**1. Introduction**

240 Biodiversity Loss in a Changing Planet

who were also exposed to a climate noted for high rainfall, strong winds and cold winters, malnutrition with limited vitamin C intake, dioxin exposure, low herd immunity and lack of health care personnel. These factors are all in stark contrast to the successful society on Lord Howe Island. It is clearly not possible to tease out attributable percentages to each factor, but lack of biodiversity as in North America probably contributed to morbidity and mortality, and ultimately the failure of the society on St Kilda necessitating evacuation.

[1] Maclean C. St Kilda: island on the edge of the world. Edinburgh: Canongate; 1972.

[4] Robson M. St Kilda Church, visitors and 'natives'. Lewis: Islands Book Trust; 2005.

[7] Stride P. The St Kilda epidemic of 1727, smallpox or chickenpox? *J R Coll Physicians Edinb* 

[8] Martin M. Description of the Western Islands of Scotland circa 1695 and a Voyage to St

[12] Stride P Survival of the fittest: a comparison of medicine and health on Lord Howe

Island and St Kilda *J R Coll Physicians Edinb* 2010; 40:368–73

[9] Stride P Dioxin, diet and disease on St Kilda *J R Coll Physicians Edinb* 2009; 39:370–4 [10] Stride P. St Kilda, the neonatal tetanus tragedy of the nineteenth century and some twenty-first century answers. *J R Coll Physicians Edinb* 2008; 38:70–7. [11] Stride P. The St Kilda boat cough under the microscope. *J R Coll Physicians Edinb* 2008;

http://www.undiscoveredscotland.co.uk/usebooks/martinwesternislands/index.

[5] Macaulay K. The history of St. Kilda. London: Beckett and de Hondt; 1764.

[2] Steel T. The life and death of St Kilda. London: Fontana; 1975 [3] Harman M. An isle called Hirte. Skye: Maclean Press; 1997.

Kilda. Edinburgh: Birlinn; 1999. Available from:

[6] Sykes B Adam's Curse Bantam Press London 2003

2009; 39:276–9.

html

38:250–60.

**14. References** 

Biodiversity is defined by the Convention on Biological Diversity 1 as "the variability among living organisms from all sources including *inter alia*, terrestrial, marine and other aquatic ecosystems, and the ecological complexes of which they are part; this includes diversity within species, between species and of ecosystems". Thus in this definition diversity can also be described by listing of species even though such lists may not show the quality of diversity being described. For plants, assessments of biodiversities are complex because of the magnitude of numbers of species compositions in a setting. In the tropics alone, it has been reported that there are more than 200,000 species of flowering plants, which also include many tree species2. Furthermore, variations in species compositions between different geographical areas make biodiversity assessment even more complicated. In tropical African forests for example it has been observed that in an area of about 106 km2, there can be between 30,000 and 120,000 of flowering plant species alone; and in smaller areas such as plots of about 0.1 and 1 hectares this variation has been found to be between 30 and 300 of tree species3. Nevertheless, it is acknowledged that patterns and processes of diversity analyses have improved as per FAO forest resource assessments 4,5. With regard to habitats, it is noted that there is a lack of detailed survey information on habitat types, species or genetic diversity in many forests in the tropics6. In addition, the complexity in assessments is exacerbated in the tropics because of the introductions of exotic plant species such as was the case in most of the East African highlands during the last century7.

The interest in forest biodiversity has increased lately due to the many threats forest ecosystems face in many regions of the world. These threats not only affect the ecosystem co-benefits such as biodiversity; and cultural and aesthetic values but also the service provisions and regulatory functions of the forests. In Kenya, there are nineteen habitats and ecosystems which exclude agricultural and barren lands that are valued for their high biodiversity. One such is the highland moist forests ecosystem which occupies 2% of the land area of the country8 and occurs in altitudinal ranges of 1400-2000m. Similarly at the global level, the mountain cloud forests have received considerable attention because of their ecological values and threatened stability9. The Taita Hills forest ecosystem occurs within the highland moist ecosystems. These forests belong to the only existing mountain cloud forests in East Africa and form a part of the Eastern Arc Mountains which stretch from Tanzania to south-west Kenya. These forests form the northern most parts of these Mountains. The Taita Hills rise from 1400m in the southeastern slopes to above 1700 m altitude

Native Tree Species Regeneration and Diversity in the Mountain Cloud Forests of East Africa 243

In this chapter, the observation from research work conducted in three out of the 12 forest fragments considered larger in sizes are discussed. The study sought to assess the diversity of native tree species regenerated within the native and exotic forest plantations. The study assessed this biodiversity by evaluating the species diversity, richness and similarity of the regenerated species between the exotic plantations of pine, eucalyptus and cypress; as well as between native and exotic forests. Other factors such as levels of disturbance were established as not only affecting the ecological functions of these forests but also the loss in some of the species vital for use for medicinal purposes. The perceptions of the communities on how the species composition has affected the ecological functions of the forests was reported as effect on water yield into the streams. Finally, potential management activities

