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.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Temporal-Spatial Variation in Questing Tick Activity in the Netherlands: The Effect of Climatic and Habitat Factors
Hartemink, Nienke ; Vliet, Arnold Van; Sprong, Hein ; Jacobs, Frans ; Garcia-Martí, Irene ; Zurita-Milla, Raul ; Takken, Willem - \ 2019
Vector-Borne and Zoonotic Diseases 19 (2019)7. - ISSN 1530-3667 - p. 494 - 505.
Ixodes ricinus - phenology - population dynamics - saturation deficit - soil structure - temperature - vegetation

Longitudinal studies are fundamental in the assessment of the effect of environmental factors on tick population dynamics. In this study, we use data from a 10-year study in 11 different locations in the Netherlands to gauge the effects of climatic and habitat factors on the temporal and spatial variation in questing tick activity. Marked differences in the total number of ticks were found between locations and between years. We investigated which climatic and habitat factors might explain this variation. No effects of climatic factors on the total number of ticks per year were observed, but we found a clear effect of temperature on the onset of tick activity. In addition, we found positive associations between (1) humus layer thickness and densities of all three stages, (2) moss and blackberry abundance and larval densities, and (3) blueberry abundance and densities of larva and nymphs. We conclude that climatic variables do not have a straightforward association with tick density in the Netherlands, but that winter and spring temperatures influence the onset of tick activity. Habitats with apparently similar vegetation types can still differ in tick population densities, indicating that local composition of vegetation and especially of wildlife is likely to contribute considerably to the spatial variation in tick densities.

Prediction of soil pH patterns in nature areas on a national scale
Wamelink, G.W.W. ; Walvoort, Dennis J.J. ; Sanders, Marlies E. ; Meeuwsen, Henk A.M. ; Wegman, Ruut M.A. ; Pouwels, Rogier ; Knotters, Martin - \ 2019
Applied Vegetation Science 22 (2019)2. - ISSN 1402-2001 - p. 189 - 199.
acidity - kriging - pH - relevé - soil type - vegetation

Question: To assess the acidification process, nationwide information about soil pH on a site level is called for. Measurements of soil pH may be used, however there are not sufficient measurements available to map soil pH nationwide on site level. Instead we developed a soil pH map based on vegetation data. Location: Natural terrestrial areas in The Netherlands. Methods: 271,693 vegetation plots were used to estimate average soil pH per plot with indicator values, based on field measurements, of plant species. By spatial interpolation average pH values between the plots, with the soil type, groundwater table and vegetation management type as ancillary explanatory variables we created a soil pH map. The map covers all terrestrial nature areas (all areas that are not built up areas, agricultural areas and infrastructural areas) in the Netherlands with a map resolution of 25 × 25 m2 raster cells. Results: The predicted pH of the map varied between 3.0 and 8.6 with standard errors between 0.13 and 0.93. Most of the standard errors range from 0.4 to 0.55, with an average just below 0.5 pH unit. Cross-validation shows that for 33% the difference between observed and predicted is between −0.1 and 0.1 pH-unit and for 83% the difference is between −0.5 and 0.5 pH-unit. Validation shows that the pH map is unbiased (mean error is almost zero), accurate (root mean squared error is 0.64) and nicely captures spatial patterns (r = 0.77). We applied the pH map to assess the impact of acidification on the abiotic quality of nature areas in the Netherlands. Conclusions: The model fit in the predicted soil pH is in good resulting in a low standard error and a high correlation. The measures taken to prevent acidic deposition causing further acidifying of nature areas can be considered as successful.

Homoeostatic maintenance of nonstructural carbohydrates during the 2015–2016 El Niño drought across a tropical forest precipitation gradient
Dickman, Lee Turin ; McDowell, Nate G. ; Grossiord, Charlotte ; Collins, Adam D. ; Wolfe, Brett T. ; Detto, Matteo ; Wright, S.J. ; Medina-Vega, José A. ; Goodsman, Devin ; Rogers, Alistair ; Serbin, Shawn P. ; Wu, Jin ; Ely, Kim S. ; Michaletz, Sean T. ; Xu, Chonggang ; Kueppers, Lara ; Chambers, Jeffrey Q. - \ 2019
Plant, Cell & Environment 42 (2019)5. - ISSN 0140-7791 - p. 1705 - 1714.
climate - ENSO - NSC - Panama - storage - sugars - tropics - vegetation

Nonstructural carbohydrates (NSCs) are essential for maintenance of plant metabolism and may be sensitive to short- and long-term climatic variation. NSC variation in moist tropical forests has rarely been studied, so regulation of NSCs in these systems is poorly understood. We measured foliar and branch NSC content in 23 tree species at three sites located across a large precipitation gradient in Panama during the 2015–2016 El Niño to examine how short- and long-term climatic variation impact carbohydrate dynamics. There was no significant difference in total NSCs as the drought progressed (leaf P = 0.32, branch P = 0.30) nor across the rainfall gradient (leaf P = 0.91, branch P = 0.96). Foliar soluble sugars decreased while starch increased over the duration of the dry period, suggesting greater partitioning of NSCs to storage than metabolism or transport as drought progressed. There was a large variation across species at all sites, but total foliar NSCs were positively correlated with leaf mass per area, whereas branch sugars were positively related to leaf temperature and negatively correlated with daily photosynthesis and wood density. The NSC homoeostasis across a wide range of conditions suggests that NSCs are an allocation priority in moist tropical forests.

