Drought and vegetation change in sky island mountains: remotely sensed phenology
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Drought and vegetation change in sky island mountains: remotely sensed phenology along gradients of woody plant cover Jennifer E. Davison a,b, David D. Breshears a,c,d, Willem J. D. van Leeuwen b,e a School of Natural Resources, b Office of Arid Lands Studies, c Institute for the Study of Planet Earth, d Ecology and Evolutionary Biology, e Geography and Regional Development University of Arizona, Tucson, AZ davisonj@email.arizona.edu Sky Islands Knowledge Gaps Landscape-scale patterns of vegetation dynamics within and among Sky Islands Phenology and productivity Spatial and temporal heterogeneity Dynamics of drought-induced vegetation change along elevation gradients Objectives: vegetation dynamics and drought Relate spatial patterns of vegetation dynamics to environmental and vegetation characteristics within a sky island across sky islands Veg Develop general insights etat io to those of climate and vegetation n gr Relate temporal vegetation trends adie nt Climate into vegetation dynamics and drought across elevation gradients Phenology Productivity Gradients of woody plant cover Landscape-scale Productivity Forest Woodland Shrubland Grassland Percent Woody Cover Vegetation Growth Vegetation dynamics and precipitation Year 1 Year 2 Grassland Precipitation Time Vegetation Growth Vegetation dynamics and precipitation Year 1 Year 2 Shrubland Grassland Precipitation Time Vegetation Growth Vegetation dynamics and precipitation Year 1 Year 2 Deciduous woodland Shrubland Grassland Precipitation Time Vegetation Growth Vegetation dynamics and precipitation Year 1 Year 2 Evergreen forest Deciduous woodland Shrubland Grassland Precipitation Time Global-warming-type drought and woody plant cover Landscape-scale Productivity Forest Woodland Reference Drought Shrubland Grassland Pre-disturbance Percent Woody Cover Global-warming-type drought and woody plant cover Landscape-scale Productivity Forest Woodland Reference Drought Shrubland Grassland Pre-disturbance Percent Woody Cover Study Area: Santa Rita Mountains AZ Tucson Santa Rita Mountains Elevation 2883 m 0m Quantifying vegetation dynamics • Normalized Difference Vegetation Index (NDVI) – MODIS sensor – 250 m spatial resolution – 16-day composite (23 periods per year) – February 2000 - February 2007 • Derived seasonal metrics of vegetation dynamics: – 6 seasons (2001-2006) – 9 metrics NDVI time-series integration 2001 2002 2003 2004 2005 2006 2007 0.6 NDVI 0.5 0.4 0.3 0.2 20 40 60 80 100 Period 120 140 160 NDVI time-series integration 2001 2002 2003 2004 2005 2006 2007 Peak 0.6 NDVI 0.5 0.4 0.3 0.2 Start Length 20 40 60 80 100 Period End 120 140 160 NDVI time-series integration 2001 2002 2003 2004 2005 2006 2007 Peak value 0.6 NDVI 0.5 Amplitude 0.4 0.3 0.2 Base value 20 40 60 80 Small integral Large integral 100 Period 120 140 160 2003: Season Start (DOY) 0 352 Base NDVI value 0 Season Length (Days) 0.75 0 560 Seasonal Productivity (large integral) 0 30.1 Explanatory variables •Percent woody cover •Plant functional type •Soil hydrologic group •Plant available water •Mean annual precipitation •Mean annual maximum temperature •Mean annual minimum temperature Exclusion of Florida fire, 2005 Spatial variation of all vegetation dynamics • Multiple analysis of variance across all metrics: – Mean annual minimum temperature – Mean annual precipitation * mean annual maximum temperature – Plant functional type (trees, shrubs, herbs) * woody plant cover – Soil hydrology * plant available water Spatial variation in each metric Metric Season start β1 β2 β3 AdjR2 β4 Functional Type Soil hydrology MAP (-) Minimum temp. (+) 0.170 Season peak Soil hydrology Functional Type Woody cover (+) MAP (-) 0.210 Season end Soil hydrology Functional Type Minimum temp. (+) Woody cover (+) 0.279 Season length Soil hydrology Functional Type Minimum temp. (+) Woody cover (+) 0.242 Base greenness MAP (+) Woody cover (+) Soil hydrology Functional 0.620 Type Peak greenness Minimum temp. (-) Avail. H2O cap. (+) MAP (+) Functional 0.569 Type Season amplitude Minimum temp. (-) MAP (+) Functional Type Avail. H2O cap. (+) 0.401 Season dynamics Soil hydrology Minimum temp. (-) Functional Type Avail. H2O cap. (+) 0.432 MAP (+) Woody cover (+) Soil hydrology Functional 0.586 Type Season productivity Temporal patterns: start of season and annual precipitation Annual Precipitation (mm) 215 1036 2001 2002 2003 2004 2005 Season Start (MODIS period) 0 22 2006 Temporal patterns: seasonal productivity and annual precipitation Annual Precipitation (mm) 215 1036 2001 2002 2003 2004 2005 Seasonal Productivity (Integrated NDVI) 0 30.1 2006 Slope of seasonal productivity 2001-2006 -289.1 – -87.1 -87.1 – -59.2 -59.2 – -39.5 -39.5 – -21.4 -21.4 – 0.0 0.0 – 202.7 What do we know so far • The Southwest is poised for more drought • Sky Island elevation gradients might be barometers of these impacts – Sensitivity – Biodiversity • Spatio-temporal patterns in vegetation dynamics might provide insights into effects of global-warming-type drought Any questions, comments, feedback greatly appreciated, thank you! davisonj@email.arizona.edu
