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Lecture Notes. Colin Tudge, The Tree: A Natural History of What Trees Are, How They Live, and Why They Matter. Preface I. What is a Tree?. Preface. The Royal Oak at Boscobel House in Shropshire, England may have hidden King Charles II from Cromwell in 1651 .
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Lecture Notes Colin Tudge, The Tree: A Natural History of What Trees Are, How They Live, and Why They Matter. Preface I. What is a Tree?
Preface The Royal Oak at Boscobel House in Shropshire, England may have hidden King Charles II from Cromwell in 1651. Charles II hiding in an English Oak Descendant of Royal Oak
Giant Redwoods Giant redwoods of California were ancient when Christopher Columbus landed. “General Sherman” Redwood, Sequoia National Park
The Oldest Trees in the World Giant redwoods are not as ancient as California bristlecone pines (Pinus aristata), 3000-5000 years. Bristlecones: “Methuselah” and “Prometheus,” White Mountains, CA Gayle Samuels tells their story in Enduring Roots.
What Trees Provide • Trees provide food and shelter for insects, birds, and animals, but trees must also compete for water, nutrients, air, and space from seed to old age for hundreds or even thousands of years. • Trees must also reproduce by attracting pollinators to their flowers, setting fruit, and dispersing seeds. • Human beings, civilization could not exist without trees: wood for fuel, ships, structures.
Spirit of Reverence Tudge reminds us that the founders of science—Pythagoras, Galileo, Newton—equated research with reverence. The author wrote his book in the same spirit—a book about the science of trees and what we know about trees from modern research—in a spirit of reverence for nature.
Connoisseurs of Nature And since trees are the key to survival of all life on land, let’s aspire to be “connoisseurs of nature,” as Tudge suggests by conserving through knowledge and caring.
Sacred Trees Trees have always been associated with the sacred Artist rendering of 40 memorial groves of red and sugar maples to line the walkway descending to Sacred Ground, Flight 93 National Memorial, PA
I. What is a Tree? Trees in Mind: Simple Questions with Complicated Answers Keeping Track
1. Trees in Mind: Simple Questions with Complicated Answers • We create definitions of nature for convenience, for our own purposes, and to make sense of it. Our definitions influence the way we treat nature. • “A tree is a big plant with a stick up the middle—or it could be, if it grew in the right circumstance; or is very closely related to other plants that are big and have a stick up the middle; or resembles a big plant with a stick up the middle.”
Why be a Tree? • Life’s requirements: metabolism (staying alive), reproduction, and getting along with others. • Two main reproductive strategies: k & r • K-strategists produce a few, large offspring to give them a good start and tend to be long lived; e.g., elephants, eagles, orangutans, humans.
R-Strategists R-strategists produce enormous numbers of small offspring with little chance of survival, but for safety in numbers; e.g. codfish = 2 million eggs at a time. Most are eaten but as long as 2 survive and reproduce, cod survive. Other r-strategists can run through several life cycles in a few weeks, e.g., flies.
Trees often combine both k and r-strategies Oaks produce millions of seeds that are large and do not have to germinate immediately so most survive. The down side is that most trees must mature, grow for several decades, before they can reproduce. acorns acres of acorns oak seedlings
The Land Wants to be Forest • Trees take advantage of changes in climate and colonize new areas as birches and alders did in inhospitable regions after the last ice age. • Early successional trees in temperate forests are conifers—pine and juniper— which colonize old farm fields, clearings, and repopulate forests after clear cutting and fire.
Forest Succession • Succession is a natural pattern of change that takes place over time in a forest. When trees are removed, the forest generates and matures in a predictable order: annual weeds, perennials, shrubs, conifers, and finally hardwoods.
Exotic Invasive Species Vacant lots, disturbed woods, and road sides in cities and suburbs are colonized by fast growing exotic invasive trees, opportunistic tree species often called weed trees such as Ailanthus.
