data. Vegetation composition was related to three major environmental gradients representing climate and elevation, soil moisture, and soil fertility. The geographic distributions of vegetation communities exhibited predictable but weak correspondence to the geographic distributions of individual environmental factors. Our findings emphasize the overriding importance of climate and topography and the secondary importance of soil factors in controlling vegetation pattern at the regional scale.
Post‐fire seedling establishment in Florida sand pine scrub
Authors: Carrington Mary E.
Published: May 2006

Abstract. This study deals with a quantification of pre‐ and post‐fire seedling establishment and microsite characteristics in two Florida sand pine scrub sites burned in May 1993. In addition, life history characteristics related to seedling establishment are described for five perennial species –Calamintha ashei, Chapmannia floridana, Eriogonum floridanum, Garberia heterophylla and Palafoxia feayi. Post‐fire seedling establishment in sand pine scrub was sparse (median = 1, 12 seedling/m2), with 17 of 35 species establishing seedlings. Chapmannia, Eriogonum, Garberia and Palafoxia resprouted and flowered after fire; Eriogonum and Garberia had strong post‐fire seedling establishment responses within 19 months post‐fire. Calamintha individuals were killed by fire, but this species had a strong post‐fire seedling establishment response, presumably from seeds in a soil seed bank. Eriogonum and Calamintha seedlings established preferentially in plots centered on conspecific adults. For these species with poor seed dispersal, spatial patterns of seedling establishment may be influenced more by pre‐fire adult plant location than by post‐fire microsite conditions. Post‐fire seedling density in sand pine scrub was much lower than in California chaparral and South African sand plain lowland fynbos.
Response of plant functional types to changes in the fire regime in Mediterranean ecosystems: A simulation approach
Authors: Pausas Juli G.
Published: May 2006

Abstract. In the Mediterranean basin, the climate is predicted to be warmer and effectively drier, leading to changes in fuel conditions and fire regime. Land abandonment in the Mediterranean basin is also changing the fire regime through the increase in fuel loads. In the present study, two simulation models of vegetation dynamics were tested in order to predict changes in plant functional types due to changes in fire recurrence in eastern Spain. The two modelling approaches are the FATE‐model (based on vital attributes) and the gap model BROLLA (based on the gap‐phase theory). The models were arranged to simulate four functional types, based mainly on their regenerative strategies after disturbance: Quercus (resprouter), Pinus (non‐resprouter with serotinous cones), Erica (resprouter), and Cistus (non‐resprouter with germination stimulated by fire). The simulation results suggested a decrease in Quercus abundance, an increase in Cistus and Erica, and a maximum of Pinus at intermediate recurrence scenarios. Despite their different approaches, both models predicted a similar response to increased fire recurrence, and the results were consistent with field observations.
Seed banks of grazed and ungrazed Baltic seashore meadows
Authors: Jutila b. Erkkilä Heli M.
Published: May 2006

Abstract. The seed banks of three grazed and three ungrazed seashore meadows were studied on the west coast of Finland. 8486 seedlings (mean 13 669 seedlings/m2) germinated from cold‐treated samples (n = 343; depth = 10 cm). Most seedlings and species were monocots and perennials. The seed bank flora included 54 dicots vs. 28 monocots and 66 perennials vs. 16 annuals. The most abundant species were Juncus gerardii, Schoenoplectus tabernaemontani, Eleocharis uniglumis, Agrostis stolonifera, Juncus bufonius and Carex nigra, which made up 73% of the seed bank.

Numbers of species and seedlings differed between elevation classes. Species richness was highest in elevation class 50–70 cm. The highest seed density occurred in class 20–50 cm. A model for size and species composition of the seed bank in relation to elevation is presented. The seed bank was larger and richer in species in the ungrazed than in the grazed sites, but not so in the upper elevations and closest to the open sea. Grazing reduced the size of the seed bank of Agrostis stolonifera, A. capillaris, Calamagrostis stricta, Elymus repens, Juncus bufonius, Limosella aquatica and Schoenoplectus tabernaemontani, but increased that of J. gerardii. 32 species germinated only from ungrazed samples and 11 species only from grazed ones. Multivariate classification resulted in nine sample groups. The ordination scatter was best explained by the flooding stress variables, elevation, the distance from the water line and the number of helophyte species in samples.

