The Year of the Forest – 2011
2011 has been declared the year of the forests by the United Nations and therefore I found it fitting that we begin the year looking at forests, their structure, their function and their future. For most of us the word forest conjures up images of the mighty Amazon rain forests, its tree tops reaching to the clouds and it’s murky under depths filled with exotic creepy crawlies, spectacular birds of paradise with exquisite plumage and a cacophony of frogs with bulging eyes. Although rainforests are one of many different types of forests found on earth they are often the poster child for “save the forest” campaigns internationally, their mysteries and plethora of species have fascinated scientists from all sectors of the biological sciences for decades.
Forests are found scattered across the globe, from the snow covered Arctic, to cooler temperate regions as well as the steaming jungles of the tropics. In each region, forests have evolved along with the landscape and climate making them a thriving biome. Forests can be classified in different way, one way to classify them is in terms of the leaf longevity of the dominant species; whether they are evergreen or deciduous. Another distinction is whether the forest is composed predominantly of broad leaf trees,coniferous (needle-leaved) trees, or a mixture of species.
Tropical rain forests/ jungles occupy 3% of the land surface area but are home to more than half of the world’s species. They occur mainly along the tropics and sub tropics examples of such forests are the Amazon, Congo and rain forests of New Guinea. The boreal forests are located in the higher latitudes, the conifers being adapted to the colder climates. An example of such is the Taiga forest, located between (50°N and the Arctic circle); this is the largest forest on earth, containing one third of all the trees in the world, more than all the trees in all the rainforests combined. The Taiga forest produces so much oxygen that it replenishes the atmosphere of the entire planet. The Temperate zones support both broadleaf deciduous forests and evergreen coniferous forests. These seasonal forests contain some of the largest organisms on the planet and the tallest trees in the world. The giant redwood trees in the forests along the pacific coast of North America are said to be over 3000 years old. These ancient giants are the lungs of the planet and play a vital role in the carbon and oxygen cycles of the earth’s atmosphere.
Forests can be differentiated from woodlands by the extent of canopy coverage; with forest tree canopies being denser with fewer gaps in forest cover due to the branches and foliage of separate trees meeting and even interlocking to form a consistent foliage cover. But forests are home to other organisms apart from trees, there are a multitude of birds, insects, mammals and other plants which all have a place in the forest biome. Living among the trees, organisms have evolved and adapted to forest life, each becoming specific in terms of food and territories, enabling a multitude of species to live alongside one another within the area. The density of forest growth often contributes to a high biomass per unit area in comparison to other vegetation communities and interestingly much of this biomass is found in the forest soils, among the trees’ root systems.
At first glance, the dark humid appearance of the forest floor can give the impression that little life exists there, but on closer examination there are various organisms thriving within the leaf litter. Inside the forest with its high humidity, slime moulds expand, feeding off bacteria and rotting vegetation and there is an abundance of life below the soil, with bacterial and fungal colonies thriving in the moist, dark environment. These organisms form symbiotic relationships with tree roots creating a zone around the roots which traps moisture and makes vital mineral and organic compounds available to the roots. The roots in turn provide a surface area for the fungi and bacteria. In rain forests this is particularly important because much of the organic nutrients are wash away in rain; the and bacteria and fungi colonies quickly break down the dead organisms and leaf litter and recycle the nutrients directly back to the trees root systems. It is estimated that there are more than 1 million species of fungi in the tropics, most of which are unknown to man and yet without fungi, rain forests would cease to exist. Additionally, there are other larger organisms which inhabit the soil, playing a role in decomposition activities and cycling organic nutrients through the system as well as aerating the soil as they burrow through the different layers along their journey.
