The Tree

 

 

Life Cycle

Phase 1. seeds on forest floor

Phase 2. seedling establishment

Phase 3. growth and development

Phase 4. seed production and dispersal

 

Seeds on the Forest Floor

Germination:

  1. imbibition
  2. activation of metabolic processes
  3. embryo growth

Seed dormancy is defined as the failure of the seed to germinate under favorable conditions. This trait is advantageous for seeds disseminated in fall, as they do not germinate immediately and are held over until the spring. The cold of winter could kill seedlings resulting from fall germination.

  • Physiological Dormancy - internal, metabolic changes must occur
  • Physical Dormancy - seed coat may be impermeable to water and gases or be mechanically constraining
  • Dormancy can be removed by stratification (cool moist treatment for physiological dormancy) or scarification (reduce seed barrier by abrasion for physical dormancy).

Vegetative Reproduction - root-collar - lignotuber - root sprouts - fragmentation - stolons, runner, layering, tipping

Seedling Establishment

Pioneer species - bare areas, loblolly pine

Gap-phase species - under closed canopies and later released by opening of a gap, yellow birch

Growth and Development

Primary growth - apical meristems at tips of roots and stems, growth in length

  • fixed growth: intermittent, resting bud, initiation in bud and elongation separated in time
  • free growth: continuous, initiation and elongation concurrent

Secondary growth - lateral meristems, cambium, growth in girth, growth distribution and periodicity

Tree form

  • excurrent, conical; conifers in northern and alpine
  • decurrent, deliquescent; deciduous, broadleaf, southern pines

 

Seed Production and Dispersal

Flowering characteristics of common tree species

Age at which forest trees begin producing abundant seed crops

Typical developmental period required to produce mature seed in common tree species

Phenology of seed production in common conifers

Periodicity in production of good seed crops in common tree species

Factors influencing periodicity in seed crops: 

Site - earlier, heavier and more consistent in southern part of range - dry south exposure, early seed production,- poor sites seem to stimulate early seed production

Climate - strong relationships are not clear

Insects - effects most noticeable in light seed years

Disease

Birds and mammals

Physiological

Seed Dispersal

wind, water, animals - see table of major dispersal types

most seeds are dispersed close to parent - 40 to 50 meters; advantage = local adaptation, disadvantage = growing in competition with parent