Presentation on theme: "Evergreen tree dynamics in tropical savanna"— Presentation transcript:
1 Evergreen tree dynamics in tropical savanna Lindsay Hutley and friends
2 Talk Outline Evergreen savanna trees species Australian savannas dominated by evergreen tree speciesAll other savannas of the world dominated by deciduous woody speciesHow do evergreen species survive in a strongly seasonal climate?Impacts tree removal from system ?
3 Australian tropical savanna Savanna - trees (C3) and grass (C4)Open-forest/woodland savanna of the wet-dry tropics25% of Australia, approximately 2 million sq kmMiningTourismPastoralismAboriginal land management
4 Howard Springs mesic tropical savanna Overstorey LAIWet to dryEucalyptus dominatedSoils – red earthsUnderstorey LAIWet to drySarga dominatedFrequently burntRainfall 1700 mmBA m2 ha-1Stems ha-1 700
6 Climate and soil/groundwater Wet-dry climate reflected in patterns seen here, with strong seasonal signal in groundwater levels - about a 10 m amplitudeNote the increasing height of min water levels over time, not being matched by increases in level peaks
7 Savanna climate - monsoonal Howard Springs1700 mm y-1
16 WATER TABLE (April/May) SOIL PROFILEfrom Kimber (1974)ASandLoamySandB100SandyClay LoamB/CDuricrust200CSandy clayLaterite - derived from Latin word ‘later’ meaning brickTypical of tropical regions,Higly weathered and leached profileDuricrust/ferecrete - accumulation zoneWater table well within root zone of treesWhile deep rooting, low root biomass below duricrust3005 m rooting depthWATER TABLE (April/May)
17 Macropores in laterite Deep drainageMacropores in lateriteTree roots at 4 m
18 Volumetric soil water content Sub-soilUpper soil
19 Soil water balance – end of dry season S = soil water store(mm)Dry seasontree water use(~0.9 mm d-1)=
20 Features of savanna water use carbon allocation Dual root systems – maximise carbon and water uptake in seasonal climateWet season, 0-1 m depthSurface fine roots – water and nutrient uptakeStem increment possibleDry season, 2-5 m depthNo surface soil moisture, limited nutrient availability, no stem growth possibleAccount for dry season ET using soil water balanceTrees using up to 5 m of soil for dry season water requirementsSub-soil water storage criticalPhotosynthesis maintainedCarbon partitioned into maintenance of deep roots, storage in lignotuber and reproductionPartitioning of soil water usagegrasses: m (wet)trees: m (wet and dry)competition with grasses limited or avoided
23 Tree clearing and hydrology Depth profile - soil moisture content (m3/m3)Uncleared5-60 mm drainageClearedmm drainage
24 Tree clearing and carbon Chen, Hutley, Eamus (2005)Loss of SOC ~ 2 t C y-1 post clearing
25 Conclusions Fluxes of carbon and water rapid in tropical ecosystem Hydrological change after 5 years following clearingyears in temperate systemsCarbon 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 aloneClearing impact is likely to be significant
27 Hydrological cycle - conceptual model TNTTower Network of the NTMoisture inputsCatchment processesOutflowmeasurements
28 Current study areaAdditional sites required to cover range of land types, soil types, climate gradient
29 Project 4.1 objectivesDetermine the fate of rainfall falling on catchments, and partition this into evapotranspiration, recharge and surface runoff.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.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.Assess the suitability of surface water – groundwater models for water resource management.
30 Daly River towers – part of TNT Cleared native pasture – 5 yoDaly unclearedCleared improved pasture – 25 yo
31 Savanna vegetation and climate Evergreen trees dominates savanna vegetationAdaptation to long dry seasonZero rainfall, Epan mm d-1Deep rootedUse of deep soil reserves and groundwater likely
32 Scaling heat pulse measures tree water use v size Combine with plot surveysTree water use in mm d-1
33 Eucalypt savanna evapotranspiration EoTotal ETEu/sGenerate data for water use over the wet-dry cycleSeparated into components of savanna vegetationEtree
34 Use of groundwater - conclusions Impact of tree removalincrease deep drainage by mmsignificant amount of waterimpacts on stream flow and water table ??Offset by increased grass growth and soil evaporation (limited)
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