Why protect big trees?

If you ask any practitioner in my field of urban forestry why we need trees in urban areas, they’re sure to enumerate a litany of benefits ranging from environmental to economic to human health and well-being. Science has made much progress in quantifying these benefits to human society through advances in ecosystem service research; today we can even ascribe monetary values to these services. Using its tool i-Tree Eco, the USDA Forest Service estimates the annual functional value of Philadelphia’s urban forest to include $3.6 million/year from carbon sequestration, $19.0 million/year from pollution removal, and $6.9 million/year from reduced energy costs.