Impacts of nitrogen addition on plant species richness and abundance : A global meta-analysis
Midolo, Gabriele ; Alkemade, Rob ; Schipper, Aafke M. ; Benítez-López, Ana ; Perring, Michael P. ; Vries, Wim de - \ 2018
Global Ecology and Biogeography (2018). - ISSN 1466-822X
anthropogenic impacts - biodiversity - eutrophication - global change - GLOBIO - soil acidification - vegetation

Aim: Experimental nitrogen (N) addition (fertilization) studies are commonly used to quantify the impacts of increased N inputs on plant biodiversity. However, given that plant community responses can vary considerably among individual studies, there is a clear need to synthesize and generalize findings with meta-analytical approaches. Our goal was to quantify changes in species richness and abundance in plant communities in response to N addition across different environmental contexts, while controlling for different experimental designs. Location: Global. Time period: Data range: 1985–2016; Publication years: 1990–2018. Major taxa studied: Plants. Methods: We performed a meta-analysis of 115 experiments reported in 85 studies assessing the effects of N addition on terrestrial natural and semi-natural plant communities. We quantified local-scale changes in plant biodiversity in relationship to N addition using four metrics: species richness (SR), individual species abundance (IA), mean species abundance (MSA) and geometric mean abundance (GMA). Results: For all metrics, greater amounts of annual N addition resulted in larger declines in plant diversity. Additionally, MSA decreased more steeply with N that was applied in reduced (NH4 +) rather than oxidized ((NO 3)) form. Loss of SR with increasing amounts of N was found to be larger in warmer sites. Furthermore, greater losses of SR were found in sites with longer experimental durations, smaller plot sizes and lower soil cation exchange capacity. Finally, reductions in the abundance of individual species were larger for N-sensitive plant life-form types (legumes and non-vascular plants). Main conclusions: N enrichment decreases both SR and abundance of plants in N-addition experiments, but the magnitude of the response differs among biodiversity metrics and with the environmental and experimental context. This underlines the importance of integrating multiple dimensions of biodiversity and relevant modifying factors into assessments of biodiversity responses to global environmental change.

Comparison of ecosystem services provided by grasslands with different utilization patterns in China’s Inner Mongolia Autonomous Region
Du, Bingzhen ; Zhen, Lin ; Hu, Yunfeng ; Yan, Huimin ; Groot, Rudolf de; Leemans, Rik - \ 2018
Journal of Geographical Sciences 28 (2018)10. - ISSN 1009-637X - p. 1399 - 1414.
ecosystem services - grasslands utilization pattern - household livelihoods - natural resource management - soil - vegetation

Although several previous studies in Inner Mongolia examined the effects of ecological conservation on the delivery of ecosystem services, they were often limited in scope (few ecosystem services were assessed) and often suffered from confounding by spatial variation. In this study, we examined the impact of conservation measures (changes in grassland utilization patterns) on the provision of selected ecosystem services in three types of grasslands (meadow steppe in Hulun Buir, typical steppe in Xilin Gol, and semi-desert steppe in Ordos) in Inner Mongolia. We examined five utilization patterns: no use (natural grasslands), light use, moderate use, intensive use, and recovery sites (degraded sites protected from further use). Through household surveys and vegetation and soil surveys, we measured the differences in ecosystem services among the different grassland utilization patterns. We also identified spatial factors that confounded the quantification of ecosystem services in different types of grasslands. We found that light use generally provided high levels of ecosystem services in meadow steppe and typical steppe, with the main differences in the supporting ecosystem services. Surprisingly, we found no consistently positive impacts of strict conservation activities across the sites, since the results varied spatially and with respect to differences in the land-use patterns. Our study suggests that appropriate grassland utilization patterns can enhance the supply of ecosystem services and reduce negative effects on both household livelihoods and the environment.

Modelling the distribution and compositional variation of plant communities at the continental scale
Jiménez-Alfaro, Borja ; Suárez-Seoane, Susana ; Chytrý, Milan ; Hennekens, Stephan M. ; Willner, Wolfgang ; Hájek, Michal ; Agrillo, Emiliano ; Álvarez-Martínez, Jose M. ; Bergamini, Ariel ; Brisse, Henry ; Brunet, Jörg ; Casella, Laura ; Dítě, Daniel ; Font, Xavier ; Gillet, François ; Hájková, Petra ; Jansen, Florian ; Jandt, Ute ; Kącki, Zygmunt ; Lenoir, Jonathan ; Rodwell, John S. ; Schaminée, Joop H.J. ; Sekulová, Lucia ; Šibík, Jozef ; Škvorc, Željko ; Tsiripidis, Ioannis - \ 2018
Diversity and Distributions 24 (2018)7. - ISSN 1366-9516 - p. 978 - 990.
community distribution models - ecosystem properties - extent of occurrence - generalized dissimilarity modelling - habitat conservation - plant communities - vegetation
Aim: We investigate whether (1) environmental predictors allow to delineate the distribution of discrete community types at the continental scale and (2) how data completeness influences model generalization in relation to the compositional variation of the modelled entities. Location: Europe. Methods: We used comprehensive datasets of two community types of conservation concern in Europe: acidophilous beech forests and base-rich fens. We computed community distribution models (CDMs) calibrated with environmental predictors to predict the occurrence of both community types, evaluating geographical transferability, interpolation and extrapolation under different scenarios of sampling bias. We used generalized dissimilarity modelling (GDM) to assess the role of geographical and environmental drivers in compositional variation within the predicted distributions. Results: For the two community types, CDMs computed for the whole study area provided good performance when evaluated by random cross-validation and external validation. Geographical transferability provided lower but relatively good performance, while model extrapolation performed poorly when compared with interpolation. Generalized dissimilarity modelling showed a predominant effect of geographical distance on compositional variation, complemented with the environmental predictors that also influenced habitat suitability. Main conclusions: Correlative approaches typically used for modelling the distribution of individual species are also useful for delineating the potential area of occupancy of community types at the continental scale, when using consistent definitions of the modelled entity and high data completeness. The combination of CDMs with GDM further improves the understanding of diversity patterns of plant communities, providing spatially explicit information for mapping vegetation diversity and related habitat types at large scales.
Crevasse Splays Versus Avulsions : A Recipe for Land Building With Levee Breaches
Nienhuis, Jaap H. ; Törnqvist, Torbjörn E. ; Esposito, Christopher R. - \ 2018
Geophysical Research Letters 45 (2018)9. - ISSN 0094-8276 - p. 4058 - 4067.
crevasse splay - Delft3D - river avulsion - sediment diversion - soil consolidation - vegetation

