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5.5: Stand Growth and Development Over Time - Biology

5.5: Stand Growth and Development Over Time - Biology

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5.5 Stand Growth and Development Over Time

In addition to giving us a snapshot of current stand conditions, stand exams can also provide clues to stand development over time if conducted periodically on the same site. Although this is the subject of future ecology and silviculture classes, a brief introduction here will give you a better understanding of the crown dynamics you observe as you are measuring in the forest.

Evenaged stands typically originate after large-scale disturbances occur on a site – wildfire, harvesting, windthrow, etc. Resulting forest development tends to follow a pattern of progression through four or more identifiable stages as described by Oliver and Larson (1996):

Stand initiation or open shrub stage: the open condition after disturbance allows colonization by a variety of plants. Forest floor herbs, shrubs and seedlings may have survived the disturbance, as well as new individuals and pioneer species that appear over a period of several years. This is generally a period of diverse species composition. Planted seedlings are part of this stage (Figure 5.9A below).

Figure 5.9A. The open shrub stage is dominated by shrubs, grasses, and seedlings.

Figure 5.9B. The stem exclusion stage is typified by low levels of understory vegetation.

Stem exclusion stage: crown closure occurs as tree crowns touch and available growing space is occupied. Overstory competition for light and growing space intensifies, and roots compete for soil moisture and nutrients. Some species die out and understory seedlings become scarce. This is generally a period of low biodiversity (Figure 5.9B).

Understory reinitiation stage: small gaps of light in the canopy are created by breakage or death of individual trees – those lost to suppression, pests, windthrow, etc. This creates an opportunity for new species or individuals to establish in the understory, or for shade tolerant saplings already established in the understory to grow quickly into the gap. This stage generally contains more plant and animal species than the stem exclusion stage, but fewer than the stand initiation stage (Figure 5.9C).

Figure 5.9C. In the understory reinitiation stage, saplings occupy pockets of light that develop in the understory.

Figure 5.9D. The old growth/complex stage is multistoried with woody debris on the ground.

Old-growth stage: large overstory trees are replaced by younger understory trees. As the original cohort making up the crown gradually dies, very large gaps allow the trees in the lower forest layers to grow into the canopy. This happens in an irregular fashion, so a multilayered structure emerges. This is the stage of the greatest structural diversity, and is complemented by high species diversity (Figure 5.9D).

During all stages of stand development, plants are competing for light, nutrients, water, and growing space. Different species have different strategies for maximizing their ability to accumulate these resources, but the reality is clear; there is only so much to go around. During the stand initiation or open shrub stage, the forest may be dominated by herbs, shrubs and small seedlings. During this time, shrubs may grow the fastest, often outcompeting trees for sunlight. Seedlings overtopped by shrubs will die out, but the trees that grow taller than the shrubs begin to dominate the light source. As they fill out their crowns and get big enough to touch each other, crown closure occurs. Trees generally have high LCR’s and nearly all occupy dominant crown classes as the stand enters the stem exclusion stage. Competition between trees for light becomes particularly intense during this stage, as nearly all the crowns are about the same height and size. Light to the understory is drastically reduced, as evidenced by the limited number and abundance of understory plants.

As trees continue to grow, they require more physical space for branch and crown expansion, and differentiation into crown classes becomes evident. The healthiest trees, able to grow faster and occupy more space, become the dominant trees. Slower growing trees become codominant, and inferior trees lag behind, creating the intermediate crown classes. These trends become more and more pronounced with time. Large dominants remain dominant, while those that are not as competitive become codominant as their LCR’s shrink. Some codominants are outcompeted and become intermediates, while the weakest trees become suppressed and eventually die. This is called self-thinning, and continues throughout the life of the stand as the trees get larger and larger (Figure 5.10). Thus, an area initially supporting 600 seedlings per acre may only support 200 trees per acre when they reach 50 years, or 30 trees per acre by the time they reach old-growth.

Figure 5.10. Trees differentiate into crown classes with time, as competition for growing space increases. (Emmingham and Elwood 1993)

A direct relationship exists between a tree’s diameter and its leaf biomass. The greater the volume of space a crown occupies, the more foliage a tree can support, and the more light it can capture. The more sugar it produces from those leaves, the more energy it has available for growth and the more wood it can produce each year. On the other hand, the smaller a tree’s crown is, the less space it has for foliage, and the smaller its growth rings will be. Thus we arrive at the diameter distribution in Figure 4-5. There is a range of diameters from 6”-36”, even though all trees are in the same canopy layer or cohort. Subordinate crown classes in the overstory with low LCR’s account for the small diameter trees, and dominant trees make up the larger diameter classes.

A fascinating exercise that demonstrates the interrelationships among neighboring trees as they compete for light and growing space over time, is to chart individual tree diameter growth from increment core samples. The growth rings reflect individual tree crown expansion, and can help explain why some trees become dominant, while others are classified as intermediate.

The illustration below shows diameter growth of four Douglas-fir trees growing side by side in an evenaged stand (Figure 5.11). Cores were taken at dbh, so no data are available to chart how many years it took each tree to reach dbh or which year each tree germinated and began to grow. But as you can see, the tree classified as intermediate (Tree10), appears to be about 10 years younger than the other three trees, and although its growth rates are on par with the other trees for the first 15 years, its curve flattens off after 1973, revealing its inability to capture much crown space, even though it occupies the same canopy layer as the larger trees. (This tree illustrates why even-layered is not necessarily evenaged, and why the term “cohort” rather than “age class” is preferred by some when discussing forest structural layers.) The dominant tree (Tree 11) maintains its high growth rate throughout its lifespan, and really pulls away from the other trees after 1983. The codominants (Trees 14 and15) display early growth equal to dominant Tree 11, then taper off over the last 25-30 years. It is likely that the stem exclusion stage began around 1968, and the effects of the more intense competition for light and growing space become evident over the following 5 -10 years.

