Meyer, Katrin Mareike

[["dc.bibliographiccitation.firstpage","63"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","Perspectives in Plant Ecology, Evolution and Systematics"],["dc.bibliographiccitation.lastpage","72"],["dc.bibliographiccitation.volume","10"],["dc.contributor.author","Meyer, Katrin M."],["dc.contributor.author","Ward, David"],["dc.contributor.author","Wiegand, Kerstin"],["dc.contributor.author","Moustakas, Aristides"],["dc.date.accessioned","2017-09-07T11:44:38Z"],["dc.date.available","2017-09-07T11:44:38Z"],["dc.date.issued","2007"],["dc.description.abstract","Coexistence of trees and grasses in savannas should be possible if competition between the woody and the grassy components is less intense than the competition within each component. Although several studies have investigated competition between trees and grasses, little is known about tree-tree interactions. We used a multi-proxy approach to examine the spatial pattern of Acacia mellifera and other savanna woody species in a semi-arid savanna in South Africa. Spatial analysis of the point patterns of young and reproductively mature shrubs detected decreasing aggregation with size/age over all spatial scales. This indicated the prevalence of competition although the overall spatial shrub pattern was aggregated. In contrast to point pattern statistics that detect changes only when competition has led to the death of the inferior competitor, we also applied methods identifying the competitive effect on sizes of individual trees. Competition should lead to a negative spatial autocorrelation in size, which we observed in half of the studied cases. Quantile regressions show that nearest-neighbour distance increased steeply with combined size of the target shrub and its neighbours indicating strong competitive effects. The medians of the distributions of maximum root lengths of A. mellifera, of the scale of regular patterns, and of negative autocorrelations were not significantly different, suggesting that overlapping root systems mediate competitive interactions. A competitor removal experiment did not lead to increased shrub sizes, which may be due to the limited duration of the experiment. From the nearest neighbour and autocorrelation analyses, we conclude that competition had a strong impact on growth rates of savanna woody species. Competition-induced mortality only becomes obvious when analysing the shift towards less aggregated spatial patterns when shrubs become reproductively mature. As the overall clustered spatial pattern masks the perceptible effect of competition, a time component should always be included in spatial pattern-based inference of competition."],["dc.identifier.doi","10.1016/j.ppees.2007.09.002"],["dc.identifier.gro","3148942"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/5584"],["dc.language.iso","en"],["dc.notes.intern","Wiegand Crossref Import"],["dc.notes.status","public"],["dc.notes.submitter","chake"],["dc.relation.issn","1433-8319"],["dc.relation.orgunit","Abteilung Ökosystemmodellierung"],["dc.subject.gro","Acacia mellifera"],["dc.subject.gro","Competitor removal experiment"],["dc.subject.gro","Nearest-neighbour distance"],["dc.subject.gro","Quantile regression"],["dc.subject.gro","Spatial autocorrelation"],["dc.subject.gro","Spatial point pattern analysis"],["dc.title","Multi-proxy evidence for competition between savanna woody species"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","no"],["dc.type.subtype","original_ja"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","1306"],["dc.bibliographiccitation.issue","6"],["dc.bibliographiccitation.journal","Journal of Ecology"],["dc.bibliographiccitation.lastpage","1315"],["dc.bibliographiccitation.volume","95"],["dc.contributor.author","Meyer, Katrin M."],["dc.contributor.author","Wiegand, Kerstin"],["dc.contributor.author","Ward, David"],["dc.contributor.author","Moustakas, Aristides"],["dc.date.accessioned","2017-09-07T11:44:41Z"],["dc.date.available","2017-09-07T11:44:41Z"],["dc.date.issued","2007"],["dc.description.abstract","1. Patch dynamics is a new, potentially unifying mechanism for the explanation of tree-grass coexistence in savannas. In this scale-explicit paradigm, savannas consist of patches in which a cyclical succession between woody and grassy dominance proceeds spatially asynchronously. The growing ecological and economic problem of shrub encroachment is a natural transient phase in this cycle. 2. An important step towards understanding patterns at the landscape scale is achieved by investigating mechanisms at a smaller scale. We developed the spatially explicit individual-based simulation model SATCHMO to test the null hypothesis that cyclical succession cannot emerge from a realistic patch scale simulation model of the population dynamics of savanna woody species. 3. We calculated the partial temporal autocorrelation coefficient for 100 simulated time series of shrub cover over 500 years for time lags of up to 200 years to establish the existence and duration of successional cycles. We found a significant positive autocorrelation indicating the existence of cycles with a typical duration of about 33 years. 