Characterization of Households and its Implications for the Vegetation of Urban Ecosystems

Our understanding of the dynamics of urban ecosystems can be enhanced by examining the multidimensional social characteristics of households. To this end, we investigated the relative significance of three social theories of household structure—population, lifestyle behavior, and social stratification—to the distribution of vegetation cover in Baltimore, Maryland, USA. Our ability to assess the relative significance of these theories depended on fine-scale social and biophysical data. We distinguished among vegetation in three areas hypothesized to be differentially linked to these social theories: riparian areas, private lands, and public rights-of-way (PROWs). Using a multimodel inferential approach, we found that variation of vegetation cover in riparian areas was not explained by any of the three theories and that lifestyle behavior was the best predictor of vegetation cover on private lands. Surprisingly, lifestyle behavior was also the best predictor of vegetation cover in PROWs. The inclusion of a quadratic term for housing age significantly improved the models. Based on these research results, we question the exclusive use of income and education as the standard variables to explain variations in vegetation cover in urban ecological systems. We further suggest that the management of urban vegetation can be improved by developing environmental marketing strategies that address the underlying household motivations for and participation in local land management.     

Housing Market Activity is Associated with Disparities in Urban and Metropolitan Vegetation

In urban areas, the consistent and positive association between vegetation density and household income has been explained historically by either the capitalization of larger lawns and lower housing densities or landscaping and lifestyle districts that convey prestige. Yet cities with shrinking populations and rising land burdens often exhibit high vegetation density in declining neighborhoods. Because the observed associations do not directly address the causal connection between measures of social privilege and vegetation in urban landscapes, it is difficult to understand the forces that maintain them. Here, we compare patterns of household income with new measures derived from housing market data and other parcel-level sources—sale prices, tax foreclosures, new housing construction, demolitions, and the balance of construction and demolition. Our aim is to evaluate whether these spatially, temporally and semantically finer measures of neighborhood social conditions are better predictors of the distribution of urban vegetation. Furthermore, we examine how these relationships differ at two scales: within the City of Detroit and across the Detroit metropolitan area. We demonstrate, first, that linear relationships between income or home values and urban vegetation, though evident at broad metropolitan scales, do not explain recent variations in vegetation density within the City of Detroit. Second, we find that the real estate and demolition records demonstrate a stronger relationship with changes in vegetation density than corresponding changes in US Census measures like income, which suggests they hold at least as much interest for understanding how the relationships between biophysical changes and neighborhood change processes come about.     

Are all urban green spaces a favourable habitat for pollinator communities? Bees,butterflies and hoverflies in different urban green areas

1. Urban ecosystems create suitable habitats for many plant and animal species, including pollinators. However, heterogenic habitats in city centres and suburban areas have various effects on pollinators due to variations in the composition of vegetation and in landscape management by humans. 2. This study compared the abundance and species richness of three main groups of pollinators – wild bees, butterflies, and hoverflies – in Poznań, western Poland, and in three different types of urban green areas – urban grasslands, urban parks, and green infrastructure in housing estates. 3. The total abundance of pollinators was higher in urban grasslands than in housing estates and urban parks. Species composition of pollinator communities differed between the three habitat types. 4. The study results showed that species richness and abundance of butterflies varied between habitat types, whereas no such differences were found in the case of wild bees and hoverflies. Cover of green area, vegetation structure, and plant height were important for the pollinator community; however, these variables had different effects depending on habitat type. 5. These findings revealed that not all urban green areas are equally valuable in terms of local biodiversity. High‐quality urban habitats such as urban grasslands are capable of supporting rich and abundant populations of pollinators. Therefore, it is important to protect high‐value urban green areas and simultaneously strive to improve intensively managed urban habitats through effective planning and new management practices.     

