1

Dr. Bertrand BoekenDry Rangeland Ecology and Management LabThe Wyler Dept. of Dryland AgricultureJacob Blaustein Institute for Desert ResearchBen-Gurion University of the NegevSede Boqer Campus 84990 Israel

Ben-Gurion University of the Negev

Plant responses to climate change in the Negev

© BBoeken 2010

40km0

50mm

75

100

150

200

300

N

?

2

Plant responses to climate change

in the Negev

• Possible changes in climate

– CO2, Temperatures, Rainfall

• Effects on Negev plants

– Individuals plants

– Populations

– Spatial distributions

– Plant communities

– Patterns of vegetation

• Consequences for landscape structure

and land degradation (desertification)

3

Changes in climate

• Greenhouse gases

– Global increase of atmospheric

CO2 and CH4 concentrations

– Causes global warming

• Regional temperature change

– Higher averages, minima and/or maxima?

– At higher latitudes (N) higher winter minimum temperatures

observed

– Uncertain what happens in the Negev

(after last year’s frost, the average is lower anyway!)

4

Changes in rainfall in the Negev

More, same or less total rainfall per

year?

– Lower mean in the last decades:

~150mm/yr, vs. 200mm/yr (long-term)

– Possibly greater variance

– Higher frequency of drought years

with ≤ 50% long-term mean)

Probable changes in distribution of

rainfall during the rainy season

– Higher intensity of rain events

– Longer droughts between rain events

Total annual rainfall in Park Shaked

0

50

100

150

200

250

300

19

92

19

94

19

96

19

98

20

00

20

02

20

04

20

06

20

08

20

10

Rain

fall

(mm

)

5

Effects on individual plants• Higher temperatures

– Increased growth during the rainy seasonBiochemical processes increase with temperature

– Earlier seed germinationIn species with low-temperature inhibition of germination

– Fewer seeds germinateIn species that require low temperature

– Earlier flowering

In species without strict day-length response

– A-synchrony with pollinatorsIf insects have different developmental temperature

response

• Higher CO2– Increased growthPhotosynthesis assimilates CO2 to produce sugars,

used for growth

– Lower water lossFewer stomates open

Temperature

Gro

wth

or

ger

min

ati

on

ra

te

6

• Heavier rainfall

– Not just more growth

– But more damage

– Greater variability of soil moisture

Indirect effect: more runoff, erosion, and

local accumulation

Sources of runoff become drier,

sinks become fewer but wetter

• Longer droughts

– Shorter growing season

– Less growth

– More mortality

– Less reproduction

– Less germination

Effects of rainfall changes

Less

water in

source More water

in sink

Runoff

Infiltration

Time

So

il m

ois

ture

Current vs

Expected

Drought period

Rain intensity

7

• Changes in temperature, rainfall intensity and drought

have different positive or negative effects on vital rates

1. Seed survival and germination

2. Seedling establishment and survival

3. Juvenile growth and survival

4. Growth, maturation and flowering

5. Adult survival

6. Seed production (fecundity)

7. Seed dispersal

(6 x 7 x 1). Reproductive success (fertility)

• Effects vary a lot between

– Species

– Life forms (annuals, shrubs)

– Environments (exposed or shaded patches)

• Net result is population growth and expansion, or decrease and extinction

• No single prediction of climate change effects

Effects on populations

Plant life-cycle (polycarpic perennial)

Z

S

1

2 4

7

J A

5

6

3

8

Effects on species• Annuals

– Fast-growing dominants may decrease

Need ample water

Dominant grasses: No seed dormancy,

germination of new seeds every year

– Slower-growing species may increase

Need less water

Have dormant seed bank

Will be less suppressed by dominants

– Species requiring good sites (runoff sinks, more water, shade)

