II. Plant survival and tropical biomes

Question 1

What are the range of temperature increases associated with the IPCC (2014) RCPs?

Answer 1

Worst case (8.5): +4 
Best case: +1.5

Question 2

How is climate change projected to alter the climate in the tropics?

Answer 2

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.

Question 3

What are the key changes that will occur in plants in response to changes in temp, soil moisture etc.? (x7)

Answer 3

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

Question 4

What options to plants have in the face of increased stress?

Answer 4

Climate change will change niche spaces -> will have to migrate, adapt, or die.

Question 5

How might plants migrate, and what evidence is there for this?

Answer 5

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)

Question 6

What are the barriers to plant migration?

Answer 6

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

Question 7

How might plants adapt, and what evidence is there?

Answer 7

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

Question 8

How might plants die?

Answer 8

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

Question 9

What have Chaves et al. (2003) found regarding plant responses to drought?

Answer 9

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

Question 10

What have van der Molen et al. (2011) said about ecosystem responses to drought?

Answer 10

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.

Question 11

How have tropical forests responded to the 2015/16 El Nino?

Answer 11

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

Question 12

What have Pecl et al. (2017) said about biodiversity redistribution under climate change?

Answer 12

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.

Question 13

What are the main features of the tropical rain forest?

Answer 13

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)

Question 14

Give some key adaptations of tropical rain forest.

Answer 14

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

Question 15

What are the main features of the savanna?

Answer 15

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)

Question 16

Give some key adaptations of savanna (Cerrado).

Answer 16

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

Question 17

What are the main features of the dry forest?

Answer 17

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)

Question 18

Give some key adaptations of dry forest.

Answer 18

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’

Question 19

What traits have plants adapted for fire-survival?

Answer 19

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

Question 20

What traits have plants adapted for drought-survival?

Answer 20

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)

Question 21

What role do nutrients have in the tropical biomes?

Answer 21

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

Question 22

What biome transitions might/might not occur under hotter, drier climates? Why?

Answer 22

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).

Question 23

What did Viani et al. (2011) find in their Cerrado and Caatinga tree transplant experiment?

Answer 23

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?

Question 24

What has Pellegrini (2016) found about nutrient limitation in tropical savannas?

Answer 24

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.

Question 25

How will climate change affect Latin America’s tropical biomes?

Answer 25

All likely to experience shifts in environmental conditions, but these will be distinctly different for savanna, dry forest and rain forest.

Question 26

What is important to note regarding understanding the effect climate change could have within a specific biome?

Answer 26

That each, despite being distinctly different, are highly heterogenous with different plant adaptations.

Question 27

What is significant about the differences between the Latin American tropical biomes in the context of climate change?

Answer 27

Likely to be large barriers to species successfully moving between them, so these biomes are likely to be highly threatened, particularly those subject to large amounts of human activity.