The influences of climatic variation and vegetation on stream biota: lessons from the Big Dry in southeastern Australia

Aquatic biodiversity faces increasing threats from climate change, escalating exploitation of water and land use intensification. Loss of vegetation in catchments (= watersheds) has been identified as a substantial problem for many river basins, and there is an urgent need to better understand how climate change may interact with changes in catchment vegetation to influence the ecological condition of freshwater ecosystems. We used 20 years of biological monitoring data from Victoria, southeastern Australia, to explore the influences of catchment vegetation and climate on stream macroinvertebrate assemblages. Southeastern Australia experienced a severe drought from 1997 to 2009, with reductions of stream flows >50% in some areas. The prolonged drying substantially altered macroinvertebrate assemblages, with reduced prevalence of many flow‐dependent taxa and increased prevalence of taxa that are tolerant of low‐flow conditions and poor water quality. Stream condition, as assessed by several commonly used macroinvertebrate indices, was consistently better in reaches with extensive native tree cover in upstream catchments. Prolonged drought apparently caused similar absolute declines in macroinvertebrate condition indices regardless of vegetation cover, but streams with intact catchment and riparian vegetation started in better condition and remained so throughout the drought. The largest positive effects of catchment tree cover on both water quality and macroinvertebrate assemblages occurred above a threshold of ca. 60% areal tree cover in upstream catchments and in higher rainfall areas. Riparian tree cover also had positive effects on macroinvertebrate assemblages, especially in warmer catchments. Our results suggest that the benefits of extensive tree cover via improved water quality and in‐channel habitat persist during drought and show the potential for vegetation management to reduce negative impacts of climatic extremes for aquatic ecosystems.     

南京城市街区湿球温度时空变化特征及其影响因子

全球气候变化和局地城市热岛加剧了城市热胁迫问题,但针对城市街区的研究仍不多见。湿球温度指示气温和湿度的综合效应,能更准确地反映人体热舒适度。本研究以南京市江北新区为对象,在不同时段、季节和天空状况下,基于移动观测方法获取气温、相对湿度和地理信息等数据,分析了街区尺度湿球温度的时空分布特征;结合天空状况、地表覆盖和城市形态指标(天穹可见度),探究了城市街区湿球温度的影响机制。结果表明: 1)南京城市街区湿球温度的时空特征与气温较为一致;与水汽压相比,气温对湿球温度的变化起主导作用;该地区湿球温度的极端高值主要是由于气温和水汽压协同增长所致。2)天穹可见度在白天与湿球温度呈显著正相关,夜间为负相关关系。植被覆盖比率的增加能够降低湿球温度,不透水面则呈现相反的作用。阴天条件下,湿球温度明显降低并且空间分布更均匀。3)植被和不透水面对湿球温度的水平尺度效应存在昼夜和季节差异,并且在夜间这一效应对天空状况更敏感;与植被相比,冬季夜间不透水面的影响范围比夏、秋季更大;两者对湿球温度的水平尺度效应与气温一致。研究结果可为改善和优化城市街区热环境、缓解城市热胁迫提供有效的科学支持和理论依据。     

中国森林生态系统地表径流调节特征

径流调节是森林生态系统重要生态服务功能之一,包含着大气、水分、植被和土壤等生物物理过程,其变化将直接影响区域气候水文、植被和土壤等状况,是区域生态系统状况的重要指示器。在区域尺度上评估森林生态系统地表径流特征,对于科学认识和合理保护森林生态系统水源涵养功能具有重要意义。以森林生态系统定位监测数据为基础,探讨地表径流与降水,径流系数与植被的关系,建立径流系数与植被的回归方程,分析全国森林生态系统地表径流调节特征。结果表明:(1)各森林类型地表径流与降水相关性显著,其对地表径流的影响为37%—76%。此外,径流系数与植被也显著相关,其对径流系数的解释能力为27%—47%。(2)基于植被覆盖数据,通过植被与径流系数回归方程估算全国森林生态系统的地表径流调节特征。全国各森林生态系统径流调节能力存在差异,强弱顺序为:落叶针叶林落叶阔叶林针阔混交林常绿针叶林常绿阔叶林。     

Relationship between Riparian Vegetation and Stream Benthic Communities at Three Spatial Scales