Figure 5.11. Diameter growth of four neighboring trees over time, taken from core samples. Data collected in an evenaged stand on a west slope by MHCC Forest Measurements I students January 2004.

There are two interesting sidelights to observe with the codominant trees. Look at Tree 14. Its growth is similar to dominant Tree 11 until a sharp decline starts in 1968. Was there an event between 1968 and 1973 that would have resulted in a sudden loss of growth during that period? Many trees in this stand showed crooks in the trunks at about the same height, indicating that perhaps the 1969 ice storm caused top breakage in the stand. However, the last 15 years show that this tree has recovered, and is again displaying fairly rapid growth. Codominant Tree 15 on the other hand, shows a gradual slowdown and relatively flat growth rate since 1983. Does this indicate lower vigor? Will this tree ultimately become an intermediate tree as the surrounding stronger trees garner more and more light and growing space? At this point, it certainly appears that it is losing ground to the other trees. It is amazing what you can learn from four cores samples!


27 5.3 Live Crown Ratio

A useful measurement to indicate tree vigor is live crown ratio (LCR). This is the ratio of crown length to total tree height, or the percentage of a tree’s total height that has foliage (Figure 5.7).

Figure 5.7. Live Crown Ratio: the ratio of live crown to total tree height expressed as a percentage.

Crown length is partly a function of species’ shade tolerance. For example, Douglas-fir and most pines will self-prune (drop their lower branches as they become shaded). However, a shade tolerant species such as western hemlock will keep more lower branches in medium shade. Therefore, a western hemlock will have a longer crown (and higher LCR) under low light conditions than a Douglas-fir. Consider the data in Table 5.2. This young, evenaged forest stand (≈ 40 yrs.) was growing on a southern slope. It had a substantial riparian component supporting the hardwoods. Note that the red alder, cherry and Douglas-fir had shorter LCR’s than the more shade tolerant hemlock and cedar. The hardwoods were shorter, but all the conifers were approximately the same height.

Table 5.2. Mean Live Crown Ratio (LCR) and Height by Species for an Evenaged Stand in the Latourell Creek Watershed, Corbett, OR. Source: Data collected by Mt. Hood Community College Forest Measurements I class March, 2003.

Douglas-fir trees in this region with large crown ratios (>50%) tend to be dominant trees, and/or trees growing with adequate light. Douglas-fir trees with ratios of less than 30 percent generally have low vigor, and typically either a) occupy intermediate or suppressed crown classes, or b) are growing in very dense, uniform young stands. In the latter case, their root systems do not develop well, and the trees become subject to windthrow over time. These “dog hair stands” are often a result of planting seedlings at a high density, and failing to thin them later at the appropriate time.

In general, LCR will reflect crown class, regardless of species. Trees growing in the dominant crown classes tend to have the longest crowns overall, followed by trees in the codominant, intermediate, and suppressed crown classes respectively (Table 5.3). The exception to this may be unevenaged or two-aged stands in which distinct second and third layers are composed primarily of shade tolerant trees. In these cases, each layer must be evaluated independently.


Glossary

Definitions presented are from The Dictionary of Forestry (Helms 1998) and Forest Measurements (Avery and Burkhart 2002) where possible. Remaining definitions are from other sources.

annual ringsee growth ring

broken top A tree whose uppermost whorls of branches and main stem have broken off the main trunk. – note: a flattened top appears, and commonly rot is introduced to the main stem

butt swell Flare of the main stem at the base of a tree providing mechanical support to keep the tree upright

caliper(s) An instrument for determining tree and log diameters by measuring their rectangular projection on a straight, graduated rule via two arms at right angles to (and one of them sliding along) the rule itself

canopy The foliar cover in a forest stand (may consist of one or several layers) generally refers to the top or overstory layer

clinometer An instrument for measuring angles of elevation or depression

codominant – see crown class

competition The extent to which each organism maximizes fitness by both appropriating contested resources from a pool not sufficient for all, and adapting to the environment altered by all participants – note: competition among individuals of the same species is termed intraspecific competition competition between different species is termed interspecific competition

crown The part of a tree or woody plant bearing live branches and foliage

crown class A category of tree based on it crown position relative to those of adjacent trees

codominant – a tree whose crown helps to form the general level of the main canopy in even-aged stands, or in uneven-aged stands, the main canopy of the tree’s immediate neighbors, receiving full light from above and comparatively little from the sides

dominant – a tree whose crown extends above the general level of the main canopy in even-aged stands, or in uneven-aged stands, above the crowns of a tree’s immediate neighbors and receiving full light from above and partial light from the sides

intermediate – a tree whose crown extends into the lower portion of the main canopy in even-aged stands, or in uneven-aged stands, into the lower portion of the canopy formed by the tree’s immediate neighbors, but shorter in height than the codominants, and receiving little direct light from above and none from the sides

suppressed or overtopped – a tree whose crown is completely overtopped by one or more neighboring trees

cruise intensity The percentage of a population that is sampled

dendrochronology The study and interpretation of annual growth rings of trees and their use in dating past variations in climate and in archaeological investigations

density The size of a population in relation to some unit of space – note: density is usually expressed as the number of individuals or the population biomass per unit area or volume

determinate height growth (determinate growth) Growth whose structures are initiated by a meristem in one year but do not complete development until the meristem resumes growth in the following year

