# Presentation: 523334

## Modern and Future Forest Ecosystems

- Richard J. Norby
- Environmental Sciences Division
- Oak Ridge National Laboratory

- Snowbird, Utah
- December 8, 2001

## Trees that are planted today will be growing in a higher CO2 concentration tomorrow

**Trees that are planted today will be growing in a higher CO****2**** concentration tomorrow**

## Trees respond to atmospheric [CO2]

**The rate of photosynthesis in tree leaves increases with increasing [CO****2****], as with any C****3**** plant**
**Myriad secondary and tertiary effects follow**

- Trees respond to atmospheric [CO2]

## Physiological adjustments, biogeochemical feedbacks, ecological interactions, and the influence of other environmental factors will alter the primary response to elevated [CO2]

**Net effect on forests is uncertain**
**Implications of any effect are unclear**
**Detection of effects is difficult**

- Aber *et al*. 2001

**Physiological adjustments, biogeochemical feedbacks, ecological interactions, and the influence of other environmental factors will alter the primary response to elevated [CO****2****]**

##  - Paul Kramer, 1981

* **- ***Paul Kramer, 1981**

## - Boyd Strain & Fakhri Bazzaz, 1983

**- Boyd Strain & Fakhri Bazzaz, 1983**

## Forestry Issues with Rising Atmospheric CO2

**Forestry Issues with Rising Atmospheric CO****2**

**Global Carbon Cycle**
**flux   storage**

- Net primary
-  productivity

**Vegetation Response**
**“****CO****2 ****fertilization**”

- Forest composition
- and biomass

- Deforestation,
- reforestation

**Climatic Change**
**“****greenhouse effect**”

## Has increasing [CO2] influenced today’s forests?

**Has increasing [CO****2****] influenced today’s forests?**

***Evidence***
**Tree-ring chronologies**
**Forest inventory**
**13****C analysis**
**Stomatal density**

## Tree-Ring Evidence for Past Effects of [CO2]

**LaMarche *****et al*****. (1984) claimed that increased growth of subalpine conifers since 1960 could be attributed to increasing [CO****2****]. **

**Graumlich *****et al*****. (1989) attributed recent increases in tree growth in western Washington to increased temperature – CO****2**** effects were unimportant**

**Jacoby and D’Arrigo (1997) concluded “The present tree-ring evidence for a possible CO****2**** fertilization effect under natural environmental conditions appears to be very limited.” *****PNAS***** 94:8350**

*Science* 225:1019 (1984)

*Ecology* 70:405 (1989)

**Tree-Ring Evidence for Past Effects of [CO****2****]**

## Inventory analysis suggests limited influence of CO2 on C accumulation in eastern forests

- Discrepancies are assumed to be due to changes in growth rates over time.

**Inventory analysis suggests limited influence of CO****2**** on C accumulation in eastern forests**

- Caspersen et al. (2000) *Science* 290:1148

- The fraction of regional ANEP due to growth enhancement is no more than 7.0% (average = 2.0 ± 4.4%)
- Growth enhancement is net effect of increased CO2, N deposition, ozone, etc.
- Forest regrowth is by far the dominant factor governing the rate of C accumulation

## Forests in a future atmosphere

- Forest physiology, productivity, and ecology in a future, CO2-enriched atmosphere can be addressed through:
-  direct observation
-  manipulative experiments
-  modeling

- The most important problems concern issues of scaling across time and space

## Tree-ring analysis at a CO2 spring 

- Tree-ring analysis at a CO2 spring

**Geothermic CO****2**** spring in Tuscany**

**Ring-width chronologies of *****Quercus ilex***** and *****Q. pubescens***** show no effect of [CO****2****]**

**Cumulative basal area was lower for *****Q. ilex***** in high CO****2**** and higher (ns) in *****Q. pubescens*****. Other species showed no effect at all.**

**Tognetti et al. (2000). *****New Phytologist***** 146: 59**

## The scale of experimental studies has been gradually increasing

- It is not possible to create a simulation of a future forest – rather, we rely on experimental systems

## Tree species respond to elevated CO2 like other plants

- higher photosynthesis  faster growth
*Result*: plants are bigger at the end of the experiment
- N concentration usually is lower
- stomatal conductance often is reduced
- no large changes in allocation

- Tree species respond to elevated CO2 like other plants

## Does Tree Growth Increase in High CO2?

- Dry matter increase is confounded by increasing leaf area and exponential growth
- These results do not predict the response of a forest, and they do not represent fundamental differences between species

**Does Tree Growth Increase in High CO****2****?**

## Does Tree Growth Increase in High CO2?

- Expressing annual growth per unit leaf area adjusts for exponential growth pattern
- Response is uniform across species and conditions: 29% increase at ~650 ppm CO2
- Growth per unit leaf area separates the functional response from the structural response
- This approach may allow for prediction after canopy closure, but it breaks down if allocation changes

## Can we predict the responses of the future forest from the responses of individual saplings?

- How can data from relatively short-term experiments be used to address the long-term responses of a forest?

