TY - JOUR A1 - Lohmann, Dirk A1 - Guo, Tong A1 - Tietjen, Britta T1 - Zooming in on coarse plant functional types-simulated response of savanna vegetation composition in response to aridity and grazing JF - Theoretical ecology N2 - Precipitation and land use in terms of livestock grazing have been identified as two of the most important drivers structuring the vegetation composition of semi-arid and arid savannas. Savanna research on the impact of these drivers has widely applied the so-called plant functional type (PFT) approach, grouping the vegetation into two or three broad types (here called meta-PFTs): woody plants and grasses, which are sometimes divided into perennial and annual grasses. However, little is known about the response of functional traits within these coarse types towards water availability or livestock grazing. In this study, we extended an existing eco-hydrological savanna vegetation model to capture trait diversity within the three broad meta-PFTs to assess the effects of both grazing and mean annual precipitation (MAP) on trait composition along a gradient of both drivers. Our results show a complex pattern of trait responses to grazing and aridity. The response differs for the three meta-PFTs. From our findings, we derive that trait responses to grazing and aridity for perennial grasses are similar, as suggested by the convergence model for grazing and aridity. However, we also see that this only holds for simulations below a MAP of 500 mm. This combined with the finding that trait response differs between the three meta-PFTs leads to the conclusion that there is no single, universal trait or set of traits determining the response to grazing and aridity. We finally discuss how simulation models including trait variability within meta-PFTs are necessary to understand ecosystem responses to environmental drivers, both locally and globally and how this perspective will help to extend conceptual frameworks of other ecosystems to savanna research. KW - Traits KW - Dryland KW - Degradation KW - Shrub encroachment KW - Simulation KW - Eco-hydrological model KW - EcoHyD Y1 - 2018 U6 - https://doi.org/10.1007/s12080-017-0356-x SN - 1874-1738 SN - 1874-1746 VL - 11 IS - 2 SP - 161 EP - 173 PB - Springer CY - Heidelberg ER - TY - JOUR A1 - Gärtner, Mirijam A1 - Nottebrock, Henning A1 - Fourie, Helanya A1 - Privett, Sean D. J. A1 - Richardson, David M. T1 - Plant invasions, restoration, and economics perspectives from South African fynbos JF - Perspectives in plant ecology, evolution and systematics N2 - Restoration is gaining importance in the management of plant invasions. As the success of restoration projects is frequently determined by factors other than ecological ones, we explored the ecological and financial feasibility of active restoration on three different invaded sites in South Africa's Cape Floristic Region. The aim of our study was to identify cost-effective ways of restoring functional native ecosystems following invasion by alien plants. Over three years we evaluated different restoration approaches using field trials and experimental manipulations (i.e. mechanical clearing, burning, different soil restoration techniques and sowing of native species) to reduce elevated soil nutrient levels and to re-establish native fynbos communities. Furthermore we investigated the possibility of introducing native fynbos species that can be used for sustainable harvesting to create an incentive for restoration on private land. Diversity and evenness of native plant species increased significantly after restoration at all three sites, whereas cover of alien plants decreased significantly, confirming that active restoration was successful. However, sowing of native fynbos species had no significant effect on native cover, species richness, diversity or evenness in the Acacia thicket and Kikuyu field, implying that the ecosystem was sufficiently resilient to allow autogenic recovery following clearing and burning of the invasive species. Soil restoration treatments resulted in an increase of available nitrogen in the Acacia thicket, but had no significant effects in the Eucalyptus plantation. However, despite elevated available soil nitrogen levels, native species germinated irrespective whether sown or unsown (i.e. regeneration from the soil seed bank). Without active introduction of native species, native grasses, forbs and other shrubs would have dominated, and proteoids and ericoids (the major fynbos growth forms) would have been under-represented. The financial analysis shows that income from flower harvesting following active restoration consistently outweighs income following passive restoration, but that the associated increase in income does not always justify the higher costs. We conclude that active restoration can be effective and financially feasible when compared to passive restoration, depending on the density of invasion. Active restoration of densely invaded sites may therefore only be justifiable if the target area is in a region of high conservation priority. KW - Biological invasions KW - Cost-benefit analysis KW - Degradation KW - Exotic species KW - Flower harvesting KW - Rehabilitation Y1 - 2012 U6 - https://doi.org/10.1016/j.ppees.2012.05.001 SN - 1433-8319 VL - 14 IS - 5 SP - 341 EP - 353 PB - Elsevier CY - Jena ER - TY - JOUR A1 - Mazurek-Budzyńska, Magdalena A1 - Behl, Marc A1 - Razzaq, Muhammad Yasar A1 - Nöchel, Ulrich A1 - Rokicki, Gabriel A1 - Lendlein, Andreas