IB Syllabus focus:
‘Warming drives poleward and upslope biome shifts.’
Climate change is altering ecosystems worldwide, forcing biomes to shift their traditional ranges. Rising temperatures drive poleward and upslope movements, profoundly reshaping biodiversity and ecosystem dynamics.
Biome Shifts under Climate Change
Biomes are large ecological zones characterised by specific climatic conditions, flora, and fauna. As global temperatures rise, these biomes undergo significant redistribution. The IB syllabus specifies that climate change results in poleward (toward the poles) and upslope (to higher altitudes) shifts. These movements reflect species’ responses to altered environmental conditions, as they seek suitable climates for survival.
Poleward Shifts
Poleward shifts occur when warming temperatures make conditions unsuitable in lower latitudes.
Boreal forests are expanding northwards, encroaching into tundra regions.
Temperate forests extend into zones previously dominated by grasslands.
Marine biomes such as coral reefs are seeing tropical species migrate into subtropical and even temperate seas.
Upslope Shifts
In mountainous regions, warming drives species to higher altitudes where cooler conditions persist.
Composite images (1953 vs 2005) show the elevational advance of spruce forest into tundra in Denali National Park, with treeline positions marked by contours and arrows. The right-hand panel maps summer sun exposure as an abiotic factor influencing pattern and rate of advance (extra detail beyond syllabus scope). Source.
Alpine meadows retreat further uphill as tree lines advance.
Species restricted to mountain peaks face habitat loss, as there is no further upslope habitat available.
This leads to risks of local extinction for organisms with narrow ecological niches.
Key Ecological Concepts Linked to Shifts
Climate Tolerance and Species Range
Climate Tolerance: The range of climatic conditions under which a species can survive, grow, and reproduce.
Species distributions are constrained by their climate tolerance. As climates warm, the range of tolerable conditions shifts geographically, driving biome redistribution.
Phenology and Migration Patterns
Phenology is the study of the timing of biological events such as flowering, breeding, and migration. Climate change disrupts phenological patterns:
Earlier flowering and breeding seasons.
Migratory birds altering arrival times.
Disrupted synchrony between species (e.g., pollinators and plants).
These changes can accelerate biome shifts when species fail to adapt at the same pace.
Ecological Impacts of Biome Shifts
Biodiversity Impacts
Habitat fragmentation occurs as biomes shift irregularly, leaving species trapped in unsuitable environments.
Species with narrow niches or limited dispersal ability face high extinction risks.
Shifts create opportunities for invasive species to expand into new regions, altering ecosystem balance.
Ecosystem Services
Biomes provide critical ecosystem services such as carbon sequestration, water regulation, and soil fertility. Shifting biomes disrupt these services:
Loss of tundra ecosystems reduces long-term carbon storage.
Expansion of deserts diminishes soil fertility and agricultural productivity.
Shifts in forest types alter hydrological cycles.
Human Implications
Humans rely heavily on stable biomes for food, resources, and climate regulation. Biome shifts impact:
Agriculture: Changing temperature and rainfall patterns affect crop suitability zones.
Health: Spread of vector-borne diseases like malaria as mosquitos expand into new ranges.
Livelihoods: Communities dependent on specific ecosystems (fishing, forestry, pastoralism) face disruption.
Case Studies and Evidence of Biome Shifts
Terrestrial Evidence
Arctic tundra replaced by boreal forest expansion.
Mediterranean ecosystems experiencing desertification.
African savannas shifting due to variable rainfall patterns linked with global warming.
Marine Evidence
Coral reefs shifting poleward as warm-water corals colonise subtropical regions.
Distribution changes in commercially important fish species, such as cod and mackerel, altering fishing grounds.
Maps compare the locations of Arctic (purple), central (yellow), and Atlantic (red) fish communities in 2004 and 2012, revealing a marked northward shift into formerly colder waters. This figure focuses on community envelopes and does not quantify depth changes (extra detail on depth is discussed elsewhere by EPA/NOAA). Source.
