Hydrological and Nutrient Controls on the Structure and Function of Southern African Savannas

K.K. Caylor, Paolo D’Odorico,

Christelle Hély, Greg Okin, S.A. Macko, Natalie

Mladenov, Lydia Ries, Susan Ringrose, T.M.

Scanlon, H.H. Shugart, R.J. Swap, Matt Therrell, Lixin Wang and Robert

Washington-Allen

Kalahari Transect

•Wet and dry season field campaigns for basic ecological process and detailed structural measurements of vegetation

Kalahari Transect

•Wet and dry season field campaigns for basic ecological process and detailed structural measurements of vegetation•Detailed soil characterizations

Kalahari Transect

•Wet and dry season field campaigns for basic ecological process and detailed structural measurements of vegetation•Detailed soil characterizations•Instrumented long-term physical data records

Kalahari Transect

•Wet and dry season field campaigns for basic ecological process and detailed structural measurements of vegetation•Detailed soil characterizations•Instrumented long-term physical data records•Field fertilization experiments with phosphorus and nitrogen and stable isotope analysis in experimental and spatially distributed contexts

Strong rainfall gradient, seasonal climate

Uniform sandy soils – ‘Kalahari sands’

Heterogeneous vegetation; tree, shrub and grass in woodland, savanna, and shrubland mixtures.

High net plant productivity, widespread biomass burning, high carbon turnover

IGBP Kalahari Transect

Mean annual rainfall

along the Kalahari Transect

Kalahari Rainfall – 1901-1996

Kalahari Rainfall – 1901-1996

Kalahari Rainfall – 1901-1996

Kalahari Rainfall – 1901-1996

Kalahari Rainfall – 1901-1996

Vegetation Patterns on the Kalahari Transect

Plant interactions dominate pattern

Landscape interactions dominate pattern

Spatial Variation in NDVI at Different Spatial Scales

Pattern and Process

Vegetation structural characteristics along the Kalahari Transect

More Southerly and Drier

DecreasingTree Cover

Grass Cover

Dispersed

Clumped

Depends on the

Prior History

is not equivalent to vnecessarily

A Landscape Vegetation Model

LeafPatch

Multi-Patch Structure

UMD Tree Cover Data

LiveNon-woody

LiveTree

Leaves

DeadNon-woody

DeadTree

Leaves

Could you tell me again where we’re going with

all this?

LeafPatch

Multi-Patch Structure

Regional Emissionsto the Atmosphere

or

WildfiresIndustrial

Domestic

Along with wildfires, there are other significant sources of emissions to the atmosphere.

WildfiresIndustrial

Domestic

We have some understanding of the contribution of these different sources.

WildfiresIndustrial

Domestic

Regional Emissions

Transport

Deposition

LiveNon-woody

LiveTree

Leaves

DeadNon-woody

DeadTree

Leaves

Does this have any practical

implications?

Grazing Pressure across Southern Africa

Grazing Impact across Southern Africa during a Wet Year.

Grazing Impact across Southern Africa in a Dry Year.

In wet versus dry years, the impact varies regionally

Wet Dry

is not equivalent to vnecessarily