What can history tell us about our ability to
influence the condition of natural resources?
Ted Lefroy

What can history tell us about our
ability to influence the condition
of natural resources?
Ted Lefroy
University of Tasmania

Water quality in Tasmanian rivers and estuaries
Oral history, sediment
Water quality data
cores
Response to intervention
Large infrequent events
1. Sediment cores
2. Space-for-time exp.
**
3. Air photo analysis
Historic WQ data,
space for time exp.
Disturbance thresholds for 4. WQ/veg condition data
Tasmanian rivers *
5. Historical records
6. Oral history
Sediment cores, air photos, historical records
Biotic cycles and Large infrequent events

Little Swanport
1948
* 1967
1973
2003

Sediment cores, air photos, historical records
C/N ratios, seagrass fragments, biogenic Si,
isotopes, sand, tsunamite, ash
Epiphyte growth Epiphyte crash
Seagrass decline Seagrass recovery
Catastrophic seagrass decline Seagrass recovery
Flood or tsunami Epiphyte crash
Seagrass recovery
Catastrophic seagrass declinedecline
Catastrophic seagrass
Anthropogenic
Flood or tsunami
?
Seagrass recovery
1. Biotic cycles
* 2. Large infrequent events
3. Human influence

Duck, Montagu, Black & Detention
Rivers
*

Duck River
Oral history, air photos, sediment dating
Black River, Detention River
Cobble bottom
Sediment dating
Oral history
Mud banks
Duck River, Montagu River

Water quality data & space-for-time
experiment
AusRivAs dataset 1999 & 2006
781 sampling events
Water quality, Biota,
Geomorphology
Habitat
100
90
80
70
60
50
Threshold: > 42% grazing
40
30
20
10
0
0 0.5

Substituting space for time
Blue - grazing
Hatched - cropping
Green - conservation
Red - forestry

Substituting space for time
Threshold 55%
 flow  light  temp
terrestrial carbon  algal dominated

Detecting recovery
The Pet River
*

The Pet River
 16 km2 catchment
 5-25% of sub-catchments treated
 12 sub-catchments monitored for 7 years
 No detectable change in N or P

Vegetation change 1946-2006
1946
2006
% Canopy cover
?
Large Infrequent Events: Gold, Fire
Slow drivers: rabbits, sheep, Landcare, wool prices, tree change
1800 1870 1940 2010
Regeneration = 2 x Revegetation Private investment ~ 2 x Public

Summary 1
1. Multiple lines of evidence
– Sediment cores
– Space-for-time experiments
– Air photo analysis
– Historic WQ/veg condition data
– Oral history
– Historical records

Summary 2
2. In combination, they can be used to identify
– Biotic cycles
– Large infrequent events
– Human disturbance
– Recovery in vegetation extent
3. ….but its more challenging to
– Document recovery in water quality
– Document change in vegetation condition

Acknowledgements
Estuarine research – John Gibson, Barry Gallagher, Jeff Ross and Christine Crawford
Fresh water – Nelli Horrigan, Reg Majierowski, Steve Read and Peter Davies
Riparian – Shane Broad, Bill Cotching and Ross Corkery
Vegetation change – Garreth Kyle, Dave Duncan, Libby Rumpf and Graeme Newell
www.landscapelogic.org.au

The Environment
Institute