Reversing paddock tree decline in Australia's temperate grazing zone

Joern Fischer, Jenny Stott, Andre Zerger, Garth Warren, Kate Sherren, Robert Forrester(and other collaborators)

The Fenner School of Environment and SocietyThe Australian National University2 July 2009

Outline

Background on grazing and woodlands Problem definition and aims of our recent study Methods, results, discussion of our recent

study The interdisciplinary context of this work

Many results presented here were published in early June 2009 in Proceedings of the National Academy of Sciences USA:Fischer, J., Stott, J., Zerger, A., Warren, G., Sherren, K., Forrester, R. (2009). Reversing a tree regeneration crisis in an endangered ecoregion. The paper is open-access – you can download it from anywhere.

Livestock grazing globally

Demand for agricultural goods projected to more than double between 2000 and 2050

Livestock grazing covers more land than any other land use

1. Tilman D, Cassman KG, Matson PA, Naylor R, Polasky S (2002) Agricultural sustainability and intensive production practices. Nature 418:671-677.

2. Foley JA, et al. (2005) Global consequences of land use. Science 309:570-574.

3. Asner GP, Elmore AJ, Olander LP, Martin RE, Harris AT (2004) Grazing systems, ecosystem responses, and global change. Annu Rev Environ Resour 29:261-299.

Livestock grazing in Australia

More than half the continent commercially grazed

Temperate woodlands internationally recognised as ‘threatened ecoregion’

Left: McIntyre, S., McIvor, J., Heard, K. (2002). Managing and conserving grassy woodlands. CSIRO Publishing.

Right: http://www.anra.gov.au/topics/agriculture/beef/index.html

Modification levels

McIntyre, S., McIvor, J., Heard, K. (2002). Managing and conserving grassy woodlands. CSIRO Publishing.

Photo: Jenny Stott

Extent and bias in clearing

In Australia’s temperate grazing region, often 80-95% of land cleared

Large patches remain largely on top of hills

Here: the Upper Lachlan catchment (Fischer et al. in press. Frontiers in Ecology and the Environment)

Many small patches and scattered trees

Plantstree per se

seed source

other plants

Abiotic

stem flow

nutrient enrichment

hydrology (salinity, infiltration)

Landscape functions

Continuity through time

Animals

shelter

hollows

shade,litter, food

Total amount of tree cover Connectivity for tree species Connectivity for animals Restoration nuclei

Ecosystem function Biodiversity Resilience Biological legacies

Local functions

Manning, A., Fischer, J., Lindenmayer, D. (2006). Biological Conservation.

Photo: Kate Sherren

The living dead?“There are those that are standing, living and breathing,

but as dead as is the litter, since they have no reproductive future. They are the living dead.”

(Janzen 1986, Annu Rev Ecol Syst)

No regeneration at 87% of sites studied (Spooner et al. 2002)

Not a single tree regenerated since 1920 in the patch studied(Saunders et al. 2003)

Regeneration absent at the vast majority of sites studied(Manning et al. 2005)

Eucalypt regeneration absent at 73% of sites in northern VIC(Dorrough et al. 2005)

Regeneration unlikely at 38% of sites in SW slopes, NSW (across all types of tenure) (Weinberg et al. 2005)

The background for our work

An over-cleared region Much remnant tree cover in small patches and

scattered trees These areas have been historically ignored Under status quo management, trees are not

regenerating in these areas

Critical knowledge gaps

Our work builds on past research, recognising that:

The extent of the tree regeneration (failure?) must be systematically quantified;

Management practices conducive to tree regeneration must be identified, preferably at low costs to commodity production;

Policies must be developed and implemented to enable sustainable management practices.

