bluuebunny/crossref_metadata_2025 huggingface dataset:
Estimating net primary production of boreal forests in Finland and Sweden from field data and remote sensing
Authors: Zheng Daolan , Prince Stephen , Hame Tuomas
Published: February 2009

We calculated annual mean stem volume increment (AMSVI) and total litter fall to produce forest net primary production (NPP) maps at 1‐km2 and half‐degree resolutions in Finland and Sweden. We used a multi‐scale methodology to link field inventory data reported at plot and forestry district levels through a remotely sensed total plant biomass map derived from 1‐km2 AVHRR image. Total litter fall was estimated as function of elevation and latitude. Leaf litter fall, a surrogate for fine root production, was estimated from total litter fall by forest type. The gridded NPP estimates agreed well with previously reported NPP values, based on point measurements. Regional NPP increases from northeast to southwest. It is positively related to annual mean temperature and annual mean total precipitation (strongly correlated with temperature) and is negatively related to elevation at broad scale. Total NPP (TNPP) values for representative cells selected based on three criteria were highly correlated with simulated values from a process‐based model (CEVSA) at 0.5°× 0.5° resolution.

At 1‐km2 resolution, mean above‐ground NPP in the region was 408 g/m2/yr ranging from 172 to 1091 (standard deviation (SD) = 134). Mean TNPP was 563 (252 to 1426, SD = 176). Ranges and SD were reduced while the mean values of the estimated NPP stayed almost constant as cell size increased from 1‐km2 to 0.5°× 0.5°, as expected. Nordic boreal forests seem to have lower productivity among the world boreal forests.
Holocene land uplift and its influence on fire history and ecosystem development in boreal Sweden
Authors: Hörnberg Greger , Wallin Jan‐Erik , Påsse Tore , Wardle David A. , Zackrisson Olle
Published: February 2009

Lake Uddjaur in northern Sweden was formed as a consequence of non‐uniform glacio‐isostatic uplift in which a forested valley was gradually flooded and high elevation areas became islands. We hypothesized that small islands in Lake Uddjaur burnt through lightning strike more frequently when they were part of a large forested area compared to when they became true islands, and that this reduction in fire impact has enhanced the domination of late successional species and humus accumulation. Fire history and vegetation dynamics were studied by analysis of macroscopic charcoal (> 0.5 mm) and pollen in humus profiles from two islands. According to a model of isostatic uplift, the islands became gradually isolated from the mainland between ca. 2000 to 1000 BP, i.e. during the same time that fire impact declined. Prior to that, both islands were part of a Pinus‐Betula forest landscape affected by fires from ca. 5800 to ca. 1500 BP. Thereafter fire influence ceased and the islands became more strongly characterized by late successional species, e.g. Picea. This change was associated with substantial humus accumulation. The decreased fire influence on these islands contrasts with the regional increase in fire influence during the last 1000 yr. Long‐term influence of wildfire is important in vegetation dynamics and humus accumulation and, thus, post‐glacial isostatic land uplift can indirectly have a substantial influence on ecosystem development. Consequently, this effect should be further considered in long‐time ecosystem studies of areas with large, non‐uniform land uplift such as those found in northern Fennoscandia and eastern Canada.
Changes in soil and vegetation during dune slack succession
Authors: Sýkora Karle V. , van den Bogert Jeroen C.J.M. , Berendse Frank
Published: February 2009

Many rare plant species occur in Dutch wet dune slacks, particularly in the Junco baltici‐Schoenetum nigricantis. For nature management it is important to understand the processes controlling the presence of these basiphilous early successional communities, which is why we investigated vegetation and soil development during succession in coastal dune slacks. We compared 12 chronosequential stages of 0, 2, 4, 9, 10, 13, 25, 30, 43, 60, 70 and 85 yr in five different dune slack systems. In four of these locations turf had earlier been removed in order to restore the basiphilous pioneer stage.

The main variation in the vegetation is related to the acidification/soil enrichment gradient and the salinity/maritime gradient. During succession, organic matter accumulates and acidification takes place. Maritime influence can buffer the soil and postpone the succession of basiphilous pioneer communities for many years. A significant correlation with age was found for 18 variables. Multiple regressions predicted changes in the vegetation (dependent variables: biomass, cover of Salix repens, Calamagrostis epigejos and Schoenus nigricans) as a function of acidification, organic matter accumulation, increase in available P and presence of Na in the soil.

