A few studies describe the tree as having strong internal conductivity, letting lightning current flow through without building up damaging heat like a well-insulated wire. Because they tend to grow large — up to 130 feet (40 meters)—and live for centuries, a single tonka bean tree is estimated to be struck at least five times after reaching maturity.A few studies describe the tree as having strong internal conductivity, letting lightning current flow through without building up damaging heat like a well-insulated wire. Because they tend to grow large — up to 130 feet (40 meters)—and live for centuries, a single tonka bean tree is estimated to be struck at least five times after reaching maturity.