75 species were found both in the seed bank and in the vegetation, but there was a significant lack of resemblance (in the Mantel test) due to over‐representation of some species. Eight species occurring only in the seed bank were mainly annuals or biennials (63%); those occurring only in the established vegetation (86 species) were mainly perennials (86%).
A model for the explanation of vegetation stripes (tiger bush)
Authors: Lejeune O. , Tlidi M.
Published: May 2006

Abstract. Regular vegetation patterns appear on aerial views of plateaux in SW Niger where densely and sparsely populated zones alternate with each other. This spatial organization of the vegetation is an endogenous phenomenon which is not limited to specific plants or soils; it is a characteristic landscape of many arid regions throughout the world. The phenomenon is interpreted as the result of a spatial range difference between two biologically distinct interactions operating at the plant population level. The proposed mechanism is independent of external heterogeneities deriving from soil geomorphology or meteorology. We present a model to simulate the genesis of vegetation stripes. In addition, the model predicts the occurrence of vegetation hexagons corresponding to higher or lower density spots arranged in a hexagonal lattice. The distinction between the two spatial symmetries is discussed in terms of their Fourier transforms.
Small‐scale plant mobility in a species‐rich grassland
Authors: Klimeš Leoš
Published: May 2006

Abstract. Plant mobility was studied in a species‐rich grassland in S. Moravia (Czech Republic) at scales from 0.0025 to 2.25 m2. Cumulative species numbers, cumulative species frequencies and the distribution of distances between sites of occurrence in particular years were established using data collected from 1991 to 1997. The observed values were compared with null models of completely random and restricted random movement of the plants. Most plants persisted at a spot more frequently than expected from the completely random model and with a few exceptions they also spread to neighbouring subplots more often than expected. Cumulative species numbers were between the ranges predicted by the two random models and increased linearly during the 7‐yr period at all scales, indicating a large species pool. The role of clonal spreading and of generative reproduction depended on the growth form of the species. I conclude that a high species richness is not necessarily linked with a high plant mobility, even if coexistence of plant species may be promoted by plant mobility.
Effects of herbivory on the growth and reproduction of Picris hieracioides in the Mediterranean region
Authors: Escarré J. , Lepart J. , Sans X. , Sentuc J.J. , Gorse V.
Published: May 2006

Abstract. The impact of herbivorous insects on the growth and reproduction of Picris hieracioides (Compositae) was followed in three consecutive years by comparing plants treated with an insecticide and untreated plants in an old‐field population abandoned for 15 yr (P15). In the third year the interactions between herbivory and competition were analysed as well. Pre‐dispersal seed predation of seed heads was investigated in three adjacent old‐fields abandoned for one (P1), 15 (P15) and 40 yr (P40) in the region of Montpellier, France. Fields differed in vegetation cover and floristic composition and also in density and above‐ground biomass of Picris hieracioides plants (from 246 g per plant in P1, 13.3 g in P15, down to 3.3 g in P40, for the first year of study). The cumulative rainfall between January and July, the period of Picris growth, decreased from 1992 to 1994. Moreover, in 1992, three times as much rainfall occurred in May and June – the period of stem elongation – as in 1993 and 1994. As a consequence, environmental stress increased during the study period.

Herbivorous invertebrates had a negative effect on the growth and reproduction of individual plants of Picris hieracioides in P15. The effect was not constant with time, being apparent in only two years out of three. These two years (1992 and 1994) had contrasting climatic characteristics, whereas the year with no apparent effect (1993) was climatically intermediate. When herbivory had effects on growth, the insecticide‐treated plants had a significantly higher above‐ground biomass and produced twice as many seed heads as the control plants. There was no interaction between herbivory and competition.

