Plant strategies and agricultural landscapes: survival in spatially and temporally fragmented habitat

In agricultural landscapes many plant species are limited to the network of landscape elements that are not used for agricultural production. This habitat is fragmented in space and time due to anthropogenic, biotic and abiotic factors. Therefore, plant populations are spatially sub-divided and their persistence might be dependent on the spatial dynamics in the network of local populations. Dispersal characteristics and seed bank persistence are main determinants of colonization ability which in turn is a key determinant of metapopulation viability. We propose a conceptual model that relates plant population dynamics to habitat quality, configuration and dynamics. In this model, the habitat is arranged as a network of suitable and unsuitable patches,and the distribution of the patches is assumed to be dynamic in time. Based on dispersal and seed bank characteristics four plant strategies are distinguished:species having either long (> 100 m) or short (< 100m) distance dispersal and either a long (> 5 yr)or short (< 5 yr) term persistent seed bank. We expect that species with contrasting strategies have different survival probabilities in landscapes with contrasting habitat arrangement in space and time. We found few empirical studies for testing the hypotheses based on the model. Therefore the relation between landscapes and plant survival needs to be further explored,especially the quantitative aspects. We propose an iterative process of empirical and modelling research to determine this relation and to define management options for multifunctional farms in which biodiversity is one of the land use aims. This revised version was published online in July 2006 with corrections to the Cover Date.     

Vacant lots: An underexplored resource for ecological and social benefits in cities

Vacant lots make up a large proportion of urban land and are of interest to many stakeholder groups. While they are often viewed as dangerous or unsightly, they can be an economic, social, and ecological resource. Here we present a literature review focused on restoring biodiversity in vacant lots, emphasizing the intersection of human and wildlife needs. We focus on the benefits, challenges, and processes of restoration in vacant lots and synthesize ecological, social, and economic information across these domains. We suggest that fast, inexpensive restoration techniques could be implemented in vacant lots and would be well suited to increasing greenspace in low-income areas. Furthermore, we emphasize that land managers, ecologists, sociologists, urban planners, and local communities must work together to conceptualize, carry out, and monitor restoration projects, as these projects are often characterized by disparate goals and insufficient follow-up. Vacant lot restoration is best addressed by an interdisciplinary approach that combines economic, social, and environmental needs and concerns into a holistic urban land use paradigm.     

Indigenous and spontaneous vegetation: their relationship to urban development in the city of Leeds, UK

The concepts of indigenous and spontaneous vegetation are considered as subsets of the broader category, semi-natural vegetation. Indigenous vegetation is conceptualised as that which has originated in a rural landscape and developed over a time period of several centuries or more, either naturally or as a result of traditional management methods, together with the environmental conditions supporting it. In contrast, spontaneous vegetation is that which has naturally colonised derelict urban sites, mainly within the last century. An investigation, using map and aerial photographic data, examined the relative proportions of potentially indigenous and spontaneous vegetation on proposed development sites in Leeds, a large industrial city in the UK. Results suggested that spontaneous vegetation occupied approximately 13% by area of the development sites while possible indigenous vegetation occupied as little as 5%. However, further analysis suggested that approximately 25% of the proposed development sites were within 0.5 km of a designated site containing indigenous vegetation. It is argued that both types of semi-natural vegetation can make positive contributions to the urban environment but that public perception of spontaneous vegetation and, in particular, the locations where it occurs, are often negative. Further research into public perceptions of semi-natural vegetation and ways of incorporating it into urban development are required.     

