Global patterns of diversity in the urban forest: Is there evidence to support the 10/20/30 rule?

Diversity in the urban forest is important as it reduces risks from pests and diseases and from climate change and improves resilience in the supply of ecosystem services. To manage and improve diversity, there has been wide-spread acceptance of the 10/20/30 ‘rule of thumb’ proposed by Santamour, which states that municipal forests should comprise no more than 10% of any particular species, 20% of any one genus or 30% of any single family. While the implementation of targets based on Santamour's rule has contributed to a more diverse and resilient urban forest in many cities, there has been little empirical investigation of actual patterns of diversity occurring globally in different climates and land uses. In this study, we explored diversity and the relative abundance of the most common species, genus and family in 151 urban forest inventories from 108 different cities around the world. Observed patterns showed that relative abundance of the most common taxon was a good predictor of diversity and could be a useful measure of diversity for urban forest managers. Relative abundance of the most common taxon was much higher than the proposed benchmark at the species level, but comparable with proposed benchmarks at the genus and family level. Patterns varied by both climate and land use. Diversity was consistently lower in Continental climates and in streetscapes, and higher in Temperate climates and in urban forests that spanned multiple land uses. Further considerations in setting diversity benchmarks are discussed.     

Different long-term and short-term responses of land snails to clear-cutting of boreal stream-side forests

Effects of clear-cutting on biodiversity have mainly been studied in the short-term, although knowledge of longer term effects are often more important for managers of forest biodiversity. We assessed relatively long-term effects of clear-cutting on litter dwelling land snails, a group with slow active dispersal and considered to be intolerant to microclimate changes. In a pair wise design we compared snail abundance, species density, and species composition between 13 old seminatural stream-side stands and 13 matched young stands developed 40-60 years after clear-cutting. Using a standardized semi-quantitative method, we identified all snail specimens in a 1.5 l subsample of a pooled litter sample collected from small patches within a 20 × 5 m plot in each stream-side stand. From the young stands a mean of 135 shells and 9.5 species was extracted which was significantly higher than the 58.1 shells and 6.9 species found in old forests. Only two of the 16 species encountered showed a stronger affinity to old than to young forests. In short-term studies of boreal stream-side forests land snail abundance is reduced by clear-cutting. Our results indicate that this decline is transient for most species and within a few decades replaced by an increase. We suggest that local survival in moist stream-side refugia makes the land snails able to benefit from the higher pH and more abundant non-conifer litter in young than in old boreal forests. Our results highlight the importance of longer term studies as a basis for management guidelines for biodiversity conservation.     

Effects of historical and present fragmentation on plant species diversity in semi-natural grasslands in Swedish rural landscapes

Habitat loss and fragmentation of natural and semi-natural habitats are considered as major threats to plant species richness. Recently several studies have pinpointed the need to analyse past landscape patterns to understand effects of fragmentation, as the response to landscape change may be slow in many organisms, plants in particular. We compared species richness in continuously grazed and abandoned grasslands in different commonplace rural landscapes in Sweden, and analysed effects of isolation and area in three time-steps (100 and 50 years ago and today). Old cadastral maps and aerial photographs were used to analyse past and present landscape patterns in 25 sites. Two plant diversity measures were investigated; total species richness and species density. During the last 100 years grassland area and connectivity have been reduced by about 90%. Present-day habitat area was positively related to total species richness in both habitats. There was also a relationship to habitat area 50 years ago for continuously grazed grasslands. Only present management was related to species density: continuously grazed grasslands had the highest species density. There were no relationships between grassland connectivity, present or past, and any diversity measure. We conclude that landscape history is not directly important for present-day plant diversity patterns in ordinary landscapes, although past grassland management is a prerequisite for the grassland habitats that can be found there today. It is important that studies are conducted, not only in very diverse landscapes, but also in managed landscapes in order to assess the effects of fragmentation on species.     

Exploiting the effect of dietary supplementation of small ruminants on resilience and resistance against gastrointestinal nematodes

This paper focuses on targeted nutritional supplementation as a means to reduce the requirement for chemotherapeutic control of gastrointestinal nematode infection of small ruminants and considers the limitations to practical application. Supplementary feeding, particularly with additional dietary protein, can assist resilience to infection during times when metabolic resources are being directed towards dealing with the pathophysiological effects of infection and away from production of meat, milk and fibre. Substantial experimental evidence from studies of both sheep and goats supports this hypothesis particularly in relation to young lambs and kids after weaning and in ewes around parturition. In addition, nutritional supplementation frequently increases resistance to infection, as indicated by decreased faecal worm egg counts and worm burdens. As a result, supplementation has the potential to reduce the requirement for anthelmintic treatment. Practical application of this knowledge can, however, be quite complex in many small ruminant production systems. In general, strategic supplementation should target those times when nutrient requirements are greatest and provide those nutrients which are deficient whether protein, energy, minerals or trace elements. Complexity arises when we consider that nutrient requirements will differ between localities for different species and breed of host, at different stages of growth and reproduction, with differing seasonal availability of forage, with different species of nematodes and different levels of established infections and exposure to infective stages. As a starting point, the provision of nutrients to optimize rumen function and animal performance in the particular production system should assist in maintaining resilience to nematode infection. Provision of nutrients in excess of this requirement, if economically feasible, may yield further benefits in some situations and reduce the need for alternative control measures for gastrointestinal nematode parasites.     