We examined the influence of riparian vegetation on macroinvertebrate community structure in streams of the Upper Thames River watershed in southwestern Ontario. Thirty-three μ-basins (129–1458 ha) were used to identify land cover variables that influenced stream macroinvertebrates. Micro-basins represented the entire drainage area of study streams and were similar in stream order (first, second) and land cover (agricultural or forest; no urban). We described the structure and composition of riparian vegetation and benthic macroinvertebrate communities at the outflow reach. The nature of the land cover was quantified for the stream network buffer (30 m) and the whole μ-basin. The objective of this study was to measure the magnitude and nature of the relationship between the riparian vegetation and benthic macroinvertebrate community at the outflow reach, stream network buffer, and whole μ-basin scales. Taxon richness (including total number of Ephemeroptera, Plecoptera, and Trichoptera taxa) and Simpson’s diversity of the macroinvertebrate community all increased with increased tree cover in the riparian zone at the outflow reach scale. Simpson’s equitability was lower with greater agricultural land cover in the stream network buffer. No relationship between the macroinvertebrate community and land cover was found at the whole μ-basin scale. Analysis of the influence of land cover on stream communities within a spatial hierarchy is important for understanding the interactions of stream ecosystems with their adjacent landscapes.     

How widespread is woody plant encroachment in temperate Australia? Changes in woody vegetation cover in lowland woodland and coastal ecosystems in Victoria from 1989 to 2005

Aim Encroachment or densification by woody plants affects natural ecosystems around the world. Many studies have reported encroachment in temperate Australia, particularly in coastal ecosystems and grassy woodlands. However, the degree to which published studies reflect broad-scale changes is unknown because most studies intentionally sampled areas with conspicuous densification. We aimed to estimate changes in woody vegetation cover within lowland grassy woodland and coastal ecosystems in Victoria from 1989 to 2005 to determine whether published reports of recent encroachment are representative of broad-scale ecosystem changes. Location All lowland grassy woodland and coastal ecosystems (c. 6.11 × 10⁵ ha) in Victoria, Australia. Four major ecosystems were analysed: Plains woodlands, Herb-rich woodlands, Riverine woodlands and Coastal vegetation. Methods Changes in woody vegetation cover from 1989 to 2005 were assessed based on state-wide vegetation maps and Landsat analyses of woody vegetation cover conducted by the Australian Greenhouse Office’s National Carbon Accounting System. The results show changes in woody cover within mapped patches of native vegetation, rather than changes in the extent of woody vegetation resulting from clearing and revegetation. Results When pooled across all ecosystems, woody vegetation increased by 18,730 ha from 1989 to 2005. Woody cover within Riverine woodlands and within Plains woodlands each increased by >7000 ha. At the patch scale, the mean percentage cover of woody vegetation in each polygon increased by >5% in all four ecosystems: Riverine woodlands (+9.2% on average), Herb-rich woodlands (+7.6%), Plains woodlands (+6.7%) and Coastal vegetation (+5.9%). Regression models relating degree of encroachment to geographic and climatic variables were extremely weak (r² ≤ 0.026), indicating that most variation occurred at local scales rather than across broad geographic gradients. Main conclusions At the scale of observation, woody vegetation cover increased in all lowland woodland and coastal ecosystems over the 16-year period. Thus, published examples of encroachment in selected coastal and woodland patches do appear to reflect widespread increases in woody vegetation cover in these ecosystems. This densification appears to be associated with changes in land management rather than with post-fire vegetation recovery and is likely to be ongoing and long-lasting, with substantial implications for biodiversity conservation and ecosystem services.     

Sampling grain influences trends in vegetation composition and diversity with time since fire in Australian heathland

