Garden Size, Householder Knowledge, and Socio-Economic Status Influence Plant and Bird Diversity at the Scale of Individual Gardens

Domestic gardens collectively cover substantial areas within cities and play an important role in supporting urban biodiversity and ecosystem functioning. The extent of their contribution to urban biodiversity is ultimately determined by the attitudes, motivations, and practices of their owners. We identified variables characterizing individual householders and their properties that explained variation in perennial plant and avian species richness and plant diversity among 55 gardens in New Zealand. The size of the vegetated area was most important in explaining bird and plant diversity, independent of property size. Also important and positively associated with plant richness were socio-economic status and ability to discriminate between native and exotic species. Median housing age and neighborhood green space were less important. Contrary to expectations, better educated householders who demonstrated pro-environmental orientation (NEP) did not necessarily have gardens with greater plant diversity, however, people with higher NEP scores tended to have gardens with more structurally complex vegetation. Similar variables were important in explaining native and exotic species richness, but higher exotic plant diversity was associated with older people with smaller properties of lower value. Avian species richness increased primarily with vegetated area, but also the areas of beds and hedges. We demonstrate that although householder knowledge is an important determinant of garden biodiversity, vegetated area is most important. Promoting urban garden biodiversity requires that larger vegetated properties be supported and encouraged, and that planners should consider biodiversity when formulating policies concerning garden size, property size, and consents that may result in a progressive increase in the proportion of built over/paved areas.     

Challenges and trade-offs in the management of invasive alien trees

Over 430 alien tree species worldwide are known to be invasive, and the list is growing as more tree species are moved around the world and become established in novel environments. Alien trees can simultaneously bring many benefits and cause substantial environmental harm, very often leading to conflicts over how they should be managed. The impacts grow over time as invasions spread, and societal perceptions of the value of alien trees also change as understanding grows and as values shift. This leads to a dynamic environment in which trade-offs are required to maximise benefits and minimise harm. The management of alien tree populations needs to be strategic and adaptive, combining all possible management interventions to promote the sustainable delivery of optimal outcomes. We use examples, mainly from South Africa (where issues relating to invasive alien trees introduced for forestry have received most attention), to argue for holistic and collaborative approaches to alien tree management. Such approaches need to include bold steps, such as phasing out unsustainable plantation forestry that is based on highly invasive species, and in which the costs are externalised. Furthermore, it would be advisable to impose much stricter controls on the introduction of alien trees to new environments, so that problems that would arise from subsequent invasions can be avoided.     

From the backyard to the backcountry: how ecological and biological traits explain the escape of garden plants into Mediterranean old fields

To explain current ornamental plant invasions, or predict future ones, it is necessary to determine which factors increase the probability of an alien species becoming invasive. Here, we focused on the early phases of ornamental plant invasion in order to identify which plant features and cultivation practices may favor the escape of ornamental plants from domestic gardens to abandoned agricultural land sites in the Mediterranean Region. We used an original approach which consisted in visiting 120 private gardens in an urbanizing rural area of the French Mediterranean backcountry, and then visited surrounding old fields to determine which planted species had escaped out of the gardens. We built a database of 407 perennial ornamental alien species (most of which were animal-dispersed), and determined nineteen features that depicted the strength of species’ propagule pressure within gardens, the match between species requirements and local physical environment, and each species’ reproductive characteristics. Using standard and phylogenetic logistic regression, we found that ornamental alien plants were more likely to have escaped if they were planted in gardens’ margins, if they had a preference for dry soil, were tolerant to high-pH or pH-indifferent, and if they showed a capacity for clonal growth. Focusing only on animal-dispersed plants, we found that alien plants were more likely to have escaped if they were abundant in gardens and showed preference for dry soil. This suggests that gardening practices have a primary impact on the probability of a species to escape from cultivation, along with species pre-adaptation to local soil conditions, and capacity of asexual reproduction. Our results may have important implications for the implementation of management practices and awareness campaigns in order to limit ornamental plants to becoming invasive species in Mediterranean landscapes.     