Globally, biodiversity hotspots previously covered an area of 15.7% of the global land surface14 but currently cover only 2.3% 16 and they are still experiencing different forms of disturbances which constantly threaten their existences. In most cases, these disturbances are due to changes in land use, overexploitation of resources and introductions of exotic species. In addition, ineffective implementation of policies by national institutions exacerbates the losses of biodiversity in many countries, because less attention is given to ensuring that regulations that are in place for the management of these forests are implemented. The Taita Hills forests also faced similar threats until, the 1990s when their conservation was taken seriously. As a result, the disturbances they suffered not only impacted on the biodiversity loss but also on other functions and services of the forests. Farmers in Chawia, for instance, during a Participatory Rural Appraisal exercise by Lekasi16 recalled that water availability and soil fertility had been reduced from the 1920s to 2005 due to what they perceived as the destruction of forests and the introduction of unsuitable exotic tree species; and that they are presently conserving the forest to improve water yield

The sources of disturbances to these forests were anthropogenic and caused mainly by the demographic dynamics. In particular, population growth without corresponding increase in farm holding sizes prompted people to encroach into the forests. As a result, forests were cleared for agricultural production. In addition, other activities such as: firewood collection, charcoal production and grazing18,19 occurred, which rapidly contributed to the degradation of the forests to the extent that 90% of forest cover loss is estimated to have occurred during the last 200 years11. These forests are also red listed by IUCN20 because 236 of their plants are classified as either endangered or vulnerable. Furthermore, the exotic plantations of pine (*Pinus patula.* Schiede ex Schlecht. & Cham), eucalyptus (*Eucalyptus saligna* R. Baker) and cypress (*Cupressus lusitanica* Miller) that were established between the 1960s and 1980s as forest stands within the native forests and as individual trees for enrichment planting22 have further led to changes in species composition. These were part of management plans to provide softwood production, protection of the native forests and to mitigate against soil erosion. All these activities inadvertently exacerbated the threats to the biodiversity in these forests23. Another reason for the loss in forest cover was the ineffective implementation of the forest policies in place. For instance, despite a national policy in 1977 which banned the logging of the native forests without licence19, the people continued to encroach and log from these forests; as a result of unsustainable use of forest resources akin to property of the commons24 and without a well defined forest management strategy, the forests lost much of

that can be instituted to restore the biodiversity are suggested.

**1.1 Causes for biodiversity loss** 

through reforestation with native species17.

in the northwestern slopes10, and as it is typical with most cloud mountain forests; these forests are the home to a variety of native tree and animal species. The forests host some endemic plant species such as the wild coffee, *Coffea fadenii* Bridson. In all, the plants they host are categorized as follows: 40% of the plant species, 2% of the genera and 13 taxa that are endemic to Taita Hills forests, and additional 22 plants that are endemic only to Kenya and Tanzania11,12,13. Due to these diversities, the forests are ranked among the 34 biodiversity hotspots of the world with respect to high ratios of endemic plants and vertebrate species per area14,15. Presently, there are only four out of twelve fragments of that are of appreciable coverage in area remaining in these hills and these are: Ngangao (120 ha), Chawia (86 ha), Mbololo (185 ha) and Irizi (47 ha), the largest of the three were investigated (Fig.1).

Fig. 1. The location of Taita Hills in Kenya and the three forests studied. (Source; Omoro et al., 2010)

In this chapter, the observation from research work conducted in three out of the 12 forest fragments considered larger in sizes are discussed. The study sought to assess the diversity of native tree species regenerated within the native and exotic forest plantations. The study assessed this biodiversity by evaluating the species diversity, richness and similarity of the regenerated species between the exotic plantations of pine, eucalyptus and cypress; as well as between native and exotic forests. Other factors such as levels of disturbance were established as not only affecting the ecological functions of these forests but also the loss in some of the species vital for use for medicinal purposes. The perceptions of the communities on how the species composition has affected the ecological functions of the forests was reported as effect on water yield into the streams. Finally, potential management activities that can be instituted to restore the biodiversity are suggested.

#### **1.1 Causes for biodiversity loss**

242 Biodiversity Loss in a Changing Planet

in the northwestern slopes10, and as it is typical with most cloud mountain forests; these forests are the home to a variety of native tree and animal species. The forests host some endemic plant species such as the wild coffee, *Coffea fadenii* Bridson. In all, the plants they host are categorized as follows: 40% of the plant species, 2% of the genera and 13 taxa that are endemic to Taita Hills forests, and additional 22 plants that are endemic only to Kenya and Tanzania11,12,13. Due to these diversities, the forests are ranked among the 34 biodiversity hotspots of the world with respect to high ratios of endemic plants and vertebrate species per area14,15. Presently, there are only four out of twelve fragments of that are of appreciable coverage in area remaining in these hills and these are: Ngangao (120 ha), Chawia (86 ha),

Mbololo (185 ha) and Irizi (47 ha), the largest of the three were investigated (Fig.1).