Scale‐dependency of pattern and process is well‐understood for many ecological communities; however, the influence of spatial scale (sampling grain) in detecting temporal change in communities is less well‐understood. The temperate lowland heathlands of south‐east Australia are one of the most fire‐prone ecosystems on earth. Despite the extensive literature documenting the effect of time since fire on heathlands, we know little about how sampling grain influences trends in vegetation variables over time, and whether these trends are scale‐dependent. Using 3500 ha of heathland in the Gippsland Lakes Coastal Park, south‐east Australia, we investigated how above‐ground species composition and diversity, and trends in these variables with increasing time since fire, were influenced by sampling grain (1 m², 10 m², 100 m², 900 m², 1 ha, 4 ha). Sampling grain influenced patterns detected in vegetation variables and in some instances, significantly affected their relationship with time since fire. Richness decreased with time since fire, with mean richness decreasing at three of the four grains, while total richness decreased at half of the sampled grains. Evenness (J) decreased with increasing time since fire for all grains except 1 m². The decline in diversity (H) with time since fire appeared to be independent of scale, as all grains decreased significantly with increasing time since fire. Community heterogeneity demonstrated a weak response to time since fire across most grains. Changes in composition among young (0–6 years since fire), intermediate (9–19 years) and old (23–27 years) sites were dependent on sampling grain, with all grains exhibiting significant differences in composition, apart from the 1 m² grain and the 100 m² grain (presence/absence data). Overall, species composition, richness, evenness, diversity and community heterogeneity were dependent on the scale at which the vegetation was sampled. In addition, trends in many of these vegetation variables with increasing time since fire were scale‐dependent. This work provides strong evidence that sampling at multiple grains contributes substantially to understanding pattern and process in heathlands.     

Ground‐ and satellite‐based evidence of the biophysical mechanisms behind the greening Sahel

After a dry period with prolonged droughts in the 1970s and 1980s, recent scientific outcome suggests that the decades of abnormally dry conditions in the Sahel have been reversed by positive anomalies in rainfall. Various remote sensing studies observed a positive trend in vegetation greenness over the last decades which is known as the re‐greening of the Sahel. However, little investment has been made in including long‐term ground‐based data collections to evaluate and better understand the biophysical mechanisms behind these findings. Thus, deductions on a possible increment in biomass remain speculative. Our aim is to bridge these gaps and give specifics on the biophysical background factors of the re‐greening Sahel. Therefore, a trend analysis was applied on long time series (1987–2013) of satellite‐based vegetation and rainfall data, as well as on ground‐observations of leaf biomass of woody species, herb biomass, and woody species abundance in different ecosystems located in the Sahel zone of Senegal. We found that the positive trend observed in satellite vegetation time series (+36%) is caused by an increment of in situ measured biomass (+34%), which is highly controlled by precipitation (+40%). Whereas herb biomass shows large inter‐annual fluctuations rather than a clear trend, leaf biomass of woody species has doubled within 27 years (+103%). This increase in woody biomass did not reflect on biodiversity with 11 of 16 woody species declining in abundance over the period. We conclude that the observed greening in the Senegalese Sahel is primarily related to an increasing tree cover that caused satellite‐driven vegetation indices to increase with rainfall reversal.     

Urban Morphology Drives the Homogenization of Tree Cover in Baltimore,MD, and Raleigh,NC

Heterogeneous land cover patterns contribute to unique ecological conditions in cities and little is known about the drivers of these patterns among cities. We studied tree cover patterns in relationship to urban morphology (for example, housing density, parcel size), socioeconomic factors (for example, education, income, lifestyle characteristics), and historical legacies in Baltimore, Maryland, and Raleigh, North Carolina. Utilizing a multimodel inference approach and bivariate analyses, we analyzed two primary datasets employed in previous research predicting urban tree cover—one comprising continuous data (US Census), and the other consisting of categorical variables (Claritas PRIZM) that incorporate consumer purchasing data. Continuous data revealed that urban morphological characteristics were better predictors of tree cover patterns than socioeconomic factors in Raleigh and Baltimore at the parcel and neighborhood scales. Although the categorical dataset provided some evidence for the importance of socioeconomic and lifestyle characteristics in predicting tree cover patterns, the hierarchical nature of these data preclude separating the impacts of these factors from levels of urbanization. Bivariate analyses of continuous and categorical variables revealed that the highest correlation coefficients were associated with variables describing urban morphology—parcel size, percent pervious area, and house age. In Baltimore, historical census data were better predictors of present-day tree cover than census data from recent years. Most notably, parcel size, a key predictor of tree cover, has decreased with time in Raleigh to sizes consistently seen in Baltimore. Our findings demonstrate that urban morphology, the main driver of tree cover patterns in these cities, may lead to the homogenization of tree canopy in Raleigh and Baltimore in the future.     

