Ward, David Mercer

[["dc.bibliographiccitation.firstpage","229"],["dc.bibliographiccitation.issue","4"],["dc.bibliographiccitation.journal","Perspectives in Plant Ecology, Evolution and Systematics"],["dc.bibliographiccitation.lastpage","242"],["dc.bibliographiccitation.volume","7"],["dc.contributor.author","Wiegand, Kerstin"],["dc.contributor.author","Saltz, David"],["dc.contributor.author","Ward, David"],["dc.date.accessioned","2017-09-07T11:44:40Z"],["dc.date.available","2017-09-07T11:44:40Z"],["dc.date.issued","2005"],["dc.description.abstract","The coexistence of woody and grassy plants in savannas has often been attributed to a rooting-niche separation (two-layer hypothesis). Water was assumed to be the limiting resource for both growth forms and grasses were assumed to extract water from the upper soil layer and trees and bushes from the lower layers. Woody plant encroachment (i.e. an increase in density of woody plants often unpalatable to domestic livestock) is a serious problem in many savannas and is believed to be the result of overgrazing in ‘two-layer systems’. Recent research has questioned the universality of both the two-layer hypothesis and the hypothesis that overgrazing is the cause of woody plant encroachment. We present an alternative hypothesis explaining both tree–grass coexistence and woody plant encroachment in arid savannas. We propose that woody plant encroachment is part of a cyclical succession between open savanna and woody dominance and is driven by two factors: rainfall that is highly variable in space and time, and inter-tree competition. In this case, savanna landscapes are composed of many patches (a few hectares in size) in different states of transition between grassy and woody dominance, i.e. we hypothesize that arid savannas are patch-dynamic systems. We summarize patterns of tree distribution observed in an arid savanna in Namibia and show that these patterns are in agreement with the patch-dynamic savanna hypothesis. We discuss the applicability of this hypothesis to fire-dominated savannas, in which rainfall variability is low and fire drives spatial heterogeneity. We conclude that field studies are more likely to contribute to a general understanding of tree–grass coexistence and woody plant encroachment if they consider both primary (rain and nutrients) and secondary (fire and grazing) determinants of patch properties across different savannas."],["dc.identifier.doi","10.1016/j.ppees.2005.10.001"],["dc.identifier.gro","3148947"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/5590"],["dc.language.iso","en"],["dc.notes.intern","Wiegand Crossref Import"],["dc.notes.status","final"],["dc.notes.submitter","chake"],["dc.relation.issn","1433-8319"],["dc.relation.orgunit","Abteilung Ökosystemmodellierung"],["dc.subject.gro","Fire"],["dc.subject.gro","Grazing"],["dc.subject.gro","Honeycomb rippling model"],["dc.subject.gro","Inter-tree competition"],["dc.subject.gro","Spatio-temporal rainfall variation"],["dc.subject.gro","Tree-grass coexistence"],["dc.title","A patch-dynamics approach to savanna dynamics and woody plant encroachment – Insights from an arid savanna"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","no"],["dc.type.subtype","original_ja"],["dspace.entity.type","Publication"]]

[["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","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","47"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","Frontiers of Biogeography"],["dc.bibliographiccitation.lastpage","53"],["dc.bibliographiccitation.volume","2"],["dc.contributor.author","Moustakas, Aristides"],["dc.contributor.author","Wiegand, Kerstin"],["dc.contributor.author","Meyer, Katrin M."],["dc.contributor.author","Ward, David"],["dc.contributor.author","Sankaran, Mahesh"],["dc.date.accessioned","2017-09-07T11:50:52Z"],["dc.date.available","2017-09-07T11:50:52Z"],["dc.date.issued","2010"],["dc.identifier.doi","10.21425/F5FBG12335"],["dc.identifier.gro","3147839"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/5165"],["dc.language.iso","en"],["dc.notes.status","final"],["dc.notes.submitter","chake"],["dc.relation.issn","1948-6596"],["dc.relation.orgunit","Abteilung Ökosystemmodellierung"],["dc.title","Learning new tricks from old trees: revisiting the savanna question"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","no"],["dc.type.subtype","original_ja"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","135"],["dc.bibliographiccitation.journal","Ecological Modelling"],["dc.bibliographiccitation.lastpage","144"],["dc.bibliographiccitation.volume","320"],["dc.contributor.author","Accatino, Francesco"],["dc.contributor.author","Wiegand, Kerstin"],["dc.contributor.author","Ward, David"],["dc.contributor.author","Michele, Carlo de"],["dc.date.accessioned","2017-09-07T11:52:25Z"],["dc.date.available","2017-09-07T11:52:25Z"],["dc.date.issued","2015"],["dc.description.abstract","We develop a model to investigate how trees can invade the grass stratum in humid savannas despite repeated fires. In the literature, it is clear that fire reduces tree canopy in savannas. However, fire alone may not be sufficient to prevent tree invasion because there are ecological mechanisms that hamper fire spread by undermining the continuity and density of the grass stratum, which