A time series of urban forestry in Los Angeles

There has been an increasing interest in the evolution of urban forests. This research uses historic and digital aerial photography to quantify changes in tree density in Los Angeles, California since the 1920’s. High-resolution geographic information system analysis (4 to 6 time periods) of three regions (San Fernando Valley, Hollywood, Los Angeles Basin) of Los Angeles reveals that there has not always been an increase in tree density with time. Tree densities on public and private land were highest in the 1940’s in Hollywood, while the San Fernando Valley and Los Angeles Basin experienced a near linear increase in tree density on both private and public land since the 1920’s. When historic tree density reconstructions were examined for the 15 Los Angeles city council districts from the 1920’s, 1950’s and 2006, most districts in Los Angeles have experienced a significant increase in tree density, however, there has been wide variation in tree densities among city council districts. Trees densities have generally been higher on private land since the 1920’s and currently tree densities on private land are significantly higher than on public land. Results suggest the evolution of urban forests in Los Angeles mirrors the dynamics of urban forests in desert and grassland cities. It is possible to reconstruct the development of urban forests in sections of cities using historic and contemporary aerial photography. We estimated that Los Angeles averages approximately 104 trees per hectare (82 private land, 22 public land) based on 2006 imagery at 0.3 m resolution, however, field validation suggests that we identified only 73% of trees. Although there is still space to plant trees on public land, private land owners will need to be heavily involved in order to achieve the goals of Los Angeles’ Million Tree Initiative.     

Urban growth patterns and growth management boundaries in the Central Puget Sound, Washington, 1986–2007

Many regions of the globe are experiencing rapid urban growth, the location and intensity of which can have negative effects on ecological and social systems. In some locales, planners and policy makers have used urban growth boundaries to direct the location and intensity of development; however the empirical evidence for the efficacy of such policies is mixed. Monitoring the location of urban growth is an essential first step in understanding how the system has changed over time. In addition, if regulations purporting to direct urban growth to specific locales are present, it is important to evaluate if the desired pattern (or change in pattern) has been observed. In this paper, we document land cover and change across six dates (1986, 1991, 1995, 1999, 2002, and 2007) for six counties in the Central Puget Sound, Washington State, USA. We explore patterns of change by three different spatial partitions (the region, each county, 2000 U.S. Census Tracks), and with respect to urban growth boundaries implemented in the late 1990’s as part of the state’s Growth Management Act. Urban land cover increased from 8 to 19% of the study area between 1986 and 2007, while lowland deciduous and mixed forests decreased from 21 to 13% and grass and agriculture decreased from 11 to 8%. Land in urban classes outside of the urban growth boundaries increased more rapidly (by area and percentage of new urban land cover) than land within the urban growth boundaries, suggesting that the intended effect of the Growth Management Act to direct growth to within the urban growth boundaries may not have been accomplished by 2007. Urban sprawl, as estimated by the area of land per capita, increased overall within the region, with the more rural counties within commuting distance to cities having the highest rate of increase observed. Land cover data is increasingly available and can be used to rapidly evaluate urban development patterns over large areas. Such data are important inputs for policy makers, urban planners, and modelers alike to manage and plan for future population, land use, and land cover changes.     

A comparative study of urban fragmentation patterns in small and mid-sized cities of Idaho

Urbanization has a massive impact on ecological function and impedes the provisioning of environmental services. The interaction between urbanization and the environment has been researched extensively. However, the existing research focused on the urbanization characteristics of large metropolitan areas. In this paper, we investigate the urban fragmentation patterns of small and mid-sized cities in Idaho, USA. To capture the urban morphology for each site within the study we use both concentric ring and transect analysis as well as several spatial/landscape metrics. Our results show that the characteristics of urbanization in small and mid-sized cities (and those in second-tier regions that attract relatively little scholarly attention) are consistent with growth phase theory of urbanization, urbanization along a gradient, and urbanization patterns of metropolises.     

Alien plant species do have a clear preference for different land uses within urban environments

Since neophytes can become invasive in the future, untangling their ecological preferences is of paramount importance, especially in urban areas where they represent a substantial proportion of the local flora. Studies exploring alien species assemblages in urban environments are however scarce. This study aims to unravel alien plant species preferences for five urban land uses (densely built-up areas, open built-up areas, industrial areas, broadleaved urban forests, and agricultural areas and small landscape elements). We took the city of Brussels as a model, in which we recorded all vascular species growing spontaneously in grid cells of 1 km². We tested two different ways of classifying the 1-km² cells: (1) We simply associated each cell with its dominant land cover; (2) We used a fuzzy approach for which the degree of association of a given cell to a given land cover depended on the proportion of that land cover within the cell. For both classification methods, we calculated the indicator species of the resulting land cover types based on alien species only. The crisp and fuzzy classifications identified 33 and 49 species, respectively, with a clear preference for some urban land use types (from a total of 129 alien plant species analyzed). Results showed that urban land use types having apparently similar environmental conditions can actually harbor different neophyte assemblages. Fine-tuning the categorization of urban environments in future ecological studies is therefore important for understanding spatial patterns of alien species occurrence.     