Plant establishment on a green roof under extreme hot and dry conditions: The importance of leaf succulence in plant selection

Plant selection for extensive green roofs has largely been based on cool, temperate climate research. However, as green roof implementation in hotter and drier climates increases, there is a need to evaluate plant performance under these climatic conditions. Succulents have been shown to be successful in hot and dry green roofs, although survival differs between species and the role of leaf succulence in survival has not been fully explored. For non-succulent plants, habitats with conditions similar to green roofs (‘habitat templates’) have been used to select plants, although few studies have discussed the performance of these selections under green roof conditions. Therefore, we evaluated establishment of 32 plant species on an unirrigated extensive (125 mm deep) green roof in Melbourne, Australia over a 42 week period (from winter through summer into autumn). Plants were selected on the basis of life-form, succulence, appropriate habitat templates and/or successful use on green roofs internationally. Climatic conditions during the experiment were often extreme, with evaporation regularly exceeding rainfall and a hot and dry summer (mean maximum air temperature 35 °C and 80.6 mm total rainfall), leading to roof temperatures of 65 °C. After 42 weeks, only succulent plants remained alive and only three of the succulent species had 100% survival. Survival was positively related to the degree of leaf succulence (g H₂O leaf area cm⁻¹) making this a useful trait for plant selection for unirrigated green roofs in hot, dry climates. The failure of most species, despite being chosen from appropriate habitats, demonstrates the need to evaluate potential plants on green roofs under extreme climatic conditions. Supplementary irrigation may be essential to sustain non-succulent species during extreme weather in hot and dry climates.     

北京西瓜产业发展40年来回顾及展望

西瓜作为北京市的主要农作物,是农民增收致富的重要产业.1980年至今北京西瓜产业经历了提高总产保供应、优质化多样化、全面提升和绿色高质量发展四个阶段.笔者回顾了40年来北京西瓜产业发展的四个阶段,总结了发展中存在的问题,提出了发展对策,并对北京西瓜产业发展进行了展望.     

Performance of native succulents,forbs, and grasses on an extensive green roof over four years in subtropical Australia

To achieve enduring low-maintenance green roofs that provide maximum benefit in the subtropics, plants need to be well adapted to the local climate with extensive green coverage. The use of native plants contributes to ecological restoration, yet there is very limited information available on their performance in the subtropics. This study aimed to determine the performance of nine species of Australian native forbs, succulents, and grasses in monofunctional and functionally-mixed plant communities on an extensive green roof in Brisbane over four years. Green coverage and survival were monitored via image analysis and observational visits. Forbs established slowly, but successfully (82 % green coverage, 67 % survival after four years) with species Hibbertia scandens (100 % survival) and Dianella brevipedunculata (58 % survival and extensive recruitment) performing the best. Grasses, including Themeda triandra, Poa labillardieri and Cymbopogon refractus, achieved a fast initial green coverage (47 % after 10 months), but showed high seasonal variability and declined to 2 %. Contrary to expectations, succulents performed poorly (<5 % green coverage, 14 % survival). Green coverage had an inverse trend to plant survival in successful plots (forbs, functionally-mixed) indicating a gap-filling effect by high performing species. Survival was more strongly linked to individual species than to functional type or plant community arrangement. Based on the results of this study, we recommend consideration of functionally-mixed green roof plantings with a variety of indigenous plants including forbs for low maintenance and resilient green coverage in the subtropics. Habitats that provided suitable plant species for this study were coastal headlands, dunes, montane areas, and open eucalypt forests. Analogous habitats in other regions can be explored to find new native plant species to increase the plant palette of potentially suitable species. It would be beneficial to trial more plants from these habitats over multiple years to increase the knowledge of suitable species available to green roof designers.     

Geospatial assessment of urban ecosystem disservices: An example of poisonous urban trees in Berlin,Germany

Urban trees play an important role in green infrastructure planning for the ecosystem services they provide. These services include carbon sequestration, the provision of clean air through oxygen production and filtering of airborne pollutants, and the offsetting of the urban heat island effect by providing shade and cooling. In addition to the well-studied positive effects of urban trees, under specific conditions, there are some unwanted side effects that need to be considered. Such negative side effects, such as allergies caused by tree pollen, traffic hazards from falling trees or tree parts or damage from roots or branches in resource supply or waste disposal infrastructures, are termed ecosystem disservices. An ecosystem disservice that is not very often illuminated in the urban context is the presence of poisonous urban trees. This paper provides a spatially explicit view of the distribution of poisonous urban trees in the city of Berlin, relating the spatial distribution of the hazard from this urban ecosystem disservice with the conditions under which it can have the most damaging effect by considering nearby playgrounds and areas with a high population density of children under 5 years old, the most vulnerable group within the urban population.     

