TY - GEN A1 - Köchy, Martin T1 - Effects of simulated daily precipitation patterns on annual plant populations depend on life stage and climatic region N2 - Background: To improve the understanding of consequences of climate change for annual plant communities, I used a detailed, grid-based model that simulates the effect of daily rainfall variability on individual plants in five climatic regions on a gradient from 100 to 800 mm mean annual precipitation (MAP). The model explicitly considers moisture storage in the soil. I manipulated daily rainfall variability by changing the daily mean rain (DMR, rain volume on rainy days averaged across years for each day of the year) by ± 20%. At the same time I adjusted intervals appropriately between rainy days for keeping the mean annual volume constant. In factorial combination with changing DMR I also changed MAP by ± 20%. Results: Increasing MAP generally increased water availability, establishment, and peak shoot biomass. Increasing DMR increased the time that water was continuously available to plants in the upper 15 to 30 cm of the soil (longest wet period, LWP). The effect of DMR diminished with increasing humidity of the climate. An interaction between water availability and density-dependent germination increased the establishment of seedlings in the arid region, but in the more humid regions the establishment of seedlings decreased with increasing DMR. As plants matured, competition among individuals and their productivity increased, but the size of these effects decreased with the humidity of the regions. Therefore, peak shoot biomass generally increased with increasing DMR but the effect size diminished from the semiarid to the mesic Mediterranean region. Increasing DMR reduced via LWP the annual variability of biomass in the semiarid and dry Mediterranean regions. Conclusion: More rainstorms (greater DMR) increased the recharge of soil water reservoirs in more arid sites with consequences for germination, establishment, productivity, and population persistence. The order of magnitudes of DMR and MAP overlapped partially so that their combined effect is important for projections of climate change effects on annual vegetation. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 097 Y1 - 2008 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-33747 ER - TY - GEN A1 - Köchy, Martin A1 - Mathaj, Martin A1 - Jeltsch, Florian A1 - Malkinson, Dan T1 - Resilience of stocking capacity to changing climate in arid to Mediterranean landscapes N2 - Small livestock is an important resource for rural human populations in dry climates. How strongly will climate change affect the capacity of the rangeland? We used hierarchical modelling to scale quantitatively the growth of shrubs and annual plants, the main food of sheep and goats, to the landscape extent in the eastern Mediterranean region. Without grazing, productivity increased in a sigmoid way with mean annual precipitation. Grazing reduced productivity more strongly the drier the landscape. At a point just under the stocking capacity of the vegetation, productivity declined precipitously with more intense grazing due to a lack of seed production of annuals. We repeated simulations with precipitation patterns projected by two contrasting IPCC scenarios. Compared to results based on historic patterns, productivity and stocking capacity did not differ in most cases. Thus, grazing intensity remains the stronger impact on landscape productivity in this dry region even in the future. N2 - Kleinvieh ist eine wichtige Lebensgrundlage für die Landbevölkerung in trockenen Regionen. Wie stark wird sich der Klimawandel auf die Tragfähigkeit der Weideflächen auswirken? Wir benutzten hierarchische Modellierung, um das Wachstum von Sträuchern und einjährigen Kräutern, das wichtigste Futter für Ziegen und Schafe, quantitativ auf die Fläche von Landschaften in der östlichen Mittelmeerregion zu dimensionieren. Die Produktivität ohne Beweidung stieg sigmoidal mit dem mittleren Jahresniederschlag. Je trockener die Landschaft, desto stärker verminderte Beweidung die Produktion. An einem Punkt knapp unter der Tragfähigkeit der Vegetation, sank die Produktion stark mit zunehmender Beweidung, weil die Samenproduktion der Kräuter zu gering war. Wir wiederholten die Simulationen mit Niederschlagsverteilungsmustern gemäß zweier gegensätzlicher IPCC-Szenarien. Zukünftige Produktivität und Tragfähigkeit unterschieden sich in den meisten Fällen nicht von Ergebnissen auf Grund von historischer Niederschlagsverteilung. Allerdings war die zukünftige Produktivität in trockenen Habitaten der semiariden und trocken-mediterranen Regionen niedriger. Somit hat auch in Zukunft die Besatzdichte die größere Auswirkung auf die Produktivität dieser trockenen Landschaft als das Klima. "This abstract is provided by the authors, and is for convenience of the users only. The author certifies that the translation faithfully represents the official version in the language of the journal, which is the published Abstract of record and is the only Abstract to be used for reference and citation." T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 066 KW - topography KW - spatially explicit model KW - climate change KW - Middle East KW - stocking capacity Y1 - 2008 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18720 ER - TY - GEN A1 - Köchy, Martin A1 - Bråkenhielm, Sven T1 - Separation of effects of moderate N deposition from natural change in ground vegetation of forests and bogs N2 - The effect of moderate rates of nitrogen deposition on ground floor vegetation is poorly predicted by uncontrolled surveys or fertilization experiments using high rates of nitrogen (N) addition. We compared the temporal trends of ground floor vegetation in permanent plots with moderate (7–13 kg ha−1 year−1) and lower bulk N deposition (4–6 kg ha−1 year−1) in southern Sweden during 1982–1998. We