T1 - Hydrolytic stability of aliphatic poly(carbonate-urea-urethane)s: Influence of hydrocarbon chain length in soft segment JF - Polymer Degradation and Stability N2 - Poly(carbonate-urethane)s (PCUs) exhibit improved resistance to hydrolytic degradation and in vivo stress cracking compared to poly(ester-urethane)s and their degradation leads to lower inflammation of the surrounding tissues. Therefore, PCUs are promising implant materials and are considered for devices such as artificial heart or spine implants. In this work, the hydrolytic stability of different poly(carbonate-urethane-urea)s (PCUUs) was studied under variation of the length of hydrocarbon chain (6, 9, 10, and 12 methylene units) between the carbonate linkages in the precursors. PCUUs were synthesized from isophorone diisocyanate and oligo(alkylene carbonate) diols using the moisture-cure method. The changes of sample weight, thermal and mechanical properties, morphology, as well as the degradation products after immersion in a buffer solution (PBS, pH = 7.4) for up to 10 weeks at 37 degrees C were monitored and analyzed. In addition, mechanical properties after 20 weeks (in PBS, 37 degrees C) were investigated. The gel content was determined based on swelling experiments in chloroform. Based on the DSC analysis, slight increases of melting transitions of PCUUs were observed, which were attributed to structure reorganization related to annealing at 37 degrees C rather than to the degradation of the PCUU. Tensile strength after 20 weeks of all investigated samples remained in the range of 29-39 MPa, whereas the elongation at break e(m) decreased only slightly and remained in the range between 670 and 800%. Based on the characterization of degradation products after up to 10 weeks of immersion it was assessed that oligomers are mainly consisting of hard segments containing urea linkages, which could be assigned to hindered-urea dissociation mechanism. The investigations confirmed good resistance of PCUUs to hydrolysis. Only minor changes in the crystallinity, as well as thermal and mechanical properties were observed and depended on hydrocarbon chain length in soft segment of PCUUs. (C) 2019 Published by Elsevier Ltd. KW - Poly(carbonate-urea-urethane)s KW - Hydrolytic stability KW - Degradation Y1 - 2019 SN - 0141-3910 SN - 1873-2321 VL - 161 SP - 283 EP - 297 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Schulz, Katharina A1 - Voigt, Karsten A1 - Beusch, Christine A1 - Almeida-Cortez, Jarcilene S. A1 - Kowarik, Ingo A1 - Walz, Ariane A1 - Cierjacks, Arne T1 - Grazing deteriorates the soil carbon stocks of Caatinga forest ecosystems in Brazil JF - Forest ecology and management N2 - Grazing by domestic ungulates can have substantial impacts on forests in arid and semi-arid regions, possibly including severe loss of carbon from the soil. Predicting net livestock impacts on soil organic carbon stocks remains challenging, however, due to the dependence on animal loads and on soil and environmental parameters. The objective of this study was to better understand grazing effects on soil organic carbon in seasonal tropical dry forests of north-eastern Brazil (Caatinga) by quantifying carbon stocks of the upper soil profile (0–5 cm depth) and greater soil depths (>5 cm depth down to bedrock) along a gradient of grazing intensity while accounting for other influencing factors such as soil texture, vegetation, landscape topography, and water availability. We analysed soil organic carbon, soil clay content, altitude above sea level, soil depth to bedrock, distance to the nearest permanent water body, species diversity of perennial plants and aboveground biomass on 45 study plots located in the vicinity of the Itaparica Reservoir, Pernambuco, Brazil. Livestock (mainly goats and cattle) are unevenly distributed in the studied ecosystem, thus grazing intensity was accounted for based on the weight of livestock droppings per square metre and classified as no or light, intermediate, or heavy grazing. The mean soil organic carbon in the area was 16.86 ± 1.28 Mg ha−1 C with approximately one-quarter found in the upper 5 cm of the soil profile (4.14 ± 0.43 Mg ha−1 C) and the remainder (12.57 ± 0.97 Mg ha−1 C) in greater soil depths (>5 cm). Heavy grazing led to significantly lower soil organic carbon stocks in the upper 5 cm, whereas no effect on soil organic carbon of the soil overall or in greater soil depths was detectable. The soil’s clay content and the altitude proved to be the most relevant factors influencing overall soil organic carbon stocks and those in greater soil depths (>5 cm). Our findings suggest that grazing causes substantial release of carbon from Brazilian dry forest soils, which should be addressed through improved grazing management via a legally compulsory rotation system. This would ultimately contribute to the conservation of a unique forest system and associated ecosystem services. KW - Carbon cycle KW - Degradation KW - Desertification KW - Livestock KW - Semi-arid KW - Soil Y1 - 2016 U6 - https://doi.org/10.1016/j.foreco.2016.02.011 SN - 0378-1127 SN - 1872-7042 VL - 367 SP - 62 EP - 70 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Machatschek, Rainhard Gabriel A1 - Lendlein, Andreas T1 - Fundamental insights in PLGA degradation from thin film studies JF - Journal of controlled release : official journal of the Controlled Release Society and of the Japanese Society of Drug Delivery Systems N2 - Poly(lactide-co-glycolide)s are commercially available degradable implant materials, which are typically selected based on specifications given by the manufacturer, one of which is their molecular weight. Here, we address the question whether variations in the chain length and their distribution affect the degradation behavior of Poly[(rac-lactide)-co-glycolide]s (PDLLGA). The hydrolysis was studied in ultrathin films at the air-water interface in order to rule out any morphological effects. We found that both for purely hydrolytic degradation as well as under enzymatic catalysis, the molecular weight has very little effect on the overall degradation kinetics of PDLLGAs. The quantitative analysis suggested a random scission mechanism. The monolayer experiments showed that an acidic micro-pH does not accelerate the degradation of PDLLGAs, in contrast to alkaline conditions. The degradation experiments were combined with interfacial rheology measurements, which showed a drastic decrease of the viscosity at little mass loss. The extrapolated molecular weight behaved similar to the viscosity, dropping to a value near to the solubility limit of PDLLGA oligomers before mass loss set in. This observation suggests a solubility controlled degradation of PDLLGA. Conclusively, the molecular weight affects the degradation of PDLLGA devices mostly in indirect ways, e.g. by determining their morphology and porosity during fabrication. Our study demonstrates the relevance of the presented Langmuir degradation method for the design of controlled release systems. KW - PDLLGA KW - Degradation KW - Langmuir monolayer Y1 - 2019 U6 - https://doi.org/10.1016/j.jconrel.2019.12.044 SN - 0168-3659 SN - 1873-4995 VL - 319 SP - 276 EP - 284 PB - Elsevier CY - New York ER - TY - JOUR A1 - Piluso, Susanna A1 - Lendlein, Andreas A1 - Neffe, Axel T. T1 - Enzymatic action as switch of bulk to surface degradation of clicked gelatin-based networks JF - Polymers for advanced technologies N2 - Polymer degradation occurs under physiological conditions in vitro and in vivo, especially when bonds susceptible to hydrolysis are present in the polymer. Understanding of the degradation mechanism, changes of material properties over time, and overall rate of degradation is a necessary prerequisite for the knowledge-based design of polymers with applications in biomedicine. Here, hydrolytic degradation studies of gelatin-based networks synthesized by copper-catalyzed azide-alkyne cycloaddition reaction are reported, which were performed with or without addition of an enzyme. In all cases, networks with a stilbene as crosslinker proofed to be more resistant to degradation than when an octyl diazide was used. Without addition of an enzyme, the rate of degradation was ruled by the crosslinking density of the network and proceeded via a bulk degradation mechanism. Addition of Clostridium histolyticum collagenase resulted in a much enhanced rate of degradation, which furthermore occurred via surface erosion. The mesh size of the hydrogels (>7nm) was in all cases larger than the hydrodynamic radius of the enzyme (4.5nm) so that even in very hydrophilic networks with large mesh size enzymes may be used to induce a fast surface degradation mechanism. This observation is of general interest when designing hydrogels to be applied in the presence of enzymes, as the degradation mechanism and material performance are closely interlinked. Copyright (c) 2016 John Wiley & Sons, Ltd. KW - Hydrogel KW - Biopolymer KW - Degradation Y1 - 2017 U6 - https://doi.org/10.1002/pat.3962 SN - 1042-7147 SN - 1099-1581 VL - 28 SP - 1318 EP - 1324 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Wasiolka, Bernd A1 - Blaum, Niels T1 - Comparing biodiversity between protected savanna and adjacent non-protected farmland in the southern Kalahari JF - Journal of arid environments N2 - In this study we investigated the effect of different land use options (wildlife versus livestock) on species richness of plants and reptiles in the protected Kgalagadi Transfrontier Park (KTP) versus adjacent non-protected farmland within the same savanna habitat type (Aoub dune veld) in the southern Kalahari, South Africa. Our results show that both plant and reptile species richness as well as plant cover and reptile abundance was significantly higher in the protected KTP than in the non-protected farmland. The higher proportion of shrub but lower proportions of perennial grass cover, herb cover, and herb species richness in the farmland can be explained by higher stocking rates and the differences in feeding behaviour between native wild ungulates (e.g. Antidorcas marsupialis, Oryx gazella) and livestock (mainly sheep). The reptile's prey availability and microhabitats (perennial grass tussocks and rodent burrows) for thermoregulation and protection against predators were significantly lower in the farmland. To conclude, our results clearly show that long term effects of different land use options (wildlife in protected KTP versus extensive livestock production in the non-protected farmland) even within the same habitat type have led to significant changes in vegetation composition, availability of microhabitat structures and in the reptile community. KW - Kgalagadi Transfrontier Park KW - Rangeland KW - Degradation KW - Species richness KW - Conservation KW - Reptile Y1 - 2011 U6 - https://doi.org/10.1016/j.jaridenv.2011.04.011 SN - 0140-1963 VL - 75 IS - 9 SP - 836 EP - 841 PB - Elsevier CY - London ER -