L7: Global change and terrestiral ecosystem

Ecosystem

Interdependent association of living plants and animals and their physical environment

Ecosystem services

Direct and indirect benefits that ecosystems provide to humans

• Provisioning

• Regulating

• Cultural

• Supporting

Vegetation

Plants considered collectively, especially in a particular area

Relationship between climate and vegatation

• Climate is a major determinant of vegetation

• Vegetation releases water vapour during photosynthesis → Alters surface energy fluxes and leads to potential cloud formation

• Climate change leads to extreme precipitation events that can disturb plant growth

Transpiration

• Water absorbed from soil by roots

  • Pressure difference between roots and leaves

• Water flows via xylem along pressure gradient to replace lost water from leaves

• Light energy evaporates water from leaf via stomata

Gas exchange in plants

• CO2 in, O2 out

• Guard cells control opening of stomata

NPP

Net photosynthesis for an entire plant community

Land carbon sink

Fossil fuels and cement + Land use change

→ Atmospheric growth

→ Land sink

→ Ocean sink

Walter’s climate system

• Classification of regions based on seasonal patterns of temperature and precipitation

• Predict similar ecosystems in places with similar climates

Tropical rainforest

• Slight annual variation in temperature

• Lots of precipitation

Tropical dry forest

• Variable temperature

• Climate alternates between very wet and very dry

Temperate forest

• Moderate variation in temperature

• Temperature coniferous forests → Seasonal drought

• Temperate deciduous forests → Low seasonal variation in precipitation

Boreal forest

• Great temperature variation

  • Proximity to sea affects temperature

• Limited growing season

• Modified temperature + precipitation → Cold, dry climate

Tundra

• Low precipitation

• Proximity to sea affects temperature

• Short growing season

What changes affect ecosystems?

• Temperature

• Activities and distribution of other species

• Rainfall / Moisture

• pH

What changes are species and ecosystems experiencing?

• Phenology

• Physiology

• Range + distribution

• Risk of disturbance

Climate change shifts

• Spatial or temporal changes in regular or extreme climate

• Include geographic, elevation, and seasonal shifts

• Can prompt changes in areas of suitability for specific habitats and lead to changes in species composition

What is biodiversity made up of?

• Ecosystem diversity

• Species diversity

• Genetic diversity

What is the physiology of plants?

All plants face a trade-off between growth (productivity) and safety (survival) that is influenced by a number of changing environmental factors:

• Increasing chronic and acute temperatures

• Changes in water availability

• Increasing CO2

Productivity (CO2 fertilisation effect)

Increased CO2 → Increased rate of photosynthesis while limiting leaf transpiration in plants

Water use efficiency

Higher CO2 → Stomata open less → Less water used

Phenology

Timing of many events is linked to temperature and precipitation regimes

• Flowering

• Leaf turnover

• Migration

• Reproduction

Forest phenology

1. Leaf flush

2. Flowering

3. Fruiting

4. Seeding

5. Leaf senescence

How does global warming affect phenology?

• Increasing accumulated growing degree days (AGDD) and precipitation delay the onset of key phenophases

• Mismatch between availability of resources and life cycles of species that depend on them

• Spring phenology advanced, autumn delayed

Risk of disturbance

• Diseases and pests

• Droughts and floods

• Fire regime

Diseases and pests

• Many pathogens and insect pests are temperature sensitive

• Some grow well at temps that cause stress in their hosts

Increase of frequency and severity of droughts and floods

• Primary response of trees to drought is to reduce NPP and water use

  • Tree mortality

• Prolonged flooding leads to plant death

  • Landward migration is limited by human infrastructure and activities

Infrequent and intense precipitation

• Upper soil saturation (runoff > infiltration)

• Flooding

• Lower canopy interception

• Greater soil erosion and nutrient loss

Fire regime

Higher climate temp = More burned area

Non-climate pressures

• Habitat fragmentation / Loss

• Unsustainable extraction

• Loss of key wildlife species

• Invasive species

• Air + water pollution

Earth is greening

• Increased LAI

• More global warming → Longer growing season → More photosynthesis

• Greening has slowed in recent years

  • More water stress → Decelerate vegetative productivity

  • Terrestrial ecosystems are now close to their tipping points

Interannual variability of vegetation productivity

• El Nino events → Globally increased droughts

• ENSO droughts → Increased tree mortality + increased fire events

El Nino effects on land carbon sink

• Warming of ocean surface in Pacific Ocean

• Causes severe droughts and heat waves in tropics → Reduced plant growth

• Increased atmospheric CO2

Dynamic Global Vegetation Models (DGVM)

• Simulates plant physiological processes to infer vegetation type over time

• Based on soil and climatic info (hourly to yearly)

• Landscape to global

Climate Envelope Models (CEM)

• Predicts potential tree and wildlife species distribution using statistical models based on climate variables

• Represents a snapshot in time

• Variable scale (usually small)

Uncertainties of modelling

• Multiple forcings - Climate, CO2 etc.

• Emission scenarios - dependent on future economies and policies

• Modeled climate sensitivity - esp. at regional level

• Modeled ecological sensitivity - e.g. CO2 effect