Tree Prospectors?

There might be a new way of collecting rare metals, without the environmental damage of mining (https://www.theguardian.com/science/2021/apr/21/plantwatch-the-trees-that-feed-on-metal). Some trees actually concentrate particular metals. For example, Pycnandra acuminata has bright blue/green sap, which is 25% nickel. The Macadamia tree has leaves and sap, that are rich in manganese. The nut is without the metal. Metal-concentrating trees could be grown in particular areas. Burning their wood would result in ash that was a rich source of the metal. It is unclear why the trees concentrate these highly toxic metals. One possibility is that it enables the plant to resist attacks by insects and/or fungi.