Records 1 - 20 / 1080
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.
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.
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
graslanden - dijken - graslanden, conditie - wortels - vegetatie - graslandbeheer - afsluitdijk - nederland - grasslands - dykes - grassland condition - roots - vegetation - grassland management - afsluitdijk - 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.
Landelijke Vegetatie Databank : technische documentatie, Status A
Hennekens, S.M. ; Boss, M. ; Schmidt, A.M. - \ 2016
Wageningen : Statutory Research Tasks Unit for Nature & the Environment (WOt-technical report 74) - 59
vegetatie - databanken - planten - nederland - vegetation - databases - plants - netherlands
Dit document bevat een beschrijving van de technische omgeving, hulpmiddelen en modellen die van belang zijn voor het beheer van de landelijke vegetatiedatabank. Het is bedoeld om de processen en procedures
vast te leggen. Het verkrijgen van kwaliteitsstatus A is hierbij geen doel op zich maar is wel de stip op de horizon waar dit document aan bijdraagt. Het doel van de landelijke vegetatiedatabank is het op een gestructureerde manier vastleggen van gegevens over het voorkomen van vegetaties en daarmee ook
plantensoorten in Nederland. De procedures voor het verzamelen en beheren van deze gegevens zijn beschreven in dit document
Friese en Groninger Kwelderwerken : monitoring en beheer 1960-2014
Duin, W.E. van; Jongerius, H. ; Nicolai, A. ; Jongsma, J.J. ; Hendriks, A. ; Sonneveld, C. - \ 2016
Wageningen : Wettelijke Onderzoekstaken Natuur & Milieu (WOt-technical report 68) - 95
zoutmoerassen - monitoring - vegetatie - ecologische successie - natuurbescherming - natuurbeheer - groningen - friesland - kweldergronden - kustgebieden - salt marshes - vegetation - ecological succession - nature conservation - nature management - salt marsh soils - coastal areas
Een belangrijk ecologisch doel voor de Waddenzee is een zo groot en natuurlijk mogelijk areaal kwelders. Mede daarom wordt in de half-natuurlijke kwelderwerken langs Friese en Groninger vastelandskust het beheer geleidelijk aangepast naar duurzamer en minder kunstmatig. Langetermijnmonitoring door
Rijkswaterstaat van hoogte- en vegetatieontwikkeling begeleidt deze verandering. Het gemiddelde areaal kwelder en pionierzone voldoet ruimschoots aan de voor de kwelderwerken gestelde eisen. Echter door opslibbing worden kwelders hoger, waarbij de vegetatie door successie verandert en er uiteindelijk een soortenarme vegetatie van Zeekweek kan ontstaan. Een bijkomend effect in de kwelderwerken is dat er door successie, op termijn, weinig ruimte overblijft in de overgangszone van laaggelegen wad naar hooggelegen horizontaal uitbreidende kwelder voor pioniervegetatie met Zeekraal, terwijl de Waddenzee daar het belangrijkste gebied voor is. Beweiding vertraagt weliswaar de ontwikkeling naar climaxvegetatie, maar voor grotere algehele natuurlijkheid zou meer dynamiek, waarbij aangroei en afslag van kwelders in evenwicht zijn door cyclische successie, uitkomst kunnen bieden. Er gaat onderzocht worden of een aangepast beheer van de rijshoutdammen hierbij kan helpen.
Resilience of Amazonian forests : the roles of fire, flooding and climate
Monteiro Flores, B. - \ 2016
Wageningen University. Promotor(en): Marten Scheffer, co-promotor(en): Milena Holmgren Urba; Jose de Attayde. - Wageningen : Wageningen University - ISBN 9789462578876 - 128
forests - resilience of nature - fire - flooding - floods - climate - floodplains - vegetation - amazonia - bossen - veerkracht van de natuur - brand - inundatie - overstromingen - klimaat - stroomvlakten - vegetatie - amazonia
The Amazon has recently been portrayed as a resilient forest system based on quick recovery of biomass after human disturbance. Yet with climate change, the frequency of droughts and wildfires may increase, implying that parts of this massive forest may shift into a savanna state. Although the Amazon basin seems quite homogeneous, 14% is seasonally inundated. In my thesis I combine analyses of satellite data with field measurements and experiments to assess the role of floodplain ecosystems in shaping the resilience of Amazonian forests.
First, I analyse tree cover distribution for the whole Amazon to reveal that savannas are relatively more common on floodplains. This suggests that compared to uplands, floodplains spend more time in the savanna state. Also, floodplain forests seem to have a tipping point at 1500 mm of annual rainfall in which forests may shift to savanna, whereas the tipping point for upland forests seems to be at 1000 mm of rainfall. Combining satellite and field measurements, I show that the higher frequency of savannas on floodplain ecosystems may be due to a higher sensitivity to fire. After a forest fire, floodplains lose more tree cover and soil fertility, and recover more slowly than uplands (chapter 2).