Natural-levee breaches can not only initiate an avulsion but also, under the right circumstances, lead to crevasse splay formation and overbank sedimentation. The formative conditions for crevasse splays are not well understood, yet such river sediment diversions form an integral part of billion-dollar coastal restoration projects. Here we use Delft3D to investigate the influence of vegetation and soil consolidation on the evolution of a natural-levee breach. Model simulations show that crevasse splays heal because floodplain aggradation reduces the water surface slope, decreasing water discharge into the flood basin. Easily erodible and unvegetated floodplains increase the likelihood for channel avulsions. Denser vegetation and less potential for soil consolidation result in small crevasse splays that are not only efficient sediment traps but also short-lived. Successful crevasse splays that generate the largest land area gain for the imported sediment require a delicate balance between water and sediment discharge, vegetation root strength, and soil consolidation.

Trait-based approaches for guiding the restoration of degraded agricultural landscapes in East Africa
Lohbeck, Madelon ; Winowiecki, Leigh ; Aynekulu, Ermias ; Okia, Clement ; Vågen, Tor Gunnar - \ 2018
Journal of Applied Ecology 55 (2018)1. - ISSN 0021-8901 - p. 59 - 68.
agricultural land - agroecology - agroforestry - erosion - functional diversity - functional traits - land degradation - soil health - soil organic carbon - vegetation
Functional ecology provides a framework that can link vegetation characteristics of various land uses with ecosystem function. However, this application has been mostly limited to [semi-]natural systems and small spatial scales. Here, we apply functional ecology to five agricultural landscapes in Kenya, Uganda and Ethiopia, and ask to what extent vegetation characteristics contribute to soil functions that are key to farmers’ livelihoods. We used the Land Degradation Surveillance Framework (LDSF), a multi-scale assessment of land health. Each LDSF site is a 10 × 10 km landscape in which vegetation cover and erosion prevalence were measured, a tree inventory was carried out, and topsoil (0–20 cm) samples were collected for organic carbon (SOC) analysis in approximately 160 × 1,000 m2 plots. Land degradation is a recurring phenomenon across the five landscapes, indicated by high erosion prevalence (67%–99% of the plots were severely eroded). We used mixed models to assess if vegetation cover, above-ground woody biomass and the functional properties of woody vegetation (weighted-mean trait values, functional diversity [FD]) explain variation in SOC and erosion prevalence. We found that the vegetation cover and above-ground biomass had strong positive effects on soil health by increasing SOC and reducing soil erosion. After controlling for cover and biomass, we found additional marginal effects of functional properties where FD was positively associated with SOC and the abundance of invasive species was associated with higher soil erosion. Synthesis and applications. This work illustrates how functional ecology can provide much-needed evidence for designing strategies to restore degraded agricultural land and the ecosystem services on which farmers depend. We show that to ensure soil health, it is vital to avoid exposed soil, maintain or promote tree cover, while ensuring functional diversity of tree species, and to eradicate invasive species.
Dunes, above and beyond : The interactions between ecological and geomorphological processes during early dune development
Puijenbroek, Marinka E.B. - \ 2017
Wageningen University. Promotor(en): F. Berendse, co-promotor(en): J. Limpens. - Wageningen : Wageningen University - ISBN 9789463432146 - 183
dunes - geomorphology - ecology - vegetation - duneland plants - beaches - duinen - geomorfologie - ecologie - vegetatie - duinplanten - stranden

Coastal dunes occur along the sandy shores of most continents where they serve as coastal defence against flooding, provide areas for recreation, store drinking water and harbour unique biodiversity. Coastal dunes and the services they provide are threatened by climate-induced sea-level rise. This threat may be mitigated by the spontaneous formation of new dunes, for example in combination with mega-nourishments aimed at increasing beach width. Coastal dunes form by the interaction between vegetation, wind and wave action. Persistent dune development begins with the establishment of vegetation on the beach: the vegetation traps the wind-blown sand, forming an embryo dune. Over time an embryo dune can develop into a bigger foredune, increasing coastal safety. The formation and development of embryo dunes into foredunes depend on the vegetation establishment on the beach, dune growth over summer and dune erosion during winter. Although vegetation succession and geomorphological processes are each well described, the interaction between ecological and geomorphological processes during embryo dune development are not well known. The thesis aimed at further exploring these interactions, using a combination of experiments and high-resolution dune monitoring to study the mechanisms underlying early dune development and their implications for mega-nourishment design.

To explore whether soil salinity, salt spray or storms determine the vegetation limit of dune building plant species on the beach, we performed a field transplantation experiment and a glasshouse experiment with two dune building grasses Ammophila arenaria and Elytrigia juncea. In the field growth of grasses transplanted into four vegetation zones from sea to dune was monitored for over a year and the response of these species to salt spray and soil salinity was tested in a glasshouse experiment. In the field, the vegetation zones were associated with differences in summer soil salinity: zones with both species present were significantly less saline than zones with only E. juncea or the zones without any vegetation. However, in our experiments the transplanted A. arenaria performed equal or better than E. juncea in all vegetation zones, suggesting soil salinity did not limit species performance at the studied site. Both species showed severe winter mortality. In the glasshouse experiment, A. arenaria biomass decreased linearly with soil salinity, presumably as a result of osmotic stress. Elytrigia juncea showed a nonlinear response to soil salinity with an optimum at 0.75% soil salinity and a decrease in biomass at higher salt concentrations. Our findings suggest that soil salinity stress either takes place in winter during storm inundation, or that development of vegetated dunes is less sensitive to soil salinity than hitherto expected.

