The treeline on the Mexican volcanoes is fragmented by fire. Burning the tussock grassland is thought to improve pasture quality. Given the frequency of the fires forests cannot recruit outside block fields. Similar treelines occur on Popocatepetl, Iztaccihuatl and Nevado de Toluca, all at precisely 4000 m, irrespective of slope direction.

1 - Pinus hartwegii on Pico de Orizaba (5610 m), treeline at 4000 m

2 & 3 - Groups of trees at 4000 m elevation

4 - Pinus hartwegii, 3850 m

29 August 2011
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