We conclude that natural ageing of the vegetation and the associated process of accumulation of biomass drive succession in this hydrosere. The underlying soil processes are acidification and organic matter accumulation. During succession dominance shifts from S. nigricans to S. repens or C. epigejos. Maintenance of the pioneer character of the habitat is only possible by local intervention or by natural or man‐induced dune forming. The effect of sod‐stripping depends on the environmental conditions and, in case of acidification, success is limited. Succession can be postponed by mowing.
Establishment of co‐existing Mediterranean tree species under a varying soil moisture regime
Authors: Lloret Francisco , Peñuelas Josep , Ogaya Romà
Published: February 2009

We investigated the responses of two co‐existing Mediterranean trees with different regeneration strategies (Phillyrea latifolia seedlings and Quercus ilex sprouts) to experimental drought below the forest canopy. We considered different recruitment stages and used leaf isotopic discrimination to estimate water use efficiency (WUE) and nitrogen availability and use. Drought decreased the emergence and survival of seedlings and sprouts. Survival and growth of older saplings were not influenced by drought. Seedling emergence of P. latifolia was higher than Q. ilex sprout production, but Q. ilex sprouts had higher survival and growth rates. These differences disappeared in the sapling stage. Carbon isotopic discrimination suggested that Q. ilex sprouts had higher WUE than P. latifolia seedlings. Drought increased WUE of recruits, particularly in Q. ilex. Water use regulation increased with ageing, particularly in P. latifolia. Q. ilex had higher δ15N values than P. latifolia; these were also higher under drier soil conditions. Current year seedlings had higher δ15N than saplings, particularly in P. latifolia, suggesting they exploit superficial soil layers. These results suggest that sprouts obtain benefit from resources stored in parent plants. At earlier stages, they perform better than seedlings. This response is not coupled to adult vulnerability to drought for these species, revealing the difficulty of predicting species dynamics during climate change.
Long‐term forest structure and regeneration after wildfire in Russian Karelia
Authors: Lampainen Johanna , Kuuluvainen Timo , Wallenius Tuomo H. , Karjalainen Leena , Vanha‐Majamaa Ilkka
Published: February 2009

We examined forest structure and regeneration in a 350‐ha forest dominated by Pinus sylvestris 31 yr after a wildfire in the Vienansalo wilderness, Russian Karelia. In most parts of the area, the 1969 fire was not stand replacing but had left larger trees alive so that the area generally remained forest covered. In some localities, however, all trees apparently died and distinct gaps were formed, suggesting that the fire severity varied considerably, contributing to increased variation in stand structure. Living and dead wood volumes were similar, 112 and 96 m3.ha‐1, respectively. The tree species proportions of dead vs living wood indicated that prior to fire disturbance Picea was more common in the area. Regeneration was abundant (saplings, ca. 14 000 ind.ha‐1, height 20 ‐200 cm) and tree seedling recruitment had occurred over a long period of time. Regeneration density was highest on the mesic Vaccinium‐Myrtillus forest site type, decreasing towards nutrient‐poor site types. The most common regeneration microsites were level ground (56% of saplings), immediate surroundings of decayed wood (23%) and depressions (11%). The high proportion of saplings on level ground suggests that after the fire regeneration conditions have been favourable across the whole forest floor. Nevertheless, the areas in the vicinity of decayed wood have been particularly important microsites for seedling establishment. The results provide an example of the effects of wildfire on forest structure in a natural Pinus sylvestris dominated forest, demonstrating the non stand replacing character of fire, high variability in stand structure and the abundance of post‐fire regeneration.
Wavelet analysis for detecting anisotropy in point patterns
Authors: Rosenberg Michael S.
Published: February 2009

Although many methods have been proposed for analysing point locations for spatial pattern, previous methods have concentrated on clumping and spacing. The study of anisotropy (changes in spatial pattern with direction) in point patterns has been limited by lack of methods explicitly designed for these data and this purpose; researchers have been constrained to choosing arbitrary test directions or converting their data into quadrat counts and using methods designed for continuously distributed data. Wavelet analysis, a booming approach to studying spatial pattern, widely used in mathematics and physics for signal analysis, has started to make its way into the ecological literature. A simple adaptation of wavelet analysis is proposed for the detection of anisotropy in point patterns. The method is illustrated with both simulated and field data. This approach can easily be used for both global and local spatial analysis.
Scale‐dependent frequency distributions of plant species in dune slacks: Dispersal and niche limitation
Authors: Bossuyt B. , Honnay O. , Hermy M.
Published: February 2009

Question: How do distribution patterns change with increasing scale level, and can this shift be attributed to dispersal and/or niche limitation?

Location: Dune slacks at the Belgian and North French coast.

Method: Frequency distribution patterns of species were tested over different scale levels (ranging from 0.008 to 45 km2). Analyses were executed for the total species pool and for subsets of species with high and low dispersal rates and habitat generalist and specialist species.

Results: Species distributions for the total species pool on scale levels larger than 1.5 km2 were unimodal, with an overrepresentation of rare species. With decreasing scale level, the proportion of common species increased, leading to weak bimodality. Distributions of subsets of slowly dispersing and habitat specialist species are on all scale levels characterised by a strongly unimodal pattern. The subset of species with high dispersal rates and habitat generalist species has a higher proportion of common species, leading to a significant core peak.

