Forests in a Global Context

Q1
What is the relationship between human evolution and grassland and how does this relate to global distribution of forests?
Grasslands developed approximately 25 million years ago, and together with the modern homosapiens residing in Africa, they both helped each other. The relationship between grasslands and humans is extremely complex, the grasslands provide a majority of human nutrition and in turn the humans assist in their spread. By felling once tall standing forests and turning them into grasslands, the humans had a way to feed the animals they herded which in turn provided them with a source of meat and other vital nutrition necessary to sustain life for growth. Furthermore the grasslands also provided a fertile region for he humans to plant various types of crops such as maize, rice and wheat etc., further providing evidence that humans were once not only hunters but also gatherers.
Once all existing value was used from the grassland, the prehistoric humans used fire as a mean to control the grassland, thereby expanding it to allow more area for animals to graze and for them to gather, or as a mean of clearing out and inhibiting woody vegetation in a new area for them to use. Burning the area when soil became infertile provided many benefits. The young plants provided an excellent source for the herds to graze on and also acted as bait to attract wild animals (potential food).
Humans have affected the global distribution of forests by burning off and implementing the slash and burn method which in turn were a major factor in seed and plant dispersal where seeds of plants were incoherently taken and planted elsewhere. The humans also cut down forests to use as a source of maritime and also trading power. An example of this is with the ancient Cedrus Libani forests. The ancient Phoenicians cultivated this cedar to use in building warships. The once magnificent forests were all cut down to use as fuel, trading and other resources. Today the forests don’t even exist anymore albeit a few scattered and degraded cedars located randomly.

Q2 How does an understanding of the chemical reaction of photosynthesis explain the climatic and soil factors that determine the nature and distribution of forests?

Understanding the chemical reactions of photosynthesis helps to determine the distribution of forests. The 6 major factors: Carbon dioxide, radiation, temperature, water, nutrients and oxygen all play a major role in where forests lie. The basic photosynthesis equation where carbon dioxide, water and light energy is transformed into glucose and oxygen provides use with the backbone to determine the distribution of forests.
Forests are more productive is regions that are more moist, warm, well drained and on fertile soils. Such climactic factors which determine the nature and distribution of forests are radiation, temperature and water availability. The most optimized climate for the growth of forests are places with a lot of light, especially in the equatorial region where sunlight and temperatures are both high with high rainfall means that the forests there are able to grow extremely fast and densely. The moist atmosphere means that water is readily available; as a result there plant is not under water stress so the stomata can remain open during the daytime without much transpiration, even in high temperatures. The high temperature and sunlight provide the required amounts of light radiation for photosynthesis to occur. Furthermore regions of high rainfall will also yield more forest productivity as it allows the stomata to be open longer which increases CO2 uptake and provide H2O to the roots.
Soils also make a major impact on the nature and distributions of forests as the will be more productive on fertile soils or on soils where fertilisers are added. Soils which are deep contain more essential nutrients and water which include N, K, Ca, Mg, P, S, Cl, Fe, B, Mn, Zn, Cu, Ni, Mo which are all necessary for the plant to survive and grow. Soil texture also has a factor on the nature and distribution of forests, sands which have plenty of oxygen, don’t contain adequate CO2, and clays inversely can hold plenty of H2O but not much oxygen. Neither of which are able to support a fully fledged rainforest. Loams contain a large range of particle sizes so they are in turn able to hold adequate amounts of air and water and thus can is the best type of soil for forests.

Q3 What are the features of tropical forests and under what environmental conditions do they occur

Tropical forests can typically be divided into 3 similar but distinct forests, which are all governed by the length of the dry seasons. The 3 types include rainforest, moist deciduous and dry forests.
Tropical rainforest are largely located in South America, central western African and south East Asia. Due to most being located on the equator the day length is relatively constant, without any seasonal change in temperature or climate. Humidity is high all year around with an evenly distributed high rainfall and warm temperatures all year round. Their high rainfall often results in tall trees which gives the canopies multiple distinct layers. Within these canopies lies a diverse ecosystem which contains up to 70% of all animals and plants, 30% of birds and 90% of all invertebrates and other microorganisms. On the rainforest floor, the warm and wet conditions results in a rapid decomposition system which leaves little debris behind, as a result all the nutrition is located at the surface and trees have very shallow roots, which have grown buttresses to hold them upright against the wind. Tropical forests can refer to both tropical moist deciduous forests and also tropical dry forests. Tropical moist deciduous forests being located next to adjacent to rainforests mean they also straddle the equator. Moist deciduous like rainforests also have high annual rainfall but with a pronounced dry season albeit with a much less diverse ecosystem. They like rainforests have high annual rainfall but with a distinct dry season. As a result the evergreen tree’s present in rainforests have been replaced with deciduous trees such as Tectona grandis which lose their leaves during the dry season to reserve water.
Tropical dry forests have the longest length of dry seasons, which at times can be quite severe. As a result, dry forest trees are often very small and wildly scattered. Due to the lack of water during the dry season they are not able to grow tall and are either deciduous or semi deciduous and encompass an important family of plants, the large and economically important leguminosae family of plants, which also happen to the be the 3rd largest land plant family.