Perceptions and representations of biodiversity in Lausanne,Switzerland: Acknowledging the importance of residential environments

While the ecological mechanisms involved in biodiversity loss within urban environments are widely studied, the literature often overlooks its social-ecological drivers. One of these drivers is the relationship between perceptions and representations of ecosystems and species within specific residential contexts. This study therefore aims to address the following questions: how do residents perceive biodiversity in relation to their social representation of nature within specific residential environments? Are there differences in the social representation and perception of greenspace types and species based on residents' demographic attributes (gender and age) and characteristics of their place of residence (district and housing types)? Through a quantitative survey and the analysis of 148 responses from Lausanne residents using textometry, cartography, and inferential statistics, this research demonstrates two main findings. Firstly, it confirms that the perception of species remains limited, which aligns with previous scholarly work. Secondly, it reveals that the social representations of nature and biodiversity can either correlate with or be disconnected from the perceptual process at the ecosystem level, depending on the residents' living environments. The impact of residential environments on biodiversity perception and representations is discussed, along with the implications of iconic biodiversity traps for raising public awareness about biodiversity preservation in cities.     

Using suitability analysis to select and prioritize naturalization efforts in legacy cities: An example from Flint,Michigan

Given the lack of market demand and the abundance of vacant lots in legacy cities, not all vacant lands can be redeveloped or even maintained in a highly manicured state. While many vacant lots are being creatively reused as community gardens and side lots, in areas where residents are few and vacancy is high, the best use for vacant lands may be in a naturalized state such as meadows or forests. The author argues that in legacy cities, the critical question is not whether to naturalize (i.e. to stop mowing lots and allow for succession), but rather how to determine which properties to naturalize, in what order, and how. Using the example of Flint, Michigan, the author proposes suitability analysis as a method for selecting and prioritizing naturalization. Every property in the city of Flint was assigned a naturalization score derived by calculating subscores on nine variables, weighing the subscores by their importance, and summing. The nine variables included were contiguous vacant land, prospective vacancy, public ownership, land use designation, parks adjacency, proximity to industry, waterway buffers, property values, and population change. The naturalization scores can be combined with the results of a prior study to create a vacant land use decision tree pre- and post-demolition. Ultimately, the purpose of the paper is to facilitate property selection for naturalization while encouraging public discourse around what should happen with vacant lots in legacy cities.     

Cities vs countryside: An example of a science-based peri-urban landscape features rehabilitation in Milan (Italy)

Urban-rural boundaries are often abrupt and unmitigated, a trait that significantly enhances their ecological vulnerability. Nonetheless, such fringe systems enclose a high potential in furnishing buffering and resilience functions and services towards the city. Our study intends to give a contribution on the understanding of the ecological behaviour of peri-urban landscape features (PLFs) systems, showing how floristic-vegetational and landscape ecology studies can inform their multi-functional phytocoenoses ecological reconfiguring. Analyses were led among a fringe context of Milan city. An agri-environmental extra-local scale analysis framed the forthcoming finer scale results. Landscape mosaic structural and functional main traits were interpreted, outlining a current impairment of the landscape system capacity to support ecological functions across the area. In parallel, floristic traits were studied through chorological, life forms and Ellenberg’s ecogram analysis (total flora and single sub-areas values). The main phytocoenoses types were qualitatively described and related to the dynamic patterns of reference vegetation series. Results highlighted a significant deterioration of floristic-vegetational traits, if compared to the local potential. Recurrent anthropic disturbances, open space conditions were identified as the major impact factor on phytoconoeses evolution towards higher diversity, complexity and stability traits. Spontaneous recolonization processes were acknowledged as currently unable to change these trends, while past reforestation interventions showed positive effects. These results informed the building of a functional-dynamic interpretative approach, focused on the ecological roles and physical habitat conditions currently influencing phytocoenoses dynamics, and on which to intervene. Accordingly, the current and potential ecological functions of 9 key PLFs categories were inspected. Consequently, design criterions for corrective interventions were outlined. This brought to the identification of the optimal structural and functional patterns of PLFs to be integrated throughout the urban-rural boundary, as well as their floristic-vegetational design specificities, by pursuing a rebalancing effect on the peri-urban agroecosystem inner complexity and environmental stability parameters.     

