Arthur's Pass National Park straddles the Southern Alps, and as such has a varied climatical range and therefore vegetation profile. In the west is predominantly podocarp forests, along the backbone of the mountains is alpine and sub-alpine vegetation zones. Moving eastwards the forest is mostly mountain beech with small areas of red beech. The eastern braided rivers and areas further east display a mix of manuka stands, drier mountain beech, tussocklands, and alpine scree plant communities. A great deal of the land through the Castle Hill Basin has been converted dramatcally by human activity.
Throughout the eastern valleys of the park, mountain beech usually monopolises the forest canopy from valley floor to bushline. The general distribution of mountain beech shows it to be a remarkably versatile species capable of growing from sea level to altitudes of more than 1500 metres, in both dry and boggy conditions. Mountain beech thrives on catastrophe, and is quick to regenerate after storm damage and slips.
There are some areas of silver beech in the upper poulter valley, and also mid-slope pockets of red beech. Enlarge picture below to see different beech leaves.
There is little understorey in the drier south-eastern areas of the park, but as you get closer to the divide, the beech forest becomes more complex with understoreys of small trees such as broadleaf, koromiko, tree daisies and ribbonwoods.
The forests of the western side of the park are much more complex, diverse and denser than the simple beech forests of the east. Mountain, silver and red beech all occur west, but red and silver being the most striking.
Podocarps tend to dominate the valley floors and mountain sides.