Fire Effects on Vegetation

1. Fire Effects on Vegetation September 16, 2010

2. 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.

4. 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

5. Fire’s 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 • Temporarily reduces resource competition • Increase in moisture, nutrients, and light • Any plant can be killed by a fire of sufficient severity!!!

6. Understanding the Plant Response • Plant adaptations based on strategies of resource allocation

7. Plant mechanisms for establishing after fire • Survival – due to “fire adaptive traits” • Tolerance - persistence of same individual • Vegetative regeneration • Post-fire regeneration (of new plants) • Seed survival (protection) • Seed dispersal • Adaptation to post-fire conditions

8. Many pine species have high tolerance of fire (“resistance”)(Jack, Ponderosa, Longleaf pine) • Thick bark • Self pruning • Deep root system

9. Species with 1.0 to 1.3cm bark thickness are resistant to fire. • Intense-fast moving fire • Plant protected • Intense-slow moving fire • Greater susceptibility to damage or mortality • Mature > young Thick bark of Ponderosa Pine

10. Fire tolerance of seedlings Longleaf pine - “grass stage” • Prolonged grass stage • Store large amounts of carbohydrates in roots • Thick, moist foliage cover protects terminal bud • Plant height grow fast after fire - terminal bud lift up before the next fire

11. Vegetative Regeneration (sprouting) • Part of an individual plant survives and fire stimulates resprouting • Allocation of resources in different ways • Both aboveground and belowground possible

12. Root collar sprouts • Dormant buds insulated from fire by bark and store energy required for sprouting

13. Lignotubers • Swellings at the base/root collar of shoots of shrub species • Fire stimulates sprouting Eucalyptus shrubs in Australia

14. Root suckering from adventitious buds • Adventitious buds: Develop from places other than the shoot apical meristem (stems, roots, leaves) • Root suckers are stimulated by fire in some species

15. Basal Meristems • Grasses have meristems at leaf base (protected from heat and damage) • High root-to-shoot ratio • Some grasses (e.g., Pandanus) also receives protection from leaf sheaths

16. Above-ground Resprouting • Some plants re-sprout from dormant epicormic buds beneath the bark (often deep) – stimulated by fire • The ability to survive and re-sprout depends on: • Tree height • Scorch and char heights • Tree species • Tree age • Fire severity • Examples: • Oaks • Eucalyptus

17. Mechanisms of Post-Fire Regeneration • Seed Survival (protection from fire) • Stored in the soil (“soil seed bank”) • Enclosure within fruits in the canopy • Seed dispersal • Adaptation to post-fire conditions

18. 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

19. Seed Protection: soil seed bank survives fire Tradeoff between survival of seeds from fire and germination of seeds in different depths (Whelan 1995)

20. Ground orchids start to bloom after rains following a fire (buried seed)

21. Scarification of seed coat • Heat from fire scarifies (breaks open) the hard seed coat and stimulates rapid germination Lupine

22. Seed dispersal • Dessication: Many seeds retained in fruits and heat of the fire dessicate the fruit and causes to release seeds. (Eg: Sun Flower Seeds) • Small seeds dispersed far distances by wind. • Dispersal by birds, mammals

23. Dormant cells in seeds in dehydrated state tolerate high temperatures • Sun flower seeds – Tolerates 70-90°C for 4 hours • Jack pine seeds– Tolerates 370°C for 15 Seconds

24. Adaptation to post-fire conditions • How might post-fire conditions favor plant establishment and growth? • Some seeds germinate best on scarified (bare) soils • Lodgepole pine • Some plants only grow well under conditions of high resource availability and low competition • some early successional colonizing species

25. Community Response • Mortality and response of plants to fire varies among plant species and plants of different age/developmental stage • Fire can shift plant community structure and composition • Influences successional processes • Example: Tallgrass prairie • Spring burn has differential influence on cool and warm season grasses

26. Studying Fire Effects • Burned vs. Unburned • Pre vs. post-burn • What assumptions are being made?

27. 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

28. Scottish heathland example

29. TTYP FIRE FIRE

30. Fire Regimes and Vegetation • Fire frequency • Season of fire • Severity • Duration • Extent of burning

31. Fire frequency Plant species may be eliminated from a site if fire occurs too often. (Determines the species composition) Short fire free intervals (<20 years) Intermediate fire free intervals (20-75 years) Long fire free intervals (>100 years)

32. Short fire free intervals (<20 years) Low-severity surface fires will occur Fire tolerant herbaceous species will dominate. Species composition will not change. Intermediate fire free intervals (20-75 years) Fuel buildups and continuous in distribution. High-severity fire results. Greater changes in plant composition. Long fire free intervals (>100 years) High-severity fire results Postfire & prefire vegetation are markedly different

33. Season of fire Affects plant survival and flowering. Eg: Spring fire on rangelands in the Western United States damage to annual grasses and favors to dormant perennials.

34. Fire Severity • Low severity fire damage to fire sensitive species. • Moderate or high severity fire: stimulate germination, renew plant community, change in species composition.

35. Duration of fire • Long durationof fire increase the mortality of plants. • Causes to produce high temperatures in below ground. • Large extent of fire • Limit seed dispersal from neighboring systems. • Prone to eliminate more species. • Results more dry and warm conditions.