Forest resiliency

1. Improving Resiliency of
Forests in Arkansas
Andrew Nelson, Assistant Professor
Arkansas Forest Resources Center, UA Division of
Agriculture
September 24, 2014

2. What is Forest Resiliency?
Capacity of a forest to respond to a
disturbance, by resisting damage and
recovering quickly

3. Is this stand
resilient?
Slow growth
Tree mortality

4. What about
this stand?

5. Which
stand is
more
resilient to
wildfire?

6. Resilient Vs.
Non-Resilient
Forests
Rist and Moen. 2013. FEM 310: 416-427
Resilient Forest
Non-Resilient Forest
Disturbance
Disturbance
Resilient forests often
rebound quicker
following disturbance
and have greater
overall production
than non-resilient
forests

7. Some recent events have tested
the resiliency of Arkansas forests
Source: Delta Farm Press Source: Arkansas Democrat-Gazette

8. Ozark red oak decline was another
event that tested forest resiliency

9. General strategies for enhancing
forest resilience
1. Increase composition of species tolerant of a
particular disturbance/stress
2. Reduce and maintain lower tree density
3. Increase average tree size and vigor
4. Plant genotypes adapted to conditions
5. Re-introduce disturbances that mimic natural
processes

10. Examples of improving resiliency in
Arkansas
• Mitigating losses of pine growth and yield from
drought and wildfire
• Conversion of bottomland sites from pine to
hardwood
• Restoring Ozark forests with prescribed burning
and overstory disturbance

11. Consequences of drought for pine
production
• Drought = lower growth & greater mortality
• RESULT is lower stand yields and possibly longer
rotations
• Loss of money

12. Drought effects on pine seedlings
Slash pine seedling mortality during drought
Credit: David Moorhead, UGA, bugwood.org

13. Drought effects on mature trees
Pine shedding foliage in
response to drought
Credit: Robert Anderson, USFS-FS, bugwood.org
• Water is necessary for trees to
maintain physiological
functioning
• Required for
photosynthesis
• Required for wood
production (cell wall
expansion)
• Less foliage = less growth

14. Extended droughts were common in
Arkansas throughout the 20th century
Source: http://www.ncdc.noaa.gov/cag/time-series
61% of the last
119 years in SE
Arkansas were
in mild to
severe
drought
Dust
Bowl

15. Recent droughts have been severe

16. All trees are susceptible to drought
• Varies by age, site conditions, density, genetics
• Smaller trees (seedlings and saplings) most likely to
experience mortality from lack of water
• Larger trees are more likely to exhibit declines in
growth

17. Effects of precipitation on pine
basal area growth
Basal area growth in response to annual precipitation
Amateis et al. 2013. SRS-GTR-175. pp.193-196
Reducing
precipitation by
half can result
in 33% declines
in basal area
growth for a
given site index
and latitude
18
16
14
12
10
8
6
4
2
0
34.5 37 39.5 42 44.5 47 49.5 52 54.5 57 59.5 62 64.5 67 69.5 72
Basal area growth (ft2/ac/yr)
Annual precipitation (in)
59.2 ft2/ac
74.2 ft2/ac
89.2 ft2/ac

18. Insect attacks increase with
drought stress
• Bark beetles tend to
attack stressed trees
• Insects can then
spread to non-stressed
trees causing an
outbreak
Ips engraver beetle outbreak in a loblolly pine
stand in Texas during a drought
Credit: Ronald Billings, TX Forest Service, Bugwood.org

19. Strategies for enhancing pine
resiliency to drought
• Site preparation
• Early competition control
• Selecting appropriate planting stock
• Density management
• Mid-rotation hardwood management

20. Site preparation to enhance
resiliency
Fracturing soil and
bedding result is
more water near
tree roots
Poorly-drained flatwood site in FL
Burger & Pritchett. 1988. For Sci 34: 77-87
Compared to no
site prep

21. Early competition control
• Seedling roots are primarily near the soil surface
• More non-pine vegetation increases competition for
water, increasing chance of mortality
• Removal of non-pine vegetation allows pine seedlings
to capture more water
Pine seedlings
Credit: James Miller, US Forest Service, Bugwood.org

22. Selecting appropriate planting stock
• Container vs. bare-root
seedlings
• Container seedlings
experience less initial
planting shock after placed
in the ground than bare-root
• Planting seedlings selected
for drought tolerance
• Plant genotypes from
appropriate geographical
provinces
Genetically similar loblolly pine
populations
Neale & Kremer. 2011. Nature Genetics. 12:111-122

