TY - JOUR A1 - Jeltsch, Florian A1 - Groeneveld, Jürgen A1 - Wissel, Christian A1 - Wucherer, W. A1 - Dimeyeva, L. T1 - Seed dispersal by cattle may cause shrub encroachment of Grewia flava on southern Kalahari rangelands Y1 - 2005 SN - 3-86537-386-0 ER - TY - JOUR A1 - Jeltsch, Florian A1 - Wiegand, K. A1 - Ward, D. T1 - Seed dispersal by cattle may cause shrub encroachment of Grewia flava on southern Kalahari rangelands Y1 - 2004 ER - TY - JOUR A1 - Jeltsch, Florian A1 - Tews, Jörg A1 - Schurr, Frank Martin T1 - Seed dispersal by cattle may cause shrub encroachment of Grewia flava on southern Kalahari rangelands N2 - Shrub encroachment, i.e. the increase in woody plant cover, is a major concern for livestock farming in southern Kalahari savannas. We developed a grid-based computer model simulating the population dynamics of Grewia flava, a common, fleshy-fruited encroaching shrub. In the absence of large herbivores, seeds of Grewia are largely deposited in the sub-canopy of Acacia erioloba. Cattle negate this dispersal limitation by browsing on the foliage of Grewia and dispersing seeds into the grassland matrix. In this study we first show that model predictions of Grewia cover dynamics are realistic by comparing model output with shrub cover estimates obtained from a time series of aerial photographs. Subsequently, we apply a realistic range of intensity of cattle-induced seed dispersal combined with potential precipitation and fire scenarios. Based on the simulation results we suggest that cattle may facilitate shrub encroachment of Grewia. The results show that the severity of shrub encroachment is governed by the intensity of seed dispersal. For a high seed dispersal intensity without fire (equivalent to a high stocking rate) the model predicts 56% shrub cover and 85% cell cover after 100 yr. With fire both recruitment and shrub cover are reduced, which may, under moderate intensities, prevent shrub encroachment. Climate change scenarios with two-fold higher frequencies of drought and wet years intensified shrub encroachment rates, although long-term mean of precipitation remained constant. As a management recommendation we suggest that shrub encroachment on rangelands may be counteracted by frequent fires and controlling cattle movements to areas with a high proportion of fruiting Grewia shrubs Y1 - 2004 ER - TY - CHAP A1 - Rossmanith, Eva A1 - Blaum, Niels A1 - Keil, Manfred A1 - Langerwisch, F. A1 - Meyer, Jork A1 - Popp, Alexander A1 - Schmidt, Michael A1 - Schultz, Christoph A1 - Schwager, Monika A1 - Vogel, Melanie A1 - Wasiolka, Bernd A1 - Jeltsch, Florian T1 - Scaling up local population dynamics to regional scales BT - an integrated approach N2 - In semi-arid savannas, unsustainable land use can lead to degradation of entire landscapes, e.g. in the form of shrub encroachment. This leads to habitat loss and is assumed to reduce species diversity. In BIOTA phase 1, we investigated the effects of land use on population dynamics on farm scale. In phase 2 we scale up to consider the whole regional landscape consisting of a diverse mosaic of farms with different historic and present land use intensities. This mosaic creates a heterogeneous, dynamic pattern of structural diversity at a large spatial scale. Understanding how the region-wide dynamic land use pattern affects the abundance of animal and plant species requires the integration of processes on large as well as on small spatial scales. In our multidisciplinary approach, we integrate information from remote sensing, genetic and ecological field studies as well as small scale process models in a dynamic region-wide simulation tool.
Interdisziplinäres Zentrum für Musterdynamik und Angewandte Fernerkundung Workshop vom 9. - 10. Februar 2006. Y1 - 2006 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-7320 N1 - [Poster] ER - TY - JOUR A1 - Popp, Alexander A1 - Vogel, Melanie A1 - Blaum, Niels A1 - Jeltsch, Florian T1 - Scaling up ecohydrological processes : role of surface water flow in water-limited landscapes N2 - In this study, we present a stochastic landscape modeling approach that has the power to transfer and integrate existing information on vegetation dynamics and hydrological processes from the small scale to the landscape scale. To include microscale processes like ecohydrological feedback mechanisms and spatial exchange like surface water flow, we derive transition probabilities from a fine-scale simulation model. We applied two versions of the landscape