Economic development and natural amenity: An econometric analysis of urban green spaces in China

Rapid urbanization and spontaneous economic development has brought about profound changes in urban landscapes throughout the world. The task of managing transforming urban landscapes, particularly urban green spaces, so as to provide sufficient natural amenity for increasing urban populations, is one of the critical challenges facing policy makers. However, little empirical evidence exists about the evolving path of urban green spaces along with economic development and urbanization. This study attempts to fill in this knowledge gap through an econometric analysis of panel data across 285 Chinese cities during a period of rapid urbanization and economic growth (2001–2010). The results point to the existence of an N-shaped environmental Kuznets curve (EKC) for an important aspect of environmental quality: urban green spaces. Urban green space coverage increases at the initial stage of economic development, and then it starts to decrease as GDP per capita exceeds RMB50,855 and then increases again at a high GDP per capita level (RMB107,558). Large elasticity (>1) is expected as GDP per capita grows to a higher level (beyond RMB128,095). By the end of 2010, 30% of Chinese cities are still located on the downward-sloping path and only four cities have attained elasticities greater than one. The findings present a challenging and pressing call for policy makers to effectively manage the tradeoffs between continuous economic development and better natural amenities.     

白鹤芋胚性细胞悬浮培养和高效植株再生体系的建立

以白鹤芋（Spathiphyllum cannifolium）试管苗叶柄为外植体诱导获得胚性愈伤组织,建立了胚性细胞悬浮培养系并高频率再生出植株。结果表明,最优的悬浮培养条件为：装有20 mL液体培养基的100 mL三角瓶中接种0.3 g胚性细胞团,悬浮培养基为MS + 0.5 mg ? L-1 TDZ + 1.0 mg ? L-1 2,4-D + 30 g ? L-1蔗糖或麦芽糖,pH 5.8;继代间隔14 d;每个继代周期,胚性细胞团可增殖至接种量的5倍以上;植株再生最优的分化培养基为1/2MS + 0.3 mg ? L-1 6-BA + 30 g ? L-1蔗糖 + 8.0 g ? L-1琼脂粉,pH 5.8,平均每个胚性细胞团可分化再生出25.1株小植株;胚性细胞的快速增殖和高频率植株再生的状态可保持24周。     

Taxonomic diversity,functional diversity and evolutionary uniqueness in bird communities of Beijing's urban parks: Effects of land use and vegetation structure

The importance of biodiversity conservation is well recognized, and the loss of biodiversity is particularly evident in highly urbanized areas. On the other hand, green spaces inside cities, as parks, can provide a resource for maintaining and increasing biodiversity, especially for bird species. However, only a few studies have addressed the effects of vegetation structure and land use composition on different components of biodiversity.Here, we explored the response of bird community composition to environmental differences related to land use composition and vegetation structure in green spaces in the city of Beijing, China. We compared the values of taxonomic diversity, functional diversity and community evolutionary distinctiveness in breeding bird communities, among ten urban parks of the world's third most populous city. Variation partitioning analysis and generalized linear mixed models were used to explore the unique and shared effects of land use composition and vegetation structure on each biodiversity metric.Park size was not associated with the diversity of bird communities in Beijing. Land use composition was the best predictor of change in bird community composition, followed by vegetation structure at ground level and the intersection between land use and vegetation structure at tree level. Water coverage increased bird species richness, while the presence of large trees increased both taxonomic diversity and bird functional richness in urban parks. Finally, the presence of patches of deciduous trees showed a positive effect on the average score of evolutionary distinctiveness of bird communities. In conclusion, we highlight that different elements of the environment are supporting different components of bird community diversity.     