In floodplains of the Negro river, I studied the recovery of blackwater forests after repeated fires, using field data on tree basal area, species richness, seed availability, and herbaceous cover. Results indicate that repeated fires may easily trap blackwater floodplains in an open-vegetation state, due the sudden loss of forest resilience after a second fire event (chapter 3).
Analyses of the soil and tree composition of burnt floodplain forests, reveal that a first fire is the onset of the loss of soil fertility that intensifies while savanna trees dominate the tree community. A tree compositional shift happens within four decades, possibly accelerated by fast nutrient leaching. The rapid savannization of floodplain forests after fire implies that certain mechanisms such as environmental filtering may favor the recruitment of savanna trees over forest trees (chapter 4).
In chapter 5, I experimentally tested in the field the roles of dispersal limitation, and environmental filtering for tree recruitment in burnt floodplain forests. I combine inventories of seed availability in burnt sites with experiments using planted seeds and seedlings of six floodplain tree species. Repeated fires strongly reduce the availability of tree seeds, yet planted trees thrive despite degraded soils and high herbaceous cover. Moreover, degraded soils on twice burnt sites seem to limit the growth of most pioneer trees, but not of savanna trees with deeper roots. Our results suggest a limitation of forest trees to disperse into open burnt sites.
The combined evidence presented in this thesis support the hypothesis that Amazonian forests on floodplains are less resilient than forests on uplands, and more likely to shift into a savanna state. The lower ability of floodplains to retain soil fertility and recover forest structure after fire, may accelerate the transition to savanna. I also present some evidence of dispersal limitation of floodplain forest trees. Broad-scale analyses of tree cover as a function of rainfall suggest that savannas are likely to expand first in floodplains if Amazonian climate becomes drier. Savanna expansion through floodplain ecosystems to the core of the Amazon may spread fragility from an unsuspected place.
Roots in the tundra : relations between climate warming and root biomass and implications for vegetation change and carbon dynamics
Wang, Peng - \ 2016
Wageningen University. Promotor(en): Frank Berendse, co-promotor(en): Monique Heijmans; Liesje Mommer. - Wageningen : Wageningen University - ISBN 9789462578609 - 168
roots - biomass - climatic change - vegetation - carbon - global warming - tundra - ecosystems - decomposition - siberia - wortels - biomassa - klimaatverandering - vegetatie - koolstof - opwarming van de aarde - toendra - ecosystemen - decompositie - siberië
Global climate has been warming up for the last decades and it will continue in this century. The Arctic is the part of the globe that warms fastest and is more sensitive to climate warming. Aboveground productivity of Arctic tundra has been shown to increase in response to warmer climates. However, belowground responses of tundra vegetation are still unclear. As the major part of plant biomass in tundra lies belowground, it is pivotal to investigate changes in the belowground parts of tundra vegetation for our understanding of climate warming effects on tundra ecosystems.
To get a general idea of how belowground plant biomass may change in a warmer climate, we synthesized published data on the belowground biomass of tundra vegetation across a broad gradient of mean annual air temperature from −20 to 0 °C. We found that aboveground biomass of tundra biomass indeed increases with mean annual temperature as well as summer air temperature, while belowground biomass did not show a significant relationship with temperature. The increases in the aboveground biomass were significantly larger than belowground biomass, resulting in reduced below/above ratios at higher temperatures. The shifted biomass allocation with temperature can influence the carbon dynamics of tundra ecosystems. Future tundra studies need to focus more on the species or functional type composition of belowground biomass and species or functional type specific belowground responses to climate warming.
To determine the seasonal changes and vertical distribution of root biomass of different plant functional types, we sampled roots at a Siberian tundra site in the early and late growing season, from vegetation types dominated by graminoids and shrubs respectively. We distinguished the roots of graminoids and shrubs, and found that shrub roots grew earlier and shallower than graminoid roots, which enables shrubs to gain advantage over graminoids at the early growing season when nutrient pulses occur during snowmelt and soil thaw. The deeper roots of graminoids can help them to be more competitive if climate warming induces more nutrient release in the deeper soil.
In a soil thawing and fertilization experiment, we further investigated the effects of increased thawing depth and nutrient supply in the upper soil, which can be the consequences of climate warming, on root biomass and its vertical distribution. In this study we distinguished between the roots of grasses, sedges, deciduous shrubs and evergreen shrubs. The study was done in a moist tussock tundra site with similar abundance of the different plant functional types. We found that only sedges benefited from the increased thawing depth, probably through their deepest root distribution among the four functional types, while the shrubs, which were shallower-rooted, benefited from the increased nutrient availability in the upper soil. The deep-rooted grasses had the highest plasticity in vertical root distribution, which enabled them also to benefit greatly from the fertilization. Our results show that tundra plants with different rooting strategies can show different responses to climate warming dependent on the relative warming impacts on the nutrient supply in shallow and deeper soil layers. This insight can help to predict future tundra vegetation dynamics.
