L4 - Ecology of Native Pastures

factors that affect native pasture composition, yield:

natural

-soil

-climate

-plant adaptation

factors that affect native pasture composition, yield:

man

-grazing

-animal spp differences

-burning

summary:

soil type

-provides nutrients

-stores moisture

key soil attributes that affect productivity and ecology

-soil nutrient fertility

-permeability

-water holding capacity

-susceptibility to soil erosion

soil types across N Aus:

clay soils

-brigalow belt

-darling downs

-mitchell grasslands

soil types across N Aus:

soil types across N Aus:

deep sands

-spinifex (trioda) country

soil types across N Aus:

massive earths

cape york

soil types across N Aus:

shallow stony soils

mulga country

soil types across N Aus:

texture contrast soil

-sandy top w clay in the lower horizon

-speargrass country

summary:

weather and climate

-greater influence on productivity & ecology than soil

-key parameters are amt, seasonality, variability of rainfall

-T less influential

summary:

droughts

-severe droughts occur once every 10 yrs

-need drought strategies

what is used to predict rainfall patterns?

SOI (southern oscillation index)

practical implications of climate constraints

-carrying capacity determined by worst part of year

-annual animal management tied to seasonal nutrition

-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

what has invaded this pasture?

Bothriochloa pertusa (Indian couch)

plant growth adaptions (2)

-to low fertility

-to drought

adaptations:

drought

-dormancy and germination mechanisms in arid areas → long term survival of seed in soil

-morphological adaptation to moisture stress

-physiological tolerance of moisture stress, e.g. ability to grow at low leaf tissue water potentials

-some spp long lived

effects of grazing

-light grazing, regular burning

-Europeans increased grazing P, 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 grasses decrease under grazing

-Less palatable perennial & annual grasses, weeds increase under grazing

grazing:

animal preferences

-palatable species

-relatively tree free

-flat terrain

-water

-shade

what type of diet do horses prefer?

-grass (90%)

-herbs/forbs (4)

-browse (6)

diet preference:

cattle

-grass (70%)

-herbs/forbs (20%)

-browse (10%)

diet preference:

sheep

-grass (60%)

-herbs/forbs (30%)

-browse (10%)

diet preference:

goats

-grass (30%)

-herbs/forbs (40%)

-browse (30%)

diet preference (%):

kangaroos

-grass - 60

-herbs/forbs - 30%

-browse - 10

how is excessive tree growth due to over-grazing controlled?

-burning at beginning of wet season

reasons to burn

Control woody regrowth

Remove unpalatable material & stimulate regrowth

Reduce fire hazard

Attract animals to ungrazed areas

Destroy animal and plant pests

Prepare seedbeds

Control pasture composition

Improve wildlife habitat

reasons not to burn

-Fire may kill green plant material & soil surface is laid bare

-Perennial plants reduced, opening up community for undesirable plants

-Seed may be destroyed, or scarified causing no/high germination

-Fire consumes all herbage, creating a short term shortage

-Destroy wildlife habitats

characteristics:

shallow stony soils

-infertile

-avg permeability

-low water storage

-high erosivity

characteristics:

deep sands

-v infertile

-high permeability

-low water storage

-high erosivity

examples of tall grass (N. Aus)

-fire grass

-ribbon grass

-native sorghum

-blady grass (coast)

-black spear grass

what grasses are found in inner QLD?

-brigalow

-wire grass/blue grass

-Mitchell grass

-Mulga

which soil types are infertile? (3)

-shallow stony soils

-red, yellow, gray earths

-texture contrast soils

N. Aus:

fertile soils

-cracking clays

N. Aus:

VERY infertile soils

deep sands

high erosivity soils (N. Aus)

-shallow stony soils

-deep sands

-texture contrast soils

low erosivity soils (N. Aus)

-cracking clays

avg erosivity soils (N. Aus)

-red, yellow, gray Earths

high permeability soils (N. Aus)

-deep sands

avg permeability soils (N. Aus)

-shallow stony soils

-cracking clays

-red, yellow, gray earths

low permeability soils (N. Aus)

-texture contrast soils

high water storage soils (N. Aus)

-red, yellow, gray earths

low water storage soils (N. Aus)

-shallow stony soils

-deep sands

-texture contrast soils (low-avg)

avg water storage soils (N. Aus)

-cracking clays

what biological factor has the least impact on soil?

T

what biological factor(s) has the highest influence on soil?

-weather

-climate

-land invaded by Bothriochloa pertusa (Indian couch)

Kangaroo grass

Themeda triandra

(tolerant to low fertility)

example of long-lived spp?

-Kangaroo grass

(Themeda triandra)

how do goats graze?

-eat more browse

-graze higher layers of vegetation (no direct competition with sheep, cattle)

definition:

browsing

-eating leaves, twigs, bark, and shrubs (woody plants, bushes, small trees)

definition:

grazing

-eating grasses and herbaceous (non-woody) plants at ground level