The Risk to Forest Health Posed by Biotech-Modified Trees Gary - - PowerPoint PPT Presentation

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The Risk to Forest Health Posed by Biotech-Modified Trees

Gary Lovett Forest Ecologist

“Forest Health”

A squishy but useful term

• If it is to be quantified, best understood like human health, as a

series of metrics that have a “normal” range*

• Metrics must be readily measurable to be useful

* With the understanding that some outliers can be outside the normal range but still “healthy”

Forest Ecosystem Health: Which Metrics?

Metric Measurable index Primary productivity ANPP (wood growth + litterfall) or GPP (eddy covariance CO2 flux) Nutrient acquisition Foliar chemistry Mortality Mortality rate or standing dead trees Nutrient retention Leaching (soil water) Water use/evapotranspiration (Precip. – streamflow) or eddy covariance H2O flux Resilience to moderate stress Mortality after stress event Physical structure, age structure and plant spp. composition Direct measurement through forest inventory/ canopy assessment Food web structure Monitoring of animal populations Soil quality Forest floor mass and chemistry; soil chemistry

Imported Forest Pests: Ecological Impacts

Introduced pests are the only threat that can reduce major canopy species to ecological insignificance in a matter of decades

American chestnut

Chestnut grove in North Carolina, ca. 1910

(Photo: Forest History Society, Durham, NC)

Death of trees Warming of streams may impact fish

Impacts of Forest Pests Reverberate Though the Ecosystem

Short- and long-term changes in carbon storage and nutrient losses Decline of some bird species Decline of old-growth forests, release of invasive plants Hemlock Woolly Adelgid

(Photo: Barry Baldigo)

Pest/pathogen Forest species composition Forest ecosystem characteristics: Structure, productivity, nutrient cycling, food web Feedbacks Host tree species: Damage or death Feedback Effects on embedded or adjacent ecosystems e.g., streams, lakes, wetlands

Forest Pests: Short- and Long-Term Effects

Lovett et al. Bioscience 2006 Long-term studies Chronosequence studies Modeling

Spe-CN: An ecosystem model with individual tree species

• Simulates pools of C & N,

monthly time step

• Species parameterized by

specific traits; e,g, foliar N, litter lignin, mycorrhizal type

• User sets scenarios:
• Rate & type of change

in species composition

• N deposition regime
• Harvest or

disturbance history

• Assess effects of tree

species change on forest productivity, C storage, N retention/leaching

Crowley et al. 2016 Forest Ecol & Mgmt Crowley & Lovett 2017 Can J For Res

Available nitrogen in soil Tree growth Litterfall Nitrate leaching to lakes and streams Carbon (C) Nitrogen (N) C & N Decomposition & Soil C & N storage Carbon dioxide

Climate change Invasive pests Nitrogen emissions

Precip. Temp. Nitrogen deposition Changes in tree species composition & abundance

Harvest regime

0.0 0.2 0.4 0.6 1800 2000 2200 2400

NO3- leaching (g N m-2 y-1) Year

Leaching - spp constant Leaching - spp transition 0.0 0.2 0.4 0.6 1800 2000 2200 2400

NO3- leaching (g N m-2 y-1) Year

Leaching - spp constant Leaching - spp transition 0.0 0.2 0.4 0.6 1800 2000 2200 2400

NO3- leaching (g N m-2 y-1) Year

t n

Loss of Catskills white ash due to emerald ash borer, with replacement by different species

Ash  Maple Ash  Oak Ash  Beech

Transition begins 80% harvest

Crowley & Lovett 2017 Can J For Res

NO3

• leaching (g N m-2 y-1)

1800 2000 2200 2400

Year

• Sp. constant
• Sp. change

Bugwood.org

Pest/pathogen Forest species composition Forest ecosystem characteristics: Structure, productivity, nutrient cycling, food web Feedbacks Host tree species: Damage or death Feedback Effects on embedded or adjacent ecosystems e.g., streams, lakes, wetlands

What About Biotech Modified Trees?

Lovett et al. Bioscience 2006

X

Forest species and trait composition

• Plant survival strategies involve trade-offs among traits.
• Plants generally have limited energy available, so they

can’t do everything well.

• If we modify plant traits for pest/disease resistance, we

need to understand what traits are reduced or lost.

• Some traits are important to ecosystem function, for example:
• Growth
• Drought resistance
• Seed production
• Traits can have indirect and unforeseen consequences
• “Nightmare scenarios” may be screened with field trials

Modifying Plant Traits

What do we know about plant traits?

• We have large global databases of plant traits
• Models often use known relationships between traits and functions
• But for many ecosystem functions, we lack knowledge about how they are

influenced by plant traits

• Plant performance and ecosystem function are often influenced by

combinations of traits

Word cloud from TRY global plant trait database https://www.try-db.org/TryWeb/Home.php

Conclusions and Research Needs

• Impacts of modified trees are likely to be minor compared to impacts of pests
• Forest ecosystem processes typically are resilient to mild to moderate stresses
• Long-term impacts of introduction of biotech-modified trees can be modeled

with trait-based models, particularly if we have

• better knowledge of trait influences on ecosystem function
• better knowledge of trait trade-offs in plants
• Field studies involving experimental plantings in otherwise “natural” forests

would be very instructive, and very helpful for modeling

• We should increase our forest health monitoring, especially in areas where

releases of modified trees are planned. Need to start prior to release to get a

• baseline. Key variables are understood and measurable.