diameter at breast height (DBH) The diameter of the stem of a tree measured at breast height 4.5 ft or 1.37 m) from the ground – note: on sloping ground the measure is taken from the uphill side

diameter class Any of the intervals into which a range of diameters of tree stems or logs may be divided for classification and use – e.g., the 6 inch diameter class includes diameters from 5.0 to 6.9 inches

diameter tape A tape measure specially graduated so that the diameter can be read directly from the circumference of a tree stem or log

disturbance Any relatively discrete event in time that disrupts ecosystem, community, or population structure and changes resources, substrate availability, or the physical environment

dominantsee crown class

evenaged (stand) A stand of trees composed of trees of the same, or approximately the same age

forked tree A tree whose main stem splits into two or more main stems

global positioning system (GPS) A satellite-based positioning system that gives a user’s position anywhere on earth

growth ring The cumulative layers of cells produced during a single growing season, and characteristically containing earlywood and latewood cells of differing morphology

hypsometer Any instrument based on geometric or trigonometric principles for measuring the heights of standing trees

increment borer An auger-like instrument with a hollow bit and an extractor used to extract thin radial cylinders of wood (increment cores) from trees having annual growth rings, to determine increment or age

intermediatesee crown class

live crown ratio The ratio of the length of live crown to total tree height

merchantable (tree) height The commercial height above ground or (in some countries) above stump height

multistoried stand The cultivation of a large variety of mostly multipurpose plants in various vegetation layers to maximize the use of environmental factors such as water, nutrients, and sunlight

old-growth (forest) The late successional stage of forest development – note 1: old-growth forests are defined in many ways generally, structural characteristics used to describe old-growth forests include (a) live trees: number and minimum size, (b) canopy conditions: commonly including multilayering, (c) snags: minimum number of specific size, and (d) down logs and coarse woody debris: minimum tonnage and numbers of pieces of specific size – note 2: stand age, although a useful indicator of old growth, is often considered less important than structure because (a) the rate of stand development depends more on environment and stand history than age alone, and (b) dominants are often multiaged – note 3: due to large differences in forest types, climate, site quality, and natural disturbance history (e.g., fire, wind, and disease and insect epidemics), old-growth forests vary extensively in tree size, age classes, presence and abundance of structural elements, stability, and presence of understory

old-growth stage A temporal stage of forest development typified by old-growth stand structure – see old-growth

open shrub stage A temporal stage of forest stand development immediately following disturbance characterized by low or no tree cover and dominated by understory plants

overstory that portion of trees forming the uppermost canopy layer

overtoppedsee crown class

percent slope A slope ratio with rise expressed as a % of the run. –see slope

pith The central core of a stem, branches, and some roots representing the first year of growth, and consisting mainly of soft tissue

profiles A side view of a hillslope, illustrating the changes in surface gradient

rise The vertical distance between two points

run The horizontal distance between two points

shade tolerance (tolerant) Having the capacity to compete for survival under shaded conditions

site class A classification of site quality, usually expressed in terms of ranges of dominant tree height at a given age

site index A species-specific measure of actual or potential forest productivity (usually for even-aged stands), expressed as the average height of dominant, codominant trees at a specified index or base age

site quality The productive capacity of a site, usually expressed as volume production of a given species –synonym site productivity

site tree A tree used to determine site index note: site trees must meet defined criteria

slope A measure of change in surface value over distance, expressed in degrees or as a percentage – e.g., a rise of 2 m over a distance of 100 m (or 2 ft over 100 ft) describes a 2 percent slope

slope distance The extent of space between two points on a sloped surface

stand A contiguous group of trees sufficiently uniform in age-class distribution, composition, and structure, and growing on a site of sufficiently uniform quality, to be a distinguishable unit

stand density A quantitative measure of stem crowding within a stocked area

stand structure The horizontal and vertical distribution of components of a forest stand including the height, diameter, crown layers, and stems of trees, shrubs, herbaceous understory, snags, and down woody debris

stand table A tabulation of the total number of stems per acre by dbh and species

stem 1. The principal axis of a plant from which buds and shoots develop 2. The trunk or main stem of a tree

stem exclusion stage A temporal stage of forest stand development following crown closure

succession The gradual supplanting of one community of plants by another. – note: the sequence of communities is called a sere, or seral stage

suppressed –see crown class, overtopped

suppression The process whereby a tree or other vegetation loses vigor and may die when growing space is not sufficient to provide photosynthate or moisture to support adequate growth

topographic slope A ratio of rise over run expressed as a one unit of change in elevation for every 66 units of change in horizontal distance – see slope

total (tree) height Height of the main stem of a tree from a one-foot stump (generally) to the very tip of its leader

understory All forest vegetation growing under an overstory

understory reinitiation stage A temporal stage of forest development characterized by gaps in the forest overstory caused by suppression and introduction of new seedlings in the forest understory

uneven-aged (stand) A stand with trees of three or more distinct age classes, either intimately mixed or in small groups

whorl A circle of leaves, flowers, branches, or other organs developed from one node


30 5.6 Application of LCR and Crown Class in Forest Management

Live crown ratio and crown class are descriptors of tree crown characteristics and indicators of tree vigor. One of the ways foresters use these terms is to communicate decisions about stand management. For example, let’s say a forester wants to improve stand vigor by doing the following:

  • decreasing tree density to reduce competition for resources
  • concentrating growth on the healthiest trees and
  • removing trees with evidence of disease.

These are general concepts and overall directions for the stand. But how does one decide which individual trees to cut or leave, and how does one communicate that information, especially to a crew of people marking the trees? Each acre of ground and each individual tree in the forest are unique. Until one actually walks through the entire stand, decisions about individual trees cannot be made. So a set of specific directions describing cut and leave trees must be written to more clearly explain a forester’s intentions.

