Presentation on theme: "Lindsay Hutley and friends Evergreen tree dynamics in tropical savanna."— Presentation transcript:
Lindsay Hutley and friends Evergreen tree dynamics in tropical savanna
Talk Outline Evergreen savanna trees species –Australian savannas dominated by evergreen tree species –All other savannas of the world dominated by deciduous woody species How do evergreen species survive in a strongly seasonal climate? Impacts tree removal from system ?
Australian tropical savanna Savanna - trees (C3) and grass (C4) Open-forest/woodland savanna of the wet-dry tropics 25% of Australia, approximately 2 million sq km Mining Tourism Pastoralism Aboriginal land management
Howard Springs mesic tropical savanna Understorey LAI Wet to dry Sarga dominated Frequently burnt Overstorey LAI Wet to dry Eucalyptus dominated Rainfall 1700 mm BA m 2 ha -1 Stems ha Soils – red earths
Wet-dry climate and rainfall
Climate and soil/groundwater
Savanna climate - monsoonal 1700 mm y -1 Howard Springs
Seasonality – Leaf Area Index Dry season
Seasonality - tree increment
Seasonality – fine root turnover
Wet-dry climate and rainfall
Vegetation response to climate Tree water use Prediction ??
Tree water use and leaf photosynthesis - aseasonal response Tree water use Amax umol m 2 s -1 Amax umol m 2 s -1
How is this possible ? Root distribution of savanna vegetation
SOIL PROFILE Sandy clay Sand C Loamy Sand A B B/C Sandy Clay Loam from Kimber (1974) WATER TABLE (April/May) Duricrust 5 m rooting depth
Macropores in laterite Tree roots at 4 m Deep drainage
Volumetric soil water content Sub-soil Upper soil
Soil water balance – end of dry season Dry season tree water use (~0.9 mm d -1 ) = S = soil water store (mm)
Features of savanna water use carbon allocation Dual root systems – maximise carbon and water uptake in seasonal climate Wet season, 0-1 m depth Surface fine roots – water and nutrient uptake Stem increment possible Dry season, 2-5 m depth No surface soil moisture, limited nutrient availability, no stem growth possible Account for dry season ET using soil water balance Trees using up to 5 m of soil for dry season water requirementsTrees using up to 5 m of soil for dry season water requirements Sub-soil water storage critical Photosynthesis maintained Carbon partitioned into maintenance of deep roots, storage in lignotuber and reproduction Partitioning of soil water usage grasses: m (wet) trees: m (wet and dry) –competition with grasses limited or avoided
Impact of clearing ?
Impacts of land use change
Tree clearing and hydrology Depth profile - soil moisture content (m 3 /m 3 ) Uncleared 5-60 mm drainage Cleared mm drainage
Tree clearing and carbon Chen, Hutley, Eamus (2005) Loss of SOC ~ 2 t C y -1 post clearing
Conclusions Fluxes of carbon and water rapid in tropical ecosystem –Hydrological change after 5 years following clearing years in temperate systems –Carbon turnover rapid, ~5 years (Chen et al. 2003) Carbon gain can be rapid - NBP 2-4 t C ha -1 y -1, Beringer et al 2007) Carbon loss can be rapid – 2 t C ha-1 y-1 in soil alone –Clearing impact is likely to be significant
Hydrological cycle - conceptual model Moisture inputs Catchment processes Outflow measurements TNT Tower Network of the NT
Current study areaCurrent study area Additional sites required to cover range of land types, soil types, climate gradientAdditional sites required to cover range of land types, soil types, climate gradient
Project 4.1 objectives 1.Determine the fate of rainfall falling on catchments, and partition this into evapotranspiration, recharge and surface runoff. 2.Investigate historical patterns of surface water availability, particularly as they relate to persistence of dry season water holes and changes in inundation extent during the wet season. 3.Develop simple models that can be used to predict changes in surface water and groundwater availability that might result from changes in land use or climate change. 4.Assess the suitability of surface water – groundwater models for water resource management.
Daly River towers – part of TNT Daly uncleared Cleared improved pasture – 25 yo Cleared native pasture – 5 yo
Savanna vegetation and climate Evergreen trees dominates savanna vegetation Adaptation to long dry season –Zero rainfall, E pan mm d -1 –Deep rooted –Use of deep soil reserves and groundwater likely
Scaling heat pulse measures tree water use v size Combine with plot surveys Tree water use in mm d -1
Eucalypt savanna evapotranspiration EoEo E tree E u/s Total ET
Use of groundwater - conclusions Impact of tree removal –increase deep drainage by mm –significant amount of water –impacts on stream flow and water table ?? –Offset by increased grass growth and soil evaporation (limited)