Availability of understorey forage plants

Inthe

study

^{area, shrubs andforbsare}abundant and

they

form the bulk of the

understorey herbage composition

while grasses constitute

only

^asmall

part. Conversely,

in the open

Tsamdrogs,

grasses make up the

major portion

^{of the}

ground vegetation

while shrubsand forbsare

negligible.

All three sites in the

study

^areahave almostthesame

ground

vegeta¬

tion

species composition,

^{with the}

exception

^{of the}southwest aspect, which^{has some un¬}

known grasses and shrubs. The abundanceof

ground vegetation

^{differsacross the sites}

depending

^onforest stand. Grassestendto

prefer

open and less dense forest stands

(south¬

west

aspect)

while forbs and shrubs fare well on all three sites. Theresult is

normal,

^as

onewouldexpect^the

quantity

^of

ground vegetation, especially

grasses, ^toincrease witha

decreaseintree

density.

^This

relationship

^wasdemonstrated

by

exhaustive studies carried outinthe southernwestern

pine

^{forests of the}United States

(Smith 1949,

cited in FAO

1953).

^{Itwasfound that}

forage production

^{reached 290}

kg dry

^matter

(DM) ha"1

_persea¬

sonwheretree

density

^{was 560stemsha"'};

forage production

^{increasedto595}

kg

^{DM ha"}

under stands with 75 treesper ha.

On all three

sites, significant

differencesin the total

ground vegetation

^{atthetworecorded}

seasons show that

forage

^{resources become scarce inwinter. Palatable shrubs andforbs}

that are

plentiful

ⁱⁿ summer are scarcein

winter3

as

they

^areeither

grazed

^offor

dry

^out.

Although

the total number ofgrasses^recordedinwinter andsummerdoesnotseemtodif¬

fer

significantly,

^{the mean}

heights

of grasses^are

significantly

^reducedin the winter

(see

transect survey

result,

^{Table4.4 in}

Chapter 4,2,3).

The winter feed

shortage

^{is a well}

known

problem

^{andis the main}

limiting

^factorfor

development

of livestock programs in Bhutan

(Roder, 1997).

5. Thestudy^areaisawinter grazingground

3.6.1.1 Grasses

Native grasses recorded

during

^the

inventory

^{in the}

study

^{were limitedto}

Paspalum

^and

Digitaria species. They

^fallunderthe

Chrysopogon/ Cynodon/Paspalum grassland

type thatoccurbelow 2500m

throughout

^Bhutan

^{(Tsuchida, 1987).}

Other genera,

namely Isaclme,

Saccarum, Miscanthus, ^Panicumand

Oplismenus

^{were seenin the}

study

^area

while

cruising

^the

inventory lines,

^{butdid notfall on the}

plots.

^Millar

(1987) reported Oplismenus compositus

^as the dominant grass species found^ontheforest floor around Dala

village (1850

^{m). Not}much information on the abovenative grassesis available.

Kikiyu

grass

(Pennisetum clanclestinum),

^{which is}

gradually invading

the open^Tsam¬

drogs

^andforest

clearings

^was first introduced in the

nearby

government livestock farm for

forage. Kikiyu

grass is said^tobe

highly palatable

under humid conditions and its

growth

^becomes

aggressive

^under

dry

conditions whileits

palatability

^decreases

(Garri¬

son and

Pita, 1992).

^A

spine-noded bamboo,

Chimonobambusa

callosa,

^{is acommon} bamboo in the

study

^area. It appears that this bamboo

species

^{is nota}

preferred

^fodderas

it is

only

^browsed

by

cattle when other

forage

^is

unavailable7. _They

are cut

extensively

andwovenintomats tobeusedasroofs andwalls in

temporary

^sheds.Inthe

higher

^reach¬

es,the Yushania

species

and Arundinariaracemosa

(an important forage

for cattle and

yak) replace

^them

(Numata, 1987).

3.6.1.2 Palatable forbs/shrubs

Palatable forb/shrub

species

^{suchas Viola,}

Pilea,

Elatostema,

Aporasora,

Persicaria, ^Gi-

rardinea, Aconogonon,

^{Rubia, Rubus andSolonumformthebulkofcattle feedin the}

study

^area. The number of

Viola, Pilea,

^{Elatostemaand}

Aporosa

^is

high,

but their contri¬

butionto

herbage production

for animal intake is

negligible

^as

they

^are

tiny

^herbaceous

plants. They usually

growin abundanceunder tree

canopies,

^andtheir presence ^orcondi¬

tionon thesitescould be used toassess

grazing intensity.

Shrubs such as

Girardinea, Aconogonon,

Rubia,Rubus and Solonum make up^the

major

^{feed forthecattlein the}

study

area. These shrubs areindicators of the succession toshrub

land;,

^if

they

^{arenot main¬}

tained

they

^are

replaced by unpalatable

^and

thorny plants (Tsuchida 1987). They

^{die back}

in winter andare not availableto

cattle,

which makes the

forage

situation critical.

