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What causes the trees to develop gnarls? I can't find anything on internet other than dictionary definitions.
Are they caused by a mold, like the burls?
If I understand what you're talking about by "gnarl", they are usually caused by a bacterium like Agrobacterium tumescens infecting and creating a gall.
Update: Forgot, also in some cases caused by insects.
3 Tree Structures Where Growth Occurs
Little of a tree's volume is actually "living" tissue. Just 1% of a tree is actually alive and composed of living cells. The major living portion of a growing tree is a thin film of cells just under the bark (called the cambium) and can be only one to several cells thick. Other living cells are in root tips, the apical meristem, leaves, and buds.
The overwhelming portion of all trees is made up of non-living tissue created by a cambial hardening into non-living wood cells on the inner cambial layer. Sandwiched between the outer cambial layer and the bark is an ongoing process of creating sieve tubes which transport food from leaves to roots.
So, all wood is formed by the inner cambium and all food-conveying cells are formed by the outer cambium.
Figure 1. Only a few of the more than one million known species of insects are represented in this beetle collection. Beetles are a major subgroup of insects. They make up about 40 percent of all insect species and about 25 percent of all known species of organisms.
Why do biologists classify organisms? The major reason is to make sense of the incredible diversity of life on Earth. Scientists have identified millions of different species of organisms. Among animals, the most diverse group of organisms is the insects. More than one million different species of insects have already been described. An estimated nine million insect species have yet to be identified. A tiny fraction of insect species is shown in the beetle collection in Figure 1.
As diverse as insects are, there may be even more species of bacteria, another major group of organisms. Clearly, there is a need to organize the tremendous diversity of life. Classification allows scientists to organize and better understand the basic similarities and differences among organisms. This knowledge is necessary to understand the present diversity and the past evolutionary history of life on Earth.
Scientists use a tool called a phylogenetic tree to show the evolutionary pathways and connections among organisms. A phylogenetic tree is a diagram used to reflect evolutionary relationships among organisms or groups of organisms. Scientists consider phylogenetic trees to be a hypothesis of the evolutionary past since one cannot go back to confirm the proposed relationships. In other words, a “tree of life” can be constructed to illustrate when different organisms evolved and to show the relationships among different organisms (Figure 2).
Each group of organisms went through its own evolutionary journey, called its phylogeny. Each organism shares relatedness with others, and based on morphologic and genetic evidence, scientists attempt to map the evolutionary pathways of all life on Earth. Many scientists build phylogenetic trees to illustrate evolutionary relationships.
How seeds become trees
Once the seed has found the right conditions, it needs to secure itself. The first root breaks through the seed, anchoring it and taking in water for the developing plant. The next stage in germination is the emergence of the embryonic shoot.
The shoot pushes up through the soil, with the shoot leaves either poking above ground or rotting underneath as the rest of the shoot grows above.
A shoot becomes a seedling when it is above ground. This stage is when trees are most at risk from diseases and damage like deer grazing.
A tree becomes a sapling when it is over 3ft tall. The length of the sapling stage depends on the tree species, but saplings have defining characteristics:
- Flexible trunks
- Smoother bark than mature trees
- An inability to produce fruit or flowers.
Trees with really long life spans like yews and oaks are saplings for much longer than shorter-lived species like silver birch and wild cherry.
A tree becomes mature when it starts producing fruits or flowers. This is when the tree is at its most productive. How long it will stay productive depends on the species.
A typical English oak tree starts producing acorns at around 40 years old, peaking in productivity around 80-120 years. Oaks, in general, can be productive for 300 years then rest for 300 years before moving on in the life cycle. In contrast, rowan starts producing berries after around 15 years, and by 120 years or so it is already at the end of its life.
These fruits are dispersed and the life cycle repeats, but that’s not the end of a tree’s journey.