Livestock reduces juvenile tree growth of alien invasive species with a minimal effect on natives: a field experiment using exclosures

Many alien invasive tree species were originally introduced to their non-native ranges for use in forestry and as urban trees. These alien species were selected for their fast growth and not necessarily for possessing mechanisms which deter browsing. Instead, many tree species native to semiarid areas of the world evolved mechanisms which deter browsing, presumably at the cost of slower growth. In a semiarid rangeland we observed that livestock exclusion greatly promoted the growth of juveniles of several alien species but not of native species, and we hypothesized that this increase in growth of aliens was due to livestock preference for alien and not native trees. With the objective of quantifying our observations and understanding the mechanism underlying the increased growth rates of alien juvenile trees under livestock exclusion, we assessed growth and browsing levels in juveniles of two alien invasive and four abundant native tree species within three parcels where livestock was excluded and three parcels with livestock at 0.20 cattle equivalents.ha^?1. Alien species grew around four-fold faster under livestock exclusion than with livestock and, as predicted, received five times more browsing than natives. Instead, native species did not significantly increase their growth rate with livestock exclusion. The results support our hypothesis and the implications for management would be that stocking paddocks with livestock to browse existing alien juveniles and re-growth of felled adults should be effective in delaying invasions of trees used for forestry without significantly affecting the growth of the most abundant native trees.     

Invasion trajectory of alien trees: the role of introduction pathway and planting history

Global change is driving a massive rearrangement of the world's biota. Trajectories of distributional shifts are shaped by species traits, the recipient environment and driving forces with many of the driving forces directly due to human activities. The relative importance of each in determining the distributions of introduced species is poorly understood. We consider 11 Australian Acacia species introduced to South Africa for different reasons (commercial forestry, dune stabilization and ornamentation) to determine how features of the introduction pathway have shaped their invasion history. Projections from species distribution models (SDMs) were developed to assess how the reason for introduction influences the similarity between climatic envelopes in native and alien ranges. A lattice model for an idealized invasion was developed to assess the relative contribution of intrinsic traits and introduction dynamics on the abundance and extent over the course of simulated invasions. SDMs show that alien populations of ornamental species in South Africa occupy substantially different climate space from their native ranges, whereas species introduced for forestry occupy a similar climate space in native and introduced ranges. This may partly explain the slow spread rates observed for some alien ornamental plants. Such mismatches are likely to become less pronounced with the current drive towards ‘eco gardens’ resulting in more introductions of ornamental species with a close climate match between native and newly introduced regions. The results from the lattice model showed that the conditions associated with the introduction pathway (especially introduction pressure) dominate early invasion dynamics. The placement of introduction foci in urban areas limited the extent and abundance of invasive populations. Features of introduction events appear to initially mask the influence of intrinsic species traits on invasions and help to explain the relative success of species introduced for different purposes. Introduction dynamics therefore can have long‐lasting influences on the outcomes of species redistributions, and must be explicitly considered in management plans.     

Urban nectarivorous bird communities in Cape Town,South Africa,are structured by ecological generalisation and resource distribution

Biological communities are increasingly faced with novel urban habitats and their response may depend on a combination of biological and habitat traits. The response of pollinator species to urban habitats are of particular importance because all species involved in the pollination mutualism may be affected. Nectarivorous bird communities worldwide show varying tolerances to urban areas, but studies from Africa are lacking. We investigated nectarivorous bird communities in a medium‐sized South African city and asked which biological and garden traits best predict the community assembly of specialist and opportunistic nectarivorous birds. Information was collected on garden traits and the frequency of nine nectarivorous bird species for 193 gardens by means of a questionnaire. Information on biological traits of birds was obtained from published literature. Habitat generalism and tree nesting were identified as the most important biological traits influencing bird occurrence in gardens. A greater diversity of indigenous bird‐pollinated plants and the presence of sugar water feeders increased the numbers of nectar specialist birds and species richness of nectarivorous birds. While bird baths increased the species richness of nectar specialist birds, opportunistic birds’ urban adjustment was further facilitated by large vegetated areas in gardens and limited by the distance to the nearest natural habitat. In conclusion, though some biological traits and dispersal barriers seem to limit urban adjustment, a combination of natural and artificial nectar resource provisioning could facilitate this adjustment.     

