# Presentation: 405264

## Impacts of Changing Land Use, Climate, and Atmospheric Chemistry on Forests of the Chesapeake Bay Watershed

- Richard Birdsey, Yude Pan, John Hom, Kevin McCullough
- USDA Forest Service
- Eric Sprague
- The Conservation Fund

## Motivation for Assessment

- Chesapeake Bay Watershed is protected by 24 million acres of forests that:
- Absorb pollutants
- Sequester atmospheric CO2
- Maintain air and water quality
- Forest health and services are threatened by:
- Land use change
- Climate change
- Increasing exposure to ground-level ozone and nitrogen deposition

## Science Questions

- To what extent are forests threatened by air pollution and land use change?
- What is the current and future capacity of forests to sequester atmospheric CO2?
- What are current nitrogen (N) loss and retention rates under chronic N deposition?
- Will forest continue to retain N in the future, and which forests will be more sensitive to N loss?

## Overview of Presentation

- Analysis of Chesapeake Bay Watershed  land cover and forest trends
- Climate trends and air pollution
- Nitrogen deposition, retention by forests, and future scenarios
- Complications of multiple stressors
- Support for decision making

## Land cover     of the Chesapeake Bay Watershed

| Forest | 61 |
| --- | --- |
| Agriculture | 29 |
| Wetland | 3 |
| Developed | 7 |

**Percent Cover**

## Slide 6

## Forest Types     of the Chesapeake Bay Watershed

**Forest Types     of the Chesapeake Bay Watershed**

| Oak-hickory | 53 |
| --- | --- |
| Maple-beech-birch | 23 |
| Loblolly pine | 9 |
| Other types | 15 |

**Percent of total 24 million acres**

## Forest Dynamics

| Forest Type | Area             (1000 ac) | Change from 1990-2000 |
| --- | --- | --- |
| Oak-hickory | 12,461 | -34 |
| Maple-beech-birch | 5,371 | +779 |
| Loblolly pine | 2,081 | -180 |
| Other types | 3,725 | -553 |
| Total | 23,574 | +13 |

- Area by age class

## Forest Carbon Budget, 1990-2000 FORCARB-2 estimators (Heath et al.)

- Chesapeake Bay Watershed forests gained 17 million metric tons C per year
- Forests are highly productive – gains represent 9% of the total for all U.S. forests on just 3% of the land area
- Oak-hickory and maple-beech-birch forests gained the most C
- Land-use change caused loss of 2 million metric tons C per year

## Climate and CO2 Trends in the Mid-Atlantic Region

**Average annual temperature +1****o****F**

**Average annual precipitation +10%**

**From Mid-Atlantic Regional Assessment**

## Nitrogen Deposition and Tropospheric Ozone Exposure, 1990-1999

**Nitrogen Deposition and Tropospheric Ozone Exposure, 1990-1999**

- SUM60 Ozone Exposure During the Growing Season

## Slide 12

## Slide 13

## PnET-C/N Parameters and Validation Data Sets

- USFS Forest Inventory and Analysis (FIA)
- USGS National Aquatic and Wetlands Assessment (NAWQA)
- Intensive ecosystem observations (e.g. LTER)
- Results of experiments (e.g. FACE)

## Constant

- Increasing

## Slide 16

## Retention of N Deposition by Forests Through 2050

**Min: 18**
**Mean: 88**
**Max: 98**

**Min: 0**
**Mean: 84**
**Max: 98**

**Min: 1**
**Mean: 77**
**Max: 98**

## Retention of N Deposition by Forests Through 2100

**Min: 18**
**Mean: 88**
**Max: 98**

**Min: 0**
**Mean: 47**
**Max: 98**

**Min: 0**
**Mean: 28**
**Max: 98**

## N-saturation Effect: Non-linear Increase in N loss

**                                   ****(kg N /ha/yr)      (kg N /ha/yr)   (Mg N /yr)       (vs. 2000)**
**2000 N  dep.                   10.04                 1.23                11,617                   ****−**
**2050 constant                10.04                 1.56                 14,791              + 27%**
**2100 constant                10.04                 5.30                 50,087            + 331%**
**2050 increasing             15.77                 3.62                 34,250            + 195%**
**2100 Increasing             21.51               15.38               145,345          + 1151%**

**N-saturation Effect: Non-linear Increase in N loss**

## Effects of Changing Land Use on N Export

- Current forests export 11,500 Mg/yr
- Loss of 10% of forest cover increases N export by 4,000 Mg/yr (35% increase)
- Gain of 10% forest cover decreases N export by 3,900 Mg/yr (34% decrease)

## The current N retention rate is 88% 
Constant N deposition for 50 years would lower retention to 84% and increase total N export 27%
Constant N deposition for 100 years would lower retention to 47% and increase total N export by 330%
Increasing N deposition for 50 years would lower retention to 77% and increase total N export by 195%  
Increasing N deposition for 100 years would lower retention to 28% and increase total N export by 1151%  
Continued N deposition will “saturate” forests causing an increasing inability to retain N
Increasing N export from forests will dramatically increase the load on N in Chesapeake Bay and it estuaries  

**Constant N deposition for 50 years would lower retention to ****84%**** and increase total N export 27%**
**Constant N deposition for 100 years would lower retention to ****47%**** and increase total N export by 330%**
**Increasing N deposition for 50 years would lower retention to ****77%**** and increase total N export by 195% **
**Increasing N deposition for 100 years would lower retention to ****28%**** and increase total N export by 1151% **
**Continued N deposition will “saturate” forests causing an increasing inability to retain N**
**Increasing N export from forests will dramatically increase the load on N in Chesapeake Bay and it estuaries  **

**Conclusions about N Deposition and Retention by Forests**

## Run 1: control

**Factorial Model Experiments**

- Run 2: scenario
- Run 3: scenario
- Run 4: scenario
- Run 5: scenario
- Run 6: Scenario
- Run 7: Scenario

**N ****dep.**

**Running years:**
**1800-2000**

**  ****Clm**

**Mean climate**

**Historical climate**

**Complications Regarding Effects of Multiple Factors**

## Effects of Interactions of Climate Change and Air Pollution on Forest Productivity

## The Combined Effects of Increasing CO2, Tropospheric Ozone, and N deposition on Forest Productivity = +20% NPP 

- The Combined Effects of Increasing CO2, Tropospheric Ozone, and N deposition on Forest Productivity = +20% NPP

- The N saturation effect is significantly reduced with increasing CO2

## Comments on Science Questions and Information Needs

- Scientists need to hear what questions are important from the decisionmakers
- Attributing responses of ecosystems to single factors is complicated by interactions with multiple factors
- It is a great challenge to convey the complexity of ecosystem responses in ways that highlight options for decisionmakers
- Maps
- Graphs
- Focused summary statements
- Simulation tools

## Effective Communication about Complex Issues

- Instill confidence that information is based on sound science
- Increasing use of integrated data-model approaches (results are realistic)
- Good old-fashioned “resource analysis” is essential

## Barriers to Using Climate Information in Decisionmaking

- Our ability to influence climate is rather limited, so there is a tendency to focus on things we can control
- Climate is just one of many factors affecting ecosystems
- The role of climate could be integrated into analyses as....
- ...a source of uncertainty
- ...an issue of risk management

## How to Maintain Dialogue with Decision Makers

- Seek opportunities to use scientific models as decision-support tools in assessments
- Work with stakeholders to develop decision-support tools for more general applications
- Make available summary data sets, model parameters, and functional relationships