Wiegand, Kerstin

[["dc.bibliographiccitation.firstpage","473"],["dc.bibliographiccitation.issue","4"],["dc.bibliographiccitation.journal","Journal of Vegetation Science"],["dc.bibliographiccitation.lastpage","484"],["dc.bibliographiccitation.volume","11"],["dc.contributor.author","Wiegand, Kerstin"],["dc.contributor.author","Jeltsch, Florian"],["dc.contributor.author","Ward, David"],["dc.date.accessioned","2017-09-07T11:44:43Z"],["dc.date.available","2017-09-07T11:44:43Z"],["dc.date.issued","2000"],["dc.description.abstract","We investigated the spatial pattern of A. raddiana in the Negev desert of Israel in order to gain insights into the factors and processes driving the dynamics of this species. Using a scale‐dependent measure, the ring statistic, we analysed both patterns observed in the field and time series of spatial tree distributions produced by a simulation model. In the field, random spacing was the predominant pattern observed. However seedlings were clumped on small scales. We ran the model under two contrasting scenarios representing hypotheses that explain the clumping of seedlings and the random distribution of trees. One hypothesis is that there is spatial heterogeneity in seed distribution, germination and seedling mortality, but that these heterogeneities are not correlated with each other in space. The second hypothesis assumes a correlation between these heterogeneities leading to areas suitable for establishment. However, the suitability of the sites is temporally variable. Furthermore, the second hypothesis assumes density‐dependent tree mortality due to competition. Both hypotheses lead to spatial distributions that are in qualitative agreement with the patterns observed in the field. Therefore, the classical view that a clumped seedling distribution and a random pattern of older trees is due to clumped regeneration and density‐dependent mortality may not hold for Acacia trees in the Negev."],["dc.identifier.doi","10.2307/3246577"],["dc.identifier.gro","3148944"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/5586"],["dc.language.iso","en"],["dc.notes.intern","Wiegand Crossref Import"],["dc.notes.status","final"],["dc.notes.submitter","chake"],["dc.relation.issn","1100-9233"],["dc.relation.orgunit","Abteilung Ökosystemmodellierung"],["dc.subject.gro","Acacia raddiana"],["dc.subject.gro","Negev"],["dc.subject.gro","point pattern analysis"],["dc.subject.gro","simulation model"],["dc.subject.gro","spatio-temporal population dynamics"],["dc.title","Do spatial effects play a role in the spatial distribution of desert-dwelling Acacia raddiana?"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","no"],["dc.type.subtype","original_ja"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","363"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","Oecologia"],["dc.bibliographiccitation.lastpage","372"],["dc.bibliographiccitation.volume","141"],["dc.contributor.author","Wiegand, Kerstin"],["dc.contributor.author","Jeltsch, Florian"],["dc.contributor.author","Ward, David"],["dc.date.accessioned","2017-09-07T11:44:39Z"],["dc.date.available","2017-09-07T11:44:39Z"],["dc.date.issued","2004"],["dc.description.abstract","There is concern about the lack of recruitment of Acacia trees in the Negev desert of Israel. We have developed three models to estimate the frequency of recruitment necessary for long-term population survival (i.e. positive average population growth for 1,000 years and <10% probability of extinction). Two models assume purely episodic recruitment based on the general notion that recruitment in arid environments is highly episodic. They differ in that the deterministic model investigates average dynamics while the stochastic model does not. Studies indicating that recruitment episodes in arid environments have been overemphasized motivated the development of the third model. This semi-stochastic model simulates a mixture of continuous and episodic recruitment. Model analysis was done analytically for the deterministic model and via running model simulations for the stochastic and semi-stochastic models. The deterministic and stochastic models predict that, on average, 2.2 and 3.7 recruitment events per century, respectively, are necessary to sustain the population. According to the semi-stochastic model, 1.6 large recruitment events per century and an annual probability of 50% that a small recruitment event occurs are needed. A consequence of purely episodic recruitment