广州的外来植物

该文分析了127种广州外来植物的种类及其生长型、原产地、现状、生境和季节变化。结果表明:具有较强繁殖能力的草本、灌木和藤本植物以及一些世界广布或热带性科属的植物和原产美洲、非洲的一些植物具有较强的入侵能力;受人为干扰较强的路边、荒地、池塘、果园、菜园和人工林容易为外来植物入侵,而人为干扰较少的自然生境则不易为外来植物入侵。此外,文章对物种的入侵性和生境的入侵性问题进行了讨论,认为这实际上是一个问题的两个方面,物种的入侵性总是与被入侵的生境联系在一起并相互影响的。     

Gardens in urbanizing rural areas reveal an unexpected floral diversity related to housing density

The increasing urbanization of rural areas leads to a strong development of horticultural flora, which is the main source of alien and invasive plants. In order to assess the pool of cultivated species under different urbanization pressures, the diversity and distribution of horticultural flora were studied in 120 Mediterranean gardens belonging to three housing density types. The results showed a great richness and heterogeneity of this flora, and similarities in species composition between gardens of the same housing density types. Twenty-four percent of the cultivated species are well adapted to the Mediterranean climate, and 21 species known to be invasive on the French territory have emanated from gardens. Inventorying areas adjoining gardens would be useful in identifying escaped garden plants and to assess the associated risks for biological diversity. The results also suggested a detailed analysis of the influence of social, economic and regional factors on planting practices, in order to identify the drivers of these original floral patterns.     

Woody plant composition and diversity of urban green spaces in Istanbul,Turkey

Abstract

The high urbanization rate of Istanbul in response to rapid population decreased the size and amount of green spaces. Thereby, every green space types are of vital importance in terms of conservation of urban biodiversity. In this study, it was aimed to compare woody species composition of main green space types consist of artificial and natural sites. Botanical gardens had the highest diversity followed by gardens. Residential areas showed to be important in terms of shrub (52%) and evergreen species (58%), which are mostly exotics (71%). The ratio of the invasive plants in the composition was higher in parks, which contain highway greenings and public gardens. Since the most tree species used in public green areas of Istanbul were mostly same with the species used in European cities, all of the green space categories having varied composition must be considered as interconnected habitat patches in urban planning.     

Restoration of invaded Cape Floristic Region riparian systems leads to a recovery in foliage-active arthropod alpha- and beta-diversity

The Cape Floristic Region of South Africa is a global biodiversity hotspot threatened by invasive alien plants (IAPs). We assessed the effect of plant invasions, and their subsequent clearing, on riparian arthropod diversity. Foliage-active arthropod communities were collected from two native and one invasive alien tree species. Alpha- and beta-diversity of their associated arthropod communities were compared between near pristine, Acacia-invaded and restored sites. Arthropod alpha-diversity at near pristine sites was higher than at restored sites, and was lowest at invaded sites. This was true for most arthropod taxonomic groups associated with all native tree species and suggests a general trend towards recovery in arthropod alpha-diversity after IAP removal. Overall, arthropod species turnover among sites was significantly influenced by plant invasions with communities at near pristine sites having higher turnover than those at restored and invaded sites. This pattern was not evident at the level of individual tree species. Although arthropod community composition was significantly influenced by plant invasions, only a few significant differences in arthropod community composition could be detected between restored and near pristine sites for all tree species and arthropod taxonomic groups. Assemblage composition on each tree species generally differed between sites with similar degrees of plant invasion indicating a strong turnover of arthropod communities across the landscape. Results further suggest that both arthropod alpha- and beta-diversity can recover after IAP removal, given sufficient time, but catchment signatures must be acknowledged when monitoring restoration recovery.     

