• nountain birch,
• kountain birch,
• jountain birch,
• miuntain birch,
• mkuntain birch,
• mluntain birch,
• mpuntain birch,
• m0untain birch,
• m9untain birch,
• moyntain birch,
• mohntain birch,
• mojntain birch,
• mointain birch,
• mo8ntain birch,
• mo7ntain birch,
• moubtain birch,
• moumtain birch,
• moujtain birch,
• mouhtain birch,
• mounrain birch

The adjective form of "mountain birch" is "mountain birch". It is the same as the noun form and does not change when used as an adjective.

The plural form of the word "mountain birch" is "mountain birches".

The singular form of the word "mountain birch" is simply "mountain birch". The word does not change when referring to a single tree or multiple trees.