Landscape-scale effects of the 2008 Chaiten (Chile) eruption on vegetation disturbance and regeneration from satellite image analysis

The Chaiten eruption affected all components of old-growth temperate evergreen forest -- trees, canopy epiphytes, vines, and understory - over ~ 400 km2. Vegetation responses differed depending on initial vegetation type, phenologic stage of the vegetation, landscape position, and the character and chronology of geophysical processes. Four distinct phases of the eruption and associated disturbances affected vegetation greenness in satellite imagery: (1) the initial eruption in early May 2008 produced a lateral blast-like pyroclastic density current (PDC) to N and NE and deposited tephra to NE, E, and SE, (2) >650 mm of precipitation May 13-20 caused flooding and redistributed deposits from hillslopes into channels and downstream, (3) collapse of dome in February 2009 caused PDC into Rio Chaiten to S, (4) floods in 2009 (second winter after eruption) rearranged deposits and wood in channels, and exhumed areas buried in earlier phases of the eruption. Vegetation effects included (a) ash deposition on foliage, (b) foliage/branch removal, (c) tree blowdown and scorching of foliage, and (d) burial, removal, and redeposition of wood and sediment. Three trajectories of vegetation change are apparent in satellite imagery: (1) loss of greenness from Dec 2007 to Dec 2008, followed by recovery of greenness in second growing season (Dec 2008-Apr 2009). Field observations indicated (a) tephra washed off trees whose underlying canopies were still intact (thin deposition zone W of volcano), (b) regeneration/sprouting of vegetation whose leaves had been removed or killed (Rio Rayas bridge), (c) regeneration/sprouting of vegetation exhumed by removal of overlying deposits such as in some river channels (Rio Amarillo), or (d) sprouting of understory (Rio Michinmahuida). (2) Initial loss of greenness that persisted through first two growing seasons. Field observations indicated that (a) trees were blown down and little sprouting has occurred (N flank), (b) vegetation was buried in thin (<0.5 m) tephra but little sprouting is occurring, perhaps due to suffocation of root systems by tephra deposits or to chronic Cl deposition in mist and rain (upper Rio Chaiten), or (c) vegetation with shallow (<1 or 2m) initial deposits has been further buried (to 30 m) by redistribution of tephra deposits from upstream (S fork of Rio Rayas). (3) No loss of greenness from Dec 2007 to Dec 2008 followed by loss of greenness from Dec 2008 to Apr 2009. Field observations indicated that riparian vegetation was not affected by the initial eruption, but was (a) buried and boles scorched by the Feb 2009 PDC (Rio Chaiten), or (b) buried by sediment redistribution from upstream (Rio Rayas and tributaries draining N flank).