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Forest resiliency
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Improving Resiliency of
Forests in Arkansas Andrew Nelson, Assistant Professor
Arkansas Forest Resources Center, UA Division of Agriculture
September 24, 2014
What is Forest Resiliency?
Capacity of a forest to respond to a disturbance, by resisting damage and
recovering quickly
Is this stand resilient?
Tree mortality
Slow growth
What about this stand?
Which stand is more
resilient to wildfire?
Resilient Vs. Non-Resilient
Forests
Rist and Moen. 2013. FEM 310: 416-427
Resilient ForestNon-Resilient Forest
Resilient Forest
Non-Resilient Forest
Dist
urba
nce
Dist
urba
nce
Resilient forests often rebound quicker
following disturbance and have greater
overall production than non-resilient
forests
Some recent events have tested the
resiliency of Arkansas forests
Source: Delta Farm Press Source: Arkansas Democrat-Gazette
Ozark red oak decline was another event that tested forest resiliency
General strategies for enhancing forest
resilience1. Increase composition of species tolerant of a
particular disturbance/stress2. Reduce and maintain lower tree density3. Increase average tree size and vigor4. Plant genotypes adapted to conditions5. Re-introduce disturbances that mimic natural
processes
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
Consequences of drought for pine
production
• Drought = lower growth & greater mortality
• RESULT is lower stand yields and possibly longer rotations
• Loss of money
Drought effects on pine seedlings
Slash pine seedling mortality during drought
Credit: David Moorhead, UGA, bugwood.org
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
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
Recent droughts have been severe
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
Effects of precipitation on pine basal area
growth
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
34.5 43.200000000000151.900000000000360.600000000000469.30000000000010
2
4
6
8
10
12
14
16
18Basal area growth in response to annual precipitation
59.2 ft2/ac
74.2 ft2/ac
89.2 ft2/ac
Annual precipitation (in)
Basa
l are
a gr
owth
(ft2/
ac/y
r)
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
Strategies for enhancing pine
resiliency to drought• Site preparation• Early competition control• Selecting appropriate planting stock• Density management• Mid-rotation hardwood management
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
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
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
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
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
Drought can also increase wildfire frequency and severity
Young pine stand where almost all tree died from wildfire
The number of wildfires & acres burned are related to summer
drought
Source: National Interagency Fire Center
Year
2005 2006 2007 2008 2009 2010 2011 2012 2013
Nu
mb
er o
f F
ires
0
500
1000
1500
2000
2500
3000
Th
ou
san
d A
cre
Bu
rned
0
10
20
30
40
50
60
70
80
Number of Fires
Acres Burned
Source: http://www.ncdc.noaa.gov/cag/time-series
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
Older stands tend to be more resistant to wildfire
Thinning may reduce loss from wildfire
Crown bases were scorched, but there is enough living foliage that the trees may not
die
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)?
Planting pine on hardwood sites
Loblolly pine
Bottomland Hardwoods
Planting pine on hardwood sites
Loblolly pine
Mississippi River
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
Deodor weevil can kill pine trees on bottomland hardwood sites
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
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
Re-introducing fire back into Ozark forests
• Oak species in these stands are often low vigor and susceptible to drought and insect/pathogen attack
Prescribed burning can be used to reduce density of fire intolerant
species
Credit: Kyle Cunningham, UAEX
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
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
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
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
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.