Humans,bees, and pollination services in the city: the case of Chicago,IL (USA)

Despite the global trend in urbanization, little is known about patterns of biodiversity or provisioning of ecosystem services in urban areas. Bee communities and the pollination services they provide are important in cities, both for small-scale urban agriculture and native gardens. To better understand this important ecological issue, we examined bee communities, their response to novel floral resources, and their potential to provide pollination services in 25 neighborhoods across Chicago, IL (USA). In these neighborhoods, we evaluated how local floral resources, socioeconomic factors, and surrounding land cover affected abundance, richness, and community composition of bees active in summer. We also quantified species-specific body pollen loads and visitation frequencies to potted flowering purple coneflower plants (Echinacea purpurea) to estimate potential pollination services in each neighborhood. We documented 37 bee species and 79 flowering plant genera across all neighborhoods, with 8 bee species and 14 flowering plant genera observed on average along each neighborhood block. We found that both bee abundance and richness increased in neighborhoods with higher human population density, as did visitation to purple coneflower flower heads. In more densely populated neighborhoods, bee communities shifted to a suite of species that carry more pollen and are more active pollinators in this system, including the European honey bee (Apis mellifera) and native species such as Agapostemon virescens. More densely populated neighborhoods also had a greater diversity of flowering plants, suggesting that the positive relationship between people and bees was mediated by the effect of people on floral resources. Other environmental variables that were important for bee communities included the amount of grass/herbaceous cover and solar radiation in the surrounding area. Our results indicate that bee communities and pollination services can be maintained in dense urban neighborhoods with single-family and multi-family homes, as long as those neighborhoods contain diverse and abundant floral resources.     

长三角地区植被覆盖演变城乡差异及其原因

城市生态环境和城市化之间的关系是城市可持续发展的关键。研究不同城市化水平下植被覆盖的长时间演变趋势,对理解城市化过程对植被生长动态的影响,城市更新以及推进城市绿化的科学管理具有重要意义。然而,目前对城市内部沿城乡梯度植被生长趋势差异的认识还比较有限。以我国城市化发展最为强烈的长三角地区为研究对象,基于2000-2020年长三角归一化植被指数数据,采用趋势分析和地理探测器方法,探究了长三角地区城市内部植被覆盖演变城乡差异,并从土地利用/覆被变化和城市化发展的角度解析其成因。研究结果表明：（1）2000-2020年长三角地区植被总体呈绿化趋势,植被明显绿化占最大比例（52.06%）,轻微绿化与稳定不变地区占31.68%,零星分布的褐化区占6.82%。（2）城市老城区植被覆盖变化总体呈现返绿趋势（0.016/10 a）,新城区褐化明显（-0.019/10 a）,农郊区绿化突出（0.023/10 a）。在上海、南京和杭州等人口城市化水平较高的城市中,老城区土地利用变化强度最高,其绿化趋势也最高,体现了城市更新过程对绿地空间的促进作用;而在人口城市化水平相对较低的宣城、蚌埠和阜阳等城市,土地利用变化强度相对较低的农郊区也呈现明显的绿化趋势,更多的是受到区域生态保护的影响。（3）土地城市化是长三角地区老城区和新城区植被覆盖变化的主导因子,而城市化因子对农郊区解释程度总体不显著。从长三角总体区域看,城镇人口比重、不透水面积/总面积以及地区生产总值三者对植被覆盖演变存在显著影响,其中城镇人口比重影响最大。     

京津冀地区城市化对植被覆盖度及景观格局的影响

定量研究了2000—2010年,京津冀地区植被覆盖度及其景观格局的动态变化,揭示了城市化进程对植被景观的干扰过程及生态质量的影响。结果表明:(1)2000—2010年,城市化进程显著是京津冀城市群土地变化的一大特点,人工表面面积从2000年的1.79×10~4km~2增加至2.16×10~4km~2,增幅高达21.16%;(2)京津冀平均植被覆盖度呈增加趋势但不显著(P=0.46),存在明显的时空动态差异。在覆盖度结构上形成了以中低和中植被覆盖度为主导的格局;(3)从景观空间格局变化来看,中低、高覆盖度区域植被景观更加破碎,而低、中等覆盖度区域的植被面积增加,景观破碎度减小;尤其是低植被覆盖度为主的城市区域,景观格局变化幅度大,表现为绿地面积有所增加,景观破碎化程度降低,生态质量有所改善;(4)在整个研究区范围,城市化对区域植被覆盖度存在负面影响,表现为城市化程度与区域平均植被覆盖度存在负相关(P=0.08);但是在低植被覆盖度的区域(主要为城市区域),城市化程度与植被覆盖面积呈显著正相关(P0.001),表明城市区域在城市化进程中植被覆盖面积有所提高,生态质量有所改善,与城市化过程中,日益重视城市绿地的建设有关。     

