Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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    Alpha diversity of vascular plants in European forests
    Večeřa, Martin ; Divíšek, Jan ; Lenoir, Jonathan ; Jiménez-Alfaro, Borja ; Biurrun, Idoia ; Knollová, Ilona ; Agrillo, Emiliano ; Campos, Juan Antonio ; Čarni, Andraž ; Crespo Jiménez, Guillermo ; Ćuk, Mirjana ; Dimopoulos, Panayotis ; Ewald, Jörg ; Fernández-González, Federico ; Gégout, Jean Claude ; Indreica, Adrian ; Jandt, Ute ; Jansen, Florian ; Kącki, Zygmunt ; Rašomavičius, Valerijus ; Řezníčková, Marcela ; Rodwell, John S. ; Schaminée, Joop H.J. ; Šilc, Urban ; Svenning, Jens Christian ; Swacha, Grzegorz ; Vassilev, Kiril ; Venanzoni, Roberto ; Willner, Wolfgang ; Wohlgemuth, Thomas ; Chytrý, Milan - \ 2019
    Journal of Biogeography 46 (2019)9. - ISSN 0305-0270 - p. 1919 - 1935.
    diversity - Europe - European Vegetation Archive (EVA) - forest vegetation - plant community - predictive modelling - Random Forests - species-richness patterns - vascular plants - vegetation-plot database

    Aim: The former continental-scale studies modelled coarse-grained plant species-richness patterns (gamma diversity). Here we aim to refine this information for European forests by (a) modelling the number of vascular plant species that co-occur in local communities (alpha diversity) within spatial units of 400 m2; and (b) assessing the factors likely determining the observed spatial patterns in alpha diversity. Location: Europe roughly within 12°W–30°E and 35–60°N. Taxon: Vascular plants. Methods: The numbers of co-occurring vascular plant species were counted in 73,134 georeferenced vegetation plots. Each plot was classified by an expert system into deciduous broadleaf, coniferous or sclerophyllous forest. Random Forest models were used to map and explain spatial patterns in alpha diversity for each forest type separately using 19 environmental, land-use and historical variables. Results: Our models explained from 51.0% to 70.9% of the variation in forest alpha diversity. The modelled alpha-diversity pattern was dominated by a marked gradient from species-poor north-western to species-rich south-eastern Europe. The most prominent richness hotspots were identified in the Calcareous Alps and adjacent north-western Dinarides, the Carpathian foothills in Romania and the Western Carpathians in Slovakia. Energy-related factors, bedrock types and terrain ruggedness were identified as the main variables underlying the observed richness patterns. Alpha diversity increases especially with temperature seasonality in deciduous broadleaf forests, on limestone bedrock in coniferous forests and in areas with low annual actual evapotranspiration in sclerophyllous forests. Main conclusions: We provide the first predictive maps and analyses of environmental factors driving the alpha diversity of vascular plants across European forests. Such information is important for the general understanding of European biodiversity. This study also demonstrates a high potential of vegetation-plot databases as sources for robust estimation of the number of vascular plant species that co-occur at fine spatial grains across large areas.

    Accounting for the decrease of photosystem photochemical efficiency with increasing irradiance to estimate quantum yield of leaf photosynthesis
    Yin, X. ; Belay, D. ; Putten, P.E.L. van der; Struik, P.C. - \ 2014
    Photosynthesis Research 122 (2014)3. - ISSN 0166-8595 - p. 323 - 335.
    temperature response functions - chlorophyll fluorescence - co2 uptake - electron-transport - c-3 photosynthesis - biochemical-model - limited photosynthesis - mesophyll conductance - vascular plants - o-2 evolution
    Maximum quantum yield for leaf CO2 assimilation under limiting light conditions (UCO2LL) is commonly estimated as the slope of the linear regression of net photosynthetic rate against absorbed irradiance over a range of low-irradiance conditions. Methodological errors associated with this estimation have often been attributed either to light absorptance by non-photosynthetic pigments or to some data points being beyond the linear range of the irradiance response, both causing an underestimation of UCO2LL. We demonstrate here that a decrease in photosystem (PS) photochemical efficiency with increasing irradiance, even at very low levels, is another source of error that causes a systematic underestimation of UCO2LL. A model method accounting for this error was developed, and was used to estimate UCO2LL from simultaneous measurements of gas exchange and chlorophyll fluorescence on leaves using various combinations of species, CO2, O2, or leaf temperature levels. The conventional linear regression method under-estimated UCO2LL by ca. 10–15 %. Differences in the estimated UCO2LL among measurement conditions were generally accounted for by different levels of photorespiration as described by the Farquhar-von Caemmerer–Berry model. However, our data revealed that the temperature dependence of PSII photochemical efficiency under low light was an additional factor that should be accounted for in the model.