To understand the boundary conditions for embryo dune development over a longer time period we explored the effects of beach morphology, meteorological conditions and sand nourishment on early dune development using a 30 year time series of aerial photographs and beach profile monitoring data. We concluded that 1) beach morphology is highly influential in determining the potential for new dune development, with wide beaches enabling development of larger embryo dune fields, 2) sand nourishments stimulate early dune development by increasing beach width, and 3) weather conditions and non-interrupted sequences of years without high-intensity storms determine whether progressive dune development will take place.

Dune development is the result of the interaction between vegetation development and sedimentation and erosion processes. To disentangle the effects of vegetation characteristics and that of dune size we monitored a natural dune field of 8 hectares for one year using an Unmanned Aerial Vehicle (UAV) with a camera. By constructing a digital surface model and a geometrical corrected image (an orthomosaic) for each flight campaign we calculated changes in dune volume over summer and winter and related these changes to vegetation, dune size and degree of shelter. The dune growth over summer was mainly determined by dune size, whereas dune growth over winter was determined by vegetation characteristics. Degree of shelter determined whether dune growth was limited by storm erosion (exposed dunes) or sand supply (sheltered dunes). These results suggest that vegetation characteristic may be particularly important for resisting storm erosion and speeding up recovery after erosion.

Embryo dunes have been hypothesised to facilitate development of species rich green beach vegetation in the sheltered location between the embryo dunes and the primary foredunes. To test this hypothesis we explored the relative impacts of abiotic soil conditions as affected by the geomorphological setting on the species richness and species turn-over of green beach vegetation. To this end we characterised the geomorphology and measured abiotic conditions and species composition of green beach vegetation along transects from beach to foredune. We found that the geomorphological setting influenced plant species composition indirectly by affecting soil salinity and rate of sand burial. We found that plant species richness declined less at sheltered conditions, where there was a build-up of organic matter and no sand burial. Our results further suggest a non-linear relationship between embryo dune volume and number of green beach species: embryo dunes can be a source of shelter, thus stimulating green beach development, but can also compete for space, reducing green beach development. The net effect of embryo dunes most likely depends on the sediment budget of the beach and storm intensity.

Mega-nourishments are single large sand nourishments that are applied locally, and are expected to exist for about 20 years, providing opportunities for the development of embryo dunes and rare pioneer plant communities (green beach vegetation). We explored this potential by comparing growth and development of dune building species on natural beaches with the results of plant transplantation and monitoring data of two mega-nourishments: the low-elevated Hondsbossche Duinen and the high-elevated Sandmotor. Our results suggest that establishment of dune building species on high-elevated mega-nourishment proceed slower than on natural beaches due to dispersal limitation. Once vegetation has established however, embryo dune development on high-elevated mega-nourishments may proceed faster than natural beaches due to low salinity and protection against storm erosion. Development of dune-building vegetation on the low-elevated mega-nourishment Hondsbossche Duinen showed the same rate and pattern as that on a natural beach. The potential for embryo dune development on mega-nourishments is far bigger than the potential for green beach development, since green beach vegetation develops under a narrower range of abiotic conditions. Such abiotic conditions can develop behind the shelter of embryo dunes or foredunes at low beach elevations.

In conclusion this thesis shows that, 1) the potential of embryo dune development depends on a large beach width and low storm erosion which determines the vegetation limit. 2) Embryo dune growth over summer is mainly determined by existing dune volume and sand supply. 3) Heavy storms limit embryo dune development during winter, although dune erosion can be mitigated by vegetation composition. 4) On accreting beaches which continuously provide area for the development of new embryo dunes green beach vegetation can develop. 5) The design of a mega-nourishment determines the potential for the development of embryo dunes and green beach vegetation. Our findings provide insights in the interaction between ecological and geomorphological processes that determine embryo dune development. This knowledge can help to obtain better predictions of embryo dune development under the threat of sea-level rise.

A clash of plants : Vegetation succession and its interaction with permafrost dynamics in the Arctic lowland tundra
Li, Bingxi - \ 2017
Wageningen University. Promotor(en): F. Berendse, co-promotor(en): M.M.P.D. Heijmans. - Wageningen : Wageningen University - ISBN 9789463436168 - 100
ecological succession - ecology - plant succession - vegetation - tundra - permafrost - lowland areas - arctic regions - siberia - ecologische successie - ecologie - plantensuccessie - vegetatie - toendra - permafrost - laaglandgebieden - arctische gebieden - siberië

Arctic ecosystems have been affected by severe climate change during the last decades. The increase in temperature in the Arctic has been almost double of the global rate of warming since the beginning of the 20th century. Like other ecosystems in the high latitude region, Arctic tundra appears to be extremely sensitive to the continuous warming of the past decades, which has led to dramatic vegetation changes such as rapid shrub expansion. While researchers are keen to talk about the shrubification of the Arctic tundra, there has been rather little attention for alternative vegetation shifts, such as those related to local permafrost collapse in lowland tundra. The general vegetation succession route of the ice-rich lowland tundra ecosystem is yet largely unknown. Therefore, we choose a typical Arctic lowland site (Kytalyk natural reserve) in the Northeastern Siberia to explore how vegetation is changing in this ecosystem, and how changes in the abiotic environment and vegetation succession interact.

On the basis of field observations I assumed that the plant species composition of each vegetation patch at the study site changes continuously following cycles over time. To test this assumption, two multiple-year field experiments (Chapter 2 and Chapter 3) were carried out. In addition, we applied dendrochronological techniques (Chapter 4 and Chapter 5) and molecular tools (Chapter 4). On the basis of the results of these studies, I depicted a complete vegetation succession loop in the Arctic lowland tundra, which is closely related to the dynamics of the permafrost. In this vegetation succession loop, four stages with distinctive vegetation types have been identified.

