Mechanistic Simulation of Tree Effects in an Urban Water Balance Model 1

Urbanization is responsible for some of the fastest rates of land-use change around the world, with important consequences for local, regional, and global climate. Vegetation, which represents a significant proportion of many urban and suburban landscapes, can modify climate by altering local exchanges of heat, water vapor, and CO 2 . To determine how distinct urban forest communities vary in their microclimate effects over time, we measured stand-level leaf area index, soil temperature, infrared surface temperature, and soil water content over a complete growing season at 29 sites representing the five most common vegetation types in a suburban neighborhood of Minneapolis-Saint Paul, Minnesota. We found that seasonal patterns of soil and surface temperatures were controlled more by differences in stand-level leaf area index and tree cover than by plant functional type. Across the growing season, sites with high leaf area index had soil temperatures that were 7°C lower and surface temperatures that were 6°C lower than sites with low leaf area index. Site differences in mid-season soil temperature and turfgrass ground cover were best explained by leaf area index, whereas differences in mid-season surface temperature were best explained by percent tree cover. The significant cooling effects of urban tree canopies on soil temperature imply that seasonal changes in leaf area index may also modulate CO 2 efflux from urban soils, a highly temperature-dependent process, and that this should be considered in calculations of total CO 2 efflux for urban carbon budgets. Field-based estimates of percent tree cover were found to better predict mid-season leaf area index than satellite-derived estimates and consequently offer an approach to scale up urban biophysical properties.

Section: Seasonal Patterns Of Lai and Microclimate Variablesmentioning

confidence: 68%

Influence of seasonality and vegetation type on suburban microclimates

Peters

McFadden

2010

“…The highest rainfall intensity was recorded for summer and autumn (the leafed period), while in winter (the leafless period) rainfall intensity was significantly lower. Rainfall of high intensity and short duration presents lower interception values than low intensity, long duration events (Scatena 1990;Veneklaas and Van Ek 1990;Xiao et al 1998;Wang et al 2008;Asadian and Weiler 2009), as shown in the leafless period at Ljubljana Meteorological Station (Fig. 3).…”

Section: Canopy Interception In Relation To Rainfall Characteristicsmentioning

confidence: 99%

Canopy precipitation interception in urban forests in relation to stand structure

Kermavnar

Vilhar

2017

Urban forests provide important ecosystem services. In terms of hydrological benefits, forest ecosystems in urban environments represent qualitative and quantitative filter for rainwater. We quantified the canopy interception in relation to urban forest stand structure and rainfall intensity in an urban transect of the mixed (upland) forest in the city centre, towards a riparian pine forest and a floodplain hardwood forest in the City of Ljubljana, Slovenia. Bulk precipitation in open areas and throughfall were measured with fixed rainfall collectors in each forest. Stemflow was estimated from a review of relevant literature. We found that canopy interception in selected urban forests was mainly affected by tree species composition and other stand structure variables, such as canopy cover and tree dimensions. Average annual canopy interception was highest in the mixed forest (18.0% of bulk precipitation), while the riparian pine forest had the lowest level (3.9% of bulk precipitation) and the floodplain hardwood forest had the intermediate level for interception (7.1% of bulk precipitation). The mixed forest exhibited the stand structure factors that contributed to the highest canopy interception among the studied forests: high assemblage of dominant coniferous trees, denser canopy cover and the highest growing stock. Furthermore, rainfall intensity has proven to be an important factor for the seasonal partitioning (comparing the leafed and leafless period) of canopy interception. A better understanding of precipitation interception processes in urban forests is needed to assist urban forest managing and planning, aiming at maximizing canopy interception for the mitigation of stormwater runoff and flooding in urbanized watershed.

“…Recently, several city-scale models have been developed to quantify some aspects of urban tree function, most commonly carbon and pollutant uptake, and shading (McPherson et al 2005;Nowak and Crane 2000;Nowak et al 2008). However, water use of urban trees has seldom been incorporated in models of the costs and benefits of urban trees (but see Wang et al 2008).…”

Section: Introductionmentioning

confidence: 99%

Drivers of variability in water use of native and non-native urban trees in the greater Los Angeles area

McCarthy

Pataki

2010

Trees in urban ecosystems are valued for shade and cooling effects, reduction of CO 2 emissions and pollution, and aesthetics. However, in arid and semi-arid regions, urban trees must be maintained through supplemental irrigation, in competition with other water needs. Currently, a comprehensive understanding of the factors which influence water use of urban tree species is lacking. In order to study the drivers of whole tree water use of two common species in the Los Angeles Basin urban forest, four sites in Los Angeles and Orange County were instrumented with sap flow and meteorological sensors. These sites allowed comparisons of the water use of a native riparian (Platanus racemosa Nutt.; California sycamore) and non-native (Pinus canariensis C. Sm.; Canary Island pine) Mediterranean species, as well as the spatial variability in water use under different environmental and management conditions. We found higher rates of sapflux (J O ) in native California sycamore as compared to non-native Canary Island pine. Within each species, we found considerable site-to-site variability in the magnitude and seasonality of J O . For Canary Island pine, the majority of inter-site variability derived from differences in water availability: response to vapor pressure deficit was similar during a period without water limitations. In contrast, California sycamore did not appear to experience water limitation at any site; however, there was considerable spatial variability in water use, potentially linked to differences in nutrient availability. Whole tree transpiration (E) was similar for the two species when water was not limiting, but Canary Island pine was able to withstand unirrigated conditions with a very low E. These results add to the currently small pool of data on urban tree water use and ecophysiology, and contribute to establishing a more quantitative understanding of urban tree function.