the deep roots of the oak regeneration problem
TRANSCRIPT
The Future of Oak Forests
The Deep Roots of the Oak Regeneration Problem
Charles CanhamSenior Scientist
Cary Institute of Ecosystem StudiesMillbrook, NY
Marc Abrams, Bioscience, 1998
Greg Nowacki and Marc Abrams, BioScience 2008
Marc Abrams, BioScience 2003
The roots of the problem…
The issue locally… Changes in oak abundance since pre-settlement times
Is fire suppression responsible for a reduction in the regional dominance of oak species in many parts of the eastern US?
Has the reduction in the abundance of oaks over the past 200 years fundamentally altered the flammability of these forests?
Is there a future for oak in our forests?
http://oaksavannas.org/fire-fuel.html
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Oaks Hickories Hemlock Pine Maples
Presettlement Forests
Current Forests
Perc
ent
Tree Species
composition of the Cary Institute forests
? Have the forests “recovered”?(and, to what?)
Land clearing, cultivation, and abandonment: Conversion of oak forests to forests dominated by maples, birches, and pines
The loss of oak from the best soils
Where are our oaks today?(on hilltops and in old pastures)
Essentially none of the pre-settlement oak forest regenerated by fire is present today
Oaks today are largely limited to lands with two very different land-use histories:
Highlands and hilltops that were heavily and repeatedly cut for timber and firewood
Pastures, in which scattered oaks were left for shade and acorns
Conditions under which they regenerated 50 - 150 years ago:
Heavy cutting followed by sprouting
Absence of deer
Quercus - The Oak genus worldwide
Distributed in north temperate regions worldwide (North America, Europe, Asia)
Evolved in dry, savanna-like conditions, 40-60 million years ago
Center of evolution was in what is now the Southwest US and Mexico
~ 350 species of true “oaks” (subgenus Euquercus) worldwide
North America has the highest diversity of true oaks
Quercus is the largest genus of trees native to the US
Oak species make up 9 of the 50 most common tree species in eastern U.S. (more than any other genus)
Our most important oaks locally…
Scarlet oakQuercus coccinea
Northern red oakQuercus rubra
Black oakQuercus velutina
White oakQuercus alba
Chestnut oakQuercus prinus
THE “RED OAK” GROUP(Erythrobalanus)
THE “WHITE OAK” GROUP(Lepidobalanus)
Photos by Jerry Jenkins,Northern Forest Atlas Project
Relative abundance of northern red oak and white oak in US Forest Service Forest Inventory plots
To give you a sense of their importance…
Salient features of the ecology of our oaks
The species vary, but all are generally not very shade tolerantRed oak is the most shade tolerant, but even those seedlings have high
mortality when they receive < 10% of full sunlight
Canopy oaks are fierce competitors when dominant, but highly sensitive to suppression when overtopped
They sprout vigorously from cut stumps, but sprout vigor is reported to decline if the trees are very large when cut
A good online source:
Silvics of North America (USDA Agriculture Handbook 654)http://www.na.fs.fed.us/spfo/pubs/silvics_manual/table_of_contents.htm
Reproduction in oaks
White Oak Group
Flowers every few years in spring
Acorns mature and drop that fall
Germinate almost immediately after seedfall
Red Oak Group
Flowers every few years in spring
Acorns mature and drop in fall of following year
Stay dormant overwinter then germinate in spring
Current threats to oak abundance in the region
Air pollution
Pests and Pathogens
Climate change
Current harvest practices
Deer
Air Pollution... Ozone exposure
CO2 fertilization
Acid deposition and soil calcium depletion
Nitrogen deposition
Thomas, R. Q., C. D. Canham, K. C. Weathers, and C. L. Goodale. 2010. Increased tree carbon storage in response to nitrogen deposition in the US. Nature Geoscience 3:13-17.
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Nitrogen deposition generally increases forest productivity region wide,
But species other than oaks tend to benefit the most…
Pests and Pathogens
Arguably the most pervasive human impacts* on eastern US forests over the past century have been from the introduction of new pests and pathogens…
Chestnut blight
Dutch elm disease
Gypsy moth
Beech bark disease
Hemlock wooly adelgid
Emerald ash borer
Asian longhorned beetle
…? (including changes inoutbreaks of native pestsand pathogens)
Heavily diseased and resistant beech trees13
*on distribution and abundance of specific tree species
Climate change…
Since oaks are even more abundant in warmer climates, will they benefit from climate change?
Over time, will new oak species migrate northward?
Well, not much, and not anytime soon…
The Cary Computer Cluster(used to analyze the data from thousands of USFS forest inventory plots, and simulate future forests)
Predicted changes in distribution and abundance: Northern red oak
(under current logging regimes, with and without climate change)
Predicted changes in distribution and abundance: White oak
(under current logging regimes, with and without climate change)
Similar or even more precipitous declines predicted for black oak and chestnut oak
Current harvest practices in northeastern forests
Clearcutting has been replaced by selective logging as the dominant harvest regime in northeastern forests
(except in a few forest types)
Percent of biomass harvested
Perc
ent
of
area
logg
ed
Impacts of over-abundant white-tailed deer
• It seems clear that hunting can solve this problem, at least on larger landholdings
• it has worked remarkably well for us in the Cary Institute forests
• But the hunting population is getting smaller and older – can we reverse this?
The future for oaks in the northeast… The conditions that created the pre-settlement oak forests and existing post-settlement oak forests no longer exist
Four factors currently work against oaks
The absence of fire
The increase in more shade tolerant tree species, particularly maples
The abundance of deer,
Light selective harvests
In the absence of deliberate management, it seems inevitable that most of the region’s species of oak will continue to gradually decline in abundance.