is that all recruitment episodes produce extremely large numbers of recruits (i.e. at odds with field observations), an evaluation that holds even when considering that rare events must be large. Thus, the semi-stochastic model appears to be the most realistic model. Comparing the prediction of the semi-stochastic model to field observations in the Negev desert shows that the absence of observations of extremely large recruitment events is no reason for concern. However, the almost complete absence of small recruitment events is a serious reason for concern. The lack of recruitment may be due to decreased densities of large mammalian herbivores and might be further exacerbated by possible changes in climate, both in terms of average precipitation and the temporal distribution of rain."],["dc.identifier.doi","10.1007/s00442-003-1439-5"],["dc.identifier.gro","3148933"],["dc.identifier.pmid","14666416"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/5574"],["dc.language.iso","en"],["dc.notes.intern","Wiegand Crossref Import"],["dc.notes.status","final"],["dc.notes.submitter","chake"],["dc.relation.issn","0029-8549"],["dc.relation.orgunit","Abteilung Ökosystemmodellierung"],["dc.subject.gro","Acacia"],["dc.subject.gro","Arid environments"],["dc.subject.gro","Extinction"],["dc.subject.gro","Simulation models"],["dc.title","Minimum recruitment frequency in plants with episodic recruitment"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","no"],["dc.type.subtype","original_ja"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","203"],["dc.bibliographiccitation.issue","2-3"],["dc.bibliographiccitation.journal","Ecological Modelling"],["dc.bibliographiccitation.lastpage","224"],["dc.bibliographiccitation.volume","117"],["dc.contributor.author","Wiegand, Kerstin"],["dc.contributor.author","Jeltsch, Florian"],["dc.contributor.author","Ward, David"],["dc.date.accessioned","2017-09-07T11:52:25Z"],["dc.date.available","2017-09-07T11:52:25Z"],["dc.date.issued","1999"],["dc.description.abstract","Most trees in the Negev desert, Israel, are either Acacia raddiana, A. tortilis or A. negevensis. They provide food and shelter for many desert animals and are a major source of livestock feed and firewood for the native Bedouin people. High mortality and low recruitment of these trees have been reported. To develop sustainable conservation strategies it is necessary to understand the population dynamics of the Acacia trees. Therefore, on the basis of demographic data gained by field studies, a spatially-explicit, individual-based computer simulation model of the population dynamics of A. raddiana has been developed. We evaluate the relative importance of different processes such as seed production and seed infestation by parasites, germination, mortality, and mistletoe infestation to the survival and recruitment of Acacia trees in the Negev. Mortality rates at different life stages, the production of uninfested seeds and the weather regime were most influential. The infection of trees by semi-parasitic mistletoes proved to be of minor importance. The most important result is that an increase in the germination rate of Acacia seeds, such as may result from passage through the digestive tract of large mammalian herbivores, is capable of counteracting the detrimental effect of unfavourable climatic conditions. Consequently, we discuss the use of increased large mammalian herbivore densities as a possible management option for enhancing the survival of Acacia populations in the Negev."],["dc.identifier.doi","10.1016/s0304-3800(98)00199-9"],["dc.identifier.gro","3148912"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/5550"],["dc.language.iso","en"],["dc.notes.intern","Wiegand Crossref Import"],["dc.notes.status","final"],["dc.notes.submitter","chake"],["dc.relation.issn","0304-3800"],["dc.relation.orgunit","Abteilung Ökosystemmodellierung"],["dc.subject.gro","Acacia raddiana"],["dc.subject.gro","Indirect parameter estimation"],["dc.subject.gro","Individual-based simulation model"],["dc.subject.gro","Population dynamics"],["dc.subject.gro","Sensitivity analysis"],["dc.title","Analysis of the population dynamics of $ trees in the Negev desert, Israel with a spatially-explicit computer simulation model"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","no"],["dc.type.subtype","original_ja"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","473"],["dc.bibliographiccitation.issue","4"],["dc.bibliographiccitation.journal","Journal