Conclusions: On all scale levels both dispersal and niche limitation are hampering the wider distribution of rare species. However, since isolation and habitat heterogeneity are limited on the smaller scale levels, a larger proportion of well dispersing and habitat generalist species is able to occupy a high number of patches, resulting in a significant core peak for the total species pool.
Interpretation of soil δ13C as an indicator of vegetation change in African savannas
Authors: Gillson L. , Waldron S. , Willis K.J.
Published: February 2009

Question:The relationship between carbon‐13 in soil organic matter and C3and C4plant abundance is complicated because of differential productivity, litter fall and decomposition. As a result, applying a mass balance equation to δ13C data from soils cannot be used to infer past C3and C4plant abundance; only the proportion of carbon derived from C3and C4plants can be estimated. In this paper, we compare δ13C of surface soil samples with vegetation data, in order to establish whether the ratio of C3:C4plants (rather than the proportion of carbon from C3and C4plants) can be inferred from soil δ13C.

Location:The Tsavo National Park, in southeastern Kenya.

Methods:We compare vegetation data with δ13C of organic matter in surface soil samples and derive regression equations relating the δ13C of soil organic matter to C3:C4plant abundance. We use these equations to interpret δ13C data from soil profiles in terms of changes in inferred C3:C4plant ratio. We compare our method of interpretation with that derived from a mass balance approach.

Results:There was a statistically significant, linear relationship between the δ13C of organic matter in surface soil samples and the natural logarithm of the ratio of C3:C4plants in the 100m2surrounding the soil sample.

Conclusions:We suggest that interpretation of δ13C data from organic matter in soil profiles can be improved by comparing vegetation surveys with δ13C of organic matter in surface soil samples. Our results suggest that past C3plant abundance might be under‐estimated if a mass balance approach is used.
Do different competitive abilities of three fern species explain their different regional abundances?
Authors: Rünk K. , Moora M. , Zobel M.
Published: February 2009

Question: Do different competitive abilities of three fern species explain their different regional abundances?

Location: Estonia, Europe.

Methods: The factorial pot experiment, in which single individuals of three fern species were grown in natural soil with 0, 2,4, and 8 neighbouring individuals of Deschampsia flexuosa.

Results: The response patterns of different biomass fractions and morphological parameters of fern species were similar to each other. The diploid D. expansa was the most vulnerable to competition, while tetraploid D. carthusiana and D. dilatata were more tolerant. D. carthusiana allocated relatively more to below‐ground parts than the other two species and allocation to roots increased when neighbour density increased. For D. expansa and D. dilatata, allocation to below‐ground parts decreased at high neighbour density, while in D. dilatata also the relative length of the stipe increased. Thus, the response of D. carthusiana corresponds to a ‘persistence type’ and that of D. dilatata to a ‘foraging type’.

Conclusions: Lower vulnerability of D. carthusiana to competition, compared to D. expansa, may explain the higher regional and local abundance of the former. The rarity of D. dilatata in Estonia, however, could rather be explained by the impact of climatic factors, since this species is near its northeastern distribution limit in Estonia.
Importance of tolerance to herbivory for plant survival in a British grassland
Authors: del‐Val E. , Crawley M.J.
Published: February 2009

Question: Is plant capacity to regrow under different herbivore treatments related to herbivore increaser/decreaser plant status?

Location: Grassland in Southeast England (GR 41/944691).

Methods: A field experiment was established in order to understand the role of plant tolerance to herbivory in explaining the abundance of nine grassland species previously known as herbivore increasers or decreasers. Tolerance was measured as a plant's capacity to regrow after exposure to herbivores. The experiment was designed to measure the impact of rabbits, molluscs, insects and clipping (artificial damage). Plants were propagated by stolons, exposed to different treatments in the field and then allowed to recover in the greenhouse for a month.

Results: Previous studies have stated that plants that are able to persist in a herbivore environment could be tolerant or resistant, in agreement with the later our results showed that rabbit increaser plants were tolerant to herbivory in terms of biomass regrowth. Nonetheless, insect and mollusc increasers did not show any particular pattern related to plant compensation and some decreaser species were intolerant.

Conclusions: This study shows that tolerance to herbivory could be an important mechanism for rabbit increaser species survival in grazed ecosystems.
Urban domestic gardens (III): Composition and diversity of lawn floras
Authors: Thompson Ken , Hodgson John G. , Smith Richard M. , Warren Philip H. , Gaston Kevin J.
Published: February 2009

Question: How do lawn floras compare with those of semi‐natural grasslands? Are the compositions of lawn floras determined by local, within‐garden factors (e.g. lawn management and size) or by regional factors (e.g. climate and location)? Are lawn floras nested (like semi‐natural grasslands) or not (like cultivated parts of gardens)? Are there gradients of species composition within lawns?

Location: Sheffield, UK.

Methods: We examined the composition of the floras of entire lawns and of two 1‐m2 lawn quadrats in 52 gardens.