model, one that includes and one that disregards spatial exchange of water to the situation of a sustainably used research farm and communally used and degraded rangeland in semiarid Namibia. Our simulation experiments show that including spatial exchange of overland flow among vegetation patches into our model is a precondition to reproduce vegetation dynamics, composition, and productivity, as well as hydrological processes at the landscape scale. In the model version that includes spatial exchange of water, biomass production at light grazing intensities increases 2.24-fold compared to the model without overland flow. In contrast, overgrazing destabilizes positive feedbacks through vegetation and hydrology and decreases the number of hydrological sinks in the model with overland flow. The buffer capacity of these hydrological sinks disappears and runoff increases. Here, both models predicted runoff losses from the system and artificial droughts occurring even in years with good precipitation. Overall, our study reveals that a thorough understanding of overland flow is an important precondition for improving the management of semiarid and arid rangelands with distinct topography. Y1 - 2009 UR - http://www.agu.org/journals/jg/ U6 - https://doi.org/10.1029/2008jg000910 SN - 0148-0227 ER - TY - JOUR A1 - Giladi, Itamar A1 - May, Felix A1 - Ristow, Michael A1 - Jeltsch, Florian A1 - Ziv, Yaron T1 - Scale-dependent species-area and species-isolation relationships: a review and a test study from a fragmented semi-arid agro-ecosystem JF - Journal of biogeography N2 - Aim Patterns that relate species richness with fragment area (the species-area relationship, SAR) and with isolation (the species-isolation relationship, SIR) are well documented. However, those that relate species density - the number of species within a standardized area - with fragment area (D-SAR) or isolation (D-SIR) have not been sufficiently explored, despite the potential for such an analysis to disentangle the underlying mechanisms of SARs and SIRs. Previous spatial theory predicts that a significant D-SAR or D-SIR is unlikely to emerge in taxa with high dispersal limitation, such as plants. Furthermore, a recent model predicts that the detection and the significance of D-SARs or D-SIRs may decrease with grain size. We combined a literature review with grain size-dependent sampling in a fragmented landscape to evaluate the prevalence and grain size-dependent nature of D-SARs and D-SIRs in plants. Location Worldwide (review) and a semi-arid agro-ecosystem in Israel (case study). Methods We combined an extensive literature review of 31 D-SAR studies of plants in fragmented landscapes with an empirical study in which we analysed grain size-dependent D-SARs and D-SIRs using a grain size-dependent hierarchical sampling of species density and species richness in a fragmented, semi-arid agro-ecosystem. Results We found that significantly increasing D-SARs are rare in plant studies. Furthermore, we found that the detection of a significant D-SAR is often possible only after the data have been stratified by species, habitat or landscape characteristics. The results from our case study indicated that the significance and the slopes of both D-SARs and D-SIRs increase as grain size decreases. Main conclusions These results call for a careful consideration of scale while analysing and interpreting the responses of species richness and species density to fragmentation. Our results suggest that grain size-dependent analyses of D-SARs and D-SIRs may help to disentangle the mechanisms that generate SARs and SIRs and may enable early detection of the effects of fragmentation on plant biodiversity. KW - species density KW - isolation KW - scale-dependence KW - habitat fragmentation KW - extinction debt KW - Conservation biogeography KW - species-area relationship KW - island ecology KW - habitat islands KW - island biogeography theory Y1 - 2014 U6 - https://doi.org/10.1111/jbi.12299 SN - 0305-0270 SN - 1365-2699 VL - 41 IS - 6 SP - 1055 EP - 1069 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Giladi, Itamar A1 - Ziv, Yaron A1 - May, Felix A1 - Jeltsch, Florian T1 - Scale-dependent determinants of plant species richness in a semi-arid fragmented agro-ecosystem JF - Journal of vegetation science N2 - Aims: (1) Understanding how the relationship between species richness and its determinants depends on the interaction between scales at which the response and explanatory variables are