Uses of Tree Bark
There are many commercial uses for bark, and it is often stripped away from the heartwood to be processed. The dead outer bark can be used to make shingles and siding. The outer bark is also known as cork, and can be ground to make cork products like corkboard, cork flooring, and even specialty items like yoga mats. Throughout history, bark has been used to make everything from boats to shingles, as its waterproof nature remains until it disintegrates. Historically, the inner bark has even been used to create flour and make breads out of, though the nutritional capacity pales in comparison to normal cereals.
Some species of plants also accrue peculiar substances in their bark which are good for making spices, sunblock and insect repellent. The inner bark is an important commercial resource for resins, tannins, and even the precursors to products such as latex gloves. In agriculture, there is a technique in which the bark is stripped below ripening fruit. This allows the sugars to remain concentrated in the fruit, and gives a better harvest. This technique is known as girding, and is sometimes used to produce extraordinarily sized fruit. If a branch is girdled, and all but one fruit on that branch is picked, the plant will put all of the sugars and metabolites from the leaves on that branch into the one remaining fruit.
1. Which of the following layers is NOT considered bark?
A. Vascular cambium
B. Secondary Phloem
2. Why is it not a good idea to strip all the bark off a tree?
A. The tree will dry out
B. The tree will grow too fast
C. The tree’s fruit will be too sweet
3. Which of the following is a possible use for bark?
A. Water storage container
C. Source of living tree cells
Photosynthesis & Respiration
All organisms, animals and plants, must obtain energy to maintain basic biological functions for survival and reproduction. Plants convert energy from sunlight into sugar in a process called photosynthesis. Photosynthesis uses energy from light to convert water and carbon dioxide molecules into glucose (sugar molecule) and oxygen (Figure 2). The oxygen is released, or “exhaled”, from leaves while the energy contained within glucose molecules is used throughout the plant for growth, flower formation, and fruit development.
The ends of both the xylem and phloem transport systems can be seen within each leaf vein (Figure 3). The structure of xylem and phloem in a plant is analogous to arteries and veins in humans, which move blood to and from the heart and lungs.
For more information regarding the structure and function of xylem and phloem, review the Irrigation and Rootstock sections.
Leaves contain water which is necessary to convert light energy into glucose through photosynthesis. Leaves have two structures that minimize water loss, the cuticle and stomata. The cuticle is a waxy coating on the top and bottom of leaves which prevents water from evaporating into the atmosphere (Figure 3a).
Although the cuticle provides important protection from excessive water loss, leaves cannot be impervious because they must also allow carbon dioxide in (to be used in photosynthesis), and oxygen out. These gases move into and out of the leaf through openings on the underside called stomata (Figure 3b). After carbon dioxide enters the leaf through stomata it moves into the mesophyll cells where photosynthesis occurs and glucose is constructed.
Photosynthesis is the process by which plants use light energy to convert carbon dioxide and water into sugars. The sugars produced by photosynthesis can be stored, transported throughout the tree, and converted into energy which is used to power all cellular processes. Respiration occurs when glucose (sugar produced during photosynthesis) combines with oxygen to produce useable cellular energy. This energy is used to fuel growth and all of the normal cellular functions. Carbon dioxide and water are formed as by-products of respiration (Figure 4).
Respiration occurs in all living cells, including leaves and roots. Since respiration does not require light energy, it can be conducted at night or during the day. However, respiration does require oxygen which can be problematic for roots which are overwatered or in soils with poor drainage. If roots are inundated for long periods of time they cannot take up oxygen and convert glucose to maintain cell metabolic processes. As a result, waterlogging and excessive irrigation can deprive roots of oxygen, kill root tissue, damage trees, and reduce yield.
Talking Trees—Secrets of Plant Communication
Forests are nurseries of health and well-being. New discoveries are showing that this doesn’t happen by accident. The trees are working together.
Come with me on an imaginary journey through a woodland wonderland. As we wind down the shaded path, damp moss on the forest floor brushes our bare feet. The scent of white cedar tickles our noses, while filtered morning light enchants our eyes. A gray squirrel chatters overhead in the ancient oaks, and nearby a white-breasted nuthatch chitters to its mate.
