Woody Species Structure and Regeneration Status in Kafta-Sheraro National Park Forest, Tigray Region, Ethiopia

The natural vegetation study was conducted in Kafta-sheraro national park (KSNP) North, Ethiopia to explore floristic composition, structure and regeneration of woody species in the home of African elephant. In the park, the above information is not well documented which is necessary for conservation. Data were collected From August to December 2018. The vegetation data were collected from 161 quadrats of size 20m×20m, 5mx5m for shrub ̸ tree, sapling and seedling respectively. Individual trees and shrubs DBH >=2.5cm and height >=2m were measured using Tape meter and Clinometer respectively. DBH, frequency, density, basal area, and IVI were used for vegetation structure. A total of 70 woody species 46 (65.7%) trees, 18 (25.7%) shrubs and 6 (8.6%) tree  ̸shrub) were identified. The total basal area and density of 79.3 m ha, and 466 ±12.8 (S.E.) individuals ha were calculated for 64 woody species. Fabaceae was the most dominant family occupied 16 species (23.0%) followed by Combretaceae 8 species (11.4%). Acacia mellifera and Combretum hartmannianum were the most dominant and frequent species. Abnormal patterns of selected woody species were dominantly identified. Regenerating status all the woody plant species was categorized as “Fair” (18.75%), “Poor” (7.81 %) and “None” (73.44%). However, there is good initiation for conservation of the park; still the vegetation of the park was threatened by firewood collection, charcoal production, fire, intensive farming, mining and over grazing. Therefore, the study area as the habitat for the population of the African elephant; the KSNP should be recommended the highest conservation priority and studied the soil seed bank of species having poor regeneration condition.


Introduction
Ethiopia is considered as one of the top twenty five biodiversity richest countries in the world (WCMC, 1994). It is estimated to around 6000 species of higher plants, of which about 10%

Sampling design
A reconnaissance survey was taken from August, 18 to 25-2018 in order to have an impression of the forest sites and systematic sampling design was applied following (Kent and Coker, 1992).
According to Cain, (1959Cain, ( ,1938 and McIntosh, (1985) species-area curve (minimal area) concept; the plot size was decided. Then a quadrats size of 20mx20m (400m 2 ) were established along a line-transects following (Muller-Dombois and Ellenberg, 1974;Kumlachew and Tamrat, 2002;Getaneh et al., 2019). A total of 161 plots and adjacent 32 transects were placed at a distance of 200m and 300m apart respectively following (Kflay and Kitessa, 2014;Tiwari et al., 2010). All transects and plots located on the ground using compass and GPS navigation system.

Data collection
The detail vegetation data were collected during flowering and fruiting season from August, 26-30 December, 2018. Trees and shrubs: In each the main sample plots (400m 2 ); individual plants (stems) of all tree and shrub species with diameter at breast height (DBH) ≥2.5 cm abudndance were counted and recorded their circumferance (diameter). Height of individual trees and shrubs >2m were recorded for every woody individual plants having DBH >=2.5 cm (Gemedo et al., 2006;Hasan et al., 2011;Tesfaye et al., 2017b). Diameter and height were measured using tape meter and clinometer respectively. Trees with multiple stems arising from the ground level were measured individually and developed a common DBH of all stems by summing up their square roots following (Brundrett et al., 1996).

Rainfall Temperature
Sapling and seedlings: To collect data on abundance of sapling and seedling of each woody plant species, sub-plots of 5 m x 5 m (25m 2 ) were set up within the main plot. Height of each samplings and seedlings measured using tape meter. Saplings are young woody plants with DBH < 2.5 and height >1m<2m where as seedlings as woody plants with DBH < 2.5 cm and height ≤ 1m (Chauhan et al., 2008a;Abyot et al., 2014).
Plant species identification: was started in the field by recording the local name through asking to local elders and referring the scientific name identification using Flora of Ethiopia and Eritrea Volume-1 toVolume-8 (Hedberg and Edwards, 1989;Edwards et al., 1995;Phillips, 1995;Edwards et al., 1997;Hedberg et al., 2003;Mesfin Tadesse, 2004;Hedberg et al., 2006Hedberg et al., , 2009aHedberg et al., , 2009b. Specimens of identified and unidentified species were collected, pressed and dried properly, following standard Herbarium procedures, and taken to the National Herbarium (ETH) at Addis Ababa University for further confirmation and for identification of specimens of those species which could not be identified in the field.