    Assessing the spatial variability in peak season CO2exchange characteristics across the Arctic tundra using a light response curve parameterization
    Mbufong, H.N. ; Lund, M. ; Aurela, M. ; Molen, M.K. van der - \ 2014
    Biogeosciences 11 (2014)17. - ISSN 1726-4170 - p. 4897 - 4912.
    carbon-dioxide exchange - net ecosystem exchange - photosynthetically active radiation - growing-season - thermal-acclimation - vascular plants - tussock tundra - climate-change - energy flux - alaska
    This paper aims to assess the spatial variability in the response of CO2exchange to irradiance across the Arctic tundra during peak season using light response curve (LRC) parameters. This investigation allows us to better understand the future response of Arctic tundra under climatic change. Peak season data were collected during different years (between 1998 and 2010) using the micrometeorological eddy covariance technique from 12 circumpolar Arctic tundra sites, in the range of 64-74° N. The LRCs were generated for 14 days with peak net ecosystem exchange (NEE) using an NEE-irradiance model. Parameters from LRCs represent site-specific traits and characteristics describing the following: (a) NEE at light saturation (Fcsat), (b) dark respiration (Rd), (c) light use efficiency (a), (d) NEE when light is at 1000 µmol m-2s-1(Fc1000), (e) potential photosynthesis at light saturation (Psat) and (f) the light compensation point (LCP). Parameterization of LRCs was successful in predicting CO2flux dynamics across the Arctic tundra. We did not find any trends in LRC parameters across the whole Arctic tundra but there were indications for temperature and latitudinal differences within sub-regions like Russia and Greenland. Together, leaf area index (LAI) and July temperature had a high explanatory power of the variance in assimilation parameters (Fcsat, Fc1000and Psat, thus illustrating the potential for upscaling CO2exchange for the whole Arctic tundra. Dark respiration was more variable and less correlated to environmental drivers than were assimilation parameters. This indicates the inherent need to include other parameters such as nutrient availability, substrate quantity and quality in flux monitoring activities.
    Plant movements and climate warming: intraspecific variation in growth responses to nonlocal soils
    Frenne, P. De; Coomes, D. ; Schrijver, A. De; Staelens, J. ; Alexander, J.M. ; Bernhardt-Romermann, M. ; Brunet, J. ; Chabrerie, O. ; Chiarucci, A. ; Ouden, J. den - \ 2014
    New Phytologist 202 (2014)2. - ISSN 0028-646X - p. 431 - 441.
    local adaptation - latitudinal gradient - vascular plants - forest herbs - nitrogen deposition - seed dispersal - range shifts - germination - colonization - temperature
    Most range shift predictions focus on the dispersal phase of the colonization process. Because moving populations experience increasingly dissimilar nonclimatic environmental conditions as they track climate warming, it is also critical to test how individuals originating from contrasting thermal environments can establish in nonlocal sites. We assess the intraspecific variation in growth responses to nonlocal soils by planting a widespread grass of deciduous forests (Milium effusum) into an experimental common garden using combinations of seeds and soil sampled in 22 sites across its distributional range, and reflecting movement scenarios of up to 1600 km. Furthermore, to determine temperature and forest-structural effects, the plants and soils were experimentally warmed and shaded. We found significantly positive effects of the difference between the temperature of the sites of seed and soil collection on growth and seedling emergence rates. Migrant plants might thus encounter increasingly favourable soil conditions while tracking the isotherms towards currently ‘colder’ soils. These effects persisted under experimental warming. Rising temperatures and light availability generally enhanced plant performance. Our results suggest that abiotic and biotic soil characteristics can shape climate change-driven plant movements by affecting growth of nonlocal migrants, a mechanism which should be integrated into predictions of future range shifts.