云南省蚕豆抗逆简化栽培技术

总结了一套云南省蚕豆抗逆简化栽培技术,包括品种选择、开沟整地、规格播种、科学管水、合理施肥、中耕除草、整枝摘心、植物保护、适时采收、密闭储藏等措施。     

Risk and economic sustainability of crop farming systems

In economic terms, resilience in farming has to do with the capacity of a farm business to survive various risks and other shocks. Despite its importance, resilience has seldom been directly considered in evaluations of economic sustainability. A whole-farm stochastic simulation model over a 6-year planning horizon was used to analyse organic and conventional cropping systems using a model of a representative farm in Eastern Norway. The relative economic sustainability of alternative systems under changing assumptions about future technology and price regimes was examined in terms of financial survival to the end of the planning period. The same alternatives were also compared in terms of stochastic efficiency. To model the risk of business failure adequately there is a need to deal with the risk of bankruptcy, and a modification of traditional analysis was used for that purpose. The organic farming system was found to be somewhat less economically sustainable than the conventional system, especially if the organic price premiums and the organic area payments were to be phased out. The results illustrate possible conflicts between pursuit of risk efficiency and economic sustainability. The model developed could be used to support farmers’ choices between farming systems as well as to help policy makers develop more sharply targeted policies.     

Response of microbial community composition and activity in agricultural and grassland soils after a simulated rainfall

Rainfall in Mediterranean climates may affect soil microbial processes and communities differently in agricultural vs. grassland soils. We explored the hypothesis that land use intensification decreases the resistance of microbial community composition and activity to perturbation. Soil carbon (C) and nitrogen (N) dynamics and microbial responses to a simulated Spring rainfall were measured in grassland and agricultural ecosystems. The California ecosystems consisted of two paired sets: annual vegetable crops and annual grassland in Salinas Valley, and perennial grass agriculture and native perennial grassland in Carmel Valley. Soil types of the respective ecosystem pairs were derived from granitic parent material and had sandy loam textures. Intact cores (30 cm deep) were collected in March 1999. After equilibration, dry soil cores (approx. −1 to −2 MPa) were exposed to a simulated Spring rainfall of 2.4 cm, and then were measured at 0, 6, 24, and 120 h after rewetting. Microbial biomass C (MBC) and inorganic N did not respond to rewetting. N₂O and CO₂ efflux and respiration increased after rewetting in all soils, with larger responses in the grassland than in the agricultural soils. Phospholipid fatty acid (PLFA) profiles indicated that changes in microbial community composition after rewetting were most pronounced in intensive vegetable production, followed by the relict perennial grassland. Changes in specific PLFA markers were not consistent across all sites. There were more similarities among microbial groups associated with PLFA markers in agricultural ecosystems than grassland ecosystems. Differences in responses of microbial communities may be related to the different plant species composition of the grasslands. Agricultural intensification appeared to decrease microbial diversity, as estimated from numbers of individual PLFA identified for each ecosystem, and reduce resistance to change in microbial community composition after rewetting. In the agricultural systems, reductions in both the measures of microbial diversity and the resistance of the microbial community composition to change after a perturbation were associated with lower ecosystem function, i.e. lower microbial responses to increased moisture availability.     

Do secondary forests act as refuges for old growth forest animals? Recovery of ant diversity in the Atlantic forest of Brazil

The extent to which secondary forests occupying degraded and abandoned lands provide suitable habitat for forest-adapted species is an important conservation issue in times of vanishing old growth forests. We used ants (Hymenoptera: Formicidae), a functionally important and diverse group of invertebrates, to investigate the recovery of soil taxa during secondary forest succession in the Atlantic Forest of Southern Brazil. We compared the resilience of epigeic vs. hypogeic ant assemblages. For this purpose we established 27 sites that encompassed a chronosequence from pastures to old growth forests on two contrasting soil types. Our results are based on a collection of 35 508 individuals in 40 genera.Richness and composition of ant assemblages in secondary forests have recovered slowly and have not approached conditions typical of old growth forests. The distribution of genera along the successional stages was arranged in a nested pattern where ant genera of younger successional stages were a subset of genera present in older stages. Edaphic conditions had no influence on the recovery process. Overall, richness of ants was lower at study sites with water-logged soils than at sites where soils did not exhibit hydromorphic properties. The hypogeic ant assemblage recovered more slowly than the epigeic assemblage.Our results show that secondary forests do not act as refuges for many forest-adapted animals which are currently restricted to discontinuous patches of old growth forest in the highly endangered Atlantic Forest of Brazil. Moreover, estimated recovery times of 50 to several hundred years suggest it would take much longer than previously presumed for complete recolonization.     

迷宫流道内沙粒壁面碰撞模拟与PTV实验

以单个沙粒为对象,研究了沙粒与灌水器流道壁面的碰撞过程.采用计算流体力学CFD数值模拟方法,分析了沙粒与壁面碰撞反弹系数Rc对灌水器抗堵性能的影响.结果表明,反弹系数对灌水器抗堵性能影响较大.利用粒子跟踪测速技术PTV,观测了复杂迷宫流道内沙粒与壁面碰撞过程,测定了不同压力点下矩形流道的碰撞反弹系数,为灌水器数值模拟时反弹系数的设定提供了实验依据,从而可以更加准确评估灌水器抗堵性能.