The carbon balance of tundra ecosystems also depends on the decomposition of plant litter, particularly the root litter, which may account for a larger part of annual litter input than leaf litter in tundra ecosystems. Vegetation shifts also change litter quality which ultimately influences carbon dynamics. To investigate the differences in the decomposition of leaves and roots of graminoids and shrubs, we performed a litter transplant experiment. We found that although the decomposability of leaf litter did not differ between the graminoid and shrub, root decomposability might be lower for the shrub. However, this cannot be extrapolated to the overall decomposition in different vegetation types, as these different plant communities differ in rooting depths. We also found evidence of home-field advantage in the decomposition in Arctic tundra, and we show that the early stage of litter decomposition at our research site could be driven by the phosphorus concentration of the litter. To get a full understanding of the carbon balance of tundra ecosystems, much more efforts are needed to quantify litter input and decomposition.
In this thesis we show that belowground parts, which account for a major part of plant biomass in tundra, can show a different response to climate warming from aboveground parts. Belowground responses to climate warming can have crucial impacts on the competitive balance between tundra plants, and consequently result in vegetation shifts in tundra. Such shifts in species composition can have large effects on carbon dynamics through altered input and decomposability of plant litter, particularly root litter.
Invloed van beekbegeleidende bomen op de ecologische kwaliteit van Noord-Brabantse beken
Verdonschot, R.C.M. ; Brugmans, Bart ; Scheepens, Mark ; Coenen, Daniël ; Verdonschot, P.F.M. - \ 2016
H2O online (2016)28 juli.
aquatische ecologie - waterlopen - bomen - noord-brabant - monitoring - beschaduwen - gegevensanalyse - waterschappen - vegetatie - waterplanten - waterkwaliteit - aquatic ecology - streams - trees - noord-brabant - monitoring - shading - data analysis - polder boards - vegetation - aquatic plants - water quality
Monitoringsdata van Brabantse beken laat zien dat bomen belangrijk zijn voor het halen van ecologische doelen. Echter, voor maximale effectiviteit met betrekking tot vegetatieontwikkeling en koeling van het beekwater voldoet alleen de zwaarste beschaduwingsklasse (>70%) en moet gestreefd worden naar lange beschaduwde trajecten. Macrofauna profiteert vooral via de door bomen gegenereerde substraatdifferentiatie. Het toepassen van beschaduwing brengt voor de waterschappen wel grote uitdagingen met zich mee. Verder blijkt uit de data-analyse dat jaarrond voldoende stroming een vereiste is voor de ecologische doelrealisatie in de trajecten.
Herstel kwaliteit van natte heide in het zandlandschap
Wallis de Vries, M.F. ; Bobbink, R. ; Jansen, A.J.M. ; Vogels, J.J. - \ 2016
Landschap : tijdschrift voor landschapsecologie en milieukunde 33 (2016)2. - ISSN 0169-6300 - p. 110 - 115.
016-3951 - natuurbeheer - ecologisch herstel - heidegebieden - bodemkwaliteit - flora - vegetatie - fauna - toegepast onderzoek - bodems van waterrijke gebieden - grondwater - nature management - ecological restoration - heathlands - soil quality - flora - vegetation - fauna - applied research - wetland soils - groundwater
Het verspreidingsgebied van natte heiden is in omvang min of meer gelijk gebleven sinds de laatste ontginningen. De kwaliteit blijft echter een dalende trend vertonen door de inwerking van stikstofdepositie en verdroging. Tegelijkertijd zijn er veelbelovende resultaten geboekt door nieuwe vormen van herstelbeheer. OBN heeft daarvoor de kennisbasis ontwikkeld. In dit artikel worden de daaruit voortvloeiende inzichten uiteen gezet en worden uitdagingen voor de toekomst geschetst.
Opslibbing en vegetatie kwelder Ameland-Oost, jaarrapportage 2015
Groot, A.V. de; Regteren, M. van; Weide, B.E. van der - \ 2016
Den Helder : IMARES Wageningen UR (Rapport / IMARES C049/16) - 32
vegetatiemonitoring - vegetatie - sedimentatie - monitoring - bodemdaling - nederlandse waddeneilanden - vegetation monitoring - vegetation - sedimentation - monitoring - subsidence - dutch wadden islands
In 2015 zijn op de kwelder van Ameland-Oost de opslibbing en vegetatieontwikkeling gemeten, als onderdeel van de lopende monitoring naar de effecten van de bodemdaling door gaswinning. De meting vindt plaats op twee raaien, in totaal bestaande uit 38 permanente kwadraten (pq’s) met SEBs (Sedimentatie-Erosiebalk). De observaties over 2015 passen grotendeels binnen de tot nu toe gemeten trends in maaiveldhoogte en vegetatieontwikkeling op Ameland en de natuurlijke variatie in opslibbing en vegetatieontwikkeling.
