## 1 Introduction  
The infiltration rate of underlying surfaces quickly decreases during rapid urbanization due to the dramatic increase in impervious land area. This has led to increases in urban runoff and waterlogging risk. Woody plants have been proven as a new effective tool in urban stormwater management because woody plants can increase soil porosity and preferential flow by living roots growth and dead roots decay [1; 2; 3]. [PERSON] et al. [4] investigated the biomass-infiltration relationships from nearly 50 vegetation communities that spanned from hyperarid deserts to the humid tropics (representing a full spectrum of soil types). They found that soil permeability increased as a power law function of aboveground biomass in water-limited ecosystems. [PERSON] et al. [5] observed that roots of Black oak (_Quercus velutina Lam._) and red map (_Acer rubrum L._) trees could penetrate the geotextile and subsoil. In structural soil profile study, trees increased the average infiltration rate 27-fold compared to unplanted controls. In a greenhouse study, trees increased infiltration rate by an average of 153%. [PERSON] and [PERSON] [6] also reported that the soil porosity and soil water holding capacity increased from 41.2% to 46.3% and from 4.3 to 4.8 g kg\({}^{-1}\) with the growth of _Prosopis juliflora_ (a woody plant) within 3 years. They also reported that the bulk density of surface soil decreased from 1.66 to 1.37 t m\({}^{-3}\). With the growth of _Malus bacata_ with fibrous roots and _Sophora japonica_ with tap roots, [PERSON] et al. [7] observed that water infiltration rates increased at ratios of 19% and 118%, respectively. A larger increase of infiltration rate by _S. japonica_ was observed due to its deeper and more vertical tap roots. For living roots, the growth of roots can split soil into larger pores and increase soil porosity by 30% [1; 3]. These larger pores generated by living roots can let more air enter into the soil and promote animals breathing and activities. The soil pores are key factors affecting water infiltration and hydraulic conductivity in soil by controlling the resistance against gravity and suction [8; 9]. [PERSON] and [PERSON] [10] and [PERSON] et al. [11] found that soil porosity had a positive influence (R\({}^{2}>0.9\)) on infiltration rates, and soil pore distributions were mainly affected by roots distribution [12; 13; 14]. Many relationships between the distribution of different pore sizes and hydraulic conductivities have been derived by different researchers including [PERSON] and [PERSON] [15], [PERSON] [16], [PERSON] et al. [17], and [PERSON] et al. [18]. Moreover, during the growth of roots, roots and microorganisms in the rhizosphere can increase organic matter in soil [19] and produce hyphae and exudate [20; 21]. They could positively affect soil pores and soil structure by releasing organic compounds and combining and aggregating soil particles [22]. [PERSON] et al. [23] found that the green forest which had the highest organic matter had the highest infiltration rates, and _Spartocytisus_ which had the lowest organic matter had the lowest infiltration rates. For dead roots, [PERSON] et al. [24] reported that only 35% of initial mass, on average, of 35 woody plant roots decayed after 6 years of exposure in the field. Root channels and preferential flow channels are formed in place by decaying roots [25; 26]. After roots decay, many spaces were left to become macropores [27; 28], which increased pore air volume, increased water infiltration rate, and reduced soil interaction [29]. [PERSON] et al. [25] reported that dead alfalfa with taproot growth could produce stable macropores and improve water infiltration rates in soil; however, dead wheat with fibrous roots had no significant influence on water infiltration rates in soil. Moreover, during the decay of woody plant roots, organic matter also is generated and can improve soil porosity by altering soil structure [30; 31].