Volcanic eruptions can have devastating effects on the plants and animals that make up the surrounding biosphere. In addition to the destruction caused by the volcanic explosion or lava flow, eruptions can also lead to death from famine, earthquakes, tsunamis or by increasing water acidity.
Plants, wild animals and livestock in the area surrounding a volcano are often almost completely wiped out after an eruption. However, these effects are usually quite short term, as plants and animals quickly return to these areas. In fact, volcanic soil is quite nutrient rich, meaning plants can come back within a few years, depending on the climate. For instance, some lava flows on the island of Hawaii's rainy side have started to become repopulated with plants in as little as two years, while lava flows on the dry side have stood bare for over a decade.
Although volcanoes usually only affect the biosphere in their immediate vicinity, large enough explosions can have global effects. When an explosion is large enough to propel ash and debris into the stratosphere, it may lead to a sudden global warming or cooling that could have devastating effects on many species. Small particles in the stratosphere may block out the sunlight and lead to a decrease in global temperatures. Larger particles may let the sunlight in, but trap any heat radiation from escaping the planet, leading to a temperature increase.