Results: A total of 159 species of vascular plants was recorded, 60 of them only once. Most lawn species were forbs, but most lawn cover consisted of grasses. Lawn species were predominantly natives. Bigger lawns had more species, but richness was not closely linked to other environmental or management variables. Composition of lawn floras varied with altitude, with woodland and wetland plants more common in the higher west of the city, and weeds of waste ground in the east. The species‐area curve derived from 1‐m2 lawn quadrats was very similar to that of semi‐natural grasslands. Lawn quadrats were significantly nested, with rarer species mostly confined to more species‐rich quadrats. Trampling‐tolerant Poa annua was more abundant in the part of the lawn nearer the house.

Conclusions: In most respects, lawns behaved much more like semi‐natural grasslands than like cultivated flower beds and borders. Species composition of lawns is strongly influenced by local climate. Most lawns show an internal gradient of composition, linked to a gradient of intensity of use.
Nutrient limitation and nutrient‐driven shifts in plant species composition in a species‐rich fen meadow
Authors: van der Hoek Dick , van Mierlo Anita J.E.M. , van Groenendael Jan M.
Published: February 2009

Question: We studied the development and persistence of the effects of nutrient pulses on biomass production and species composition in a fen meadow.

Location: Nature reserve, central Netherlands, 5 m a.s.l.

Methods: Single pulse fertilization with N and P in a factorial design on an undrained central and a drained margin site in a species‐rich fen meadow (Cirsio dissecti‐Molinietum). Biomass production and species composition were monitored during four years.

Results: At the central site, N addition boosted biomass production, but only during one year. The species composition was not changed. P fertilization increased the biomass production and changed the species composition from a vegetation dominated by Carex panicea to a grassland community with abundant Holcus lanatus, but not before the second year. At the margin site, P fertilization changed the species composition in a similar way, but biomass production was not increased. N fertilization had no effect. At both sites the P induced shift in species composition persisted for four years although the P effect declined during the experiment.

Conclusions: The biomass responses show that N was limiting in the central site. Another nutrient, besides N and P (probably K) must have been limiting in the marginal site. The fast decline of the N effect on biomass is ascribed to increased denitrification and biomass removal. The delay in the P effect on biomass and species composition and the persistence of the P effect on species composition are ascribed to fast immobilisation and subsequent slow release of fertilizer P in the peat soil. Recurrence of the P pulses is expected to cause permanent changes in species composition.
Structural complexity and land‐surface energy exchange along a gradient from arctic tundra to boreal forest
Authors: Thompson C. , Beringer J. , Chapin F.S. , McGuire A.D.
Published: February 2009

Question: Current climate changes in the Alaskan Arctic, which are characterized by increases in temperature and length of growing season, could alter vegetation structure, especially through increases in shrub cover or the movement of treeline. These changes in vegetation structure have consequences for the climate system. What is the relationship between structural complexity and partitioning of surface energy along a gradient from tundra through shrub tundra to closed canopy forest?

Location: Arctic tundra‐boreal forest transition in the Alaskan Arctic.

Methods: Along this gradient of increasing canopy complexity, we measured key vegetation characteristics, including community composition, biomass, cover, height, leaf area index and stem area index. We relate these vegetation characteristics to albedo and the partitioning of net radiation into ground, latent, and sensible heating fluxes.

Results: Canopy complexity increased along the sequence from tundra to forest due to the addition of new plant functional types. This led to non‐linear changes in biomass, cover, and height in the understory. The increased canopy complexity resulted in reduced ground heat fluxes, relatively conserved latent heat fluxes and increased sensible heat fluxes. The localized warming associated with increased sensible heating over more complex canopies may amplify regional warming, causing further vegetation change in the Alaskan Arctic.
Seed bank assembly follows vegetation succession in dune slacks
Authors: Bossuyt Beatrijs , Hermy Martin
Published: February 2009

Question: Is the seed bank in dune slacks during the whole successional range mainly composed of early successional species or does it vary according to the changing vegetation?

Location: Belgium, western part of the coast.

Methods: We investigated the soil seed bank composition using a seedling germination method in a chronosequence of 20 dune slacks, ranging in age from five to 55 yr.

Results: Both seed density and species richness in the seed bank were very low in the first successional stages and increased with age, mainly as a result of increasing seed production. The similarity between seed bank and vegetation was higher in older slacks. A comparison of characteristics between seed bank and vegetation showed that the seed bank was, to a large extent, composed of later successional species. Occurrence patterns of individual species also showed that seeds become incorporated in the soil after the species has established in the vegetation.

Conclusion: The seed bank is not likely to be the driving force for successional changes in the vegetation, and successional changes rely on dispersal. Some early successional species persist in the seed bank, but generally only in low numbers. The results also confirm that most typical dune slack species do not form persistent seeds, so that re‐establishment from the seed bank is not to be expected when the species has disappeared from the vegetation.
Biomass distribution of two subalpine dwarf‐shrubs in relation to soil moisture and nutrient content
Authors: Gerdol Renato , Anfodillo Tommaso , Gualmini Matteo , Cannone Nicoletta , Bragazza Luca , Brancaleoni Lisa
Published: February 2009

Question: Do soil water content and/or soil nitrogen (N) content and/or soil phosphorus (P) content affect the biomass of Vaccinium myrtillus and V. vitis‐idaea in a sub‐alpine heath?