    How Does Tree Density Affect Water Loss of Peatlands? A Mesocosm Experiment
    Limpens, J. ; Holmgren, M. ; Jacobs, C.M.J. ; Zee, S.E.A.T.M. van der; Karofeld, E. ; Berendse, F. - \ 2014
    PLoS ONE 9 (2014)3. - ISSN 1932-6203 - 11 p.
    sphagnum mosses - vascular plants - carbon-dioxide - climate-change - boreal mire - scots pine - vegetation - bogs - evapotranspiration - table
    Raised bogs have accumulated more atmospheric carbon than any other terrestrial ecosystem on Earth. Climate-induced expansion of trees and shrubs may turn these ecosystems from net carbon sinks into sources when associated with reduced water tables. Increasing water loss through tree evapotranspiration could potentially deepen water tables, thus stimulating peat decomposition and carbon release. Bridging the gap between modelling and field studies, we conducted a three-year mesocosm experiment subjecting natural bog vegetation to three birch tree densities, and studied the changes in subsurface temperature, water balance components, leaf area index and vegetation composition. We found the deepest water table in mesocosms with low tree density. Mesocosms with high tree density remained wettest (i.e. highest water tables) whereas the control treatment without trees had intermediate water tables. These differences are attributed mostly to differences in evapotranspiration. Although our mesocosm results cannot be directly scaled up to ecosystem level, the systematic effect of tree density suggests that as bogs become colonized by trees, the effect of trees on ecosystem water loss changes with time, with tree transpiration effects of drying becoming increasingly offset by shading effects during the later phases of tree encroachment. These density-dependent effects of trees on water loss have important implications for the structure and functioning of peatbogs.
    Biogeographic patterns of base-rich fen vegetation across Europe
    Jiménez-Alfaro, B. ; Hájek, M. ; Ejrnaes, R. ; Rodwell, J. ; Pawlikowski, P. ; Weeda, E.J. - \ 2014
    Applied Vegetation Science 17 (2014)2. - ISSN 1402-2001 - p. 367 - 380.
    environmental gradients - ecological gradients - plant associations - vascular plants - temperate zone - plot size - north - classification - mires - water
    Questions What is the distribution of base-rich fen vegetation and the specialist species along European biogeographic regions? How do the gradients in species composition correlate to geography and climate at continental scale? What are the implications of such patterns for the classification of these habitats? Location Fifteen countries of Central, Western and Northern Europe. Methods We compiled a vegetation plot database of base-rich fens and related communities including vascular plants and bryophytes. The initial data set with 6943 plots was filtered according to the presence of specialists using discriminant analysis. We used DCA to analyse the correlation of species composition with geography and climate, and kriging interpolation for mapping gradients in the study area. Modified TWINSPAN was used to detect major vegetation groups. The results of the whole data set (plot size 1–100 m2) were compared with those obtained from two subsets with plots of 1–5 m2 and 6–30 m2. Results Most of the specialists were distributed among all the biogeographic regions, but many were more represented in the Alpine than in the Atlantic, Boreal and Continental regions. Variation in species composition was mainly correlated to temperature, precipitation and latitude in the three data sets, showing a major gradient from (1) alpine belt fens characterized by spring species to (2) small sedge fens mainly distributed in mountain regions and (3) boreo-temperate fens reflecting waterlogged conditions. Conclusions Base-rich fen communities are widely distributed across European biogeographic regions, but the Alpine region can be considered as the compositional centre of this vegetation type. Large-scale gradients of species composition are mainly explained by climate, while the influence of latitude is probably correlated to increasing water table in the boreo-temperate regions. These gradients can be better understood by differentiating three major vegetation types, which should be considered when establishing classification systems of base-rich fens in Europe.
    Pan-Arctic modelling of net ecosystem exchange of CO2
    Shaver, G.R. ; Rastetter, E.B. ; Salmon, V. ; Street, L.E. ; Weg, M.J. van de; Rocha, A. ; Wijk, M.T. van; Williams, M. - \ 2013
    Philosophical Transactions of the Royal Society B. Biological sciences 368 (2013)1624. - ISSN 0962-8436
    leaf-area index - primary productivity - vascular plants - carbon balance - climate-change - temperature - vegetation - sensitivity - nitrogen - alaska
    Net ecosystem exchange (NEE) of C varies greatly among Arctic ecosystems. Here, we show that approximately 75 per cent of this variation can be accounted for in a single regression model that predicts NEE as a function of leaf area index (LAI), air temperature and photosynthetically active radiation (PAR). The model was developed in concert with a survey of the light response of NEE in Arctic and subarctic tundras in Alaska, Greenland, Svalbard and Sweden. Model parametrizations based on data collected in one part of the Arctic can be used to predict NEE in other parts of the Arctic with accuracy similar to that of predictions based on data collected in the same site where NEE is predicted. The principal requirement for the dataset is that it should contain a sufficiently wide range of measurements of NEE at both high and low values of LAI, air temperature and PAR, to properly constrain the estimates of model parameters. Canopy N content can also be substituted for leaf area in predicting NEE, with equal or greater accuracy, but substitution of soil temperature for air temperature does not improve predictions. Overall, the results suggest a remarkable convergence in regulation of NEE in diverse ecosystem types throughout the Arctic.
