Lecture 4 - Ecology of Native Pastures

What are natural factors that affect native pasture composition + yield?

• Soil Type

• Climate

• Plant Adaptation

What are man related influences/factors that affect native pasture composition + yield?

• Grazing (rotational/cell/time grazing)

• Animal species differences

• Burning

How does soil type affect pasture growth?

• Soil provides the nutrients + stores the moisture

• Soil is underlying factor, if you don’t have a nutritous or relatively good soil, your production level will be affected

What are the key soil attributes that affect productivity + ecology?

• Soil nutrient fertility

• Permeability

• Water holding capacity (water goes right through sand, while clay can hold water)

• Susceptibility to soil erosion (grasses hold soil together well)

Shallow Stony Soils

Shallow Stony Soils

• Infertile

• Average Permeability

• Low Water Storage

• High Erosivity

• Mulga Country

Deep Sands

Deep Sands

• Very Infertile

• High Permeability

• Low Water Storage

• High Erosivity

• Spinifex (trioda) country

Cracking Clays

Cracking Clays

• Fertile

• Average Permeability

• Average Water Storage

• Low Erosivity

• Brigalow belt, Darling Downs, Mitchell Grasslands

• Most of dairy pastures is on clay soils

Massive Earth - Red, Yellow, Gray

Massive Earth - Red, Yellow, Gray

• Infertile

• Average Permeability

• Highwater Storage

• Average Erosivity

• Cape York

Texture Contrast

Texture Contrast (also known as duplex soil)

• Infertile

• Low Permeability

• Low-average Water Storage

• High Erosivity

• Sandy top w clay in the lower horizon (2 levels of soil, sandy top or a bit of alluvial soil on top and underneath heavy clay soil, sometimes issues with water sitting on top layer for a while, or it can stop some roots from penetrating down further into the soil)

• Speargrass country

What has a greater influence on productivity + ecology on pastures than soil?

WEATHER AND CLIMATE

• Key parameters are amount, seasonality, variability of rainfall

• Temperature has less influence

What can cause pasture degradation?

Droughts!

• Severe droughts occur once every 10 years

• The southern oscillation index (SOI) is used to predict rainfall patterns

• Drought strategies required as native pasture degradation greatest during drought

PRACTICAL IMPLICATIONS OF CLIMATIC CONSTRAINTS

PRACTICAL IMPLICATIONS OF CLIMATIC CONSTRAINTS

• Carrying capacity determined by worst part of year.

• Annual animal management tied to seasonal nutrition e.g. cows conceive when nutrition good.

• Year to year variability of forage supply much greater than ability to vary livestock numbers.

• Livestock numbers often out of phase with forage supply.

• Unusual rainfall occurrences leads to large scale death or recruitment of plants e.g. drought years cause pasture degradation

What are some plant growth adaptations?

Adaption to Low Fertility

• Most native species are tolerant of low fertility

Adaption to Drought

• Dormancy + Germination mechanisms in arid area - ensures long term survival of see in soil

• Morphological adaptation to moisture stress (like deeper roots)

• Physiological tolerance of moisture stress (ability to grow at low leaf tissue water potentials)

• Some species long live (some like Kangaroo gras can live over 9 years)

Adaption to Regular Grazing

• Some countries like African countries, have landscapes that animals have transversed for thousands of years and over time the plant species have become adapted to grazing pressure, so we go to countries like this + find new plants to bring to Australia

• One introduced species, green panic, has started to become more grazing tolerant

Effects of Grazing

• Historically light grazing with regular burning

• Europeans (1800-2024):

   Increased grazing pressure

   Less frequent burning

   Changes in composition in native pasture communities

• Rangelands vary in their response to grazing

Grazing Effects on ecology of native pastures

• Native perennial, productive, palatable (3P) grasses decrease under grazing

• Less palatable perennial & annual grasses, weeds increase under grazing.

What is patch grazing?

• You start a paddock with a set amount of different species and you put a bit of grazing pressure (the animals are going to gravitate to the desirable ones)

• Example: The paddock has patches of Heteropogon (H) + Aristida (A)

• Overtime, you’ll end up with patches of (A) becoming bigger and patches of (H) becoming fewer

• So the animals will just keep putting pressure on the (H) until you get less + less of it because they like to eat it more

What are some ways to overcome patch grazing?

• Reduce the stocking rate for a little while (run less animals through the paddock)

• Some people may do burns of the native pastures (fire would reset the paddocks)

• Fertilizers in improved pastures (not native pastures)

• Goats have broader utilization + will eat more options than the other animals (they still have a preference though)

Where do animals prefer to graze?

• Abundance of palatable species

• Pasture that is relatively free of trees

• Terrain is flat

• Water is available

• Shade is available

Cattle are _______ selective than sheep and eat taller species

Cattle are LESS selective than sheep and eat taller species

Sheep pick out small grasses and forbs, sheep diets are _______ quality than cattle

Sheep pick out small grasses and forbs, sheep prefer HIGHER quality diets than cattle

_______ lose weight more quickly than _______ when competing on same pasture

CATTLE lose weight more quickly than SHEEP when competing on same pasture

Goats eat more ______ + ________ higher

Goats eat more browse and graze higher

Horses have a narrow bite, sharp teeth, graze ___________, select favored species

Horses can be very severe on pastures

Horses have a narrow bite, sharp teeth, graze all the way to the ground, select favored species

“Horse Sick Pastures” are -

Horse sick pastures, are mature horse pastures that are heavily grazed, unglazed rank zones where the horses urinate and defecate, ingress of weeds

Kangaroos mainly eat ______

Kangaroos mainly eat grass. Some landowners look at controlling kangaroo population because the kangaroos will eat the live stock grass

Rabbits will seek out last remaining green feed and graze close to their ________

Rabbits will seek out last remaining green feed and graze close to their warren

Horse diet consists of

Horse Diet

• 90% grasses

• 4% herbs/forbs

• 6% browse (shrubs)

Cattle Diet consists of

Cattle Diet

• 70% grass

• 20% herbs

• 10% browse (shrubs)

Sheep diet consists of

Sheep Diet

• 60% grass

• 30% herbs

• 10% browse (shrubs)

Kangaroo diet is same as sheep diet

Goat diet consists of

Goat Diet

• 30% grass

• 40% herbs

• 30% browse

Reasons to BURN pastures

• Control Woody Regrowth

• Remove unpalatable material + stimulate growth

• Reduce Fire Hazard

• Attract animals to ungrazed areas

• Destroy animal + plant pests

• Prepare seedbeds

• Control pasture composition

• Improve wildlife habitat

What are reasons to NOT burn pastures?

• Fire may kill green plant material + soil surface is laid bare

• Perennial plants reduced, opening up community for the undesirable plants

• Seeds may be destroyed or scarified causing no/high germination

• Fire consumes all herbage, creating a short term shortage

• Destroy wildlife habitats