<P> Adverse effects may be indirectly related to acid rain, like the acid's effects on soil (see above) or high concentration of gaseous precursors to acid rain . High altitude forests are especially vulnerable as they are often surrounded by clouds and fog which are more acidic than rain . </P> <P> Other plants can also be damaged by acid rain, but the effect on food crops is minimized by the application of lime and fertilizers to replace lost nutrients . In cultivated areas, limestone may also be added to increase the ability of the soil to keep the pH stable, but this tactic is largely unusable in the case of wilderness lands . When calcium is leached from the needles of red spruce, these trees become less cold tolerant and exhibit winter injury and even death . </P> <Table> <Tr> <Td> </Td> <Td> This section needs expansion . You can help by adding to it . (July 2013) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This section needs expansion . You can help by adding to it . (July 2013) </Td> </Tr>

Which of the following are natural causes of acid rain