    Overexpression of IRM1 Enhances Resistance to Aphids in Arabidopsis thaliana
    Chen, X. ; Zhang, Z. ; Visser, R.G.F. ; Broekgaarden, C. ; Vosman, B. - \ 2013
    PLoS ONE 8 (2013)8. - ISSN 1932-6203 - 9 p.
    green peach aphid - electrical penetration graph - phloem-feeding insects - myzus-persicae - plant defense - probing behavior - vascular plants - xylem ingestion - responses - activation
    Aphids are insects that cause direct damage to crops by the removal of phloem sap, but more importantly they spread devastating viruses. Aphids use their sophisticated mouthpart (i.e. stylet) to feed from the phloem sieve elements of the host plant. To identify genes that affect host plant resistance to aphids, we previously screened an Arabidopsis thaliana activation tag mutant collection. In such mutants, tagged genes are overexpressed by a strong 35S enhancer adjacent to the natural promoter, resulting in a dominant gain-of-function phenotype. We previously identified several of these mutants on which the aphid Myzus persicae showed a reduced population development compared with wild type. In the present study we show that the gene responsible for the phenotype of one of the mutants is At5g65040 and named this gene Increased Resistance to Myzus persicae 1 (IRM1). Overexpression of the cloned IRM1 gene conferred a phenotype identical to that of the original mutant. Conversely, an IRM1 knockout mutant promoted aphid population development compared to the wild type. We performed Electrical Penetration Graph analysis to investigate how probing and feeding behaviour of aphids was affected on plants that either overexpressed IRM1 or contained a knockout mutation in this gene. The EPG results indicated that the aphids encounter resistance factors while reaching for the phloem on the overexpressing line. This resistance mechanism also affected other aphid species and is suggested to be of mechanical nature. Interestingly, genetic variation for IRM1 expression in response to aphid attack was observed. Upon aphid attack the expression of IRM1 was initially (after 6 hours) induced in ecotype Wassilewskija followed by suppression. In Columbia-0, IRM1 expression was already suppressed six hours after the start of the infestation. The resistance conferred by the overexpression of IRM1 in A. thaliana trades off with plant growth.
    Persistent versus transient tree encroachment of temperate peat bogs: effects of climate warming and drought events
    Heijmans, M.M.P.D. ; Knaap, Y.A.M. ; Holmgren, M. ; Limpens, J. - \ 2013
    Global Change Biology 19 (2013)7. - ISSN 1354-1013 - p. 2240 - 2250.
    raised bog - vegetation composition - plant-communities - ombrotrophic bogs - vascular plants - boreal mire - scots pine - sphagnum - ecosystems - responses
    Peatlands store approximately 30% of global soil carbon, most in moss-dominated bogs. Future climatic changes, such as changes in precipitation patterns and warming, are expected to affect peat bog vegetation composition and thereby its long-term carbon sequestration capacity. Theoretical work suggests that an episode of rapid environmental change is more likely to trigger transitions to alternative ecosystem states than a gradual, but equally large, change in conditions. We used a dynamic vegetation model to explore the impacts of drought events and increased temperature on vegetation composition of temperate peat bogs. We analyzed the consequences of six patterns of summer drought events combined with five temperature scenarios to test whether an open peat bog dominated by moss (Sphagnum) could shift to a tree-dominated state. Unexpectedly, neither a gradual decrease in the amount of summer precipitation nor the occurrence of a number of extremely dry summers in a row could shift the moss-dominated peat bog permanently into a tree-dominated peat bog. The increase in tree biomass during drought events was unable to trigger positive feedbacks that keep the ecosystem in a tree-dominated state after a return to previous ‘normal’ rainfall conditions. In contrast, temperature increases from 1 °C onward already shifted peat bogs into tree-dominated ecosystems. In our simulations, drought events facilitated tree establishment, but temperature determined how much tree biomass could develop. Our results suggest that under current climatic conditions, peat bog vegetation is rather resilient to drought events, but very sensitive to temperature increases, indicating that future warming is likely to trigger persistent vegetation shifts. Keywords: alternative states, climate change, ecosystem model, extreme events, peatlands, pulse, rainfall, Sphagnum, temperature increase, vegetation shift
    Photosynthetic Quantum Yield Dynamics: From Photosystems to Leaves
    Hogewoning, S.W. ; Wientjes, E. ; Douwstra, P. ; Trouwborst, G. ; Ieperen, W. van; Croce, R. ; Harbinson, J. - \ 2012
    The Plant Cell 24 (2012)5. - ISSN 1040-4651 - p. 1921 - 1935.
