Banyan tree roots only 40 cm deep, tree doctors find Daan Forest Park soil too hard
Taipei's Daan Forest Park turns 20 this year, yet it is far from thriving. After Typhoon Soulik last year, over a hundred trees fell. On the 12th of this month, the Daan Forest Park Friends Foundation invited three Japanese "tree doctors" and Professor Chang Wen-liang of National Taiwan University's Department of Environmental Engineering to give the park a "health checkup." The diagnosis report came out yesterday: because the soil was backfilled too compactly during excavation, the geology is too hard, and tree roots can barely penetrate it. Banyan roots that could normally grow to 1 m deep grow less than 40 cm in the park. It is estimated that 10 years and 300 million yuan will be needed to improve the situation.
Soil too hard, banyan roots only 40 cm
Taipei's Daan Forest Park covers nearly 26 hectares and is called Taipei's "green lung." The Daan Forest Park Friends Foundation, just established this year, held yesterday with the Taipei City Government and the Forestry Research Institute of the Council of Agriculture the "2014 International Symposium on Tree Protection - Using Daan Forest Park as an Example to Discuss Preventive Measures Against Natural Disasters," because Daan Forest Park, though now grown up, is still thin and small, nothing like a "forest," and fallen trees and broken branches are frequently heard of, affecting public safety.
From the 12th to the 16th of this month, a Taiwan team cooperated with the Japan Street Tree Diagnosis Association to conduct an unprecedented "full-body health check" of Daan Forest Park. Three Japanese tree doctors specializing in root systems, pruning and hazardous tree assessment, through geological drilling and microclimate surveys, preliminarily found that overly hard soil and excessively high groundwater are the two main culprits preventing the trees from growing large.
Kasa Matsu Shigehisa, vice president of the Japan Street Tree Diagnosis Association, was surprised to find that the roots of the autumn maple trees in Daan Forest Park are only 10 cm deep, almost all distributed in the lawn, and a day and a half after rain, the water still had not drained away; the roots of camphor trees and ring-cupped oaks are also only 10 cm deep; Professor Chang Wen-liang of National Taiwan University's Department of Bioenvironmental Systems Engineering diagnosed that banyan trees over 5 m tall in the park have roots only 20 to 40 cm deep.
The Japan Street Tree Diagnosis Association once monitored that banyan trees in Okinawa under natural conditions can send taproots down to 1.3 m deep; moreover, normal banyan trees should grow thicker and thicker, but the banyan trees in Daan Forest Park grow thinner and taller, because the tree density is too high and they cannot get sunlight, so they can only keep growing upward.
Kasa Matsu Shigehisa revealed that at first they dug by hand, but the geology was so hard they could not dig, so they had to bring in electric drills; air cannot get into soil that is too hard, so roots can only grow sideways, or even upward, and can barely survive that way, but if it does not rain for several days and there is no water in the ground, the trees are also prone to drying up and dying; and this problem exists not only in Daan Forest Park, but in the soil near buildings throughout Taipei.