*Can we predict the responses of the future forest from the responses of individual saplings?*

## Questions for new experiments at the forest stand scale

**Will maximum stand leaf area increase with increasing [CO****2****]?**
**Will growth per unit leaf area increase after canopy closure?**
**Will fine root turnover increase after standing crop not reaches a maximum?**
**Is growth downregulated through feedbacks from the N cycle?**
**Is stand water use predicted from effects on stomata?**

## Oak Ridge Experiment on CO2 Enrichment of Sweetgum

**Oak Ridge Experiment on**** CO****2**** Enrichment of Sweetgum**

**To understand how the eastern deciduous forest will be affected by CO****2**** enrichment of the atmosphere, and what are the feedbacks from the forest to the atmosphere. **
**This goal will be approached by measuring the integrated response of an intact forest ecosystem, with a focus on stand-level mechanisms.**

**Goal**

## 
Each plot is 25 m diameter (20 m diameter inside buffer) 
Full year of pre-treatment measurement in 1997
CO2 exposure (560 ppm) started spring, 1998
Exposure is 24 hours per day, April through October
Brookhaven exposure system

**Each plot is 25 m diameter (20 m diameter inside buffer) **
**Full year of pre-treatment measurement in 1997**
**CO****2**** exposure (560 ppm) started spring, 1998**
**Exposure is 24 hours per day, April through October**
**Brookhaven exposure system**

**CO****2**** Enrichment of a Deciduous Forest: The Oak Ridge Sweetgum Experiment**

***Liquidambar styraciflua***** plantation started in 1988**
**2 elevated, 3 control plots (2 with blowers)**

## Calculation of NPP

- <date/time>

**Calculation of NPP**

- Oak Ridge Experiment on CO2 Enrichment of Sweetgum

**Stem**
**Allometry : DM = f(BA, H, taper, density)**

**Fine root**
**Minirhizotrons and in-growth cores**

**Coarse root**
**Allometry: DM = f(BA)**

**Understory**
**Harvest**

**Leaf**
**Litter traps**

## Net Primary Productivity

- <date/time>

**Net Primary Productivity**

**CO****2**** effect on NPP was:                27% in 1998,   17% in 1999, 19% in 2000.**
**GPP was 27% higher in elevated CO****2****.**
**Allocation of the extra C changed from stem to fine root.**

- Oak Ridge Experiment on CO2 Enrichment of Sweetgum

## Aboveground Woody Increment

- <date/time>

**Aboveground Woody Increment**

**No difference in growth prior to treatment (1997).**
**CO****2**** significantly increased growth in 1st year of treatment (35%), but not in 2nd (15%) or 3****rd**** (7%).**
**The CO****2**** effect on stem growth also has disappeared in the Duke prototype FACE ring, but it has been sustained for 5 years in the fully replicated study.**

- Oak Ridge Experiment on CO2 Enrichment of Sweetgum

## Fine Root Productivity

- <date/time>

**Fine Root Productivity**

**Delay in fine root response may be related to accumulation of CHO in coarse roots.**
**Fine root C turns over faster than wood C through soil processes.**
**Analyze soil heterotrophic respiration:**
**	****	****- ****integrate CO****2**** efflux**
**	****	****- subtract root respiration**
**	****	****- add litter decomposition**

- Oak Ridge Experiment on CO2 Enrichment of Sweetgum

## Net Ecosystem Productivity

- <date/time>

**Net Ecosystem Productivity**

**NEP was positive each year.**
**CO****2**** effect on heterotrophic respiration was less than effect on NPP. **

- Oak Ridge Experiment on CO2 Enrichment of Sweetgum

## Dynamics of Carbon Storage

**Short-term C sequestration (NEP) was enhanced by CO****2**** enrichment**
**With an increasing fraction of the additional C storage allocated to short-term pools rather than to wood, the gains are likely to be short-lived**

**Dynamics of Carbon Storage**

## Interactions between CO2 and Water

**CO****2**** effects on leaf-level transpiration are mitigated as the scale increases to a whole canopy, stand, and region**

**Elevated CO****2**** often reduces stomatal conductance and leaf-level transpiration and increases water-use efficiency**

**Interactions between CO****2**** and Water**

## Interactions between CO2 and Warming

**Effects are non-linear, time-dependent, and highly dependent on initial conditions**
**Warming can stimulate productivity through increased photosynthesis and longer growing season**
**Warming can decrease productivity through increased stress**
**Elevated CO****2**** is likely to ameliorate negative effects of warming**

**Interactions between CO****2**** and Warming**

## CO2 x temperature interactions in maple

**CO****2**** x temperature interactions in maple**

**Red maple and sugar maples leafed out earlier in warmer chambers, increasing growth.**
**Photosynthesis was higher in elevated CO2 and warmer air, also increasing growth**
**However, a high temperature stress event caused a net negative effect on growth **
**Positive effects of CO****2**** and negative effects of temperature were additive**

## Prediction of NPP with Three Biogeochemical Models

**Predictions are for 2025-2034 (425 ppmv CO****2****)**
**All three models predict increased NPP with climate change and increased CO****2**** for both climate simulations**
**Increases are smaller (or become decreases) when CO****2**** is not included**
**Increases are less with the Canadian climate simulation**

**Prediction of NPP with Three Biogeochemical Models**

## Predicted Shift in Distribution with Climate Change

- Prasad, A. M. and L. R. Iverson. 1999-ongoing. A Climate Change Atlas for 80 Forest Tree Species of the Eastern United States [database]. **http://www.fs.fed.us/ne/delaware/atlas/index.html**, Northeastern Research Station, USDA Forest Service, Delaware, Ohio.

**Sugar maple**

**Red maple**

**Predicted Shift in Distribution with Climate Change**

## Dominant Forest Types

**1960-1990**

**2070-2100**

**Hadley**
**scenario**

**Canadian**
**scenario**

**Dominant Forest Types**

## Forest Productivity

**Forest Productivity**

## Conclusions

- Increasing atmospheric CO2 concentration has almost certainly affected modern forests and will affect forests in the future -- but the effects may be difficult to detect
- Net primary productivity of forests is likely to increase with increasing [CO2] -- but the additional carbon may not accumulate in the ecosystem
- Physiological and process understanding should be used to inform ecosystem models -- but many responses are moderated as the scale increases from a tree to a forest
- Regional scale analyses should not be taken as predictions of the future – but they can help to define the sensitivities and vulnerabilities of forests to future environmental conditions

## Slide 35