measured. (2) Quantifying the relative contributions of local, intermediate and large-scale determinants of species richness in a fragmented agro-ecosystem. (3) Testing the hypothesis that the relative contribution of these determinants varies with the grain size at which species richness is measured. Location: A fragmented agro-ecosystem in the Southern Judea Lowland, Israel, within a desert-Mediterranean transition zone. Methods: Plant species richness was estimated using hierarchical nested sampling in 81 plots, positioned in 38 natural vegetation patches within an agricultural matrix (mainly wheat fields) among three land units along a sharp precipitation gradient. Explanatory variables included position along that gradient, patch area, patch isolation, habitat heterogeneity and overall plant density. We used general linear models and hierarchical partitioning of variance to test and quantify the effect of each explanatory variable on species richness at four grain sizes (0.0625, 1, 25 and 225m(2)). Results: Species richness was mainly affected by position along a precipitation gradient and overall plant density, and to a lesser extent by habitat heterogeneity. It was also significantly affected by patch area and patch isolation, but only for small grain sizes. The contribution of each explanatory variable to explained variance in species richness varied with grain size, i.e. scale-dependent. The influence of geographic position and habitat heterogeneity on species richness increased with grain size, while the influence of plant density decreased with grain size. Main conclusions: Species richness is determined by the combined effect of several scale-dependent determinants. Ability to detect an effect and effect size of each determinant varies with the scale (grain size) at which it is measured. The combination of a multi-factorial approach and multi-scale sampling reveals that conclusions drawn from studies that ignore these dimensions are restricted and potentially misleading. KW - Habitat fragmentation KW - Hierarchical partitioning of variance KW - Multi-grain sampling KW - Scale-dependence KW - Species density KW - Uniform sampling Y1 - 2011 U6 - https://doi.org/10.1111/j.1654-1103.2011.01309.x SN - 1100-9233 VL - 22 IS - 6 SP - 983 EP - 996 PB - Wiley-Blackwell CY - Malden ER - TY - JOUR A1 - Schiffers, Katja A1 - Tielboerger, Katja A1 - Tietjen, Britta A1 - Jeltsch, Florian T1 - Root plasticity buffers competition among plants theory meets experimental data JF - Ecology : a publication of the Ecological Society of America N2 - Morphological plasticity is a striking characteristic of plants in natural communities. In the context of foraging behavior particularly, root plasticity has been documented for numerous species. Root plasticity is known to mitigate competitive interactions by reducing the overlap of the individuals' rhizospheres. But despite its obvious effect on resource acquisition, plasticity has been generally neglected in previous empirical and theoretical studies estimating interaction intensity among plants. In this study, we developed a semi-mechanistic model that addresses this shortcoming by introducing the idea of compensatory growth into the classical-zone-of influence (ZOI) and field-of-neighborhood (FON) approaches. The model parameters describing the belowground plastic sphere of influence (PSI) were parameterized using data from an accompanying field experiment. Measurements of the uptake of a stable nutrient analogue at distinct distances to the neighboring plants showed that the study species responded plastically to belowground competition by avoiding overlap of individuals' rhizospheres. An unexpected finding was that the sphere of influence of the study species Bromus hordeaceus could be best described by a unimodal function of distance to the plant's center and not with a continuously decreasing function as commonly assumed. We employed the parameterized model to investigate the interplay between plasticity and two other important factors determining the intensity of competitive interactions: overall plant density and the distribution of individuals in space. The simulation results confirm that the reduction of competition intensity due to morphological plasticity strongly depends on the spatial structure of the competitive environment. We advocate the use of semi-mechanistic simulations that explicitly consider morphological plasticity to improve our mechanistic understanding of plant