# Presentation: 408856

## Consequences of Climate Change for Rangelands: Unexpected Consequences of More Extreme Rainfall Patterns

**Consequences of Climate Change for Rangelands: Unexpected Consequences of More Extreme Rainfall Patterns**
**Alan K. Knapp  **
*Colorado State University*** **
**Jana Heisler-White**
*University of Wyoming*
** ****Melinda D. Smith**
*Yale University*
** ****John M. Blair**
*Kansas State University*

## Why should we care about climate change? – The Grassland Ecologist’s Perspective

- We may be witnessing one of the most profound climatic changes in the Earth's history.
- Predictions for the 21st century show _warming_ of the troposphere especially in the Arctic, an _increase in precipitation extremes_, a _decrease in snow and ice cover_, and an _increase in sea level_.
- The danger facing society today is that anthropogenic global warming may be too fast to allow humans, and other species, to adapt to its detrimental impacts.

- T. Riley and J.A. Klein

**Grasslands, rangelands, steppe, tundra, savanna and shrub-grasslands cover ~ 40% of the Earth’s land surface**

## Ecosystem Services Grasslands Provide:

**Ecosystem Services Grasslands Provide:**
** ****Forage for domestic livestock**
** ****Habitat for native ungulates**
** ****Habitat for grassland plants/animals**
** ****Migratory birds – breeding/forage**
** ****Soil erosion control**
** ****Carbon sequestration**

## Setting the stage...

- Sala et al. 1988

**Grasslands (most) are water limited systems... **

- Rainfall vs. Production across the Central US

## The world is getting warmer.... (thermometer evidence)

- The world is getting warmer.... (thermometer evidence)

- Dave Theobald

- Plant evidence...

**Notes:**
TEXT FROM WEBSITE:
This map supersedes U.S. Department of Agriculture Miscellaneous Publication 814, "Plant Hardiness Zone Map," which was revised in 1965.  This 1990 version shows in detail the lowest temperatures that can be expected each year in the United States, Canada, and Mexico.  These temperatures are referred to as "average annual minimum temperatures" and are based on the lowest temperatures recorded for each of the years 1974 to 1986 in the United States and Canada and 1971 to 1984 in Mexico.  The map shows 10 different zones, each of which represents an area of winter hardiness for the plants of agriculture and our natural landscape.  It also introduces zone 11 to represent areas that have average annual minimum temperatures above 40 F (4.4 C) and that are therefore essentially frost free 
The average annual minimum temperature data were analyzed for Mexico, the United States, and Canada.  Of 14,500 stations that measured temperature during the period of interest, almost 8,000 could be identified by latitude and longitude and by a valid average annual minimum temperature (i.e., an average based on at least 10 years of data).  Data from only the latter stations were used in the map.  The data were archived by Servicio Meteorologico Nacional (Tucubaya, D.F., Mexico), the National Climatic Data Center (Asheville, NC), and Environment Canada - Canadian Climate Centre (Downsville, Ontario).  Temperature data were compiled and maps prepared under contract with the Meteorological Evaluation Services Co., Inc., 165 Broadway, Amityville, New York 11701.   The map is an Albers Equal Area Projection.  Standard parallels of 29.5 , and 45.5 , were used to generate the map of the three countries.  The map was computer generated by latitude and longitude.  Because of the large area involved, it is not possible to draw one map that is accurate for all of North America.  The part representing the United States has the least distortion.  The Agricultural Research Service proposes to periodically evaluate weather data and issue updated maps as necessary and appropriate. 

- Dave Theobald

## History provides few analogs for the type of climate change forecast...we are in uncharted waters...

- Overpeck et al. 2003

- Little Ice Age: 1600-1700’s - bitter winters, famine in Europe

- Younger Dryas – 1300 yr cold period (11,000 BP), then rapid warming

**IPCC predictions**

## Water, temperature (and CO2) are linked in grasslands and most ecosystems... 

**Water, temperature (and CO****2****) are linked in grasslands and most ecosystems... **

## Global Climate Model (GCM) predictions for changes in mean annual rainfall changes are inconsistent with each other in magnitude and sign...But more extreme weather as the atmosphere warms is consistently predicted. 

- Global Climate Model (GCM) predictions for changes in mean annual rainfall changes are inconsistent with each other in magnitude and sign...But more extreme weather as the atmosphere warms is consistently predicted.

