Netanili “Nili” Niu, an arborist supervisor with the Public Works Bureau of Urban Forestry, can trace his love for trees back to his childhood in Hawaii. A certified arborist with 30 years of experience, including two decades with Public Works, Niu is part of a team of tree pros who look after the more than 125,000 street trees in San Francisco. Aside from keeping a watchful eye on our many street trees to make sure they grow tall and strong and stay healthy, arborists like Niu also jump into action whenever a storm barrels through San Francisco, leaving downed trees, broken branches and mangled limbs in its wake.