Scale‐dependent variation in visual estimates of grassland plant cover

Abstract. Plant cover was visually estimated by five observers, independent of each other, in a species‐rich grassland in the Bílé Karpaty Mts., southeastern Czech Republic, in seven plots ranging from 0.001 to 4 m². Variation of total plant cover among the observers was high at small scales: 0.001–0.016 m²; coefficient of variation, CV = 35 to 45%, but much lower at larger scales: 0.06–4 m²; CV = 7 to 15%. Differences between visual estimates of plant cover of individual species made by different observers were affected by plot size, total cover and morphology of particular plants. CV of the cover of individual species ranged from 0 to 225% and decreased with increasing plot size. For abundant plants the CV attained ca. 50%, independent of plot size. In spite of a very high number of sterile plants with similar leaf morphology and colour, the observed variation in cover estimates in the studied grassland was comparable with results reported from other vegetation types. Differences between estimates by individual observers were often larger than usual year to year changes in undisturbed grasslands. Therefore, I suggest that to avoid difficulties in the interpretation of results based on plant cover data obtained from visual estimates, several observers should always work together, adjusting their extreme estimates.     

不同修复措施对黄河源退化高寒草甸植物群落与土壤养分的影响

为了揭示退化高寒草甸逆向转变的驱动因子，通过野外调查和室内分析相结合的方法探究了黄河源不同修复措施（施有机肥F、免耕补播N、施有机肥+免耕补播FN）处理高寒草甸植物群落特征、土壤理化性质和两者相关性的变化规律，阐明不同修复措施对黄河源退化高寒草甸植物群落与土壤养分的影响。结果表明：免耕补播显著增加草甸物种丰富度指数（P<0.05）；施有机肥+免耕补播显著增加草甸植物盖度、总生物量、Shannon Wiener多样性指数和Pielous均匀度指数（P<0.05）。不同人工修复后草甸植物功能群地上、地下生物量变化趋势基本一致（除豆科）。和对照相比，莎草科，杂类草地上和地下生物量含量在N、FN处理分别降低83.04%、73.86%、30.43%、92.37%和96.51%、84.09%、85.68%、95.36%；禾本科地上和地下生物量含量在F、N和FN处理分别增加7.29%、23.45%、17.93%和6.04%、4.03%、10.52%；豆科地上生物量含量基本保持不变，地下生物量含量在F、N和FN处理分别降低24.43%、82.19%和42.61%。F显著增加土壤有机碳含量（P=0.033）；N显著降低土壤NO₃^--N含量（P=0.009）；FN显著降低土壤pH和增加土壤速效磷含量（P=0.024）；F和FN显著增加土壤含水量（P=0.000），N则显著降低土壤含水量（P=0.000）；F显著降低土壤容重（P=0.018）。相关性分析表明植物Shannon Wiener多样性和Pielous均匀度与土壤速效磷含量呈显著正相关（P=0.037；P=0.033），土壤有机碳和含水量与总生物量呈显著正相关（P=0.027；P=0.032），pH与盖度呈显著负相关（P=0.049）。冗余度分析结果表明土壤有机碳含量和含水量显著影响了植物群落结构特征，解释率分别为30.3%和19.7%。研究结果表明，因地制宜进行退化高寒草甸施有机肥+免耕补播修复措施，能够明显提高草地生产力，改善草甸植物群落及其土壤养分和水分环境。     

Population dynamics ofGlaux maritima (L.) along a distributional cline

Population fluctuations ofGlaux maritima, along a transect on a Baltle sea shore meadow, were recorded between 1979 and 1983. A bimodal distribution in numbers along the transect reflects the variation in factors regulating numbers: The two maintenance systems of the species, vegetative propagation and sexual reproduction play different roles. Vegetative propagation is fast and responds quickly to variations in the environment. The seeds germinate in strongly fluctuating temperatures which are triggered by disturbances such as flooding, damaging the vegetation.     

Scale‐dependent biases in species counts in a grassland

Abstract. Numbers of plant species were recorded in species‐rich meadows in the Bílé Karpaty Mts., SE Czech Republic, with the aim to evaluate the sampling error made by well‐trained observers. Five observers recorded vascular plants in seven plots ranging from 9.8 cm² to 4 m² independently and were not time‐limited. In larger plots a discrepancy of 10–20% was found between individual estimates, in smaller plots discrepancy increased to 33%, on average. The gain in observed species richness by combining records of individual observers (in comparison with the mean numbers estimated by single observers) decreased from the smallest plot (27–82% for two to five observers) to the largest one (13–25%). However, after misidentified and suspicious records were eliminated, the gain was much lower and became scale‐independent; two observers added 12% species, on average, and the increase by combining species lists made by three or more observers was negligible (3% more on average). It is concluded that most discrepancies between individual observers were caused by misidentification of rare seedlings and young plants. We suggest that in species‐rich meadows plants should be recorded by at least three observers together and that they should consult all problematic plant specimens together in the field, to minimize errors.     

