age of the landscape has meant that the soils are remarkably infertile and frequently laterised. Even soils derived from granitic bedrock contain an order of magnitude less available phosphorus and only half as much nitrogen as soils in comparable climates in other continents. Soils derived from extensive sandplains or ironstone are even less fertile, nearly devoid of soluble phosphate and deficient in zinc, copper, molybdenum and sometimes potassium and calcium. The infertility of most of the soils has required heavy application by farmers of fertilizers. These have resulted in damage to invertebrate and bacterial populations. The grazing and use of hoofed mammals and, later, heavy machinery through the years have resulted in compaction of soils and great damage to the fragile soils. Large-scale land clearing for agriculture has damaged habitats for native flora and fauna. As a result, the South West region of the state has a higher concentration of rare, threatened or endangered flora and fauna than many areas of Australia, making it one of the world's biodiversity "hot spots". Large areas of the state's wheatbelt region have problems with dryland salinity and the loss of fresh water. Climate The southwest coastal area has a Mediterranean climate. It was originally heavily forested, including large stands of karri, one of the tallest trees in the world. This agricultural region is one of the nine most bio-diverse terrestrial habitats, with a higher proportion of endemic species than most other equivalent regions. Thanks to the offshore Leeuwin Current, the area is one of the top six regions for marine biodiversity and contains the most southerly coral reefs in the world. Average annual rainfall varies from 300 millimetres (12 in) at the edge of the Wheatbelt region to 1,400 millimetres (55 in) in the wettest areas near Northcliffe, but from November to March, evaporation exceeds rainfall, and it is generally very dry. Plants are adapted to this as well as the extreme poverty of all soils. The central two-thirds of the state is arid and sparsely inhabited. The only significant economic activity is mining. Annual rainfall averages less than 300 millimetres (8–10 in), most of which occurs in sporadic torrential falls related to cyclone events in summer. An exception to this is the northern tropical regions. The Kimberley has an extremely hot monsoonal climate with average annual rainfall ranging from 500 to 1,500 millimetres (20–60 in), but there is a very long almost