Q4
Discuss trends in the rates of forest loss and forest gain. Where is this occurring? What are the trends in plantation establishment? Discuss the differences between tropical forests and boreal forest in the distribution of carbon in biomass and soil.
The 2 forms of forest loss can occur in is deforestation and forest degradation. Deforestation is the destruction of forest and converting it to an alternative permanent forestless land. Although having adverse effects on the ecosystem, it is necessary to survive on the earth and if the population is to continue to grow.
Degradation of forests is the process where a forest’s ecosystem is degraded, but the area remains forested which enables the forest to return. Since the time of the hunter gathers, deforestation rate has increased since the age of agriculture. Over the past 10000 years forest cover across the globe as been reduced from half the globe’s surface to about one quarter today. There have been multiple cycles of depletion and recovery, with a current trend of deforestation occurring only in the tropics and forest gains the temperate forests. Although forestation has an extremely high rate, it has since 2000 decreased. Deforestation is almost exclusively occurring within the tropical developing world where they need the space to expand for agriculture and better land use; appearing in places such as Brazil, Indonesia and Africa. Australia too has a deforestation record; however it was due to the decommissioning of large areas which were previously classified as forest due to improved remote sensing technology and to a smaller extent fire and drought.
Plantations around the world are increases and as a result 7% of all forested area in 2010 is from these establishments. Furthermore, North America and Europe at both continents which are reforesting, with Asia also having the highest change of planted forests from 1990 to 2010. Currently China is the only country which has a net gain of forest of more than half a million hectare according to the FRA from 2005 to 2010 and thus is the world leader in forest plantation establishments and forest rejuvenation.
Located around the equator, tropical forests store most of their nutrients which includes carbon within in the biomass where as boreal forests, which are located mainly in the northern hemisphere have most of the nutrients and carbon within the soil mass.

Q5
Accepting the occurrence of fire is necessary for those living in or near the Australian bush. How do we balance conservation of a ‘natural’ forested environment against the need to reduce risks to life and property?

Q6
Outline the potential impacts of forest fire on water quality and water yield, and briefly explain why these impacts can vary for different forest types.
Following the events of a forest fire, rates of runoff and erosion often increase as a result of the disturbance of the landscape. Typically the most effect section by the fires is the soil surface which in turn affects the quality of the drinking water and how much water it yields.
The combustion of organic matter and heating the soil up results in the production of ash and charcoal like substances which will then in turn contribute to the release of numerous other nutrients such as metals and toxins harmful to humans into the water ways and aqueducts leading to the major reservoirs. The loss of vegetation reduces the amount of plants
Several factors may contribute to water quality impacts following fire. Rates of runoff and erosion often increase as a result of landscape disturbance, particularly on the soil surface – i.e. increased soil water repellence, loss of surface vegetation and canopy cover, and ash sealing of soil pores (Shakesby and Doerr, 2006; Sheridan et al., 2007b). Combustion of organic matter, soil heating and the production of ash and charcoal contribute to the release of numerous nutrients, metals and toxins that might otherwise be unavailable for transport into waterways. For example, ash contains particulate carbon, various nutrients, trace metals and other contaminants (Amiro et al., 1996; Goforth et al., 2005; Johansen et al., 2003). The loss of riparian vegetation reduces the buffer effect that traps sediment before it enters streams and means that there is less shade to prevent increases in stream temperatures (BAER, 2009). Fire suppression activities may also contribute to water quality impacts, particularly the construction of control lines with bulldozers and possibly the use of fire retardants and fire suppressant foams (Boulton et al., 2003; BAER, 2009).
The impact of bushfires on water quality can be highly variable for many of the individual water quality constituents (Smith et al., 2011). This variability is caused by a number of landscape influences and climatic factors, most notably rainfall. High magnitude and intensity rainfall events soon after fire generate the largest impacts on water quality and sometimes trigger extreme erosion events (e.g. localised flash floods, large floods and debris flows). For example: two large storm events eroded most of the annual sediment yield in two small headwater catchments of the East Kiewa River in the first year after fire in north-eastern Victoria (Lane et al., 2006) a very high intensity, short duration storm event in the burnt Upper Buckland River catchment (north-east Victoria) generated debris flows resulting in very high sediment concentrations (59,000 mg L-1 or 129,000 NTU – Nephelometric Turbidity Units) (Leak et al., 2003) and dissolved oxygen concentrations near zero levels (EPA 2003) a large rainfall event in the burnt catchment area of the Gippsland Lakes in eastern Victoria caused flooding which resulted in elevated nutrient concentrations and a prolonged blue-green algae (cyanobacteria) bloom (Cook et al., 2008), and an intense summer storm in the catchment area for the Ovens River in north-eastern Victoria resulted in concentrations of iron, copper, zinc, chromium, arsenic and lead that were 47, 32, >50, 40, 4 and 33 times the pre-event concentrations, respectively (North East Water, 2003).
Debris flows in burnt forest environments are an emerging area of research in Australia and have only recently been recognised as a major contributor to water quality impacts following fire (Nyman et al., 2011). Occurring in steep, upland terrain they are a fast moving mass of unconsolidated saturated debris, which cause large amounts of channel scour and deliver large quantities of sediment downstream.