Land Management Issues

Introduction to Ecosystem Services & the Millennium Ecosystem Assessment

Humanity has always depended on the goods and services provided by the biosphere and its ecosystems.  These goods and services such as; food, fiber, clean water, oxygenated air, and climate regulation, are known as ecosystem goods and services.  However, in our efforts to develop and provide resources for an increasing human population our actions are diminishing the ability of many ecosystems to provide goods and services to meet human demands (Daily 1997; MA 2005).

Humans are obviously having a massive impact on ecosystems.  To get an overview of the current state of the world’s ecosystem, a project called the Millennium Ecosystem Assessment (MA) was started in 2000.

The MA was an international work program designed to meet the needs of decision makers and the public for scientific information concerning the consequences of ecosystem change for human well being and the options for responding to these changes (MA 2005). 

Sustainable management of tropical savanna and rainforest areas is especially important as these areas are under increasing development pressure. 

There are many and varied land management issues facing these systems worldwide.  Nevertheless, based on the findings of the MA and other research, four key issues were identified as the forefront of sustainable management of tropical rainforest and savanna ecosystems;

• deforestation and land clearing,
• grazing and altered fire regimes leading to woody thickening in savannas, or conversion to grasslands,
• the effect of these issue on the carbon cycle and the effect of climate change on tropical ecosystems, and
• the loss of ecosystem services due to the degradation of tropical ecosystems

The management of these issues among others will be covered in module 4.  The following subsections introduce each of these four issues and draw on readings referred to again in module 4.

Deforestation & Land Clearing

Tropical deforestation and land clearing is currently the most significant threat to global biodiversity.  This is due to both the rapid rate and extent of clearing and degradation as well as the ecological complexity and diversity of these ecosystems (Laurance 1999; Hill and Hill 2001). 

Actual rates of deforestation are difficult to determine and estimated rates of loss vary.  Based on FAO data an average of 15.4 million ha of tropical forest was destroyed annually during the 1980’s, while another 5.6 million ha was logged.  During the 1990’s the rate of global tropical deforestation decreased to around 10.2 million ha annually, however, estimates of global tropical deforestation from 2000-2005 indicate that average annual losses have increased to 10.40 million hectares (FAO data discussed by (Butler 2006)).  This is equivalent to an area of tropical forest twice the size of Tasmania lost annually.  Although, analysis by other organisations have produced lower estimates e.g. 5.8 millon ha of tropical forest lost annual between 1990 and 1997, with a further 2.3 million ha visibly degraded (Achard, Eva et al. 2002). 

Figure 5. Extent of Terrestrial Biome Conversion Before 1990’s (powerpoint) Figure from the animated MA powerpoint presentation 2005

In addition to deforestation of tropical rainforests, extensive areas of tropical savannas are cleared and/or degraded through grazing, harvested for fuel-wood or converted to alternative land uses, such as cash cropping or cultivation, mining, or human habitation.

Fire & Grazing

Tropical Savannas

Humans have modified two important savanna determinants – fire regimes and herbivore regimes – in different ways in different savanna areas.  In some regions this has resulted in severe land degradation and an associated loss of land productivity.  The effects of altered fire and grazing regimes has resulted in two contrasting phenomena, woody thickening and the conversion of savanna to grass dominated systems.

In savanna ecosystems fire is an inevitable consequence of the annual cycle of profuse herbaceous growth during the wet season followed by curing of this material in the dry season, when conditions are ideal for burning (Hutley and Setterfield 2005).  Savanna fires typically burn through the ground surface fuels and high soil temperatures persist for mere seconds, exerting limited impact on seed banks and below ground regenerative plant parts. 

Likewise, herbivory, in the form of native ungulates and invertebrates, such as; grasshoppers, caterpillars, ants and termites is a natural determinant of savanna ecology.  However, human induced changes to fire frequencies and grazing pressure have exacerbated the effects of these factors.  For further details refer to the sections of fire and herbivory in the additional reading listed below.

Additional Reading

• Hutley, L. and Setterfield, S. (2008, in press) “Ecosystems: Savanna”

Tropical Rainforests

Within tropical rainforest systems fire is predominantly a human induced ecological disturbance that increases fragmentation, erodes forest edges and degrades these ecosystems. 

Burning alters rainforest composition and structure and while common tree species suffer the greatest total mortality, rare species are most likely to become locally extinct and often do not  return to the system (Gerwing 2002). 

The crux of the fire problem in tropical rainforests is not so much the introduction of fire into these ecosystems, but the frequency with which they are being burned and the increased vulnerability to fire due to increased fragmentation and forest edges (Cochrane 2003).  For further details refer to the additional reading below.

