TY - JOUR A1 - Peltzer, Duane A1 - Köchy, Martin T1 - Competitive effects of grasses and woody plants in mixed-grass prairie N2 - Variation in the competitive ability of plant species is suggested to determine their persistence and abundance in communities. In this study, we examine competition between grasses and woody plants, a phenomenon that occurs word-wide in savannas and along the margins between grasslands and forests. Specifically, we quantified the per- gram competitive effects of grasses and woody plants in native mixed-grass prairie by manipulating the natural vegetation. We separated the competitive effects of grasses, shrubs, and intact vegetation using selective herbicides to create four competition treatments: no neighbours (NN), no shrubs (NS), no grasses (NG), and all neighbours (AN). Competition treatments were applied to 2m x 2m experimental plots located in either prairie- or shrub- dominated habitats. Herbicides were applied starting one year prior to the study to create the four competition treatments. The effects of grasses and shrubs on resource availability (light, water, nitrogen) and the growth of two transplant species, Bouteloua gracilis, a perennial tussock grass, and Elaeagnus commutata, a common shrub, were measured over two growing seasons. Resource availability (i.e. light, soil moisture, soil available nitrogen) was two- to tenfold higher in no neighbour (NN) plots than in vegetated plots (NS, NG, AN). Both grasses and shrubs reduced resource levels to about the same extent. Light penetration declined linearly with increasing grass or shrub biomass, to a minimum of about 30% incident light at 500 g/m² neighbour shoot mass. Soil resources (i.e. water, nitrogen) did not decline with increasing neighbour shoot or root mass for either grasses or shrubs. Thus, for soil resources, the presence of neighbours was more important than their mass (i.e. abundance). Transplant growth did not decline with increasing neighbour biomass; the only exception to this pattern was a linear decline in Bouteloua growth with increasing neighbour shoot mass in plots containing only shrubs (NG). Competition was equally intense in prairie-dominated and shrub-dominated habitats for transplants of Bouteloua, but was less intense in shrub-dominated habitats for the shrub Elaeagnus. These results raise the interesting possibility that variation in the persistence and abundance of plants in communities is more strongly controlled by variation in competitive effects than by differences in competitive response ability. Y1 - 2001 ER - TY - JOUR 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. Y1 - 2008 UR - http://www.biomedcentral.com/1472-6785/8/4 ER - TY - JOUR A1 - Leifso, A. A1 - MacDougall, A. S. A1 - Husband, B. A1 - Hierro, J. L. A1 - Köchy, Martin A1 - Pärtel, M. A1 - Peltzer, D. A. T1 - Expansion of a globally pervasive grass occurs without substantial trait differences between home and away populations JF - Oecologia N2 - The global expansion of species beyond their ancestral ranges can derive from mechanisms that are trait-based (e.g., post-establishment evolved differences compared to home populations) or circumstantial (e.g., propagule pressure, with no trait-based differences). These mechanisms can be difficult to distinguish following establishment, but each makes unique predictions regarding trait similarity between ancestral ('home') and introduced ('away') populations. Here, we tested for trait-based population differences across four continents for the globally distributed grass Dactylis glomerata, to assess the possible role of trait evolution in its worldwide expansion. We used a common-environment glasshouse experiment to quantify trait differences among home and away populations, and the potential relevance of these differences for competitive interactions. Few significant trait differences were found among continents, suggesting minimal change during global expansion. All populations were polyploids, with similar foliar carbon:nitrogen ratios (a proxy for defense), chlorophyll content, and biomass. Emergence time and growth rate favored home populations, resulting in their competitive superiority over away populations. Small but significant trait differences among away populations suggest different introductory histories or local adaptive responses following establishment. In summary, the worldwide distribution of this species appears to have arisen from its pre-adapted traits promoting growth, and its repeated introduction with cultivation and intense propagule pressure. Global expansion can thus occur without substantial shifts in growth, reproduction, or defense. Rather than focusing strictly on the invader, invasion success may also derive from the traits found (or lacking) in the recipient community and from environmental context including human disturbance. KW - Invasion ecology KW - Common-environment trial KW - Competition KW - Plant functional traits KW - Orchard grass Y1 - 2012 U6 - https://doi.org/10.1007/s00442-012-2370-4 SN - 0029-8549 VL - 170 IS - 4 SP - 1123 EP - 1132 PB - Springer CY - New York ER - TY - JOUR 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.Abstract auch auf deutsch vorhanden: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. Y1 - 2007 UR - http://www.sciencedirect.com/science/journal/14391791 U6 - https://doi.org/10.1016/j.baae.2006.04.002 SN - 1439-1791 ER - TY - JOUR A1 - Schaldach, Rüdiger A1 - Wimmer, Florian A1 - Koch, Jennifer A1 - Volland, Jan A1 - Geissler, Katja A1 - Köchy, Martin T1 - Model-based analysis of the environmental impacts of grazing management on Eastern Mediterranean ecosystems in Jordan JF - Journal of environmental management N2 - Eastern Mediterranean ecosystems are prone to desertification when under grazing pressure. Therefore, management of grazing intensity plays a crucial role to avoid or to diminish land degradation and to sustain both livelihoods and ecosystem functioning. The