Intersexual variation in the foraging ecology of sexually monochromatic Western Wood‐Pewees

ABSTRACT Investigators generally pool observations of males and females in studies of the foraging behavior of sexually monochromatic songbirds. However, such pooling can obscure possible intersexual differences. We compared the foraging behavior of male and female Western Wood‐Pewees (Contopus sordidulus), a sexually monochromatic species, in the Sierra Nevada Mountains of California during the breeding seasons of 2007 and 2008. We recorded 143 foraging observations (male N= 74, female N= 69). Overall, mean foraging rates of females (2.8 attacks/min) were higher (P < 0.001) than those of males (1.1 attacks/min). In addition, female foraging rates were significantly higher during incubation than during the nest building, nestling, and fledgling periods. When foraging, males perched higher above ground than females (means = 17.1 and 6.7 m, respectively). Differences between male and female Western Wood‐Pewees in foraging rates and perch heights suggest that males may spend more time on vigilance while females focus on foraging quickly during incubation and when feeding nestlings. Because metrics such as foraging attack rates are sometimes used as indicators of habitat quality and we found that rates can differ between the sexes and among nesting stages, investigators should consider the possibility of such differences when assessing habitat quality, especially for sexually monochromatic species of birds.     

Flowering requirements of Scandinavian Festuca pratensis

Flowering requirements of three Scandinavian cultivars of Festuca pratensis Huds, have been studied in controlled environments. At 3 and 6°C, primary induction was independent of photoperiod, while short days (8 h) were more effective than long days (24 h) at higher temperatures. The critical temperature for induction was about 15°C in short days and about 12°C in long days. Saturation of induction required 18–20 weeks of exposure to optimal conditions. At temperatures below 12°C both induction and initiation of inflorescence primordia took place in long days, while a transition to long days was required for inflorescence initiation after primary induction in short days. A minimum of 8 long-day cycles were required for flowering of plants primary induced in short days and saturation of flowering required more than 16 cycles. The critical photoperiod for secondary induction was about 13 h. High temperature (21°C) had some devernalization effect in primary induced plants, suppressing flowering compared with 15°C.     

Indirect effect of nitrogen enrichment modified invertebrate herbivory through altering plant community composition in an alpine meadow

Aims Nitrogen enrichment may affect ‘community invertebrate herbivory’ (hereafter ‘herbivory’) directly by changing plant species’ specific herbivory, or indirectly by altering the composition of natural plant communities. Here, we investigated how community composition altered the community herbivory in natural ecosystems and compared the relative importance of direct and indirect effects of nitrogen addition on community herbivory.     

Precipitation and seasonality affect grazing impacts on herbage nutritive values in alpine meadows on the Qinghai-Tibet Plateau

Aims Grasslands used for animal husbandry are chosen depending on the nutritive values of dominant herbage species. However, the influence of grazing in combination with precipitation and growing season on the nutritive values of dominant species has not been explicated.     

模拟增温对西藏高原高寒草甸土壤供氮潜力的影响

过去几十年青藏高原呈现显著的增温趋势,冬季增温幅度显著高于生长季的季节非对称特征。气候变暖会对生态系统氮素循环产生重要影响,但关于全年增温与冬季增温对高寒生态系统氮循环的不同影响仍缺乏研究。在青藏高原高寒草甸区开展模拟增温试验,研究季节非对称增温对高寒草甸生态系统氮循环的影响。该试验布设于2010年7月,设置3种处理(不增温、冬季增温与全年增温)。研究结果发现,开顶箱增温装置造成了小环境的暖干化:显著提高了地表空气温度和表层土壤温度,降低了表层土壤含水量。冬季增温会加剧土壤中氮素的流失,所以在经历了冬季增温后土壤氮含量显著降低;在生长季节,土壤氮素周转速率受土壤水分的调控,在降雨较少的季节,增温引起的土壤含水量降低会抑制土壤氮周转速率。对于土壤微生物量而言,高寒草甸土壤微生物量碳表现出明显的季节动态,在生长季旺盛期较低,在生长季末期和初冬季节反而较高,这说明为了降低对土壤养分的竞争,高寒草甸植物氮吸收与土壤微生物氮固持在时间上存在分离。研究结果表明,冬季增温导致的土壤养分含量变化会影响随后生长季植物群落的生产力、结构组成与碳氮循环等过程,对生态系统过程产生深远的影响。