LECTURE18 Human Disruption and Ecological Restoration Human impacts The ways of human disruption of ecosystems: -Over-hunting, overharvesting, overgrazing etc. -Deforestation, Pollution, Cultural reasons. Introduction of exotic species, Development, Urbanization, Change of land use, Simplifying ecosystems: In modifying natural ecosystems for our use, we usually simplify them; in the case of forests and woodlands – into monoculture. We spend a lot of time, energy, and money trying to protect monocultures from continual invasion by unwanted pioneer species, which we call weeds if they are plants, pests if they are insects or other animals, and pathogens if they are fungi, viruses or disease-causing bacteria. Often species undergo natural selection; a process illustrating Garret Hardin’s first law of ecology: “We can never do merely one thing”. Any intrusion into nature has multiple effects, many of them unpredictable because of our limited understanding of how nature works. Our actions should take into account the second law of ecology, or principle of connectedness: “Everything is connected to and intermingled with everything else”; we are all in it together. There is no independence in nature. Need for ecological restoration More than a century of severe habitat alteration has changed our forests and ecosystems to such an extent that they can no longer heal themselves. Restoration is a multi-faceted discipline, ranging from hands-on work to theory, covering everything in the entire "ecosystem" from the smallest insects all the way up to us as responsible humans. Need for ecological restoration The motivations for ecological restoration range across ideas such as biodiversity loss; research into the functioning of ecosystems; compliance with public mandates The concept of restoration is simple-choose an ecosystem to emulate and try to recreate it in a chosen area But ecosystems are dynamic entities which vary not only in space but also in time Understanding ecological restoration 1: is protecting or managing the natural environment to maintain the beauty, interest, biodiversity, and other intrinsic values of the natural world 2: establishing a balance between our own species and the rest of the biosphere. The two aspects are interrelated! Examples of Species Interaction Process - Some grasses that grow in open areas form dense mats that prevent seeds of trees from reaching the soil and germinate (Tai Mo Shan) Later successional species cannot germinate or obtain light, water & nutrient Examples of Species Interaction Ecological restoration is an activity at which everyone wins: when successful, we are rewarded by having returned a fragment of an ecosystem to its former state; when we fail, we learn a lot about how ecosystems work, provided we are able to determine why the failure occurred. Examples of Species Interaction The success of ecological restoration can be judged by five criteria: Sustainability; Invasibility; Productivity; Nutrient retention; and Biotic interactions Species Interaction Sustainability; is the reconstructed community capable of perpetuating itself? Or can it be sustained only if managed by people? Species Interaction Invasibility; does the reconstruction yields a community that resists invasions by new species? Species Interaction Productivity; is dependent upon efficacy. A restored community should be as productive as the original. This is a useful measure of community performance as it integrates many processes; including photosynthesis, respiration, herbivory, and death. Species Interaction Nutrient retention; Although all ecosystems are open to nutrient fluxes, some are more open than others. Species Interaction Biotic interactions; Reassembly of formerly associated plant populations often – but not always – leads to reconstruction of the entire community. Species Interaction There are fundamental of ecological questions, illustrating the profound contribution restoration ecology could make to ecological science; some of these questions are: Species Interaction does increasing the species diversity of a community increase its stability and resilience? how does genetic diversity within component species influence the stability of an ecological community? Species Interaction if species evolve together, do they tend to become more compatible or less so? how does the age structure of component species influence an ecological community? Etc. Species Interaction In all operations, whatever the endpoint, the following are important considerations: (1) speed of attainment; (2) cheapness; (3) reliability in attainment; and (4) stability; In doing restoration: There are a number of ideas and steps: Soil replacement: Direct treatment: Physical treatments: Nutrient addition: Treating toxicities: Adding species: In doing restoration: Soil replacement: simply disregard its individual problems and import a new soil surface, on which a new ecosystem can quickly be established. In a crude sense, this may require little understanding of what is wrong with the site. In doing restoration: Direct treatment: in many situations, however, soil cannot be imported or replaced, and the material existing on a site has