examined whether trends differed between growth forms (vascular plants and bryophytes) and vegetation types (three types of coniferous forest, deciduous forest, and bog). Trends of site-standardized cover and richness varied among growth forms, vegetation types, and deposition regions. Cover in spruce forests decreased at the same rate with both moderate and low deposition. In pine forests cover decreased faster with moderate deposition and in bogs cover decreased faster with low deposition. Cover of bryophytes in spruce forests increased at the same rate with both moderate and low deposition. In pine forests cover decreased faster with moderate deposition and in bogs and deciduous forests there was a strong non-linear increase with moderate deposition. The trend of number of vascular plants was constant with moderate and decreased with low deposition. We found no trend in the number of bryophyte species. We propose that the decrease of cover and number with low deposition was related to normal ecosystem development (increased shading), suggesting that N deposition maintained or increased the competitiveness of some species in the moderate-deposition region. Deposition had no consistent negative effect on vegetation suggesting that it is less important than normal successional processes. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 034 KW - Nitrogen deposition KW - Vascular plants KW - Bryophytes KW - Species richness KW - Succession KW - Understorey Y1 - 2008 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-16621 ER - TY - GEN A1 - Köchy, Martin T1 - Opposite trends in life stages of annual plants caused by daily rainfall variability BT - interaction with climate change N2 - Global Circulation Models of climate predict not only a change of annual precipitation amounts but also a shift in the daily distribution. To improve the understanding of the importance of daily rain pattern for annual plant communities, which represent a large portion of semi-natural vegetation in the Middle East, I used a detailed, spatially explicit model. The model explicitly considers water storage in the soil and has been parameterized and validated with data collected in field experiments in Israel and data from the literature. I manipulated daily rainfall variability by increasing the mean daily rain intensity on rainy days (MDI, rain volume/day) and decreasing intervals between rainy days while keeping the mean annual amount constant. In factorial combination, I also increased mean annual precipitation (MAP). I considered five climatic regions characterized by 100, 300, 450, 600, and 800 mm MAP. Increasing MDI decreased establishment when MAP was >250 mm but increased establishment at more arid sites. The negative effect of increasing MDI was compensated by increasing mortality with increasing MDI in dry and typical Mediterranean regions (c. 360–720 mm MAP). These effects were strongly tied to water availability in upper and lower soil layers and modified by competition among seedlings and adults. Increasing MAP generally increased water availability, establishment, and density. The order of magnitudes of MDI and MAP effects overlapped partially so that their combined effect is important for projections of climate change effects on annual vegetation. The effect size of MAP and MDI followed a sigmoid curve along the MAP gradient indicating that the semi-arid region (≈300 mm MAP) is the most sensitive to precipitation change with regard to annual communitie KW - Klimaänderung KW - Klimawandel KW - Einjahrespflanzen KW - Schwankung KW - tägliche Regenmenge KW - Israel KW - climate change KW - daily rainfall variability KW - annual plant KW - Israel Y1 - 2006 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-14699 SP - 347 EP - 357 ER - TY - GEN A1 - Köchy, Martin T1 - Stochastic time series of daily precipitation for the interior of Israel N2 - This contribution describes a generator of stochastic time series of daily precipitation for the interior of Israel from c. 90 to 900 mm mean annual precipitation (MAP) as a tool for studies of daily rain variability. The probability of rainfall on a given day of the year is described by a regular Gaussian peak curve function. The amount of rain is drawn randomly from an exponential distribution whose mean is the daily mean rain amount (averaged across years for each day of the year) described by a flattened Gaussian peak curve. Parameters for the curves have been calculated from monthly aggregated, long-term rain records from seven meteorological stations. Parameters for arbitrary points on the MAP gradient are calculated from a regression equation with MAP as the only independent variable. The simple structure of the generator allows it to produce time series with daily rain patterns that are projected under climate change scenarios and simultaneously control MAP. Increasing within-year variability of daily precipitation amounts also increases among-year variability of MAP as predicted by global circulation models. Thus, the time series incorporate important characteristics for climate change research and represent a flexible tool for simulations of daily vegetation or surface hydrology dynamics. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 029 KW - stochastische Zeitreihen KW - täglicher Niederschlag KW - Israel KW - Klimawandel KW - stochastic time series KW - daily precipitation KW - Israel KW - climate change Y1 - 2006 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-13155 ER - TY - GEN A1 - Köchy, Martin A1 - Tielbörger, Katja T1 - Hydrothermal time model of germination : parameters for 36 Mediterranean annual species based on a simplified approach N2 - Germination rates and germination fractions of seeds can be predicted well by the hydrothermal time (HTT) model. Its four parameters hydrothermal time, minimum soil temperature, minimum soil moisture, and variation of minimum soil moisture, however, must be determined by lengthy germination experiments at combinations of several levels of soil temperature and moisture. For some applications of the HTT model it is more important to have approximate estimates for many species rather than exact values for only a few species. We suggest that minimum temperature and variation of minimum moisture can be estimated from literature data and expert knowledge. This allows to derive hydrothermal time and minimum moisture from existing data from germination experiments with one level of temperature and moisture. We applied our approach to a germination experiment comparing germination fractions of wild annual species along an aridity gradient in Israel. Using this simplified approach we estimated hydrothermal time and minimum moisture of 36 species. Comparison with exact data for three species shows that our method is a simple but effective method for obtaining parameters for the HTT model. Hydrothermal time and minimum moisture supposedly indicate climate related germination strategies. We tested whether these two parameters varied with the climate at the site where the seeds had been collected. We found no consistent variation with climate across species, suggesting that variation is more strongly controlled by site-specific factors. N2 - Keimungsgeschwindigkeit und Anteil gekeimter Samen lassen sich gut mit dem Hydrothermalzeit-Modell bestimmen. Dessen vier Parameter Hydrothermalzeit, Mindesttemperatur, Mindestbodenfeuchte und Streuung der Mindestbodenfeuchte müssen jedoch durch aufwendige Keimungsversuche bei Kombinationen von mehreren Temperatur- und Feuchtigkeitsstufen bestimmt werden. Für manche Anwendungen des Hydrothermalzeit-Modells sind aber ungefähre Werte für viele Arten wichtiger als genaue Werte für wenige Arten. Wenn die Mindesttemperatur und die Streuung der Mindestfeuchte aus Veröffentlichungen und Expertenwissen geschätzt würde, können die Hydrothermalzeit und Mindestbodenfeuchte aus vorhandenen Daten von Keimungsversuchen mit nur einer Temperatur- und Feuchtigkeitsstufe berechnet werden. Wir haben unseren Ansatz auf einen Keimungsversuch zum Vergleich der Keimungsquote wilder einjähriger Arten entlang eines Trockenheitsgradienten in Israel angewendet. Mit diesem Ansatz bestimmten wir die Hydrothermalzeit und Mindestfeuchtigkeit von 36 Arten. Der Vergleich mit genauen Werten für drei Arten zeigt, dass mit unserem Ansatz Hydrothermalzeit-Parameter einfach und effektiv bestimmt werden können. Hydrothermalzeit und Mindestfeuchtigkeit sollten auch bestimmte klimabedingte Keimungsstrategien anzeigen. Deshalb testeten wir, ob diese zwei Parameter mit dem Klima am Ursprungsort der Samen zusammenhängen. Wir fanden jedoch keinen für alle Arten übereinstimmenden Zusammenhang, so dass die Unterschiede vermutlich stärker durch standörtliche als durch klimatische Ursachen hervorgerufen werden. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - paper 022 KW - Keimungsrate KW - Dormanz KW - Hydrothermalzeit-Modell KW - einjährige Pflanzen KW - Mittelmeerraum KW - germination rate KW - dormancy KW - hydrothermal time model KW - annual plant species KW - Mediterranean Y1 - 2006 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-12406 ER - TY - GEN A1 - Köchy, Martin T1 - Photodegradation of grass litter in semi-arid grasslands : a global perspective N2 - In a recent contribution in Nature (vol. 442, pp. 555-558) Austin & Vivanco showed that sunlight is the dominant factor for decomposition of grass litter in a semi-arid grassland in Argentine. The quantification of this effect was portrayed as a novel finding. I put this result in the context of three other publications from as early as 1980 that quantified photodegradation. My synopsis shows that photodegradation is an important process in semi-arid grasslands in South America, North America and eastern Europe. KW - Laubstreu KW - semi-arides Grasland KW - abiotische Zersetzung KW - UV-Licht KW - Schatten KW - leaf litter KW - semi-arid grassland KW - abiotic decomposition KW - UV radiation KW - shade Y1 - 2006 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-12006 ER - TY - GEN A1 - Köchy, Martin A1 - Wilson, Scott D. T1 - Variation in nitrogen deposition and available soil nitrogen in a forest–grassland ecotone in Canada N2 - Regional variation in nitrogen (N) deposition increases plant productivity and decreases species diversity, but landscape- or local-scale influences on N deposition are less well-known. Using ion-exchange resin, we measured variation of N deposition and soil N availability within Elk Island National Park in the ecotone between grassland and boreal forest in western Canada. The park receives regionally high amounts of atmospheric N deposition (22 kg ha⁻¹ yr⁻¹). N deposition was on average higher ton clayrich luvisols than on brunisols, and areas burned 1 – 15 years previously received more atmospheric N than unburned sites. We suggest that the effects of previous fires and soil type on deposition rate act through differences in canopy structure. The magnitude of these effects varied with the presence of ungulate grazers (bison, moose, elk) and vegetation type (forest, shrubland, grassland). Available soil N (ammonium and nitrate) was higher in burned than unburned sites in the absence of grazing, suggesting an effect of deposition. On grazed sites, differences between fire treatments were small, presumably because the removal of biomass by grazers reduced the effect of fire. Aspen invades native grassland in this region, and our results suggest that fire without grazing might reinforce the expansion of forest into grassland facilitated by N deposition. KW - fire KW - grazing KW - vegetation type KW - soil type KW - shrubland KW - forest invasion KW - subboreal KW - aspen parkland KW - Canada Y1 - 2004 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-5768 ER -