Biodiversity, deforestation and conservation

Last time

Before we start: last time, in The nitrogen cycle, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.

Every species counts

A tropical forest can hold thousands of species in a single hectare. When the trees are cut, many of those species lose their home and may vanish for ever. Today: biodiversity, why habitats are destroyed, what deforestation does, and how endangered species can be protected.

Biodiversity

Biodiversity is the number of different species that live in an area. A rainforest has very high biodiversity. A wheat field, with one crop and few other species, has very low biodiversity. Biodiversity matters: species form food webs, give us medicines and food, and are part of stable ecosystems.

Habitat destruction

A habitat is destroyed when land is cleared for farming, housing, roads, mining or logging. Pollution of water and soil also destroys habitats, and so does draining wetlands. When the habitat goes, the species lose food, shelter and breeding sites, and their numbers fall.

Deforestation

Deforestation is the permanent removal of forests. Trees are cut for timber, fuel, farmland and building. It reduces biodiversity, since species lose their habitat and food webs break down. Fewer trees means less photosynthesis, so less carbon dioxide is absorbed, and burning the wood adds more.

Soil and water

Tree roots hold the soil together. Without them, rain washes the soil away: soil erosion. Trees also take up water and release it by transpiration. Without them there is more run-off and flooding. Eroded soil can end up in rivers, and the land may turn into desert: desertification.

Endangered species

An endangered species has so few individuals left that it may become extinct. The main causes are habitat destruction, hunting, pollution, climate change and invasive species. Extinction is permanent: once the last individual dies, the species cannot return.

Conservation methods

Protected areas, such as national parks, safeguard the habitat. Laws and quotas stop hunting and fishing too much. Captive breeding in zoos raises numbers, and the animals can be released later. Artificial insemination and IVF help them breed. Seed banks store seeds of rare plants, as a back-up in case wild plants die out. Education and monitoring populations help people to protect species.

Reforestation

Replanting trees restores habitat, holds the soil, and takes carbon dioxide out of the air by photosynthesis. It takes decades for new trees to match the biodiversity of an old forest, so protecting forests is better. Sustainable logging cuts only some trees, and replants them, so the forest keeps its structure.

Why species matter

Wild species are a source of medicines and of genes for future crops, so losing one loses something we may need. Removing one species can upset a food web and affect many others. Many people also value wildlife for its beauty and for tourism.