of Vegetation Science"],["dc.bibliographiccitation.volume","17"],["dc.contributor.author","Moustakas, Aristides"],["dc.contributor.author","Guenther, Matthias"],["dc.contributor.author","Wiegand, Kerstin"],["dc.contributor.author","Mueller, Karl-Heinz"],["dc.contributor.author","Ward, David"],["dc.contributor.author","Meyer, Katrin M."],["dc.contributor.author","Jeltsch, Florian"],["dc.date.accessioned","2017-09-07T11:44:42Z"],["dc.date.available","2017-09-07T11:44:42Z"],["dc.date.issued","2006"],["dc.description.abstract","Question: Is there a relationship between size and death in the long-lived, deep-rooted tree, Acacia erioloba, in a semi-arid savanna? What is the size-class distribution of A.erioloba mortality? Does the mortality distribution differ from total tree size distribution? Does A. erioloba mortality distribution match the mortality distributions recorded thus far in other environments? Location: Dronfield Ranch, near Kimberley, Kalahari, South Africa. Methods: A combination of aerial photographs and a satellite image covering 61 years was used to provide long-term spatial data on mortality. We used aerial photographs of the study area from 1940, 1964, 1993 and a satellite image from 2001 to follow three plots covering 510 ha. We were able to identify and individually follow ca. 3000 individual trees from 1940 till 2001. Results: The total number of trees increased over time. No relationship between total number of trees and mean tree size was detected. There were no trends over time in total number of deaths per plot or in the size distributions of dead trees. Kolmogorov-Smirnov tests showed no differences in size class distributions for living trees through time. The size distribution of dead trees was significantly different from the size distribution of all trees present on the plots. Overall, the number of dead trees was low in small size classes, reached a peak value when canopy area was 20-30m2, and declined in larger size-classes. Mortality as a ratio of dead vs. total trees peaked at intermediate canopy sizes too. Conclusion: A.erioloba mortality was size-dependent, peaking at intermediate sizes. THe mortality distribution differs from all other tree mortality distributions recorded thus far. We suggest that a possible mechanism for this unusual mortality distribution is intraspecific competition for water in this semi-arid environment."],["dc.identifier.doi","10.1111/j.1654-1103.2006.tb02468.x"],["dc.identifier.gro","3148953"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/5596"],["dc.language.iso","en"],["dc.notes.intern","Wiegand Crossref Import"],["dc.notes.status","public"],["dc.notes.submitter","chake"],["dc.relation.issn","1100-9233"],["dc.relation.orgunit","Abteilung Ökosystemmodellierung"],["dc.subject.gro","competition"],["dc.subject.gro","long-term data"],["dc.subject.gro","remote sensing"],["dc.subject.gro","savanna"],["dc.subject.gro","size dependent mortality"],["dc.subject.gro","size distribution"],["dc.subject.gro","tree"],["dc.title","Long-term mortality patterns of the deep-rooted Acacia erioloba: The middle class shall die!"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","no"],["dc.type.subtype","original_ja"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","93"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","Basic and Applied Ecology"],["dc.bibliographiccitation.lastpage","101"],["dc.bibliographiccitation.volume","14"],["dc.contributor.author","Jeltsch, Florian"],["dc.contributor.author","Blaum, Niels"],["dc.contributor.author","Brose, Ulrich"],["dc.contributor.author","Chipperfield, Joseph D."],["dc.contributor.author","Clough, Yann"],["dc.contributor.author","Farwig, Nina"],["dc.contributor.author","Geissler, Katja"],["dc.contributor.author","Graham, Catherine H."],["dc.contributor.author","Grimm, Volker"],["dc.contributor.author","Hickler, Thomas"],["dc.contributor.author","Huth, Andreas"],["dc.contributor.author","May, Felix"],["dc.contributor.author","Meyer, Katrin M."],["dc.contributor.author","Pagel, Jörn"],["dc.contributor.author","Reineking, Björn"],["dc.contributor.author","Rillig, Matthias C."],["dc.contributor.author","Shea, Katriona"],["dc.contributor.author","Schurr, Frank