Decline of street trees is one of the important problems for maintaining healthy environment in urban areas. Planted Cercidiphyllum japonicum Sieb. et Zucc. trees often show symptoms of decline such as trunk-rot and top-dieback. We studied leaf characteristics, photosynthetic rate, transpiration rate, water potential, leaf nitrogen content, leaf area and leaf mass per area in healthy and declining trees to evaluate the physiological status of the damaged trees. Trunk-rot trees showed significant reduced leaf area and daily carbon gain. Marked low predawn water potential was found in top-dieback and trunk-rot trees. It is suggested that trunk-rot trees suffer from water-stress under soil water deficiency, and this stress also affects leaf expansion. Leaf area and predawn water potential was not different in healthy and top-dieback trees; we suggest that water stressed leaves were already fallen, whilst the remaining system of soil-plant continuum functions normally.
On 20 August 2004, typhoon 0415, carrying a strong salt spray, passed offshore along Akita Prefecture where it caused severe crop damage. Here, we have documented the salt spray damage on trees in Akita Prefecture, and compared the wind- and salt-break functions of healthy coastal pine forest stands to those damaged by pine wilt disease. Severe damage was observed within 10-km inland areas south of Oga Peninsula. Tree damage was characterized by withering at tree crowns and branches and by reduction of foliage. We also compared the subsequent year's growth of 13 common species under the same habitat conditions and found substantial between-species differences in the extent of damage. That is: whereas Quercus serrata, Castanea crenata and Euonyms alatus were heavily damaged, Pinus thunbergii and Cryptomeria japonica showed slight damage. In addition, the damage on broad-leaved species was reduced when located behind wind shelters or within healthy pine stands, compared to those in the open or those in a stand heavily damaged by pine wilt disease, respectively. These results support the general notion that the health of costal pine forests is important in maintaining the wind- and salt-break functions.