The rehabilitation value of a small culturally significant island based on the arthropod natural capital

Small islands are particularly vulnerable to degradation by invasive species and often lack source populations to replace those lost during localized extinctions. Robben Island, a significant South African cultural heritage site, has a long history of anthropogenic impact. Introduced alien mammals and trees have resulted in numerous localized plant extinctions with their impact on arthropod biodiversity remaining unclear. We used Robben Island’s arthropod fauna as focal group to investigate the rehabilitation potential of this transformed island. Ground surface-living, foliage-inhabiting and flower-visiting arthropods were collected using five sampling techniques. Arthropod diversity was highest in the two ‘natural’ habitats compared to alien Eucalyptus plantations. Arthropod compositional diversity differed significantly between alien plantations and natural habitats. Nevertheless, a remarkable 17 % of all species were confined to plantations. However, when we corrected for the effect of rarity, only 15 species (4 %) were unique to alien plantations and all those identified to species level were either alien in origin or were widespread generalists only normally associated with transformed areas. This emphasizes the need to identify species that drive similarity indices to fully comprehend the conservation value of alien vegetation. Arthropods found in the remaining natural vegetation showed remarkable tolerance of long-term grazing pressures from introduced alien mammals. Only eight Orthoptera species were sampled, yet one was a rediscovery of a rare species and another a range extension. All indigenous species showed strong preferences for natural habitats. Thus, Robben Island could still hold conservation value if the natural habitats are rehabilitated and the Eucalyptus plantations removed.     

华南地区外来入侵和归化植物分析

为了解华南地区外来植物现状,通过野外调查和查阅文献等,确定华南地区有外来入侵和归化植物45科141属223种,以菊科(Asteraceae,38种)、豆科(Fabaceae,36种)、禾本科(Poaceae,19种)植物为主,其中草本植物和原产美洲的植物占优势,分别有204种(占总数的91.5%)和163种(占73.1%)。广东外来入侵植物有159种,归化植物23种;广西有入侵植物135种,归化植物16种;海南有入侵植物111种,归化种15种;香港有入侵植物105种,归化植物9种;澳门有入侵植物89种,归化种4种;华南5省区共有的外来入侵和归化植物为57种(55种为入侵植物,2种为归化植物)。广东是外来植物种类最多的地区,与其他4省区共有的外来入侵和归化植物种类也最多,说明广东同时是外来植物输入和输出大省。由于气候和生态生境的相似性,各省区都面临着其他植物从周边地区入侵的风险,因此在治理入侵植物时,应建立联合防控机制对外来入侵植物的联合监测和防控,以提升外来入侵植物的治理成效和降低其对人类健康和生态安全的威胁。     

外来树种的耗水特征及其对环境水资源的影响

外来树种常被作为"先锋树种"广泛引种,在荒山造林和水土保持方面发挥了积极作用;然而,不少外来树种具有高耗水和强抗旱的水分利用特性,耗水量大、水分消耗快,若不加甄别地引种会影响甚至危害本土森林生态系统的健康。目前,部分被引种的外来树种已造成入侵;同时,在当前水资源缺乏的形势下,外来树种的引种安全问题已成为全球关注的生态环境问题。本文综述了外来树种在生态系统、整树、叶片及枝条水平的耗水特性,分析了外来树种对引种地水资源的影响。前期的研究结果显示,被引种的外来树种在生态系统及整树水平的耗水量普遍高于乡土树种,但对水资源的影响却因受控于多个因素如环境、气候、植物个体等而不尽相同;同时还显示,外来树种在叶片和枝条水平的耗水特性更多地体现了其应对环境变化的水分利用策略。研究还就提高外来树种耗水特性研究的准确性和提升外来树种危害风险的预警能力方面,提出了若干研究方向,旨在为森林管理者和政府部门平衡外来树种的经济效益和生态效应提供借鉴和指导,以期降低外来树种引种风险,增进生态安全。     

Urban Power Line Corridors as Novel Habitats for Grassland and Alien Plant Species in South-Western Finland