    chlorophyll-protein complexes - singlet energy-transfer - plastid redox signals - arabidopsis-thaliana - light environment - state transitions - action spectrum - leaf photosynthesis - vascular plants - beta-carotene
    The mechanisms underlying the wavelength dependence of the quantum yield for CO2 fixation (a) and its acclimation to the growth-light spectrum are quantitatively addressed, combining in vivo physiological and in vitro molecular methods. Cucumber (Cucumis sativus) was grown under an artificial sunlight spectrum, shade light spectrum, and blue light, and the quantum yield for photosystem I (PSI) and photosystem II (PSII) electron transport and a were simultaneously measured in vivo at 20 different wavelengths. The wavelength dependence of the photosystem excitation balance was calculated from both these in vivo data and in vitro from the photosystem composition and spectroscopic properties. Measuring wavelengths overexciting PSI produced a higher a for leaves grown under the shade light spectrum (i.e., PSI light), whereas wavelengths overexciting PSII produced a higher a for the sun and blue leaves. The shade spectrum produced the lowest PSI:PSII ratio. The photosystem excitation balance calculated from both in vivo and in vitro data was substantially similar and was shown to determine a at those wavelengths where absorption by carotenoids and nonphotosynthetic pigments is insignificant (i.e., >580 nm). We show quantitatively that leaves acclimate their photosystem composition to their growth light spectrum and how this changes the wavelength dependence of the photosystem excitation balance and quantum yield for CO2 fixation. This also proves that combining different wavelengths can enhance quantum yields substantially.
    Biomass and diversity of dry alpine plant communities along altitudinal gradients in the Himalayas
    Namgail, T. ; Rawat, G.S. ; Mishra, C. ; Wieren, S.E. van; Prins, H.H.T. - \ 2012
    Journal of Plant Research 125 (2012)1. - ISSN 0918-9440 - p. 93 - 101.
    species richness - elevational gradient - biodiversity conservation - socioeconomic changes - indian changthang - vascular plants - ladakh - herbivores - patterns - plateau
    A non-linear relationship between phytodiversity and altitude has widely been reported, but the relationship between phytomass and altitude remains little understood.We examined the phytomass and diversity of vascular plants along altitudinal gradients on the dry alpine rangelands of Ladakh, western Himalaya. We used generalized linear and generalized additivemodels to assess the relationship between these vegetation parameters and altitude. We found a humpshaped relationship between aboveground phytomass and altitude.Wesuspect that this is engendered by low rainfall and trampling/excessive grazing at lower slopes by domestic livestock, and low temperature and low nutrient levels at higher slopes.Wealso found a unimodal relationship between plant species-richness and altitude at a singlemountain as well as at the scale of entire Ladakh. The species-richness at the single mountain peaked between 5,000 and 5,200 m, while it peaked between 3,500 and 4,000 m at entire Ladakh level.
    Climatic modifiers of the response to nitrogen deposition in peat-forming Sphagnum mosses: a meta-analysis
    Limpens, J. ; Granath, G. ; Gunnarson, U. ; Hoosbeek, M.R. ; Heijmans, M.M.P.D. - \ 2011
    New Phytologist 191 (2011)2. - ISSN 0028-646X - p. 496 - 507.
    global change - nutritional constraints - terrestrial ecosystems - carbon accumulation - species richness - ombrotrophic bog - vascular plants - n deposition - water-table - growth
    • Peatlands in the northern hemisphere have accumulated more atmospheric carbon (C) during the Holocene than any other terrestrial ecosystem, making peatlands long-term C sinks of global importance. Projected increases in nitrogen (N) deposition and temperature make future accumulation rates uncertain.• Here, we assessed the impact of N deposition on peatland C sequestration potential by investigating the effects of experimental N addition on Sphagnum moss. We employed meta-regressions to the results of 107 field experiments, accounting for sampling dependence in the data.• We found that high N loading (comprising N application rate, experiment duration, background N deposition) depressed Sphagnum production relative to untreated controls. The interactive effects of presence of competitive vascular plants and high tissue N concentrations indicated intensified biotic interactions and altered nutrient stochiometry as mechanisms underlying the detrimental N effects. Importantly, a higher summer temperature (mean for July) and increasedannual precipitation intensified the negative effects of N. The temperature effect was comparable to an experimental application of almost 4 g N m-2 yr-1 for each 1°C increase.• Our results indicate that current rates of N deposition in a warmer environment will strongly inhibit C sequestration by Sphagnum-dominated vegetation
    Ecosystem responses to reduced and oxidised nitrogen inputs in European terrestrial habitats
    Stevens, C.J. ; Manning, P. ; Berg, L.J.L. van den; Graaf, M.C.C. de; Wamelink, G.W.W. ; Boxman, A.W. ; Bleeker, A. ; Vergeer, P. ; Arroniz-Crespo, M. ; Limpens, J. ; Lamers, L.P.M. ; Bobbink, R. ; Dorland, E. - \ 2011
    Environmental Pollution 159 (2011)3. - ISSN 0269-7491 - p. 665 - 676.
