This is the second part of blog written by Dr Heather McHaffie Edinburgh Network co-ordinator and Scottish Plants Officer at the Royal Botanical Garden in Edinburgh. We are very grateful to her for this wonderful introduction to the usefulness of plants.
Plants are increasingly being used as a source of fuel. There are not indefinite reserves of fossil fuels, such as coal, oil and gas, and provision must be made for a cleaner future without them. Willow is one of the plants grown to provide wood chip that is described as carbon-neutral as it is using wood grown and consumed over a short period, rather than eating into fossil fuel reserves. There is still more energy used in the harvesting and distribution than is available to provide domestic heat and this needs be considered. Other plants such as maize, cereals and oil-seed rape have been used to make bio-ethanol but currently only sugar cane is currently cost-effective and there are problems in using potential food to make fuel when this might not be the best use of resources in a world with inadequate supplies of food.
Our clothes can be made from plants. Historically nettles were a significant source of fibre, but they have been almost replaced with flax (providing linen), cotton, hemp and even bamboo. Clothing made from synthetic materials does not readily decompose and adds to the landfill problems which are already excessive.
Wood has a long history of use as a building material and still compares well with modern materials. Weight for weight wood is stronger than concrete, it can last for hundreds of years but will rot down eventually. Manufacturing cement from limestone releases large quantities of fossil CO2 into the atmosphere. It is not easily recycled and will last for a very long time.
The medicinal use of plants also has a long history. Some compounds such as digitalis derived from foxglove and aspirin from willow can be made synthetically. Others still require direct harvesting of plant material. An extract from the bark of the Pacific Yew was found to be effective in the treatment of cancer but there were insufficient slow-growing trees in the wild to provide sustainable quantities. Then it was found that the same extract, named Taxol, was present in greater amounts in the leaves of the European Yew (Taxus baccata). Arrangements have been made to collect yew clippings from large gardens and this has proved to be an excellent source.
Plants are regularly used in wetlands to purify water. Small septic tanks in country areas have an overflow that usually goes into a watercourse, but this can contain excessive amounts of phosphate causing algal blooms and un-naturally vigorous plant growth. Sending the overflow through constructed reed beds means the phosphate is taken up by growing plants. The plants can be harvested or the phosphate slowly released as the reeds decay in the winter. Plants are also used in bio-remediation for the removal of heavy metals. Some species take up unusually large amounts of zinc and lead – even gold! When harvested and carefully disposed of they can aid in the cleansing of a polluted site.
Unfortunately there are some plants in the wrong places that we do not need. Over the centuries people have taken plants from around the world and planted them in their gardens, far away from their original source. Most plants stay in gardens but some have proved unexpected vigorous and might have seeded, spread or been dumped into the countryside. These plants then multiply, become invasive and can colonise large areas to the detriment of our own native plants. Native species associate with a complex range of other species such as insects, fungi and birds. Invasive plants might provide no useful nectar, have no predators or pathogens to naturally reduce their vigour and many have become a serious problem. Examples include Giant Hogweed, undoubtedly attractive but with large, smothering leaves and dangerous to control as sunlight on sap can raise blisters on the skin. Many estates planted different species of rhododendron but only Rhododendron ponticum has increased in an alarming way, covering whole hillsides and still continuing to expand rapidly. Expensive eradication programmes are attempting to eliminate these plants.
A final benefit from plants is simple enjoyment. There are health benefits from time spent in a green environment. People appreciate the aesthetic side of woods in springtime, bluebells beneath the trees, or a meadow with a mixture of scented flowers. We can have plants in our gardens, or window boxes and can to look for opportunities to grow them in church gardens too. The best species are those that provide nectar, pollen and seed rather than some modern varieties that have large flowers but offer little else to wildlife. Wildlife-friendly gardening does not have to involve a jungle of nettles and brambles but can be achieved with careful selection of species. Minimalist gardening with hard surfaces and a few neat shrubs will not provide the assortment of habitats of a less manicured plot perhaps with a small pond and a mixture of plant-types. The latter garden will be a rewarding place to spend time, enjoying the added interest of species which spontaneously arrive where the appropriate conditions are provided. Living in a part of the world rich in natural resources, enough rain and enough sunshine, we are very fortunate and need to take time to appreciate what we have and to take care of it.
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