Above ground there a smaller plant species, living on the forest floor, these plants are adapted to low light intensity and thrive in the shadows of the forest cover, new saplings of forest dwelling trees will also take root and grow in the undergrowth waiting for a gap in forest cover when older trees die and fall to the floor. Each species has developed its own strategy to take over the gap created by a fallen tree and for the most part it’s the fast growing broad leaved pioneer species who win. Their saplings will shoot up quickly under the streaming sunlight but these short lived species are eventually replaced by the slow growing hard wood species which make up the main component of the forest community, they will produce the next generation of the forest, and so the cycle continues.
Rain forests receive on average two meters of rain fall each year and 12 hours of sunlight a day, only 2% of this sunlight actually reaches the forest floor. For this reason most of the animal life in the forest is found within the canopy. Because the climate is fairly stable the life cycles of the different tree species is not seasonal, rather they each flower at different times of the year, providing food for the animal species all year round. Although there is often an abundance of food, collecting it is difficult and therefore forest animals tend to be smaller, more agile creatures, than those found on the open savannahs. Rain forests are home to almost 80% of all insects. This group has evolved and become specialised to individual niches allowing for a multitude of species to occupy the area, although competition for resources and parasitism maintain the balance within the system, and prevents any one species from becoming dominant. Nothing goes to waste in a forest ecosystem, each element has its place and every organism will eventually become food for another. The evolution and advancement of forests over time has made them some of the most finely balanced ecosystems in the world. However, this leaves them vulnerable to disturbance and human pressure has had a severe impact on this delicate balance.
As mentioned earlier, coniferous forests are found in the more temperate and arctic regions, their leaves being adapted to retain moisture and contain resin which makes them inedible to most animals. Overall, coniferous forests have more living matter than in rain forests, but this is found largely in the trees themselves as other animals and plants are scarce in these harsh climates.
The deciduous seasonal forests in the more temperate regions are yet another wonderful example of the circle of life. Theses broad leaved trees have edible leaves and fruits thus supporting more life forms that the coniferous evergreens. In spring the forest floor is a flush of brightly coloured flowering plants, taking advantage of the sunlight which streams through the branches of the trees, still bare from the winter. The spring blooms are a magnificent sight and draw an abundance of life to the forest; hibernating creatures emerge from their winter slumber and take advantage of the new blooms and the abundance of food provided by the new growth. As summer approaches, the leaves grow and broaden shutting out the light from the forest floor and the forest canopy expands and thickens. The warm, long days of summer are eventually replaced by the autumn winds, the forest becomes awash with shades of orange and reds as the trees shut off their leaves and prepare for the long cold winter. This spectacular transformation is so extensive that the colour change can even be observed from space.
Forests truly are spectacular systems, each fine tuned and specialized to the climate and landscape in which they exist and home to equally specialised creatures within their leafy boughs. Their abundance of biodiversity is something to behold and has been a resource for communities living along their fringes for generations. Yet these resources are now being plundered by civilizations living far beyond the borders of the forests, the demand for timber has seen commercial logging of forests increase exponentially in the last 100 years and the conversion of forest to pastures and agricultural land is further driving deforestation across the globe. Sadly the soils are not often very fertile and so within a few years the crop or grassland is unproductive and abandoned and where once mighty trees stretched into the heavens supporting an abundance of living things, there is nothing but a waste land. In the last 20 years we have lost 6 million hectares of primary forests, through logging, illegal charcoal trade, pasteurization and urbanization. For many of the specialized species the loss of their habitat is pushing them to the brink of extinction, others have already been lost forever. Forests play a role not only in creating oxygen, they also cycle water, minerals and nutrients; storing vast amounts of organic carbon within their ancient tree trunks. A tree which has grown for over 1000 years can be cut down in minutes by the relentless whirr of a chainsaw. Fortunately many countries have recognised the value of their forests and are making positive decisions and changes to protect these national treasures. Regulated logging and selective logging help to manage the forests and allow for regeneration to occur simultaneous with the logging. Some countries have banned logging entirely in an effort to protect their forests and have instead found other sources of income.
But the change needs to come from individuals as well as government, we need to recognise our part in the forests future and support the conservation of forests internationally.