M."],["dc.contributor.author","Schröder, Boris"],["dc.contributor.author","Tielbörger, Katja"],["dc.contributor.author","Weiss, Lina"],["dc.contributor.author","Wiegand, Kerstin"],["dc.contributor.author","Wiegand, Thorsten"],["dc.contributor.author","Wirth, Christian"],["dc.contributor.author","Zurell, Damaris"],["dc.date.accessioned","2017-09-07T11:52:18Z"],["dc.date.available","2017-09-07T11:52:18Z"],["dc.date.issued","2013"],["dc.description.abstract","Improving our understanding of biodiversity and ecosystem functioning and our capacity to inform ecosystem management requires an integrated framework for functional biodiversity research (FBR). However, adequate integration among empirical approaches (monitoring and experimental) and modelling has rarely been achieved in FBR. We offer an appraisal of the issues involved and chart a course towards enhanced integration. A major element of this path is the joint orientation towards the continuous refinement of a theoretical framework for FBR that links theory testing and generalization with applied research oriented towards the conservation of biodiversity and ecosystem functioning. We further emphasize existing decision-making frameworks as suitable instruments to practically merge these different aims of FBR and bring them into application. This integrated framework requires joint research planning, and should improve communication and stimulate collaboration between modellers and empiricists, thereby overcoming existing reservations and prejudices. The implementation of this integrative research agenda for FBR requires an adaptation in most national and international funding schemes in order to accommodate such joint teams and their more complex structures and data needs. {\\textcopyright} 2013 Gesellschaft f{\\\"{u}}r {\\\"{O}}kologie."],["dc.identifier.doi","10.1016/j.baae.2013.01.001"],["dc.identifier.gro","3148895"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/5533"],["dc.language.iso","en"],["dc.notes.intern","Wiegand Crossref Import"],["dc.notes.status","public"],["dc.notes.submitter","chake"],["dc.relation.issn","1439-1791"],["dc.relation.orgunit","Abteilung Ökosystemmodellierung"],["dc.subject.gro","Biodiversity experiments"],["dc.subject.gro","Biodiversity theory"],["dc.subject.gro","Conservation management"],["dc.subject.gro","Decision-making"],["dc.subject.gro","Ecosystem functions and services"],["dc.subject.gro","Forecasting"],["dc.subject.gro","Functional traits"],["dc.subject.gro","Global change"],["dc.subject.gro","Interdisciplinarity"],["dc.subject.gro","Monitoring programmes"],["dc.title","How can we bring together empiricists and modellers in functional biodiversity research?"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","no"],["dc.type.subtype","original_ja"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","97"],["dc.bibliographiccitation.issue","1/2"],["dc.bibliographiccitation.journal","Plant Ecology"],["dc.bibliographiccitation.lastpage","114"],["dc.bibliographiccitation.volume","150"],["dc.contributor.author","Wiegand, Kerstin"],["dc.contributor.author","Ward, David"],["dc.contributor.author","Thulke, Hans-Herman"],["dc.contributor.author","Jeltsch, Florian"],["dc.date.accessioned","2017-09-07T11:44:44Z"],["dc.date.available","2017-09-07T11:44:44Z"],["dc.date.issued","2003"],["dc.description.abstract","The African Acacia species A. raddiana is believed to be endangered in the Negev desert of Israel. The ecology of this species is not well understood. The main idea of our study is to learn more about the long-term population dynamics of these trees using snapshot information in the form of size frequency distributions. These distributions are highly condensed indices of population dynamics acting over many years. In this paper, we analyse field data on recruitment, growth, and mortality and use an existing simulation model of the population dynamics of A. raddiana (SAM) to produce contrasting scenarios of these live history processes that are based on the analysed field evidence. The main properties of simulated as well as observed tree size frequency distributions are characterised with Simpson's index of dominance and a new permutation index. Finally, by running the SAM model under the different scenarios, we study the effect of these different processes on simulated size frequency distributions (pattern) and we compare them to size distributions observed in the field, in order to identify the processes acting in the field. Our study confirms rare recruitment events as a major factor shaping tree size frequency distributions and shows that the paucity of recruitment has been a normal feature of A. raddiana in the Negev over many