基于FVC指数的中国西北干旱区植被覆盖变化Markov过程

基于1982-2000年NOAA/AVHRR影像的FVC数据,对中国西北干旱区采用先分区再因海拔而异的分类方法进行植被覆盖的遥感分类,并在8 km×8 km空间分辨率下,对研究区植被覆盖变化的任意两年、连续平均和间隔平均转移概率矩阵下Markov过程进行分析与检验,探讨了研究区植被覆盖变化的Markov过程及其指示意义.结果表明：研究区植被覆盖变化受随机过程的控制和长期稳定的驱动因子影响,其转移变化是多重的Markov过程;仅使用两期的植被覆盖变化不能准确预测植被覆盖变化的发展趋势,无论这两期的时间是连续还是有一定时间间隔;对中国西北干旱区而言,连续10年以上的数据变化信息基本可以反映大部分影响该区植被覆盖的因素,采用长期平均转移概率矩阵可以得到较稳定的模拟与预测;植被覆盖变化是长期的动态平衡,平衡一旦被打破,建立新平衡是一个很长的时间过程.     

1990-2020年三峡库区植被覆盖转型及其驱动因素

探索山区植被覆盖转型,全面评估各驱动因素对其的影响,是理解全球气候变化和碳循环等生态系统过程的重要途径。三峡库区是长江流域生态环境的重要保护区,提供多种生态系统服务。基于植被覆盖(NDVI)数据提出山区植被覆盖转型理论,并运用地理探测器分析了潜在因素对1999—2020年三峡库区腹地植被覆盖的相对贡献。结果表明：(1)近30年三峡库区腹地植被覆盖整体呈良性发展趋势,增长率为0.006/a,空间特征为“东西低,南北高;中间低,四周高”;(2)不同时段植被覆盖的空间演化呈现“整体改善,局部退化”,空间转型总结为稳定型、波动型、退化型和恢复型4种模式,且以稳定型分布为主,时间上经历了减少、过渡和恢复3个阶段;(3)植被覆盖主要受土壤类型0.225>地貌0.200>土地利用程度0.181>海拔0.158>岩性0.152的驱动,人为和气候因素的作用较弱,表明自然因素是影响植被覆盖的主导因子。此外,双因子的交互作用在影响植被覆盖方面比每个因子单独作用更为重要。这些发现有利于更好的解析山区植被变化的复杂机制,为脆弱生态系统植被的管理和保护提供参考。     

Response of vegetation phenology to urbanization in the conterminous United States

The influence of urbanization on vegetation phenology is gaining considerable attention due to its implications for human health, cycling of carbon and other nutrients in Earth system. In this study, we examined the relationship between change in vegetation phenology and urban size, an indicator of urbanization, for the conterminous United States. We studied more than 4500 urban clusters of varying size to determine the impact of urbanization on plant phenology, with the aids of remotely sensed observations since 2003–2012. We found that phenology cycle (changes in vegetation greenness) in urban areas starts earlier (start of season, SOS) and ends later (end of season, EOS), resulting in a longer growing season length (GSL), when compared to the respective surrounding urban areas. The average difference of GSL between urban and rural areas over all vegetation types, considered in this study, is about 9 days. Also, the extended GSL in urban area is consistent among different climate zones in the United States, whereas their magnitudes are varying across regions. We found that a tenfold increase in urban size could result in an earlier SOS of about 1.3 days and a later EOS of around 2.4 days. As a result, the GSL could be extended by approximately 3.6 days with a range of 1.6–6.5 days for 25th ~ 75th quantiles, with a median value of about 2.1 days. For different vegetation types, the phenology response to urbanization, as defined by GSL, ranges from 1 to 4 days. The quantitative relationship between phenology and urbanization is of great use for developing improved models of vegetation phenology dynamics under future urbanization, and for developing change indicators to assess the impacts of urbanization on vegetation phenology.     