The rise (and fall?) of a state land bank

Land markets in most poor cities do not work very effectively and contribute to making social housing unaffordable. One once popular response was to set up a public land bank. In truth, few such banks were terribly successful and, with the onset of neo-liberalism, the approach fell out of fashion. However, one government recently established a state land bank in an attempt to slow the growth of illegal settlement and to improve housing conditions for the poor. Bogotá's efforts have had some measure of success although the agency could never achieve the ambitious goals set for it. The paper describes the different approaches of the agency over the last decade, the problems that it has faced and what it has managed to achieve. Today, the agency no longer buys land and prefers to work in association with private landowners; in effect, Bogotá no longer has a state land bank. However, what it does have is an interesting set of tools with which to confront land speculation and to discourage owners from holding on to serviced land. Whether this set of tools will be able to confront the perennial problem of providing land for affordable social housing remains to be seen. Nevertheless, Bogotá provides many lessons for governments in poorer cities about how and why they should take measures to improve the working of the land market.     

Methods for spatial and temporal land use and land cover assessment for urban ecosystems and application in the greater Baltimore-Chesapeake region

Understanding contemporary urban landscapes requires multiple sets of spatially and temporally compatible data that can integrate historical land use patterns and disturbances to land cover. This paper presents three principal methods: (1) core analysis; (2) historic mapping; and (3) gradient analysis, to link spatial and temporal data for urban ecosystems and applies their use in the Baltimore-Chesapeake region. Paleoecological evidence derived from the geochronology of sediment cores provides data on long-term as well as recent changes in vegetative land cover. This information, combined with contemporary vegetation maps, provides a baseline for conducting trend analyses to evaluate urbanization of the landscape. A 200-year historical land use database created from historical maps, census data, and remotely sensed data provides a spatial framework for investigating human impacts on the region. A geographic information system (GIS) integrates core analyses with historic data on land use change to yield a comprehensive land use and land cover framework and rates of change. These data resources establish the regional foundation for investigating the ecological components of an urban ecosystem. Urban-rural gradient analyses and patch analyses are proposed as the most appropriate methods for studying the urban ecosystem as they link ecological and social patterns and processes for varying degrees of urbanization.     

Urban forest cover of the Chicago region and its relation to household density and income

Urban forests and herbaceous open space play a vital role in the environmental and aesthetic health of cities, yet they are rarely identified in land-use inventories of urban areas. To provide information on urban forests and other vegetative land cover in Illinois cities, Landsat Thematic Mapper (TM) data from June 27, 1988, were classified for the Chicago metropolitan region (9,717 km²). Ten land-cover classes were identified, including two types of forestland (occupying 5.8% of the total area), residential land with trees (14.6%) or without trees (7.8%), cropland (37.5%), two types of grassland (7.7%), urban with impervious surfaces (23.1%), water (1.6%), and miscellaneous vegetation (2.1%). Correlation analyses indicated that household income and household density are strongly related to land covers in the region, particularly those with tree cover and urbanized land. Population changes for 1980–1985 and 1985–2010 (projected) show a pattern of increasing density in the urbanized zone concurrent with continued urban sprawl, primarily into current cropland.     

Spatial disintegration and arable land security in Egypt: A study of small- and moderate-sized urban areas

While commonly associated with regional ‘mega-cities’, rapid urbanization in the less-developed world has also begun to define growth in small- and moderate-sized settlements on the periphery of major metropolitan areas. The dispersal of population growth to these smaller areas holds significant implications for environmental, economic, and social health, and threatens local food security, increases congestions, and induces difficulty in service provision. This study examines the effects of spatial disintegration and rapid urbanization in the stock of arable land in Egypt. To assess this issue, the study will meet three objectives. First, we evaluate the relationship between population growth and urban land cover expansion in small- and moderate-sized settlements in Egypt. Second, we consider the role of selected geographic determinants in influencing the growth of these areas through the use of a regression model. The selection of an appropriate model type is a sub-objective and will be discussed further. Third, these drivers of growth will be assessed through their effects on the country’s stock of arable land. These objectives will be met through the development and application of the regression models, in order to examine the relationship between urban land expansion and several independent variables. An increase in population is found to have a positive and statistically significant effect on corresponding urban land cover area. Surprisingly, the variables commonly associated with urbanization in Egypt - proximity to major roads, the capital of Cairo, and the Nile River - though exhibiting a positive relationship with urban growth, are not statistically significant in the selected case studies. This research underlines the necessity for a combined approach to policy formation - with input from policy fields as varied as agriculture, urban planning, and land reclamation - to slow outward growth and maintain arable land stocks.     

