Woody Species Diversity , Structure , and Regeneration Status of Yemrehane Kirstos Church Forest of Lasta Woreda , North Wollo Zone , Amhara Region , Ethiopia

This study is aimed at generating data on woody species diversity, structure, and regeneration status of some species and was conducted in Yemrehane Kirstos Church Forest of Lasta Woreda, North Wollo Zone, Amhara Region, Ethiopia. Six transect lines were laid following altitudinal gradient. Quadrats of size 20 m × 20 m (400m) were used to collect data that were established systematically at every 100 m interval along the transect lines. Data on woody species was collected from a total of 34 sampling quadrats of 400m. To collect data on seedlings and saplings, five subplots of 1 m × 1m (1m) size located at the four corners and centre of the main plot were used. Species diversity was determined using the Shannon-Wiener index (H). A total of 39 woody species belonging to 38 genera and 29 families were identified in Yemrehane Kirstos Church Forest. The overall Shannon-Wiener diversity index (H) and evenness values for the entire forest were 2.88 and 0.79, respectively.The six most abundant woody species in their order of highest density were Juniperus procera,Olea europaea subsp. cuspidata,Maytenus arbutifolia,Osyris quadripartita, Calpurnia aurea, and Debregeasia saeneb. The densities for mature woody species, saplings, and seedlings were 506.6, 514.7, and 415.4 individuals ha, respectively. The basal area of the forest is 72 m ha. The population structure and regeneration status of the forest indicated that there have been high forest degradation and severe anthropogenic disturbances in the area and, therefore, conservation of species, ecosystem restoration, and sustainable use of the forest genetic resources are recommended as a result of this study.


Introduction
1.1.Background and Justification.Loss of forest cover and biodiversity due to anthropogenic activities is a growing concern in many parts of the world [1,2].Africa's forest cover is estimated to be 650 million ha, constituting 17 percent of the world's forests including a number of global biodiversity hotspots [3].Ethiopia is regarded as one of the most important countries in Africa with respect to biological resources (flora and fauna) [4].The major challenge facing Ethiopia is environmental degradation manifested in the degradation of land and water resources as well as loss of biodiversity [5].Deforestation is one of the major factors contributing to land degradation by exposing the soil to various agents of erosion.Rapid human population growth, poverty, forest clearing, overgrazing, and lack of proper policy framework are some of the major factors that contribute to the loss of forest resources in Ethiopia [6].In general topography, soil, climate, and geographical locations of a region influence the vegetation diversity of the forest ecosystem [7].Lack of integration of the local people living around the conservation areas into the conservation efforts is the major constraint to the overall conservation effort in Ethiopia [8].However, the current government of Ethiopia has started to protect forests through participatory forest management.Therefore, as a strategy for development interventions, initiation of forest management through local community participation would essentially be contributing to the reduction of forest degradation in Ethiopia [9,10].However, availability of accurate data on forest resources is an essential requirement for management and planning within the context of sustainable development [11].Likewise, as a conservation approach, scientific studies on floristic composition, vegetation structure, and regeneration status of a given forest patch are needed to determine the status of the forest and take appropriate conservation measures.Yemrehane Kirstos Church Forest, one of the most important and heritage priority areas, is currently not well managed and most of the forest area is degraded and converted to agricultural and grazing land [12].The systematic investigation of forest vegetation for this area is lacking.Thus, the current work on floristic composition, diversity, structural analysis, and regeneration of the vegetation in the area is believed to contribute a lot to the effective conservation and management of this heritage forest.The major objective of this study was to determine floristic composition of woody species, regeneration status, and structure of woody species in Yemrehane Kirstos Church Forest.

Location and Description of the Study Area.
The study was conducted in Yemrehane Kirstos Church Forest, Lasta Woreda, North Wollo Zone, Amhara National Regional State, characterized by a rugged mountain landscape, in the river valley of gorges and high clips of north Wollo, Lalibela, Ethiopia.It is located between 12 ∘ 07  39.9  -12 ∘ 08  36.2  N and 039 ∘ 04  00.8  -039 ∘ 04  24.3  E (Figure 1) and extends over an altitudinal range from 2565 to 3135 m with the total area of 200ha [12].The main types of soil in the area are loamy soil.

Sampling Design
Systematic sampling design was used to collect vegetation data from the study site.Appropriate transect lines and sampling quadrats were made based on the total area of the study site for vegetation data collection.Six transect lines were laid following the altitudinal gradient and quadrats of size 20 m × 20 m (400m 2 ) were established systematically at every 100 m interval.To collect data on seedlings and saplings, five subquadrats of 1 m × 1m (1m 2 ) size located at the four corners and centre of the main quadrats were used.

