Effects of overgrazing and rainfall variability on the dynamics of semiarid banded vegetation patterns: A simulation study with cellular automata

The effects of factors acting at small scale (grass/grass and grass/shrub biological interactions) and landscape scale (overgrazing and rainfall changes) on the development and permanence of banded vegetation patterns (VB) are assessed with a spatially explicit cellular automaton model. In particular, the influence of two environmental factors that are changing in many VB arid lands (rainfall and grazing pressures) is studied. Three rainfall regimes (representing 0.5, 1.0, and 2.0 times the long-term rainfall average), five grazing intensities, two types (reversible and irreversible) of grazing disturbance, two grazing periodicities (chronic and pulse), two levels of grass colonization ability, positive and negative interactions between shrubs and grasses, and the efficiency of endozoochorous seed dispersal are simulated.The results show that the permanence of undisturbed VB depends on the interaction of two factors, rainfall regime and grass colonization ability. Type and intensity of grazing also modify VB cover and permanence; furthermore, long-term overgrazing may convert mixed grass/shrub plant communities to pure scrublands dominated by endozoochorous-dispersed shrubs due to competitive interactions between shrubs and grasses.Besides providing an adequate representation of the system’s dynamics, the model is a useful tool that may be used to explore the consequences of climate change on management scenarios.     

Fire behavior characteristics of buffelgrass-fueled fires and native plant community composition in invaded patches

Buffelgrass invasions have been documented in Australia to North America, pointing to an end result of large-scale wildfires. In heavily populated areas such as Nogales, Sonora and Tucson and Phoenix, Arizona buffelgrass populations are growing exponentially. Although much research has been conducted on buffelgrass, relatively little is known about fire behaviors produced by a buffelgrass-fueled fire. To determine which abiotic and biotic characteristics best predict fire behavior, fire-behavior characteristics were measured in four prescribed fires in southern Arizona. Given that buffelgrass is known to decrease native plant richness in other ecosystems, the relationship between buffelgrass abundance and native plant cover was evaluated. Buffelgrass fires are more intense than fires in surrounding ecosystems, even in communities with comparable fuels. There is a strong negative relationship between buffelgrass cover and native plant cover. In addition, buffelgrass appears to be invading favorable microsites rather than species-poor communities and is radiating from the former sites. Historically, fire was rare in arid regions, but with the increase in fuels and because arid regions have weather that promotes intense fire behavior, as observed in this study, managers will increasingly observe and need to mitigate hazardous fires.     

草鱼不同养殖模式底泥间隙水与上覆水营养盐的分布特征

于2009年6～10月采集草鱼(Ctenopharyngodon idellus)不同养殖模式围隔底泥的样品,对上覆水和间隙水中营养盐形态与含量进行分析,探讨间隙水和上覆水中营养盐浓度间的相关关系。结果表明:草鱼不同养殖模式围隔大部分间隙水中营养盐浓度要高于上覆水,上覆水与间隙水中PO43--P浓度呈极显著的正相关性(P<0.01)。上覆水和间隙水中的NO2--N和NO3--N浓度垂直分布特征随月变化规律较一致。养殖期间,间隙水溶解态无机氮(DIN)中NH4+-N比例最高,占95%以上。间隙水中NH4+-N浓度随深度增加而逐渐升高(0～10cm),而NO2--N和NO3--N浓度则随深度增加而减小(0～4cm)。表层底泥在0→1cm方向PO43--P浓度明显增加,从2～3cm层后多数养殖模式下浓度缓慢下降,而4→10cm方向上浓度会随深度增加而明显下降。总体而言,三元混养组中(GSL2)上覆水中营养盐的浓度一般要低于GSL1组和GSL3组,且养殖期间该组底层水DO浓度要高于GSL1组和GSL3组,初步认为是一种较为优化的草鱼混养模式。     

丁香油和乙醇混合液对福瑞鲤的麻醉效果

将丁香油溶与乙醇混合进行对福瑞鲤麻醉,结果表明:丁香油与70%乙醇按1︰1.5得到的混合液与丁香油相比,使用3min时对福瑞鲤具有更好的麻醉效果;混合液的半致死浓度为0.2233mL/L,0.1 mL/L混合液在鱼密度达到1尾/L时的麻醉率最高;将处理过的样品血清进行生化指标检测,丁香油处理样品的CREA比对照显著高,而混合液处理样品所有血清指标与对照差异都不显著。     

Long-term dynamics of a semiarid grass steppe under stochastic climate and different grazing regimes: A simulation analysis

We built a grid-based spatial explicit stochastic model that simulates grazing events and basic processes like seedling establishment, growth or mortality of the dominant species in the grass steppes of Patagonia. After evaluating the model with field data, we performed simulation experiments aimed to explore the interaction of precipitation and grazing regimes on vegetation dynamics. Grazing generated a reduction in tussock density which results in a decline in aboveground net primary production (ANPP). Both response variables presented a non-linear behavior including high temporal variability and delay effects, which may prolong for decades. There was a clear threshold in the response of the variables to stock density, though changes become evident only when a highly selective grazing scenario was used. Under high stock density conditions, precipitation use efficiency (PUE) was 82% lower than the values for non-grazed runs. The inter-annual variability of precipitation was more important than the grazing regime in explaining differences in tussock density. Simulation results highlight important issues regarding rangeland management: grazing regime might be as important as stocking density as a degradation agent, temporal lags might obscure degradation processes for decades, the definition of monitoring variables need to consider their response time constants.     

