Plant responses to climate change in the Negev

Transcription

1 Ben-Gurion University of the Negev Plant responses to climate change in the Negev ? Dr. Bertrand Boeken Dry Rangeland Ecology and Management Lab The Wyler Dept. of Dryland Agriculture Jacob Blaustein Institute for Desert Research Ben-Gurion University of the Negev Sede Boqer Campus Israel mm 0 40km N BBoeken

2 Plant responses to climate change in the Negev Possible changes in climate CO 2, Temperatures, Rainfall Effects on Negev plants Individuals plants Populations Spatial distributions Plant communities Patterns of vegetation Consequences for landscape structure and land degradation (desertification) 2

3 Changes in climate Greenhouse gases Global increase of atmospheric CO 2 and CH 4 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!) 3

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) Total annual rainfall in Park Shaked Rainfall (mm) Probable changes in distribution of 0 rainfall during the rainy season Higher intensity of rain events Longer droughts between rain events 4

5 Effects on individual plants Higher temperatures Increased growth during the rainy season Biochemical processes increase with temperature Earlier seed germination In species with low-temperature inhibition of germination Fewer seeds germinate In species that require low temperature Earlier flowering In species without strict day-length response A-synchrony with pollinators If insects have different developmental temperature response Growth or germination rate Higher CO2 Increased growth Photosynthesis assimilates CO 2 to produce sugars, used for growth Lower water loss Fewer stomates open Temperature 5

6 Effects of rainfall changes 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 Runoff Less water in source Infiltration More water in sink Longer droughts Shorter growing season Less growth More mortality Less reproduction Less germination Soil moisture Rain intensity Current vs Expected Time Drought period 6

7 Effects on populations 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) Plant life-cycle (polycarpic perennial) 1 Z Seed dispersal (6 x 7 x 1). Reproductive success (fertility) S J 2 4 A Effects vary a lot between Species Life forms (annuals, shrubs) Environments (exposed or shaded patches) 3 5 Net result is population growth and expansion, or decrease and extinction No single prediction of climate change effects 7

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 Stipa capensis 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 Noaea mucronata and Atractylis serratuloides 8

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 9

10 Spatial distributions Geographical distributions will change By local extinction of existing populations By colonization of unoccupied areas (invasion) Ranges can move along the aridity gradient 75 Species can colonize locations where they were absent due to lower temperatures or competitive exclusion Or in wetter sink patches 50mm N Distributions can become very restricted If extinction >> colonization 0 40km as colonization is inhibited by the physical impacts of climate change (strong runoff, erosion) 10

11 Landscape structure Shrubs form sink patches Shrub seedling 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 Shrub patch Under or around shrub canopy High annual species richness Shelter and food for herbivores and granivores 11

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 12

13 Shrub cover may decrease Landscape changes In shrub species that are sensitive to drought And if their patches are easily eroded As in Atractylis and Noaea mucronata (at 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 mm/yr) But with negative effects on annuals If the annuals grow around shrubs And shrub patches merge 13

14 Reduction of patch density and size Land degradation Fewer sinks for runoff Fewer hot-spots for herbaceous vegetation More runoff Resource loss High energy Erosion Positive feedback Low shrub establishment Runoff Rain Restoration necessary 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 14

15 Summary Higher CO 2 and temperature Positive and negative effects on all biota Many possible effects on plants On recruitment, growth, survival and reproduction 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 Community changes Landscape changes Dominance, species diversity 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 Variable population responses Local or regional species extinctions Shifts in spatial distributions Reduction/expansion, colonization/invasion 15