    spruce picea-abies - soil solution chemistry - pinus-sylvestris l - atmospheric ammonia - throughfall deposition - nitrate reduction - acidic grasslands - intracellular ph - species richness - vascular plants
    While it is well established that ecosystems display strong responses to elevated nitrogen deposition, the importance of the ratio between the dominant forms of deposited nitrogen (NHx and NOy) in determining ecosystem response is poorly understood. As large changes in the ratio of oxidised and reduced nitrogen inputs are occurring, this oversight requires attention. One reason for this knowledge gap is that plants experience a different NHx:NOy ratio in soil to that seen in atmospheric deposits because atmospheric inputs are modified by soil transformations, mediated by soil pH. Consequently species of neutral and alkaline habitats are less likely to encounter high NH4+ concentrations than species from acid soils. We suggest that the response of vascular plant species to changing ratios of NHx:NOy deposits will be driven primarily by a combination of soil pH and nitrification rates. Testing this hypothesis requires a combination of experimental and survey work in a range of systems.
    Field Simulation of Global Change: Transplanting Northern Bog Mesocosms Southward
    Breeuwer, A.J.G. ; Heijmans, M.M.P.D. ; Robroek, B.J.M. ; Berendse, F. - \ 2010
    Ecosystems 13 (2010)5. - ISSN 1432-9840 - p. 712 - 726.
    increased nitrogen deposition - increased n deposition - water-table depth - vascular plants - sphagnum mosses - litter quality - climate-change - boreal mire - peat bogs - mass-loss
    A large proportion of northern peatlands consists of Sphagnum-dominated ombrotrophic bogs. In these bogs, peat mosses (Sphagnum) and vascular plants occur in an apparent stable equilibrium, thereby sustaining the carbon sink function of the bog ecosystem. How global warming and increased nitrogen (N) deposition will affect the species composition in bog vegetation is still unclear. We performed a transplantation experiment in which mesocosms with intact vegetation were transplanted southward from north Sweden to north-east Germany along a transect of four bog sites, in which both temperature and N deposition increased. In addition, we monitored undisturbed vegetation in control plots at the four sites of the latitudinal gradient. Four growing seasons after transplantation, ericaceous dwarf shrubs had become much more abundant when transplanted to the warmest site which also had highest N deposition. As a result ericoid aboveground biomass in the transplanted mesocosms increased most at the southernmost site, this site also had highest ericoid biomass in the undisturbed vegetation. The two dominant Sphagnum species showed opposing responses when transplanted southward; Sphagnum balticum height increment decreased, whereas S. fuscum height increment increased when transplanted southward. Sphagnum production did not differ significantly among the transplanted mesocosms, but was lowest in the southernmost control plots. The dwarf shrub expansion and increased N concentrations in plant tissues we observed, point in the direction of a positive feedback toward vascular plant-dominance suppressing peat-forming Sphagnum in the long term. However, our data also indicate that precipitation and phosphorus availability influence the competitive balance between Sphagnum, dwarf shrubs and graminoids.
    Travelling to a former sea floor: colonization of forests by understorey plant species on land recently reclaimed from the sea
    Pierik, M. ; Ruijven, J. van; Bezemer, T.M. ; Berendse, F. - \ 2010
    Journal of Vegetation Science 21 (2010)1. - ISSN 1100-9233 - p. 167 - 176.
