Livestock grazing for weed management - Ecological Management of Agricultural Weeds - page 414

Table 9.1. Grazing management by plant growth stage to favor or disfavor the growth
of specific forages and weeds

Actions to favor relative Actions to disfavor

Growth stage plant performance relative plant perfomance

Germination and seedling • graze to create gaps in sward • maintain complete plant

establishment • graze to reduce growth of • cover

• vegetation around seedling • trample seedlings

• reduce grazing pressure • graze seedlings heavily

• after seedling emergence

Vegetative growth • allow sufficient leafarea for • defoliate completely

• regrowth • graze to eliminate buds

• graze to limit excessive self- • repeat defoliation at short

• shading ofleaves • intervals

• remove animals to allow
• recovery ofleafarea and roots

Flowering and seed • in annuals,graze to encourage • graze to reduce flowering

production • seeding • and seeding

• in tillering perennials,graze to • reduce grazing to promote
• avoid flowering to promote

• flowering to senesce plant

• tiller vigor and number

Accumulation ofreserves • reduce grazing when reserves • graze when reserves are low

• cannot be restored • graze when regrowth will

• reduce grazing when growing • deplete reserves

• conditions are unfavorable

after the completion of frond expansion, when rhizome carbohydrate levels
were at their low point, caused decreased bracken biomass production for the
following two years. Burning in the spring or fall when carbohydrate reserves
were high increased bracken biomass in the following years.
Excessive herbivory, either in frequency or intensity or when growing con-
ditions do not favor plant regrowth, reduces root growth, retards bud and
tiller development, and may lead to plant death.Table 9.1 contrasts the use of
herbivory in different growth stages to either weaken a plant or to strengthen
its position relative to neighboring plants. This format can be applied to spe-
cific weeds to identify and exploit their relative weaknesses.

Weeds in a plant community
Any land unit used for grazing is occupied by plant species in differ-
ent proportions with different life histories, growth habits, and ecophysiol-
ogies (Figure 9.1). At any point in time, each species consists of a dispersed
quantity of leaves, stems, buds, roots, and seeds (Figure 9.1). Fluctuations and
changes in this vegetation complex in response to grazing, trampling, and