to be treated directly to achieve restoration. In doing restoration: Physical treatments: efforts are made to loosen subsoil and topsoil by ripping the substrate to depths up to 1 meter. This is then followed by shallower cultivations, to about 20 cm. Finally, the soil surface is carefully prepared to provide a good seedbed, and a favorable season is chosen for sowing. In doing restoration: Nutrient addition: after all the above problems, there is obviously the need for nutrients. Treating toxicities: Adding species: In doing restoration: Ecological restoration is now being recognized as an important tool that can produce additional improvements in the quality of our resources to support diverse, productive communities of plants and animals that provide significant ecological and social benefits. In doing restoration: Restorationists use the best ecological science available to understand and reverse the sources of damage, restoring the diverse native plant and animal communities, reinstating natural disturbance regimes such as light surface fires, and developing harmonious relationships between people and the land. Why can't we just let nature take its course? More than a century of severe habitat alteration has changed our forests and ecosystems to such an extent that they can no longer heal themselves. Why can't we just let nature take its course? The goals of ecological restoration are to approximate natural ecosystem structure (plant and animal compositions and patterns) and processes (e.g. disturbance regimes such as fire, nutrient cycling, and productivity) that were characteristic of the system before disturbance. Why can't we just let nature take its course? These natural ecosystem structures and processes are critical for maintaining an ecologically sustainable forest and restoring the diversity of wildlife and plants that depend on it. Why can't we just let nature take its course? The model is based on rigorous science and incorporates some of the longest-running ecosystem monitoring data, inventory, and research. An ecologically based treatment is site specific. Principles and framework Scientific framework; Social and political framework; Operational framework; Ecosystem Management framework; Economic framework; Ethical framework; Temporal framework. Principles and framework Scientific framework; Restoration treatments are constantly adapted to reflect new scientific understanding Social and political framework; Ecological restoration recognizes the important role people play in the landscape Principles and framework Operational framework; This defines where treatments are applied on the grounds Ecosystem management framework; integrated with overall ecosystem conservation and management goals Principles and framework Temporal framework; A balance between short term (1-10yr) and long term perspectives is essential Tai Tong: Success or failure Tai Tong East Borrow Area is located in the northwestern New Territories. The site comprises of dissected ridges radiating from it to the Yuen Long Plain. Besides the deeply incised valleys, which run parallel in a northwesterly direction, gullies are also abundant. Tai Tong: Success or failure The vegetation was dominated by the secondary growth of Pinus massoniana, a large proportion of which had been killed by the nematode disease Excavation began in the early 1990s; and the site is excavated to an average depth of 8 metres, Tai Tong: Success or failure This human action resulted in complete removal of the vegetation and topsoil, which is a typical example of soil destruction After excavation the soil is depleted in organic matter and nitrogen, and also acidic and infertile compared to the original soil. This poses great problem in ecological restoration of the site. Tai Tong: Success or failure Nonetheless, the excavated site was rehabilitated. The slopes were recontoured to blend with the surrounding topography, covered with a 500-mm layer of in situ materials, hydroseeded, and pit planted with trees. Tai Tong: Success or failure Hydroseeding technique was introduced to Hong Kong in the late 1970s. It is developed for the rapid establishment of grasses, and sometimes shrubs, slopes or disturbed areas. The slurry containing a mixture of seeds, fertilizer, mulch fiber, soil solidifying agent and malachite green is sprayed onto the soil by use of a high-pressure jet. Tai Tong: Success or failure Tai Tong: Success or failure The established grasses help to moderate microclimate conditions and ameliorate soil. This will then pave the way for the planting of trees to enhance biodiversity and accelerate development. Six months after germination of the hydroseeded grasses, the slope is planted with trees to further stabilize the soil, accelerate forest development and enhance biodiversity. Summary When damaged landscapes are restored, they undergo a process of recovery known as “succession” Understanding succession helps answer questions about characteristics of wilderness & help ecosystem restoration Summary Early successional species are fast growing During succession, changes in species are due to facilitation, interference, life-history differences & chronic patchiness