Location: Dolomites, northern Italy, 1800 m a.s.l.

Methods: We determined above‐ground and below‐ground biomass of the shrubs at three sites, each on a different substrate type. At each site, we determined soil N‐ and P‐contents. We also determined leaf water potential (Psi;1), N‐ and P‐concentrations in plant tissues and litter, as well as δ13C and δ15N in mature leaves.

Results: V. myrtillus biomass was highest at the silicate site, V. vitis‐idaea biomass was highest at the carbonate site. Both shrubs had low biomass at the peat site, possibly due to a toxic effect of waterlogging in wet soils. For both species, pre‐dawn Psi;1 indicated optimal hydration and midday Psi;1 did not show any sign of water stress. Water use efficiency (WUE) did not differ among sites for any species. Whole‐plant nutrient concentrations showed that, with increasing biomass, N was diluted in V. myrtillus tissues while P was diluted in V. vitis‐idaea tissues. Foliar N‐concentration was higher overall for V. myrtillus. Foliar P‐concentration in V. myrtillus peaked at the silicate site. Foliar N : P ratios suggested that V. myrtillus was primarily P‐limited and V. vitis‐idaea primarily N‐limited.

Conclusions: Water content affected the distribution of the two shrubs in a similar way, higher P‐availability in the soil enhanced V. myrtillus rather than V. vitis‐idaea.
Palm distribution patterns in Amazonian rainforests: What is the role of topographic variation?
Authors: Vormisto Jaana , Tuomisto Hanna , Oksanen Jari
Published: February 2009

Question:Are soil properties and topographic variation related with palm (Arecaceae) species composition and distribution patterns? If so, are species distribution patterns consistent across sites?

Location:100–200 m a.s.l, non‐inundated Amazonian rainforest, NE Peru.

Methods:One 0.65‐ha line transect divided into 5 m by 5 m subunits was inventoried for all palm individuals at each site. Soil samples were collected, and topography was measured.

Results:A total of 56 palm taxa were recorded. Floristic similarity among transects clearly corresponded with similarity in soil cation content when species abundances were taken into account, but less so when only presence‐absence data were used. Taxon‐wise distribution analyses were done for the 37 most abundant palm taxa. Quite a few of these taxa proved not to be randomly distributed along the transects, but instead were clearly more abundant in some topographic positions than in others. However, the consistency of the distribution patterns across study sites proved to be rather low, and many of the palm taxa showed different distribution patterns at different sites.

Conclusions:The ambiguity in distribution patterns across study sites may partly be due to the complexity of topography as a measure of ecological conditions, and the probability that it is related to the variation in different environmental variables at different sites.
How doesReynoutriainvasion fit the various theories of invasibility?
Authors: Bímová Kateřina , Mandák Bohumil , Kašparová Ivana
Published: February 2009

Questions:1. How does species richness of recipient communities affectReynoutriainvasion? 2. How doesReynoutriainvasion change host community structure? 3. Are there any differences in habitat preferences among three closely relatedReynoutriataxa? 4. How does the genetic structure ofReynoutriapopulations change along the course of a river?

Location:River Jizera basin, north Bohemia, Czech Republic.

Methods:Nine 0.25 km2plots were chosen along the river. Within each plot all main habitat types were determined and sampled using the Braun‐Blanquet scale to determine the invasibility of various communities. The patches invaded byReynoutriataxa and surroundingReynoutria‐freevegetation in the same habitat type were sampled as relevé pairs to compare the composition of invaded and non‐invaded vegetation. In addition, to characterize the genetic structure ofReynoutriapopulations along the river, 30 samples from different clones were collected.

Results and conclusions:1. The species richness of communities has no influence on the success ofReynoutriainvasion in the area studied. The combination of environmental conditions and propagule spread is more important to the invasion success than the number of species in the host community. 2.Reynoutriainvasion greatly reduces species diversity. 3.R. japonicainvaded more habitat types thanR. sachalinensisandR.×bohemica. The hybridR.×bohemicaoutcompetes the parental taxa at sites where both taxa co‐occur. 4. Isozyme analysis revealed phenotype variability in the hybrid in contrast to the parental taxa. Different hybrid phenotypes are distributed randomly on the middle and lower reaches of the River Jizera; one of them dominates and the other three occur occasionally. This pattern supports the hypothesis that sexual reproduction occasionally occurs withinReynoutriataxa.
Population responses of Ulex shrubs to fire in a lowland heath community
Authors: Stokes K.E. , Allchin A.E. , Bullock J.M. , Watkinson A.R.
Published: February 2009

Question: How does the frequency of heathland fire events affect population growth rates of two woody shrub species, Ulex gallii and U. minor?

Location: Dry heathland on the south coast of England, UK.