    bosecologie - habitatfragmentatie - plantenkolonisatie - klimaatverandering - flevoland - forest ecology - habitat fragmentation - plant colonization - climatic change - flevoland - central new-york - seed dispersal - agricultural landscape - relative importance - potential impact - vascular plants - climate-change - woodlands - migration
    Questions: What are important forest characteristics determining colonization of forest patches by forest understorey species? Location: Planted forests on land recently reclaimed from the sea, the Netherlands. Methods: We related the distribution of forest specialist species in the understorey of 55 forests in Dutch IJsselmeer polders to the following forest characteristics: age, area, connectivity, distance to mainland (as a proxy for distance to seed source) and path density. We used species of the Fraxino-Ulmetum association for the Netherlands as reference for species that could potentially occur in the study area. Results: Area and age of the surveyed forests explained a large part of the variation in overall species composition and species number of forest plant species. The importance of connectivity and distance to the mainland of forest habitats became apparent only at a more detailed level of dispersal groups and individual species. The importance of forest parameters differed between dispersal groups and also between individual species. After 60 years, 75% of the potential pool of wind-dispersed species has reached the polders, whereas this was only 50% for species lacking specific adaptations to long-distance dispersal. However, the average percentage of successful colonizing species present per forest was substantially lower, ranging from 15 to 37%. Conclusions: The data strongly suggest that the colonization process in polder forests is still in its initial phase, during which easily dispersed species dominate the vegetation. Colonization success of common species that lack adaptations to long-distance dispersal is affected by spatial configuration of the forests, and most rare species that could potentially occur in these forests are still absent. Implications for conservation of rare species in fragmented landscapes are discussed
    Potential of endozoochorous seed dispersal by sheep in calcareous grasslands: correlations with seed traits.
    Kuiters, A.T. ; Huiskes, H.P.J. - \ 2010
    Applied Vegetation Science 13 (2010)2. - ISSN 1402-2001 - p. 163 - 172.
    vascular plants - cattle dung - species richness - large herbivores - establishment - restoration - landscape - impact - communities - migration
    Questions: What is the potential of sheep to serve as seed dispersers via ingestion and defecation in calcareous grasslands? Is the presence of viable seeds from dung correlated with specific seed traits? Location: Calcareous grasslands, South Limburg, the Netherlands/Belgium. Methods: Dung samples (n=24) from sheep were collected between September 2006 and November 2007 from five sites with Mesobromion plant communities, and communities of Nardo-Galion saxatilis. Germinability and identity of seeds in the dung samples were ascertained from germination of seedlings under glasshouse conditions. Seed traits of species with viable seeds in dung were compared with those present in the local species pool. Results: Seventy-two plant species from 23 plant families had viable seeds in sheep dung. The plant families encountered most frequently were Gramineae and Compositae. The most abundant and frequently recorded plant species in dung samples was Urtica dioica, accounting for >80% of the total number of seeds. Mean seed density in sheep dung was 0.8 seeds g-1 dry matter. Seeds with low seed mass and a high seed longevity index were over-represented in dung. Viable seeds >2.5 mg were infrequent in the dung samples. Conclusions: We conclude that sheep are potentially important dispersers of plant species in Dutch calcareous grasslands. Although smaller seeds were relatively abundant in sheep dung, it cannot be excluded that this was mainly caused by differences in seed abundance.
    Linking habitat modification to catastrophic shifts and vegetation patterns in bogs
    Eppinga, M.B. ; Rietkerk, M. ; Wassen, M.J. ; Ruiter, P.C. de - \ 2009
    Plant Ecology 200 (2009)1. - ISSN 1385-0237 - p. 53 - 68.
    increased n deposition - vascular plants - self-organization - simulation-model - boreal peatlands - sphagnum mosses - peat formation - climate-change - raised bogs - water-level
    Paleoecological studies indicate that peatland ecosystems may exhibit bistability. This would mean that these systems are resilient to gradual changes in climate, until environmental thresholds are passed. Then, ecosystem stability is lost and rapid shifts in surface and vegetation structure at landscape scale occur. Another remarkable feature is the commonly observed self-organized spatial vegetation patterning, such as string-flark and maze patterns. Bistability and spatial self-organization may be mechanistically linked, the crucial mechanism being scale-dependent (locally positive and longer-range negative) feedback between vegetation and the peatland environment. Focusing on bogs, a previous model study shows that nutrient accumulation by vascular plants can induce such scale-dependent feedback driving pattern formation. However, stability of bog microforms such as hummocks and hollows has been attributed to different local interactions between Sphagnum, vascular plants, and the bog environment. Here we analyze both local and longer-range interactions in bogs to investigate the possible contribution of these different interactions to vegetation patterning and stability. This is done by a literature review, and subsequently these findings are incorporated in the original model. When Sphagnum and encompassing local interactions are included in this model, the boundaries between vegetation types become sharper and also the parameter region of bistability drastically increases. These results imply that vegetation patterning and stability of bogs could be synergistically governed by local and longer-range interactions. Studying the relative effect of these interactions is therefore suggested to be an important component of future predictions on the response of peatland ecosystems to climatic changes.