What a special place to retreat from our hectic, dysfunctional world and experience peace and tranquility! But there’s more to the forest than meets our eyes (and noses, ears, and feet).
The psalmist declared, “ Let the field be joyful, and all that is in it. Then all the trees of the woods will rejoice before the Lord ” ( Psalm 96:12 ). It’s poetry, certainly, emphasizing that God’s creation yearns for the Lord to return and restore peace on earth.
Stresses constantly threaten to destroy the forest’s surface harmony, and yet modern scientific research is revealing how marvelously the Creator has equipped His woodlands to respond to these stresses, keeping alive these reminders of harmony that once existed and will be restored someday through Christ.
Researchers are discovering that trees form communities that “talk” to each other, sharing their needs and providing mutual assistance. Yes, you heard me correctly. It’s mindboggling, even for someone like me who has spent his life studying nature’s wonders (forest ecology in particular).
Now, it’s important to remember that forests aren’t human or alive in any sense like animals (they lack the “breath” of life, or nephesh, according to God ’s Word). Unfortunately, some current researchers blur the line, imbuing plants with animal or human attributes, such as feelings and consciousness, which they don’t have. The science itself is fascinating, without any need to make trees sound human-like.
When the Bible proclaims that “the trees of the woods” give glory to God , this metaphor may be a reality in unexpected ways.
Trees can’t run from danger or visit their neighbors to ask for a cup of sugar like we can. To sidestep peril and meet their changing needs in a fallen world, cursed because of man’s rebellion against God, their Creator imbued trees with unique abilities. They can communicate with other trees and with other creatures, seeking help. Why would this be necessary, if the Lord made plants to provide food and shelter for animals and people (see Genesis 1:29–30 )? Well, for one thing, they need to survive—no matter what abuses they suffer at the hands of heedless clearcutters or unrestrained insects in our fallen world—to meet the needs of future generations.
One of their defenses against being overeaten is producing chemicals that make them taste bad. At the same time, other chemicals warn nearby trees that a swarm of voracious beetles or other animals have invaded. These chemicals are specifically tailored for this purpose.
In addition to chemical warnings, some oak and beech leaves and spruce needles will produce electrical signals when an insect predator eats them. Electrical impulses generate messages to the rest of the tree so that, within an hour, the tree will hopefully taste so bad that the insects flee.
Experiments in the African savannah suggest that when a giraffe arrives and starts ingesting acacia leaves, plants will soon be inedible but will also warn nearby trees. Leaves send out the warning gas ethylene, and other trees in the vicinity detect the scent and start producing their own defense chemicals before the giraffe arrives. How do plants “smell” the gas and then mount their own defense before the giraffe begins eating them? More research is needed.
To avoid being overeaten when giraffes begin munching on them, acacia trees can change the flavor of their leaves and also warn other trees to do the same.
As hungry insects salivate on elms and pines, the trees can chemically analyze the insects’ saliva, reproduce it in mass quantities, and broadcast the chemical to the forest community. This cry for help alerts predators who like to eat the insects. They promptly come flying to the location, eliminating the insects that are attacking the tree.
It’s easy to imagine why God originally designed systems to produce chemicals with many different smells—to bless other creatures in the forest. Many woodland scents are still just as pleasant to animals as they are to us. In fact, the trees that produce flowers and fruit purposefully send out sweet-scented messages in a wide variety of colors, patterns, and perfumes to invite animals to come, explore, and partake.
Communication is happening below our feet as it is above. If we could carefully remove the loam at the base of a forest tree, we’d see a root system that spreads out twice as far as the canopy above our heads. This root system reaches depths of 1–5 feet (0.3–1.5 m), depending on the location. More astonishingly, roots may connect directly with the roots of other trees. Trees can distinguish members of their own kind and establish connections with them.