The mountain vegetation of South Peru : syntaxonomy, ecology, phytogeography and conservation
Montesinos-Tubée, D.B. - \ 2016
Wageningen University. Promotor(en): Karle Sykora; Frank Berendse, co-promotor(en): Antoine Cleef. - Wageningen : Wageningen University - ISBN 9789462576797 - 334
vegetation - mountains - phytogeography - ecology - taxonomy - nature conservation - andes - peru - vegetatie - gebergten - plantengeografie - ecologie - taxonomie - natuurbescherming - andes - peru
THE MOUNTAIN VEGETATION OF SOUTH PERU: SYNTAXONOMY, ECOLOGY, PHYTOGEOGRAPHY AND CONSERVATION
This thesis presents an overview and revision of plant communities from xerophytic and mountain landscapes in the dry Andes of South Peru. The revision is based on comparison of the collected vegetation data with other regional and interregional studies. This phytosociologic overview comprises the arid and semi-arid montane vegetation of the province of Arequipa and besides the plant communities of Moquegua from the prepuna between 3470 and 3700 m, the puna between 3750 and 4500 m and the superpuna between 4450 and 4800 m. The Braun-Blanquet approach and multivariate ordination and classification methods have been applied to classify the different plant communities and to study the relation between plant communities and environmental variables, such as altitude, slope degree and exposition, rock and stone cover percentage, manure cover and grazing. Furthermore the results are presented of a phytogeographical analysis of the Andean puna flora (at vascular genus level) and its relation to other tropicalpine regions in South America. Finally, the descriptions of six recently published new species are included in this thesis. The results provide an important database for nature conservation issues, stressing the significance of protecting the fragile and diverse ecosystems of the Moqueguan Andes. The results of this vegetation survey can be used to prioritize the selection and assignment of nature reserves.
A landscape ecological vegetation map of Saba (Lesser Antilles)
Freitas, J. de; Rojer, A.C. ; Nijhof, B.S.J. ; Debrot, A.O. - \ 2016
Den Helder : IMARES (Report / IMARES C195/15) - 48
vegetation mapping - vegetation - flora - islands - saba - vegetatiekartering - vegetatie - flora - eilanden - saba
A semi-detailed landscape-based vegetation map (scale: 1: 37,500) is presented for the 13 km2 Lesser Antillean steep volcanic island of Saba, Netherlands Caribbean. The map is based on a total of 49 vegetation plots that were sampled in 1999 using a stratified random sampling design and analysed using TWINSPAN cluster analysis. Three hundred and fourteen (314) plant species, representing 56% of the total known flora (565 species), were recorded in the sample plots. The principal lower sections of the island possess a tropical savannah climate whereas the upper slopes reaching a maximum altitude of 870 m can best be characterized as a tropical rainforest climate.
Objective prioritization of intervention areas for the NAGA Foundation in the Kenya Tanzania border area
Maat, H.W. ter; Hutjes, R.W.A. ; Fleskens, L. ; Querner, E.P. ; Klostermann, J.E.M. ; Jaspers, A.M.J. - \ 2016
Alterra, Wageningen-UR (Alterra-rapport 2711) - 67
hydrology - restoration management - climate - soil - geographical information systems - vegetation - models - tanzania - kenya - hydrologie - herstelbeheer - klimaat - bodem - geografische informatiesystemen - vegetatie - modellen - tanzania - kenya
The NAGA foundation aims to establish Hydrologic Corridors, wherein re-greening and restoration of
the landscape interacts with regional rain-bringing wind patterns to intensify the local hydrologic cycle
to a point that a permanently greener and more productive ecosystem can be sustained. The initial
search area, as defined by NAGA, targets the Kenya-Tanzania border region and identified four
possible Hydrological Corridors. This report supports an objective prioritisation of potential
intervention locations in this larger domain. Therefore, readily available, geographically explicit
information on soil, vegetation, hydrology and climate, as well as institutional settings that may affect
the likelihood of success of such projects, were collected and analysed, and some climate-modelling
experiments were performed.
Combining the findings of the four themes: hydrology, soil restoration, climate, and institutions, and
ranking the four potential corridors objectively in order of priority, favours re-greening projects in the
Tanzanian corridors could provide the best starting point: especially the most eastern one. In this
area, many applicable land management options exist in combination with a high potential for
restoring soil organic matter, the highest rainfall recycling potential in the more favourable long rainy
season, and the apparent reliability of the Tanzanian governments at both national- and at local
levels. The GIS data facilitate further focus on this particular corridor in search of specific project