## Slide 13

## Dust Bowl of 1930’s in US

**Dust Bowl of 1930’s in US**

**Drought in Senegal**

- More intense hurricanes and floods

## Abundant evidence that rainfall regimes are changing

**Abundant evidence that rainfall regimes are changing**

- Oklahoma

## To what extent will altered rainfall patterns  affect ecological processes in grasslands?

- 12 rainfall manipulation plots
- Collect, store, and reapply natural rainfall on intact grassland plots

- The Rainfall Manipulation Plot (RaMP) Experiment

- Address the impact of changes in ***size and***** *****timing**** *of growing season rainfall

## Experimental manipulation:  50% longer 

- inter-rainfall periods, larger individual rain events

_**No**_** change in total precipitation quantity**

## Key driver of responses:  Soil moisture dynamics

- “typical” seasonal pattern
- Altered ppt timing:
- repeated deficits
- more extreme wetting and drying cycles

**Average soil water content in top 30 cm:**
- - reduced by 12%

**Variability in soil moisture:**
- - increased by 27%

## All rainfall treatments

## What about the Shortgrass steppe – & semi-arid and arid grasslands?

**What about the Shortgrass steppe – & semi-arid and arid grasslands?**

## Frequent small events (10 day intervals, 15 mm events)

- Infrequent big events (30 day intervals, 47 mm events)

- All received “average” MAP amounts

**2005 - Shortgrass steppe**

## (9 events)

**- Heisler et al. 2008**

## Regional perspective

- Ojima and Lackett 2002

**Precipitation**
**gradient**

_**Regional perspective**_

**Notes:**
Grassland account for nearly 40% of the US land mass, and are highly influenced by precipiation and temperature variability in space and time.

The Central Plains are characterized by the familiar west-to-east transition from shortgrass to tallgrass prairie

There is a strong west to east gradient in not only composition but productivity, corresponding to the west to east gradient in annual precipitation.

There is also a well defined north to south mean annual temperature gradient, associated with a southward increase in the proportion of C4 species.

## With the same experimental design, how will these different grasslands respond?

_***Semi-arid grassland***_
**Extreme rainfall events**
**Long dry intervals**
**Increases ANPP?**

## Experimental alteration of rainfall patterns across the Great Plains of North America

- Frequent, small events		              Fewer, infrequent large 							     events

- VS.

- A = 12 events
- B = 6 events
- C = 4 events
- Total = 191 mm

- A = 12 events
- B = 6 events
- C = 4 events
- Total = 450 mm

- KNZ

- Semi-arid

- Mesic

- Jana Heisler

## Mesic Grassland

- A shift from 12 to 4 events results in a 15% _decrease_ in productivity.

**More “extreme” rainfall regime**

- Shift to more extreme (large) rainfall events  reduced productivity

## Semi-arid Grassland

- A shift from 12 to 4 events resulted in a 30% increase in productivity.

**More “extreme” rainfall regime**

- Shift to more extreme (large) rainfall events  increased productivity

## Sevilleta LTER – Central New Mexico

## Seasonally averaged soil water content, plant water status, photosynthesis, and production were highest in plots receiving a small number of large events

**Collins, Thomey, Johnson, Brown, Natvig, Friggens**

**20 mm events**

**5 mm events**

**20 mm events**

**5 mm events**

## Why do dry vs. mesic grasslands respond differently?

- Two aspects of more extreme rainfall regimes:
- 1. Larger rain events
- 2. Longer dry periods between events
- When soils are usually moist, longer dry periods are most important...
- When soil are already dry, larger rain events cause the greater response...

## Wet relative to ambient

**Wet relative to ambient**

**Dry relative to ambient**

## Responses to climate change depends on location even in the same grassland biome – this make generalizations a challenge...

- Sala et al. 1988

**Responses to climate change depends on location even in the same grassland biome – this make generalizations a challenge...**

## Climate Change is but one facet of “Global Change” 

**Goldewijk and Battjes (1997)**

**Reid & Miller (1989)**

**NOAA**

- Ecological Systems

- Climate Change is but one facet of “Global Change”

**Grazing**

- J.A. Klein

## ...we are changing Earth more rapidly than we are understanding it.

- -Vitousek et al. 1997

- We have moved beyond questions such as “Is climate change happening?” There is little uncertainty about this.
- The uncertainty is with the consequences of climate change...

## Key Points:

- Research indicates that subtle climate change can have surprising consequences.
- 1. Even “subtle” changes toward more extreme rainfall patterns can alter  production and the sensitivity of the grasslands to changes in rainfall amounts
- 2. Grasslands can respond in opposing ways to the same form of climate change