The percentage of damaged seed heads was significantly lower in the P1‐field than in the P40‐field. The P15‐field had intermediate levels of predation. Predation on seed heads increased whereas biomass and reproductive output decreased between 1992 and 1994 in the three old‐fields. Therefore, the results on seed predation (but not for above‐ground biomass and reproduction) tend to confirm‘the environmental stress hypothesis’ of Mattson & Haack (1987) that states that plants under stress are more liable to be attacked by grazers.
Influence of a developing tree canopy on the yield of Pennisetum pedicellatum sown on a mine spoil
Authors: Singh Arvind , Jha A.K. , Singh J.S.
Published: May 2006

Abstract. Shoot and root biomass yield of a sown grass, Pennisetum pedicellatum, were measured at below‐canopy, canopy edge and open locations in young monoculture stands of eight tree species planted on a coalmine spoil. Incident light as percentage of full sunlight decreased from open to canopy edge to below‐canopy locations. The shoot and root weights of Pennisetum in different tree stands for each of the three locations were significantly different and were significantly related to each other, and to percentage sunlight across all tree species plots and locations. The gradient of incident light was the principal factor governing the gradient of grass biomass under developing canopies of tree plantations on the mine spoil.
Prediction of yield in the Rothamsted Park Grass Experiment by Ellenberg indicator values
Authors: Hill M.O. , Carey P.D.
Published: May 2006

Abstract. The Rothamsted Park Grass Experiment was established in 1856, with experimental plots subjected to annual applications of fertilizer and twice‐yearly cutting of hay. There were two major responses to fertilizer, one reflecting high ammonium‐nitrogen and increased acidity and the other reflecting high herbage yield without increased acidity. We calculated mean Ellenberg indicator values for N (nitrogen) and R (soil reaction) for the hay harvested between 1948 and 1975, using both unweighted and abundance‐weighted means. Plot Ellenberg values were compared with herbage yield and with fertilizer application rates and published soil data. Annual yield of hay varied from 1.5 to 7.4 t/ha and was well predicted by the unweighted mean Ellenberg N‐values (r = 0.91). Relatively large negative residuals from the relationship were found in plots whose soil combined low K and low pH. Soil pH was poorly predicted by the unweighted mean R‐value, but showed a moderately good relation with weighted mean R (r = 0.73). The fact that Ellenberg N‐values correlated better with yield than with applied nitrogen suggests that they might rather be called productivity values.
Permutation of Two‐Term Local Quadrat Variance Analysis: General concepts for interpretation of peaks
Authors: Campbell Jonathan E. , Franklin Scott B. , Gibson David J. , Newman Jonathan A.
Published: May 2006

Abstract. Many ecological studies use Two‐Term Local Quadrat Variance Analysis (TTLQV) and its derivatives for spatial pattern analysis. Currently, rules for determining variance peak significance are arbitrary. Variance peaks found at block size 1 and at > 50 % of the transect length are the only peaks whose use is explicitly prohibited. Although the use of variance peaks found at block sizes > 10 % of the transect length have also been warned against, many researchers interpret them regardless. We show in this paper that variance peaks derived from TTLQV are subject to additional ‘rules of thumb’. Through the use of randomization and permutation analyses on real and simulated data of species abundance in contiguous plots along a single transect, we show that variance peaks found at block sizes 1, 2 and 3 occur frequently by chance and thus likely do not indicate biologically meaningful patterns. The use of multiple replicate transects decreases the probability of Type II error.
Primary succession on glacier forelands in the subantarctic Kerguelen Islands
Authors: Frenot Y. , Gloaguen J.C. , Cannavacciuolo M. , Bellido A.
Published: May 2006