The Betula nana L. shrubs mainly dominate the well-drained elevated areas. In a field experiment, removal of B. nana shrubs resulted in abrupt permafrost degradation, rapid soil moisture increase and invasion of the grass species Arctagrostis latifolia (R. Br.) Griseb. After a short time period, when small ponds or drainages had developed, this fast-responding grass species is replaced by Eriophorum sedges. In the subsequent stage the Sphagnum mosses invade the sedge vegetation. The new Sphagnum moss carpets not only suppress the growth of Eriophorum sedges, but also create moist but unsaturated substrates that appear to be appropriate for the germination of B. nana seeds. These conditions provide new opportunities for B. nana shrubs to establish.

The reproduction mode of B. nana at the study site has been studied using molecular tools (micro- satellites), as it may explain how existing B. nana patches developed and how shrub vegetation may expand in the future (Chapter 4). The conventional point of view is that sexual reproduction of perennial plants in the Arctic tundra, like B. nana, is rare due to the pressure of the harsh environment. However, the results of our molecular study (Chapter 4) tell a different story. While vegetative reproduction of B. nana is common, sexual reproduction of B. nana is more prevalent. Seed dispersal of B. nana between different patches at the study site is not hampered by the short between-patch distances, but vegetative reproduction of B. nana appeared to be restricted to 1-2 m distances from the parent plants.

The influences of the climate on B. nana shrubs were further investigated using the dendrochronological analyses (Chapter 4 and Chapter 5). The radial growth of B. nana is positively correlated with early summer temperature, while relatively high summer precipitation during the warm years also stimulates the growth of B. nana. Moreover, sufficient summer precipitation facilitates the establishment of B. nana seedlings. Since sexual reproduction is prevalent at the site, it is suggested that the present B. nana shrubs established simultaneously, during periods with suitable climate conditions.

Along with the vegetation succession cycles, permafrost underlying the vegetation experiences clear degradation-recovery cycles. We detected a close interaction between vegetation shifts and permafrost dynamics. While abrupt permafrost degradation drove a quick vegetation shift from the B. nana dominated stage to the water-logged Eriophorum sedge dominate stage, the changes of vegetation cover affect the stability of the permafrost as well. The removal of B. nana shrub cover triggered rapid permafrost degradation (Chapter 2), while the development of Sphagnum moss carpets, which have a high isolation capacity, reduced permafrost temperature, facilitating permafrost recovery (Chapter 3).

Vegetation composition in the Arctic tundra not only influences permafrost stability, but also affects the methane emission of the site. Eriophorum sedges are able to transport methane from deep soil to the air via their aerenchyma tissues, leading to high methane fluxes. In contrast, the Sphagnum mosses significantly suppress the methane emission, since endophytic CH4-oxidizing bacteria are widespread inside the aerobic unsaturated Sphagnum carpets (Chapter 3).

To sum up, our findings provide crucial information to better understand changes in the Arctic tundra ecosystem, helping to obtain better predictions of future vegetation shifts and the associated consequences for greenhouse gas emissions, permafrost stability and the heat balance of the Earth surface.

Land use as a driver of soil fertility and biodiversity across an agricultural landscape in the Central Peruvian Andes
Valença, Anne W. De; Vanek, Steven J. ; Meza, Katherin ; Ccanto, Raul ; Olivera, Edgar ; Scurrah, Maria ; Lantinga, Egbert A. ; Fonte, Steven J. - \ 2017
Ecological Applications 27 (2017)4. - ISSN 1051-0761 - p. 1138 - 1154.
Andean forest - cropping systems - land use intensification - pasture - soil biology - soil degradation - soil macrofauna - vegetation

Land use change and intensification in agricultural landscapes of the Andean highlands have resulted in widespread soil degradation and a loss in soil-based ecosystem services and biodiversity. This trend threatens the sustainability of farming communities in the Andes, with important implications for food security and biodiversity conservation throughout the region. Based on these challenges, we sought to understand the impact of current and future land use practices on soil fertility and biodiversity, so as to inform landscape planning and management decisions for sustainable agroecosystem management. We worked with local communities to identify and map dominant land uses in an agricultural landscape surrounding Quilcas, Peru. These land uses existed within two elevations zones (low-medium, 3200-3800 m, and high elevation, 3800-4300 m). They included three types of low-medium elevation forests (eucalyptus, alder, and mixed/native species), five pasture management types (permanent pasture, temporal pasture [in fallow stage], degraded pasture, high-altitude permanent pasture, and high-altitude temporal pasture [in fallow stage]) and six cropping systems (forage crops, maize/beans, and potato under four types of management). Soil fertility was evaluated in surface soils (0-20 cm) with soil physicochemical parameters (e.g., pH, soil organic matter, available nutrients, texture), while soil biological properties were assessed using the abundance and diversity of soil macrofauna and ground cover vegetation. Our results indicated clear impacts of land use on soil fertility and biological communities. Altitude demonstrated the strongest effect on soil physicochemical properties, but management systems within the low-mid elevation zone also showed important differences in soil biological communities. In general, the less-disturbed forest and pasture systems supported more diverse soil communities than the more intensively managed croplands. Degraded soils demonstrated the lowest overall soil fertility and abundance of soil macrofauna, but this may be reversible via the planting of alder forests. Our findings also indicated significant covariation between soil physicochemical parameters, soil macrofauna, and ground vegetation. This suggests that management for any one of these soil properties may yield unintended cascading effects throughout the soil subsystem. In summary, our findings suggest that shifts in land use across the landscape are likely to have important impacts on soil functioning and biodiversity.

Hydrological controls on salinity exposure and the effects on plants in lowland polders
Stofberg, Sija F. - \ 2017
Wageningen University. Promotor(en): S.E.A.T.M. van der Zee; J.P.M. Witte. - Wageningen : Wageningen University - ISBN 9789463431873 - 172
hydrology - lowland areas - soil salinity - temperate climate - fens - surface water - vegetation - fen soils - salinization - polders - hydrologie - laaglandgebieden - bodemzoutgehalte - gematigd klimaat - laagveengebieden - oppervlaktewater - vegetatie - laagveengronden - verzilting - polders

The Dutch lowlands may be subject to salinization, through saline upward seepage and increased salt concentrations in the surface water, which may affect agriculture and nature areas with floating fens.

