FORESTS, DROUGHT AND GLOBAL CHANGE. Maurizio Mencuccini. School of GeoSciences, University of Edinburgh, (UK) ICREA at CREAF (Barcelona, Spain)

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1 FORESTS, DROUGHT AND GLOBAL CHANGE Maurizio Mencuccini School of GeoSciences, University of Edinburgh, (UK) ICREA at CREAF (Barcelona, Spain)

2 plants, trees, forests water carbon nutrients physiology modelling Tropics Amazon Africa Borneo

3 Structure -Water and climate change globally -Characteristics of soils and plants that affect the water cycle: plant functional traits - Causes of drought-induced mortality around the word - Case studies of local-regional mortality

4 Forests, drought and global change

5 Important forest-atmosphere feedbacks: energy budget, hydrology, C cycle, land use Bonan (Science, 2008)

6 Water as greenhouse gas Most important GH gas (more than CO 2 ) More CO 2 More heat More vapour More heat (esp. tropics) Small GH effect compared to CO 2

Global water cycle Consequences of increased air vapour pressure: Greater greenhouse effect (positive feedback) More clouds (more reflection of radiation negative feedback) Positive

7 Global water cycle Consequences of increased air vapour pressure: Greater greenhouse effect (positive feedback) More clouds (more reflection of radiation negative feedback) Positive feedback > negative feedback More transport of heat (clouds more buoyant, more wind, more storms) More vapour for rain and snow (more storms, more floods, heavier rains, more snow in places)

8 Drought predictions worldwide Change in annual runoff for the period relative to : IPCC (2008)

9 Water in soil Soil organic matter affect water holding capacity of soils link between C, nutrient and H 2 O cycles

10 Water in plants Stomata in leaves inescapable trade-off between CO 2 uptake and water loss Water use efficiency

11 Water in atmosphere Paradox of warming: More water in atmosphere (in absolute terms) But plants perceive less water in atmosphere (in relative terms!!! Deficit in vapour pressure increases with T Atmospheric drought Increased plant water loss

12 Strategies to cope with drought Drought sensitive Drought tolerant (e.g., agave, cacti) Drought avoiders (e.g., Tamarix)

13 The concept of stress A load on biological systems that modifies metabolic processes and produces a strain in the organism.

14 Definitions 1. Functional traits: organismal features (e.g., leaf size, rooting depth, leaf [N], phenology, seed size, etc.) relevant for the species response to the environment and for biotic interactions. 2. Functional diversity: the value, abundance and distribution of organismal functional traits in a community.

15 1) Wood economics spectrum

16 Water transport / Mechanical support / Storage / Decay resistance Angiosperms Gymnosperms

17 Example: Effect of drought on wood hydraulics Development of emboli inside a Scots pine stem as drought increases (left to right)

18 Xylem water potential Free water with no solutes at sea level: WP=0 Typical values: well watered: WP=-1.5 MPa= -15 atm Drought-stressed: WP=-3.0 / -6.0 MPa= -30 / -60 atm

19 Global synthesis 190 angiosperms, 32 gymnosperms Vertical distance from diagonal is hydraulic safety margin from hydraulic failure No differences across major biomes Choat et al (2012)

21 1) Leaf economics spectrum About 3,000 spp. (Wright et al 2004, Nature) wet dry low LMA high %N high A mass low LMA low leaf lifespan low resistance to herbivory

22 Leaf structure Angiosperms Gymnosperms Carbon dioxide water and oxygen

23 Leaf mass per area Leaf mass / leaf area Sources of variability in MLA: - Leaf thickness - Volume of air space - Number/size of mesophyll cells - Thickness/density epidermis

Quantifying and scaling global plant trait diversity TRY is a network of vegetation scientists headed by DIVERSITAS, IGBP, the Max Planck Institute for

Main objectives Provide a global archive of plant traits Promote trait-based approaches in ecology and biodiversity science Support the design of a new

24 Quantifying and scaling global plant trait diversity TRY is a network of vegetation scientists headed by DIVERSITAS, IGBP, the Max Planck Institute for Biogeochemistry and an international Advisory Board. Main objectives Provide a global archive of plant traits Promote trait-based approaches in ecology and biodiversity science Support the design of a new generation of global vegetation models Current state of database and network 3 million trait records for about plant species 591 participants from 207 scientific institutes worldwide 256 scientific projects requesting plant trait data from TRY

25 Dynamic Global Vegetation Models Combined with global atmospheric circulation models DGVM predict major processes of terrestrial biosphere at temporal scales varying from months to centuries

26 Plant functional types in DGVMs PFT= Broad groups of species with common physiological/morphological traits (e.g., needleleaf evergreen or deciduous trees, broadleaf evergreen or deciduous trees, shrubs, grasses, crops) Look-up tables of main traits for each group

27 Functional traits and response to stresses In plants, we measure strain, not stress directly When elastic strain stops, metabolism recovers When plastic strain stops, metabolism is modified

28 Example: Effects of high temperatures on photosynthetic traits

29 Short-term repair after heat stress

30 Response of plants to stresses Over longer time scales, plants respond to stress Repair, hardening, acclimation, evolution