Spatiotemporal patterns of urbanization over the past three decades: a comparison between two large cities in Southwest China

China’s economic development over the past three decades has been remarkable due to the establishment of the “Reform and Opening-up” program. Meanwhile, urbanization, one of the most intensive human activities, has significantly changed the land cover across China. Here we used remote sensing data and landscape metrics to explore the spatiotemporal patterns of urbanization in two large Chinese cities, Chengdu (1978–2010) and Chongqing (1976–2010). Results suggested that urban land in both cities experienced a significant growth and became 9.8 and 6.3 times larger than the initial for Chengdu and Chongqing, respectively. The edge-expansion was the major urban growth form for both cities, accounting for more than 40 % of total three types (i.e., edge-expansion, infilling, and outlying) although fluctuating during the whole period. Both cities started a spurt growth in the 1990s although the starting times were different (1992 and 1996 for Chengdu and Chongqing, respectively) because of different policies. Spatial distribution of the newly developed urban lands was largely constrained by topography. Landscape analysis not only revealed an increasing fragmentation and complexity in the study area under the impact of urbanization, but also tested the hypothesis on urbanization patterns.     

Estimating stormwater runoff for community gardens in New York City

Community gardens are critical ecological infrastructure in cities providing an important link between people and urban nature. The documented benefits of community gardens include food production, recreational opportunities, and a wide number of social benefits such as improving community stability, reducing crime, and physical and mental health benefits. While much of the literature cites community gardens as providing environmental benefits for cities, there is little empirical evidence of these benefits. Here we examine the stormwater runoff benefits of community gardens by comparing two methods to estimate absorption rates of stormwater runoff in urban community gardens of New York City. The first method uses general land cover classes as determined by a land cover dataset; the second methods adds a land cover specific to community gardens — raised beds, typically used for food production. We find that in addition to the stormwater mitigation performed by pervious surfaces within a garden site, community gardens in New York City may be retaining an additional 12 million gallons (~45 million liters) of stormwater annually due to the widespread use of raised beds with compost as a soil amendment.     

Environmental and social predictors of phosphorus in urban streams on the Island of Montréal,Québec

Researchers have identified the importance of social characteristics for understanding ecological patterns in cities but the use of these characteristics in urban stream research has yet to be fully explored. Urban development is currently the second-largest cause of stream impairment in North America due in part to nutrient loading. However, research into factors that influence nutrient concentrations in urban streams is lacking. We sampled seven streams on the island of Montréal daily to measure phosphorus (P) concentration and P flux in each stream. We then compared stream P concentration and flux to several watershed characteristics commonly used to predict stream nutrients (e.g., watershed imperviousness, land use, existence of a riparian buffer) as well as several socio-economic characteristics of the watersheds (e.g., average home value, median household income). Overall, impervious surface cover and measures of land use were most effective at explaining the variation in P concentration and P flux in streams on the island of Montréal, while the riparian buffer and socio-economic variables were less effective. However, dollars spent on fertilizer per hectare of residential land and percent residential land use became important predictors of stream P concentration when impervious surface cover was removed from the regression model. This suggests that after accounting for the impact of physical watershed characteristics, social factors may be important predictors of urban stream P concentration. The results of our study suggest that more research is needed to determine the role that socio-economic variables play with respect to urban stream P.     

Relationships between landscape pattern metrics,vertical structure and surface urban Heat Island formation in a Colorado suburb

Change in land surface temperature (LST) due to urbanization is a critical influence on the ecohydrological function and human health in cities. Past research has emphasized land cover composition and planimetric landscape pattern as drivers of LST patterns, but there have been few empirical studies examining the effects of vertical structure on thermal variation in cities. We used agglomerative cluster analysis to group 5 ha grid cells with similar land cover composition from high-resolution land cover data for our Aurora, Colorado, USA study area. We then compared the importance of different planimetric landscape pattern metrics and lidar-derived vertical structure variables as predictors of LST estimated from Landsat 5 thermal band data for each group. Variation in LST between cluster groups was analyzed with landscape and vertical structure data using random forest regression models and conditional variable importance metrics. Cluster analysis produced 7 distinct groups differing in land cover composition, planimetric landscape pattern, and vertical structure. Clusters with greater tree cover and higher mean tree height were generally cooler, while the height difference between buildings and trees had high conditional variable importance in random forest regression models. We found that the specific planimetric landscape pattern and vertical structure metrics most important for individual clusters differed, suggesting that the relative importance of variables depends on land-use and land cover. Our results highlight the importance of including vertical structure in empirical analyses of urban LST.     

