The energy savings produced could be used to assign an economic value to the micro-climate regulating services provided by the green space. Animal-mediated pollination is an important ecological process that supports many benefits . For example, bee pollination can increase agricultural crop quantity, food quality, and market value . However, bee populations have been declining due to pollution, higher pathogen prevalence, and lower genetic diversity . Additionally, development and urbanization cause habitat fragmentation which can lead to changes in species and functional diversity .Pollinators, such as bees and birds, can connect these habitat patches as they move along plants to feed and collect pollen . Increased suitable habitat and connectivity may facilitate the recovery of pollinator populations and create more resilient communities that can recover from disturbances, e.g. disease or long periods of intense drought . Habitat patches have been shown to maintain distinct bee communities that, in aggregate, retain a significant amount of local species diversity . The value of pollination services is typically associated with increases in agricultural productivity ,vertical grow rack but has also been evaluated in urban settings. Breeze et al. estimated WTP for non-market pollination services in the United Kingdom using a discrete choice experiment. Their estimates suggest taxpayers are willing to pay 13.4£ annually per person to maintain these benefits.
Visual indicators for potential pollination services include the presence of animal-pollinators as well as flowering plants. Quantification of this service requires data on the frequency of animal-to-flower visits as well as connectivity among NTS and other areas.NTS can have built-in, public spaces that human communities can utilize. Walking trails, bike lanes, benches, and wildlife viewing sites can provide recreational services . Urban green spaces have been linked to improvements in physical and mental health . They have also been linked to more active and healthy lifestyles overall . In Los Angeles County, which has the third highest population density in California , these types of spaces can be important in the midst of a denselypopulated and highly-urban area. The travel cost method is most often used to calculate the value of recreational services, but it may not be appropriate for hyper-local neighborhood amenities because of little-to-no cost associated with access . Contingent valuation and hedonic pricing have also been employed . The latter alludes to an equity question regarding who is paying for these spaces and who is benefitting from them. In Porto, Portugal, Graça et al. found that lower socioeconomic areas have the most green space but they are unlikely to be developed in ways that provide services to the community. This suggests that recreational services provided by green spaces can be a luxury.NTS present an opportunity for education and public outreach regarding storm water issues, pollution, watershed and urban ecology, urban planning and management, and climate change. For example, Ocean View Growing Grounds is a community garden within a food desert in inland San Diego.
OVGG incorporates bioswales into its landscape, meant to prevent crops from flooding. UC San Diego researchers have partnered with community leaders to host outreach events about hydrology, soil, and urban ecology. Greater understanding and awareness of NTS and the services they provide may lead to safer gardening practices and more efficient water use. In Los Angeles, many of the sites have educational information posted about the project, their goals, and their motivations . As part of the Elmer Avenue Green Street project, local residents participated in the planning and design processes, actively engaging in storm water issues and how to address them. Scientific research on storm water issues have proven useful, especially in developing countries where water quality is often a main concern but resources and infrastructure for large treatment plants are lacking .NTS can introduce undesired services, such as installation of unattractive elements, accumulation of pollutants, and proliferation of disease vectors. The aesthetics of NTS may not be favorable to all people, especially when they are not regularly maintained. Southern California receives very little precipitation which can be fatal for plants that are not drought resistant. Additionally, plant communities in NTS by the ocean have an added stressor of salt . This may highlight the need for use of native vegetation in NTS in order to facilitate their survival. Whether or not they are also the most aesthetically-pleasing is subjective. Regular maintenance can, not only help plant survival, but also prevent build-up of debris and pollutants, which NTS are designed to intercept. Debris degrades aesthetic value but other pollutants can cause environmental damage. Heavy metals can leach into surrounding soil and groundwater . Ponding areas, that allow microbial communities to remove contaminants, can also provide habitat for mosquitoes which pose health hazards in the form of infectious diseases and allergies.