interactions. KW - Bromus hordeaceus KW - competition intensity KW - morphological plasticity KW - nutrient analogues KW - plant density KW - PSI (plastic sphere of influence) KW - zone-of-influence model Y1 - 2011 SN - 0012-9658 VL - 92 IS - 3 SP - 610 EP - 620 PB - Wiley CY - Washington ER - TY - JOUR A1 - May, Felix A1 - Grimm, Volker A1 - Jeltsch, Florian T1 - Reversed effects of grazing on plant diversity : the role of below-ground competition and size symmetry N2 - Grazing is known as one of the key factors for diversity and community composition in grassland ecosystems, but the response of plant communities towards grazing varies remarkably between sites with different environmental conditions. It is generally accepted that grazing increases plant diversity in productive environments, while it tends to reduce diversity in unproductive habitats (grazing reversal hypothesis). Despite empirical evidence for this pattern the mechanistic link between modes of plant-plant competition and grazing response at the community level still remains poorly understood. Root-competition in particular has rarely been included in theoretical studies, although it has been hypothesized that variations in productivity and grazing regime can alter the relative importance of shoot- and root-competition. We therefore developed an individual-based model based on plant functional traits to investigate the response of a grassland community towards grazing. Models of different complexity, either incorporating only shoot competition or with distinct shoot- and root-competition, were used to study the interactive effects of grazing, resource availability, and the mode of competition (size-symmetric or asymmetric). The pattern predicted by the grazing reversal hypothesis (GRH) can only be explained by our model if shoot- and root-competition are explicitly considered and if size asymmetry of above- and symmetry of below-ground competition is assumed. For this scenario, the model additionally reproduced empirically observed plant trait responses: erect and large plant functional types (PFTs) dominated without grazing, while frequent grazing favoured small PFTs with a rosette growth form. We conclude that interactions between shoot- and root-competition and size symmetry/asymmetry of plant-plant interactions are crucial in order to understand grazing response under different habitat productivities. Our results suggest that future empirical trait surveys in grassland communities should include root traits, which have been largely ignored in previous studies, in order to improve predictions of plants" responses to grazing. Y1 - 2009 UR - http://www3.interscience.wiley.com/journal/118531693/home U6 - https://doi.org/10.1111/j.1600-0706.2009.17724.x SN - 0030-1299 ER - TY - JOUR A1 - Moloney, Kirk A. A1 - Holzapfel, Claus A1 - Tielbörger, Katja A1 - Jeltsch, Florian A1 - Schurr, Frank Martin T1 - Rethinking the common garden in invasion research N2 - In common garden experiments, a number of genotypes are raised in a common environment in order to quantify the genetic component of phenotypic variation. Common gardens are thus ideally suited for disentangling how genetic and environmental factors contribute to the success of invasive species in their new non-native range. Although common garden experiments are increasingly employed in the study of invasive species, there has been little discussion about how these experiments should be designed for greatest utility. We argue that this has delayed progress in developing a general theory of invasion biology. We suggest a minimum optimal design (MOD) for common garden studies that target the ecological and evolutionary processes leading to phenotypic differentiation between native and invasive ranges. This involves four elements: (A) multiple, strategically sited garden locations, involving at the very least four gardens (2 in the native range and 2 in the invaded range); (B) careful consideration of the genetic design of the experiment; (C) standardization of experimental protocols across all gardens; and (D) care to ensure the biosafety of the experiment. Our understanding of the evolutionary ecology of biological invasions will be greatly enhanced by common garden studies, if and only if they are designed in a more systematic fashion, incorporating at the very least the MOD suggested here. Y1 - 2009 UR - http://www.sciencedirect.com/science/journal/14338319 U6 - https://doi.org/10.1016/j.ppees.2009.05.002 SN - 1433-8319 ER -