II. Plant survival and tropical biomes Flashcards
What are the range of temperature increases associated with the IPCC (2014) RCPs?
Worst case (8.5): +4 Best case: +1.5
How is climate change projected to alter the climate in the tropics?
5-7C increase in average temp.
Models don’t agree with rainfall, but strong declines and rises in RCP8.5 (and I’ve read that delayed rainy season could be a thing).
Drier, less soil moisture.
More extreme events e.g. El Nino, heat waves, flash floods, cyclones, storms.
What are the key changes that will occur in plants in response to changes in temp, soil moisture etc.? (x7)
Higher temps -> water loss (drought), photosynthetic and respiration change
Precipitation change -> drought/water logging
Reduced soil moisture from more evaporation and % runoff -> hydraulic stress
Increased radiation -> photosynthetic change
Reduced relative humidity -> hydraulic stress + water loss
Reduced low temp days -> seasonal changes, flowering/leaves
Greater exposure to extreme weather -> increased mortality
What options to plants have in the face of increased stress?
Climate change will change niche spaces -> will have to migrate, adapt, or die.
How might plants migrate, and what evidence is there for this?
Up e.g. Morueta-Holme et al. (2015) found altitude of plants on Chumborazo recorded by Humboldt have moved up >500m over 210 years.
North (latitude) e.g. Pecl (2017)
Feeley et al. (2011): found tropical Andean trees to move slowly, 2.5-3.5 vertical m/yr (but only 5-yr study)
What are the barriers to plant migration?
Abiotic factors -> gradient change e.g. soil, water, pH, nutrients; might not change with climate
New pest and herbivore attack
Dispersal ability
Anthropogenic pressure, fragmentation
How might plants adapt, and what evidence is there?
Acclimation: an organism changes or adjusts to new environmental conditions within single lifetime [can be reversible in time, not instantaneously reversible]. Potential for this is very uncertain, but found varying plasticity between plant species -> an evolved capacity to rapidly adjust; specific traits likely to be correlated with this.
Chaves et al. (2003) - drought response
Atkin et al. (2005) - changes in gene expression to respire differently in new temps
How might plants die?
Carbon starvation (plant must close stomata to reduce water loss, runs out of energy)
Hydraulic failure (cavitation of xylem can’t get water to leaves, more likely to kill, Rowland et al. 2015)
Biotic attack (pest pressures)
Disturbance (increased chance of fire ignition)
High mortality already happening e.g. El Nino response, peat fires
What have Chaves et al. (2003) found regarding plant responses to drought?
Progression in understanding of processes underlying plant response to drought at molecular + whole plant levels e.g. plasticity, acclimation, resistance - rolled leaves and stomata closure, reduced growth, shedding, partial dormancy, rigid cell walls, chemical responses
What have van der Molen et al. (2011) said about ecosystem responses to drought?
Drought interacts with carbon cycle differently than ‘gradual’ climate change. Plants must respond to prevent excessive water loss; species-specific water use strategies -> consequences for carbon uptake by photosynthesis.
Plant strategies to be more explicitly incorporated in veg models.
Role of stomata, carbohydrate reserves, insects, fire, cavitation, carbon starvation, hydraulic failure, root adaptation, species competition and nutrient recycling.
How have tropical forests responded to the 2015/16 El Nino?
Liu et al. (2017): carbon fluxes - heterogenous response of plants, mostly increases in C release in the tropics; anomalies occured.
Wigneron et al. (2020): slow recovey, biomass still lower than surrounding mature forest
What have Pecl et al. (2017) said about biodiversity redistribution under climate change?
Distribution of species changing in response to anthropogenic CC: affects global functioning, human wellbeing, climate dynamics, food security, patterns of disease transmission, C sequestration, albedo.
E.g. ~34% of European forest currently covered with timber will be suitable only for Mediterranean oak by 2100.
Poorer regions: major effects to coffee-growers.
What are the main features of the tropical rain forest?
High rainfall (>2000 mm yr-1, even >4000mm!)
Low annual variation in average temp, pretty static
Fertile soils (relative to savannah– but mostly in surface humic soil layer, with lower fertility deeper soils).
Mostly seasonal (dry and wet season), but with some areas experiencing limited or no seasonality.
Continuous closed canopy
Mostly deciduous vegetation – not like UK, but trees do drop their leaves; quick flushing; variable times
Highly layered canopy, often with dense understory (high total leaf area per m-2)
Very high gross primary production (total photosynthetic production)
Give some key adaptations of tropical rain forest.
Tall trees; 50m or more – light comp.