A simple approach was proposed to estimate root zone salinization in areas with fresh water lenses that float on upward seeping saline groundwater, based on analytical solutions and approximations, which could be used for prioritization.

The hydrology of floating fens was investigated and important processes and parameters were identified, which could be used to estimate root zone exposure to salinity. The flow processes are mostly controlled by the root mat geometry, which determines which part of the root mat floats within the surface water.

A greenhouse experiment showed that salinity may affect the growth of some plant species from floating fens, which implies that salinization may affect species composition in these nature areas.

Turbulent exchange of energy, momentum, and reactive gases between high vegetation and the atmospheric boundary layer
Shapkalijevski, M.M. - \ 2017
Wageningen University. Promotor(en): M.C. Krol; J. Vilà-Guerau de Arellano, co-promotor(en): A.F. Moene; H.G. Ouwersloot. - Wageningen : Wageningen University - ISBN 9789463430845 - 163
vegetation - atmospheric boundary-layer - atmosphere - energy exchange - gases - canopy - meteorology - vegetatie - atmosferische grenslaag - atmosfeer - energie-uitwisseling - gassen - kroondak - meteorologie

This thesis deals with the representation of the exchange of energy, momentum and chemically reactive compounds between the land, covered by high vegetation, and the lowest part of the atmosphere, named as atmospheric boundary layer (ABL).

The study presented in this thesis introduces the roughness sublayer (RSL), the layer just above the tall vegetation canopy in which the atmospheric flow is directly affected by the presence of roughness elements, as an important part of the ABL system. Our focus is on the exchange of the thermodynamic, as well as the chemical properties of the boundary layer. Our methodology combines observational analysis using high resolution meteorological and chemistry measurements from the Canopy Horizontal Array Turbulence Study (CHATS) and modelling framework of the soil-vegetation-atmospheric boundary layer system. The systematic investigation in this thesis showed the relevance of the RSL for the turbulent exchange processes between the atmosphere and the land surface characterized by high vegetation. More specifically, we explained and discussed how the turbulence parameterization within the roughness sublayer is strongly dependent on canopy-phenology (canopy leaf state) and atmospheric-stability changes, and provided parameterization formulations for . Our modelling analysis further showed that the CHATS boundary-layer dynamics are mainly affected and controlled by the large-scale processes (advection and subsidence), while the effect of the canopy and the roughness sublayer were relatively small. Near the canopy top however, the the canopy had a significant impact on the modelled boundary layer state variables (wind speed, potential temperature and specific humidity) and the corresponding turbulent transfer coefficients (drag coefficients for momentum and scalars), as supported by the observations. With respect to the exchange of reactive compounds, we diagnosed twice-larger magnitude of the ozone deposition fluxes when the roughness sublayer effects are taken into account in the flux-gradient relationship, compared to the method which neglects these effects. Thus, neglecting the roughness sublayer effects in the surface flux parameterization schemes of ozone in atmosphere-chemistry models can lead to significant overestimation of the ozone diurnal mixing ratio in the boundary layer.

By studying the high vegetation-atmosphere exchange processes, their quantification, and testing methods for their parameterization, we contribute to improve our understanding and representation of the roughness sublayer-atmospheric boundary-layer system.

Meer biodiversiteit met brede groene dijken? : een verkenning van de vegetatie op de Waddenzeedijken
Loon-Steensma, Jantsje M. van; Huiskes, Rik - \ 2017
Wageningen : Wageningen Environmental Research (Wageningen Environmental Research rapport 2802) - 129
dijken - breedte - vegetatie - biodiversiteit - nederlandse waddeneilanden - nederland - duitsland - denemarken - dykes - width - vegetation - biodiversity - dutch wadden islands - netherlands - germany - denmark
In dit rapport worden de vegetaties op het buitentalud van de brede groene Waddenzeedijken in Duitsland en Denemarken vergeleken met de vegetaties op het buitentalud van de gangbare Waddenzeedijken in Nederland, met als doel om inzicht te krijgen in de mogelijke meerwaarde van het Brede Groene Dijk-concept voor biodiversiteit, en voor vegetatie in het bijzonder.
Ecohydrologische systeemanalyse Liefstinghsbroek
Delft, S.P.J. van; Waal, R.W. de; Jansen, P.C. ; Bijlsma, R.J. ; Wegman, R.M.A. - \ 2017
Wageningen : Wageningen Environmental Research (Wageningen Environmental Research rapport 2790) - 133
ecohydrologie - hydrologie - vegetatie - natura 2000 - bossen - graslanden - historische geografie - groningen - ecohydrology - hydrology - vegetation - forests - grasslands - historical geography
Het Lieftinghsbroek in Oost-Groningen bestaat uit gevarieerd loofbos met enkele schraalgraslandjes in het dal van de Ruiten Aa. Het gebied is aangewezen voor Natura 2000 habitattypen bos en schraalland en is tevens bosreservaat. Om meer inzicht te krijgen in het effect van vernattingsmaatregelen in de directe omgeving van het gebied is een ecohydrologisch onderzoek uitgevoerd, waarbij geologisch/bodemkundige, hydrologische en vegetatiekundige gegevens verzameld zijn (uit literatuur en in het veld) en het historisch grondgebruik is beschreven. Voor de bossen is het gebied te nat geworden, of te zuur door het ontbreken van kwelinvloed. Ook voor Blauwgraslanden zijn de mogelijkheden beperkt. Er wordt aanbevolen aanvullende maatregelen te treffen om de sterke vernatting te verminderen door minder neerslagwater vast te houden in het gebied.
Dynamics of rainwater lenses on upward seeping saline groundwater
Eeman, Sara - \ 2017
Wageningen University. Promotor(en): Sjoerd van der Zee, co-promotor(en): Toon Leijnse. - Wageningen : Wageningen University - ISBN 9789462579330 - 158
seepage - rain - water - groundwater - saline water - vegetation - kwel - regen - water - grondwater - zout water - vegetatie

