Wildfires are burning more severely and more often, urban noise pollution is growing into a global public health menace, and phenological mismatches are causing ecological consequences. 

These critical environmental issues, requiring greater attention, are highlighted in the new Frontiers Report published by the UN Environment Programme (UNEP).

The report, titled — Noise, Blazes and Mismatches: Emerging Issues of Environmental Concern — draws attention to emerging environmental concerns with the potential to wreak regional or global havoc, if not addressed early.

What is phenology?

• Phenology is the timing of recurring life cycle stages, driven by environmental forces, and how species interacting within an ecosystem, respond to changing conditions.

• Plants and animals in terrestrial, aquatic and marine ecosystems use temperature, day length or rainfall as cues for when to bear fruit, migrate or transform in other ways.

• Plants and animals often use temperature, daylength, the arrival of rains, or other physical changes as cues for the next stage in their seasonal cycle. When spring arrives earlier, many birds react by breeding sooner, matching the advanced emergence of food for their nestlings as temperatures warm. 

• Because temperature is such a strong influence on these cues, phenological shifts over the past decades are among the most visible consequences of global climate change, at least in temperate and polar regions of the world. 

• Phenological shifts in crops in response to seasonal variations will be challenging for food production in the face of climate change.

• Shifts in the phenology of commercially important marine species and their prey have significant consequences for stock and fisheries productivity. 

Major causes of phenological shifts

• Climate change disrupts these natural rhythms as plants and animals are being pushed out of sync with their natural rhythms, leading to mismatches, such as when plants shift life cycle stages faster than herbivores.

• Temperature is not the only environmental variable that affects phenology.  At higher latitudes, another critical variable is photoperiod, or daylength,  varying at different times of year.

• The reason for varying shifts is that each organism is sensitive to different environmental drivers, or shows different levels of sensitivity to a single environmental driver.

• Anthropogenic climate change leads to phenological shifts in both terrestrial and aquatic ecosystems. These shifts can lead to mismatches, with major consequences for individuals, populations, communities and whole ecosystems. Climate change is accelerating too quickly for many species to adapt through their natural phenological capacity.

• Asynchronous changes in the phenology of a broad range of interacting species have the potential to disrupt the functioning of whole ecosystems and the provision of ecosystem services on which human systems depend.

• Shifts in the phenology of commercially important marine species and their prey have significant consequences for all aspects of fisheries.

• Phenological responses in crops to seasonal variations will be challenging food production in the face of climate change. For example, fruit trees that bloom early and then experience late-season frosts result in large economic losses for orchards. 

• Phenological shifts are already complicating climate-smart agricultural adaptation for major crops around the world.

The challenge of mistimed migration

• Migration is a behavioural adaptation to seasonality. Periodic movements of animals between habitats allows them to optimize resources in multiple locations at different times of year. Migration is also necessary when seasonal air or water temperatures become unfavourable for breeding or rearing offspring. 

• Most migratory species are therefore from high latitude regions where changes in season and available resources are most marked.

• Diverse species of insects, crustaceans, reptiles, fish and mammals migrate, and many cover remarkable distances. 

• Some avian migrants nest in the high Arctic and escape its winter to lower latitudes. Cetaceans migrate between the equator and polar feeding grounds. Migrating herbivorous mammals follow seasonal changes in vegetation across continents.

• Long-distance migrants are particularly vulnerable to phenological change caused by climate warming effects, which are not uniform across regions. Local climatic cues that normally trigger migration may no longer accurately predict conditions at both destination and stopover sites along the route. The challenge is even greater for migrants returning to polar regions where the speed and magnitude of climate change are greatest.

• Consequently, many migratory species struggle to arrive when quality food is still abundant, weather is suitable for specific life-cycle stages, predation or competition pressure is lower, or parasites and pathogens are fewer.

• Advancing spring phenology in high latitudes has caused increasing degrees of ecological mismatch for migratory species, with potential demographic consequences.

How to tackle this issue?

• Phenological shifts and mismatches, attributed to climate change, have been affecting agricultural ecosystem services for decades.

• To ameliorate problems of advanced growing seasons, growing stages curtailed by heat or drought, and other climate-change repercussions, farmers have been selecting more climate-resilient cultivars.

• Adopting new techniques, trying new seeds, sharing seed banks, and exploiting extension services are all aspects of climate-smart agriculture, promoted by the Food and Agriculture Organisation of the United Nations, many NGOs, and national and sub-national agencies.

• Larger-scale efforts to strengthen the integrity of biological diversity will build resilience and adaptability throughout ecosystems. Rehabilitating habitats, building habitat corridors to enhance ecological connectivity and genetic diversity, adjusting protected-area boundaries as species’ ranges shift, and conserving biodiversity in productive landscapes are all necessary immediate management interventions.

• Preserving the integrity of functioning biological diversity, ending habitat destruction, and pursuing ecosystem restoration will bolster the natural systems upon which we depend. 

• However, without continued efforts to drastically reduce greenhouse gas emissions, these conservation measures will only delay the loss of those essential ecosystem services. For species and ecosystems to match accelerated rhythms set by climate change, time and opportunity to achieve new harmonies will be needed.

• Limited research has studied how phenological shifts and mismatches affect natural resource management and biodiversity conservation, with managers often unclear on how to incorporate the data into practice.

• The impact of phenological mismatches require further research. Maintaining suitable habitats and ecological connectivity, strengthening the integrity of biological diversity, coordinating international efforts along migratory routes, supporting resilience and maintaining genetic variation within species are crucial conservation goals. Above all, limiting the rate of warming by reducing CO2 emissions is essential.

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