Arid Zone Ecology

By: Muhammad Khizer Hayat

1. Semester: 4
th

Session: 2016
-
218 (spring) Department: Botany

Written By: M.Khizer Hayat



Ernst Haeckel (1866) defined ecology as the study of interrelationship of
organisms with their environment. Odum defined ecology as the study of
structure and function of nature (Surrounding environment). Reiter
defined ecology as study of organism on their homes.
What is interaction?
It is the relation of organism with one another and
with their surrounding threshold associate ecology
with economics which have 2 concepts!
1) Allocation of resources
2) Cost benefit ratios
What is Organism?
It is the system of organ composed of cells and genes.
What is Population?
It is the group of individuals of any kind/species inhibiting in certain
specific area.
What is Community?
Collection of many populations in a given area/group of individuals of different species in a certain specific area.
Divisions of ecology: 1) Autecology 2) Synecology
But on levels of organization following classes
1) Species ecology is concerned with energy relations of individual
species, their metabolism, size, tolerance, productivity, effect of light,
temperature, H
2O, humidity, evaporation, soil and other
physical/chemical factors.
2) Population ecology deals with organism to organism relationships
within the same species.
3) Community ecology is related to assemblage/grouping of different species.
Belongs to Phytosociology

Oikos=household/dwelling place
Logos =to study

2. Semester: 4
th

Session: 2016
-
218 (spring) Department: Botany

Written By: M.Khizer Hayat

4) Ecosystem ecology deals with an ecological system comprising the living
organisms and non-living substances which interact with one another.
Ecology is also divided on taxonomic basis. Divisions of ecology on the basis of habitat.
1) Hydro ecology is the study of organism in relation to aquatic environment
.It may be marine ecology (salty) or fresh water ecology (flowing).
2) Terrestrial ecology is the study of interrelationships of organisms
and their terrestrial environment in which is Arid Zone Ecology
defined as the study of relationship of organism with themselves as
well as with their dry land habitat. i.e., land with scarcity of H
2O
which may be temporary/permanent.
3 important features control arid zone ecosystem dynamics
i. Unpredictable rainfall (Highly variable)
ii. Occasionally heavy and prolonged rainfall
iii. An ancient well stored infertile land
3 basic forms of arid zones are
i. Ridges (Sand dune) and rocky areas
ii. Clay plains/deserts
iii. Dry lake beds
Information of arid zone is
i. An important input to biodiversity issues
ii. Conservation to biodiversity
iii. Recommendations will be given to manage these barren areas having infertile
land to fulfill human necessities, nutrition/compensate needs of humans.
Xerophytes: Plants growing in xeric habitat, i.e., in inadequate amount of
H
2O.Depending on habitat 2 types of this habitat:
1) Physically Dry Habitat
2) Physiologically Dry Habitat
1- Physically Dry Habitat: Physical conditions of land is of a such a
type where is unavailability of H
2O naturally e.g., arid zone, rocks,
slopes, sandy soils. Plants growing in this habitat are as follows
Where water retaining capacity of the soil is very low
and the climate is dry e.g. Desert, Rock surface etc.
Places where water is present in excess amount,
but it is not absorbed by the plants easily.

3. Semester: 4
th

Session: 2016
-
218 (spring) Department: Botany

Written By: M.Khizer Hayat

i. Drought Avoiding Xerophytes
These are those which avoid unfavourable conditions emerge from
seed complete their life cycle in a very short period of favourable
conditions. These are also called Annuals/Ephemerals. Whereas
Perennials/tropophytes are plants having changing nature. These
plants have tendency to cease to cease their growth their growth
and development in unfavourable conditions appear as leafless, dry
and dead plant and sprout during favourable conditions during
which become mesophyte that’s why these are called tropophytes
i.e., typical xerophytes.
ii. Drought Resisting Xerophytes_which resist drought by
undergoing many modifications 2-types
1)
Large amount of H 2O stored in tissues called succulents. If H 2O
stored in stem- stem succulents, if in leaf called leaf succulents.

2) Non succulents in which transpiring areas are reduced into
spines/thorns, e.g., Zizyphus succulents have
a) Well developed parenchyma
b) Vacuole very large
c) Reduction of intracellular air spaces
Phylloclade in this the photosynthetic activity is taken over by stem, e.g.,
Cactus, Euphorbia, Opuntia (stem succulents), stem with thick cuticle
(Ammala) few and non functional in leaf succulent and sunken stomata,
e.g., Aloe, Agave, Yucca. In these stems are reduced and leaves are radical
(leaves appear to come off from root but really arising a very short stem at
ground level) or placed vertically. Roots are of 2 types
a) Surface Feeders – The primary root persists throughout the life of
plant but does not go deep into the soil and stops its growth after sometime secondary root develop quite strong but on surface of it.
b) Deep Feeders – The primary root continues to grow and penetrates
the soil to considerable depth and is very prominent. Secondary and
tertiary roots are smaller than primary roots.