Integration in land research for Third World development planning: An applied aspect of landscape ecology

In the practical application of landscape ecology to development planning it is essential that there be interdisciplinary collaboration. Three ways of developing this collaboration are discussed. These are (1) use of environmental concepts which directs specialists to focus on landscape interrelationships; (2) geomorphic differentiation to provide a common framework for analysis and (3) a unified methodology based on mathematical modelling, hypothesis testing, and application of statistical theory. Broader implications to policy and administration are also examined.     

Responses of morphology and drought tolerance of Sedum lineare to watering regime in green roof system: A root perspective

The presence of drought tolerant vegetation is essential for the longevity of an extensive green roof when irrigation is not installed. Earlier studies have examined performance of green roof plants under contrasting watering regimes and found that higher watering frequency provided better growth and survival rates. The effect of early watering regimes on the subsequent response of plants to persistent drought stress in extensive green roofs, however, has not been extensively studied. In order to evaluate the effects of watering regime during the establishment period of Sedum lineare on its growth and drought tolerance, two greenhouse experiments using simulated green roofs were conducted. It was found in the first experiment that a 2-day-interval watering regimen at the early planting stage produced greater root biomass and root size than those of 6-day- and 13-day-interval watering, indicating that deficit watering tended to induce thinner roots in S. lineare. In the second experiment, the remaining plants were subsequently subjected to a 28-day drought treatment. The roots of plants watered at 13-day-interval maintained the highest respiration activity among all plants during the drought period. Results suggest that an appropriate deficit watering regimen at the early planting stage may lead to smaller root size and higher root:shoot ratios in S. lineare, and thereby improve its drought tolerance performance on extensive green roofs.     

An approach to the evaluation and management of natural carbon sinks: From plant species to urban green systems

The maintenance and improvement of current natural carbon sinks, as well as the creation of others, are presently considered among the main strategies by which to address global climate change, and are pursued in parallel to the implementation of policies of carbon emission reduction. To date, this approach has been applied mainly to forest areas, obtaining relevant results that help to identify areas of weakness in the strategy and to design appropriate management measures. Nevertheless, under the current situation, and at territorial level, urban areas and infrastructures, in which urban green systems play a significant role, present opportunities for contributing towards carbon sink potential. Various studies conducted by our research group have emphasized the role of urban green systems as natural carbon sinks, including research conducted under initiatives from European authorities (“Climeport project/Mediterranean Ports’ Contribution to Climate Change”), regional government (Andalusian Strategy against Global Climate Change) and Andalusian universities (Andalusian University Rectors Climate Change Pact). Through these projects, we have assessed entire systems, identifying the species of urban trees and shrubs with the greatest sink potential under different climate scenarios, proposing garden management schemes, and providing a basis for the creation, design, management and improvement of natural carbon sinks in the cities.     

Greening cities through urban planning: A literature review on the uptake of concepts and methods in Stockholm

Nature-based solutions (NBS) represent the most recent of several "greening" concepts proposed to support spatial planning and decision-making towards sustainable metropolitan regions. Despite similarities, the concepts stem from different disciplines and policy arenas and reflect various models of people-nature relations. This paper aims to analyze the uptake of greening concepts in scientific planning literature focusing on (urban) nature and landscape in the metropolitan region of Stockholm, Sweden, over the last three decades. It investigates what changes this evolution has brought in terms of the topics adopted, methods applied, and types of planning support put into practice. We identified 574 articles that reflect substantial research on greening concepts in the Swedish planning context. The articles demonstrate an initial prevalence of biodiversity with later increases of interest in ecosystem services and NBS. A detailed analysis of the studies focusing on Stockholm revealed Population growth/densification, Green space management and Biodiversity conservation as the most commonly addressed societal challenges. The most frequently mentioned type of green and blue element is Parks and (semi-)natural urban green areas, including urban forests. Methods applied were mostly quantitative, while mixes with qualitative approaches were only apparent in ecosystem services articles. Half of the studies involved practitioners or decision-makers, but only four seemed related to real-life planning processes. Taken together, the influence of scientific literature on the uptake of greening concepts in spatial planning seems to have been limited. Future mainstreaming of greening concepts in Stockholm and beyond could benefit from available data, methods and experiences, but will require more active translation and boundary management. Further research into science-policy-planning interfaces at city scale is thus imperative to advance more sustainable pathways for people and nature in metropolitan regions.     

