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The Deep Roots of the Oak Regeneration Problem

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Speaker: Charles Canham. Science and Management Forum at the Cary Institute of Ecosystem Studies. www.caryinstitute.org

Published in: Environment

The Deep Roots of the Oak Regeneration Problem

  1. 1. The Future of Oak Forests The Deep Roots of the Oak Regeneration Problem Charles Canham Senior Scientist Cary Institute of Ecosystem Studies Millbrook, NY
  2. 2. Marc Abrams, Bioscience, 1998 Greg Nowacki and Marc Abrams, BioScience 2008 Marc Abrams, BioScience 2003 The roots of the problem…
  3. 3. 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 0 10 20 30 40 50 60 70 80 Oaks Hickories Hemlock Pine Maples Presettlement Forests Current Forests Percent Tree Species composition of the Cary Institute forests
  4. 4. ? 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
  5. 5. 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
  6. 6. 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)
  7. 7. Our most important oaks locally… Scarlet oak Quercus coccinea Northern red oak Quercus rubra Black oak Quercus velutina White oak Quercus alba Chestnut oak Quercus prinus THE “RED OAK” GROUP (Erythrobalanus) THE “WHITE OAK” GROUP (Lepidobalanus) Photos by Jerry Jenkins, Northern Forest Atlas Project
  8. 8. Relative abundance of northern red oak and white oak in US Forest Service Forest Inventory plots To give you a sense of their importance…
  9. 9. Salient features of the ecology of our oaks  The species vary, but all are generally not very shade tolerant Red 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
  10. 10. 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
  11. 11. Current threats to oak abundance in the region  Air pollution  Pests and Pathogens  Climate change  Current harvest practices  Deer
  12. 12. 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. 12 Nitrogen deposition generally increases forest productivity region wide, But species other than oaks tend to benefit the most…
  13. 13. 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 in outbreaks of native pests and pathogens) Heavily diseased and resistant beech trees 13 *on distribution and abundance of specific tree species
  14. 14. 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)
  15. 15. Predicted changes in distribution and abundance: Northern red oak (under current logging regimes, with and without climate change)
  16. 16. 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
  17. 17. 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 Percentofarealogged
  18. 18. 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?
  19. 19. 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.

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