Fresh water is generally a limited resource in coastal areas which are often densely populated. In low-lying areas, groundwater is mostly saline and both agriculture and freshwater nature depend on a thin lens of rainwater that is formed by precipitation surplus on top of saline, upward seeping groundwater. Understanding the dynamics of such lenses is vital for sustainable food production and development of natural vegetation and biodiversity under changing conditions like sea level rise and climate change. The thickness of the mixing zone between the fresh and saline water is substantial and characteristics of this mixing zone cannot be neglected. In this thesis we have studied the behaviour of these thin rainwater lenses and their mixing zones.

To study the basic relations of such a system, we considered the development of a rainwater lens, starting from initially saline conditions using a numerical model. The ratio of seepage over precipitation, density difference and to a lesser extent the geometry of the flow domain, significantly influence the thickness of the lens and mixing zone. The thickness of the mixing zone is also significantly influenced by dispersion (as the lens grows), diffusion (at steady state) and distance from a drain (caused by convergence). Field observations show that geological layering influences these processes importantly and that head differences often overrule the effects of density difference. Groundwater salinity is furthermore influenced by re-mixing of soil- and rainwater, dual porosity and preferential flow. If there is significant seepage, the thickness of a lens can be estimated by an analytical solution.

The effects of weather and climate variations were numerically studied using sinusoidal and actual net precipitation patterns. The average lens thickness is hardly influenced by weather fluctuations and we can relate minimum and maximum lens thickness to this average thickness. The thickness of the mixing zone can be derived from the “travelled distance” from its center: thickness increases with increasing vertical movement due to alternating precipitation and evaporation. Field observations confirm this, but show concentration of dynamics in the top of the lens. This is not contradictory since the mixing zone for the studied site starts very near the ground water table, so indeed the mixing zone thickness is influenced by precipitation events. Convolution theory can be used to determine the impulse-response function for a thin lens which enables derivation of the delay and amplitude of a lens reaction to changes in climate.

The cation exchange process was investigated using a numerical model based on field data. On the short term, the process is characterized by the salt-shock caused by the large difference in concentration between rainwater and seepage water. The pore water quality changes quickly from saline to relatively fresh and from sodium and magnesium dominated to calcium dominated. On the long term, changes of the soil complex occur. This is a process of several centuries (even for the shallow systems studied), since the amount of cations in the fresh solution is very small compared to the amount of cations adsorbed to the soil. Initially, both calcium and magnesium in the sorption complex increase and later magnesium is outcompeted by calcium. The net flux downward has a much larger effect on the mixing process than short-term variations and the influence of tile drainage. Although the main flow component is horizontal, the water quality and soil complex are only influenced by the vertical flow that causes mixing of water with different composition. Comparison of the numerical model with field data from both study sites in Zeeland confirm our results and show that equilibrium has not yet been reached.

Influence of saline groundwater on vegetation development has been assessed simulating combinations of different vegetation types, soil characteristics and groundwater levels and –salinities for two different climates. We assessed the relative importance of these parameters on the fresh water availability and stress experienced by vegetation and put this in perspective of stress due to drought and lack of oxygen. Soil type and climate are shown to be the most important parameters. Salinity stress is substantial, but small compared to stress caused by lack of oxygen and drought. For areas with groundwater with limited salinity, salt tolerance may be a parameter that can be used to improve sustainability of agriculture. Where groundwater is more saline, soil and ground water management are the most effective tools.

Large herbivores as a driving force of woodland-grassland cycles : the mutual interactions between the population dynamics of large herbivores and vegetation development in a eutrophic wetland
Cornelissen, Perry - \ 2017
Wageningen University. Promotor(en): Frank Berendse; Karle Sykora, co-promotor(en): Jan Bokdam. - Wageningen : Wageningen University - ISBN 9789463430159 - 151
grasslands - woodlands - herbivores - population dynamics - vegetation - wetlands - graslanden - bosgebieden - herbivoren - populatiedynamica - vegetatie - wetlands

