Chapter 5: Plant growth

Meristems Meristems -regions of active cell division that are sources of indeterminate plant growth Apical meristems- primary growth that lengthens roots and stems Produces primary xylem, phloem and epidermis Lateral meristems- secondary growth that thickens roots and stems Vascular cambium –produces secondary xylem and phloem Cork cambium – produces “secondary epidermis” (bark) Why is indeterminate growth so critical to plants??

Meristems -primary and secondary growth

Xylem –Heartwood vs. sapwood Heartwood –cavitated, inactive xylem Provides structural support Often darker as a result of antimicrobial compounds Important determinate of wood quality and value Sapwood- active xylem (1-12 rings)

Growth rings Early wood (spring wood) –lighter part of growth ring larger lumen for greater water transport capacity Late wood (summer wood) –darker part ring (its what you count) smaller lumen with greater cell wall thickening to prevent cavitation

Growth rings in angiosperms Ring-porous wood -vessels produced primarily in spring wood (e.g. oaks, sassafras) Diffuse-porous wood –vessels produced in spring and summer wood (e.g. sugar maple, aspen) Describe a climate scenario where diffuse-porous wood be advantageous

Dendrochronology Science of tree ring dating and climate interpretation

Dendrochronology five of the 28 trees died or were cut earlier than 1847, meaning the pioneers harvested trees both live and dead. The 1840s were drier than any other decade in this tree-ring history, which spans the years 1702 to 1863,” said BYU professor Matthew Bekker, whose findings are published in the current issue of the academic journal Tree-ring Research. “It was a really rough time to establish a settlement based on irrigated agriculture.” The tree ring pointed out at the right was grown in 1847, the year the first Mormon settlers arrived in Utah. Bekker's analysis of the ring width indicates 1847 was the 10th driest year in the 162 year tree-ring history.

Bark gas exchange Suberin in cell wall of bark cells blocks oxygen transport Lenticels – small opening in bark that allows gas exchange -rapid division and growth of cork cells splits the epidermis

World-wide wood consumption Trends -1996 world-wide consumption = ~3400 million cubic meters -55% fuelwood, 45% industrial roundwood = paper, construction wood -Types of wood usage very different in developed and developing countries

Wood products Wood –fuel, paper, construction materials Wood fluids – latex (rubber), resins, syrup

Sustainable forestry New forestry –management strategies that allow the return of healthy forests following timber harvest Selective harvesting- leaving mature trees Seedling plantings

Challenges to sustainable forestry Nutrient depletion -with the wood you take nutrients from the ecosystem Seedling establishment is not trivial –competition, herbivory

Chapter 5 Homework questions Explain what indeterminate growth is, how plants do it, and why it is so important to their survival. (T) Describe the anatomical differences between ring-porous and diffuse-porous wood and explain the climate patterns that would favor each strategy. Give several examples of wood products important to humans; define sustainable forestry and present two major challenges to forest sustainability following logging.