Regularly managed electric power line corridors may provide habitats for both early-successional grassland plant species and disturbance-dependent alien plant species. These habitats are especially important in urban areas, where they can help conserve native grassland species and communities in urban greenspace. However, they can also provide further footholds for potentially invasive alien species that already characterize urban areas. In order to implement power line corridors into urban conservation, it is important to understand which environmental conditions in the corridors favor grassland species and which alien species. Likewise it is important to know whether similar environmental factors in the corridors control the species composition of the two groups. We conducted a vegetation study in a 43 kilometer long urban power line corridor network in south-western Finland, and used generalized linear models and distance-based redundancy analysis to determine which environmental factors best predict the occurrence and composition of grassland and alien plant species in the corridors. The results imply that old corridors on dry soils and steep slopes characterized by a history as open areas and pastures are especially suitable for grassland species. Corridors suitable for alien species, in turn, are characterized by productive soils and abundant light and are surrounded by a dense urban fabric. Factors controlling species composition in the two groups are somewhat correlated, with the most important factors including light abundance, soil moisture, soil calcium concentration and soil productivity. The results have implications for grassland conservation and invasive alien species control in urban areas.     

Influence of Invasive Tree Kill Rates on Native and Invasive Plant Establishment in a Hawaiian Forest

Fire tree (Morella faya) has invaded extensive areas of wet and mesic forest on the Island of Hawai’i, forming nearly monospecific stands. Our objective was to identify a method of controlling M. faya, which would allow native plants to establish while minimizing establishment by invasive plants. Treatments (logging all trees, trees left standing but girdled, and incremental girdling over 20 months) were selected to kill M. faya stands at different rates, thereby creating different conditions for species establishment. Leaf litter was either removed or left in place; seeds and seedlings of three native pioneer species, three native forest species, and three alien invasive species were then added to determine their ability to establish. Native pioneer species established best in the log and girdle treatments, whereas seedling emergence of native forest species was higher in the girdle and incremental girdle treatments. Seedlings of invasive species emerged faster than the natives, but each of them responded differently to the stand treatments. Leaf litter reduced seedling emergence for all species, with small‐seeded species (<1 mg/seed) affected most under low light conditions. No single method eliminated all invaders, but girdling of M. faya provided suitable conditions for most native species. If combined with selective removal of the most disruptive alien species and native seed additions, girdling could be an effective general strategy for restoring native forests that have been overwhelmed by woody invaders.     

2008-2016年间广州市外来入侵植物的变化分析

为了解2008-2016年广州市外来入侵植物的变化,采用文献查阅和实地考察相结合的方式,近期对广州市外来入侵植物进行了调查。结果表明,2016年广州市外来入侵植物共有38科112属144种,比2008年分别增加了40.7%、89.8%和97.3%。新增加的71种植物主要有豆科（Fabaceae） 14种、菊科（Asteraceae） 13种、旋花科（Convolvulaceae） 6种、禾本科（Poaceae） 6种和茜草科（Rubiaceae） 5种。外来入侵植物主要来源于美洲（共104种）,多为陆生草本植物。广州约一半以上的外来植物是通过人为有意引进,进而形成入侵的。恶意和严重入侵的植物种类约占入侵物种总数的40%,表明广州的城市森林生态系统已经面临着严重威胁。因此,需加强对广州市外来植物入侵动态的监测,提高对外来陆生草本植物引入危害风险的评估,并开展对外来入侵植物资源开发和利用的研究,以构建稳定的生态安全格局,保障绿色生态城市建设。     

Assessing the risks of plant invasions arising from collections in tropical botanical gardens

