Conifer Adaptations

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Introduction

Conifers are a relatively small group of plants (673 Gymnosperm species; 520 conifer species)

Angiosperms are a more adaptable group-- all life forms (very small herbs with short lifespan to large trees very long potential life span through vegetative propagation (e.g. Populus tremuloides clones may be 8000 yrs old)

Possible reasons for Angiosperm diversity

-- pollination by animals might promote speciation
-- seeds produced in ovaries that develop into fruit
-- wide variety of dispersal characteristics
-- efficient water conducting vessels (flow rate of water through vessels is ca. 250 times that of tracheids)
-- ability to vegetatively reproduce, allow survival in environments where plants are frequently physically damaged (fire, herbivory, avalanches) and extreme climatic stress (don't have to go through seedling stage.

Nevertheless, conifers dominate large portions of northern hemisphere

-- high northern latitudes
-- semi-arid parts of North America and Asia
-- mild, maritime climates of the Pacific Northwest

What is the reason for the widespread success of conifers in these regions????

LIST OF BENEFICIAL TRAITS OF CONIFERS

 Photosynthesis occurs at relatively low temperatures

Conifers carry out high rates of photosynthesis at relatively low temperatures compared to deciduous species

Douglas-fir:

Douglas-fir caries out relatively high rates of photosynthesis in non-summer months-- spring and fall
Cold, clear days in winter are too cold
Warm summer days are too warm

Generally true for other conifers-- may help them be successful in areas of cold climates

 Evergreen foliage (except Larix)

Allows trees to photosynthesize as soon as conditions become favorable (good for short periods of favorable climate)

--short warm season at northern latitudes, don't have to wait for the production of new leaves (don't waste valuable portion of short growing season on time it takes for leaves to flush)
-- short wet season in arid areas (eg New Mexico, Arizona, California), can take advantage of rains whenever they might occur (in non-growing season)

Allows trees to conserve nutrients- don't have to produce entire set of leaves each year (good for soils with low nutrient content and environments with slow decomposition rates)

Tracheids are "safe" water-conducting cells

-- tracheids are long, narrow-diameter cells
-- narrowness prevents bubbles formation in spring when stems thaw
-- air bubbles form as water freezes and air molecules go out of solution to form gas (like ice cubes in freezer)
-- small diameter of tracheids only allow small bubbles to form
-- small bubbles are likely to redissolve

vessels of Angiospersm-- bubbles often do not dissolve

--air bubbles are break in water column and prevent water from being drawn up to leaves (like air holes in straw)

Thus, tracheid may not be as efficient as moving water as are vessels of Angiosperms, but they may be "safer" way to ensure reliable supply of water to crown of tree and necessary for living in cold winter climates

Structure of Stomates

Sunken stomates with waxy deposits
Sunken stomates reduce evaporation because chamber around stomate is not exposed to dry air and turbulent airflow

Reduction in water loss is important for survival in contrasting situations

1. dry climates (as you might expect)-- generally reduces water loss
2. cold climates-- helps prevent winter desiccation, when air warms in spring but soil is still cold/frozen and water can't move into tree fast enough to replenish loss of water from leaves

Effective Fire Adaptations (although Angiosperms also have effective fire adaptations--by resprouting)

We've discussed before (2 contrasting types of fires)

* low intensity, gound fires-- thick bark, high crown, flamable litter, live through fire eg Pinus ponderosa, Sequoiadendron giganteum

* high intensity, crown fires-- serotinous cones, highly flammable dead branches that remain on trees (fire ladders) e.g., Pinus contorta -- numerous others

 Why do conifers dominate in mild climates of PNW?-- i.e., not harsh climate as in other areas dominated by conifers

Seasonal pattern of temperature and precipitation