ABSTRACT The aims of this study were to investigate the impact of biological soil crusts’ (biocru... more ABSTRACT The aims of this study were to investigate the impact of biological soil crusts’ (biocrust) developmental stage on soil physical structures in sand dunes under two different rainfall regimes. It was hypothesized that biocrust’s developmental stage and function, as affected by the aridity level, may impact soil surface properties, pedogenesis and hydrology. Bio-physiological parameters of the biocrust (polysaccharide, protein and chlorophyll contents) were studied for the determination of its developmental stage. The soil physical surface properties that were measured included the surface breaking pressure and granulometry. Hydrological measurements included the infiltration rate and soil moisture regime in deep layers and structure granulometry. These measurements were taken over two years, in scraped top soil surfaces and in homogeneous sandy dunes, and were compared with natural biocrust surfaces. Higher precipitation at the northern site, with a more advanced developmental stage of the natural biocrust compared to the southern site, has affected the structure granulometry by increasing the cohesive fractions of clay and very-fine silt within the soil surface layer. Higher infiltration rates and soil moisture (%) below the biocrust were obtained with the cyanobacterial crust at the dry southern site. Biocrust controls water infiltration into the soil sub-surface by affecting the surface penetrability. The infiltration controlled by the crust was inversed to the rainfall gradient. The novelty of this study is that by characterizing the bio-physiological parameters of biocrusts as affected by aridity levels, it is possible to imitate climate change scenarios on soil moisture in specific sites.
Site-specific weed management can allow more efficient weed control from both an environmental an... more Site-specific weed management can allow more efficient weed control from both an environmental and an economic perspective. Spectral differences between plant species may lead to the ability to separate wheat from weeds. The study used ground-level image spectroscopy data, with high spectral and spatial resolutions, for detecting annual grasses and broadleaf weeds in wheat fields. The image pixels were used to cross-validate partial least squares discriminant analysis classification models. The best model was chosen by comparing the cross-validation confusion matrices in terms of their variances and Cohen's Kappa values. This best model used four classes: broadleaf, grass weeds, soil and wheat and resulted in Kappa of 0.79 and total accuracy of 85 %. Each of the classes contains both sunlit and shaded data. The variable importance in projection method was applied in order to locate the most important spectral regions for each of the classes. It was found that the red-edge is the most important region for the vegetation classes. Ground truth pixels were randomly selected and their confusion matrix resulted in a Kappa of 0.63 and total accuracy of 72 %. The results obtained were reasonable although the model used wheat and weeds from different growth stages, acquisition dates and fields. It was concluded that high spectral and spatial resolutions can provide separation between wheat and weeds based on their spectral data. The results show feasibility for up-scaling the spectral methods to air or spaceborne sensors as well as developing ground-level application.
We use the context of dryland vegetation to study a general problem of complex pattern-forming sy... more We use the context of dryland vegetation to study a general problem of complex pattern-forming systems: multiple pattern-forming instabilities that are driven by distinct mechanisms but share the same spectral properties. We find that the co-occurrence of two Turing instabilities when the driving mechanisms counteract each other in some region of the parameter space results in the growth of a single mode rather than two interacting modes. The interplay between the two mechanisms compensates for the simpler dynamics of a single mode by inducing a wider variety of patterns, which implies higher biodiversity in dryland ecosystems.
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2013
Drylands are pattern-forming systems showing self-organized vegetation patchiness, multiplicity o... more Drylands are pattern-forming systems showing self-organized vegetation patchiness, multiplicity of stable states and fronts separating domains of alternative stable states. Pattern dynamics, induced by droughts or disturbances, can result in desertification shifts from patterned vegetation to bare soil. Pattern-formation theory suggests various scenarios for such dynamics; an abrupt global shift involving a fast collapse to bare soil, a gradual global shift involving the expansion and coalescence of bare-soil domains, and an incipient shift to a hybrid state consisting of stationary bare-soil domains in an otherwise periodic pattern. Using models of dryland vegetation we address the question which of these scenarios can be realized. We found that the models can be split into two groups: models that exhibit multiplicity of periodic-pattern and baresoil states, and models that exhibit, in addition, multiplicity of hybrid states. Furthermore, in all models we could not identify parameter regimes in which bare-soil domains expand into vegetated domains. The significance of these findings is that while models belonging to the first group can only exhibit abrupt shifts, model belonging to the second group can also exhibit gradual and incipient shifts. A discussion of open problems concludes the paper.
Sand dunes are often covered by vegetation and biogenic crusts. Despite their significant role in... more Sand dunes are often covered by vegetation and biogenic crusts. Despite their significant role in dune stabilization, biogenic crusts have rarely been considered in studies of dune dynamics. Using a simple model, we study the existence and stability ranges of different dune-cover states along gradients of rainfall and wind power. Two ranges of alternative stable states are identified: fixed crusted dunes and fixed vegetated dunes at low wind power, and fixed vegetated dunes and active dunes at high wind power. These results suggest a cross-over between two different forms of desertification.
ABSTRACT The aims of this study were to investigate the impact of biological soil crusts’ (biocru... more ABSTRACT The aims of this study were to investigate the impact of biological soil crusts’ (biocrust) developmental stage on soil physical structures in sand dunes under two different rainfall regimes. It was hypothesized that biocrust’s developmental stage and function, as affected by the aridity level, may impact soil surface properties, pedogenesis and hydrology. Bio-physiological parameters of the biocrust (polysaccharide, protein and chlorophyll contents) were studied for the determination of its developmental stage. The soil physical surface properties that were measured included the surface breaking pressure and granulometry. Hydrological measurements included the infiltration rate and soil moisture regime in deep layers and structure granulometry. These measurements were taken over two years, in scraped top soil surfaces and in homogeneous sandy dunes, and were compared with natural biocrust surfaces. Higher precipitation at the northern site, with a more advanced developmental stage of the natural biocrust compared to the southern site, has affected the structure granulometry by increasing the cohesive fractions of clay and very-fine silt within the soil surface layer. Higher infiltration rates and soil moisture (%) below the biocrust were obtained with the cyanobacterial crust at the dry southern site. Biocrust controls water infiltration into the soil sub-surface by affecting the surface penetrability. The infiltration controlled by the crust was inversed to the rainfall gradient. The novelty of this study is that by characterizing the bio-physiological parameters of biocrusts as affected by aridity levels, it is possible to imitate climate change scenarios on soil moisture in specific sites.
Site-specific weed management can allow more efficient weed control from both an environmental an... more Site-specific weed management can allow more efficient weed control from both an environmental and an economic perspective. Spectral differences between plant species may lead to the ability to separate wheat from weeds. The study used ground-level image spectroscopy data, with high spectral and spatial resolutions, for detecting annual grasses and broadleaf weeds in wheat fields. The image pixels were used to cross-validate partial least squares discriminant analysis classification models. The best model was chosen by comparing the cross-validation confusion matrices in terms of their variances and Cohen's Kappa values. This best model used four classes: broadleaf, grass weeds, soil and wheat and resulted in Kappa of 0.79 and total accuracy of 85 %. Each of the classes contains both sunlit and shaded data. The variable importance in projection method was applied in order to locate the most important spectral regions for each of the classes. It was found that the red-edge is the most important region for the vegetation classes. Ground truth pixels were randomly selected and their confusion matrix resulted in a Kappa of 0.63 and total accuracy of 72 %. The results obtained were reasonable although the model used wheat and weeds from different growth stages, acquisition dates and fields. It was concluded that high spectral and spatial resolutions can provide separation between wheat and weeds based on their spectral data. The results show feasibility for up-scaling the spectral methods to air or spaceborne sensors as well as developing ground-level application.
We use the context of dryland vegetation to study a general problem of complex pattern-forming sy... more We use the context of dryland vegetation to study a general problem of complex pattern-forming systems: multiple pattern-forming instabilities that are driven by distinct mechanisms but share the same spectral properties. We find that the co-occurrence of two Turing instabilities when the driving mechanisms counteract each other in some region of the parameter space results in the growth of a single mode rather than two interacting modes. The interplay between the two mechanisms compensates for the simpler dynamics of a single mode by inducing a wider variety of patterns, which implies higher biodiversity in dryland ecosystems.
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2013
Drylands are pattern-forming systems showing self-organized vegetation patchiness, multiplicity o... more Drylands are pattern-forming systems showing self-organized vegetation patchiness, multiplicity of stable states and fronts separating domains of alternative stable states. Pattern dynamics, induced by droughts or disturbances, can result in desertification shifts from patterned vegetation to bare soil. Pattern-formation theory suggests various scenarios for such dynamics; an abrupt global shift involving a fast collapse to bare soil, a gradual global shift involving the expansion and coalescence of bare-soil domains, and an incipient shift to a hybrid state consisting of stationary bare-soil domains in an otherwise periodic pattern. Using models of dryland vegetation we address the question which of these scenarios can be realized. We found that the models can be split into two groups: models that exhibit multiplicity of periodic-pattern and baresoil states, and models that exhibit, in addition, multiplicity of hybrid states. Furthermore, in all models we could not identify parameter regimes in which bare-soil domains expand into vegetated domains. The significance of these findings is that while models belonging to the first group can only exhibit abrupt shifts, model belonging to the second group can also exhibit gradual and incipient shifts. A discussion of open problems concludes the paper.
Sand dunes are often covered by vegetation and biogenic crusts. Despite their significant role in... more Sand dunes are often covered by vegetation and biogenic crusts. Despite their significant role in dune stabilization, biogenic crusts have rarely been considered in studies of dune dynamics. Using a simple model, we study the existence and stability ranges of different dune-cover states along gradients of rainfall and wind power. Two ranges of alternative stable states are identified: fixed crusted dunes and fixed vegetated dunes at low wind power, and fixed vegetated dunes and active dunes at high wind power. These results suggest a cross-over between two different forms of desertification.
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Papers by S. Kinast