The ‘Sustainable Farms’ project

Funded by the Australian Government, via the Australian Research Council (ARC) and the Commonwealth Environment Research Facilities Program (CERF)

Some figures about the Lachlan catchment

Settled ~1815, population increase following gold in 1850s Average landholder age is 51 years Average on-property profit $22,000 prior to drought Large-scale land clearing after initial settlement, followed

by bursts of regeneration in various locations Cowra 1964-1993: 0.36 paddock trees/ha vs. 0.27 trees/ha Current tree cover ~15% Range of biophysical problems (water, soils, biodiversity)

(Sources: Lachlan Action Plan 2006; Gibbons and Boak 2002; Ozolins et al. 1999; plus various references within these reports)

Partly based on:Vesk, P. A., and J. W. Dorrough. 2006. Getting trees on farms the easy way? Lessons from a model of eucalypt regeneration on pastures. Australian Journal of Botany 54:509-519.

Management factors affecting regeneration

Location and design

Upper Lachlan Catchment 33 farms Wide range of grazing

regimes Four site types:

• Open paddock• Scattered trees• Grazed woodland• Ungrazed woodland

Soil chemistry as covariates

Different ways of grazing

In the Upper Lachlan, three broad ways of grazing livestock are apparent:

1. Continuous grazing – paddocks stocked year round

2. Slow rotation – paddocks stocked most of the year, but with rest periods for several months

3. High-intensity short-duration grazing – rotation of livestock from one paddock to another every few days

All of these can have a high or low average stocking rate

Grazing regimes at our sites

0

5

10

15

20

25

0 50 100 150 200 250 300 350 400

Days grazed per year

DS

E p

er

ha

First major set of results

Three steps of analysis:• Analysis of how much tree cover occurs at different

densities(= regional-scale background)

• Analysis of tree diameter distributions at different sites(= indication of age profile of stands of trees)

• Analysis of (i) time since last regeneration and (ii) probability of recent regeneration at different sites(= insights for future management)

Tree densities methods

Methods High-resolution SPOT5 imagery combined with

on-ground surveys of tree densities SPOT analysis: 10 m resolution tree layer

across the region On-ground tree measurements:

Diameters and densities measured at 126 sites (106 ‘primary’ + 20 ‘validation’ sites)(> 3500 trees identified and measured)

Tree densities results

Regional tree cover 18%(farm median = 12%)

Three quarters under 30% tree cover per 2 ha= about 3 million trees

Two thirds under 10% tree cover per 2 ha= about 1.5 million trees

Tree diameters methods Census or representative sampling of diameters of trees

in the 126 survey sites Diameters of a given species standardised by scaling

them against representative ‘very old’ representatives of the species= unit-free diameter index

All species scaled back to yellow box for graphs

Graphs based on:Banks, J. C. G. 1997. Tree ages and ageing in yellow box. Pages 17-28 in J. Dargavel, editor. The coming of age - forest age & heritage values. Environment Australia, Canberra.

Tree diameters results

Distribution characteristic of undisturbed systems only in ungrazed sites

Strong evidence of insufficient recruitment in low density areas

Typical diameters of 100 cm or more (well over 120 years old)

Regression methods Generalised linear mixed modelling• Random effect: ‘Farm’• Fixed effects: Grazing regimes, tree cover, soil

nutrients Response variables• Minimum diameter at the site

(= proxy for time since last regeneration)• Presence/absence of seedlings

(= proxy for recent regeneration) Models fitted first using subset of all data, then

validated on the whole dataset

Regression results

Significant variables related to regeneration:

Tree density

Phosphorus, nitrogen

Grazing regime:

Ungrazed or fast rotation significantly ‘better’ than continuous or slow rotation

Parallels to other parts of the world

Holm oak dehesas in Spain

Pulido FJ, Diaz M, de Trucios SJH (2001) Size structure and regeneration of Spanish holm oak Quercus ilex forests and dehesas: effects of agroforestry use on their long-term sustainability. For Ecol Manag 146:1-13.

Parallels to other parts of the world

Cattle pastures in Nicaragua:- 37 of 85 tree species

regenerated undercommercial grazing

Esquivel MJ, Harvey CA, Finegan B, Casanoves F, Skarpe C (2008) Effects of pasture management on the natural regeneration of neotropical trees. J Appl Ecol 45:371-380.