As discussed above a substantial proportion of cleared or logged rainforest is converted into grazing land and grazing is a significant contributing factor to the degradation of tropical rainforests, particularly in the Amazon Basin (Laurance 1999).  The conversion of closed tropical rainforest systems to more open wooded systems with a grass understorey also increases the vulnerability of remaining rainforest fragments to fire.

Additional Reading

• Cochrane, M.A. (2003) “Fire Science for Rainforests” Nature 421:913-919

Table 1.  Comparison of Fire and Vegetation Responses in Tropical Savanna and Rainforest Ecosystems

Tropical Savanna	Tropical Rainforest
Fire a regular disturbance from both natural and human induced ignition	Fire is not a regular, natural disturbance, however, human interactions have increased the role of fire in these systems
Vegetation dry and flammable	Vegetation moist and relatively fire resistant, except during periods of drought stress
Savanna plants have a suite of adaptive traits to survive and rejuvenate after regular fires	No plant adaptations to withstand fire
Savanna vegetation rejuvenates after fire and fire is a critical prerequisite for the survival and reproduction of many plant species	Fire is an unintended ecological disturbance that increases rainforest fragmentation, erodes forest edges and degrades tropical rainforests

Climate Change

The greenhouse effect and global climate change is perhaps the most significant global environmental issue.  Levels of greenhouse gases in the atmosphere have risen significantly over the last 200 yrs due to increased emissions from anthropocentric sources, refer to Figure 6.  Mean global temperatures have also risen over the last 50 years (refer to Figure 7).  Although there is some contention over the role of natural factors in producing global climate change, and the measures required to address this issue, it is increasingly evident that the Earth is undergoing relatively rapid climate change.

• Figure 6. Concentrations of Greenhouse Gases  (Powerpoint)
• Figure 7. Mean Global Temperatures  - (Powerpoint)
  Figure from the Intergovernmental Panel on Climate Change, Figures from IPCC Reports “Global temperature change, 1861-2000 and 1000-2000”    

Perhaps the most dramatic impact of global warming is a predicted average sea level rise of approximately 50cm by 2100 (IPPC 2001).  The upper limit prediction would result in a rise of nearly 1m, flooding 17% of Bangladesh and 12-15% of the arable land in Egypt and would almost destroy the island nations of the Maldives and Kiribati (Osborne 2000).

Increasing temperatures and altered rainfall patterns will also alter the geographic range of organisms including plants, animals, diseases and their vectors.  In temperate zones increased temperatures could increase plant production through extended growing season.  In the tropics, however, plant production may decline through increased heat and drought stress.  A key factor in whether plant and animal communities can adapt to global climate change is the speed and extent of the change.

Tropical rainforest and savanna ecosystems are important in the global carbon cycle as both carbon sources (though deforestation, conversion to alternative land uses, emissions from fires, and decomposition of vegetation) and carbon sinks (through rapid regrowth of savanna vegetation following disturbances, such as fire, and CO2 stimulation of photosynthesis, particularly in rainforests). 

The net role of these ecosystems in the carbon cycle and their ability to mitigate the effects of global increases in CO2 remains under contention mainly due to data limitations and scientific uncertainties (Achard and Eva 2004).  Nevertheless due to increased fossil fuel use and a decrease in the rate of tropical deforestation and land conversion the importance of terrestrial ecosystems as carbon sinks is increasing, as shown by data from the Millennium Ecosystem Assessment (2005) (Figure 8.).

MA animated slides 54 & 55 maybe combined as one picture with the two graphs side by side?

Figure 8. Sources and Sinks of Carbon Dioxide

Tropical rainforests also play an important role in climate regulation through cooling the air that passes through them and the release of water vapour which leads to cloud formation.   The removal of large areas of rainforest has lead to localised increased temperatures and decreased rainfall which could also affect regional and global climate (Couzin 1999).

Loss of Ecosystem Services

Human well-being and progress towards sustainable development are fundamentally dependent upon improved management of the Earth’s ecosystems to ensure their conservation and sustainable use (MA 2005).  However, in the process of meeting increasing demands for ecosystem goods and services such as food, clean water, and other resources, human actions are undermining the ability of ecosystems to provide these goods and services.

The maintenance of ecosystems and their provision of ecosystem services is increasingly becoming the focus of environmental management and sustainable development around the world.  This is demonstrated by the rapidly increasing research into the nature and value of ecosystem services, the widespread use of this concept through all levels of environmental management, and large international programs such as the Millennium Ecosystem Assessment (MA). 

The MA focuses specifically on ecosystem services

• How changes in ecosystem services have affected human well-being,
• How ecosystem changes may affect people and ecosystem services provision in future decades, and
• Response options that might be adopted at local, national and global scales to improve ecosystem management, thereby contributing to human well being and poverty alleviation.

 

Next - Module 1: The ecosystems services concept