Abstract. Primary succession was studied on recently de‐glaciated areas in front of the Ampère Glacier, Kerguelen Islands (49° 30′S, 69° 30′E). Vegetation, colonization processes and soil development were investigated on seven sites on the outwash plain over a distance of 5 km and representing a > 200‐yr old chronosequence. Seven species are involved in the succession, showing four patterns of change: (1)‘pioneer’ (Poa kerguelensis, Poa annua, Colobanthus kerguelensis and Cerastium fontanum); (2)‘intermediate’ (Festuca contracta); (3)‘late colonizer’ (Azorella selago); and (4)‘fluctuating’ (Agrostis magellanica). Two of the pioneers are introduced species (Poa annua and Cerastium). The total plant cover increases significantly with the age of the sites but never exceeds 4.2 %. The plant succession pattern observed in this study appears to be related to soil development. Root architecture and fine particle dynamics in the soil may explain the behaviour of the different species along the chronosequence. The pioneer species have a very shallow root system whereas the intermediate and late colonizers are deeper and longer rooted. The dominance of Azorella selago (Apiaceae) in the oldest community may be attributed to its unique root system in relation to the vertical distribution of silt cappings in the soil.
Vegetation changes caused by recent fires in the northern boreal forest of eastern Canada
Authors: Lavoie Luc , Sirois Luc
Published: May 2006

Abstract. From 1980–1989, fires burned 32 440 km2 of boreal forest, 200 km south of the forest‐tundra border in northern Québec, Canada. An assessment of the impact of fire on tree population densities was carried out by comparing the number of Pinus banksiana and Picea mariana in 83 sites before and after the sites burned in 1981, 1983, 1988 or 1989. Age structure analysis of post‐fire populations burned in 1972, 1976 and 1983, along with the rapid exhaustion of the seed bank from burned trees, suggest that the majority of seedlings were established within 3 to 10 yr after fire. Consequently, given the absence of nearby living seed bearers, little (if any) further recruitment can be expected in the even‐aged, regenerating populations. According to the tree density comparison (pre‐fire vs post‐fire), a shift from Picea‐ to Pinus‐dominated communities occurred in most of the sites burned in 1981 or 1983, and in some of the sites burned in 1988 or 1989. The 1988 fire reduced the tree population density by 95% in 10 of the 15 sites; total tree density decreased by at least 75% in 28 out of 40 sites burned in 1989. This suggests that the areas burned in 1988 and 1989 will mainly regenerate as very open forests or lichen‐heath communities that are more commonly found in the forest‐tundra zone, north of the study area. Fire intensity, short fire interval, and unfavorable climate during and after fires are three plausible mechanisms associated with these post‐fire vegetation changes.
Relationships between change in fire frequency and mortality due to spruce budworm outbreak in the southeastern Canadian boreal forest
Authors: Bergeron Yves , Leduc Alain
Published: May 2006

Abstract. We present a simple empirical model that allows an estimation of mortality due to spruce budworm (Choristoneura fumiferana) outbreak in relation to fire frequency and site characteristics. The occurrence of a recent spruce budworm outbreak around Lake Duparquet (48° 30’N, 79° 20’W, ca. 300 m a.s.l.) in northwestern Québec permitted a reconstruction of the stand composition before the outbreak, and also of the mortality of Abies balsamea due to the outbreak. The basal area of A. balsamea increases with time since fire in all site types but with increasing values for (1) rock and shallow till, via (2) till and mesic clay up to (3) hydric clay. Mortality (measured as percentage loss of basal area due to the outbreak) increases with time since fire but did not vary with site type. The increasing abundance of A. balsamea with time since fire is mainly responsible for this increase in mortality. Mortality for a specific basal area is, however, lower for the more recently burned stands suggesting a significant residual effect of time since fire. A landscape model integrating mortality due to the outbreak for stands of different age is developed. Both absolute and relative losses of basal area increased with the length of the fire cycles. According to this model, changes in fire cycle could explain a large portion of the spatio‐temporal variations observed in outbreak mortality in the southeastern boreal forest of Canada.
The role of seed rain in determining the assembly of a cliff community
Authors: Booth Barbara D. , Larson Douglas W.
Published: May 2006

