The importance of street trees to urban avifauna

Abstract

Street trees are public resources planted in a municipality's right-of-way and are a considerable component of urban forests throughout the world. Street trees provide numerous benefits to people. However, many metropolitan areas have a poor understanding of the value of street trees to wildlife, which presents a gap in our knowledge of conservation in urban ecosystems. Greater Los Angeles (LA) is a global city harboring one of the most diverse and extensive urban forests on the planet. The vast majority of the urban forest is nonnative in geographic origin, planted throughout LA following the influx of irrigated water in the early 1900s. In addition to its extensive urban forest, LA is home to a high diversity of birds, which utilize the metropolis throughout the annual cycle. The cover of the urban forest, and likely street trees, varies dramatically across a socioeconomic gradient. However, it is unknown how this variability influences avian communities. To understand the importance of street trees to urban avifauna, we documented foraging behavior by birds on native and nonnative street trees across a socioeconomic gradient throughout LA. Affluent communities harbored a unique composition of street trees, including denser and larger trees than lower-income communities, which in turn, attracted nearly five times the density of feeding birds. Foraging birds strongly preferred two native street-tree species as feeding substrates, the coast live oak (Quercus agrifolia) and the California sycamore (Platanus racemosa), and a handful of nonnative tree species, including the Chinese elm (Ulmus parvifolia), the carrotwood (Cupaniopsis anacardioides), and the southern live oak (Quercus virginiana), in greater proportion than their availability throughout the cityscape (two to three times their availability). Eighty-three percent of streettree species (n = 108, total) were used in a lower proportion than their availability by feeding birds, and nearly all were nonnative in origin. Our findings highlight the positive influence of street trees on urban avifauna. In particular, our results suggest that improved street-tree management in lower-income communities would likely positively benefit birds. Further, our study provides support for the high value of native street-tree species and select nonnative species as important habitat for feeding birds.

Exposure to airborne bacteria depends upon vertical stratification and vegetation complexity

“…These results could have important implications for landscape management and public health. Indeed, there have been widespread calls to improve urban ecosystem services by augmenting tree coverage (e.g., to help reduce urban heat island effects 42 , support wildlife 43 , 44 , improve sleep 45 , 46 , and capture precipitation to reduce flood risk 47 ). There is also a need to restore complex vegetation communities and host-microbiota interactions that provide multifunctional roles in urban ecosystems 37 , 48 , 49 .…”

Exposure to Airborne Bacteria Depends upon Vertical Stratification and Vegetation Complexity

“…These results could have important implications for landscape management and public health. Indeed, there have been widespread calls to improve urban ecosystem services by augmenting tree coverage (e.g., to help reduce urban heat island effects ( 40 ), support wildlife ( 41, 42 ), improve sleep ( 43, 44 ), and capture precipitation to reduce flood risk ( 45 )). There is also a need to restore complex vegetation communities and host-microbiota interactions that provide multifunctional roles in urban ecosystems ( 37, 46, 47 ).…”

Predicting Water Supply and Evapotranspiration of Street Trees Using Hydro-Pedo-Transfer Functions (HPTFs)

“…However, for predicting tree water supply, it becomes necessary to consider only the runoff of summer precipitation, because it might increase or decrease the amount of water supply. Thus, for each unit of the canopy area, we calculate Ro = Ps × ßs (11) where Ro is the runoff that might increase or decrease the water supply of the tree (mm), Ps is the sum of the summer precipitation from April to September (mm), and ßs = the summer runoff coefficient for various degrees of surface sealing (Table 6). Ro (mm) is the total amount of runoff during summertime that could either deliver or discharge surface water from or into the catchment area of the tree, as shown in Figure 7.…”