Ecological Risks of Shifts
Loss of Keystone Species
Keystone Species: A species with a disproportionately large effect on ecosystem structure and functioning relative to its abundance.
Biome shifts can displace or eliminate keystone species, destabilising ecosystems. For instance, sea otters regulate kelp forests, and their displacement would cause unchecked sea urchin populations.
Tipping Points
As biomes shift, some ecosystems approach tipping points where small changes trigger irreversible transformations:
Amazon rainforest potentially shifting to savanna due to reduced rainfall and increased fires.
Arctic sea ice decline accelerating global warming via positive feedback loops.
Factors Influencing Rate and Extent of Shifts
Climate Variables
Temperature increases directly drive poleward/upslope expansion.
Precipitation changes affect water availability, influencing plant and animal distributions.
Extreme weather events such as droughts, storms, and fires accelerate biome reorganisation.
Species-Specific Factors
Dispersal ability determines whether species can relocate.
Reproductive rate affects how fast populations can establish in new habitats.
Niche breadth: Generalist species adapt more easily than specialists.
Human Activity
Land-use change and urbanisation fragment potential migration pathways.
Deforestation and intensive agriculture reduce resilience of biomes to climate change.
Conservation measures such as wildlife corridors aim to aid biome adaptation.
Biome Range Shifts and Future Scenarios
The redistribution of biomes is not uniform. Some will expand, others contract:
Deserts likely to expand into semi-arid regions.
Tropical forests may fragment under increased drought stress.
Polar biomes are shrinking as ice and permafrost diminish.
Projected scenarios suggest that without mitigation, many ecosystems could be fundamentally altered within the next century.
FAQ
In terrestrial ecosystems, poleward shifts involve vegetation zones such as boreal forests encroaching into tundra or temperate forests expanding into grasslands. These shifts are constrained by soil type, topography, and human land use.
In marine systems, shifts occur more rapidly as water masses warm. Species such as fish and plankton can move quickly into higher latitudes, often altering entire food webs.
Upslope shifts are constrained by the availability of higher terrain. Once species reach the summit of a mountain, they have no further habitat to move into.
This phenomenon is called the “escalator to extinction” and is particularly critical for alpine plants, insects, and mammals adapted to cold conditions.
Species may fail to migrate due to:
Low dispersal ability (e.g., flightless insects).
Fragmented habitats that block migration routes.
Dependence on specific food sources or symbiotic partners that do not shift at the same pace.
These limitations increase the risk of local or global extinction.
As species move into new areas, they may:
Encounter new competitors or predators.
Lose long-standing mutualistic relationships, such as pollinators.
Introduce novel diseases or parasites to naïve populations.
These altered interactions can destabilise ecosystems and create unexpected feedbacks.
Scientists monitor biome shifts through:
Long-term vegetation surveys and repeat photography.
Satellite imagery showing changing forest or tundra boundaries.
Tracking the range edges of indicator species such as butterflies or fish.
Combining multiple indicators provides stronger evidence of ongoing shifts.
Practice Questions
Question 1 (2 marks)
Explain what is meant by the term “upslope biome shift” in the context of climate change.
Mark scheme
1 mark for stating that upslope biome shift refers to species or ecosystems moving to higher altitudes.
1 mark for linking this movement to rising temperatures making lower altitudes unsuitable.
Question 2 (5 marks)
Discuss two ecological consequences of poleward biome shifts caused by climate change, and explain how these shifts can affect human societies.
Mark scheme
Up to 2 marks for identifying and describing two ecological consequences (e.g., loss of biodiversity, changes in ecosystem services, habitat fragmentation, invasive species expansion). Each valid consequence = 1 mark, with an additional 1 mark for appropriate description.
Up to 2 marks for explaining how these ecological consequences impact human societies (e.g., altered agriculture zones, shifts in fishing grounds, spread of vector-borne diseases).
1 mark for overall clarity and linkage between ecological change and human impact.