Abstract. Cliff‐face communities of the Niagara Escarpment in Ontario, Canada, are dominated by long‐lived Thuja occidentalis and a consistent assemblage of other plants. Our objective was to determine whether seed rain plays a role in determining why these species are dominant. Seed rain was collected from the cliff face and from the surrounding plateau‐and talus communities at two sites over a 2‐yr period in order to compare these three adjacent, but different communities. Multivariate Discriminant Analysis first separated the two sites: primarily due to the importance of Betula papyrifera at one site. The three community types were also separated, although there was still substantial overlap. There was a predictable array of species associated with each community although the seed rain on the cliff faces differed slightly. When characterized by univariate ANOVAs, seed rain in the cliff faces and plateaus had a lower species richness and lower total seed density than the talus sites. Seeds of two of the 11 species analysed individually showed an influence of habitat type on their number. Seed morphology did not influence patterns of seed rain. Finally, there was no correlation between the seed rain and above‐ground vegetation in any of the communities. We conclude that the seed rain patterns that exist do not act to filter the plants that form the mature vegetation of cliffs.
Old‐field colonization by Daphne gnidium: seedling distribution and spatial dependence at different scales
Authors: Verdú M. , García‐Fayos P.
Published: May 2006

Abstract. This paper deals with the spatial distribution pattern of the bird‐dispersed plant Daphne gnidium in a 10‐yr abandoned field under Mediterranean conditions. Colonization of Mediterranean old‐fields by bird‐dispersed plants is expected to fit a theoretical model in which (1) seed dispersal follows a negative exponential curve with the distance from the seed source and (2) seedlings are better established under perches (nucleation sensu Yarranton & Morrison 1974). However, post‐dispersal processes such as seed predation, seed germination and seedling establishment are also spatial‐dependent and can lead to spatial autocorrelation in the seedling distribution within an old‐field.

Results show that both processes in the model (curve of seed dispersal and nucleation) significantly explained the spatial distribution of the seedlings, but some spatial variance remained unexplained. The semivariogram with the statistical residuals of the model detected spatial dependence at small (< 20 m) and large (> 250 m) distance intervals, indicating that some mechanisms with spatial components, apart from the curve of seed dispersal and nucleation under perches, also determined the distribution of seedlings colonizing fields. At scales below 20‐m intervals, semivariance increased indicating that similarity between plots is lost when distance increases between them. This pattern may be explained because the favourable micro‐environmental conditions for establishment produced under perches could be extended towards neighbour plots where perches were absent. A flat semi‐variogram between 20‐m and 250‐m intervals shows spatial independence along this range. From 250 m on, the semivariance increased again, indicating spatial dependence at coarse‐scale. It is possible that the colonization model failed at this scale because different spatial processes to those included in the model (perch presence and distance to the shrubland) could be controlling seed colonization at coarse‐scale.
Local colonization and extinction of field layer plants in a deciduous forest and their dependence upon life history features
Authors: Fröborg Heléne , Eriksson Ove
Published: May 2006

Abstract. In this study we used species inventory data collected in 1970 and 1993 from 132 plots in a 14.5ha deciduous forest to examine local extinction and colonization processes among 45 field layer species. Local colonization rate was positively related to both seed size and seed dispersal features. Local extinction rate was negatively related to seed size. Growth form (clonal vs. non‐clonal) and presence of a seed bank were not found to be associated with local dynamics. Despite an overall constancy in species composition during this period, plants exhibited a considerable mobility among the 132 plots. This pattern conformed to a suggested ‘carousel model’ of species mobility in grasslands. A tentative suggestion is that this mobility acts on a comparatively broader spatio‐temporal scale in deciduous forests as compared with grasslands. Additional data are presented indicating that species abundance (frequency) among field layer plants in deciduous forest communities is consistent among forest fragments, and when comparing local and regional scales. The main conclusion is that life history features of the seed dispersal/recruitment phase, particularly seed size, are causally associated with abundance patterns at least at a local scale, but possibly also on a broader regional scale.
Effects of cutting and rainfall pattern on resprouting vigour and growth of Erica arborea L.
Authors: Riba Miquel
Published: May 2006

Abstract. This study analyses the effects of recurrent cutting and rainfall pattern on sprout and genet growth in the resprouting shrub Erica arborea. Three different intervals between consecutive clear‐cutting events were applied: 30, 5 and 2 yr. Above‐ground genet biomass after 2 yr of treatment application was correlated with burl size and decreased with increasing recurrence of cutting, indicating that more than 5 yr were needed to re‐establish the resprouting potential of genets.