Therefore, in writing a prescription for the stand management described above, a forester would use standard terms to describe the intended management outcomes. For example, the following directions might be part of the tree marking directions.

  • Reduce tree density to 75 trees per acre. On average, space trees ≈ 24 feet apart.
  • Leave primarily Dominant trees second preference is for Codominant trees with LCR > 40%.
  • Favor trees with intact crowns.
  • Remove trees with evidence of disease or deformity.
  • Remove primarily Intermediate and Suppressed trees.
  • Remove primarily trees with LCR< 30%.

In this way, the person making the cut and leave decisions on the ground has a much clearer idea of how to achieve the overall objective to “improve stand vigor.”


Determining Live Crown Ratio

1. Never “eyeball” LCR without measuring. You will underestimate the crown ratio. Standing on the ground looking up results in a foreshortened view of the crown it will look shorter than it really is. The closer one is to the tree, and the taller the tree, the more your eye is tricked. In fact, it is an interesting exercise to guess what you think the LCR will be, then measure it, and see how close you are.

2. Determine length of crown using the same measuring techniques and equipment that you use to estimate total height.

3. It is sometimes difficult to determine where the base of the crown is. Brush or limbs from other trees may obscure it, or one side of the tree may have limbs lower than the other side. Try to get to a spot where you can see the tree to take care of the first problem. The standard for handling an uneven tree base is to sight on a spot halfway between the lowest branches on each side of the tree – “split the difference” so to speak (Figure 5.9).

Figure 5.9. Estimating LCR when crown base is uneven. Measure the base halfway between the lowest significant branches on each side of the tree.

4. Ignore a lone live branch low on the tree that is clearly not part of the overall crown.

5. Live crown ratio is generally recorded as a whole number (%), not as a fraction in decimal form. Always record to the precision of the instrument used. Note that measures cannot be accurately made to a tenth of a percentage. So, for example, if the calculator reads 53.6, then record LCR as 54.


What factors influence a person's height?

The main factor that influences a person’s height is their genetic makeup. However, many other factors can influence height during development, including nutrition, hormones, activity levels, and medical conditions.

Scientists believe that genetic makeup, or DNA, is responsible for about 80% of a person’s height. This means, for instance, that tall people tend to have children who also grow up to be tall.

People usually grow until they reach 18 years of age. Before then, a range of environmental factors can affect how tall they become.

This article covers the factors that affect a person’s height, some ways people can increase height during development, and whether or not adults can increase their height.

Share on Pinterest A nutritious diet may help maximize a child’s height.

People cannot control most of the factors that influence their height. This is because they are determined by DNA, which they cannot change.

However, some factors can increase or reduce growth during childhood and puberty. Growing children and teenagers can take some steps to maximize their adult height. These include:

Ensuring good nutrition

Nutrition plays a very important role in growth. Children without good nutrition may not be as tall as children with adequate nutrition.

Nutritionists recommend that children and young people eat a varied, balanced diet with plenty of fruit and vegetables. This will ensure that they get all the vitamins and minerals they need to thrive.

Protein and calcium are particularly important for bone health and growth. Some protein-rich foods include:

Some calcium-rich foods include:

Ensuring good nutrition during pregnancy is also important for the bone health and growth of the fetus.

The World Health Organization (WHO) recommend that pregnant women consume a variety of foods, including “green and orange vegetables, meat, fish, beans, nuts, pasteurized dairy products, and fruit.”

Getting enough sleep

Sleep promotes growth and development in children and teenagers. During deep sleep, the body releases the hormones it needs to grow. Getting enough sleep may therefore allow optimal growth.

Getting regular exercise

Regular exercise is also important for normal physical development. Playing outside or taking part in sports, for example, can make bones healthier, denser, and stronger.

Babies and children grow continuously. This is due to changes in the growth plates in the long bones of their arms and legs.

As the growth plates make new bone, the long bones get longer, and the child gets taller.

People grow the fastest in the first 9 months of life, before being born. After birth, this slows down.

Once a child is 8 years old, they will grow at an average of 2.16 inches (in), or 5.5 centimeters (cm), per year.

That said, teenagers will have a “growth spurt” around the time of puberty. After this, the growth plates stop making new bone, and the person will stop growing. The hands and feet stop growing first, then the arms and legs. The last area to stop growing is the spine.

Due to typical aging processes, people begin to lose height gradually as they get older.

The following factors can affect how tall a person will become:

DNA is the main factor determining a person’s height.

Scientists have identified more than 700 different genes that determine height. Some of these genes affect the growth plates, and others affect the production of growth hormones.

Normal height ranges are different for people from different ethnic backgrounds. Again, this is determined by their DNA.

Some genetic conditions can also affect a person’s adult height, including Down syndrome and Marfan syndrome.

Hormones

The body produces hormones that instruct the growth plates to make new bone. These include:

  • Growth hormones: These are made in the pituitary gland and are the most important hormone for growth. Some health conditions can restrict the amount of growth hormones the body makes, and this can impact height. Children with a rare genetic condition called congenital growth hormone deficiency, for example, will grow at a much slower rate than other children.
  • Thyroid hormones: The thyroid gland makes hormones that influence growth.
  • Sex hormones: Testosterone and estrogen are very important for growth during puberty.

Males tend to be taller than females. Males may also continue growing for longer than females. On average, an adult male is 5.5 in (14 cm) taller than an adult female.

