competitive interaction in forest community. interspecific competition intraspecific competition belowground competition aboveground competition

1. An assignment on topic
Competitive interaction in forest community
Sub. SAF 501: Silviculture
Submitted to,
Dr. M. B. Tandel
Assistant professor
Silviculture and agroforestry
College of Forestry
Navsari Agricultural university, Navsari
Submitted by,
Krutika Sanjaybhai Patel
M.Sc. Forestry (1st sem.)
Reg. no. 2030323008
College of Forestry
Navsari Agricultural University, Navsari
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2. Introduction
The three types of interactions in an ecosystem are competition, predation and symbiosis.
Symbiosis also contains three different types of interactions including mutualism, commensalism
and parasitism.
 Competition:
 Competition is a biological interaction between two or more organisms of the same or
different species where the species compete with each other for different resources. In the
study of community ecology, competition within and between members of a species is an
important biological interaction.
 Competition is the law of nature. There is a continuous competition in all life forms.
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3.  Most of the competitive interaction occurs for the need of food (nutrient) sources that occur in a
limited supply when compared to demand. However, organisms might compete for other
resources like water, light, and space.
 The interaction often leads to a change in fitness between the organisms that share the same
resources.
 Competition is one of the most important biological factors that determine the community
structure in an environment.
 Between the two competing organisms, the weaker organism has to either adapt or die out while
the stronger organism obtains the resources. In forest area, mainly two types of competition
occur.
1. Intraspecific competition:
 Intraspecific competition is a type of competition between the members of the same species that
compete for limited resources.
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4.  The competition between organisms is usually for space, nutrients, water, growing space etc. It
depends largely on the stocking, i.e. number of stems per unit area.
 Intraspecific competition can be intense when the population of a species is high as the individuals
have virtually identical resource requirements.
2. Interspecific competition:
 Interspecific competition is a type of competition between two individuals of different species
competing for the same resources.
 This interaction often leads to the reduction in the population of the weaker species, whereas the
stronger species survive and continue to reproduce.
 Interspecific competition is often more fierce than intraspecific competition as two distinct species
often differ in fitness which influences the extent of competition.
 Interspecific competition is an important factor that regulates ecological communities and also acts
as an agent of natural selection.
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5.  One of the major factors that influence the extent and duration of the competition is the density of
the individuals or the number of organisms residing in an area. If the number increases rapidly,
the available resources begin to deplete, leading to ecological competition.
 Competition in plants results in over-topping, suppressing and crowding out the weaker trees by
more vigorous and more aggressive individuals. This results in natural process of survival of
fittest.
 Competition for light:
 Trees convert sunlight energy into sugars (chemical energy) through the process of
photosynthesis. The tree burns, or respires, the sugar to produce the energy necessary for all its
growth and physiological processes. Trees compete with each other and with other plants for the
sunlight available on a site.
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6.  Dominant trees have crowns that extend above the general level of the canopy. They receive full
light from above and partial light from the sides. Codominant trees have crowns at the level of the
canopy. They receive full light from above but little from the sides. Intermediate trees have small
crowns crowded into the general level of the canopy that receive some light from above but none
from the sides. Suppressed trees have small crowns below the general level of the canopy and
receive no direct light.
 When trees get over- topped and shaded by others, their access to sunlight is reduced or
eliminated. As a result, the growth of overtopped trees slows or halts. Depending on the species,
trees may eventually die after being overtopped.
 Dominant trees have crowns that extend above the general level of the canopy. They receive full
light from above and partial light from the sides. Codominant trees have crowns at the level of the
canopy. They receive full light from above but little from the sides. Codominant trees have
crowns at the level of the canopy. They receive full light from above but little from the sides.
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7.  Intermediate trees have small crowns crowded into the general level of the canopy that receive
some light from above but none from the sides. Suppressed trees have small crowns below the
general level of the canopy and receive no direct light.
 Therefore, the shrubs, herbs and other vegetation are adapted to growing diffused light
condition or lesser light condition.
 Tropical deciduous forests have lesser no. of layers and species. Only three or four layers are
prominent with average no. of species of 6 to 10. The canopy structure and species
composition are simpler in dry deciduous and thorn forest. It is also simpler in montane
subtropical and temperate forest. So, there is less competition for light in these types of forest.
 Increasing the spacing between trees by removing some trees (thinning) increases the amount
of light and moisture received by the remaining trees and there- fore increases their health,
growth, and resistance to stresses.
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8.  Competition for moisture:
 Water is drawn in through the roots and pulled up through the tree to the very top and tips of
each branch. In addition to providing metabolic water, this stream also carries minerals and
nutrients essential for plant growth. Ninety-five percent of the water used by a tree or plant is
evaporated to cool the leaves, while the remainder is used in physiological processes such as
photosynthesis and respiration.
 During photosynthesis, a tree opens small pores in its leaves called stomata to allow carbon
dioxide to enter and oxygen to exit. Water vapor is also lost when the stomata are open through
a process called transpiration. This loss of water from the stomata pulls water up from the roots
to the leaves in the top of the tree through vessels in the xylem. If there is not enough soil
moisture to replace water lost through transpiration the tree must close down its stomata and
stop photosynthesis and growth.
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9.  Inadequate soil moisture can cause yellowed or withered foliage, decreased growth rate,
premature shedding of leaves or needles, and dead branches. Moisture stress also makes trees
more susceptible to attack by insects or disease.
 To be effective, water must be applied for a sufficient time and in sufficient quantity to
penetrate the soil and reach deep roots. This is not practical or economically feasible for a
forest. The most practical treatment for forest trees is to ensure that they have adequate water
by alleviating overcrowding and competition for limited water through selective thinning.
