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","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.firstpage","499"],["dc.bibliographiccitation.journal","Verhandlungen der Gesellschaft für Ökologie"],["dc.bibliographiccitation.lastpage","506"],["dc.bibliographiccitation.volume","28"],["dc.contributor.author","Wiegand, K."],["dc.contributor.author","Jeltsch, F."],["dc.contributor.author","Ward, D."],["dc.date.accessioned","2020-12-08T11:03:08Z"],["dc.date.available","2020-12-08T11:03:08Z"],["dc.date.issued","1997"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/69481"],["dc.relation.issn","0171-1113"],["dc.relation.orgunit","Abteilung Ökosystemmodellierung"],["dc.subject.gro","Acacia"],["dc.subject.gro","Acacia raddiana"],["dc.subject.gro","Anthropogenic disturbances"],["dc.subject.gro","Arid"],["dc.subject.gro","Environmental impact"],["dc.subject.gro","Ephemeral river"],["dc.subject.gro","Event-driven system"],["dc.subject.gro","Herbivores"],["dc.subject.gro","Israel"],["dc.subject.gro","Modeling"],["dc.subject.gro","Negev"],["dc.subject.gro","Negev Desert"],["dc.subject.gro","Population dynamics"],["dc.subject.gro","Road"],["dc.subject.gro","Simulation model"],["dc.subject.gro","Tree"],["dc.title","Untersuchungen zur Auswirkung von Strassen auf das Überleben der Akazien im Negev"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["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"]]

[["dc.bibliographiccitation.firstpage","338"],["dc.bibliographiccitation.issue","3"],["dc.bibliographiccitation.journal","Journal of Arid Environments"],["dc.bibliographiccitation.lastpage","343"],["dc.bibliographiccitation.volume","74"],["dc.contributor.author","Sher, A. A."],["dc.contributor.author","Wiegand, Kerstin"],["dc.contributor.author","Ward, David"],["dc.date.accessioned","2017-09-07T11:44:37Z"],["dc.date.available","2017-09-07T11:44:37Z"],["dc.date.issued","2009"],["dc.description.abstract","We investigated the spatial distribution of the three Acacia and two Tamarix tree species and related the spatial distribution of these two genera to their 18O value, i.e. their 18O/16O isotopic ratio in the Negev desert, Israel. At the regional spatial scale, there was a significant difference in the overall distributions of these two genera, although there was considerable overlap. At the 1 km2 scale, there was no deviation from homogeneity. At a finer scale, no deviation from a random distribution was found in three ephemeral rivers between the two largest trees in these two genera, Acacia raddiana and Tamarix nilotica. We found that Tamarix used deep water from aquifers while Acacia trees used an alternate source, most likely surface water. Spatial segregation of Tamarix and Acacia occurs at the large spatial scale but not at the small scale, perhaps because of the high tolerance of Tamarix species for salinity and the low tolerance of Acacia species for saline conditions. It appears that the trees are not spatially segregated on the small scale because they use different water sources."],["dc.identifier.doi","10.1016/j.jaridenv.2009.09.007"],["dc.identifier.gro","3148938"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/5580"],["dc.language.iso","en"],["dc.notes.intern","Wiegand Crossref Import"],["dc.notes.status","public"],["dc.notes.submitter","chake"],["dc.relation.issn","0140-1963"],["dc.relation.orgunit","Abteilung Ökosystemmodellierung"],["dc.subject.gro","Acacia gerrardii"],["dc.subject.gro","Acacia raddiana"],["dc.subject.gro","Acacia tortilis"],["dc.subject.gro","Coexistence"],["dc.subject.gro","Israel"],["dc.subject.gro","Spatial ecology"],["dc.subject.gro","Tamarix aphylla"],["dc.subject.gro","Tamarix nilotica"],["dc.title","Do Acacia and Tamarix trees compete for water in the Negev desert?"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","no"],["dc.type.subtype","original_ja"],["dspace.entity.type","Publication"]]