Direct and indirect effects of land use on floral resources and flower‐visiting insects across an urban landscape

Although urban areas are often considered to have uniformly negative effects on biodiversity, cities are most accurately characterized as heterogeneous mosaics of buildings, streets, parks, and gardens that include both ‘good’ and ‘bad’ areas for wildlife. However, to date, few studies have evaluated how human impacts vary in direction and magnitude across a heterogeneous urban landscape. In this study, we assessed the distribution of floral resources and flower‐visiting insects across a variety of land uses in New York City. We visited both green spaces (e.g. parks, cemeteries) and heavily developed neighborhood blocks (e.g. with high or low density residential zoning) and used structural equation modeling (SEM) to evaluate the direct and indirect effects of median income, vegetation, and development intensity on floral resources and insects in both settings. Abundance and taxonomic richness of flower‐visiting insects was significantly greater in green spaces than neighborhood blocks. The SEM results indicated that heavily‐developed neighborhoods generally had fewer flower‐visiting insects consistent with reductions in floral resources. However, some low‐density residential neighborhoods maintained high levels of floral resources and flower‐visiting insects. We found that the effects of surrounding vegetation on floral resources, and thus indirect effects on insects, varied considerably between green spaces and neighborhood blocks. Along neighborhood blocks, vegetation consisted of a mosaic of open gardens and sparsely distributed trees and had a positive indirect effect on flower‐visiting insects. In contrast, vegetation in urban green spaces was associated with increased canopy cover and thus had a negative indirect effect on flower‐visiting insects through reductions in floral resources. In both neighborhood blocks and green spaces, vegetation had a positive direct effect on flower‐visiting insects independent of the influence of vegetation on floral resources. Our results demonstrate how inter‐related components of an urban ecosystem can vary with respect to one another across a heterogeneous urban landscape, suggesting that it is inappropriate to generalize about urban systems as a whole without first addressing differences among component land use types.     

The effect of fish and aquatic habitat complexity on amphibians

Fish introductions are considered one of the most widespread anthropogenic threats to aquatic ecosystems. Their negative impact on native amphibian communities has received increasing attention in recent years. We investigated the relationship between the introduced fish, emergent vegetation cover and native amphibians in man-made ponds generated by regulation and dam building along the Tarnava Mare Valley (Romania) during the last 40 years. We inventoried amphibians and fish inhabiting 85 permanent ponds and estimated habitat complexity focusing on emergent vegetation cover. Four amphibian species were found to be negatively associated with the presence of predatory fish. Species richness of ponds without fish and ponds without predatory fish did not differ significantly, whereas ponds containing only predatory fish had significantly lower amphibian richness. A significant positive relationship was found between the emergent vegetation cover and pond occupancy of six amphibian species and amphibian species richness. As a management recommendation, we suggest the restriction of fish introductions to non predatory fish and the maintenance of high emergent vegetation cover in the ponds. Handling editor: S. Declerck     

基于植被信息季节变换的植被覆盖度变化——以福建省连江县为例

基于植被覆盖度的植被信息遥感变化检测已成为研究植被及其相关生态系统变化的主要途径,但由于云覆盖等天气条件的影响,很难获得不同年份同一季节覆盖整个研究区的光学遥感影像来进行植被变化检测,而采用季节差异的影像必然会影响植被变化检测的结果.为此,本研究利用中高分辨率遥感数据的空间分辨率优势和MODIS遥感数据的时间分辨率优势,基于二者关系的拟合,提出一种植被信息季节变换的方法,将不同季节影像的植被覆盖度变换到研究所需的季节上.结果表明: 将该方法应用到福建敖江流域连江片区发现,植被信息变换的效果较好,经过将覆盖研究区的2007年冬季和2013年春季的中高分辨率影像的植被信息统一变换到夏季后,2007年的植被覆盖度由66.5%上升到79.7%,2013年由58.6%上升到77.9%,有效消除了因季节差异而对植被覆盖度估算产生的误差,提高了结果的准确性.