Ailanthus is listed as a noxious weed in the U.S. It invades roadside woodlands, chokes out native trees, and is difficult to eradicate
How Many Kinds of Trees Are There? • Simple question, complicated answer. • Kinds = species (preferably identified by flowers). • “Two or more individuals can be considered to be of the same species if they can mate together to produce fully viable off spring.” • What if they live in the different places? • Many trees from different parts of the world brought together in gardens happily interbreed.
Hybrids • Many hybrids have been inadvertently produced in gardens in just this way. • The most famous example of interbreeding in a garden is the case of the London planetree, a cross between the American sycamore (Platanus occidentalis) and the Asian planetree (Platanus orientalis), which produced the hybrid, Platanus X acerifolia. The X indicates hybrid. • The parents had been planted in the Oxford Botanic Garden in England, interbred, and produced the hybrid commonly called the London planetree in the 17th c.
Poly, Pretty Poly • Polyploidy describes any organism with more than two sets of chromosomes. Polyploidy is very common in plants, another complication in distinguishing and counting species. • Genes: one set of chromosomes from each parent, which are said to be “haploid”. In fertilization they fuse to create an embryo that has two sets of chromosomes and is said to be “diploid.” Most organisms are diploid (humans get 23 chromosomes from each parent for a total of 46).
Doubles, Anyone? • In plants the number of chromosomes can spontaneously double. • The diploid cell becomes tetraploid with four sets of chromosomes. • Tetraploid plants can breed with other tetraploids of the same kind but not with either parent so instantly form a new species.
Tetraploids and Octoploids, Oh My • Sometimes chromosomes of tetraploids double again to produce octoploids. • The octoploids also produce a new species.
Separation Anxiety • One more complication: if tree species are separated, they eventually evolve into distinct species. • American sycamore and the Asian plane tree, among many other Asian/American relatives were probably a single species, but when the land masses separated, they evolved into distinct species. Closely related plant species like many Asian/American counterparts are called analogs.
Varieties and Supspecies In the shorter term, botanists refer to the two separated populations as varieties or subspecies of the same species, e.g. Japanese maple (Acer palmatum) Thread leaf Japanese maple (Acer palmatum var. dissectum)
Send in the Clones • Finally, plants produced vegetatively—by suckers, division, or cuttings—are genetically identical and are called “clones.” Genetically identical individuals are referred to as a “clone.” • Cultivar: in horticultural production a “cultivar” is a selection of a species propagated vegetatively (cloned), named, patented, often trademarked, and introduced for its superior characteristics such as repeat bloom, foliage coloration, cold hardiness, compact habit, or resistance to pollution, scorch, or disease.
Notable Cultivars Acer rubrum Red Sunset® is a cultivar of red maple selected for scarlet fall color, drought and heat tolerance. Magnolia grandiflora ‘Edith Bogue’ is a cultivar of southern magnolia selected in NJ for its cold hardiness in northern gardens. .
So, how many tree species are there? How many? Nobody knows! “How many?” “Nobody Knows.”
Still Counting 90% of all organisms, including trees, live in tropical forests which are difficult to study. The Amazon Rainforest
Botanists guess* that there are about 350,000 species of land plants. (*educated guess: see note p 409 for statistical models used to estimate the number of species) 300,000 flowering plant species. 1/5 or about 60,000 tree species. There are also non-flowering plants, of which the conifers are most important. About 600 species of conifers. How many species of trees? About 60,000.
The Amazon Conquistadors, plant explorers, and botanists have been studying the Amazon forests since the 16th c. and indigenous people for thousands of years before the Europeans arrived. The rainforest borders 8 countries in South America
Amazonia German plant explorer, Baron von Humboldt, botanized in the Amazon and throughout Latin America, Mexico, and Cuba. Humboldt’s Narrative of Travels to the Equinoctial Regions of the New Continent during the Years 1799-1804 influenced the young Charles Darwin.
The Amazon Rainforest Botanists continue to study the Amazon, but even after hundreds of years it’s impossible to say how many species of trees there are.