This reality contradicts the old view that woodland trees simply competed in a life-and-death struggle for limited light and nutrients. Though plants do compete in forests, current research suggests that more often, trees may be cooperating and assisting each other. When one tree is sick, nearby trees may share nutrients through their roots to help it get well again. If a lodgepole pine sapling springs up in the shade of a thick forest, older trees somehow sense that it doesn’t get enough sunlight to make food for itself, so they may share their bounty. They even change their root structure to open space for saplings.
How do plants talk in the soil? They may have several options. For example, researchers have found evidence that plants are communicating by sound. Though this sounds crazy, vibrations emanating from seedlings in laboratory settings have been detected by special instruments and measured at 220 hertz. In experiments, roots direct other roots to grow toward this low frequency. Much more research must be done, but these experiments suggest one intriguing possibility for the way plants communicate.
Trees also communicate with chemical messages, but they aren’t just talking to each other. They talk to their other soil neighbors, too. Microorganisms, such as bacteria and fungi, gather water and nutrients that the trees need. So roots produce nutritious substances, such as sugars and proteins, to attract these organisms. One researcher described this chemical advertisement as trees producing “cakes” and “cookies” to attract microbes to come and enjoy.
Special fungi recognize these chemical messages and not only partake, but also interact with roots to form partnerships. Fungi, for example, will inform the tree when they need to enter a root, and the tree will respond by softening a place in its root wall where the fungus can enter.
Fungal microbes receive all the food (sugar) they need to build their bodies, and in return they help trees obtain water and minerals, protect them from drought, absorb toxic heavy metals, and help undernourished and young trees. Trees couldn’t build their tall trunks without a steady supply of minerals from microbes that mine the soil and transport them to the tree.
This underground network of root/fungus communication acts in many ways like an underground internet. These special fungi called mycorrhizae (“fungus root”) spread a tangled highway of long microscopic tubes, called fungal hyphae, through the soil from tree root to tree root. Literally miles of tiny tubes are found within a single cubic foot of soil between two tree roots.
Trees communicate so intensely via these networks that it has been called the “underground internet” and the “wood wide web.” Electrical impulses pass through nerve-like cells from root tip to root tip, and these signals may be broadcasting news about drought conditions, predator attack, and heavy metal contamination.
Working together by means of complex communication tools such as sound, chemicals, and electricity, every member in the forest benefits. These complex relationships help maintain a healthy forest system, as the trees moderate temperature extremes, store groundwater and carbon more efficiently, produce plenty of oxygen, and provide a healthy habitat for other forest denizens.
I have not met anyone who wasn’t amazed by these findings. No matter what their religious or political view, people around the world are recognizing forests as places that promote emotional, spiritual, and physical health. Trees filter dust, pollen, pollutants, bacteria, and viruses from the air. Taking a deep breath in a virgin forest is literally a healthy experience. Research is confirming that, when stressed and driven people visit the forest, they find not only rest but lower blood pressure and an increased sense of peace.
There is no question that these phenomena have been overstated at times and greatly anthropomorphized (described in human-like terms). So how should followers of Christ make sense of these findings?
When we study the forest, we find mutually beneficial relationships, lavish provision, and steady communication. Are these not attributes of the Creator? Are they not evidence that God wants to display some of these wonderful attributes, even in nonthinking organisms?
Romans 1:20 proclaims, “ Since the creation of the world His invisible attributes are clearly seen, being understood by the things that are made, even His eternal power and Godhead, so that they are without excuse. ” The Bible highlights many of God’s attributes, including the fact that He is relational ( Genesis 2 1 Corinthians 12 ) and is a communicator ( John 1:1 Hebrews 1 ). In His creation we can see visible and finite hints of His invisible and infinite characteristics, if we have eyes to see.
All forest ecologists see the amazing relationships and interconnections within the forest. As a result, some have called the forest-and-earth biosphere a living organism. But we know from Scripture that a loving Creator is behind them. Christ the Word has filled His creation with organisms that communicate with chemicals, sounds, and electrical impulses. The recipient is designed to listen and respond in kind. What an amazing reminder that God desires to communicate with us, and He expects us to respond to His Word and help one another, too.
