CH12
Ecological Role of Solar
Radiation
阮宏华
By Dr. Honghua Ruan
南京林业大学
Nanjing Forestry University
4.3 The compensation point of light
and the saturation point of light
4.4 The shade tolerant of trees
树种耐荫性: 在林业上, 是指树种在林冠的庇荫条件
下能否正常生长并完成其更新的能力.
1) 阳性树种: 只能在全光照条件下正常生长发育,在
树冠下一般不能正常完成下种更新的树种,如: 松,
桦,杨等
2) 耐荫树种: 能忍受庇荫,在林冠下能正常生长并完
成更新的树种,如:云杉,冷杉,铁杉,杜英,红豆杉等
3) 中性树种: 介于以上两树种之间. 红松,杉木,木荷
Shade Tolerance:
One thing that any gardener and anyone
who has lived in the world long enough will
eventually realize is that some plants like
to grow in sun while others like shade. The
conditions in sun and shade are very
different.
What is a full sun environment
like?
• This picture shows cedar and black cherry, among other small plants,
growing in a recently cut field near Cambridge, Maryland. The
conditions in direct sun are quite harsh. While the sun provides the
energy that plants need to grow, it also provides destructive UV
(ultraviolet) rays and causes high rates of evaporation, causing
things to dry out. Areas in full sun tend to get a lot hotter during the
day than at night, so temperature variation is large. Think of how you
get sunburned and dehydrated when you sit out in the sun for a few
hours, and then realize that many plants have to sit in the sun all
day long. Plants need special adaptations to tolerate full-sun
conditions. They need to conserve water, and they need protection
from UV rays. On the other hand, plants in full sun have ample
energy available to them, and can afford to use that energy to
conserve water or protect from UV rays; energy is often not a
limiting factor in full sun.
What is a shady environment like?
• This picture shows a forest growing along
Tuquan Glen in Lancaster county, Pennsylvania.
The environment in shade is very different from
sun. There is much less available sunlight for
plants to use for energy. At the same time, the
environment is milder. The temperature is more
moderate, there is little threat from UV rays, and
evaporation is less of a problem. As shade
increases, the environment gets more and more
mild, but less and less energy is available to
plants. Thus, in order to adapt to shade, plants
need to conserve energy, but don't need to
worry as much about things like water
conservation.
• All large trees will have their tops in full
sun when they reach the top of the forest
canopy. But many trees begin their lives in
shade, and some medium and small trees
never reach the top of the canopy. How
well trees grow in shade varies from one
type of tree to another, and sometimes, it
depends on the conditions as well. (For
example, some species become more
shade tolerant as the soil gets richer, or in
warmer climates.)
How do shade-tolerant trees and shade-intolerant trees
compare (如何鉴别树种的耐荫性)?
Shade Tolerant
Shade Intolerant
(Pioneer)
Growth Rate
slow
fast
Seeds sprout
Under a forest canopy In open areas, on
exposed ground
Needs to conserve
Energy
Water , nutrients
Has abundant
Water, nutrients
Energy
Blossom out
late
early
Life
Long
short
CP and SP
lower
higher
others
枝叶密,枝下高低,自然整 相反
枝弱, 树冠透光度小, 林相
密
• This table is an oversimplification. Most
trees do not fit well into one category.
There are a few cases in which it is easy
to classify a tree: for example, Eastern
Hemlock in the most shade-tolerant of all
large trees in the U.S. It has all the
characteristics listed in the table above.
But most trees fall somewhere in between.
• So why is this important?
• Shade-tolerant species tend to replace intolerant species
over time, once the forest canopy becomes dense. If a
species is not shade-tolerant, it will not be able to
reproduce in a forest. Shade tolerant trees will sprout
under the forest canopy, and grow to small or moderate
sizes. When a tree dies and a gap appears, the shade
tolerant trees will already have grown to considerable
size, and they will be able to respond by growing quickly
to fill in the gap. Shade-intolerant trees, although faster
growing, usually do not have the ability to compete in
small gaps. When the trees in an area become well
established and change little over time, the ecosystem is
called a "climax community".
• If shade-tolerant species win out in the end, why are
there so many intolerant species still left?
• First, even in many mature forests, there are enough
moderate and large disturbances to open up enough
gaps for less tolerant species to survive.
• Second, there are some areas where, due to conditions,
trees in a forest never get big enough to fully close the
gaps in the canopy. This is true both in cold climates, dry
areas, areas with extremely low nutrients or poor soil,
areas prone to fire, along rivers, or in areas polluted by
humans. One of the reasons that we see fewer shadetolerant species these days, however, is that humans
have altered the environment to favor intolerant species;
there are fewer undisturbed areas where shade-tolerant
species thrive.
The factors influencing on shade
tolerant of species
1) Age
2) Climate
3) Soil
4.5 Light-energy and forest
productivity
The efficiency of light-energy using
For single leaf ,
is 5-15%
How to improve the efficiency of lightenergy using
Net primary productivity (NPP):
NPP=f ( LAI*PE*T )
Where LAI is photosynthetic Area, T is
Photosynthetic Time, PE is Photosynthetic
Efficiency.
The ways to improve the efficiency of
light-energy using
1) Increasing LAI (增加光合作用面积):
Agri-forestry,
Multi-layer structure of canopy,
mixture forest
Planting with a available density
2) Improve photosynthetic efficiency:
Tree species selecting
Forest management
Increasing photosynthetic time:
It is hard to increase photosynthetic time in a
forest.
Quiz-1
1.
Definitions:
Ecology; Ecosystem; The compensation point of light and the saturation
point of light; Ecological Pyramid; Food Chain; Ecological Efficiency
2. Ozone and Greenhouse Gases
•
Name three greenhouse gases?
•
What are the impacts of ozone in troposphere and stratosphere to the
earth’s biosphere?
3. List three ecosystem processes affecting the following:
•
Nutrient inputs
•
Nutrient outputs
4 What basic components do a ecosystem include?