Some effects of eutrophication and the removal of aquatic plants by grass carp (Ctenopharyngodon idella) on rainbow trout (Salmo gairdnerii) in Lake Parkinson,New Zealand

Temporary removal of aquatic plants in Lake Parkinson, a small, eutrophic dune lake, resulted in a number of changes to the population of stocked rainbow trout (Salmo gairdnerii). During each summer the lake stratified and low oxygen levels limited the distribution of trout to shallow (0–4 m) surface waters. In the first summer following weed removal the numbers of black shags (Phallacrocorax carbo) counted at the lake increased, and their predation resulted in a decline in trout density. However, the growth rate and condition of the trout population then exceeded that of trout present before weed removal. During the second summer after weed removal a cladoceran bloom was followed by low phytoplankton levels and high ammonia concentrations. A prolonged calm compounded this situation with the result that oxygen levels in bottom and surface waters dropped below 2 ppm. These low oxygen levels eliminated the trout population, but other fish species present survived. Elimination of aquatic plants affected the population dynamics of other fish species in the lake with potential implications for the trout. The experiment demonstrated the importance of weed beds in maintaining a stable fish community in lakes such as Lake Parkinson.     

Deep scattering layers resolved by narrow‐beam echo sounder along 35°s in the south pacific

The narrow‐beam echo sounder (3.5° half angle, 20 kHz) is capable of resolving the configuration of deep scattering layers to 750 m and was used to study the ecology and population density of organisms that make up the layers. Several layers to 1,000 m depth were identified in the South Pacific Ocean, and the population densities calculated. Swimming speeds of possible predators are estimated at 0.2–0.3 m.sec‐¹. Among organisms calculated to range in length from 0.01 m to 0.07 m, the larger were interpreted as grazing on smaller organisms, after comparing results from two echo sounders of 12 kHz and 20 kHz frequencies respectively.     

Dynamics of algae growth and nutrients in experimental enclosures culturing bighead carp and common carp:Phosphorus dynamics

This is the third paper of the series about “Dynamics of algae growth and nutrients in experimental enclosures culturing bighead carp and common carp”. In this paper, phosphorus dynamics were inves-tigated under the condition of culturing bighead carp and common carp with added fish food (nitrogen dynamics is discussed in the second paper because their behaviors are so different from each other). Nearly fifty days’ observation results indicated that the reservoir water was typical of “phosphorus limited” water, and soluble reactive phosphorus (SRP) was the main constituent of measured total phosphorus (TP). The presence of fish food resulted in significantly higher SRP, dissolved total phos-phorus (DTP) and TP concentrations in contrast with the reservoir water. Moreover, continuous supply of fish food led to the decline of total nitrogen to total phosphorus (TN:TP) from more than 100 to less than 5. Variations in the ratio of TN to TP favored the growth of blue-green algae. Fish species affected phosphorus concentrations, and culturing bait-eating common carp contributed more to reducing the SRP, DTP and TP concentrations than culturing planktivorous bighead carp. 0.5%, 4.1%and 3.1%TP can be removed in enclosures with culturing bighead carp, common carp and mixed bighead carp and common carp, respectively. Abundant phosphorus in the fish culturing activities may be present as the uneaten food, algae cells, and within the water column and sediment, which should be taken into serious con-sideration for the target of future water eutrophication prevention and safety of the drinking water supply.     

太原草温、地温变化特征分析

通过对太原基准站2009年1月一2010年12月的草温与地温同步观测资料分析,总结出草温与地温在不同季节的气候变化特征,分析了草温与地温的差异,简单阐述了产生不同特征的原因。分析表明,草温年平均值小于地温年平均值,草温各月的年平均值均小于地温;地温极端最高温度高于草温极端最高温度,草温极端最低温度低于地温极端最低温度;草温的平均最高温度在冬、秋季高于地温,草温的平均最低温度全年低于地温;草温在不同季节变化有所差异,在冬季、秋季草温的平均温度的振幅大于地表温度,草温的低温低,高温高;在秋季草温变化与冬季相仿,但幅度略小于冬季;春季、夏季草温与地温对比趋势相同,草温的高温低,低温持平,夏季草温与地温对比,草温的低温略低,高温偏高胜于春季。 草温的日较差常常大于地温的日较差,出现上述差异的主要原因：①传感器安装环境不同。②被测量的介质热容量不同,热容量愈大,物质的温度变化愈小,反之依然。③被测介质吸收到的辐射量、热传导不同。