Sustaining Ecosystems Study Guide

Polar environments, found at the Earth's highest latitudes around the North and South Poles, are defined by their extremely cold temperatures, often below freezing for most of the year, and extensive ice cover. These regions include the Arctic (a frozen ocean surrounded by landmasses) and the Antarctic (a continent covered by a massive ice sheet, surrounded by ocean). A key characteristic is the presence of permafrost, ground that remains frozen for at least two consecutive years, which influences soil structure and restricts vegetation growth. Unique ecosystems have adapted to these harsh conditions, featuring specialised flora like lichens and mosses, and fauna such as polar bears, penguins, seals, and various bird species. The low biodiversity and slow decomposition rates are also distinctive. Globally, polar environments are crucial for regulating Earth's climate. The vast ice sheets and sea ice reflect solar radiation back into space, a phenomenon known as the albedo effect, which helps to keep global temperatures stable. They also act as massive freshwater reservoirs; the Antarctic ice sheet alone holds about 70% of the world's freshwater. Changes in these environments, such as melting ice, contribute to rising sea levels and altered ocean currents, impacting weather patterns worldwide. Additionally, they are valuable for scientific research into climate change, atmospheric conditions, and unique biological adaptations, providing data essential for understanding our planet's future.

Tropical rainforests are unique ecosystems found near the Earth's equator, characterised by high temperatures and abundant rainfall throughout the year. These conditions support an incredibly diverse range of plant and animal life, making them biodiversity hotspots. A key structural characteristic is their vertical stratification, meaning the forest is organised into distinct layers from the forest floor to the emergent layer, each with its own microclimate and adapted species. Trees in these forests often have shallow roots due to the quick nutrient cycling in the thin, infertile topsoil, and many possess buttress roots for stability. The dense canopy restricts light penetration, leading to a dark, humid understory. Epiphytes, such as orchids and ferns, grow on other plants to reach sunlight. Rapid decomposition of organic matter, facilitated by high temperatures and humidity, quickly returns nutrients to the soil. The climate is driven by the Intertropical Convergence Zone (ITCZ), which brings consistent convectional rainfall. These distinctive characteristics contribute to the rainforest's exceptional productivity and vulnerability to environmental change.