Fire in Eastern deciduous forests

Oct 14, 2010

Discussion of Abrams (1993)

Fire and the development of oak forests

“In eastern North America, oak distribution reflects a variety of ecological paths and disturbance conditions.”

In pairs:

• Read a section of the paper.

• Paraphrase the section in 3 to 5 sentences.

• Create a “take-home message” for the section (1 sentence).

• Be ready to answer questions on your section (from instructors and classmates).

Paraphrasing• What?

– Putting something in your own words.

• When?– During a talk/lecture.– While reading.

• Why?– For summary/quick reference.– To explain to someone.– To check for understanding.– To avoid plagiarism!!

6 Steps to Effective Paraphrasing• Reread the original passage until you understand its full

meaning.• Set the original aside, and write your paraphrase on a note

card.• Check your rendition with the original to make sure that your

version accurately expresses all the essential information in a new form.

• Use quotation marks to identify any unique term or phraseology you have borrowed exactly from the source.

• Record the source (including the page) on your note card so that you can credit it easily if you decide to incorporate the material into your paper.

(From: http://owl.english.purdue.edu/owl/resource/619/01/ )

1. Introduction• In presettlement times, the northeastern upland forests were dominated by

chestnut, hickory, pines, and by several species of oak.

• Since these times, many disturbances and alterations have occurred in the northeastern upland forests, including: both less and more prescribed fires in different areas, logging, and land clearing by European Americans, the presence of chestnut blight, and regular numbers of naturally caused fires.

• Of these occurrences, fire seem to have directly affected the increasing dominance of oak in the northeastern forests and the decline of other native tree species.

Take home message:

Even though many disturbances have dramatically changed the species composition of the eastern deciduous forests over time, fire has been the main factor determining the distribution and dominance of oak.

2. Paleoecology of E. oak forests• 18,000 years ago pine dominated in the Southeast portion of the United States and

spruce in the North and Central portions. • Over the next 8,000 years oaks took over the Eastern U.S. leaving the North with

mostly conifers and birch. • The paleoecological record show that the populations of oak increase as the

historical amounts of charcoal increases. • Warmer and drier weather patterns tend to increase fire frequency which promotes

the development of oaks in savanna-like landscapes. • Once the weather turned cooler and wetter the fire frequency slowed changing the

density of oaks to more forest-like conditions. • Due to climate change in the future, the importance and presence of oak may

change once again.

Take home message:

Occurrence of oak species is highly related to fire and climate.

3. Ecophysiological Features of Oak

• Upland oak species are well adapted to dry and fire-driven ecosystems, but do not grow well under shade.

• Oaks have the ability to grow on poor soils and can withstand drought due to their deep roots, xeromorphic leaves and physiological measures that allow them to maintain high levels of photosynthesis yet conserve water even in extremely dry conditions.

• Unlike the later successional maple species, oaks survive fire and thrive in sunny post-fire conditions because of their thick bark, regenerative sprouts, rot resistance, and adaptive seeds.

Take home message:

Fire, drought, and nutrient poor soils favor oaks over later successional tree species.

4. Oak expansion in the tallgrass prairie region

• Before European settlement tall grass prairies made up a large triangular area from central Texas to eastern North Dakota and western Indiana.

• During pre-settlement times oak savannas were very common in some areas within the tall grass prairie region, and fire was thought to maintain these ecosystems.

• When settlers came, fire was greatly suppressed because of activities like road construction, town formation, increased agriculture, cattle grazing and recommendations to limit prairie burning.

• Because the oak savanna already provided the seed source to develop a forest, the lack of disturbance prevented new regeneration and shrubs to be knocked down thus promoting the development of oak forests.

Take home message:

Fire suppression from European settlement caused a change from prairie to oak dominated vegetation communities.

5.Red Oak expansion in northern hardwood forests

• Northern hardwood forests include Minnesota thru new England, including most of New York and part of Pennsylvania.

• Before European settlement there was a very small oak component of the northen hardwood forest’s species make-up.

• Presettlement hemlock, which was the main hardwood species, burned infrequently with a return fire interval of 1200 years.

• It was after settlement that oak began to expand. This can be attributed to a series of post-settlement land use changes: burning and logging of hardwoods, abandoned farms leading to pitch pine and white pine invasion, and later logging released the understory promoting oak dominance.

Take home message:

The burning and logging of hemlock and pine forests led to red oak expansion.

6. Mixed-oak forests on the Mid-Atlantic region

• Historic frequent fires prior to colonial settlement were due to nativeAmerican activities and were mainly concentrated in the area which they occupied.

• The Mid-Atlantic region was dominated primarily by white oak and white pine.

• Oak dominance was maintained during post colonial times due to activities related to the industrial revolution activities such as fires, clear-cutting, charcoal production and other uses of timber.

• In pine and oak-pine sites of the Mid-Atlantic region, oak gained dominance due to the lack or low frequency of fire.

Take home message:

The overall fire regime of the region is based on human activities and the species diversity is directly linked to the fire regime.

7. Southeastern coastal plain and Piedmont forests

• The Piedmont and southeastern evergreen forests contain mostly longleaf pine, with bottom land containing beech, magnolia and oak, and these have a fire interval of around two to three years which succeed to oak hickory or mixed hardwood forests.

• There are also sand pine scrub forests with sand pine in the upper story and an understory of evergreen scrub oak with very infrequent fire intervals.

• Sand hill vegetation is mostly longleaf pine with a mix of slash pine and turkey oak with frequent low intensity fires due to humans.

• The original Piedmont forests were a mix of oak, pine, and hickory which had frequent burning intervals due to Native American management purposes.

Take home message:

Piedmont and southeastern evergreen forests have a mix of deciduous hard wood trees with a mix evergreen species, and depending on where you are at the fire intervals vary due to natural causes and humans.

8. Transition status of oak forests• In general, oaks are being replaced by other species such as maple,

elm and birch mostly because of poor recruitment.

• This may change in the future because of oaks have higher survival rate and growth over competitor species in the long term.

• The successional replacement of oaks is especially prominent in areas that have had a long term reduction in fire frequency and logging.

• Studies in the southern Piedmont region suggest that oak forests may be taken over primarily by red maple.

Take home message:

Due to succession, oak species are being displaced from their native territories. Factors influencing succession include: fire suppression, reduced recruitment, and logging.

9. Oak as a late successional forest type

• Research has established that oak is a transitional species, yet there has been little research providing evidence that oak can be a late succesional species.

• For example, studies done in dry (xeric) areas of the United States have shown no evidence that oak forests are succumbing to other species.

• On the other hand, studies done in humid (mesic) regions showed signs of replacement by several species of maple and birch.

 

Take home message: 

Oak species seem to be stable only in xeric sites as their replacement is much slower under dry conditions compared to mesic.