is the means of fire propagation in savannas. Our model is spatially explicit and individual-based, and includes two important factors characterizing the interactions between fire, trees, and grass in savannas, viz. space and the strategies that trees use to cope with fire. The strategies that trees employ against fire emerge from life history traits. According to these strategies, we classify savanna trees into three categories: resprouters, which are able to resprout after their aboveground biomass is burned\\; resisters, which are able to resist fire due to a thick bark even in the juvenile stages\\; avoiders, which are very fire-vulnerable in the juvenile stages, but are able to grow fast in the absence of fire. Our results show that trees can invade the grass stratum and finally suppress fire spread because one of the following occurs: (1) trees may resprout and form a population that persists despite repeated effective fires\\; (2) trees may be fire-resistant\\; (3) if trees are fire-vulnerable they may cluster and grow in density until fire is prevented. Our results show that fire can be effective in preventing the initiation of the invasion process in the grass stratum. However, once the invasion process has begun, fire alone is not able to reverse this process because of the strategies employed by trees. Furthermore, when a high tree density is reached, grass density is insufficient to allow effective fire spread. From a management point of view, our results imply that fire must be coupled with other factors (browsing, mechanical thinning) to reduce tree density in encroached areas."],["dc.identifier.doi","10.1016/j.ecolmodel.2015.09.014"],["dc.identifier.gro","3148910"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/5548"],["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","Fire-vegetation feedbacks"],["dc.subject.gro","Individual-based model"],["dc.subject.gro","Resprouting"],["dc.subject.gro","Tree clustering"],["dc.subject.gro","Woody plant encroachment"],["dc.title","Trees, grass, and fire in humid savannas"],["dc.title.subtitle","The importance of life history traits and spatial processes"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","no"],["dc.type.subtype","original_ja"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","440"],["dc.bibliographiccitation.issue","3"],["dc.bibliographiccitation.journal","African Journal of Ecology"],["dc.bibliographiccitation.lastpage","442"],["dc.bibliographiccitation.volume","46"],["dc.contributor.author","Meyer, Katrin M."],["dc.contributor.author","Wiegand, Kerstin"],["dc.contributor.author","Ward, David"],["dc.contributor.author","Moustakas, Aristides"],["dc.date.accessioned","2017-09-07T11:50:51Z"],["dc.date.available","2017-09-07T11:50:51Z"],["dc.date.issued","2007"],["dc.description.abstract","Shrub encroachment, i.e. the increase in density of woody species, is threatening tree-grass coexistence in savannas worldwide (see e.g. Smit, 2004; Wiegand, Ward {\\&} Saltz, 2005; Wiegand, Saltz {\\&} Ward, 2006). In addition to ecological problems, shrub encroachment creates economic problems, because it reduces the extent of areas suitable for grazing of livestock. In recognition of the importance of spatial and temporal scales for savannas, Wiegand et al. (2005, 2006) proposed patch-dynamics as the driving mechanism of tree-grass coexistence in savannas including a naturally shrub encroached phase. In patch-dynamic landscapes, patches are asynchronously cycling between woody and grassy dominance. Evidence for patch-dynamic savannas is accumulating (e.g. Gillson, 2004; Wiegand et al., 2006), but simple methods for the determination of the spatial scale of patches are still lacking. In the present study, we propose a method for estimating patch sizes based on the canopy diameter and the spatial location of individuals and apply it to an example data set from a semi-arid savanna in South Africa."],["dc.identifier.doi","10.1111/j.1365-2028.2007.00834.x"],["dc.identifier.gro","3147837"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/5163"],["dc.language.iso","en"],["dc.notes.status","public"],["dc.notes.submitter","chake"],["dc.relation.issn","0141-6707"],["dc.relation.orgunit","Abteilung Ökosystemmodellierung"],["dc.title","Determining patch size"],["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","491"],["dc.bibliographiccitation.issue","6"],["dc.bibliographiccitation.journal","Basic and Applied Ecology"],["dc.bibliographiccitation.lastpage","499"],["dc.bibliographiccitation.volume","10"],["dc.contributor.author","Meyer, Katrin M."],["dc.contributor.author","Wiegand, Kerstin"],["dc.contributor.author","Ward, David"],["dc.date.accessioned","2017-09-07T11:44:39Z"],["dc.date.available","2017-09-07T11:44:39Z"],["dc.date.issued","2009"],["dc.description.abstract","Many mechanisms have been suggested to explain the coexistence of woody species and grasses in savannas. However, evidence from field studies and simulation models has been mixed. Patch dynamics is a potentially unifying mechanism explaining tree-grass coexistence and the natural occurrence of shrub encroachment in arid and semi-arid savannas. A patch-dynamic savanna consists of a spatial mosaic of patches. Each patch maintains a cyclical succession between dominance of woody species