Community Relations

Susceptibility to epidemic diseases and pests Nurse effects

• microclimate

• reduction of erosion

• enhancement of litter and humus production

Fig. 1.8A,B Acacia woodland (A) and Eucalyptus plantations (B) in the Rift Valley, Ethiopia

in Ethiopia in a region where some remnants of original native forest of Podocarpus falcatus are still preserved, but where large areas are deforested and deteriorated (Feyera et al. 2002; Lüttge et al. 2003; Fetene and Beck 2004; Lemenih and Teketay 2004; Fritzsche et al. 2006). Figure 1.9A shows the Eucalyptus forest in the background of an old solitary female tree of P. falcatus, the seeds (Fig. 1.9B) of which are dispersed by birds. As given by the data on ground cover, light penetration and

Fig. 1.9A-D Forest of Eucalyptus saligna and Podocarpus falcatus, Shashemene-Munessa State Forest, Ethiopia. A Female tree of P falcatus with Eucalyptus forest in the background. B Seeds on P. falcatus. C,D Various stages of young growth of P. falcatus inside the Eucalyptus forest

the number and density of naturally regenerated native woody species summarized in Table 1.2, the E. saligna plantation can be favourably compared with the adjacent native forest and the nurse effect of E. saligna is evident. The Eucalyptus is coppiced regularly about every 7 years which gives a certain advantage to regenerating native woody species. Moreover, physiological data comparing E. saligna and P. falcatus, the major native tree the regeneration of which is of greatest concern, also show that the Podocarpus can compete well with the Eucalyptus within the plantation. Pho-tosynthetic electron transport rates are not pronouncedly lower in P. falcatus than in E. saligna in the plantation, but the Eucalyptus needs very much more water as shown by its higher transpiration rates, /h2o, and leaf conductance for water vapour, gn2o, and its lower water use efficiency given by the higher A13C value of its leaves inside the plantation (for explanation of the latter see Sect. 2.5). Indeed, P. falcatus can readily regrow from seeds inside the Eucalyptus plantation (Fig. 1.9C,D). This suggests how an original native forest can be regenerated making use of the nurse function (Table 1.1) of an exotic tree plantation. In the case described here, P. falca-

Table 1.2 Comparison of a plantation of Eucalyptus saligna and an adjacent native forest (A) and of some ecophysiological data of the Eucalyptus and of the major and most conspicuous native tree, the dioecious gymnosperm Podocarpus falcatus (B) in the Shashemene-Munessa State Forest, eastern escarpment of the Great Rift Valley, Ethiopia (7° 13' N, 8° 37' E). ETR1000 = apparent photosynthetic electron transport rate at an irradiance of 1,000 ^molm-2s-1 obtained from instant measurements at ambient irradiation, ETRmax = maximum apparent photosynthetic electron transport rate obtained from measurements of light dependence curves (see Sect. 4.1.1, Box 4.6); for /h2o and gh2o of E. saligna the first number is of the adaxial and the second number of the abaxial leaf surface. (Data from Feyera et al. 2002, Luttge et al. 2003, Lemenih and Teketay 2004)

Table 1.2 Comparison of a plantation of Eucalyptus saligna and an adjacent native forest (A) and of some ecophysiological data of the Eucalyptus and of the major and most conspicuous native tree, the dioecious gymnosperm Podocarpus falcatus (B) in the Shashemene-Munessa State Forest, eastern escarpment of the Great Rift Valley, Ethiopia (7° 13' N, 8° 37' E). ETR1000 = apparent photosynthetic electron transport rate at an irradiance of 1,000 ^molm-2s-1 obtained from instant measurements at ambient irradiation, ETRmax = maximum apparent photosynthetic electron transport rate obtained from measurements of light dependence curves (see Sect. 4.1.1, Box 4.6); for /h2o and gh2o of E. saligna the first number is of the adaxial and the second number of the abaxial leaf surface. (Data from Feyera et al. 2002, Luttge et al. 2003, Lemenih and Teketay 2004)

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Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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