The impact of forest to urban land conversion on streamflow, total nitrogen, total phosphorus, and total organic carbon inputs to the converse reservoir, Southern Alabama, USA

High total organic carbon (TOC) concentrations in Converse Reservoir, a water source for Mobile, Alabama, have concerned water treatment officials due to the potential for disinfection byproduct (DBP) formation. TOC reacts with chlorine during drinking water treatment to form DBPs. This study evaluated how increased urbanization can alter watershed-derived total nitrogen (TN), total phosphorus (TP) and TOC inputs to the Converse Reservoir. Converse Watershed, on the urban fringe of Mobile, is projected to undergo urbanization increasing watershed urban land from 3% in 1992 to 22% urban land by 2020. A pre-urbanization scenario using 1992 land cover was coupled with 2020 projections of land use. The Loading Simulation Program C++ watershed model was used to evaluate changes in nutrient concentrations (mg L^?1) and loads (kg) to Converse Reservoir. Urban and suburban growth of 52 km² simulated from 1991 to 2005 (15 year) caused overall TN and TP loads to increase by 109 and 62%, respectively. Simulated urban growth generally increased monthly flows by 15%, but resulted in lower streamflows (2.9%) during drought months. Results indicate that post-urbanization median TN and TP concentrations were 59 and 66% higher than corresponding pre-urbanization concentrations, whereas TOC concentrations were 16% lower. An increase in urban flow caused TOC loads to increase by 26%, despite lower post-urbanization TOC concentrations.     

A spatial analysis of indigenous cover patterns and implications for ecological restoration in urban centres,New Zealand

High levels of endemism, the sensitivity of species that have evolved without humans, and the invasion of exotic species have all contributed to severe depletion of indigenous biodiversity in New Zealand. We considered the contribution that urban restoration can make to maximising biodiversity by analysing landcover patterns from two national databases along an urban–rural gradient. Thirteen of 20 land environments in New Zealand are represented in cities, and nearly three-quarters of all acutely threatened land environments are represented within 20 km of city cores nationally. Despite this, remaining indigenous landcover is low within urban cores, with less than 2% on average, but increasing to more than 10% on average in the periurban zone. Threatened lowland environments are most commonly represented within cities, and least represented within protected natural areas. Restoration of existing urban habitat is insufficient to halt biodiversity loss. Ecosystem reconstruction is required to achieve a target of 10% indigenous cover within cities. A co-ordinated national urban biodiversity plan to address issues beyond a local and regional focus is needed. Analysis of national patterns of urban land environments, indigenous cover and remnant ecosystems will support action at a regional and local level while enhancing national and global biodiversity goals.     

Land use dynamics and ecological transition: the case of South Florida

This study examines the process of land use change in South Florida. Through this discussion, a conceptual model of ecological transition is developed and presented. The model is built on the general principles of neoclassical economic theories of land rent, behavioral models of resource use, and an historical geographic account of environmental change. Central to the paper is the specification of the theoretical link between demographics, market and service demands, land use, and ecological change. This study focuses on the nature and drivers of environmental change that has occurred in South Florida since 1900. The region studied includes the southern Florida Everglades and the surrounding area. The analysis determines that massive land useland cover has taken place in the region, particularly since the end of World War II. These landscape changes are conceptualized by a model that links regional demand for both agricultural and residential land through the agency of hierarchical forces. In this model, landscape evolution and natural areas encroachment are articulated as a dynamic process in which the regime of interaction between human systems and land use changes. Three main time periods for regional ecological transition are defined: (1) frontier closure (2) articulation of a system of cities with coupled agricultural hinterlands serving national and international markets. Differing land use change dynamics are identified as specific to each time period.     

Biodiversity conservation implications of landscape change in an urbanizing desert of Southwestern Peru

Internal migration from the Peruvian highlands and rural areas has burdened urban areas with rapid growth. Urban expansion is threatening the desert habitat and unique vegetation communities surrounding Arequipa, one of Peru's largest cities. A 511 ha tract contiguous to the city of Arequipa has been informally designated an ecological park. Analysis of Landsat satellite imagery over a 16-year interval indicates that urban expansion is occurring in the direction of the park. The land use/land cover change analysis revealed other landscape patterns and processes, such as agricultural expansion, which are relevant to the study area. These dynamics, plus principles of landscape ecology, suggest that the park's size and shape may not be the most suitable. Conservation alternatives include the expansion of the park, the spatial connection to another nature reserve, or the design of co-management strategies. Given local historical events and the paucity of regional conservation efforts, social actors in Arequipa and in national governmental institutions will need to find practical ways to collaborate.     