Yet we live in a broken world full of sickness and unhealthy relationships. Even the forest suffers from genetic defects, blight, and wanton destruction. The potential harmony of the forest reminds us about what once was, before man’s rebellion against the Creator brought corruption into the world. But the Creator, Jesus Christ the Son of God, came to earth as a man to restore all things, and He will complete this restoration when He comes again ( John 1:1–14 Revelation 21:1–7 ).
Spending time in the forest is a wonderful way to meditate on God and get our life priorities back in line. Scripture proclaims, “ Seek the Lord while He may be found. . . . For you shall go out with joy, and be led out with peace the mountains and the hills shall break forth into singing before you, and all the trees of the field shall clap their hands ” ( Isaiah 55:6, 12 ).
Source: The Hidden Life of Trees: What They Feel, How They Communicate by Peter Wohlleben. (This book often overstates the human-like qualities of trees, so use biblical discernment when reading it.)
Milestones on the tree of life
Now that we know how to read a tree and consider geologic time scales, let’s relate topics of the upcoming readings: eukaryotes, green plants, fungi, animals, which are a few of the milestones of the evolution of major life forms, to the tree of life.
Phylogenetic tree of life built using ribosomal RNA sequences, after Karl Woese. Image credit: Modified from Eric Gaba, Wikimedia Commons.
Notice that the tree is divided into three clades: bacteria, archaea, and eukarya (the eukaryotes). Eukaryotes are a clade that contains green plants, fungi and animals, three taxon groups that are more closely related to each other than to all other taxa depicted on the this tree. As we move forward through the biodiversity module, use this image of the breadth of taxa on the tree to put the small fraction of life we will learn about in perspective.
The video below from the PBS series Eons summarizes key geologic time scale events and emphasizes the evolution of life milestones that will get us started to consider biodiversity.
Genetic Control of Flowers
A variety of genes control flower development, which involves sexual maturation and growth of reproductive organs as shown by the ABC model.
Diagram the ABC model of flower development and identify the genes that control that development
- Flower development describes the process by which angiosperms (flowering plants) produce a pattern of gene expression in meristems that leads to the appearance of a flower the biological function of a flower is to aid in reproduction.
- In order for flowering to occur, three developments must take place: (1) the plant must reach sexual maturity, (2) the apical meristem must transform from a vegetative meristem to a floral meristem, and (3) the plant must grow individual flower organs.
- These developments are initiated using the transmission of a complex signal known as florigen, which involves a variety of genes, including CONSTANS, FLOWERING LOCUS C and FLOWERING LOCUS T.
- The last development (the growth of the flower’s individual organs) has been modeled using the ABC model of flower development.
- Class A genes affect sepals and petals, class B genes affect petals and stamens, class C genes affect stamens and carpels.
- sepal: a part of an angiosperm, and one of the component parts of the calyx collectively the sepals are called the calyx (plural calyces), the outermost whorl of parts that form a flower
- stamen: in flowering plants, the structure in a flower that produces pollen, typically consisting of an anther and a filament
- verticil: a whorl a group of similar parts such as leaves radiating from a shared axis
- biennial: a plant that requires two years to complete its life cycle
- whorl: a circle of three or more leaves, flowers, or other organs, about the same part or joint of a stem
- apical meristem: the tissue in most plants containing undifferentiated cells (meristematic cells), found in zones of the plant where growth can take place at the tip of a root or shoot.
- angiosperm: a plant whose ovules are enclosed in an ovary
- perennial: a plant that is active throughout the year or survives for more than two growing seasons
- primordium: an aggregation of cells that is the first stage in the development of an organ
Genetic Control of Flowers
Flower development is the process by which angiosperms produce a pattern of gene expression in meristems that leads to the appearance of a flower. A flower (also referred to as a bloom or blossom) is the reproductive structure found in flowering plants. There are three physiological developments that must occur in order for reproduction to take place:
Anatomy of a flower: Mature flowers aid in reproduction for the plant. In order to achieve reproduction, the plant must become sexually mature, the apical meristem must become a floral meristem, and the flower must develop its individual reproductive organs.