The effect of rainfall on growth was evaluated through the correlations between sprout RGR and several variables related to the rainfall pattern at different regeneration stages. The effect of the rainfall pattern on sprout RGR was dependent on the regeneration age, suggesting that water availability becomes more limiting after two years of regrowth.
Effects of species partition on explanatory variables in direct gradient analysis ‐ a case study from Senegal
Authors: Lawesson Jonas E.
Published: May 2006

Abstract. Species‐environment data from Senegal, West Africa, are used to study the effects of partition of a large species data set into subsets corresponding to rare and common species respectively. The original data set contains 129 woody plant species from 909 plots and 60 explanatory variables.

By applying Canonical Correspondence Analysis to data subsets, marked differences in the forward‐selected variables were detected. The highest resemblance was found between the complete species set and the common species subset. Only one of eight selected variables was common to all species and the rare species groups. These findings were tested with partial ordination, applying the selected variables from the original species group (Vb), as variables and covariables to the analyses of common and rare species. For the common species this application resulted in a constrained ordination with higher eigenvalues as compared to the set of variables selected with reference to the common species group. Using the rare species group, the application of Vb gave a much lower sum of eigenvalues than did the ordination with selected variables based on the rare species group only. Evidently, the set of variables selected on the basis of the rare species data were more significant.

Hence, the resulting gradients depend on the frequency of the species. Gradient analysis is apparently only valid for groups of species with closely resembling characteristics. This implies that different functional types of species, with different distributions and abundances, respond individually to environmental variation. Extrapolating deduced gradients from one species group to another maybe risky, particularly when used in vegetation modelling.
Nutrient limitation in species‐rich lowland fens
Authors: Boeye Dirk , Verhagen Bart , Van Haesebroeck Véronique , Verheyen Rudolf F.
Published: May 2006

Abstract. Nitrogen, phosphorus and potassium were supplied to some Belgian fens of varying nutrient status and productivity. Plant growth in the lowest productive fen with a species‐rich Caricion davallianae vegetation was strongly P‐limited. N was ineffective when applied alone, but increased the effect of P‐addition when applied together. Summer biomass and plant nutrient concentrations were monitored for four years, and showed partial recovery of nutrient limitation. In a more productive fen dominated by Carex lasiocarpa and in a fen meadow, nutrient limitation was less strong. N limited growth in the productive fen, and N and K were co‐limiting in the fen meadow. The P‐concentration in the productive fen vegetation showed a marked increase after P‐fertilization, but it did not result in higher standing crop. The significance of P‐limitation for the conservation of species rich low productive fens is discussed. P‐limitation may be an essential feature in the conservation of low productive rich fens: because it is less mobile in the landscape than N and/or because it is an intrinsic property of this vegetation type. Plant nutrient concentrations and N:P‐ratios may be used as an indication for the presence and type of nutrient limitation in the vegetation. We found N:P‐ratios of 23 to 31 for a P‐limited site and 8 to 15 in N‐limited sites. This was in agreement with critical values from the literature: N:P > ca. 20 for P‐limitation and N:P < 14 for N‐limitation. Thus, this technique appears valid in the vegetation types that were studied here.
Effects of additional illumination and fertilization on seasonal changes in fine‐scale grassland community structure
Authors: Eek Liina , Zobel Kristjan
Published: May 2006

Abstract. Fine‐scale structure of a species‐rich grassland was examined for seasonal changes caused by manipulated changes in the availability of above and below‐ground resources (additional illumination with the help of mirrors and fertilization) in a field experiment. If changes induced by fertilization — which are expected to lead to a reduction in small‐scale diversity —are due to intensified light competition, they should be compensated for by additional light input.