4. The shrub size frequency distributions over the course of a cycle showed shifts from dominance of small shrub sizes towards larger sizes during the increasing phase of a cycle and the reverse in the declining phase. This supports the three phase explanation as follows: (i) an initial phase when spatially and temporally overlapping favourable conditions lead to mass recruitment of shrubs; (ii) a build-up phase when the shrub cohort grows; and (iii) a break-down phase when increased competition due to crowding and unfavourable conditions lead to the break-down of the shrub cohort. The frequency distribution of shrub age at death over 10 simulations was also in agreement with this explanation. 5. We investigated the relationship between shrub cover, annual precipitation and time-lagged shrub cover to identify the driver of the cyclical successions. More than 90{\\%} of the variation in shrub cover was explained by shrub cover of the previous year, precipitation, and their interaction. 6. With the demonstration of precipitation-driven cyclical succession at the patch scale, we show that the mechanistic, temporal component of patch dynamics can be used to explain tree-grass coexistence in semi-arid savannas."],["dc.identifier.doi","10.1111/j.1365-2745.2007.01289.x"],["dc.identifier.gro","3148951"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/5594"],["dc.language.iso","en"],["dc.notes.intern","Wiegand Crossref Import"],["dc.notes.status","final"],["dc.notes.submitter","chake"],["dc.relation.issn","0022-0477"],["dc.relation.orgunit","Abteilung Ökosystemmodellierung"],["dc.subject.gro","Acacia mellifera"],["dc.subject.gro","Cyclical succession"],["dc.subject.gro","Individual-based simulation model"],["dc.subject.gro","Patch scale"],["dc.subject.gro","Scale"],["dc.subject.gro","Shrub encroachment"],["dc.subject.gro","Size-frequency distributions"],["dc.subject.gro","Temporal autocorrelation"],["dc.subject.gro","Tree-grass coexistence"],["dc.title","The rhythm of savanna patch dynamics"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","no"],["dc.type.subtype","original_ja"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","377"],["dc.bibliographiccitation.issue","2-4"],["dc.bibliographiccitation.journal","Ecological Modelling"],["dc.bibliographiccitation.lastpage","391"],["dc.bibliographiccitation.volume","209"],["dc.contributor.author","Meyer, Katrin M."],["dc.contributor.author","Wiegand, Kerstin"],["dc.contributor.author","Ward, David"],["dc.contributor.author","Moustakas, Aristides"],["dc.date.accessioned","2017-09-07T11:52:23Z"],["dc.date.available","2017-09-07T11:52:23Z"],["dc.date.issued","2007"],["dc.description.abstract","Many mechanisms have been suggested to explain the coexistence of woody species and grasses in savannas, yet, evidence from field studies and simulation models has been mixed. Shrub encroachment is an ecological and economic problem in savannas worldwide which generally is attributed to overgrazing. Patch-dynamics is a new mechanism explaining tree-grass coexistence and the natural occurrence of shrub encroachment in savannas. A patch-dynamic savanna consists of patches in which cyclical succession between grassy and woody dominance proceeds spatially asynchronously. The spatially explicit, individual-based patch-scale simulation model SATCHMO was developed to investigate cyclical succession in the paradigm of patch-dynamics for arid and semi-arid savannas. SATCHMO is designed to capture within-patch shrub population dynamics based on a grid of 51 m side length and a resolution of 10 cm. The model shrub characteristics were derived from Acacia mellifera, the main encroaching species in African savannas. The aim of SATCHMO is to give a detailed small-scale understanding of above- and belowground growth, competition, and mortality of savanna woody plants and the influence of precipitation and fire on patch transition frequencies, shrub growth rates, and shrub size frequencies. With SATCHMO, we want to identify the conditions leading to cyclical successions in general and shrub encroachment in particular. Soil moisture is the most important parameter in SATCHMO influencing growth, reproduction, and mortality of shrubs and grass tufts, and that mediates competition. To acknowledge the importance of belowground interactions in savannas, shrub root growth and competition are modelled spatially explicitly. The model output was successfully validated with morphometrical and spatial data from the field site in the South African Kalahari thornveld and with recent literature data on savanna woody species cover. Global sensitivity analysis with Latin hypercube sampling shows that soil moisture is the most important driver of shrub cover dynamics in semi-arid savannas."],["dc.identifier.doi","10.1016/j.ecolmodel.2007.07.001"],["dc.identifier.gro","3148917"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/5556"],["dc.language.iso","en"],["dc.notes.intern","Wiegand Crossref Import"],["dc.notes.status","public"],["dc.notes.submitter","chake"],["dc.relation.issn","0304-3800"],["dc.relation.orgunit","Abteilung Ökosystemmodellierung"],["dc.subject.gro","Acacia mellifera"],["dc.subject.gro","Computer simulation model"],["dc.subject.gro","Cyclical succession"],["dc.subject.gro","Latin Hypercube sensitivity analysis"],["dc.subject.gro","Patch-dynamics"],["dc.subject.gro","Shrub encroachment"],["dc.subject.gro","Spatially explicit root growth"],["dc.subject.gro","Validation"],["dc.title","SATCHMO: A spatial simulation model of growth, competition, and mortality in cycling savanna patches"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","no"],["dc.type.subtype","original_ja"],["dspace.entity.type","Publication"]]