For example, two Los Angeles NTS sites had advisories about West Nile virus and its carriers. Vegetation and soil media can also provide habitat for urban pests, such as rodents and ticks . Increases in urban green space have been linked to decreases in violent crime , but may also provide spaces in which crime can happen, e.g. assault or vandalism. Several accounts of assault were cited in the South Los Angeles Wetland Park . Almost all of these issues can be avoided at some cost whether it is increased maintenance, more frequent monitoring, or a greater police presence. The main warning here is not that these costs are usually prohibitively expensive, but that they need to be considered when planning. In summary, NTS that rely on natural structures and functions, e.g. bio-retention systems and treatment wetlands, provide built ecosystems that can support a host of targeted and non-targeted benefits . While there are few data on the quantification of these benefits in NTS specifically, we can draw on examples from relevant systems to get an idea of how these processes may work and on what scale. There also exist many economic valuation techniques that can be employed to assign a value to these ecosystem services for incorporation into urban design and management. Cost is a component of NTS in which urban planners are likely interested. Total costs consist of planning and design, permitting, raw materials, installation, maintenance, and monitoring. Most NTS are implemented in order to meet water quality regulations and, although expensive, they may be cheaper than alternative approaches. Additionally, continued use of NTS may be a sign that their co-benefits can be significant. Long term monitoring is necessary in order to assess whether the benefits discussed in here truly exist.There are two distinct objectives that need to be addressed in order to assess ecosystem services associated with NTS: the first is to determine the quantity or rate at which the ecosystem service is provided ,vertical planting tower and the second is to determine the economic value of that quantity or rate. Targeted water services have been well-documented in laboratory settings but in situ, mesocosm studies are much fewer. Similarly, although non-targeted ecosystem services are acknowledged , quantitative field studies are only just beginning to emerge. Researchers from the University of California are currently working on an interdisciplinary project that assesses the form and function of urban storm water infrastructure in southern California, including potential ecosystem services . In the following section, we discuss three potential models for ecosystem services assessment in NTS: benefit transfer approaches, stochastic frontier analysis, and data envelopment analysis. Benefit transfer approaches can be used to assign physical and economic values to ecosystem services for cost-benefit analysis. The latter two approaches, represented by production frontier models, can assess how efficiently an NTS is providing ecosystem services which may be a useful assessment tool for environmental decision-makers. Although there are few data currently, these models can be used as a starting point and improved upon as more data become available.Meta-analyses provide a database on which a regression model can be built, determining the relationship between a dependent variable and multiple explanatory variables. Meta-analyses are a method of synthesizing results from multiple studies on similar topics . They are often utilized when many studies exist and interpretation of their results is difficult, and so synthesis of results can be a helpful tool . Meta-analyses can also be useful in contrasting situations in which very few studies exist for the target system but fall within the range of systems that have been studied. For example, a keyword search of “urban carbon” in the Environmental Valuation Reference Inventory yields 76 records but only 6 studies are specific to urban green space . Regression models can then be built upon the information collected during meta analyses. In the example case of ecosystem services associated with NTS, three categories of independent variables may be relevant: the biophysical and the socio-economic characteristics of the study site, and the study characteristics.
Examples of potential explanatory variables include study site size, geographic location, scale of the study , gross domestic product per capita, valuation method, and sample size. Benefit transfer approaches use regression models to provide an estimate of the dependent variable . In addition to benefit transfer based on a function estimated from a meta-analysis, a unit value or a function estimated from one study can also be used. However, the meta-analysis approach described here is preferable because it can account for differences between the policy and study sites. The “policy site” is the site of interest and “study sites” are those from which values have been transferred. The best benefit transfer estimate will be that between policy and study sites that are identical in terms of biophysical and socio-economic characteristics. However, there are generally discrepancies among commodities, currencies, user attributes, wealth measures, and cultural differences between policy and study sites that can lead to errors . Although primary studies are ideal, they are not always feasible, given the high cost of resources and time. It is useful for government agencies to sponsor studies across NTS that provide different quantities of ecosystem services and try to value that output in a way that is likely to be more accurate for a local context.Cost-benefit analysis, a widely-used tool for decision-making, compares the economic costs and benefits of one or more decisions . If the costs outweigh the benefits, then rational actors do not partake in the action, and vice-versa. However, there are additional factors that make decisions more complicated, such as the long- versus short-term, discounting, and positive and negative externalities. Cost-benefit analysis is often used in environmental decision-making but ecosystem services are often only included qualitatively because quantitative data do not exist . The use of benefit transfer approaches can help this process by taking a first-step towards economic valuation of ecosystem services.The SFA approach is a parametric economic modelling technique that allows for random shocks, or unpredicted events, within the model. The stochastic error term may make it suitable for urban systems that are subject to environmental variation, e.g. drought, precipitation events. SFA requires a priori assumptions regarding the production function form, i.e. the mathematical relationship between inputs and outputs , and the distribution of the unobserved technical inefficiency terms, which can substantially influence results. A considerable econometric literature has been developed to help determine the adequacy of the statistical fit of a particular model. The SFA approach provides a natural measure of how inefficient a particular NTS is at providing an ecosystem service relative to other NTS configurations. DEA is a nonparametric approach that does not allow for random shocks but it does not require prior knowledge of the production function form, which makes it useful for NTS-associated ecosystem services. DEA combines inputs and outputs into one efficiency score that can be easily compared, but it requires an additional regression model to identify the impacts of independent variables. Both DEA and SFA are capable of handling multiple outputs but in SFA, they must be collapsed into one basket of outputs whose weights can have a significant impact on results. One way to weight outputs is by their economic values. However, economic values for most ecosystem services associated with NTS have not been assigned, i.e. why benefit transfer approaches may be helpful. The lack of standardized monitoring data may make a nonparametric DEA approach more feasible at this time, in addition to the SFA requirement to specify a production function form. DEA also better handles multiple outputs relative to SFA and undesirable outputs, such as negative externalities .