Permanent plots of 40 cm × 40 cm were sampled by the point quadrat method at three angles (60°, 90° and 120° from the horizontal North‐South direction), using a laser beam to position the quadrats, in early July and early September. The applied treatments did not cause apparent changes in plant leaf orientation. The degree of spatial aggregation of biomass increased seasonally in fertilized, non‐illuminated plots: greater productivity at a constant light supply led to a faster growth rate of potentially dominant species, as compared to the subordinate ones. Additional illumination mitigated this effect of fertilization, indicating that the observed changes in biomass aggregation were due to increased light competition.

There was a considerable seasonal decrease of variance ratio (ratio of observed variance of richness at a point and variance expected at random) in fertilized only and in illuminated only plots. In fertilized plots this was due to the positive relationship between biomass aggregation and expected variance of richness. Biomass constancy occurs to be inversely related to deficit in variance of richness. In illuminated plots, in contrast, only the observed variance of richness decreased seasonally, indicating a more uniform use of space by different species. Evidently, a deficit in variance of richness can be caused by drastically different processes, showing that the variance ratio statistic may not have a significant explanatory value in fine‐scale community studies.
Effects of topography, soil moisture, wind and grazing on Festuca seedlings in a Patagonian grassland
Authors: Defossé Guillermo E. , Bertiller Mónica B. , Robberecht Ronald
Published: May 2006

Abstract. The effects of topography, soil moisture, wind and grazing on the emergence and survival of seedlings of Festuca spp. were examined in the steppe zone of Patagonia, Argentina. Ungrazed and grazed field treatment plots were established on a plain and a north‐facing slope at the Media Luna Ranch (43° 36′S, 71° 25′W). On the leeward and windward sides of each of 15 Festuca plants, 0.1 m × 0.4 m quadrats were censused bimonthly for seedling emergence and survival over three growing seasons. Three categories were distinguished: recently germinated and up to the first leaf, two to four leaves, and from five leaves up to one tiller. Soil moisture content, litter cover and frost heaving effects were also determined for each treatment at each sampling date. Festuca spp. showed two emergence peaks, one in late fall and the other in early to mid‐spring. Seedling emergence was significantly correlated with soil moisture content in the 0–5 cm of the soil during the three growing seasons. Seedlings that emerged in the fall had higher survivorship than those that emerged in spring. Seedling emergence and survival was significantly (p < 0.01) lower on slopes, in the grazing treatment, and on windward sides of adult plants. In this grassland, an increase in the availability of safe sites for seedling emergence and survival might be achieved by protecting vegetation from grazing, particularly on north‐facing slopes.
Sex ratio in populations of Silene otites in relation to vegetation cover, population size and fungal infection
Authors: Soldaat Leo L. , Vetter Birgit , Klotz Stefan
Published: May 2006

Abstract. In contrast to populations of most dioecious Silene species (which usually are female‐biased), populations of Silene otites have been frequently reported to be male‐biased. We describe sex ratio variation in 34 natural S. otites populations in Central Germany in relation to vegetation cover, population size and fungal infection. The overall sex ratio was unbiased in 1994 and only slightly male‐biased in 1995. Sex ratio varied among the populations from 26.6 % to 72.6 % females. The sex ratio of small populations varied strongly due to stochastic processes. Furthermore, we found that populations in habitats with high vegetation cover contained a higher percentage of females. Hermaphroditic plants, theoretically, could increase male bias as they only produce male or hermaphroditic offspring. Their frequency in the populations, however, was far too low to affect sex ratio. In 1994 12.1 % and in 1995 17.0 % of the plants were infected by the smut fungus Ustilago major. Disease incidence in the population was not related to sex ratio, suggesting equal susceptibility of males and females. The sex ratio of partially infected plants did not deviate from the population sex ratio, both under field conditions and in a greenhouse laboratory experiment. The results suggest that the frequently reported male bias in Silene otites populations is not a general pattern, but is mainly caused by environmental conditions.