Restoring the effects of degradation
Biodiversity in Australian landscapes has been very severely degraded through a multitude of activities over the last 200 plus years since European settlement. Principal activities have been those associated with clearing the land for timber, farming, grazing, various secondary industries, mining and development of urban communities. Invasion by exotic weeds has occurred in association with these activities; degradation of habitat and in some cases complete loss of all vegetation has occurred.
In the Moggill Creek Catchment connectivity between upland and lowland areas was initially lost more than 80 years ago through widespread logging of the forests followed by further clearing for agriculture, horticulture, and grazing; this was exacerbated by residential development and rural land management practices.
What has happened to the soil resources?
Extent of erosion on slopes since the land was first cleared is difficult to estimate. Sheet erosion would have been significant, associated with past farming practices (pawpaw, bananas and dairying) on steep slopes, and in specific log loading sites associated with the early forestry activities. Gully erosion would have been significant also, but later agricultural practices including ploughing and establishment of grass pastures would have hidden much of the evidence. Severe gullying has occurred in the last 30 years associated with old mountain bike trails.
When considering strategies for restoring elements of an ecosystem it is important to have some idea of the degradation that might have occurred to the soil, since it will be the main resource that will be managed to introduce vegetation.
Land degradation has severe impacts on landscape processes and soil properties. Clearing has led to major changes in land cover and interrupted the soil water and nutrient cycling associated with each of the unique ecosystems that were developed over thousands of years. Types of degradation that have ensued are:
- Loss of key soil organic matter processes important for biological health (including plant growth)
- Loss of biological diversity such as earthworms and other macro invertebrates that assist in the breakdown of soil organic matter and the maintenance of soil structure so important for air and water movement into soils,
- Soil erosion (surface and gully), and instability of stream banks and beds.
- Physical degradation (e.g. compaction and loss of soil strength) from mechanical equipment and grazing animals.
- Loss of fertility and soil acidification through unsustainable land management practices associated with practices such as fertiliser additions and introduction of certain pasture species.
- Changes in landscape and soil water processes that lead to land slip, salinisation of surface water, groundwater and soils