(San Cristobal);Santa Ana;Rennell and Bellona;the Santa Cruz Islands and three remote, tiny outliers, Tikopia,Anuta, and Fatutaka. The distance between the westernmost and easternmost islands is about 1,500 kilometres (930 mi). The Santa Cruz Islands (of which Tikopia is part), are situated north of Vanuatu and are especially isolated at more than 200 kilometres (120 mi) from the other islands. Bougainville is geographically part of the Solomon Islands, but politically Papua New Guinea. The islands' ocean-equatorial climate is extremely humid throughout the year, with a mean temperature of 27 °C (80 °F) and few extremes of temperature or weather. June through August is the cooler period. Though seasons are not pronounced, the northwesterly winds of November through April bring more frequent rainfall and occasional squalls or cyclones. The annual rainfall is about 3050 mm (120 in). The Solomon Islands archipelago is part of two distinct terrestrial ecoregions. Most of the islands are part of the Solomon Islands rain forests ecoregion, which also includes the islands of Bougainville and Buka, which are part of Papua New Guinea, these forests have come under pressure from forestry activities. The Santa Cruz Islands are part of the Vanuatu rain forests ecoregion, together with the neighboring archipelago of Vanuatu. Soil quality ranges from extremely rich volcanic (there are volcanoes with varying degrees of activity on some of the larger islands) to relatively infertile limestone. More than 230 varieties of orchids and other tropical flowers brighten the landscape. The islands contain several active and dormant volcanoes. The Tinakula and Kavachi volcanoes are the most active.