Tropical botanical gardens have played an important role in the distribution, naturalisation and spread of non-native plants worldwide. Appropriate guidance relating to risk assessments of established botanical garden collections is often scarce. This paper uses the Amani Botanical Garden (ABG), Tanzania, as a case study to highlight appropriate methods to assess the risks posed by existing and future collections in tropical botanical gardens. Key considerations included field assessments of species status using accepted definitions of naturalisation, spread and invasion, distinguishing between intentionally and unintentionally introduced species, identifying taxonomic patterns in invasion status, assessing patterns in habitats colonised, and determining how knowledge of invasion elsewhere might be useful in forecasting risk. Out of the 214 alien plant species surviving from the original plantings in the early 20th century, 35 had only regenerated, 38 had locally naturalised while 16 had spread widely in the botanical garden. A further 16 species with unclear introduction records in the garden were also found to be naturalised. A greater proportion of introduced species were potentially invasive than might be expected from previous analyses of global floras. Overall, just over half of all naturalised and spreading species were also observed in forest fragments and edges. The proportion of species that had been recorded elsewhere as naturalised/invasive was significantly related to their status in ABG, with 94% of spreading species and 79% of naturalising species being recorded as naturalised or invasive elsewhere, compared to 57% of species that were only regenerating and 49% of species only surviving. Recommendations for further risk assessments of botanical garden collections are discussed.     

Nutritional and Morphological Traits of Invasive and Exotic Fleshy‐fruits in South Africa

While fleshy‐fruited invasive alien plants are recognized as some of the worst invaders on a global scale, until recently, little consideration has been given to the frugivores that feed on these fruits and, more specifically, the fruit traits, which may influence this. We investigated a series of morphological and nutritive fruit traits for ca 30 species of fleshy‐fruited invasive alien and exotic species in South Africa. Invasive alien fruit traits were compared with comparable traits of a similar sample size of indigenous fleshy fruits, which occur in the same area. Finally, the similarity of traits for the same invasive alien species was compared with those fruits in Australia. Invasive alien fleshy fruits were similar in morphology, but greater in some nutritive aspects when compared with indigenous fruits. Furthermore, they were very similar in all aspects to their counterparts in Australia. Most seeds of invasive fleshy fruits were small and light, which may explain some of their invasive success, as benefits associated with small seededness may promote invasive potential. Nutritionally, most invasive alien fleshy‐fruits were hexose‐dominant, containing low lipid and nitrogen content. While frugivore preference trends remain to be formally investigated, this study provides insights into fruit traits, which may tentatively outline why invasive fruits are universally fed on and thus successfully spread.     

Widespread plant species: natives versus aliens in our changing world

Estimates of the level of invasion for a region are traditionally based on relative numbers of native and alien species. However, alien species differ dramatically in the size of their invasive ranges. Here we present the first study to quantify the level of invasion for several regions of the world in terms of the most widely distributed plant species (natives vs. aliens). Aliens accounted for 51.3% of the 120 most widely distributed plant species in North America, 43.3% in New South Wales (Australia), 34.2% in Chile, 29.7% in Argentina, and 22.5% in the Republic of South Africa. However, Europe had only 1% of alien species among the most widespread species of the flora. Across regions, alien species relative to native species were either as well-distributed (10 comparisons) or more widely distributed (5 comparisons). These striking patterns highlight the profound contribution that widespread invasive alien plants make to floristic dominance patterns across different regions. Many of the most widespread species are alien plants, and, in particular, Europe and Asia appear as major contributors to the homogenization of the floras in the Americas. We recommend that spatial extent of invasion should be explicitly incorporated in assessments of invasibility, globalization, and risk assessments.     

中国外来入侵植物的等级划分与地理分布格局分析

基于文献报道、野外调查、标本记录和必要的分类学考证, 整理出我国外来入侵植物72科285属515种。根据外来入侵种的生物学与生态学特性、自然地理分布、入侵范围以及所产生的危害, 将其划分为5类: 即恶性入侵类(34种)、严重入侵类(69种)、局部入侵类(85种)、一般入侵类(80种)和有待观察类(247种)。通过地理分布格局分析, 中国外来入侵植物主要分布在我国西南及东部沿海地区, 并进一步扩散到内陆各省。中国外来入侵等级划分和地理分布格局可以作为外来入侵植物风险防范和管理的依据。本工作提供我国外来入侵植物的本底资料的同时, 还对主要外来入侵植物的管理提出了具体建议。