A definition of the Planetary Boundary for Land Use Change

What is the Land Use Change in general?

The Land Use Change (LUC) is the modification of the Earth surface by humans. The human is modifying the Earth surface for different purposes like food production, animal nutrition or use of ressources (e.g. wood). This process has been executed for thousands of years and nobody will know for how long the humans can continue on this. The LUC occurs in global and regional scales all over the world (modified according to www.eoearth.org).

 Figure 1: Distribution of different land cover classes in the world in % (Source: http://www.iiasa.ac.at/Research/LUC/GAEZ/results/5_8.htm).

 The Figure 1 shows the actual distribution of different land cover classes in the world. These different classes of land cover are still important to understand the process of LUC.

How is the Planetary Boundary for Land Use Change defined by Rockström et al.?

The Planetary Boundary (PB) of the LUC is defined as the percentage of global land cover that is converted to crop land (Rockström, J., et al.: Planetary Boundaries: Exploring the Safe Operating Space for Humanity, Ecology and Society 14(2): 32, 2009). Today 12 % of the global land surface is under crop cultivation (Foley, et al.: 2005; Ramankutty, et al.: 2008). This means that this land is used for the purposes for human nutrition. The producing of bio energy plants (e.g. for bio fuel production) is not included  in this value. Rockström et al. define the PB for the converting of land cover into crop land should not exceed a value of 15 % of the global ice-free land surface. The range of uncertainty range for this PB is defined from 15 % to 20 %. So the expansion of converting land cover to crop land is only 3 %, which is around 400 Mha. 

The average range of converting land cover to crop land in the last 40 to 50 years was 0.8 % per year. If we assume this range of changing for the next years the boarder of 15% will be reached within the next 4 years (3.75 years). So the result would be that the LUC has exceeded its PB in the close future.

According to the research of Rockström et al. the exceeding of the PB can cause damage effects on other PB. For example, the changing of land cover can trigger the loss of species and by this it can accelerate the loss of biodiversity.

       

Figure 2: Cultivated systems on the Earth surface (Source: http://maps.grida.no/go/graphic/extent-of-cultivated-systems-2000).

  

If we consider not only the crop cultivated landscape surface, more than one quarter of the world is covered by cultivated systems. This is shown in Figure 2. The cultivated systems include croplands, shifting cultivation, confined livestock production and freshwater aquaculture.

In this case the boarder of 15 % (witch Rockström et al. defined) has already been exceeded at a level of 25 %. For me it is not clear why Rockström et al. only refer to the conversion of cropland. In my opinion all factors that course land use changes (e.g. intensive grazing, converting to energy plant production, shifting cultivation, etc.) are important for defining the PB of LUC.

Well, if I consider that Rockström et al. are justified with the definition of the PB, they point out that it is necessary to have croplands in the most productive areas to stay within the PB they defined. In order to stay within the PB, they mentioned that there are two points how to approach this aim. On the one hand there has to be a control of the loss of land to land degradation or competition with other land uses (e.g. fuel production) and on the other hand there has to be a control in the consumption demand of human, such as diets, per capita food consumption and wastage in the food distribution chain.

What are the thresholds for Land Use Change and what is the state of knowledge?

Figure 3: Proposed planetary boundaries (Source: Rockström et al., 2009).

Furthermore Rockström et al. also defined a threshold and the recent state of knowledge for the PB of the LUC. The threshold for this PB is on one hand the (irreversible and widespread) conversion of biomes to undesired states (witch is shown in Figure 3) and one other hand the LUC is affecting carbon storage due to changes in biodiversity and landscape hetreogeneity. The changing at the threshold is a slow variable with can influence other PB like biodiversity, water and climate.

In Figure 4 can be seen how the annual flux of carbon into the atmosphere is influenced by LUC from different parts of the world in the time range from 1850 until 2000. The flux of carbon in Latin America (light green line) and Tropical Asia (thin brownish line) was largely increasing from 1950 to 1990. I think this increasing is related to high amounts of deforestation of the tropical rain forest. 

Figure 4: Annual Effect of Land-Use Change on Atmospheric CO2 (Source:

http://www.appinsys.com/globalwarming/GW_5GH_CO2Sources.htm).

The state of knowledge in the case of LUC is listed into three points (compare to Figure 3), which are:

• sufficient scientific knowledge of impacts of land cover changes of ecosystems (large and small scale)
• improbably global threshold, but probably regional thresholds
• PB has a high uncertainty and the regional distribution of land-system change is critical

Thanks for reading and I hope you got the PB of LUC.