stand dynamics sept 9 cp

7/27/2019 Stand Dynamics Sept 9 CP

1/38

Disturbance and Stand Development


2/38

Disturbance

any relatively discrete event in time that

disrupts ecosystem, community or population

structure, and changes resources, substrate

availability or the physical environment

White and Pickett 1985

biotic or abiotic

human-caused or natural

single-tree, gap-forming or stand-replacing


3/38

Examples of forest disturbances


4/38

Recognizing forest disturbances


5/38


6/38


7/38


8/38


9/38


10/38


11/38


12/38


13/38


14/38


15/38


16/38


17/38


18/38


19/38


20/38


21/38


22/38


23/38


24/38


25/38


26/38

Stand Development


27/38

landscape

Stand spatially contiguous group of trees and associated vegetation having

similar structures and growing under similar soil and climatic conditions

- relatively homogeneous

Forest a heterogeneous mosaic of forest stands

Landscape a heterogeneous mosaic of forest stands and non-forest ecosystems


28/38

Stand Development

4 main stages of development of even-aged

stands following stand-replacing disturbance

Cohort: a group of trees regenerating after a

single disturbance until growing space is filled

Cohorts may range in age from years to

decades


29/38

Stand initiation

Stem exclusionUnderstory re-initiation

Old growth

Stages of stand development


30/38

Stand Initiation Stage

Re-colonizing the site

Available growing space and resources

Open growth

Single cohort

Many species invade

Competition with non-tree species

Foliage to the ground


31/38

Stem Exclusion Stage

no available growing space

increasing competition among trees

above ground (light)

below ground (water, nutrients)

crown closure

mortality of smaller trees

self-thinning no regeneration


32/38

Understory Re-initiation Stage

Canopy begins to open

some overstory trees die

crowns thin as trees get older

branches die, ripped off by wind

more light reaches the understory

understory trees often different species

advanced regeneration

at least two cohorts


33/38

Old-growth Stage

trees of all ages and sizes

diversity of tree and non-tree species

gaps, clumps


34/38

Crown classes

Dominant

Co-dominant

Intermediate

Suppressed

Why differentiation?

age

micro-sites

competition

genetically superior

http://www.dnr.state.md.us/education/envirothon/forestry/silviculture.html


35/38

Gap Dynamics

Gaps:

openings of any size in the overstory

death of one or several trees

late-successional species perpetuatethemselves

usually little disturbance of forest floor


36/38

Stand initiation


Old growth

Stages of stand development


37/38

Stand initiation


Old growth

Stand-replacing disturbance


38/38

Stand initiation


Old growth

Hastening stand development

stand dynamics sept 9 cp

Documents