Seasonal variation of feed values in arid mountain grasslands under grazing impact in

Qilian Shan, NW China

•Qilian Mountains are placed in between Qinghai and Gansu provinces of North West China. Being a northern outlier of Kunlun Mountains, they borders with Tibetan Plateau. • Qilian Mountains belongs to semi-arid dryland where precipitation and temperature – are two main factors determining vegetation cover - show a distinct vertical gradient•Strong differentiation of vegetation on North-facing slopes (mostly spruce forest -Picea crassifolia) and dry South-facing slopes with sparse vegetation.

to evaluate the variation in pasture quality and its dependence from environmental and landscape-related factors as well as from management characteristics (vegetation inventories).

to assess grazing-induced and spatially differentiated changes in vegetation patterns regarding to species composition, productivity and grazing value.

The objective of the research was: to examine feed values of spring/autumn and summer

pastures with subject to harvest time (1) and grazing intensities (2) along the altitudinal gradient and

to examine if grassland ecosystem suffer under degradation due to continues grazing and trampling pressure.

2003

2012

Stellera chamaejasme

Iris ensata

Xanthopappus subacaulis

For grazing value estimation was developed applied range condition scale (visual estimation scale and complex degradation index)Productivity: 2-years data on biomass wet and dry weight (235 samples), among them 115 samples were used in analyses for the feeding values (ADF, NDF, ADL) and inorganic content (macro and tracing elements)

Du Toit has suggests to estimated chemical parameters (TDM, ADF, K, Mg, Ca, N, P) of each of the forage species in order to

model the forage values for each specie presented in the pasture community by multiplying with spread total cover value to get the

agronomic value of grazing index.

ADF – Acid Detergent Fiber – the amount of indigestible forage.

NDF – Neutral Detergent Fiber – the amount of forage which could be digested

CP = Crude Protein = Nitrogen x 6,25Effective size - amount of biomass

consumed by herbivores. Effective size = (wet weight – dry weight)/ wet weight

Effect of harvest time

1 2 3

0.5

0.6

0.7

0.8

Effective size variaton during growing season

harvest

effe

ctsi

ze,g

m²

1 2 3

45

50

55

60

65

NDF values variaton during growing season

harvest

ND

F,%

1 2 3

22

24

26

28

30

32

34

ADF values variaton during growing season

harvest

AD

F,%

…on effective size of the biomass

…on NDF values …on ADF values

…on Crude Protein

1 2 3 4

45

50

55

60

65

Effect of grazing on NDF

grazing classes

ND

F,%

1 2 3 4

22

24

26

28

30

32

34

Effect of grazing on ADF

grazing classes

AD

F,%

1 2 3 4

05

00

10

00

15

00

Effect of grazing on biomass

grazing classes

we

t we

igh

t,g/m

²

…on biomass wet weight

…on NDF and ADF values …on number of species

0 500 1000 1500

05

10

15

20

Effect of species number on biomass

wet

spp

.no

1 2 3 4

51

01

5

Species number variation

grazing classes

spe

cie

s n

um

be

r

1 2 3 4

45

50

55

60

65

Effect of grazing on NDF

grazing classes

ND

F,%

1 2 3 4

22

24

26

28

30

32

34

Effect of grazing on ADF

grazing classes

AD

F,%

Carex spp, Medicago hyspida, Potentilla anserina, P. saundersiana,

P. bifurca, Kobresia capillifolia, Leymus secalinus,, Agropyron

crystatum

Medicago hyspida, Poa spp., Potentilla anserina, Geranium

pratense, Agroopyron cristatum, Stipa capillata,

Poligonum bistorta

Stipa capillata, Stellera shamaejasme, Oxytropis spp,

Heteropappus altaicus, Atriplex spp.

Stipa capillata, Medicago hyspida, Stellera shamaejasme, Artemisia spp., Oxytropis spp,

Allium cyaneum

1

2

3

4

2600 2800 3000 3200

50

01

00

01

50

0

peak biomass

Altitude

we

t

0 500 1000 1500

01

00

20

03

00

40

0

Growing season biomass

wet

dry

0 500 1000 1500

05

10

15

20

25

30

Effect of plant hight on biomass

wet

me

an

.h

Distribution of dry and wet biomass

wet vs dry weight

1 2 3

68

1012

1416

18

Mean hight variation

grazing classes

mea

n hi

ght

1 2 3 4

05

00

10

00

15

00

Effect of grazing on biomass

grazing classes

we

t we

igh

t,g/m

²

1 2 3 4

05

00

10

00

15

00

Effect of grazing on biomass

grazing classes

we

t we

igh

t,g/m

²

mean height vs dry weightdry weight vs altitude

r²=0,77 p<0,001

r²=0,50 p<0,001

12

34

0 500 1000 1500 Effe

ct o

f gra

zing

on

bio

ma

ss

gra

zing cla

sses

wet weight,g/m²

12

34

0 500 1000 1500 Effe

ct o

f gra

zing

on

bio

ma

ss

gra

zing cla

sses

wet weight,g/m²

r²=0,39 p<0,001

Median concentrations for the macro elements during growing season were P 1.470, Ca 7.97, K 18.58, Mg 2.51, S 2.21 in g/kg DM, and the trace elements were Mn 0.07, Fe 1.44, Zn 0.052 in g/kg DM. Median content of feed values was NDF 55.31%, ADF 27.45%, ADL 5.69%, CP 14.50% and median content of DM 126.82 gm²

There was no significant difference in seasonal variation of most mineral concentrations, except K (p=0,048) and Zn (p=0,0002), whereas feed values were differing significantly between harvests (p<0,05). Among grazing classes feed values were also significantly different (p<0,01), as well Zn, P and S content.

No linearity was observed in relationship between feeding values and grazing classes, although mean height of the standing biomass showed linear relation with grazing intensities (R²=0.35, p=0,008).