This thesis examines the mutual interactions between the population dynamics of large herbivores and wood-pasture cycles in eutrophic wetlands. Therefore, habitat use and population dynamics of large herbivores, the effects of large herbivores on vegetation development, and the mutual interactions between vegetation development and herbivore population dynamics were studied in the eutrophic wetland the Oostvaardersplassen. At the Oostvaardersplassen cattle, horses and red deer were introduced in a fenced area with no predators, and population numbers are bottom-up controlled by food supply. The study showed that high densities of cattle, horses and red deer were able to break down woody vegetation and create grasslands. As the populations of large herbivores increased, the amount of the preferred grass available per animal decreased. This forced the large herbivores to use other food plants in other vegetation types, such as scrub, and transforming these into grasslands. In this way, the large herbivores facilitated high numbers of geese. As geese can clip the grass very short (<2 cm), they forced the large herbivores even more to forage in alternative vegetation types. Cattle, the largest herbivore in the system, were the first to experience the negative consequences of this strong competition, and their numbers declined. This raises the question whether an assemblage of bottom-up regulated populations of cattle, horses and red deer, or other large herbivores, can sustainably coexist under these circumstances. The results of our modelling study and experiences in the field suggest that resource partitioning may be a more reliable mechanism for long term coexistence than temporal variability due to climatic extremes or disease outbreaks. The best way to provide opportunities for resource partitioning in the Oostvaardersplassen is to enlarge the area and connect it to other reserves in order to increase the heterogeneity of the grazed system. Although the results of our model suggest that weather variability and presence of geese gave minor opportunities for the coexistence of large herbivores, both factors were necessary for creating windows of opportunity for the establishment of thorny shrubs. Weather variability creates strong reductions of the large herbivore populations while geese influence the maximum and minimum numbers, which are lower when geese are present. The effects of geese on the minimum numbers are small, but apparently sufficient to make the wood-pasture cycle operate. This raises another question whether a large predator, such as the wolf, could have similar effects on these ecosystems as the geese in the model. The impact of geese combined with a possible positive effect of wolves on wood-pasture cycles could perhaps increase the frequency of the windows of opportunity and increase the survival of established thorny shrubs. Until now, we have seen that a few conditions for the wood-pasture cycle are met by the herbivores. However, a few important requirements are not satisfied: (a) a temporary reduction of large herbivore numbers allowing the establishment of light demanding thorny shrubs and the development of thorny scrubland within the created grasslands; (b) the establishment of palatable trees within these thorny scrubs; (c) the formation of closed canopies which shade out the shrubs and lead to unprotected groups of trees and groves. This means that we still cannot conclude if the large herbivores are a driving force for the whole cycle in a highly productive environment. As long as we have not experienced a complete wood-pasture cycle in the Oostvaardersplassen or any other area, it remains to be seen what will happen in the future. Whatever the outcome will be, the results of our study suggest that some adjustments would benefit the Oostvaardersplassen-system such as increasing heterogeneity through connecting the area with other large nature reserves. This will not only increase opportunities for resource and space partitioning and thus increase opportunities for the coexistence of the large herbivores, but also for wood-pasture cycles and increased biodiversity.

Climate and base-level controlled fluvial system change and incision during the last glacial–interglacial transition, Roer river, the Netherlands – western Germany
Kasse, C. ; Balen, R.T. Van; Bohncke, S.J.P. ; Wallinga, J. ; Vreugdenhil, M. - \ 2017
Netherlands journal of geosciences 96 (2017)2. - ISSN 0016-7746 - p. 71 - 92.
fluvial response - Late-glacial - meandering river - OSL dating - terraces - vegetation
The fluvial development of the Roer river in the southeastern Netherlands and western Germany is presented for the Late Pleniglacial, Late-glacial and Early Holocene periods. Reconstruction of fluvial-style changes is based on geomorphological and sedimentological analysis. Time control comes from correlation to the pollen-based biochronostratigraphic framework of the Netherlands combined with independent optically stimulated luminescence (OSL) ages. At the Pleniglacial to Late-glacial transition a system and channel pattern change occurred from an aggrading braided to an incising meandering system. Rapid rates of meander migration, as established for the Late-glacial by optical dating, were likely related to the sandy nature of the substratum and the Late-glacial incision of the Meuse that resulted in a higher river gradient in the downstream part of the Roer. In the Roer valley the Younger Dryas cooling is not clearly reflected by a fluvial system response, but this may also be related to Holocene erosion of Younger Dryas fluvial forms. An important incision and terrace formation was established at the Younger Dryas to Early Holocene transition, probably related to forest recovery, reduced sediment supply and base-level lowering of the Meuse. The results of this study show a stepwise reduction in the number of channel courses from a multi-channel braided system in the Pleniglacial, to a double meander-belt system in the Late-glacial and a single-channel meandering system in the Early Holocene. The results show that the forcing factors of fluvial-system change in the Roer valley are climate change (precipitation, permafrost and vegetation) and downstream base-level control by the Meuse.
Quickscan zodekwaliteit dijkgrasland Afsluitdijk op basis van visuele beoordeling van doorworteling, vegetatietype en bedekking; situatie 2016
Huiskes, H.P.J. ; Vries, Daisy de - \ 2016
Wageningen UR Alterra - 42 p.
graslanden - dijken - graslanden, conditie - wortels - vegetatie - graslandbeheer - afsluitdijk - nederland - grasslands - dykes - grassland condition - roots - vegetation - grassland management - netherlands
In februari 2016 is door Alterra, onderdeel van Wageningen Universiteit en Researchcentrum, een quickscan uitgevoerd om de kwaliteit van de zode van de Afsluitdijk te bepalen. Gegevens over de doorworteling van de zode, het graslandtype en de vegetatiebedekking vormen de basis om tot een kwaliteitsoordeel van de zode te komen. Daarnaast is een korte vergelijking gemaakt tussen de huidige uitkomst en de situatie van 2010. Afsluitend wordt een beheeradvies gegeven.
Procesindicatoren PAS : rapportage 2016
Smits, N.A.C. ; Mucher, C.A. ; Ozinga, W.A. ; Waal, R.W. de; Wamelink, G.W.W. - \ 2016
Wageningen : Wageningen Environmental Research (Wageningen Environmental Research rapport 2771) - 61
stikstof - indicatoren - monitoring - ecologisch herstel - habitats - vegetatie - nitrogen - indicators - ecological restoration - vegetation
In het kader van het Programma Aanpak Stikstof (PAS) is in 2016 doorgewerkt aan een aantal onderwerpen rondom de ecologische onderbouwing van het PAS, waaronder de procesindicatoren. Binnen de PAS-monitoring is afgesproken dat het proces van natuurherstel ook op korte termijn gevolgd wordt om zo snel mogelijk de effectiviteit van de herstelmaatregelen in kaart te brengen. Hiervoor zijn de PAS-procesindicatoren ontwikkeld. Deze procesindicatoren zijn vooral bedoeld om een indicatie van het herstelproces te geven. Deze procesindicatoren kunnen verschillen per habitattype en per maatregel, maar ook per gebied. Om die redenen is een flexibel systeem ontworpen met diverse parameters: luchtfoto’s, abiotische metingen, vegetatie en soorten. De huidige rapportage betreft de verslaglegging van de ontwikkelde systematiek van PAS-procesindicatoren.
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