 To reduce competition, water must be applied for a sufficient time and in sufficient quantity to
penetrate the soil and reach deep roots. This is not practical or economically feasible for a
forest. The most practical treatment for forest trees is to ensure that they have adequate water
by alleviating overcrowding and competition for limited water through selective thinning.
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10.  Competition for nutrient:
 Several elements take part in the growth and development of plants. Plants take up carbon,
oxygen and hydrogen from the air or development. Elements which have been proved to be
essential for the growth and development of plants are called essential elements. The nutrients
which are required in larger proportions are called major nutrients and those required in smaller
amounts are called minor nutrients.
 Major nutrients:
 Group I: Carbon, Hydrogen and Oxygen
 Group II: Nitrogen, Phosphorus and Potassium
 Group III: Calcium, Sulphur and Magnesium
 Minor nutrients:
 Iron, Manganese, Boron, Zinc, Copper, Molybdenum and Chlorine
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11.  Nutrients play critical roles in plant physiological processes including photosynthesis, cell
growth, nitrogen fixation, protein synthesis, respiration, water absorption, and root growth.
Plants grow best when these elements are present in sufficient quantities, and they suffer from
deficiencies when these elements are scarce.
 The quantity of these elements in forest soils is related to their presence in the soil-forming rock
and to contributions from decomposition of organic matter (roots, leaves, branches) or
atmospheric deposition. Plant-available nitrogen is present in precipitation; in air- polluted
areas, unnaturally high levels of nitrogen (NOX, nitrous oxides) in the precipitation may upset
the nutrient cycles of ecosystems on which it falls.
 A few common visual symptoms of nutrient deficiency are stunted tree growth, discolored
yellow foliage, premature death of buds and foliage, death of needle tips, and poorly developed
root structure.
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12.  Nutrient deficiencies can be treated with fertilizers after diagnosis but this is rarely done in
forest stands.
 Chemical competition (Allelopathic effect):
 Competition is not visible.
 Some trees and plants have chemical properties in their parts that influence the germination,
growth, survival, and reproduction of other organisms from the same community which is
known as allelopathic effect.
 These biochemicals are known as allelochemicals and can have beneficial (positive
allelopathy) or detrimental (negative allelopathy) effects on the target organisms and the
community. Allelopathy has been shown to play a crucial role in forests, influencing the
composition of the vegetation growth.
 Example: Eucalyptus, Neem, Juglance, Melia etc.
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14. Case studies
Case study 1: Interspecific competition among three canopy-tree species in a mixed-species
even-aged forest of central Japan
Study investigated causes and consequences of interspecific competition among canopy-tree
species with different shade-tolerance. The shading effects caused by neighbors were determined
for three tree species, shade-tolerant Fagus crenata, and intermediate tolerant Quercus crispula
and Magnolia obovata, in six even-aged stands containing different proportions of each species.
The competitive attributes (sensitivity to suppression and intensity of shading) varied considerably
among species. Shade-tolerant F. crenata caused most intensive shading effects probably because
of its deeper crown depth. Less-tolerant Q. crispula decreased its stem growth and crown depth
markedly in association with the presence of shade-tolerant F. crenata.
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15. In contrast, F. crenata and M. obovata were less influenced by their neighbors; it may be due to its
own higher shade-tolerance in the case of F. crenata and larger initial growth rates in M. obovata.
We suppose that differences in initial species composition may lead a species to have different
dominance in stand development. When shade-tolerant species are absent in mixture, less shade-
tolerant species could maintain their dominance for a long period. In contrast, mixture with tolerant
species would reduce the dominance of less-tolerant species, unless they had growth advantage in
early stage in development.
Case study 2: Competition between trees and grasses for both soil water and mineral nitrogen in
dry savannas
The co-existence of trees and grasses in savannas in general can be the result of processes
involving competition for resources (e.g. water and nutrients) or differential response to
disturbances such as fire, animals and human activities; or a combination of both broad
mechanisms.
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16. In moist savannas, the tree–grass coexistence is mainly attributed to of disturbances, while in dry
savannas, limiting resources are considered the principal mechanism of co-existence.
Virtually all theoretical explorations of tree–grass dynamics in dry savannas consider only
competition for soil water. Study investigate whether coexistence could result from a balanced
competition for two resources, namely soil water and mineral nitrogen. They introduce a simple
dynamical resource-competition model for trees and grasses and consider two alternative
hypotheses: (1) trees are the superior competitors for nitrogen while grasses are superior
competitors for water, and (2) vice-versa. They study the model properties under the two hypotheses
and test each hypothesis against data from 132 dry savannas in Africa using Kendall's test of
independence. Study find that Hypothesis 1 gets much more support than Hypothesis 2.
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17. Case study 3: Intraspecific Competition Affects Crown and Stem Characteristics of Non-Native
Quercus rubra L. Stands in Germany
Northern red oak (Quercus rubra L.) is the most commonly planted exotic deciduous tree species in
Germany, but its response to varying levels of competition intensity has not yet been adequately
explored. This study examines the responses of stem and crown characteristics of Quercus rubra to
intraspecific competition. A total of 100 dominant red oak trees were investigated in ten pure red
oak stands, located in five federal states of Germany. The external stem quality characteristics
namely stem non-circularity and bark anomalies decreased with increasing tree competition. Also,
the crown characteristics crown volume, crown surface area, maximum crown area, crown length,
and branch length declined by the degree of individual tree competition. We conclude that
individual tree properties can be controlled by competition intensity, resulting in improved timber
quality as shown for other tree species.
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