Long-term urbanization effects on tree canopy cover along an urban–rural gradient

Urban forestry can benefit from improved knowledge of urbanization??s effects on tree canopy cover (TCC), a prominent urban forest indicator. This study examined changes in TCC over a long time frame, with respect to land cover (LC) changes, and across municipal boundaries. Specifically, I used air photos at 14 dates from 1937 to 2009 to develop an exceptionally long record of TCC change in Minnesota??s Twin Cities Metropolitan Area. During the study period overall TCC nearly doubled from 17% to 33% while the proportion urban land cover rose by 47%, highlighting the opportunity for substantial TCC gains following urbanization in previously agricultural landscapes, even in regions that were forested prior to European settlement. Results demonstrate that more intensely developed sites generally had lower TCC, and older urban sites had higher TCC. Modern TCC was not adequately characterized by linear distance along the urban?Crural gradient, but instead peaked near the center of the gradient where mature residential neighborhoods are prevalent. Compared to other land cover changes, urbanization events caused the highest rate of immediate TCC loss (9.6% of events), yet urban areas had the second highest TCC (>35%) in 2009, indicating that urban land gained TCC relatively efficiently following development. The results of this study provide new historical context for urban forest management across an urban?Crural gradient, and emphasize the need to consider ecological legacies and temporal lags following land cover changes when considering TCC goals in urban settings.     

Modeling above-ground carbon storage: a remote sensing approach to derive individual tree species information in urban settings

Vegetation has gained importance in respective debates about climate change mitigation and adaptation in cities. Although recently developed remote sensing techniques provide necessary city-wide information, a sufficient and consistent city-wide information of relevant urban ecosystem services, such as carbon emissions offset, does not exist. This study uses city-wide, high-resolution, and remotely sensed data to derive individual tree species information and to estimate the above-ground carbon storage of urban forests in Berlin, Germany. The variance of tree biomass was estimated using allometric equations that contained different levels of detail regarding the tree species found in this study of 700 km², which had a tree canopy of 213 km². The average tree density was 65 trees/ha per unit of tree cover and a range from 10 to 40 trees/ha for densely urban land cover. City-wide estimates of the above-ground carbon storage ranged between 6.34 and 7.69 tC/ha per unit of land cover, depending on the level of tree species information used. Equations that did not use individually localized tree species information undervalued the total amount of urban forest carbon storage by up to 15 %. Equations using a generalized estimate of dominant tree species information provided rather precise city-wide carbon estimates. Concerning differences within a densely built area per unit of land cover approaches using individually localized tree species information prevented underestimation of mid-range carbon density areas (10–20 tC/ha), which were actually up to 8.4 % higher, and prevented overestimation of very low carbon density areas (0–5 tC/ha), which were actually up to 11.4 % lower. Park-like areas showed 10 to 30 tC/ha, whereas land cover of very high carbon density (40–80 tC/ha) mostly consisted of mixed peri-urban forest stands. Thus, this approach, which uses widely accessible and remotely sensed data, can help to improve the consistency of forest carbon estimates in cities.     

Predicting tree species richness in urban forests

There has been an increasing interest in urban forests and the levels of biodiversity they contain. Currently there are no spatially explicit maps of tree species richness in urban areas. This research tests and identifies GIS and remote sensing metrics (climate, area, productivity, three-dimensional structure) hypothesized to be associated with species richness in native forests and identifies methods that can be applied to predict and map tree species richness in cities. We quantified tree species richness, floristic composition, and structure in 28 1-ha plots in the city of Los Angeles. Climate and remote sensing metrics from high-resolution aerial imagery (10 cm), QuickBird (60 cm), Landsat (30 m), MODIS (250 m), and airborne lidar (2 m) were collected for each plot. There were 1208 individual stems and 108 trees identified to species. Species richness ranged from 2 to 31 species per ha and averaged 17 species per ha. Tree canopy cover from QuickBird explained the highest portion of variance (54%) in tree species richness followed by NDVI from Landsat (42%). Tree species richness can be higher in residential urban forests than native forests in the United States. Spatially explicit species richness maps at 1 ha can be created and tested for cities in order to identify both hotspots and coldspots of tree species richness and changes in species richness over time.