Methods: The population dynamics of U. gallii and U. minor were modelled at each phase of the heathland cycle — pioneer, building, mature and degenerate — using periodic matrix products to investigate the response to different fire regimes.

Results: Population growth rates of both Ulex species declined under annual burning. Initially, as the time between burns increased, population growth rate increased for both species. Maximum population growth rates for each Ulex species were achieved under a 16‐yr fire return interval. Fire return intervals > 16 yr resulted in declining population growth rates.

Conclusions: A species‐specific critical fire frequency can be predicted, the minimum fire return intervals permitting persistence were 4 yr for U. minor and 3 yr for U. gallii. These patterns are similar to those reported for a range of woody plant species within savanna environments.
Pathways of stand development in ageing Pinus sylvestris forests
Authors: Kint Vincent , Mohren G.M.J. , Geudens Guy , de Wulf Robert , Lust Noël
Published: February 2009

Question: What are the main pathways of long‐term stand development in forest ecosystems on oligotrophic and acidic sandy soils?

Location: Nine forest reserves at different locations in The Netherlands; all ageing Pinus sylvestris forests that are no longer managed and where massive regeneration of broad‐leaved species is often reported.

Methods: Agglomerative cluster analysis was used to define structural classes from forest reserve data. Sequences of structural classes, representing different trajectories of stand development, were constructed with the aid of a process based gap model.

Results: Four main pathways of stand development could be distinguished. Three pathways are linked to gap dynamics, and lead towards dominance of Betula, Quercus or Fagus. They differ in light availability for regeneration and/or seed tree availability. The fourth pathway comprises of development patterns after major disturbances.

Conclusions: The new methodological approach, combining the empirical strength of forest reserve data with the predictive ability of a process based model, made it possible to detail and quantify insights into structure and dynamics of forests on poor sandy soils. Some factors not included in the study can substantially influence pathways, especially those where Quercus and Fagus potentially play an important role.
Why should we constrain stress and limitation? Why conceptual terms deserve broad definitions
Authors: Weiher Evan
Published: February 2009

In his recent essay, Ch. Körner (2003) suggested that we need to clarify and narrow the meaning of limitation and stress. Current definitions and usage of these terms are not in any great need of revision. Limiting the use of ‘stress’ to only extreme situations is inappropriate because sometimes stress is indeed weak. What is needed is to use the terms within a comparative framework, a framework based on comparisons along gradients and among taxa. Recent studies on the factors controlling diversity have used such a comparative framework, and have increased our understanding of the relative roles of various types of stress. Redefining and narrowing general terms that relate to common processes would limit our ability to make comparisons and generalizations, and this should be avoided.
Why we should conserve ‘limiting factors’, at least sometimes!
Authors: Marrs R.H.
Published: February 2009

Körner's recent paper provided an excellent initial discussion of the term ‘limitation’ in ecology. I accept most of his arguments but would argue that there are some circumstances in applied ecology where the concept of limitation can be useful; these are (1) where there is a deficiency of a factor that prevents growth, and (2) where there is a need to manage an ecosystem so that a limitation is enforced.
Community‐level changes in Australian subalpine vegetation following invasion by the non‐native shrub Cytisus scoparius
Authors: Wearne Lynise J. , Morgan John W.
Published: February 2009

Question: What are the changes associated with the recent invasion by the non‐native legume, Cytisus scoparius?

Location: Subalpine vegetation (1500 m a.s.l.) in Australia.

Methods: We used multivariate techniques and regression analyses to assess vegetation and environmental changes across six study sites. Vegetation and environmental variables were investigated at three different stages of invasion: (1) recent invasion (8–10 yr), (2) mature invasion (15–16 yr) and (3) long‐term invasion (25 yr).

Results: Substantial changes in floristic composition and species richness were evident after 15 yr and these changes became more pronounced after 25 yr. Changes due to invasion were associated with a dramatic loss of native species or a reduction in their abundance. No ‘new species’ were evident under invaded stands. Forbs were most affected by the establishment of C. scoparius, although all growth forms responded negatively. Dense canopy shading and an increasingly dense, homogeneous litter layer in the understorey as a result of C. scoparius were strong environmental drivers of vegetation change. Greenhouse studies confirmed the importance of these processes on the germination and growth of two native species.

Conclusions: This study highlights the potential for C. scoparius to alter both vegetation and environmental processes in the subalpine region.
Predicting the species composition of Nardus stricta communities by logistic regression modelling
Authors: Peppler‐Lisbach Cord , Schröder Boris
Published: February 2009

Question: Predictive models in plant ecology usually deal with single species or community types. Little effort has so far been made to predict the species composition of a community explicitly. The modelling approach presented here provides a conceptual framework on how to achieve this by combining habitat models for a large number of species to an additive community model. Our approach is exemplified by Nardus stricta communities (acidophilous, low‐productive grassland).

Location: Large areas of Germany, 0–2040 m a.s.l.

