Global change effects on Bromus tectorum L. (Poaceae) at its high‐elevation range margin

Global change is likely to affect invasive species distribution, especially at range margins. In the eastern Sierra Nevada, California, USA, the invasive annual grass, Bromus tectorum, is patchily distributed and its impacts have been minimal compared with other areas of the Intermountain West. We used a series of in situ field manipulations to determine how B. tectorum might respond to changing climatic conditions and increased nitrogen deposition at the high‐elevation edge of its invaded range. Over 3 years, we used snow fences to simulate changes in snowpack, irrigation to simulate increased frequency and magnitude of springtime precipitation, and added nitrogen (N) at three levels (0, 5, and 10 g m^?2) to natural patches of B. tectorum growing under the two dominant shrubs, Artemisia tridentata and Purshia tridentata, and in intershrub spaces (INTR). We found that B. tectorum seedling density in April was lower following deeper snowpack possibly due to delayed emergence, yet there was no change in spikelet production or biomass accumulation at the time of harvest. Additional spring rain events increased B. tectorum biomass and spikelet production in INTR plots only. Plants were primarily limited by water in 2009, but colimited by N and water in 2011, possibly due to differences in antecedent moisture conditions at the time of treatments. The threshold at which N had an effect varied with magnitude of water additions. Frequency of rain events was more influential than magnitude in driving B. tectorum growth and fecundity responses. Our results suggest that predicted shifts from snow to rain could facilitate expansion of B. tectorum at high elevation depending on timing of rain events and level of N deposition. We found evidence for P‐limitation at this site and an increase in P‐availability with N additions, suggesting that stoichiometric relationships may also influence B. tectorum spread.     

Does spatial scale affect the pattern of mangrove change under different rainfall regimes? An example in southeast Queensland,Australia

The aim of this study was to investigate the interactions of natural and anthropogenic variables at different spatial scales related to changes in mangrove distribution during a relatively wet period (1972–1990) and a dry period (1991–2004) in subtropical eastern Australia. Previous research has demonstrated that mangroves are encroaching into salt marsh. Mangrove spatial change in southeast Queensland is related generally to landscape variables especially during the relatively wet period. What has not been explored is the spatial scale of the influence under the two rainfall regimes (wet and dry) and that is the aim of this paper. Ten sites were examined at different levels of resolution including catchment, sub‐catchment and two buffer zones (1000 and 500 m), under the period of relatively higher and lower rainfall. Land use was ascertained from Landsat satellite imagery using Maximum Likelihood Classification techniques. Partial least squares regression analysis was used to study the relationships between the predictor variables and the rate of change in the mangrove distribution. The research has found that the impact of land use/cover on the encroachment of mangrove into saltmarsh can vary and appears to be related to rainfall patterns, which in turn affect hydrological connectivity. A major finding of this research was that the changing spatial patterns of mangroves during the wet period was more a function of land use/cover pattern and population density at the sub‐catchment level, whereas during drier periods it was more affected by the local effects of nearby land use/cover in buffer zones.     

First Red-billed Quelea breeding record in the winter rainfall region of South Africa

The Red-billed Quelea Quelea quelea is a serious pest of agricultural crops throughout most of sub-Saharan Africa. Since the 1980s, it has expanded its range into the Eastern Cape and Western Cape, South Africa, facilitated by changes in agricultural practices. This note documents the first breeding of Red-billed Quelea in the winter rainfall region of South Africa. A colony of 350–600 nests was found, with evidence of recent breeding. Red-billed Quelea numbers were low in this region, but if numbers increase in the future in the Western Cape, winter crops could be under threat.     

Relationship between Late Soybean Diseases Complex and Rain in Determining Grain Yield Responses to Fungicide Applications

Wide distribution of soybean monoculture associated with no tillage has contributed to enhance damages caused by late diseases complex (LDC) in Argentina. LDC is a complex of diseases where Septoria glycines and Cercospora kikuchii are regarded as the major problem. Even though the use of foliar fungicides has increased, there is no rational and economic guide for their use. This is the main reason why the response to foliar fungicide applications is unpredictable. One of the main factors that contribute to the development of LDC is rainfall. The objective of this study was to evaluate the impact of rainfall during several growing seasons and different soybean growth stages on LDC severity and yield. We carried out 18 field experiments during three growing seasons (2004–2006) at several locations in the Argentine Pampas Region, to examine the relationship between rain and yield response to single fungicide applications (quinone outside inhibitors and demethylation inhibitors) at growing stages R3 and R5. The strongest associations (R² = 0.81–0.84; P < 0.001) were observed between accumulated rainfall from R3 to R5 and yield response to fungicides applied in R3 or R5. Our results suggest that a minimum of 65–90 mm rainfall during R3–R5 is required to justify fungicide application, with high probability that the use of fungicide will increase soybean yield as a consequence of disease control. These findings could lead to a simple model, useful as decision support system for use in planning and scheduling spray applications for LDC management in soybean crops.     