    The angiosperm radiation revisited, an ecological explanation for Darwin's 'abominable mystery'
    Berendse, F. ; Scheffer, M. - \ 2009
    Ecology Letters 12 (2009)9. - ISSN 1461-023X - p. 865 - 872.
    crato formation brazil - nitrogen mineralization - vascular plants - litter quality - wet heathlands - n deposition - ecosystems - decomposition - sphagnum - diversification
    One of the greatest terrestrial radiations is the diversification of the flowering plants (Angiospermae) in the Cretaceous period. Early angiosperms appear to have been limited to disturbed, aquatic or extremely dry sites, suggesting that they were suppressed in most other places by the gymnosperms that still dominated the plant world. However, fossil evidence suggests that by the end of the Cretaceous the angiosperms had spectacularly taken over the dominant position from the gymnosperms around the globe. Here, we suggest an ecological explanation for their escape from their subordinate position relative to gymnosperms and ferns. We propose that angiosperms due to their higher growth rates profit more rapidly from increased nutrient supply than gymnosperms, whereas at the same time angiosperms promote soil nutrient release by producing litter that is more easily decomposed. This positive feedback may have resulted in a runaway process once angiosperms had reached a certain abundance. Evidence for the possibility of such a critical transition to angiosperm dominance comes from recent work on large scale vegetation shifts, linking long-term field observations, large scale experiments and the use of simulation models.
    Sphagnum re-introduction in degraded peatlands: the effects of aggregation, species and water table
    Robroek, B.J.M. ; Ruijven, J. van; Schouten, M.G.C. ; Breeuwer, A.J.G. ; Crushell, P.H. ; Berendse, F. ; Limpens, J. - \ 2009
    Basic and Applied Ecology 10 (2009)8. - ISSN 1439-1791 - p. 697 - 706.
    experimental plant-communities - interspecific competition - vascular plants - growth - bog - mosses - heterogeneity - restoration - vegetation - dynamics
    In European peatlands which have been drained and cut-over in the past, re-vegetation often stagnates after the return of a species-poor Sphagnum community. Re-introduction of currently absent species may be a useful tool to restore a typical, and more diverse, Sphagnum vegetation and may ultimately improve the functioning of peatland ecosystems, regarding atmospheric carbon sequestration. Yet, the factors controlling the success of re-introduction are unclear. In Ireland and Estonia, we transplanted small and large aggregates of three Sphagnum species into existing vegetation. We recorded changes in cover over a 3-year period, at two water levels (¿5 and ¿20 cm). Performance of transplanted aggregates of Sphagnum was highly species specific. Hummock species profited at low water tables, whereas hollow species profited at high water tables. But our results indicate that performance and establishment of species was also promoted by increased aggregate size. This mechanism (positive self-association) has earlier been seen in other ecosystems, but our results are the first to show this mechanism in peatlands. Our results do not agree with present management, which is aimed at retaining water on the surface of peat remnants in order to restore a functional and diverse Sphagnum community. More than the water table, aggregate size of the reintroduced species is crucial for species performance, and ultimately for successful peatland restoration.
    Dwarf shrubs are stronger competitors than graminoid species at high nutrient supply in peat bogs
    Heijmans, M.M.P.D. ; Kool, A. - \ 2009
    Plant Ecology 204 (2009)1. - ISSN 1385-0237 - p. 125 - 134.
    alaskan tussock tundra - nitrogen deposition - vascular plants - n deposition - growth forms - fertilization - vegetation - responses - sphagnum - availability
    Climate warming is likely to increase nutrient mineralization rates in bog ecosystems which may change the plant species composition. We examined the competitive relationships between two graminoid species, Eriophorum vaginatum and Rhynchospora alba, and two ericoid species, Calluna vulgaris and Vaccinium oxycoccus, at different nutrient supply rates. In a greenhouse, the plants were grown in monocultures and mixtures at four nutrient treatments: control, high N, high P, and high N + P. The results show that the ericoids responded more strongly to the nutrient treatments than the graminoids. The dwarf shrubs showed higher growth rates and reduced root:shoot ratio at high N + P supply. When grown in mixture the ericoids increased their growth, while graminoids decreased in biomass or showed signs of nutrient limitation compared to their monoculture plants. This suggests that under increased nutrient availability, bogs are more likely to turn into dwarf shrub dominated ecosystems and not grassland
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