Methods: Logistic regression is applied for individual species models which are subsequently combined for an explicit prediction of species composition. Several parameters reflecting soil, management and climatic conditions serve as predictor variables. For validation, bootstrap and jackknife resampling procedures are used as well as ordination techniques (DCA, CCA).

Results: We calculated significant models for 138 individual species. The predictions of species composition and species richness yield good agreements with the observed data. DCA and CCA results show that the community model preserves the main patterns in floristic space.

Conclusions: Our approach of predicting species composition is an effective tool that can be applied in nature conservation, e.g. to assess the effects of different site conditions and alternative management scenarios on species composition and richness.
Relationships between plant traits and climate in the Mediterranean region: A pollen data analysis
Authors: Barboni D. , Harrison S.P. , Bartlein P.J. , Jalut G. , New M. , Prentice I.C. , Sanchez‐Goñi M.‐F. , Spessa A. , Davis B. , Stevenson A.C.
Published: February 2009

Question: What are the correlations between the degree of drought stress and temperature, and the adoption of specific adaptive strategies by plants in the Mediterranean region?

Location: 602 sites across the Mediterranean region.

Method: We considered 12 plant morphological and phenological traits, and measured their abundance at the sites as trait scores obtained from pollen percentages. We conducted stepwise regression analyses of trait scores as a function of plant available moisture (α) and winter temperature (MTCO).

Results: Patterns in the abundance for the plant traits we considered are clearly determined by α, MTCO or a combination of both. In addition, trends in leaf size, texture, thickness, pubescence and aromatic leaves and other plant level traits such as thorniness and aphylly, vary according to the life form (tree, shrub, forb), the leaf type (broad, needle) and phenology (evergreen, summer‐green).

Conclusions: Despite conducting this study based on pollen data we have identified ecologically plausible trends in the abundance of traits along climatic gradients. Plant traits other than the usual life form, leaf type and leaf phenology carry strong climatic signals. Generally, combinations of plant traits are more climatically diagnostic than individual traits. The qualitative and quantitative relationships between plant traits and climate parameters established here will help to provide an improved basis for modelling the impact of climate changes on vegetation and form a starting point for a global analysis of pollen‐climate relationships.
Decline of arctic‐alpine plants at the southern margin of their range following a decade of climatic warming
Authors: Lesica P. , McCune B.
Published: February 2009

Question:Have recent increases in temperature caused a decline in arctic‐alpine plants at the southern margin of their range?

Location:Above tree line; Glacier National Park, Montana, western USA.

Methods:We monitored the abundance of seven arctic‐alpine vascular plants at or near the southern limits of their ranges at three sites in Glacier National Park, Montana from 1989 through 2002. In addition we recorded canopy cover of all plant species in sample plots once at the beginning and again at the end of the study.

Results:Mean summer temperature during this period averaged 0.6 °C higher than the previous four decades. Results of ordinations with non‐metric multidimensional scaling suggested that vegetation moved toward the dry end of a moisture gradient at two sites during the course of the study. At the same time four of the peripheral arctic‐alpine indicator species demonstrated 31–65% declines in abundance, while none increased.

Conclusions:We cannot rigorously infer causality from our descriptive study; however, changes in both indicator species and the vegetation matrix were consistent with predictions of climate‐induced extirpation of high‐elevation species and the northern migration of floras. Our results also suggest that species responded to the decade of warming individualistically with little relationship to growth form.
Effects of drought and fire on seedling survival and growth under contrasting light conditions in a seasonal tropical forest
Authors: Marod Dokrak , Kutintara Utis , Tanaka Hiroshi , Nakashizuka Tohru
Published: February 2009

Question: How do tree seedlings differ in their responses to drought and fire under contrasting light conditions in a tropical seasonal forest?

Location: Mae Klong Watershed Research Station, 100–900 m a.s.l, Kanchanaburi Province, western Thailand.

Method: Seedlings of six trees, Dipterocarpus alatus, D. turbinatus, Shorea siamensis, Pterocarpus macrocarpus, Xylia xylocarpa var. kerrii and Sterculia macrophylla, were planted in a gap and under the closed canopy. For each light condition, we applied (1) continuous watering during the dry season (W); (2) ground fire during the dry season (F); (3) no watering/no fire (intact, I). Seedling survival and growth were followed.

Results: Survival and growth rate were greater in the gap than under the closed canopy for all species, most dramatically for S. siamensis and P. macrocarpus. Dipterocarpus alatus and D. turbinatus had relatively high survival under the closed canopy, and watering during the dry season resulted in significantly higher survival rates for these two species. Watering during the dry season resulted in higher growth rates for five species. All seedlings of D. alatus and D. turbinatus failed to re‐sprout and died after fire. The survival rates during the dry season and after the fire treatment were higher for the seedlings grown in the canopy gap than in the shade for S. siamensis, P. macrocarpus, X. xylocarpa var. kerrii and S. macrophylla. The seedlings of these species in the canopy gap had higher allocation to below‐ground parts than those under the closed canopy, which may support the ability to sprout after fire.