模拟降雨对常绿植物叶表面滞尘的影响

通过模拟降雨实验的方法,在15 mm/h和30 mm/h降雨强度的不同历时条件下,从动态变化、滞尘阈值和建立关系3个方面量化了降雨过程对叶表面不同粒径颗粒物的影响。研究结果表明:叶表面颗粒物滞留率随降雨历时先急剧下降,后趋于稳定状态。降雨初期对叶面尘的影响最为明显,降雨强度较大时洗脱时间更短。颗粒物滞留量和滞留率的阈值均随降雨强度的增加而减小。颗粒物滞留量阈值呈现出10—100μm2.5—10μm0.2—2.5μm的规律,与未降雨前一致。侧柏各粒径颗粒物均能被降雨较有效洗脱;大叶黄杨10—100μm的颗粒物更易被降雨洗脱;油松的颗粒物滞留率阈值达30%—50%,不易被洗脱。降雨量与叶表面颗粒物滞留率有良好的拟合关系,随降雨量的增大,颗粒物滞留率呈指数减小,且减小速率在降雨量10mm内较大,大于10 mm后曲线较为平缓。     

黄土高原不同降雨量带退耕地植被-生物结皮的分布格局

黄土高原退耕还林工程实施后,高等维管束植物恢复的同时,生物结皮大面积发育。然而,两者共同发育下的分布格局及空间变异却鲜有报道。通过野外调查,研究了黄土高原不同降雨量带退耕地上植被盖度、维管束植物斑块面积、个数,生物结皮组成、盖度及其空间变化。结果表明:1)在黄土高原降水量250—550 mm地区的退耕地及自然荒坡上,维管束植物与生物结皮共同存在,呈镶嵌分布。生物结皮多呈连续分布,可视为被镶嵌体,维管束植物多以斑块状存在,可视为镶嵌体。2)黄土高原生物结皮盖度变化于80.8%—55.1%之间,在不同降雨量带之间差异显著,250—350 mm降雨量带生物结皮平均盖度(77.8%)显著高于350—500 mm降雨量带(60.3%),但不同类型生物结皮盖度差异显著性不同。3)黄土高原地区不同降雨量带维管束植物冠层盖度变化于10.0%—58.7%,随降雨量的增加而增加,一定程度上限制了生物结皮的发育和演替,两者表现出了"此消彼长"的关系。4)随着降雨量的增加,高等维管束植物茎基斑块间的距离逐步减小,维管束植物覆被增加。研究结果数量化的揭示了黄土高原不同降雨量带退耕地上维管束植物与生物结皮的镶嵌式分布格局及其空间变异特征。     

Fire frequency and species associations in perennial grasslands of south-west Ethiopia

Fires play an important role in shaping species composition and associations in East African grasslands. Grassland plains of Omo National Park (ONP), Ethiopia, which are dominated by perennial grass species, exist in a fire-prone environment. Our objective was to determine if the current pattern of plant species composition in ONP's grassland plains was correlated with the historical pattern of fire frequency. Species composition was determined at 160 plots along 30 west-trending transects, approximately 2 km apart. Fire frequency for each plot was estimated using eleven Landsat satellite images that spanned a 23-year period. The Mantel and partial Mantel tests were used to test for correlation between species composition and fire frequency.
Plots in the northern grassland plain appear to burn every other year, while plots in the southern grassland plain burn once every 4–5 years. However, no significant correlation was found between patterns in species composition and fire frequency. Likewise, a selective analysis by functional group (i.e. grass, shrubs) revealed no relationship with fire frequency. It appears that fire does play a role in dictating species composition in ONP, but only in the sense that species that can tolerate the current fire regime persist. Species distribution, however, appears to be under the influence of other factors.     

Autumn bird migration phenology: A potpourri of wind,precipitation and temperature effects

Climate change has caused a clear and univocal trend towards advancement in spring phenology. Changes in autumn phenology are much more diverse, with advancement, delays, and ‘no change' all occurring frequently. For migratory birds, patterns in autumn migration phenology trends have been identified based on ecological and life‐history traits. Explaining interspecific variation has nevertheless been challenging, and the underlying mechanisms have remained elusive. Radar studies on non‐species‐specific autumn migration intensity have repeatedly suggested that there are strong links with weather. In long‐term species‐specific studies, the variance in autumn migration phenology explained by weather has, nevertheless, been rather low, or a relationship was even lacking entirely. We performed a spatially explicit time window analysis of weather effects on mean autumn passage of four trans‐Saharan and six intra‐European passerines to gain insights into this apparent contradiction. We analysed data from standardized daily captures at the Heligoland island constant‐effort site (Germany), in combination with gridded daily temperature, precipitation and wind data over a 55‐year period (1960–2014), across northern Europe. Weather variables at the breeding and stopover grounds explained up to 80% of the species‐specific interannual variability in autumn passage. Overall, wind conditions were most important. For intra‐European migrants, wind was even twice as important as either temperature or precipitation, and the pattern also held in terms of relative contributions of each climate variable to the temporal trends in autumn phenology. For the trans‐Saharan migrants, however, the pattern of relative trend contributions was completely reversed. Temperature and precipitation had strong trend contributions, while wind conditions had only a minor impact because they did not show any strong temporal trends. As such, understanding species‐specific effects of climate on autumn phenology not only provides unique insights into each species' ecology but also how these effects shape the observed interspecific heterogeneity in autumn phenological trends.