A tree regeneration crisis

The region is already over-cleared from the perspective of many species and ecological processes

Conventional practices are incompatible with the maintenance of tree cover:Fertiliser + continuous grazing = no regeneration

Under conventional practices, millions of hectares of land currently supporting tens of millions of trees will be treeless

Likely rates of tree decline In the Cowra region: 2% per year mortality

Ozolins, A., C. Brack, and D. Freudenberger. 2001. Pacific Conservation Biology 7:195-203.

Status quo prediction for scattered yellow box:50% decline over the next 50 yearsGibbons, P., D. B. Lindenmayer, J. Fischer, A. D. Manning, A. Weinberg, J. Seddon, P. Ryan, and G. Barrett. 2008. Conservation Biology 22:1309-1319.

100%

50%

0%

Years into the future

Likely consequences

Trees are important for many animal species:• Over 100 bird species• Over 25 reptile species• Over 25 mammal species (including bats)• Over half of all of these use scattered trees!

Potential for thresholds, cumulative effects, disproportionate effects of scattered trees

Also lost ecosystem services (= lost $$$):• Water infiltration, shade for livestock

Trees and water infiltration

“… both sorptivity and steady-state infiltration were significantly greater (approximately fivefold) under the timbered strata compared with the grassy slopes or cultivation …”

D. J. Eldridge, D. Freudenberger, Austral Ecology 30, 336 (May, 2005).

Trees and bats(… and their estimated economic value in the USA …)

L. F. Lumsden, A. F. Bennett, Biological Conservation 122, 205 (Mar, 2005).

Quote from a study in the USA:

“We estimate the bats' value as pest control for cotton production in an eight county region in south-central Texas. Our calculations show an annual value of $741000 per year, with a range of $121000-$1725000, compared to a $4.6-$6.4 million per year annual cotton harvest.”

C. J. Cleveland et al., Frontiers in Ecol. Environm. 5, 238 (Jun, 2006).

Trees and the Superb Parrot(threatened in NSW)

Manning et al. (2004).Biol. Conserv. 120, 363-374

Superb Parrot (Geoffrey Dabb, photogallery.canberrabirds.org.au)

Reversing the crisis

“Contrary to common wisdom, scattered trees are not doomed to be the living dead. Although low seed supply and a history of intensive land use impose constraints on tree regeneration in heavily cleared areas, reducing nutrient inputs and applying fast rotational grazing can substantially enhance regeneration.”

(Fischer et al. 2009 PNAS)

Two vital management challenges:Soil nutrients and livestock grazing

McIntyre, S., Lavorel, S. (2007). Agric. Ecosys. Environm. 119, 11-21

Benefits of low nutrient pastures

Benefits for tree regeneration Also, low-nutrient environments:• Have healthier mature trees

=> Maximising the survival of mature trees is critical to avoid population bottlenecks in the availability of key resources

• Have more native ground cover species• Have more native arthropod species

(for references, see Fischer et al. 2009 PNAS)

Benefits of altering livestock grazing

Livestock exclusion has ecological benefits, but comes at a high economic cost

Greening Australia ACT estimates the opportunity costs of complete stock removal at over $10,000 AUD per year per 100 ha

Fast rotational grazing promises to be a win-win opportunity (at least for tree regeneration)• Interesting also given rising fertiliser costs and

increasingly frequent droughts

Management options Considering our results in context:

What are the management options?

Active management:• The planting or direct seeding of new trees

Passive management:• Managing environmental conditions to encourage

natural tree regeneration

(e.g. Dorrough J, Vesk PA, Moll J (2008) Integrating ecological uncertainty and farm-scale economics for planning restoration. J Appl Ecol 45:288-295)

Management optionsActive management (planting or seeding) Establish trees along existing fence lines

(commonly done, but does nothing for scattered trees) Establish trees in scattered pattern

(done by some pioneering farmers) Exclude livestock from paddocks, prior to re-seeding and

resting them for several years(used by Greening Australia ACT)

