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LIFE HISTORY STRATEGIES

Introduction

Consider the timing and energy invested in different stages in the life cycle of trees.

Diagram of life cycle:

STAGE

Seed

Juvenile

Adult

FUNCTION

dormancy, dispersal

growth

reproduction

Note: no post reproductive period (possibly only for organisms that have long juvenile period that requires a great deal of parental care)

Question: Are there predictable patterns in how much time and energy is allocated to these stages?

Allocation-- Trees are faced with alternative ways to use energy and must make "choices"

Source of energy for plant needs-- photosynthesis
Potential uses of energy

growth (leaves, roots, branches every year)
reproduction
transport of some materials (across membranes)
tissue repair
defensive chemicals

There is a finite amount of energy produced each year but nearly infinite potential to use it. Thus energy used for one function/structure is not available for another

How does tree allocation between different needs?? (e.g., growth and reproduction)

Seed production versus growth

Large cone crops in Douglas-fir are often associated with low radial growth
Large seed crops in birch and maple correspond with low leaf production

Age of first reproduction versus growth

Dwarf apple trees-- produce fruit early, at small size-- but apple crop is small
Old-fashion large apple trees- produce fruit later, but larger tree size and larger apple crop

LIFE HISTORY DIFFERENCES BETWEEN EARLY AND LATE SUCCESSIONAL SPECIES

There are differences in the life history traits of early and late successional species:

age of 1st reproduction

seed # and size
growth rates

These differences are related to differences in the physical and biological environments of early and late successional stands and to the general consequences of reproductive strategies.

PREDICTIONS:

Make predictions about differences you expect for:

TRAIT

EARLY SUCCESSIONAL SPECIES

LATE SUCCESSIONAL SPECIES

seed size

seed number

seed defensive chemicals

frequency of seed production

growth rates

age at 1st reproduction

leaf size #, leaf placement, crown architecture (geometry)

STAGE	Seed	Juvenile	Adult
FUNCTION	dormancy, dispersal	growth	reproduction

TRAIT	EARLY SUCCESSIONAL SPECIES	LATE SUCCESSIONAL SPECIES
seed size
seed number
seed defensive chemicals
frequency of seed production
growth rates
age at 1st reproduction
leaf size #, leaf placement, crown architecture (geometry)