Changes in ecosystems Biology Stage 1 Biology Stage 3 Chapter 5 Biology ATAR Year 11 Chapter 6

Keywords Ecosystems Ice cores Ecological succession Primary succession ◦ Pioneer plants Secondary succession Climax community Natural disturbances Fire

Changes over time Ecosystems are dynamic and can change dramatically over time Evidence for change in the past can be found in the fossil record and the ice cores These indicate a wetter climate in many parts of Australia

Ice cores and evidence of change Ice cores are retrieved from the poles They are analysed for: ◦ trapped gas bubbles and the concentration of atmospheric gases ◦ presence or absence of traces of organisms This information is interpreted and may give some indication as to past climates and ecosystems.

Ice cores and evidence of change This implies that one year may therefore be represented by multiple layers It is impossible to say how many layers could actually represent one year. The further down the ice core, the more compressed the layers are Layers from the lowest levels may be so compressed that they are difficult to decipher Ice cores have layers and are used as a dating method Assumptions Each layer in the ice core is counted as one year Problems with this dating method There is evidence to show that layers represent different conditions in the one season, not that one layer represents one year

Ice cores and evidence of change Nevertheless, ice cores can still be a tool to investigate the past However: all assumptions should be clearly stated no interpretation of results can be taken as definitive

Ecological succession Succession is the gradual change that happens in an ecosystem It is the progressive change in a community over time, with one community being replaced by the next Natural disturbances or human intervention can lead to succession events Depending on the severity, type and extent of the disturbances, primary or secondary succession will follow.

Primary succession Nudation When an area is devastated by, for example, a volcanic eruption or tsunami and no living organisms are left Primary succession The first stage in the colonisation of a denuded area Pioneer plants begin the process.

Primary succession Plants Rapid growth Rapid reproduction Relatively short- lived Herbaceous ◦ eg. annual & perennial grasses, small shrubs Animals Small herbivores ◦ eg. insects, mice

Primary succession 1. Mosses & lichens Organic matter + weathered rock particles shallow soils 2. Small herbaceous plants Increased organic matter + root action deeper soils 3. Small shrubs Increased nutrients + root actionsoils become more fertile 4. Trees Mature soils

Primary succession

Secondary succession Occurs after a disturbance of an area It could be because of fire, flooding or human intervention such as logging There are still surviving organisms left in the area The recycling of matter and flow of energy are interrupted Organisms recolonise the area The number and kinds of organisms may be different from the original ecosystem

Secondary succession

Climax community The end of succession is marked by a climax community Plants ◦ Slow-growing ◦ Long-lived ◦ Woody plants Supports an abundant and diverse range of animal species Example Old-growth karri forests in WA

Impact of fire Fire has shaped the Australian landscape Types of fires Canopy Understorey Both Fire frequency 10 year cycle Shrubbery and small, fast-growing trees year cycle Eucalyptus trees become established 100+ year cycle Old growth forests

Impact of fire Biotic factors Immediate impact Loss of vegetation Reduction of leaf litter Decrease in animal numbers After the fire Proliferation of new, fresh growth  sustains animals that may have survived the fire eg. wombats & echidnas  attracts wallabies, birds, small mammals and insects Abiotic factors Ash from the fire creates nutrient-rich soil New open spaces ◦ give maximum light ◦ increase heat exposure

Adaptations to fire Most Australian plants have adapted to fire Rapid regeneration & regrowth occurs Eucalypt species Oil in leaves result in a rapid, hot fire that destroys the crowns but only chars the bark Have thick bark (protects phloem from damage) Have dormant buds under their bark, especially at the base of the stem (lignotubers) Other adaptations: Rhizomes Underground stems that can produce roots and shoots Seeds Thick, hard outer coats Heat and smoke are needed to crack them open

Fire regimes Long term changes to an ecosystem can occur from sequences of fires known as fire regimes These changes can be determined by: 1. Season in which fires occur 2. Intensity of the fire 3. Frequency of the fire Historically, Aboriginal populations regularly burned sections of the bush to aid hunting and stimulate new growth of plants for food. This human intervention disrupted the natural patterns of succession This is called deflected succession

Fire regimes Patch burning Burning smaller patches of land, leaving other areas to provide shelter and food for animals Controlled burning CALM conducts controlled burning fire regimes to reduce the undergrowth This helps to reduce the likelihood of wildfires in the summer