growth and availability of bioengineering species
although the structural characteristics are extremely important there are some other factors we need to consider when we are selecting species for bioengineering.
1 desired growth characteristics
a rapid establishment and vigour
in bioengineering we require plants which will become well-established in the season of planting so that they are able to survive the dry months until the next monsoon. many bioengineering sites have very poor soils which drain easily. this makes good establishment even more important.
when we talk about vigorous growth in a plant we mean that after the plant is quickly established it continues to grow well.
the following are some examples of plants with vigorous growth.
b persistence
many plants are annuals. this means they complete their life cycle in less than a year and then die. if we were going to use them for bioengineering we would have to replace them every year and they would never become established as strong plants.
clearly we will not want to use annual plants. neither will we want to use plants that only have a short life cycle of more than one year unless they fill a special role until a plant which lives longer can become established. many of the plants we use are trees and shrubs and others are perennial plants such as many of the grasses which will live for several years.
the ability to live several years and survive in harsh conditions is important in bioengineering species. we call this persistence.
c ease of propagation
where bioengineering is being implemented we need a large amount of planting material. this is especially the case with grasses.
Kans is an example of a bioengineering plant. It is propagated from slips. a slip is a piece separated from a clumping grass so that it has shoots with buds and as much root as possible. in a nursery we may be growing thousands of these slips. this means that, if we are using slips, we need to have a species which is easily propagated by this method.
most of the other methods of propagation that are used result in large numbers of plants. these include:
- seed;
- hardwood cuttings;
- stem cuttings; and
- culm cuttings.
2 availability
availability means the planting material has to be obtainable where it is wanted, at an affordable price, when it is required and in the required quantities.
local species are generally better suited than species from another area to conditions in a particular place. this means that our first choices are generally plants that are found in the area where the bioengineering is being implemented. nurseries are established in order to provide the planting material that is required, at the right time and in the right place. if the availability requirement is to be met they must be well managed.
health may also affect the choice if we are selecting between a species which suffers from disease and one which is resistant to disease.
selection of plant species
the following factors should be considered for the selection of plant species.
ecological zones of Nepal
vegetation zones
local species
selection of plant species according to morphological characteristics
establishment and persistence
adaptation and availability
growth and availability characteristics of bioengineering species
rapid establishment and vigour
persistence
ease of propagation
availability
selection of species based on drought factor
| a |
slope angle: |
slope
< 30º
30 - 34º
35 - 39º
40 - 44º
45 - 49º
> 49º
|
score
1
2
3
4
5
6
|
| b |
stoniness: |
fines
> 25%
20 - 25%
15 - 19%
10 - 14%
5 - 9%
< 5%
|
score
1
2
3
4
5
6
|
| c |
altitude: |
altitude
> 2500 m
2000 - 2500 m
1500 - 1950m
1000 - 1450 m
500 - 950 m
< 500 m
|
score
1
2
3
4
5
6
|
| d |
aspect: |
aspect
north
northeast
northwest
east
west
southeast
southwest
south
|
score
0
2
4
6
8
10
10
12
|
| e |
annual rainfall: |
rainfall
> 2500 mm
2000 - 2490 mm
1500 - 1990 mm
1000 - 1490 mm
500 - 990 mm
< 500 mm
|
score
1
2
3
4
6
8
|
highway slope site drought factor classes:
score
|
class
|
definition
|
< 6
6 - 11
12 - 17
18 - 23
24 - 30
> 30
|
I
II
III
IV
V
VI
|
cool, moist sites
damp sites
moderately dry sites
warm, dry sites
very hot and dry sites
very severely hot and dry sites
|
depending upon the drought factor, an appropriate species can be selected from the list provided in the Bioengineering Site Handbook, page 130-143.
selection of plant species for bioengineering
selection of plant species
site 1
you have been asked to select suitable plant species to be used on a site for bioengineering. use the manuals to select the best one tree species, three shrub species and three grass species for this site.
engineering functions required:
- anchor and catch
site description:
- slope 32°
- stoniness: % of fines 25%
- altitude 1250 m
- aspect north
- rainfall 2200 mm/yr
NB this site is used as a free grazing area by the local community.
site class: _______________________
definition of site class: _______________________
species selected:
Species Function
grass a) ________________ _________________
b) ________________ _________________
c) ________________ _________________
shrub a) ________________ _________________
b) ________________ _________________
c) ________________ _________________
tree ________________ _________________
selection of plant species
site 2
you have been asked to select suitable plant species to be used on a site for bioengineering. use the manuals to select the best one tree species, three shrub species and three grass species for this site.
engineering functions required:
- catch and support
site description:
- slope 38°
- stoniness: % of fines 13%
- altitude 600 m
- aspect south
- rainfall 1100 mm/yr
NB this site does not have any severe grazing problems.
site class: _______________________
definition of site class: _______________________
species selected:
Species Function
grass a) ________________ _________________
b) ________________ _________________
c) ________________ _________________
shrub a) ________________ _________________
b) ________________ _________________
c) ________________ _________________
tree ________________ _________________
selection of plant species
site 3
you have been asked to select suitable plant species to be used on a site for bioengineering. use the manuals to select the best one tree species, three shrub species and three grass species for this site.
engineering functions required:
- catch and armour
site description:
- slope 29°
- stoniness: % of fines 12%
- altitude 700 m
- aspect south-est
- rainfall 2400 mm/yr
NB this site is badly affected by boulders of 200 mm diameter dropping down from the slope above and damaging the side drains as well as the road surface.
site class: _______________________
definition of site class: _______________________
species selected:
Species Function
grass a) ________________ _________________
b) ________________ _________________
c) ________________ _________________
shrub a) ________________ _________________
b) ________________ _________________
c) ________________ _________________
bamboo ________________ _________________
selection of plant species
site 4
you have been asked to select suitable plant species to be used on a site for bioengineering. use the manuals to select the best one tree species, three shrub species and three grass species for this site.
engineering functions required:
- anchor and armour
site description:
- slope 30°
- stoniness: % of fines 15%
- altitude 1700 m
- aspect east
- rainfall 2000 mm/yr
NB this site does not have any severe grazing problems.
site class: _______________________
definition of site class: _______________________
species selected:
Species Function
grass a) ________________ _________________
b) ________________ _________________
c) ________________ _________________
shrub a) ________________ _________________
b) ________________ _________________
c) ________________ _________________
tree a) ________________ _________________
b) ________________ _________________
in this exercise, you will produce a transectional map of the vegetation. carry out the following activities.
1. identify the general types of vegetation.
2. identify the vegetation zones.
3. measure the slope angle, aspect, and the length.
4. draw transect
5. find the dominant and associated species.
|