years. Irregular growth, e.g., due to episodic rainfall, showed a moderate influence on size distributions. Finally, the size frequency distributions observed in the Negev reveal the information that, in this harsh environment, mortality of adult A. raddiana is independent of tree size (age)."],["dc.identifier.doi","10.1023/a:1026574303048"],["dc.identifier.gro","3148958"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/5601"],["dc.language.iso","en"],["dc.notes.intern","Wiegand Crossref Import"],["dc.notes.status","final"],["dc.notes.submitter","chake"],["dc.relation.issn","1385-0237"],["dc.relation.orgunit","Abteilung Ökosystemmodellierung"],["dc.subject.gro","Acacia raddiana"],["dc.subject.gro","Individual-based"],["dc.subject.gro","Negev desert"],["dc.subject.gro","Pattern and process"],["dc.subject.gro","Permutation index"],["dc.subject.gro","Rare recruitment"],["dc.subject.gro","SAM"],["dc.subject.gro","Size frequency distributions"],["dc.subject.gro","Spatially-explicit simulation model"],["dc.title","From snapshot information to long-term population dynamics of Acacias by a simulation model"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","no"],["dc.type.subtype","original_ja"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","211"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","Folia Geobotanica"],["dc.bibliographiccitation.lastpage","230"],["dc.bibliographiccitation.volume","35"],["dc.contributor.author","Wiegand, Kerstin"],["dc.contributor.author","Jeltsch, Florian"],["dc.contributor.author","Ward, David"],["dc.contributor.author","Schmidt, Heike"],["dc.date.accessioned","2017-09-07T11:52:24Z"],["dc.date.available","2017-09-07T11:52:24Z"],["dc.date.issued","2000"],["dc.description.abstract","Spatially-explicit and landscape-related simulation models are increasingly used in ecology, but are often criticized because their parameterization has high data requirements. A frequently suggested approach to overcome this difficulty is the linkage of spatially-explicit or landscape-related models with GIS (geographic information system) and remote-sensing technology. GIS can provide data on relevant landscape features, such as topography, and satellite images can be used to identify spatial vegetation distribution. In this paper, we use these techniques for simple, cost-inexpensive (in both time and money) parameterization based on readily-available GIS and remotely-sensed data. We use a previously developed, spatially-explicit model of the population dynamics of an Acacia species in the Negev desert of Israel (SAM, spatial Acacia model) to investigate if model initialization (measurement of current tree distribution) can be obtained from readily-available satellite images using a radiometric vegetation index (NDVI, normalized difference vegetation index). Furthermore, we investigate the applicability and the advantages of using an explicit consideration of landscape features in the model based on topographic data from a GIS. Using a DEM (digital elevation model), we compare the wadi topography to the current tree distribution observed in the field. We found that the readily-available GIS and remotely-sensed data are not sufficient to significantly support the parameterization and further development of the model. We conclude that despite the possible benefit of linking spatially-explicit models with other techniques the advantage compared to data sampling in the field is limited by a possible mismatch of scales and the dominant role of stochasticity that may override the relevance of certain spatially-explicit information."],["dc.identifier.doi","10.1007/bf02803099"],["dc.identifier.gro","3148919"],["dc.identifier.pii","BF02803099"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/5558"],["dc.language.iso","en"],["dc.notes.intern","Wiegand Crossref Import"],["dc.notes.status","public"],["dc.notes.submitter","chake"],["dc.relation.eissn","1874-9348"],["dc.relation.issn","1211-9520"],["dc.relation.orgunit","Abteilung Ökosystemmodellierung"],["dc.subject.gro","Acacia raddiana"],["dc.subject.gro","Landscape related models"],["dc.subject.gro","NDVI"],["dc.subject.gro","Simulation model"],["dc.subject.gro","Spatially-explicit"],["dc.subject.gro","Wadi morphology"],["dc.title","Linking a spatially-explicit model of acacias to GIS and remotely-sensed data"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","no"],["dc.type.subtype","original_ja"],["dspace.entity.type","Publication"]]