forestry 303 Definitions

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Hypodermis
The layer of thick-walled cells immediately below the epidermis in the leaves (needles) of gymnosperms, used primarily to further reduce water loss.
Fascicle
A close bundle of needles in Pines specifically.
Bud Scale
Scales that cover buds. Bud scales help prevent desiccation and insulate the bud from rapid temperature changes.
Adventitious buds
Buds that develop in unusual places, where you wouldn't normally expect to find them (places other than the shoot tip or leaf axil)
Abscisic acid (ABA):
A plant hormone that functions primarily as a growth inhibiting hormone, as well as other various functions.
Heat sum
a cumulative amount heat, measured in degree days, that is "counted" by a tree once a threshold temperature is met. This happens after dormancy has been broken, and ensures that the buds do not flush too early, until the sum has passed.
Decurrent Branching
The kind of branching typical of angiosperm trees. When Lateral shoots grow at narrow angles to the main stem, results in broad round crowns.
Cuticle
A layer of wax covering the epidermis of the needles, and its primary function is to reduce evaporation.
Evapotranspiration
The process by which water is transferred from land to the atmosphere by evaporation from transpiration of plants.
Hydrogen Bonding
Relatively weak electromagnetic bonds that form between 2 water molecules, from the hydrogen atom of one molecule to the oxygen atom of the other molecule. They give water a remarkably high tensile strength and give it the property of surface tension.
Light compensation point
Point where the amount of sugar produced by photosynthesis is equal to the amount of sugar burned by respiration. There is no net gain of sugar because there is not enough light.
Biotic
relating to all things living, especially in their ecological relations.
Silviculture
The growing and cultivating of trees, with specific management goals.
Shelterwood system
A silvicultural practice of management where almost all trees are cut down, save for a few mature trees, to produce seeds and regenerate the clear cut.
Coppice System
A traditional practice of woodland management where young tree stems are repeatedly cut down to ground level in order to exploit trees ability to put out new shoots from their stumps or roots.
Epigeous germination
During germination, the cotyledons come up with the shoot above the ground, and cotyls can photosynthesize.
Hypogeous germination
During germination, the cotyledons remain below ground and break down, feeding nutrients to the plant instead of photosynthesizing.
Palisade mesophyll (parenchyma)
The mesophyll (or parenchyma) is the basic tissue of the leaf, it has a lot of intercellular space to facilitate gas exchange. It is where most photosynthesis occurs.
Boundary Layer
a physical layer of relatively still, calm air that is directly adjacent to the surface of any structure, (in this context, leaves/needles).
Lateral meristem
starts as a meristem bud, and then the tissue divides to produce a branch, hence the lateral
Primordia
an aggregation of cells indicating the first traces of the development of a structure
Photoperiod
the length of day (but really it's the length of night, or absence of light ;) )
Casparian strip
a band of cell wall material deposited in the walls of the endodermis, made of wax.
Excurrent branching
When the first order shoot (stem) grows faster than the second order shoots (branches), we end up with a tree taller than it is wide (common in gymnosperms)
Buttress
shallow rooting that causes a swollen tree base, caused by roots with more cambium activity on their upperside than their lower side. adds stability to the tree.
Soil- Plant atmosphere continuum
the pathway for water movement, from soil the water is pulled up through the plant (thnx to hydrogen bonds) in the xylem by the transpiration in the leaves and then into the atmosphere
Light Saturation Point
the minimum light intensity needed to reach maximum photosynthetic rate
ecological succession
gradual process by which species are changed and replaced in a community over time, primary can take 100's of years, secondary can be 10X faster
Abiotic
relating to all things non-living, for example the non-living ecological factors like soil pH, CO2
Root Endodermis
A cell layer with waxy walls to control substances that enter and exit that water conducting tissues (xylem) and nutrient conducting tissues (phloem)
Biogeoclimatic zone
a zone broadly defined as a "a geographic area having similar vegetation and soils as a result of a homogenous climate"
the clearcut silvicultural system
a management practice where the stand of trees is entirely cut down in the selected area.
the selection silvicultural system
a management practice where foresters will go in and cherry pick trees of exceptionally high value, on occasion.
sapwood
It is the functional water conducting tissue, because it is the newest produced.
heartwood
darker tissue near the center of the stem, not functional for water transport because gummed up with resins, main function is structural support
lenticel
develop where the cork cambium is extra active, creating tissue with numerous intercellular spaces and allowing for gas movement. visible as line or crack
statocyte
gravity sensing cells, exist in the root cap and explain how roots know to grow down into soil
statolith
starch grains located inside the statocytes, heavy and sink to the bottom of the statocyte, where they are felt as an indicator of gravity