Passive management (for natural regeneration) Fencing off woodland patches

(commonly done, but does nothing for scattered trees) Drastically reduce or cease fertiliser use

(no institutional support yet, unlike in parts of Europe) Take up fast rotational grazing

(gaining popularity despite lack of institutional support)

Management optionsActive management (planting or seeding) Establish trees along existing fence lines

(commonly done, but does nothing for scattered trees) Establish trees in scattered pattern

(done by some pioneering farmers) Exclude livestock from paddocks, prior to re-seeding and

resting them for several years(used by Greening Australia ACT)

Passive management (for natural regeneration) Fencing off woodland patches

(commonly done, but does nothing for scattered trees) Drastically reduce or cease fertiliser use

(no institutional support yet, unlike in parts of Europe) Take up fast rotational grazing

(gaining popularity despite lack of institutional support)

Prioritisation and policy options

Active planting and seeding most appropriate where natural regeneration is unlikely(e.g. few parent trees or high soil nutrients)

Passive management for natural regeneration ultimately preferable:to foster a self-perpetuating farm ecosystem

Which policy tools are appropriate?Financial incentives? Education? Regulation?

The ‘Sustainable Farms’ project

Funded by the Australian Government, via the Australian Research Council (ARC) and the Commonwealth Environment Research Facilities Program (CERF)

Future plans for the ecology component

Aims: Establish links between fauna and tree cover• Surveys of birds and bats completed• Pilot study on bats in press

Project tree cover into the future under different management scenarios• To be completed over the next few months

Project the distribution of selected fauna species into the future• Preliminary results over the next few months

Back to our own data:Bird surveys 2007 and 2008

2007: 122 bird species Paddocks: 56 species Scattered Trees: 70 species Grazed Woodland: 68 species Ungrazed Woodland: 68 species Revegetation: 47 species

Detailed analysis yet to come Brown Treecreeper (Tom Green, photogallery.canberrabirds.org.au)

UNGRAZEDWOODLAND

REVEGETATION

PADDOCK

SCATTERED

TREE GRAZED WOODLAND

Welcome Swallow

Tree Martin

Rainbow Bee-eater

Cockatiel

Varied Sitella

White-browed Scrubwren

Eastern Yellow Robin

Speckled Warbler

Spotted Pardalote

Richard’s Pipit

Brown Falcon

Peaceful Dove

Common Blackbird

Rufous Songlark

White-thr. Treecreeper

Brown Treecreeper

White-winged Chough

Laughing Kookaburra

Crimson Rosella

Striated Pardalote

Eastern Rosella

Magpie-lark

Crested Pigeon

Noisy Miner

Sulphur-cr. Cockatoo

Grey-crowned Babbler

Jacky Winter

Superb Fairy-wren

Superb Parrot

Overview of social science components

+ policy analysis and economic modelling

Conclusion

Our temperate grazing systems are internationally recognised as threatened

Trees will be lost, unless urgent action is taken Negative ramifications for key ecosystem

services and biodiversity Consistent messages are emerging about what

needs to be done: • (1) altered grazing regimes, and • (2) nutrient management, both at large scales

Acknowledgements

This work was funded by the Australian Government, via the ARC and CERF programme

Thanks to all participating farmers and the Lachlan CMA

Particular thanks to many direct collaborators, especially Jenny Stott, Steve Dovers, Bob Forrester, Kate Sherren, Jacki Schirmer, Andre Zerger, Karen Stagoll, John Stein, Lorna Fitzsimmons, John Field, Garth Warren, Brad Law, Maria Adams… and others!

Thanks to my ANU colleagues for advice

The full paper is FREELY available on the PNAS website:

www.pnas.org(search for “Joern Fischer”)Fischer, J., Stott, J., Zerger, A., Warren, G.,

Sherren, K., Forrester, R. (2009). Reversing a tree regeneration crisis in an endangered ecoregion. Proceedings of the National Academy of Sciences USA.

Land sparing or wildlife-friendly farming?

Fischer, Brosi, Daily, Ehrlich, et al. (2008). Frontiers in Ecology and the Environment.