- the plant must pass from sexual immaturity into a sexually mature state
- the apical meristem must transform from a vegetative meristem into a floral meristem or inflorescence
- the flowers individual organs must grow (modeled using the ABC model)
A flower develops on a modified shoot or axis from a determinate apical meristem (determinate meaning the axis grows to a set size). The transition to flowering is one of the major phase changes that a plant makes during its life cycle. The transition must take place at a time that is favorable for fertilization and the formation of seeds, hence ensuring maximal reproductive success. In order to flower at an appropriate time, a plant can interpret important endogenous and environmental cues such as changes in levels of plant hormones and seasonable temperature and photoperiod changes. Many perennial and most biennial plants require vernalization to flower.
Genetic Control of Flower Development
When plants recognize an opportunity to flower, signals are transmitted through florigen, which involves a variety of genes, including CONSTANS, FLOWERING LOCUS C and FLOWERING LOCUS T. Florigen is produced in the leaves in reproductively favorable conditions and acts in buds and growing tips to induce a number of different physiological and morphological changes.
From a genetic perspective, two phenotypic changes that control vegetative and floral growth are programmed in the plant. The first genetic change involves the switch from the vegetative to the floral state. If this genetic change is not functioning properly, then flowering will not occur. The second genetic event follows the commitment of the plant to form flowers. The sequential development of plant organs suggests that a genetic mechanism exists in which a series of genes are sequentially turned on and off. This switching is necessary for each whorl to obtain its final unique identity.
ABC Model of Flower Development
In the simple ABC model of floral development, three gene activities (termed A, B, and C-functions) interact to determine the developmental identities of the organ primordia (singular: primordium) within the floral meristem. The ABC model of flower development was first developed to describe the collection of genetic mechanisms that establish floral organ identity in the Rosids and the Asterids both species have four verticils (sepals, petals, stamens and carpels), which are defined by the differential expression of a number of homeotic genes present in each verticil.
In the first floral whorl only A-genes are expressed, leading to the formation of sepals. In the second whorl both A- and B-genes are expressed, leading to the formation of petals. In the third whorl, B and C genes interact to form stamens and in the center of the flower C-genes alone give rise to carpels. For example, when there is a loss of B-gene function, mutant flowers are produced with sepals in the first whorl as usual, but also in the second whorl instead of the normal petal formation. In the third whorl the lack of B function but presence of C-function mimics the fourth whorl, leading to the formation of carpels also in the third whorl.
ABC model of flower development: Class A genes (blue) affect sepals and petals, class B genes (yellow) affect petals and stamens, class C genes (red) affect stamens and carpels.
Most genes central in this model belong to the MADS-box genes and are transcription factors that regulate the expression of the genes specific for each floral organ.
How does nature and nurture affect development?
Read full answer here. Accordingly, how does nature and nurture influence child development?
Both nature and nurture Nature and nurture both play a role. How we act as parents as well as our child's genes are strongly intertwined . Each child responds to parenting in different ways. We know that children bring out different responses from their caregivers, partly as a result of their genetic makeup.
Furthermore, how does nature and nurture affect personality? Both nature and nurture&mdashboth genetic and environmental influences&mdashplay a role in the development of personality. Researchers in behavioral genetics are interested in the non-genetic determinants of personality, as well. Genetic influences can't be studied without considering non-genetic factors they're all connected.
Furthermore, how does nature vs nurture affect physical development?
nurture affects our mental and physical health. In the context of the nature vs. nurture debate, &ldquonature&rdquo refers to biological/genetic predispositions' impact on human traits, and nurture describes the influence of learning and other influences from one's environment.
How does nature vs nurture affect language development?
The nature vs. nurture debate extends to the topic of language acquisition. Today, most researchers acknowledge that both nature and nurture play a role in language acquisition. However, some researchers emphasize the influences of learning on language acquisition, while others emphasize the biological influences.