and grasses, and the succession of neighbouring patches is temporally asynchronous. Evidence from empirical field studies supports the patch dynamics view of savannas. As a basis for future tests of patch dynamics in savannas, several hypotheses are presented and one is exemplarily examined: at the patch scale, realistically parameterized simulation models have generated cyclical succession between woody and grass dominance. In semi-arid savannas, cyclical successions are driven by precipitation conditions that lead to mass recruitment of shrubs in favourable years and to simultaneous collapse of shrub cohorts in drought years. The spatiotemporal pattern of precipitation events determines the scale of the savanna vegetation mosaic in space and time. In a patch-dynamic savanna, shrub encroachment is a natural, transient phase corresponding to the shrub-dominated phase during the successional cycle. Hence, the most promising management strategy for encroached areas is a large-scale rotation system of rangelands. In conclusion, patch dynamics is a possible scale-explicit mechanism for the explanation of tree-grass coexistence in savannas that integrates most of the coexistence mechanisms proposed thus far for savannas."],["dc.identifier.doi","10.1016/j.baae.2008.12.003"],["dc.identifier.gro","3148935"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/5576"],["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","Competition"],["dc.subject.gro","Cyclical succession"],["dc.subject.gro","Grasses"],["dc.subject.gro","Mosaic cycles"],["dc.subject.gro","Shrub encroachment"],["dc.subject.gro","Shrubs"],["dc.subject.gro","Simulation models"],["dc.subject.gro","Spatiotemporal scales"],["dc.subject.gro","Woody species"],["dc.title","Patch dynamics integrate mechanisms for savanna tree–grass coexistence"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","no"],["dc.type.subtype","original_ja"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","309"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","Animal"],["dc.bibliographiccitation.lastpage","317"],["dc.bibliographiccitation.volume","11"],["dc.contributor.author","Accatino, F."],["dc.contributor.author","Ward, D."],["dc.contributor.author","Wiegand, K."],["dc.contributor.author","De Michele, C."],["dc.date.accessioned","2017-09-07T11:44:34Z"],["dc.date.available","2017-09-07T11:44:34Z"],["dc.date.issued","2017"],["dc.description.abstract","Assessing the carrying capacity is of primary importance in arid rangelands. This becomes even more important during droughts, when rangelands exhibit non-equilibrium dynamics, and the dynamics of livestock conditions and forage resource are decoupled. Carrying capacity is usually conceived as an equilibrium concept, that is, the consumer density that can co-exist in long-term equilibrium with the resource. As one of the first, here we address the concept of carrying capacity in systems, where there is no feedback between consumer and resource in a limited period of time. To this end, we developed an individual-based model describing the basic characteristics of a rangeland during a drought. The model represents a rangeland composed by a single water point and forage distributed all around, with livestock units moving from water to forage and vice versa, for eating and drinking. For each livestock unit we implemented an energy balance and we accounted for the gut-filling effect (i.e. only a limited amount of forage can be ingested per unit time). Our results showed that there is a temporal threshold above which livestock begin to experience energy deficit and burn fat reserves. We demonstrated that such a temporal threshold increases with the number of animals and decreases with the rangeland conditions (amount of forage). The temporal threshold corresponded to the time livestock take to consume all the forage within a certain distance from water, so that the livestock can return to water for drinking without spending more energy than they gain within a day. In this study, we highlight the importance of a time threshold in the assessment of carrying capacity in non-equilibrium conditions. Considering this time threshold could explain contrasting observations about the influence of livestock number on livestock conditions. In case of private rangelands, the herd size should be chosen so that the spatial threshold equals (or exceeds) the length of the drought."],["dc.identifier.doi","10.1017/s1751731116001531"],["dc.identifier.gro","3148929"],["dc.identifier.pii","S1751731116001531"],["dc.identifier.pmid","27452875"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/5570"],["dc.language.iso","en"],["dc.notes.intern","Wiegand Crossref Import"],["dc.notes.status","final"],["dc.notes.submitter","chake"],["dc.relation.issn","1751-7311"],["dc.relation.orgunit","Abteilung Ökosystemmodellierung"],["dc.rights","CC BY-NC-ND 4.0"],["dc.subject.gro","drought"],["dc.subject.gro","energy deficit"],["dc.subject.gro","foraging"],["dc.subject.gro","optimal herd size"],["dc.subject.gro","water point"],["dc.title","Carrying capacity in arid rangelands during droughts: the role of temporal and spatial thresholds"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","no"],["dc.type.subtype","original_ja"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]