Data analysis a. Woody species structure
Diameter at breast height, height, basal area, tree density, frequency and important value index describes woody vegetation structure of a given forest. The following formula were utilized in Microsoft Excel spreadsheet programme and presented in descriptive statistics.
Density of species: is a count of the numbers of individuals of each species within the quadrat (Kent and Coker, 1992). The sum of individuals per species is analyzed in terms of species density ha -1 (Mueller-Dombois & Ellenberge, 1974;Martin, 1995).
Relative density (RD) = Basal area: is the area outline of a plant near ground surface and expressed in m 2 ha -1 (Kent and Coker, 1992;Martin, 1995).
Where, π = 3.14 and d =DBH (m) (5) Dominance: the degree of coverage of species as an expression of the space at ground level (Mueller-Dombois and Ellenberge, 1974) Dominance = the mean basal area per species * abundance (no) of the species (6) Relative dominance (RDO) = ( ) 100 (7) Importance Value Index (IVI): Indicating the relative ecological importance of a given woody species a particular site (Kent and Coker, 1992;Martin, 1995).
If seedling > sapling > mature tree ("good" regenerating); mature tree > sapling > seedling ("fair" regenerating); if a species survives only in the sapling stage ("poor" regenerating) (even saplings <, >, or = to mature); if a species is absent both in sapling and seedling stages but present as mature ("none" regenerating); if a species has no mature, but only sapling and/or seedling stages ("new" regenerating).

Importance value index (IVI)
The importance value index of woody species in KSNP ranged from 0.13 to 30. Ziziphus spina-christi, Sterculia Africana, Acacia Senegal, Boswellia papyrifera and Acacia oerfota had IVI value above ten were the most important species (Table 1).  (Figure 5b).
In Kafta-sheraro national park forest 18.75% of tree ̸ shrub species showed 'fair regenerating' while 7.8 % and 73.45% showed 'poor regenerating' and 'none regenerating' condition respectively. But "good" and "new" regenerating status of the tree species was absent (Figure 7b).

Acacia mellifera, Combretum hartmannianum, Terminalia brownii, Combretum molle, Balanites
aegyptiaca, Acacia oerfota, Boswellia papyrifera, Acacia Senegal, Dicrostachy scinerea occupied above 50% of the total stem density and relatively those species had higher seedling and sapling density in the study area. These species are probably due to their resistance to drought and disturbance (Abiyot et al., 2017). The absence of seedlings in some of the canopy trees of Sterculia africana and Adansonia digitata highly attributed to disturbance, seed predation, and habitat unsuitability. Disturbance and seed predation have been played sound role in reducing the seedling population of woody species (Alemayehu et al., 2009).
Frequency: contributes to indicate homogeneity and heterogeneity of vegetation of a given species (Haileab et al., 2005). The study site has high species heterogeneity; because of higher percentage numbers of species were found in the lower frequency class than higher class.
According to lamprecht (1989) low value in lower frequency and high value in higher frequency class indicate similar species composition. To the reverse low percentage number of species in the higher frequency and low percentage number of species in the higher frequency classes reported a high degree of floristic heterogeneity (Simon and Girma, 2004;Abyot et al., 2014;Amanuel and Gemedo, 2018). The variation in density and frequency between species may be attributed to habitat differences, habitat preferences among the species, species characteristics for adaptation, degree of exploitation and conditions for regeneration (Haileab et al., 2011). In KSNP important portions of the species were rare. Therefore, the study site has existence of high floristic heterogeneity. The highest basal area from individual tree species in the study was contributed by Adansonia digitata (35.5 m 2 ha -1 ) while the highest density was Acacia mellifera species (69.7 individuals ha -1 ). This indicates that species with the highest basal area do not necessarily have the highest density and the vi-versa is also true. This was indicated that size difference between species is common in natural vegetation (Tamrat, 1994;Simon and Girma, 2004).

Basal area:
Importance Value Index: is useful to compare the ecological significance of species (Lamprecht, 1989;Premavani et al., 2014). Important value index is the degree of dominancy and abundance of a given species in relation to the other species in the area (Kent & Coker, 1992). The importance value index (IVI) of woody species in the study area was generally comparable to other areas of woody vegetation (Haileab et al., 2011;Desalegn et al., 2013;Abiyot et al., 2017). For example, in Jibat forest Ilex mitis species had the highest value (27.7%) (Tesfaye et al., 2013) (Hedberg & Hedberg, 2003).
The IVI values can also be used to prioritize species for conservation, and species with high IVI value need less conservation efforts, whereas, those having low IVI value need high conservation effort. Lower IVI may indicate woody species are threatened and need immediate conservation measure (Anteneh et al., 2011;Temesgen et al., 2015). Low IVI value and poor regeneration status of species in a forest need to be prioritized for conservation (Haileab et al., 2011).
Population structure: DBH and height are important indicators of forest reproduction and health status (Schulz et al., 2009). The general pattern DBH of KSNP showed an inverted J-shaped distribution where species frequently had the highest frequency in low diameter classes and a gradual decrease towards the higher class. Inverted J shape pattern is normal population structure and shows the existence of species in healthier condition. Similar results were reported by (Abate et al. 2006;Haile et al., 2008;Ermias et al., 2008;Leul et al., 2010;Samson et al., 2010;Tesfaye et al., 2013;Kflay and Kitessa, 2014;Mligo., 2015;Tesfaye et al., 2017b;and Tesfay et al., 2019).
However, the general pattern does not clearly show trends of population dynamics and recruitment processes of a single species (Abyot et al., 2014;Getaneh et al., 2019). Other seven discontinuous (there were complete absences of individuals in some class and fairly representative of the individual in other class) patterns showed in KSNP. Irregular distribution pattern were reported by (Mekuria et al., 1999, Getachew et al., 2002, Ensermu & Teshome, 2008Haile et al., 2012a;Melkamu and Abdella, 2019). Moreover, assessing the population structure has been helped to provide initial idea about the status of regeneration pattern of woody plants (Swamy et al., 2000).