Fig. 1. The location of Taita Hills in Kenya and the three forests studied.

(Source; Omoro et al., 2010)

Globally, biodiversity hotspots previously covered an area of 15.7% of the global land surface14 but currently cover only 2.3% 16 and they are still experiencing different forms of disturbances which constantly threaten their existences. In most cases, these disturbances are due to changes in land use, overexploitation of resources and introductions of exotic species. In addition, ineffective implementation of policies by national institutions exacerbates the losses of biodiversity in many countries, because less attention is given to ensuring that regulations that are in place for the management of these forests are implemented. The Taita Hills forests also faced similar threats until, the 1990s when their conservation was taken seriously. As a result, the disturbances they suffered not only impacted on the biodiversity loss but also on other functions and services of the forests. Farmers in Chawia, for instance, during a Participatory Rural Appraisal exercise by Lekasi16 recalled that water availability and soil fertility had been reduced from the 1920s to 2005 due to what they perceived as the destruction of forests and the introduction of unsuitable exotic tree species; and that they are presently conserving the forest to improve water yield through reforestation with native species17.

The sources of disturbances to these forests were anthropogenic and caused mainly by the demographic dynamics. In particular, population growth without corresponding increase in farm holding sizes prompted people to encroach into the forests. As a result, forests were cleared for agricultural production. In addition, other activities such as: firewood collection, charcoal production and grazing18,19 occurred, which rapidly contributed to the degradation of the forests to the extent that 90% of forest cover loss is estimated to have occurred during the last 200 years11. These forests are also red listed by IUCN20 because 236 of their plants are classified as either endangered or vulnerable. Furthermore, the exotic plantations of pine (*Pinus patula.* Schiede ex Schlecht. & Cham), eucalyptus (*Eucalyptus saligna* R. Baker) and cypress (*Cupressus lusitanica* Miller) that were established between the 1960s and 1980s as forest stands within the native forests and as individual trees for enrichment planting22 have further led to changes in species composition. These were part of management plans to provide softwood production, protection of the native forests and to mitigate against soil erosion. All these activities inadvertently exacerbated the threats to the biodiversity in these forests23. Another reason for the loss in forest cover was the ineffective implementation of the forest policies in place. For instance, despite a national policy in 1977 which banned the logging of the native forests without licence19, the people continued to encroach and log from these forests; as a result of unsustainable use of forest resources akin to property of the commons24 and without a well defined forest management strategy, the forests lost much of

Native Tree Species Regeneration and Diversity in the Mountain Cloud Forests of East Africa 245

and can be used for the calculations. This calculator is freely available online (http://www.columbia.edu/itc/cerc/dunoffburg/MBD/LIMK.html). In this software, values for species derived from the data are fed in the calculator which then provides a range of diversity indices (e.g. Shannon-Weaver, Simpson and Broken stick) which one can select to use. In many cases such as in the Eastern Arc Mountain forest, the Shannon-Weaver index (H') has been commonly used for these calculations25,33. This is because it provides an account of both the abundance and evenness38 and does not disproportionately favour any species as it counts all the species according to their frequency39,40 unlike indices such as Simpson's which disproportionately highlights common species (in terms of abundance) instead of showing their frequencies (richness) in samples. One documented disadvantage of the Shannon-Weaver index is however, that it requires a large sample size in order to minimize biases41. Shannon-Weaver's indices ranges are typically from 1.5 to 3.5 and rarely reach 4.542. Other parameters such as species richness (S) and species evenness (H'E) are also

> 1 ' ln *S*

Where i, is the proportion of the species relative to the total number of species (pi) multiplied by the natural logarithm of this proportion (ln pi) and the final product

Species evenness, the proportion of individuals among species in an ecosystem is often

Where Hmax is defined as ln S. H'E values range from 0 to 1 and 1 indicates complete

The Shannon-Weaver's indices obtained in the study were converted to *effective numbers* using a method by Lou40; this can be done to obtain values that can be used to compare the differences in species diversities. The *effective numbers* are calculated as an exponential

*N of species pi exp p p*

*Effect i i*

To obtain similarities in species composition between forest fragments and forest stands,

*i H pp* 

Species richness, the number of species present in an ecosystem (S) was defined by

assessed by Shannon's equitability index (H'E) which is calculated by

the Jaccard's index43 was used. Jaccard's index (Cj) is defined by

*i i*

(1)

*S n* (2)

H'E = H' / Hmax (3)

(4)

1 ( ln ) *S*

*i*

generated from the same calculator.

Shannon's index, (H') is defined by

multiplied by -1.

evenness.

of the Shannon's index as:

**Box 1. Shannon-Weaver biodiversity Index** 

Where *n* is number of species in a community.

their ecosystem functions. A study by Himberg17 shows how the communities living around these forests decry the losses of the services such as reliable water flow and some of the medicinal plants.