dynamic land-use model LandSHIFT was applied to a case study on the country level for Jordan. The impacts of different stocking densities on the environment were assessed through a set of simulation experiments for various combinations of climate input and assumptions about the development of livestock numbers. Indicators used for the analysis include a set of landscape metrics to account for habitat fragmentation and the "Human Appropriation of Net Primary Production" (HANPP), i.e., the difference between the amount of net primary production (NPP) that would be available in a natural ecosystem and the amount of NPP that remains under human management. Additionally, the potential of the economic valuation of ecosystem services, including landscape and grazing services, as an analysis concept was explored. We found that lower management intensities had a positive effect on HANPP but at the same time resulted in a strong increase of grazing area. This effect was even more pronounced under climate change due to a predominantly negative effect on the biomass productivity of grazing land. Also Landscape metrics tend to indicate decreasing habitat fragmentation as a consequence of lower grazing pressure. The valuation of ecosystem services revealed that low grazing intensity can lead to a comparatively higher economic value on the country level average. The results from our study underline the importance of considering grazing management as an important factor to manage dry-land ecosystems in a sustainable manner. KW - Sustainable management of Mediterranean grazing land KW - Land-use modeling KW - Climate change KW - Landscape metrics KW - Ecosystem service value KW - Human Appropriation of Net Primary Production (HANPP) Y1 - 2013 U6 - https://doi.org/10.1016/j.jenvman.2012.11.024 SN - 0301-4797 SN - 1095-8630 VL - 127 IS - 9 SP - S84 EP - S95 PB - Elsevier CY - London ER - TY - JOUR A1 - Köchy, Martin A1 - Wilson, Scott D. T1 - Nitrogen deposition and forest expansion in the northern Great Plains N2 - 1 Atmospheric nitrogen (N) deposition has become one of the most important agents of vegetation change in densely populated regions, It may also contribute to forest expansion into grasslands at the northern edge of the North American Great Plains. 2 We measured N deposition and available soil N with ion-exchange resin over 2 years in six national parks in areas varying in population density and industrialization. N deposition was significantly higher in four parks in densely populated regions than in two remote parks. 3 Available soil N increased significantly with N deposition across all parks. 4 We measured N mass and N-15 abundance (delta N-15) in vegetation and soil in two parks: Elk Island, receiving 22 kg N ha(-1) year(-1), and Jasper, receiving 8 kg N ha(-1) year(-1). Differences between parks in tissue N concentrations were small, but forest expansion over five decades resulted in the mass of N in vegetation increasing by 74% in Elk Island but by only 26% in Jasper. delta N-15 in forest vegetation was significantly lower in Elk Island than in Jasper, suggesting that anthropogenic sources contribute significantly to the high rates of N entering that ecosystem. 5 We determined the rate of forest expansion within parks using six decades of aerial photographs, Parks in aspen parkland and boreal forest showed a strong positive relationship between forest expansion and N deposition. The relationships found between N deposition, available soil N and forest expansion suggest that even comparatively low rates of N deposition may accelerate the expansion of forest into temperate grasslands. Y1 - 2001 ER - TY - BOOK A1 - Köchy, Martin T1 - Opposite trends in life stages of annual plants caused by daily rainfall variability - 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 communities. Y1 - 2006 UR - http://www.martinkoechy.de/research/papers/Koechy2006.pdf ER - TY - JOUR 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. Y1 - 2008 UR - http://www.springerlink.com/content/gj0567116q770036/ U6 - https://doi.org/10.1007/s10113-008-0048-6 ER - TY - JOUR A1 - Köchy, Martin A1 - Wilson, Scott D. T1 - Semiarid grassland responses to short-term variation in water availability N2 - Standing crop and species composition in semiarid grassland are linked to long-term patterns of water availability, but grasslands are characterized by large single-season variability in rainfall. We tested whether a single season of altered water availability influenced the proportions of grasses and shrubs in a semiarid grassland near the northern edge of the North American Great Plains. We studied stands of the clonal shrub snowberry (Symphoricarpos occidentalis) and adjacent grassland dominated by the native grasses Stipa spartea and Bouteloua gracilis. Rain was excluded and water supplied in amounts corresponding to years of low, medium, and high rainfall, producing a 2 - 4-fold range in monthly precipitation among water supply treatments. There were ten replicate plots of each water treatment in both snowberry stands and grassland. Grass standing crop increased significantly with water availability in grassland but not inside snowberry stands. Total standing crop and shrub stem density increased significantly with water supply, averaged across both communities. In contrast, water had no effect on shrub standing crop or light penetration. In summary, our finding that water has significant effects on a subset of components of grassland vegetation is consistent with long-term, correlational studies, but we also found that a single season of altered water supply had no effect on other important aspects of the ecosystem. Y1 - 2004 UR - http://springerlink.metapress.com/app/home/ content.asp?wasp=1147bd873d6c4f488659db36d63e080d&referrer=contribution&format=2&page=1&pagecount=7 SN - 1385-0237 ER - TY - JOUR 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. Y1 - 2006 UR - 1960 = dx.doi.org/10.1560/IJES_55_2_103 ER -