31 Acclimation at multi-annual time scale: plasticity Plasticity is genetically controlled Species differ in how plastic they are (there is a cost) The environment as inducer of phenotypes

32 Acclimation of photosynthesis to growing temperature in oak and birch Growth T: Blue=ambient; orange=+2degree C; red=+4 degree C The thermal optimum for photosynthesis increased with the increase in growth temperature The absolute values of respiration declined with increasing growth temperature

33 Plasticity along geographical clines Study of the gas exchange and hydraulics of Scots pine across Eurasia Poyatos et al (Oecologia 2007) Trailing edge of distribution

rule) K S = stem hydraulic conductance (Wood economics) P 50 =

34 Within-species plasticity: the case of Scots pine Martinez-Vilalta et al (New Phytol 2009) A L :A S = area leaves / area stem (Corner s rule) K S = stem hydraulic conductance (Wood economics) P 50 = vulnerability to embolism (Wood economics) 13 C = Stomatal aperture (Leaf economics)

35 Limits to plasticity: mortality Mediterranean Europe: The case of Scots pine NE Spain Martínez-Vilalta & Piñol (For Eco Man, 2002) Valais (Alps) Bigler et al. (Ecosystems, 2006)

36 Drought-induced mortality 1) Direct water stress (hydraulic failure) 2) Carbon starvation MacDowell et al. (New Phyt, 2008)

37 Hydraulic failure Development of emboli inside a Scots pine stem as drought increases (left to right)

38 Carbon starvation Long-term starvation due directly to higher T? future current Adams et al. (PNAS, 2009) Pinon pine at biosphere 2

39 Impacts at community level Drought as a phenotypic filter Not intense / infrequent Acclimation Plasticity DROUGHT Phenotypic selection Genotypic selection Intense / Frequent Species filtering Funk et al (Trends Ecol Evol 2008) Trait filtering Trait convergence

40 Hydrological consequences Radiation regime Water regime (Also carbon cycle) (Also nutrients cycles)

-Carbon losses equivalent to 75% of all Canada fire emissions for 1 year.

41 Evidence of large scale mortality. Boreal. -Mountain pine beetle - British Columbia, Canada - ~80,000 km 2 affected. -Carbon losses equivalent to 75% of all Canada fire emissions for 1 year. - 10x larger than any previous known outbreak Causes: - reduced winter T - increased summer T - reduced summer rainfall Kurz et al. (Nature, 1998)

42 Evidence of large scale mortality: temperate Records of mortality in large-scale undisturbed forest reserves in the old-growth stage of development Van Mantgem et al. (Science, 2009)

43 Evidence of large scale mortality: Mediterranean Europe Quercus ilex 2005 Pinus sylvestris 1994, 1998

44 Evidence of large scale mortality: subdeserts Piñon juniper woodlands (SW USA) Up to 95% mortality in some areas Pinus edulis Juniperus monosperma MacDowell et al. (New Phytologist, 2008)

45 Evidence of large scale mortality: tropics How much has gone? ~ 16 % (depends on estimate) Current rate? Approx. 1.9 million ha yr -1 (= km 2 ): ~0.5 % yr -1 5 m km 2 of which 4 m km 2 originally forested Laurance et al. 2001, Environmental Conservation, 28, 305; Fearnside 1999, Environmental Conservation, 26, 305 de Fries et al. 2002, Proceedings of the National Academy for Sciences (PNAS)

46 Impacts Logging: reduces canopy cover (50%), increases litter fire removes larger trees creates access (agriculture, hunting), affects erosion Fire: low resistance among rain forest trees increases likelihood of short return time.total loss synergism with climate and ignition sources (e.g., roads) Fragmentation: edge effects on microclimate, fire vulnerability effect of patch size on population viability distance between patches (dispersal) invasion by exotic species (e.g., grasses) Climatic / hydrologic: Temperature change Regional and local rainfall Smoke and dust Importance of large scale events (e.g., El Niño)

47 Impacts Fragment edges; micro climate > 150 % of deforested area in 1988 (<100km 2 block, <1km to edge) - increased turbulence, temp., drought stress, competition higher mortality, esp. big trees Laurance et al. 2000, Nature, 404, 836

48 Flammability feedbacks Drought or logging may increase dry fuel load Ground fires increase the probability of return fires Additional human occupation increases number of ignition sources potential for much larger forest losses

49 Climatic feedbacks Reduced rainfall from conversion to pasture Effect magnified by dust from intense dry season fires Interaction with global climate increased local fire vulnerability, global costs Carvalho et al. 2001, Nature, 409, 131

50 Conclusions -Water cycle central to understanding of climate change -Predictions of rainfall changes are highly uncertain but likely very region specific -Water cycle in forests depend on characteristics of soils, plants and atmosphere; plant functional traits are central. - Concerns about species distribution have begun to appear for several regions around the world -Several case studies of local-regional mortality

Effects of Land Use On Climate and Water Resources: Application of a Land Surface Model for Land Use Management

Effects of Land Use On Climate and Water Resources: Application of a Land Surface Model for Land Use Management Gordon Bonan, PI National Center for Atmospheric Research Boulder, Colorado Personnel Supported: