Decoupling forest characteristics and background conditions to explain urban-rural variations of multiple microclimate regulation from urban trees

Abstract

BackgroundRapid urbanization in semi-arid regions necessitates greater cooling, humidifying, and shading services from urban trees, but maximizing these services requires an exact understanding of their association with forest characteristics and background street and weather conditions.MethodsHere, horizontal and vertical air cooling, soil cooling, shading, and humidifying effects were measured for 605 trees from 152 plots in Changchun. Additionally, weather conditions (Tair, relative humidity, and light intensity), forest characteristics (tree height, diameter at breast height (DBH), under-branch height, canopy size, tree density, and taxonomic family of trees) and background conditions (percentage of building, road, green space, water, and building height, building distance to measured trees) were determined for three urban-rural gradients for ring road development, urban settlement history, and forest types. Multiple analysis of variance and regression analysis were used to find the urban-rural changes, while redundancy ordination and variation partitioning were used for decoupling the complex associations among microclimate regulations, forest characteristics, background street and weather conditions.ResultsOur results show that horizontal cooling and humidifying differences between canopy shade and full sunshine were <4.5 °C and <9.4%, respectively; while vertical canopy cooling was 1.4 °C, and soil cooling was observed in most cases (peak at 1.4 °C). Pooled urban-rural data analysis showed non-monological changes in all microclimate-regulating parameters, except for a linear increase in light interception by the canopy (r2 = 0.45) from urban center to rural regions. Together with the microclimate regulating trends, linear increases were observed in tree density, Salicaceae percentage, Tair, light intensity outside forests, tree distance to surrounding buildings, and greenspace percentage. Redundancy ordination demonstrated that weather differences were mainly responsible for the microclimate regulation variation we observed (unique explanatory power, 65.4%), as well as background conditions (12.1%), and forest characteristics (7.7%).DiscussionIn general, horizontal cooling, shading, and humidifying effects were stronger in dry, hot, and sunny weather. The effects were stronger in areas with more buildings of relatively lower height, a higher abundance of Ulmaceae, and a lower percentage of Leguminosae and Betulaceae. Larger trees were usually associated with a larger cooling area (a smaller difference per one unit distance from the measured tree). Given uncontrollable weather conditions, our findings highlighted street canyon and forest characteristics that are important in urban microclimate regulation. This paper provides a management strategy for maximizing microclimate regulation using trees, and methodologically supports the uncoupling of the complex association of microclimate regulations in fast urbanization regions.

Associations between Road Density, Urban Forest Landscapes, and Structural-Taxonomic Attributes in Northeastern China: Decoupling and Implications

“…The structural attributes of trees are the basis of the multiple ecological services provided by urban forests, such as increasing carbon sinks [63,64], reducing air temperature [28,42,65], and decreasing storm water runoff [66]. In the low RD regions of Harbin, taller and bigger trees were more likely to be associated with lower patch aggregation (IJI) and lower patch areas (TA), as shown by the stepwise regression (Table 4) and RDA ordination results (Figure 8).…”

“…As the road development of Harbin represents a typical case in China, it has been used to study the effects of urbanization [23]. Many studies in Harbin have focused on CO 2 dynamics [36], remote sensing tree measurements [37], habitat variability [38], mycorrhizal changes [23,39], soil fertility mapping [40], forest carbon sequestrations [31], the biodiversity of trees and birds [32,41], microclimate regulations from urban trees [14,42], and the tree census method development [43]. The associations between road development and forest characteristics were not reported to date, and new studies will provide support for urban green infrastructure development.…”

“…For instance, in urban regions, both natural conditions (soil nutrients, climatic conditions, and species competition) and social development (e.g., road construction and economic development) should be fully considered to obtain a scientific understanding of the underlying process and mechanisms. The ordination and stepwise regression analyses have been used in various studies to decouple associations [42,70]. Although statistical analyses were performed in this study, conclusions regarding possible causal relationships require additional caution (Table 4, Figures 7 and 8).…”

Dominant Species Abundance, Vertical Structure and Plant Diversity Response to Nature Forest Protection in Northeastern China: Conservation Effects and Implications

“…Selecting an appropriate statistical analysis method was crucial to decouple the associations between species diversity and forest structure and find the most likely pathway of forest structural improvement, species diversity and dominant species protection [9,22,23]. We chose structural equation modeling (SEM) to identify the structural relationship among the complex associations.…”

“…However, this kind of mathematical deduction possibly has the risk of over analysis, with structural relationships as causal relations. Different methods, such as redundancy ordination, have been used to provide management hints to maximize ecological services and forest conservations during urbanization disturbance [7,22,40]. In the future, more specifically designed field experiments are needed to test this pathway and define the complex associations in the nature system, together with this kind statistical partitioning.…”