梨不同花龄自花与异花授粉的花柱内花粉管生长及坐果率的比较

对自交不亲和强度不同的梨品种丰水和菊水的不同花龄花进行自花授粉和丰水×菊水异花授粉后,用荧光显微镜观察花粉萌发及生长特性。结果表明,开花当天及以后的自花和异花授粉花粉在柱头上均有较高的萌发率;自花和异花花粉管在花柱内的生长速度及停止生长的位置不同,丰水自花授粉后花粉管生长的短且慢,菊水自花花粉管生长的长且快,而异花授粉的花粉管生长最快。自花授粉后,不同花龄对花粉管生长影响表现为:开花4d前的蕾期授粉以及开花4d后的延迟授粉,花粉管生长长度显著的长。开花6d前的各种授粉组合,花粉管生长均较差。这与田间授粉坐果率的高低基本一致,即整体表现为各个花龄的授粉都以异花授粉坐果率最高,其次为菊水自花授粉,丰水自花授粉坐果率最低。另外,自花授粉中,蕾期授粉和延迟授粉(开花2d后除外)坐果率都有提高,而异花授粉中蕾期授粉和延迟授粉的坐果率却有所下降。     

The pattern and control of reproductive development in lychee: A review

Often there is no relationship between yield and flower production in lychee (Litchi chinensis Sonn,). This is because of the high rate of premature flower and, especially, fruit abscission between floral initiation and fruit maturation. There is the possibility that low female-to-male sex ratio, lack of pollinating insects, poor pollen transfer, low pollen viability and failure of pollen tube growth may also reduce fruit set, while poor fruit development may reduce final fruit size.Detailed studies are required on the effects of genotype and environment (temperature, soil moisture, humidity and mineral nutrition) on the growth and abscission of the flowers and fruit. Potential techniques for improving the setting and retention of fruit include varietal selection, withholding of nitrogen fertilization during flowering and early fruit growth (to reduce vegetative flushing), and the maintenance of plant moisture status (irrigation, overhead misting and windbreaks).     

The use of gradient analysis studies in advancing our understanding of the ecology of urbanizing landscapes: current status and future directions

Over the past decade, the urban–rural gradient approach has been effectively used to study the ecology of cities and towns around the world. These studies have focused on understanding the distribution of plants and animals as well as ecosystem processes along gradients of urbanization that run from densely urbanized inner city to more rural exurban environments. We reviewed 300 papers investigating urbanization gradients that were published in peer-reviewed journals between 1990 and May 2007. Sixty-three percent of the papers investigated the distribution of organisms along urbanization gradients. Only five papers addressed the measures used to quantify the urbanization gradient itself. Within the papers addressing the distribution of organisms, 49% investigated the responses of birds to urbanization gradients, and <10% of the papers investigated more cryptic organisms. Most of these studies utilized a variety of broad measures of urbanization, but future advances in the field will require the development of some standardized broad measures to facilitate comparisons between cities. More specific measures of urbanization can be used to gain a mechanistic understanding of species and ecosystem responses to urbanization gradients. While the gradient approach has made a significant contribution to our understanding of the ecology of cities and towns, there is now a need to address our current knowledge gaps so that the field can reach its full potential. We present two examples of research questions that demonstrate how we can enhance our understanding of urbanization gradients, and the ecological knowledge that we can obtain from them.