Floristic Data Collection.
All the woody plant species encountered in each sample quadrats were recorded and coded with vernacular and local names whenever possible.The plant species occurring outside sample quadrats but inside the forest were recorded only as present but not used in the subsequent vegetation data analyse.These species and the rest plant specimens were collected, pressed, dried, and brought to the National Herbarium of Ethiopia (ETH), Department of Plant Biology and Biodiversity Management, Addis Ababa University, for taxonomic identification.Physiographic variables such as altitude, latitude, and longitude were recorded for each sampling quadrat using GPS.In each quadrat, trees and shrubs with DBH > 2.5 cm were measured and recorded for height and diameter at breast height (DBH) with clinometers and diameter tape, respectively.For trees and shrubs that are branched around the breast height, the circumference was measured separately and averaged.In each quadrat, the species list and number of seedlings and saplings were recorded to determine the regeneration status.
The undergrowth of woody species with a height less than 1 m was considered as seedlings, height of greater than 2 m was considered as trees and shrubs, and 1-2 m was considered as sapling [14].

Data Analysis.
The diameter at breast height (DBH), basal area, tree density, height, frequency, and important value index were used for description of vegetation structure.That accounts both for species richness and evenness, and it is not affected by sample size (Kent and Coker, 1992).
Species richness was undertaken from all species encountered in each plot.

S = number of species plot (2)
Evenness of species was calculated by dividing H by Hmax (here Hmax = ln S).

Importance Value Index (IVI).
Importance value index which combines data from three parameters (relative frequency, relative density, and relative abundance) is used to compare the ecological significance of species.The importance of value index (IVI) for each woody species was calculated using the formula indicated below [13].
Importance Value = Relative density The frequencies of the tree and shrub species in all thirty-four quadrats were computed.
Relative Frequency = Frequency of Tree species Frequency of all Tree species × 100 (8)

Density of Woody Species.
The six most abundant woody species in their order of density in Yemrehane Kirstos Church Natural Forest were Juniperus procera, Olea europaea, Maytenus arbutifolia, Osyris quadripartite Calpurnia aurea, and Debregeasia saeneb (Table 1).

Basal Area. The total basal area of Yemrehane Kirstos
Church Natural Forest was about 72 m 2 ha −1 for woody species that have DBH > 2.5 cm.Basal area provides the measure of the relative importance of the species rather than simple stem count [16].Species with higher basal area could be considered as the most important species in the study vegetation.In this study, basal area analysis across individual species revealed that there was high domination by very few or small woody species.This also indicates that species with the highest basal area do not necessarily have the highest density, indicating size difference between species [17].The following species made the largest contribution to the basal area: Juniperus procera, Olea europaea, Acacia abyssinica, Allophylus abyssinicus, and Dovyalis abyssinica, respectively (Table 2).
In general, the basal area values for present forest were higher than most of the other studied forests in Ethiopia [12].This suggests that the Yemrehane Kirstos Church Forests have better growth and potential to retain higher biomass (Table 3).

Frequency.
Frequency is an indicator of homogeneity and heterogeneity of a given vegetation type [16].The higher number of species in higher frequency classes and lower number of species in lower frequency classes show homogeneity in forest composition.And the low number of species in higher frequency classes shows heterogeneity of species.The present study revealed high percentage of species in lower frequency classes and relatively low percentage of number of species in high frequency classes.Thus, the result verifies the existence of high degree of floristic heterogeneity in Yemrehane Kirstos Church Forest [12].The relative frequency revealed that Juniperus procera was the most frequent species with frequency of 94.12 followed by Olea europaea, Maytenus arbutifolia, Osyris Quadripartite, Acacia abyssinica, Dodonaea viscosa, Allophylus abyssinicus, Calpurnia aurea, Rhus glutinosa, and Clutia abyssinica.  of species richness and evenness [18].Generally speaking, only few species were dominating the vegetation of the study area in their abundance while many of the species were very rare or low in their abundance.Reports from other studies indicated that species richness and diversity tend to peak at an intermediate altitude and decline at the lower and upper elevations [19].The result of the present study more or less agrees with this regarding species richness.Such a result reflects either adverse environmental situations or random distribution of available resource in the study area.The overall average Shannon-Wiener diversity index (H  ) and the average evenness values of Yemrehane Kirstos Church Forest were 2.88 and 0.79, respectively, which is higher than Harenna Forest (2.60) [20].According to [16], species area curve is a cumulative curve that relates the occurrence of species with the area sampled; curves that grow up and flattened at the end indicate that the numbers of plots taken are sufficient.Seven sample quadrats were taken randomly and decided the species area curves of the vegetation of Yemrehane Kirstos Church Forest.The result showed that species richness across quadrats was good and pattern of diversity curve raised up and flatted owing to the fairly enough number of quadrats observed.

Importance Value Index. IVI indicates the structural importance of a species within a stand of mixed species.
And it is used for comparison of ecological significance of species in which high IVI value indicates that the species sociological structure in the community is high.It is crucial to compare the ecological significance of species [16].It was also stated that species with the greatest importance value are the leading dominant of specified vegetation [21].The top ten leading woody species with greatest importance value and dominance in Yemrehane Kirstos Church Forest were Juniperus procera, Olea europaea, Maytenus arbutifolia, Osyris quadripartita, Acacia abyssinica, Dodonaea angustifolia, Calpurnia aurea, Allophylus abyssinicus, Rhus glutinosa, and Clutia abyssinica, compared to other species of the area (Table 4).