May have fewer good sites, but increase there

• Shrubs

– Lower seedling establishment in open sites

Due to increased runoff – greater risk of washing away

– Fewer survivors may grow better

Due to increased soil moisture in sinks

Stipa capensis

Noaea mucronata and Atractylis serratuloides

9

Community consequences• Changes in competitive relations (among annuals and among shrubs)

– Dominants may become sparser

– Some minor species may become dominant

Currently suppressed by low temperature or by dominants

Or by low soil moisture in good sites

• Invasion of new species

– Species from harsher (dry, hot)

environments (further south or east)

Most likely dominants

Currently absent due to local conditions and exclusion

Unknown how they perform –

growth, litter, soil, patch formation (shrubs)

• Herbivores and their predators,

and pathogens of plants and animals

– May locally decrease of increase

– New ones may invade

Hamada scoparia

10

Spatial distributions

40km0

50mm

75

100

150

200

300

N

• Geographical distributions will change

– By local extinction of existing populations

– By colonization of unoccupied areas (invasion)

• Ranges can move along the aridity gradient

– Species can colonize locations where they were

absent

due to lower temperatures or competitive exclusion

– Or in wetter sink patches

• Distributions can become very restricted

– If extinction >> colonization

as colonization is inhibited by the physical impacts of

climate change (strong runoff, erosion)

11

Landscape structure• Shrubs form sink patches

– Landscape modulation

• By patch and pattern formation

– Transition of open (crusted) matrix

to dense shrub patch with soil mound

• Captures runoff water, soil and OM

• Seed capture, retention

• High productivity • Shrub patches are hot-spots for species richness

– Dense annual vegetation

• Under or around shrub canopy

– High annual species richness

– Shelter and food for herbivores and

granivores

Shrub seedling

Shrub patch

12

Landscape structure• Spatial heterogeneity is essential for retaining water

– Sinks for resources (runoff, soil, nutrients and OM)

– With lower shrub density, more erosion and resource

loss down slopes and out of the watershed

• Depends on survival and establishment of current

shrub species

– Better growth and survival, or

– Slower patch formation by shrubs as erosion

increases, and

• Failure of shrub seedling establishment

– positive feedback: the fewer shrubs, the fewer new

shrubs

• Not easily replaced by new shrub species

– Establishment may fail

– They may be worse patch formers

13

Landscape changes• Shrub cover may decrease

– In shrub species that are sensitive to drought

– And if their patches are easily eroded

As in Atractylis and Noaea mucronata (at 150-250

mm/yr)

– Where annuals stabilize the shrub mound

• Or shrub cover may increase

– In species that capture runoff water efficiently

As in Sarcopoterium spinosum (at 250-400 mm/yr)

– But with negative effects on annuals

– If the annuals grow around shrubs

– And shrub patches merge

14

Land degradation

• Current cause for degradation =

Livestock grazing

– Herbivory

• Annual plant removal

• Exposure of mounds

– Trampling of shrub mounds

• Dissipation of mounds

• Erosion and loss of material

Runoff

Rain• Reduction of patch density and size

– Fewer sinks for runoff

– Fewer hot-spots for herbaceous vegetation

– More runoff

• Resource loss

• High energy

• Erosion

– Positive feedback

• Low shrub establishment

• Restoration necessary

15

Summary

• Higher CO2 and temperature

– Positive and negative effects on all biota

• Possibly increased rain intensity and drought

– Greater annual fluctuations

– Greater spatial variation in soil moisture

– More runoff: resource loss and erosion

– Fewer but wetter sink patches

• Landscape changes

– Lower heterogeneity

– Increase or reduction of shrub patch (sinks)

– Increased runoff, resource loss, erosion

• Land degradation

– Especially in combination with livestock grazing

– Restoration / rehabilitation / reclamation

• Many possible effects on plants– On recruitment, growth, survival and

reproduction

• Variable population responses– Local or regional species extinctions

• Shifts in spatial distributions– Reduction/expansion,

colonization/invasion

• Community changes – Dominance, species diversity