final Flashcards
temperate and boreal forests - geographic distribution
- predominantly in N hemisphere
- temperature forests do occur in S.America, Australia, and New Zealand
-in N hemisphere, coniferous forests form a broad circumpolar belt
temperate and boreal forests - climate
seasonal variation determined by temperature
TEMPERATE
- winter lows: -15 C to -5C
- frost free days; 120 to 150 days
- summer temps; 15 C to 27 C
- precipitation 500 to 1000 mm
CONIFEROUS
- winter lows: -30 C
- frost free days; 50 to 100 days
- summer temps; 12 C to 15 C
- precipitation <500 mm in summer and 100 mm snow in the winter
temperate and boreal forests - characteristic growth forms
TEMPERATE
- broad-leaved deciduous trees
- annuals and hemicryptophytes, forest floor
CONIFEROUS
- needle-bearing trees
- hemicryptophytes
temperate and boreal forests - characteristic species
TEMPERATE
- elm, ash, walnut, sugar maple, basswood, aspen, birch, maple, willows
CONIFEROUS
- white spruce, black spruce, jack pine, white pine, hemlock, cedar
comparison of the deciduous vs. the evergreen, coniferous habit – leaves
DECIDIOUS
- broad leaved
CONIFEROUS
- narrow, often needle-leafed
comparison of the deciduous vs. the evergreen, coniferous habit – tissue
DECIDIOUS
- vessels (perforate): wide diameter, efficient, competitive in mild climates due to efficient conduction
CONIFEROUS
- trachea’s (imperforate): narrow diameter, safe, competitive in seasonally dry environments due to ‘safety’ features
comparison of the deciduous vs. the evergreen, coniferous habit – photosynthetic rates
DECIDIOUS
- deciduous 15-35 mg CO2 dm-2h-1
-evergreen 15-18 mg CO2 dm-2h-1
-freezing results in cavitation
CONIFEROUS
- 5-18 mg CO2 dm-2h-1
-photosynthesis at temperature below freezing
temperate and boreal forests - adaptations to freezing low temps
plants cannot tolerate intracellular ice formation
- intracellular ice-crystal formation is avoided by:
(1) supercooling
(2) extracellular freezing
temperate and boreal forests - supercooling
-mestastable
- small cells
- low nucleation
- accumulation of solutes
- limit of -40 C
- wind –> ice
temperate and boreal forests - extracellular freezing
- plants decreasing in volume during freezing
- water of cell walls more dilute than cells
- as solvent extracted, depressed the freezing point
- cells potentially die of dehydration
- adaptations also at the membrane level (thawing expansion)
- lollipops, excision, fluidity
temperate and boreal forests - low temps and tree distribution
- trees species distribution is limited by low winter temperatures: both latitude and also elevation
- ring porous species restricted to milder regions (and new growth each year)
- diffuse porous species – not as limited, do not cavitate as easily in colder regions
DICOTS
a. constant size = diffuse porous
b. steady dec. in size = semi-ring porous
c. abrupt decrease in size = ring porous
CONIFERS
a. constant size
b. cell wall thickness increases gradually
c. cell wall thickness increases abruptly
temperate and boreal forests - treelines
at latitudinal extremes, conditions become too severe to support the growth of trees
- stress: physiological tissue damage due to low temperature or desiccation
- disturbance: mechanical damage due to wind abrasion, herbivory, snow loading, or fungi infection
- reproduction: reduced seedling and sapling establishment due to decreased pollination, seed development, seed dispersal, germination, or seedling establishment
- carbon balance: photosynthetic carbon gain minus respiratory demands is not enough to maintain minimum growth
- growth limitation: reduced development of new plant tissues due to low temps
the end of the tree-ed region may be abrupt, or represented by an ecotone of deformed trees: Krummholz
temperate and boreal forests- abrupt tree line
- shade tolerat deciduous species
- seedlings less tolerant of extremes than parents, establish under parents
temperate and boreal forests - krummholz tree line
- deformed tree scrub, includes coniferous species
- seedlings survive better than parents, but growth affected by environmental extremes resulting in Krummholz appearance
- Krummholz may be genetically fixed (?)
temperate and boreal forests - phenological responses
phenology in temperate and coniferous forests is in response to light : PHOTOPERIOD
- Coniferous forests slow down with decreasing light and temperature: reproduce in spring
- deciduous forests show obvious phonological responses to temperature and light
phytochrome
deciduous forests
- pigment in plants that mediates response to photoperiod
blue –> phototropins and cryptochromes
red –> phytochrome
- discovered through germination response of light requiring seeds
- exposure to red light –> germinate, far red light inhibits germination
- conversion of Pr to Pfr by red light, results in physiological responses such as seed germination
- ratios of Pr:Pfr and darkness are important in determining amount of active phytochrome and thus responses
R:FR at different times of day
daylight – 1.19
sunset – 0.96
moonlight – 0.94
deciduous trees - color change
color change in response to decreased photoperiod
- chlorophyll is broken down enzymatically
- carotenoids are unmasked
- anthocyanin are synthesized (produced as a result of altered sugar metabolism due to phosphate decrease)
- amino acids are stored till spring
deciduous tree leaf abscission
- reduce water loss, prevent damage from winter winds and snowfall, reduce insect predation
- hormonally due to IAA and ethylene
- development of an abscission zone seals off xylem, prevents further cavitation
leaf maintenance phase –> shedding induction phase –> shedding phases
deciduous tree reserves
accumulates starches (reserves for spring uses for new leaf flush) and sugars
deciduous tree bud break
occurs after a minimum cold period of one or more months followed by higher temperatures, 15 C to 20 C
- late flushing in oaks, etc., may ensure that transpirational demand remains low until new rings for conduction are formed
deciduous forests undestory
- therophytes germinate in spring
- stratification breaks dormancy of therophyes and cryptophytes
- changing light conditions on the forest floor lead to shade tolerant species becoming dominant in summer
temperate and boreal forests - sun and shade leaves
microclimates in the understories and in the tree canopies differ significantly in light
- there are shade tolerant and intolerant species
sun leaves (compared to shade) :
- thicker
- more stomata
-more soluble protein (Rubisco)
- more deeply lobed
leaf dimorphism also in conifers
temperate and boreal forests - fire
temperate deciduous forests seldom burn
- coniferous forests burn frequently
fire type: surface (needles) and/or crown
frequency: surface 1 - 10 years, crown 100 - 1000 years
intensity: low for surface fires, high for crown fires
adaptation of conifers to fires
- survive low intensity fires
- killed bu high intensity fires
- restistance correlated with
-increased bark thickness- high open branching habit
- lack of lichens
serotinous seeds
remain in the cone for up to 25 years
- resin bonds sealing cone scales melt at 60 C (in fire)
- seeds resist high temps
- released onto bare ground
fire and seed release
the third and perhaps most important agent of seed release is fire. hot air produced by locally intense fire and convected high into the canopy can dry cones, resulting in release of enormous quantities of seed over small areas. this increased seed fall coincides both spatially and temporally with fire related seedbed conditions favorable for seed germination and seedling survival.
first year giant sequoia seedlings established on treated-bulldozed or burned or both area, were 30 to 150 times more numbers than those on undisturbed forest floor
survival of sequoia seedlings for a 7 to 9 year period was 27% on areas subjected to a hot burn as opposed to 3.5% on other treated substrates
temperate deciduous forests - productivity and nutrient cycling
biomass/productivity - 120-300 t ha-1
seasonally very varied
nutrient cycling - major nutrients input from litter , quality of nutrient supply dependent on time of fall
decomposers - earthworms, nematodes, bacteria, fungi