Buttressed roots – to support height, but shallow to get humic layer nutrients
Deep canopy – large number of leaves to compete for light
Rapid growth rates (high variation though) – variations in wood density (quick growing pioneer species)
High total transpiration – due to high leaf area; high water demand
High carbon assimilation – higher leaf area -> higher photosynthetic rates -> open stomata
Leaves flush each year – rapid loss and regrowth
High diversity of plant strategies
Fire intolerant
What are the main features of the savanna?
Variable annual rainfall (e.g. 800-2500mm) but lower inter-annual variation with distinct dry and wet season
Large temperature variation (e.g. 12-30 °C)
Low fertility acidic soils, high concentrations of minerals like aluminium, toxic to many
Highly seasonal climate, distinct and regular dry season with fires.
Open canopy structure
Mostly evergreen
Lower density vegetation -> almost continuous grass layer (trees can also be absent, 100% grass layer can exist).
Lower gross primary production (total photosynthetic production)
Give some key adaptations of savanna (Cerrado).
Very low stature, <20m (10-15) – no light comp
Very deep roots (water access) ‘upside down forest’; high belowground biomass
Shallow canopy, very open
Incredibly slow-growing; limited by low nutrient availability for growth and C regen., water limited
Medium-low transpiration – stomata closed for a lot of the year
Medium-low carbon assimilation
Trees often evergreen – invest once in building leaves with as high nutrients as they can manage; too expensive to replace leaves every year.
Deciduous trees exist but rare
Fire tolerant – thick corky bark on trunks, thick leaves
Thick long-lived leaves on evergreen trees
Low pH soil – increased availability of Al, Fe, Mn
What are the main features of the dry forest?
Lower rainfall (often <1000 mm), but HUGE VARIABILTIY
Can experience regular high temps e.g. >38⁰C (dry season) & greater temp variation
Fertile soils (relative to other 2 biomes) -> great for farming
Highly seasonal, long dry season, which can be highly variable in length between years, sometimes the wet season almost completely absent.
Closed canopy, but less dense than rain forest. No grass.
Mostly deciduous vegetation
Lower density vegetation with less distinct canopy layers
Lower gross primary production (total photosynthetic production)
Give some key adaptations of dry forest.
Low stature trees, normally 25m max – no need for extreme light competition
Very deep roots to access water in dry season
Shallow canopy, not lots of shading
Very slow growing – don’t have a lot of water resources, so limited, harsher
Low total transpiration – drought-deciduous so lose leaves during dry periods (can be majority of year)
Medium to low carbon assimilation (lower photosynthesis – deciduous)
Drought deciduous with large proportion of year leafless
Fire intolerant
Very high water storage in tissues, high ‘stem capacitance’
What traits have plants adapted for fire-survival?
Flammable grasses
Re-sprouting (growth organs underground)
Serotiny (seed released post-fire)
Physical dormancy (seeds lie dormant, activate post-fire)
Very thick corky bark
Post-fire flowering or smoke-induced germination
What traits have plants adapted for drought-survival?
Embolism-resistance - resist pressure in xylem to avoid air bubbles, requires high P50 (pressure at which 50% of xylem tissue has been lost)
In dry areas have to develop hydraulic traits differently to rain forest plants (Christofferson et la., 2016)
What role do nutrients have in the tropical biomes?
Nitrogen needed for formation of rubisco – central enzyme for photosynthesis.
Phosphorus essential for formation of ATP; essential compound for photosynthesis and respiration.
Np, P and other nutrients essential for diverse set of proteins for building plant tissue.
Nutrient limitation - different soil conditions, heterogeneity i.e. low nutrient Cerrado, high nutrient rainforest
What biome transitions might/might not occur under hotter, drier climates? Why?
Rain -> dry: no (not going to go hotter/drier)
Rain -> savanna: no (soil way to poor)
Savanna -> dry: no (dry too dry/hot)
Savanna -> rain: no (savanna needs less moisture, fire, barriers, soils).
Dry -> rain: maybe (potentially too wet, high comp pressure, dispersal limit)
Dry -> savanna: maybe (soils might not be fertile enough, still going to burn if grasses).
What did Viani et al. (2011) find in their Cerrado and Caatinga tree transplant experiment?
Survival doesn’t change significantly between species grown in home soil vs alternatives
Dry forest trees could grow effectively in own soils than Cerrado but Cerrado trees grew no better in higher nutrient Caatinga soils -> SO Cerrado trees don’t necessarily need to adapt quickly to new conditions?
What has Pellegrini (2016) found about nutrient limitation in tropical savannas?
P and N in short supply, may limit plants. Fire-driven nutrient loss?
Ability of nutrients to control transitions emerges at individual and landscape scales, regulated through different mechanisms based on spatial (geology), temporal (biome transition stage) and biological (species traits, community composition) variability.