According to the Centers for Disease Control and Prevention (CDC) , in the United States, the average male is 69 in (175.2 cm) tall, and the average female is 63.6 in (161.5 cm) tall.


26 5.2 Crown Classes

Crown class is a term used to describe the position of an individual tree in the forest canopy. In the definitions below, “general layer of the canopy” refers to the bulk of the tree crowns in the size class or cohort being examined. Crown classes are most easily determined in evenaged stands, as depicted in Figure 5.5. In an unevenaged stand, a tree’s crown would be compared to other trees in the same layer. Kraft’s Crown Classes are defined as follows (Smith et al. 1997 and Helms 1998 modified for clarity):

  • Dominant trees These crowns extend above the general level of the canopy. They receive full light from above and some light from the sides. Generally, they have the largest, fullest crowns in the stand (Figure 5.5).
  • Codominant trees These crowns make up the general level of the canopy. They receive direct light from above, but little or no light from the sides. Generally they are shorter than the dominant trees.
  • Intermediate trees These crowns occupy a subordinate position in the canopy. They receive some direct light from above, but no direct light from the sides. Crowns are generally narrow and/or one-sided, and shorter than the dominant and codominant trees.
  • Suppressed trees (Overtopped trees) These crowns are below the general level of the canopy. They receive no direct light. Crowns are generally short, sparse, and narrow.

Crown classes are a function of tree vigor, tree growing space, and access to sunlight. These in turn are influenced by stand density and species shade tolerance. A “suppressed” Douglas-fir tree is likely of low vigor and will probably die out. It typically would not be able to respond to an increase in sunlight if a neighboring tree fell over. A shade tolerant “suppressed” western hemlock on the other hand, may survive very nicely and be able to take advantage of increased sunlight if a neighboring tree were to fall over.

Crown class distribution can also infer overall vigor of an evenaged stand. If most trees are in the intermediate crown class, then the stand is likely too crowded and the trees are stagnated. A stand with nearly every tree in the dominant category is either very young, with all of the trees receiving plenty of sun, or very sparse and may be considered “understocked.” A typical evenaged stand has the majority of trees in the codominant class, and the fewest trees in the suppressed class. The relative ratios of dominant and intermediate classes are generally a function of species composition. Examine the data in Figure 5.6 and Table 5.2 below.

Figure 5.6. Diameter classes of an evenaged stand near Larch Mountain, OR. Source: Data collected by Mt. Hood Community College Forest Measurements I class on January 26, 2005.

This 60 year-old stand of primarily Douglas-fir and western hemlock, displays a bell-shaped diameter distribution, characteristic of an evenaged stand. Most of the trees are clustered around the average DBH, with some smaller and some larger than the center range.

Table 5.1. Percent of each Species by Crown Class. Source: Data collected in evenaged stand near Larch Mt. by Mt. Hood Community College Forest Measurements I class in January, 2005.

Note that the majority of trees are in the codominant crown class (35% of all trees), which is typical of an evenaged stand. These trees most likely make up the bulk of the 16’’-22” diameter classes. It is interesting to examine the species composition data. The majority of dominant and codominant trees are Douglas-fir, while the intermediate and suppressed trees are primarily shade tolerant western hemlock. Therefore, healthy trees in the small diameter classes (6-10 inches) may survive over time, even though they are surrounded by large trees. Crown class by itself does always reflect vigor there is another element to examine besides position in the crown.


FACTORS THAT PROMOTE DEVELOPMENT

Before you continue reading complete the following activity.


Write down three (3) factors that promote the development of a child


Now confirm your answer as you read the following discussion.

The factors that promote development include good nutrition, emotional support, play and language training. We shall discuss each of them in detail, starting with good nutrition.

Good nutrition: Good nutrition is essential for normal growth and development. Unlike most other organs in the body, the brain is not fully developed at birth. Good nutrition in the first 6 months of life is extremely important. Malnutrition in this period may inhibit the growth of the brain. As a result of impaired brain growth, the child may suffer for the rest of life if the child does not get enough good food. A malnourished child is often tired, apathetic and not interested in learning new things that will promote normal development. Nutrition is discussed in detail in Unit 7

Emotional Support: The first 5 years of life are critical for the foundation of the skills which are developed in the following periods of the child’s life. A newborn starts with no knowledge and learns a great deal during his/her first year of life. It is very important to realize that a child is a growing and developing human being right from birth. He ought to be treated very carefully, with love and respect, so that he can develop normally. He needs full emotional support. There are eight basic needs for a healthy emotional development of a child.

  1. Love
  2. Security
  3. Acceptance an an individual
  4. Self-Respect (Self-Esteem)
  5. Achievement
  6. Recognition
  7. Independence
  8. Authority.

Let us briefly look at each in detail.

Love A child needs to feel loved continuously. A child who does not feel loved will not develop properly, and will not learn as quickly as other children. Instead, he becomes sad and lonely and no longer interested in what goes on around him.

Security A child needs to feel safe. He can only feel safe if his parents show that they love him and take good care of him. He must know that his parents will look after him and help him, that they will feed him when he is hungry, play with him, and keep him happy and comfortable. The love and security a child gets from the mother and family helps him to develop a sense of trust in people, initially the family members and later people outside the family.

Acceptance as an individual: A child enjoys being accepted as an individual. A child needs to know that his mother and family love him for what he is. They should not compare him with other children and tell him that he is slow to do this or that, or that he is not as good as some other child. They should show him that they respect him as an individual with his own likes and dislikes, and that they realize he is unique, as all children are unique.

Self respect (self-esteem). Children need to feel that they are of great value, they are able to do things by themselves, they can achieve success, and that their success will be recognized. Anything suggesting that a child is inferior is very disturbing to the child.

Achievements The child feels the need to achieve. The parents should not do anything that the children can do for themselves.

Recognition A child enjoys recognition by his or her parents. A child needs to know that his parents are happy and pleased when he has learned to do something new. Parents should help a child to do things and encourage him to make achievements. They should also teach the child because they love him and show that they are proud of him. This helps the young child to feel secure and to learn more easily.

Independence A child needs to learn how to make decisions. As the child grows he needs to be allowed to decide more and more things for himself and learn how to be independent. The parents must not unnecessarily limit the child’s independence and exploration by overprotection and over anxiety.

Authority A child needs his parents’ authority mixed with affection. The parents train the child to learn to obey the rules of the home, the neighbourhood, the school and the society. The rules indicate what the child may do and what he may not do. What a child may do is approved and encouraged with rewards. What the child may not do is clearly and firmly disproved and discouraged. The discouragement is achieved by permitting consequences of undesired behaviour. The child thus learns to accept the restrictions that are there in life.

Play Play is an essential factor the development of a child. Play is an irreplaceable source of information, stimulation for the brain, stimulation for the muscles and a lot of fun. All these are necessary for physical, mental and social development. All normal children like to play. If a young child does not play, he may be ill. Encourage playing, even if it may be noisy sometimes.

Expensive toys are not necessary for play. Young children will improvise toys from common objects such as paper (but not plastic bags), sticks and stones. The parents should make sure the child does not injure him/ herself with any of the toys. For example, parents should ensure that a toy is not too small, as a child can easily choke on small objects. To help a child play and learn properly, he needs to have:

  • Plenty of room so that he can move about and discover things for him/ herself.
  • Independence. He should be encouraged to do things he wants or enjoys.
  • Several different kinds of toys so he can practise different skills. Blocks of wood can be used for stacking, a ball for throwing, containers of water or sand for filling and pouring.
  • Encouragement and interest from the adults. It is fun to play together.

There are different kinds of play, and each type helps a child to develop properly.

Physical play: This exercises the body's large muscles and keeps the child healthy and strong. Physical plays include: running, jumping, climbing, and swimming.

Manipulative play: This is a kind of play in which the child uses the hands and the eyes. It teaches such things as the size, consistency, texture, shape and colour of objects. Things for manipulative play include: sand, earth, clay and water. Children enjoy playing with all these things.

Creative play: Painting, paper cutting, sewing, using crayons, threading beads and shells, clay modelling, and building with bricks or blocks of wood are all activities that help children to use their hands and eyes together to make things which were not there before.

Imitative play helps the child to acquire the skills of being a person. Through imitating the sound, the child acquires speech. Imitating everything, the child acquires many skills: dressing, feeding, washing etc.

Imaginative play: The child can dress up and pretend to be an adult whom he knows, or pretend to be a driver driving a car. . Children can even pretend that they are animals. This sort of play is important because it allows young children can get rid of a lot of feelings of anger, anxiety and fear.

Language Training Another factor that promotes development is language training. Children should be offered opportunities to meet, use, and play with words in conversation and in reading books. Using an adult language, the adults should talk and sing with small children and infants, encourage them to talk about what they are thinking, not laugh when children are talking, read to the children, tell stories, and listen as attentively to the children as they listen to the other adults. Try to understand how they are thinking and be happy that they want to involve you in their world.

You now know what growth and development are and the factors that promote them. In the following section we shall discuss the importance of antenatal care, perinatal care and postnatal care and the effects of not having these services.


Background

Growth is a universal and fundamental process of life on earth. The analysis and modelling of plant growth has therefore been a particular concern in plant science as well as in production biology including forestry, agriculture and fishery to name but a few. This research has the important objective to identify growth patterns in response to environmental factors or treatments.

In this context, the concept of relative plant growth, involving the analysis and modelling of plant growth relative to plant size, has proved to be a powerful tool in comparative studies of the growth performance of plants and has a long tradition in plant science (Evans 1972, p. 190ff. Pommerening and Muszta: Concepts of relative growth – a review, submitted). It first developed at the beginning of the 20 th century in what eventually became the British school of plant growth analysis, mainly at Sheffield University (Hunt 1982, p. 1, 16).

Independently of the British school another quantitative plant science group developed at Tharandt/Dresden Technical University in Germany. The Tharandt school characterised the growth of trees by using a variant of the concept of relative plant growth and on this basis eventually developed a population model and a size class model for predicting the growth of trees (Wenk et al. 1990, Wenk 1994). There is also evidence of empirical Russian work in this area (Antanaitis and Zagreev 1969) and particularly remarkable is the detailed Finnish work by Kangas (1968).

Relative growth rate is a standardised measure of growth with the benefit of avoiding, as far as possible, the inherent differences in scale between contrasting organisms so that their performances can be compared on an equitable basis (Hunt 1990, p. 6). Applications of relative growth rates include the study of dry weight, biomass, leaf area, stem volume, basal area and stem diameter. Interestingly, the concept is closely related to plant mortality (Gillner et al. 2013), i.e. low relative growth rates for extended periods of time are good indicators of imminent death. Relative growth rates are also pre-requisites for quantifying and modelling allometric relationships in plants (Gayon 2000).

Assuming that function y(t) models the state of a plant characteristic at time t, for example the weight, area, volume or biomass of a plant, relative growth velocity or instantaneous relative growth rate (RGR in forestry termed relative increment) can be expressed as

As instantaneous growth rates cannot be measured in practice, the difference between growth characteristics of interest is usually studied at discrete points in time, t 1, t 2, …, t n, which for example are scheduled survey years. In this context, the period between two discrete points in time can be denoted by Δt = t kt k – 1 with k = 2, …, n. For ease of notation in the remainder of this section we set y(t k) = y k and p(t k) = p k etc. and assume equidistant time periods. However, the notation can be modified to accommodate unequal time periods (Pommerening and Muszta: Concepts of relative growth – a review, submitted).

According to Blackman (1919), Whitehead and Myerscough (1962) and Hunt (1982, 1990), periodic relative increment or mean relative growth rate, p k, over a time period Δt is the difference of the logarithms of y k and y k 1 divided by Δt, see also Causton (1977, p. 213).

Considering a short time period, mean relative growth rate is approximately equal to the instantaneous relative growth rate p(t). Blackman (1919) originally referred to equation (2) as “efficiency index” and “specific growth rate”, see also Causton and Venus (1981, p. 37). From the last term we can see that equation (2) can be interpreted as the logarithm of the ratio of successive size measurements divided by the corresponding time interval (Pommerening and Muszta: Concepts of relative growth – a review, submitted).

According to Evans (1972, p. 197) and Hunt (1982, p. 17), the current value of a plant characteristic can be calculated from a value in the past based on equation (2) as

Equation (3) is also referred to as Blackman’s efficiency index which is supposed “to represent the efficiency of the plant as a producer of new material, and to give a measure of the plant’s economy in working” (Blackman 1919).

The exponential term in equation (3) has fascinated plant growth scientists and inspired them to devise special names. Kangas (1968, p. 50f.) coined the name growth coefficient, whereas Wenk (1972) suggested the name growth multiplier, M k (equation 4).

The growth coefficient or multiplier is obviously a function of relative growth rate and can also be defined as the ratio of a particular plant size characteristic at different times. Part of the fascination with M k stems from the fact that the growth multiplier plays a crucial role in predicting future growth based on relative growth rates (Kangas 1968, p. 19 Wenk et al. 1990, p. 95f. Murphy and Pommerening 2010).

The allometric coefficient, m k, mediates relative changes of plant size characteristics, e.g. x and y (where y has the same meaning as in the equations before). m k is an important part of the concept of relative growth (Gayon 2000). Considering short time periods it is often assumed that the allometric coefficient is constant. Wenk (1978) could show that in such a case the mean relative growth rates p x and p y of size characteristics x and y are related as

The objective of this paper is to explore how relative growth rates of individual plants as well as of plant populations can be efficiently analysed and modelled using a system of simultaneous functions of relative growth and allometric relationships developed in different research schools.

Functions of relative growth

Hunt (1982), Wenk et al. (1990, p. 79) and Zeide (1993) give a number of plant growth functions and provide detailed discussions. They are often combinations of power functions and exponential functions (Zeide 1989). Zeide (1993) and Pommerening and Muszta (Concepts of relative growth – a review, submitted) show how they relate to each other. These authors also compiled a number of functions of relative growth, which are reproduced in Table 1.

The functions in Table 1 are based on the original growth functions and on the corresponding functions of absolute growth rate, i.e. the first derivatives of the growth functions with respect to time. Most functions of relative growth rate have the advantage that they have fewer model parameters than the corresponding functions of absolute growth rate.

Kangas (1968, p. 69) independently suggested the function listed in Table 1 next to his name for modelling the growth multiplier of equation (4) and referred to it as the growth coefficient function.

Modelling individual plant growth

The strategy of modelling individual plant growth is straightforward: 1) A suitable function of relative growth rate is selected from Table 1 or from other publications. 2) A primary plant size characteristic is identified, e.g. tree volume. 3) Secondary plant size characteristics, e.g. tree height and tree diameter, are linked to the function of relative growth rate of the primary plant size characteristic through allometric relations. 4 ) The 2–3 model parameters of the function of relative growth rate and the two allometric coefficients are estimated simultaneously through nonlinear regression. Jones et al. (2009, p. 219f.) describe how such more complex types of nonlinear regression can be calculated in R using the function optim.

Wenk et al. (1990, p. 174ff.) selected primary and secondary plant size characteristics in such a way that error propagation was effectively reduced: They identified tree volume as a three-dimensional size characteristic to be the primary characteristic and one-dimensional total tree height and stem diameter as secondary characteristics. However, since this is a generic approach, there is no need to strictly follow this recommendation. Tree volume can for example also be replaced by weight or biomass.

To illustrate this combined methodology we have used stem-analyses data of four Sitka spruce (Picea sitchensis (Bong.) Carr.) trees taken from the same forest stand in Clocaenog Forest (North Wales, UK). Stem-analysis data include annual tree size characteristics such as stem volume, total tree height and stem diameter at 1.3 m above ground level. As function of relative growth we selected the well-known and frequently used Chapman-Richards function, but any of the other functions in Table 1 would perform reasonably similar (Pommerening and Muszta: Concepts of relative growth – a review, submitted). As an example, Figures 1 and 2 give a visual impression of the regression results of tree # 5000. The corresponding model parameters and other summary statistics can be found in Table 2.

The relative volume (A), height (B), and diameter (C) growth rates over time of tree # 5000 in Clocaenog Forest (North Wales, UK) at Cefn Du (plot 1).


Spoilage

The most prevalent microbiological problem facing the food industry is simple spoilage by bacteria, yeasts, or molds that are not hazardous to health. Chilling slows spoilage proper freezing, drying, canning, and pickling arrest it completely. Chilled foods must be transported to the consumer before spoilage microorganisms make them unfit for consumption. The problems of spoilage in the other processes arise only upon departure from established techniques. The incidence of product spoilage can be greatly reduced and shelf-life extended by taking appropriate precautions.