3.6.1.3 Small tree

seedlings

Smalltree

seedlings

^formasmall

part

^{of the}

ground vegetation composition.

^The

pioneer species

^of

Eurya, Casaeria, Symplocos, Lindera,

Walsura, ^Maesaand Viburnum

makeup

the

major

part^{of the smalltree}

seedling population.

^{Small tree}

seedlings

^ofthe

primary species

^of

Quercus,

Acer, Persea,

Castanopsis

^and

Elaeocarpus

^arelowin number. The numberof smalltree

seedlings

^isreduced

during

^winteronall three sites. The dense forest standhasa

significantly higher

number of smalltree

seedlings.

^Growth,

ingress

^andmor¬

tality

patterns ^{of small tree}

seedlings

^are

complex.

^Some

species

appear in ^summerand

disappear

^{in winterwhileothers dothe}

opposite.

^{It is}unclear whethertheappearance and

6. Accoiding^toTsuchida(1987). Chiwopogongiows^ondr> ^{sites. C\nodonon mesicsiteswhile}Paspalum thuves undeimoistconditions

7 Peisonal observation 1998^-Bamboosneaicowshedsshowed little sign^otgiazmg

72

disappearance

^{of small tree}

seedlings

^{is duetotheirnatural}

cyclic

^seasonal

pattern

^orto

grazing.

^Thepresent

study

^couldnotrelate their

dynamics

^tocattle

grazing.

3.6.2 State of

forage

^resources

The

increasing

^{dominanceofinvader}

species

^and

species

^{atthe bottomof}the succession tableshowsthat

forage

^resourcesare

declining

ⁱⁿ

quality. Paspalum

^is

being increasingly replaced by Digitaria species8

in the open meadows of the

study

^area.

Unpalatable

^forbs

andshrubs suchas

Eupatorium,

Pteridium, Artemisia,

Ptericanthus, Plantago

^{and Rumex}

are

gradually replacing

^the

palatable

^{forbs and shrubs} in open forest

clearings. Special

mentionshould be made here of

Eupatorium

^{weed, anexotic}

species,

^{whichnowhas nat¬}

uralizedonmany^forest

clearings

^{in the}

study

^{area. The} presence^ofGirardinea,

Aconogonon, ^Rubia,

^{RubusandSolonum} also shows that the

forage

^{situation isdeterio¬}

rating

^{in the}

study

^area.Gibson

(1991)

observed that

forage plants

ⁱⁿand around the

study

area were

overgrazed

and estimatedthe

availability

^of

herbage

^at

200kg

^DM

ha"1

_year.

Thestateof

forage

resources onthesouthwest aspect^ofthe

study

^areais

relatively ^critical,

asthe numberof cattle

currently grazing

^thereisvery

high.

^Thesituation is intensified

by

the fact thatmost

herders,

^{who in the}

past migrated

^tothe

north,

^have

stopped doing

^so.

Anassessment of

ground vegetation

^{on thesouthwest} aspect^{shows that thenumberof} grasses and shrubs ^arereduced in

winter,

^{and then even}

unpalatable

^{bamboo isbrowsed.}

Violaand Pilea

species

^thatare

generally

found under the forest canopy ^are

grazed

away.

Itis

likely

^{that the}

forage

situation deteriorate as the cattle

population

^{continues to in¬}

crease.

The decline of

forage

^{in the}

study

^{area canbe attributed to}

overgrazing;

^{the cattlecensus}

data for

Geyling

^and

Bongo

geogs

(to

^{which the}

study

^area

administratively belongs9^

suggests

that the number ofcattlein the

study

^areais

increasing.

The number of cattle has increased

steadily

^overthe years in

Geyling Geog (Table 3.37)

and has remained almost constantforsomeyears in

Bongo Geog;

^{it has}

only recently

^{started todecrease}

(1999) (Table 3.38).

Cattletype ^{1988 1989 1990 199V 1995 1999}

Local cow 1,899 ³⁵⁴⁹ 3,966 4,181 4,160 4,661

Jersey

^{cross 35 113 19 100 93 485}

Mithun cross 242 131 319 408 412 769

Total 2,176 3,793 4,304 4,689 4,665 5,915

Table 3.37 Number ofcattleby typeⁱⁿ

Geyling

Geog 1988-91,1995^{and 1999}

(DAHO 1999).

8. Tsuchida(1987)statedthatPaspalumletrogiesses^to Dii>ita>ia undethea\y glazing.

9. The northeastaspectbelongs^toBongo Geog^{andthesouth*estto}Gc\lingGeog.

Cattletype ^{1988 1989 1990 1991 1995 1999}

Localcow 3,212 3,460 3,892 3,717 3,688 ³⁴²²

Jersey^{cross 26 82 188 256 241 197}

Mithun cross 113 185 241 514 517 521

Total 3,351 3,727 4,321 4,487 4,446 4,140

Table3.38 Number of cattle by typeⁱⁿ Bongo

Geog,

1988-91,1995^and1999

(DAHO 1999).

No documento Cattle grazing - an integral part of broadleaf forest management planning in Bhutan (páginas 71-74)