Regeneration status of woody plants
Reports stated that the regeneration status of the given natural vegetation is considered as none regenerating if a species is absent both in sapling and seedling stages but present as mature (Khumbongmayum et al., 2006;Dhaulkhandi et al., 2008;Tiwari et al., 2010). Therefore, the regeneration status of Kafta-sheraro national park was considered as none regenerating since mature (88.76%) > sapling (9.22%) > seedling (2.02%). The regeneration and recruitment condition of woody species is one of the major factors that are useful to assess their conservation status (Bekele et al., 2002).The population structure, characterized by the presence of sufficient population of seedlings, saplings and adults, indicates successful regeneration of forest species (Saxena and Singh, 1984). However, climatic factors and biotic interference influence the regeneration of species in any vegetation (Henle et al., 2004;Dhaulkhandi et al., 2008 The regeneration status of the tree species of KSNP dominantly falls in "poor" and "not regenerating" status. Such situation might have been occurred through the existing disturbance like, over grazing (Emiru et al., 2007;Kuijper et al., 2010;Norden et al., 2011), firewood collection, fire, mining and poor biotic potential of tree species which either affect the fruiting or seed germination or successful conversion of seedling to sapling stage and similarly reported in Ethiopia (Haileab et al., 2011;Gebremicael et al., 2013;Tesfaye et al., 2017b;Getaneh et al., 2019;Melkamu and Abdella, 2019) and in other tropical dry forests (Ceccon et al., 2006;Anitha et al., 2010). Moreover, individuals in young stages of any species are more vulnerable to any kind of environmental stress and anthropogenic disturbance (Nagamatsu et al., 2002;Getachew et al., 2002). Poor regenerating leads poor reproduction and hampered regeneration either due to the fact that most trees are not producing seeds as a result of their old age or there has been loss of seeds by predators after reproduction (Bhuyan et al., 2003;Khumbongmayum et al., 2006;Mwavu and Witkowski, 2009). Absence of seedlings and saplings of tree species indicates urgent need for targeted forest management plan to enhance regeneration (Abyot et al., 2014;Getaneh et al., 2019). High herbaceous cover played a major role in preventing successful seed germination, seedling establishment, growth and survival (Kobe and Vriesendorp, 2011).

Conclusion and recommendation
Surveying on structure, and regeneration status of tree species would be provided baseline information and an instrument for the development of successful conservation strategies in KSNP forest. Population structure of most common species of trees and shrubs revealed different patterns of population structure, addressing a high variation among species population dynamics within the forest and an indication for low regeneration. The additional patterns were indicated the absence of populations in various DBH classes. This clearly shows tree species in different stage of development are abnormal population structure status. The regeneration status of the tree species of the study site dominantly showed "poor" and "none" regeneration status but 18% trees/shrubs species, falls under "fair" regenerating" status. Variation in population structure and regeneration status indicates that long time past disturbance of species and the whole resources of the park. The IVI values reveal the most ecologically important woody species in the forests are in poor regeneration status due to human disturbance, particularly livestock grazing, fire and cultivation.
Therefore, the regeneration status of the woody plant species in the park generally categorized under poor and none regenerating condition; research development is needed on soil seed bank and propagation method of each tree species to stimulate regeneration specifically on species of Sterculia Africana, Adansonia digitata, Tamarindus indica, Acacia seyal and Burkea Africana.
The park as the habitat for different types of wildlife particularly for the population of African elephant; government and community must give conservation and management priority for species with IVI less than 1%, species with no seedling, and families represented by only one species.
Design conservation strategies for those economically important tree species like Boswellia papyrifera which are needed for their effective productivity and this contributes to the conservation and development of other related tree species in the park.