Fire Effects on Vegetation

September 13, 2006

Tallgrass Prairie: TTYP

• First, think to yourself. Write down any causes, effects, and mechanisms that explain this landscape.

• Then, discuss with a partner and be prepared to share with the class.

Fire in Tallgrass Prairie

• Primary role in maintenance and development

• Alteration in physical environment, particularly the litter layer

• Changes in resource availability, rapid regrowth

• Plant level mechanisms• Human management and the importance

of timing

Fires Effects on Vegetation

• Fire alters the physical environment through removal of live and dead plants from the community

• Selectively eliminates part of the plant community

• Other plant species are unchanged or have adaptions for regrowth – Thick bark and self pruning of lower branches (Jack pine,

Ponderosa pine)

• Any plant can be killed by a fire of sufficient severity

Understanding the Plant Response

• Temporarily reduces resource competition– Moisture, nutrients, and light

• Plant adaptations based on strategies of resource allocation

Mechanisms of Re-vegetating

• Vegetative re-establishment

• Seed Survival– Soil stored– Canopy stored

• Seedling persistence

• Seed dispersal

Vegetative: Plant Resource Allocation Comes in Many Forms

• Part of an individual plant survives and fire stimulates resprouting

• Aboveground and belowground resources– Dormant buds insulated by bark– Root collar sprouts i.e. oaks– Lignotubers; swellings at the base/root collar

of shoots of shrub species i.e. manzanita– Root suckering from adventitious roots; roots

are formed from stem tissues i.e. aspen

http://www.forestryimages.org/images/768x512/4824098.jpg

http://www.nccpg.com

Vegetative: Another

Perspective

• Classification based on the position of the perennating buds relative to the soil surface

• What organ is missing?

Geophytes

BBasal Meristems

Example: Fire Effects in Tallgrass Prairie

• Decrease in woody species– Exposed apical meristems

• Basal meristems in grass

• Protected vegetative growth– Large mass of perennating organs

belowground; high root to shoot ratio

Seed Survival

What advantages does a post-fire environment present for seed germination

and seedling survival?

Mechanisms for Seed Survival

• Seed protection from fire

– Enclosure within fruits in the plant canopy– Seed bank survival

• Seed coat (scarification), i.e. tallgrass legumes• Seed burial

• Seed dispersal– Species killed by fire and seeds don’t survive– Seeds from outside sources

Seed Protection: enclosure within fruits

• Serotiny - Cone scales are held closed by resinous material and it melts out by the heat of fire and cause to release seeds

– Jack pine, Lodge pole pine

Seed Protection: soil seed bank

Tradeoff between survival of seeds from fire and germination of seeds in different depths (Whelan 1995)

Seedling Persistence

• Early belowground resource allocation, fast growth post-fire– Longleaf pine grass stage

Fire Regimes and Vegetation

• Timing– Resistance to fire is low during reproductive

stage of plants and high with greater carbohydrate reserves

• Severity

• Duration and Extent– Dispersal limitations

Community Response

• Mortality and response of plants to fire is differential among plant species and plants of different age/developmental stage

• Fire can shift plant community structure and composition

• Example: Tallgrass prairie– Spring burn has differential influence on cool

and warm season grasses

Studying Fire Effects

• Burned vs. Unburned

• Pre vs. post-burn

Studying Fire Effects

Assumptions: • Burned vs. Unburned

– the only difference between the two areas is the treatment i.e. soils, successional stage, disturbance history

– treatment is uniform, no within burn variation

• Pre-burn vs postburn,– treatment is uniform