Refrigerated Foods

The popularity of refrigerated/chilled foods is increasing at a surprising rate. Most of these products are convenient to use and have a “close to fresh” image. Some of these products are partially cooked or processed prior to chilling. This heat reduces the microbial population but does not render it “commercially sterile.” Because of this, refrigerated foods have a limited shelf-life. That is affected by temperature and customer abuse.

Refrigerated foods have been in our stores for many years. Products such as milk, cheese, yogurt and other dairy products, cookie and biscuit doughs, eggs, salads and processed meats are commonly found in the refrigerated section or deli. The optimum storage temperature is 33°F. or as close to freezing as possible. However, most refrigerated cases are holding near 45 or even 45°F. This temperature fluctuation reduces shelf-life of the products, and can lead to a problem of public health significance.

The Refrigerated Foods and Microbiological Criteria Committee of the National Food Processors Association has published a paper on “Safety Considerations for New Generation Refrigerated Foods” in the January, 1988 issue of Dairy and Food Sanitation. Many of the points considered in this section were derived from that paper.

Several important points on preparation, handling and distribution need to be considered. First of all, always assume pathogenic organisms are present in a food product. Secondly, refrigeration temperatures may slow or prevent replication of most pathogenic microorganisms, but some will continue to multiply (psychrotrophs). Psychrotropic pathogens include Yersinia enterocolitica, Listeria monocytogenes, non-proteolytic strains of C. botulinum some strains of enterotoxigenic E. coli and Aeromonas hydrophilia. Several other food borne disease organisms capable of growth at slightly above 41°F include: Vibrio parahemolyticus Bacillus cereus Staphylococcus aureus and certain strains of Salmonella. Thirdly, manufacturers should expect some temperature abuse of the foods during storage and distribution this includes handling at the consumer level.

The last two points for consideration deals with labeling. A “Keep Under Refrigeration” statement must be prominent on the product label and outside carton. In addition, a “Sell By” or “Use By” date needs to be used on these products. This will help processors control their product, but it is not a guarantee against problems. If the stock is not rotated properly, the out of date product will still get out.

A processor of refrigerated foods needs to incorporate as many treatments as possible that will help reduce the microbial population and minimize reproduction. Some of these treatments include: heat, acidification, preservatives, reduced water activity, and modified atmosphere packaging. Even though modified atmosphere is included as a potential barrier, it must be noted that reduced oxygen atmospheres may actually favor anaerobic pathogens. For many products modified atmosphere is really an aid to enhance product quality rather than safety.

One example of a product which successfully employs the multiple barrier principle is pasteurized cheese spread. The product uses a combination of reduced water activity (added salt and phosphates) and mild heat treatment to eliminate non-spore forming pathogens and inhibit growth of spore forming pathogenic microorganisms.

Any manufacturer who considers marketing a refrigerated food should have extensive shelf-life studies done by persons knowledgeable in the area of food microbiology.

Canned Foods

The shelf-life of canned foods results from the destruction of microorganisms capable of growth within the container during normal handling and storage. To attain this optimum situation, canners should:

  • Follow the GMP regulations for low-acid foods.
  • Reduce the spore level in the food by maintaining a sanitation program, particularly for blanchers and elsewhere where thermophilic spore formers thrive, and by monitoring ingredients for spore forming bacteria. As a general rule, food with a high spore level requires more retort time and/or temperature in the same or similar operations (Figure 6 and Table 4). A process approved by a processing authority must be filed with FDA on each low-acid and acidified food sold in the U.S. Assuming the same retort time and/or temperature, the incidence of spoilage will be higher in the canned food with a high initial spore level when all other factors are the same (Table 6).
  • Follow good sanitation and good container handling techniques during the container cooling and post-cooling period. It is also important to cool heat processed containers quickly to about l00°F (38C) since thermophilic outgrowth may occur with low spore numbers if containers are stacked or cased while hot.
  • Maintain good seams on cans and tight lids on glass containers by regular control and testing.

* After incubation of processed cans at 130°F (54.4°C)

Dry Foods

Dry foods do not spoil from microbial activity once they are adequately dry. Most foods require natural or artificial drying before they become stable. Adding sugar or salt, as in candied fruits or salted fish, accomplishes the same purpose since moisture becomes unavailable for use by microorganisms. The appropriate term to express the availability of water to microorganisms is water activity (aw).

Although microorganisms cannot grow on dry foods, those that survive the drying process remain alive for prolonged periods. They quickly resume their activity upon rehydration. Under adverse conditions of storage that permit water to enter the product, molds are usually the first to grow because of their wider range of tolerance to low aw (Watson and McFarlane, 1948) and they also have less competition from other organisms.

Fermented and Pickled Foods

Fermented and pickled foods owe their stability to the microbial development of organic acids by lactic bacteria or the addition of such acids to the foods, especially in the presence of a relatively high level of salt. Spoilage can occur either during the fermentation period or upon storage of the final product. The fermentation can fail if bacteriophage attacks the starter culture, if the temperature is unsuitable, or if the amount of fermentable carbohydrate is inadequate.

To prevent spoilage during the fermentation period:

  1. Add lactic bacteria as a starter. Keep the starter in pure culture to help eliminate bacteriophage.
  2. Add fermentable carbohydrate or organic acid.
  3. Maintain the salt level high enough to inhibit spoilage bacteria and to permit the more salt-tolerant lactics to grow.
  4. Control the temperature to favor lactics.

To reduce or eliminate spoilage during storage of the pickled or fermented food:

Watch the video: The Growth of Knowledge: Crash Course Psychology #18 (November 2024).