Answer to Question 1
Answer: There are five biomes which have trees as their predominant vegetation. For instance, there are tropical rainforests, midlatitude deciduous forests, etc. Instead, forests are a major plant association.
Answer to Question 2
Answer: Because of crustal plat movements, the continent has been isolated from the other plant and animal regions for more than 100 million years. This has allowed evolution time enough to make the species unique to Australia and not as diverse as other places in which mingling of species from other areas was able to occur.