23. Density management
• Lower density
equals less
competition for
water
• Options include
planting at lower
densities and
thinning to reduce
competition
1st commercial
thin as row thin
2nd commercial
thin to target
basal area

24. Mid-rotation vegetation control
• Pines are already competing with each other for
water. When other vegetation is present,
competition may be even greater
• Options may include herbicide or manual control
timed with a commercial thinning operations

25. Drought can also increase wildfire
frequency and severity
Young pine stand where almost all tree
died from wildfire

26. The number of wildfires & acres
burned are related to summer
drought
2005 2006 2007 2008 2009 2010 2011 2012 2013
Year
Source: National Interagency Fire Center
Number of Fires
3000
2500
2000
1500
1000
500
0
Thousand Acre Burned
80
70
60
50
40
30
20
10
0
Number of Fires
Acres Burned
Source: http://www.ncdc.noaa.gov/cag/time-series

27. Reasons drought is related to
wildfire risk
• Low precipitation creates more flammable fuels on
the forest floor: drier fuels can accelerate spread
• Drought causes trees to have less water in the
foliage, increasing flammability & greater
probability of spread from crown to crown

28. Older stands tend to be more
resistant to wildfire

29. Thinning may reduce loss from
wildfire
Crown bases were scorched, but there is
enough living foliage that the trees may not
die

30. Knowledge gaps for enhancing
pine resiliency to drought
• What are the appropriate planting densities,
genotypes, thinning intensities, and thinning
schedules to maintain pine resiliency during
drought?
• Lower density stands will be more resilient, but may also
produce less wood throughout the rotation
• How many years of repeated droughts (and at what
intensity) can forests experience before appreciable
declines in resiliency (losses in growth and yield)?

31. Planting pine on hardwood sites
Loblolly pine
Bottomland Hardwoods

32. Planting pine on hardwood sites
Loblolly pine
Mississippi River

33. Issues with planting pine on
hardwood sites
• Soil conditions are not ideal for pine
• Not matching the species to the site results in
lower pine growth than on pine sites (Coastal Plain)
• Lower yields at end or the rotation and/or longer
rotation
• Longer time to crown closure requiring greater initial
initial vegetation control
• Stressed trees are more susceptible to insects and
pathogens

34. Deodor weevil can kill pine trees
on bottomland hardwood sites

35. Management options for pine stands
on bottomland hardwood sites
• Convert stands back to species better suited to the
site
• Maintain low densities to decrease mortality from
deodor weevil

36. Restoring Ozark forests with
burning and overstory disturbance
• Ozark forest frequently burned until fire
suppression programs began in the 1920s
• Fire suppression combined with increased timber
extraction altered species composition and forest
age structure
• Many forests are now overstocked and even-aged,
with high densities of shade tolerant, fire intolerant
species

37. Re-introducing fire back into Ozark
forests
• Oak species in these stands are often low vigor and
susceptible to drought and insect/pathogen attack

38. Prescribed burning can be used to
reduce density of fire intolerant species
Credit: Kyle Cunningham, UAEX

39. Research needs for upland
hardwood restoration
• Long-term forest changes that have occurred in the
absence of fire and overstory disturbance
• Effects of repeated prescribed burning in
unharvested stands across a range of site quality
• Combined effects of prescribed burning frequency
and overstory disturbance intensity on forests

40. Sylamore Ranger District Indiana
bat habitat restoration project
• 67,151 acre project on the Sylamore RD in an area with
numerous threatened and endangered (T&E) bat species
• Approved in 2013, treatment implementation began in 2014
• Goal is to enhance T&E species habitat with combinations of
prescribed burning and overstory disturbance
• Treatments will also enhance forest health and resiliency by
reducing stem densities and enhancing tree vigor

41. Preliminary project on the
Sylamore Experimental Forest
• Established in 1934, shortly
after fire suppression
• Prescribed burned since
1977
• No intentional overstory
disturbance
• Project will examine long-term
changes in forest
vegetation following
reintroduction of fire

42. Prescribed burning before
overstory disturbance
Credit: Chris Evans, IL Wildlife Action Plan, Bugwood.org
• Reducing density of fire
intolerant stems below
the main canopy can
prepare stands to
increase chance of oak-hickory-
pine regeneration
following overstory
disturbance

43. Summary
• Numerous examples show that forest resiliency to
disturbances is important in Arkansas for
maintaining and increasing forest productivity and
health
• Silviculture plays a major role for enhancing forest
resiliency by modifying practices to reduce losses
from distrubances. Mainly focusing on improving
forest vigor.