Diameter Class of Woody Species. The general pattern of DBH class distribution of Yemrehane Kirstos Church Forest
showed an inverted bell-shaped distribution.This pattern of DBH classes indicates a good potential of reproduction and recruitment of the forest.Similar results were reported by [22,23].In this study, cumulative diameter class distribution of the population structure of the study area reflected an irregular shape, which seemed to be a bell-shaped distribution pattern, but a complete absence of individuals in some classes and a fair representation of individuals in other classes.Above sixty-five percent of the total density is restricted in the middle and higher diameter class (5-32cm), whereas the rest of density was found to be in the lower diameter classes (1-5 cm) (Figure 2).This indicated that there was drawing out of trees for various purposes by local dwellers (e.g., for fencing and fuel wood, by livestock trampling or browsing, or maybe by agricultural expansion) in the lower classes of trees in the area.

Height.
In case of population height class distribution similar results were reported in Chilimo and Menagesha Forests of central plateau of Ethiopia [17], in Denkero Forest [22], and in Menagesha Ameba Mariam Forest [24].The higher number of large-sized individuals in the upper height class in the natural forest implies the presence of a good number of adult tree species for reproduction [25].This argument holds true for Yemrehane Kirstos Church Forest.This is partly due to the absence of large scale timber exploitation.Therefore, the current study exhibited a condition of primary forest development of the Yemrehane Kirstos Church Forest.It is noteworthy that woody species with the highest DBH size were also recorded for the highest height (Figure 3).Although there is selective logging of tree species at certain height, Yemrehane Kirstos Church Forest exhibited individuals of all height classes.

Regeneration Status of Yemrehane Kirstos Church Forest.
A total of 1245 individuals, 696 seedlings and 549 saplings individuals, were counted from all quadrants.The following species were the largest contributors to the seedling and sapling counts: Becium grandiflorum, Maytenus Juniperus procera, and Dodonaea angustifolia.In general the distribution of seedlings as a whole is greater than that of saplings and mature trees, and that of saplings is less than mature International Journal of Forestry Research  trees.This ratio indicates that the number of seedlings and saplings being regenerated in the forest is about more than two times the mature trees of the forest.Analysis of seedlings and saplings of Yemrehane Kirstos Church Natural Forest indicated that the densities of seedlings and saplings of woody plants species of the forest were 415.4 and 514.7 ha −1 , respectively.Regeneration status of a forest is poor if number of seedlings and saplings are much less than mature individuals [13].In this seedling and sapling assessment Becium grandiflorum, Clutia lanceolata, Maytenus arbutifolia, Olea europaea, and Juniperus procera were found with good recruitment status relative to other species.Generally, good regeneration was more observed for most bush/shrub species than trees.

Conclusion and Recommendation
The study provides useful information on the present condition of the woody species diversity, structure, and regeneration status of Yemrehane Kirstos Church Forest.The forest has a large number of woody species bound with a high diversity.The woody species of the Yemrehane Kirstos Church Forest were dominated by Juniperus procera, and the most economical and ecologically important woody species in the forest was Acokanthera schimperi.However, the renewal of species through the regeneration was not adequate; the vulnerability of young plants to disturbance has caused slower replacement into tree size class.

Recommendation
The Yemrehane Kirstos Church Forest is currently being exploited by the local people.This calls for the need of serious attention for conservation and management of this forest.
Hence the following recommendations are made to meet these objectives: (iii) Creating mechanisms such as participatory forest management by which human impacts can be minimized, through discussion and consultation with the local communities.
(iv) Based on the finding, the forest has to be managed for biological diversities found in the area and for carbon sequestration.
(v) The present study was limited to diversity, structure of woody species, and regeneration status; thus, further studies on soil seed bank, seed physiology, herbaceous plants, and land use management system in the area are needed.

4. 4 .
Species Diversity and Evenness.Species diversity is a combination of the number of species and their relative abundance.The values of species diversity depend upon levels
(i) Subsequent ecological studies are vital concerning species composition, diversity, and distribution of possible plant communities with respect to other environmental factors.(ii) Raising awareness among local communities of the value of forest resources and ecological consequences of deforestation.

Table 1 :
Density and relative density (RD) of woody species.

Table 3 :
Mean basal area (BA) in m 2 and relative dominance of woody species.Basal area comparison of Yemrehane Kirstos Church Forest with other forests.
) 3.4.Basal Area.It is the cross-sectional area of all of the stems in a stand at breast height (1.3 m above ground level).This basal area per unit area is used to explain the crowdedness of a stand of forests.It is expressed in square meter/hectare.Its area is also used to calculate the dominance of species.Basal area = Σ (d/2)2, where D is diameter at breast height.2:

Table 4 :
The list of most frequent and most IVI of ten trees species of the forest with their corresponding frequency, relative frequency, relative density, and relative dominance in Yemrehane Kirstos Church Forest.

5 :
List of woody species collected from Yemrehane Kirstos Church Natural Forest.