4. Semester: 4
th

Session: 2016
-
218 (spring) Department: Botany

Written By: M.Khizer Hayat

iii. Epiphytes: Grown on larger plats for their physical support
mostly grow on higher plants because they are week plants
found on humid forest and tropical and sub tropical areas but
not parasite independent autotrophs and cannot stand upright
they remain unable to receive light if remain on flora of forest

e. g. Orchidaceae, Moraceae, Captaceae members possess three types of roots.
a) Aerial Roots: Found in epiphytic orchids possess special
spongy tissues at their apices. This tissue is termed as velamen (dead tissue) which has capability of absorbing and retaining the moisture so these roots help in absorbing moisture from the air.
b) Climbing Roots: Roots twine around the support like
tendrils e.g., Ficus and Hedrahelix sp.
c) Clinging Roots: Penetrate into cracks and crevices of
support and held the plant firmly e.g., in Betl plant and epiphytic orchid species. Leaves – Thick, fleshy, covered
with thick cuticle, sunken stomata.

2- Physiologically Dry Habitat (Xerophytes)
Xerophyte growing in that habitat where sufficient H 2O
available but in such form that organism cannot use it because of
high osmotic pressure and saline soil e.g., water logging and swamps
and high mineral concentration glaciers, alpines,
arctic regions 2 types
 Halophytes-Plants grow in localities with high conc. of salts and as
well as abundance found on coastal swamps marshy area e.g.
mangrove vegetation (Rhizophora mangle) other kinds include family
Chenopodiaceae, Bregnanceae, Amaranthaceae and many grasses e.g.
Suaeda fruticosa, S uaeda monica having small and succulent leaves
or modified into spines. Mangrove plant adjusted themselves to
saline conditions by followings.
1. Pneumatophores – Special respiratory roots arise from
underground roots which have tiny pores called through
which roots take oxygen for respiration.
2. Vivipary nature of germination – Germination starts
when fruit still attach to the plant.

5. Semester: 4
th

Session: 2016
-
218 (spring) Department: Botany

Written By: M.Khizer Hayat

 Alpine /Arctic vegetation – Found on higher 8,000 - 9,000 feet above
sea level altitude where there is high wind velocity have two problems .
1. Continuous high wind velocity
2. High light intensity which are -ve for plant growth cause desiccation
and excessive transpiration consist of blue violet rays
Properties:
a) Well develop deeply rooted
b) Grow in dense tuft
c) Extensive branching
d) Compact and cushion like
e) Grow in rosette form
f) Leaves small, needle like
g) Thick and succulent with waxy and hairy covering carry out
photosynthesis at low temperature
h) High sugar content and are called evergreens remain buried under
snow for long period but resume original life during favourabla
conditions.
Vegetation of Arid zone with reference to climate
Arid derived from Latin āridus, equivalent to ār(ēre) “to be dried” =
Deficiency to rain fall.
Basic factor of arid zone
1. Amount of rain fall – If rain fall is in very short amount not for useful for
growing crop_.if heavy rain fall for short time not effective because runoff
water on other hand rain fall with less speed and long period effective.
2. Effectiveness of rain fall depend on a
a) Seasonal distribution e.g., moon soon rain fall gives deciduous
evergreen vegetation and plants of arid zone store maximum water and utilize during unfavourable conditions.
b) Rate of evapotranspiration-Depends on temperature, humidity and wind
c) Actual evapotranspiration-Amount of water evapotranspired in arid climate
d) Potential evapotranspiration - amount of water transpired and
evaporated under in ideal conditions or soil moisture.
3. The nature of the soil-
4. vegetation cover

6. Semester: 4
th

Session: 2016
-
218 (spring) Department: Botany

Written By: M.Khizer Hayat

Arid Climate: If water conservation/precipitation
during greater part of the year is less than potential evapotranspiration.

Two systems of arid climate
1-Mortenn*s system - The relationship between precipitation and
temperature by which we can get accurate and general vegetation of dry
climate. In 1962 he gave arid relationship as I= nP/ t+10
n= No. of rainfall days, I= Aridity index P= Precipitation per day,
T= Temperature of any selected period. Aridity is calculated on annual basis.
Arid climate= aridity less than 20 in semi arid climate aridity more than 20
and less than 30.
2- Koppen system of dry climate (1936) - This is based on relationship
between rainfall and temperature include amount and distribution of
rainfall. 5 categories of world climate but two major climates are arid
climate annual rainfall 100-250 mm and semi arid climate_rainfall
sufficient for some specific type of vegetation but insufficient for others.
Climate_Annual conditions of certain area are divided into two types!
1- Microclimate- Climate of specific region/from the top of plant at the
base of soil /Atmospheric conditions from top of the plant at certain
depth of the soil.
2- Macroclimate- Climate of whole region/environmental conditions at
the top, above the top, and surrounding the plant.
Microclimate at plant level- Specific branch called microclimatology we
find clear cut change when we observe seedling emerging from seed near the
soil surface when there is enough air available seedling show s quick growths
as compared to germination being inside the seed. As plant growth
increases, temperature of soil surface also influences the growth and if
temperature will increase viscosity also increases less penetration.

Climate is average weather in an area over a long period of time.
Weather refers to conditions of atmosphere from day to day.