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.