Severe droughts may also follow large scale regional deforestation, particularly in tropical areas and have been implicated in the sudden collapse of older civilisations in Central America (Mayan) and southeast Asia (Angkor Wat). Recent severe droughts have been linked with widespread decline in conifer forests in many parts of the world, such as the pinyonpine ecosystems of the western USA and the Atlas mountains of Algeria and Morocco. In these areas the water-stressed trees are more susceptible to outbreaks of pests and diseases. An increase in fire frequency is also a serious associated impact. While relatively few conifers are currently assessed as threatened due to droughts as a result of climate change, several species have been identified as near threatened and in decline