Conclusions: The light conditions during the rainy season greatly affect seedling survival and resistance to fire during the subsequent dry season. Our results suggest differentiation among species in terms of seedling adaptations to shade, drought and fire.
Change over 70 years in a southern California chaparral community related to fire history
Authors: Franklin Janet , Coulter Charlotte L. , Rey Sergio J.
Published: February 2009

Question: What changes in species composition and cover have occurred in chaparral as a function of fire history across an ecoregion?

Location: San Diego County, California, USA.

Methods: Stands in which 40 mid‐elevation chaparral vegetation plots (each 400 m2 in area) were located in the 1930s were resurveyed in 2001. We stratified the stands into Infrequently versus Frequently burned (0–1 versus 2 or more fires recorded in the 91‐yr period), and Immature versus Mature (ã31 yr versus >31 yr since last fire), resulting in four groups. Ten stands were randomly selected from each of these groups for survey.

Results: There were no major shifts in life form composition, e.g., live oak trees were not invading chaparral that had experienced little or no fire, nor were subshrubs or herbaceous species replacing shrubs in areas that had experienced more frequent fires. However, there was a notable increase in the frequency of the subshrub Eriogonum fasciculatum across all fire history groups. In the mature stands with infrequent fire, average cover of resprouting shrubs increased (from 72 to 91%) and cover of obligate seeding shrubs (species with fire‐cued germination) decreased (from 21 to 6%) significantly. Mature stands with frequent fire showed a significant decrease in resprouter cover (from 87 to 80%) and increase in obligate seeders (from 10 to 16%).

Conclusions: While the tremendous changes in land use in southern California have been predicted to cause shifts in chaparral composition, these shifts are difficult to detect because species longevity and fire cycles are on the order of decades to a century. In this study, the expected trends could only be detected in groups that were mature at the time of the second survey.
Remote sensing of protected areas to derive baseline vegetation functioning characteristics
Authors: Garbulsky Martín F. , Paruelo José M.
Published: February 2009

Question: How can we derive baseline/reference situations to evaluate the impact of global change on terrestrial ecosystem functioning?

Location: Main biomes (steppes to rain forests) of Argentina.

Methods: We used AVHRR/NOAA satellite data to characterize vegetation functioning. We used the seasonal dynamics of the Normalized Difference Vegetation Index (NDVI), a linear estimator of the fraction of the photosynthetic active radiation intercepted by vegetation (fPAR), and the surface temperature (Ts), for the period 1981–1993. We extracted the following indices: NDVI integral (NDVI‐I), NDVI relative range (Rrel), NDVI maximum value (Vmax), date of maximum NDVI (Dmax) and actual evapotranspiration.

Results: f
PAR varied from 2 to 80%, in relation to changes in net primary production (NPP) from 83 to 1700 g.m‐2.yr‐1. NDVI‐I, Vmax and fPAR had positive, curvilinear relationships to mean annual precipitation (MAP), NPP was linearly related to MAP. Tropical and subtropical biomes had a significantly lower seasonality (Rrel) than temperate ones. Dmax was not correlated with the defined environmental gradients. Evapotranspiration ranged from 100 to 1100 mm.yr‐1. Interannual variability of NDVI attributes varied across the temperature and precipitation gradients.

Conclusions: Our results may be used to represent baseline conditions in evaluating the impact of land use changes across environmental gradients. The relationships between functional attributes and environmental variables provide a way to extrapolate ecological patterns from protected areas across modified habitats and to generate maps of ecosystem functioning.
Interpretation of scale in paired quadrat variance methods
Authors: Guo Qinghua , Kelly Maggi
Published: February 2009

Question: Previous interpretations of the variance plot of paired quadrat variance method (PQV) have been incomplete. The objective of this study was to clarify the interpretation of PQV, and to shed additional light on how different quadrat variance methods can be used, in concert, to measure scale in transect data.

Methods: We used artificial and real data to examine how the PQVmethod elucidates spatial pattern. Two‐term local quadrat variance (TTLQV) and new local variance (NLV) methods, together with their three‐term counterparts, were also applied to the same data sets, and the results from all methods were compared.

Results: When the mean gap size equalled the mean patch size along a transect, the first peak of the variance of PQV, NLV and TTLQV corresponded with the gap size (or patch size). However, if the mean gap size and patch size were unequal, the variance plot of PQV displayed a flat‐topped plateau, in which the first inflection represented the mean size of the smaller phase and the second inflection represented the mean size of the larger phase; TTLQV showed a clear peak and NLV displayed a distinct first peak while the second inflection was dampened. The results also indicated than the three‐term versions of quadrat variance methods did not consistently outperform their two‐term counterparts, and often confused the interpretation of scale.

Conclusions: The quadrat variance methods associated with the patch‐gap measurements were able to efficiently detect not only the size of patches, but also the size of gaps.