Appropriate amount of plant-resources relationship regulation
Plant growth and resource
availability relationship can be divided into different stages. For
example, caranaga growth and resource use relationship can be divided
into four stages in a growing season in semiarid loess hilly region of
water-limited regions (Guyuan, China). The first stage is at the dormant
period from January 1st to the second ten of April. At this period,
plants are dormant and not sensitive to water stress because plant stop
growth. The second stage is the period from the second ten of April
(caragana bud germination) to the end of Jun. (full-expansion of leaf)
and the plant was not sensitive to water stress at this stage because
the leaves of plants are not fully developed, and Caragana only absorbs
a small amount of water; The third stage started is at the fast growth
period from the end of June when the leaves were totally expansion to
the end of August. At this stage,plant grow rapidly and need a lot of
water. At this stage, plant suck much water and was very sensitive to
soil moisture in this period. If the soil water resources in the maximal
infiltration depth are lower than soil water resource use limit by
plants, the plant-water relation goes into critical period of
plant-water relationship regulation. At this time, the plant water
relationship in the key period of plant water relationship regulation is
very important, because it determines the maximum yield and benefit of a
plant community. The fourth stage is leaf fall period, ranging from
September to the end of October (complete leaf drop), the plant was
insensitive to water stress. After the leaf fall period from November
(the beginning of dormancy) to the first ten of April (the end of
dormancy), the plant-water relation goes into the dormant period and the
influence of soil moisture on plant growth was very little in this
period.
Planting density anddegree of cover relation
The degree of vegetative cover is an important index to evaluate the
function of a plant community to conserve soil and water. The
effective degree of cover is the
degree of vegetative cover when soil loss is equal to allowable soil
loss, so effective
degree of cover should be as the
cultivating standard of adult soil and water conservation vegetation or
forest (Guo 2000). The degree of
cover increased gradually with age at the same condition of species,
initially planting density and site condition. In a growing season of a
given species and site condition, the degree of cover in a plant
community increased gradually from budding in mid-April to the fully
expansion of leaf by the end of June. The degree of cover then remained
relatively constant in the period from July to October, the degree of
cover can be defined as the stable coverage degree (SCD).
The degree of cover increased with the planting density, and the
relationship between the stable
cover degree (SCD) and planting density at the third ten of July was
given by (Guo and Shao, 2013), see
figure 4
SCD = 0.2895 Ln (PD) – 1.8197
Where, SCD is stable cover degree and PD is planting density.