A tree is a long lived woody perennial plant greater than (or usually greater than) 3m in height with one or relatively few main stems or trunks.
Techncially, trees should be included as an asset in your balance sheet because they provide future economic benefits that last more than 12 months. However, this does not mean you value every tree as a separate asset. There is a specific accounting standard (AASB141) which deals with Agricultural Assets and these types of trees do not make the cut. The cost of trees and softscaping is generally not considered a "material" cost of roads but can be for major sporting facilities and community space. The cost would normally be included under a component called "softscaping" but only if it was considered material. Generally this is not the case and therefore the cost of such would normally be taken into account as just part of the normal replacement cost. Certainly however the cost of future maintenance, renewal, etc should be incorporated into an Asset Management Plan. This is a good example that demonstrates that Asset Accounting and Asset Management need to be integrated but that the figures and calculations are not the same.