Planting density and soil loss relationship
The main type of soil erosion in Chinese Loess Plateau is water erosion.
The influence of planting density on soil losses can be expressed by the
sediment concentrations in the runoff plots. The sediment in the runoff
gradually increased with the reduction of planting density. The
relationship between the sediment concentration SC (gram per liter) in
the surface runoff and planting density D can be written as follow:
SC =
Here, SC sediment concentration, g per liter, d is plant density, shrubs
per 100 m2
Under the same species, age and site condition, the biomass, the canopy
coverage and the canopy interception per unit area increased with
planting density, leading to a smaller surface runoff, suggesting that
the benefit of vegetation to conserve
soil and water is remarkable (Guo
and Shao 2013).
Appropriate
amount of plant- resources
relationship regulation
The duration of resource scarcity
refers to the period when the resource storage is less than resource use
limit by plants. If the resource
storage is smaller than resource use limit by plants, the plant-
resource relation goes into critical period of plant- resource
relationship regulation, the
plant- resource relation enters the critical period of plant-water
relationship regulation; the plant- resource relation should be
considered because it decides the maximal yield and benefits of soil and
water conservation vegetation.
After the plant-resources relation
enters the critical period of plant-
resources
relationship regulation, if the
duration of resource scarcity is more than the critical period of plant
resources relationship regulation or the existing plant density is more
than the vegetation carrying capacity in the critical period of plant
resources relationship regulation, vegetation carrying capacity should
be evaluated and plant growth should be controlled by cutting some tree
to reduce plant density and regulating
plant-resources relationship and
get the maximal yield or service.
The vegetation carrying capacity
is the ability of land resources to bear vegetation, which changes with
vegetation type caused by tree species, time period and location (Guo
2014,2021a and b) and is a suitable measure of assessing the
plant-resources relationship. vegetation carrying capacity includes
space carrying capacity for vegetation in areas rich in water and
fertilizer, soil water carrying capacity for vegetation in water-limited
regions and soil fertilizer carrying capacity for vegetation in
fertilizer limited regions (Guo 2019). Total coverage of a plant
community when plant density of indicator species in a plant community
is equal to vegetation carrying capacity is the suitable limit of
vegetation restoration.
If the plant density is more than the soil water carrying capacity for
vegetation in the critical period of
plant-resources relationship
regulation, plant-resources relationship has to be regulated to get the
maximal yield and benefits and carry out sustainable use of soil water
resources and high-quality and sustainable development (Guo 2014,2021b).
Even if the goods and benefits produced by non-native ecosystem meet the
need of increase in the population, but non-native species change
plant-resources relationship of origin vegetation and its
self-regulation and resilience is limit and cannot recover to the
balance condition once soil water resources with maximum infiltration
depth in Caragana forest land is smaller than soil water resources use
limit by plants. For example, If
the soil water resources in the
maximal infiltration depth is more than soil water resources use limit
by plant, the plant water relation enters the critical period of
plant-water relationship regulation. The soil water sever deficit is the
soil water resources in the maximal infiltration depth is more than soil
water resources use limit by plant. If the duration of soil water sever
deficit is more than critical period of plant-water relationship
regulation, the relationship between soil water supply or soil water
consumption and plant density and soil water carrying capacity for
vegetation in the critical period of plant-water relationship regulation
should be estimated. The relationship between planting density and soil
water supply SWS, soil water consumption SWC, the amount of water taken
up by the plants in the critical period of plant-water relationship
regulation in the 16-year-old caragana shrubland of semiarid loess hilly
region (Guo and Shao 2004; Guo 2014,2021) was determined by:
SWS = 92.494- 0. 29D
SWC = 0. 0118D2- 0. 7575D+ 64.759
Where SWS is soil water supply in mm, SWC is soil water consumption in
mm.
By solving the equation set, the soil water carrying capacity for
vegetation was 72 shrubs per hm2, and the
corresponding cover degree was 0.8 according to the formula:CD= 0.289
5ln72- 0.486 4. The degree of cover is the limit of canaraga
restoration. When exceeding this limit, the canaraga shrubland would
deteriorate soil water environment, and soil desiccation will be emerged
or aggravated, soil degradation and vegetation decline will happen,
which in turn influence benefits of water and soil conservation of
forest vegetation.