Woody vegetation structure in dry woodlands of Amhara National Regional State of Ethiopia

1. Woody vegetation structure in dry woodlands of Amhara National Regional State of Ethiopia Biresaw Mahtot Alemu, Department of Forest Botany, Dendrology and Geobiocoenology, Faculty of Forestry and Wood Technology, Mendel University of Agriculture and Forestry Brno, Zemedelska 3, 613 00 Brno, Czech Republic

2. Introduction Forest Resource Base Amahara nNational Regional State (ANRS) Total area 17,075,200 ha. (AFAP 1999) The forest resource base of the Region comprises natural high forests, woodlands, bushlands, plantations and on-farm (farm forestry) trees. Estimates of the size of the resource base are Forest type Area (ha) Natural high forest 0.5% Woodlands 4 % Bushland 11,6% Shrubland 19.9% Plantation 0.2% Farm Forestry 0.4% Total 36.8%

3. Introductioncontinue�

4. Introductioncontinue� The information on distribution of plants among size, or age class categories indicates the history of the past disturbance on the species and the environment and hence, used to forecast the future trend of the population of that particular species. The structure of population reflects its current size class distribution and its long-term population dynamics as well (Peters 1996). used to immediate identification of poorly represented stages of life history (Hall and Bawa 1993).

5. Introductioncontinue�

6. Materials and methodsFig. 1 Map of Ethiopia with Amhara National Regional State and study sites Study area study was carried out in two deciduous dry woodlands Mosebit and Hamusit (Figure 1) in two districts of Amhara National Regional State (ANRS) of Ethiopia. separated from each other by agricultural and/or settlement landscapes.

7. Characteristics of study sites Rainfall and Temperature Unimodal, 9-month dry season;

8. Fig. 2 Climatic data for both study sites interpolated from the closest 20 meteorological stations (Riediger 1999).

9. Methods

11. Data Analysis Quantitative analysis was carried out to quantify species abundance (density), dominance (stem basal area) and cover (canopy cover) of the woody species. as well as environmental data (soils, slope, altitude, aspects) of 15 study plots. the population structure of all species found in plots were grouped in to ten diameter size classes and nine height classes (peters 1996) and presented using and presented using Statstistic data analysis software (StatSoft, Inc. 2008). Relative density, relative dominance and relative cover of the woody species were calculated (Mutangah, 1989 and Kigomo, Savill & Woodell, 1990).

12. Results Floristic composition 32 species belonging to 13 families and 29 species belonging to 15 families were recorded from Belesa and Jawi sites respectively 51.8% were trees, 46.4% shrubs and 1.8% woody climbers. The families with the highest number of species were:- Fabaceae (17 species), Combretaceae (5 species), Burseraceae (4 species), Euphorbiaceae and Anacardiaceae (3 species each) and Sterculiaceae, Rhamnaceae, Tiliaceae and Capparidaceae (2 species each).

14. The most abundant species:- B. papyriifera, (Bureseraceae) (35.5%) Albizia amara (Fabaceae) (18.3%), Cassia arereh (Fabaceae), (10.7%) Combretum molle (combretaceae), (6.2%) The species with the highest frequency value was Boswellia papyrifera (100%), Albizia amara (66.7%), Cassia arereh (53.3%) and Sterculia africana (46.7%).

15. Figure 3. woody plant density in relation to land use intensity in both site pooled A few species of individuals were found in Cultivated woodland

16. Fig. 4 . Population structure of all woody vegetation based on diameter class distribution, all sites pooled No significance differences between plots a sort of bimodal distribution showed that there are more individuals concentrated in the lower classes (1-4 cm) sharp decreased number of individuals with increasing size classes (4�12 cm), gradually increase up to the next two classes (12- 20 cm) a gradually decline towards the upper classes. Mean dbh 13.23 +/- 10.06 cm Maximum dbh was found in Mosebit 67 cm (Sterculia setigera ). DBH size class 2= < 4 cm, 3= 4-8 cm, 4= 8-12 cm, 5= 12-16 cm, 6= 16-20 cm, 7= 20-24 cm, 8=24-28 cm, 9= 28-32 cm 10= 32-36 cm, 11= 36-40, 12= > 40

17. Figure 5. The diameter frequency distribution of B.papyrifera plants at both study sites A composition predominated by trees of medium size (Mean dbh 20.22 +/-5.36 cm ) No Boswellia idividuals were found in 1st dbh class an indication of absence of new recruitments through regenerations, and thus unstable populations. lack of establishment of seed The possible reasons for hampered regeneration are human disturbance damage caused by free grazing livestock and land use change, ? DBH size class 2= < 4 cm, 3= 4-8 cm, 4= 8-12 cm, 5= 12-16 cm, 6= 16-20 cm, 7= 20-24 cm, 8=24-28 cm, 9= 28-32 cm 10= 32-36 cm, 11= 36-40, 12= > 40

18. Fig. 6. Population structure of the most abundance species in both sites  some species possessed high number of individuals in the lower DBH classes particularly in the first class,(good regeneration potential (Albizia amara 20%, Cassia arereh 12% and Combretum molle 2%),) possessed either no or few number of individuals in the lower DBH classes, (indicates that the species are in poor regeneration status.)

19. Fig. 7. Population structure of Boswellia papyrifera in relation to landuses

20. Fig. 8. Population structure in relation to land use for all woody plant species

21. Continue�. No individuals are found in the first two dbh class (1�8 cm ) within cultivated woodlands The only land use system which does not have regeneration is cultivated land. It may be deliberately cleared for cultivation of arable crops forest land had high number of saplings In relatively preserved woodland all size class are represented

22. Population structure Boswellia based on height-class distribution at both sites. Only one individuals were found in in the 2nd 13 th plots Two individuals were recorded in 8th plot No significance differences between plots =25%-75% Non-Outlier Range , ? = Outliers, * = Extremes No or a few of individuals in the 1 st height class More concentrated in the 3rd and 4th height classes ( 4-8 m) No Boswellia idividuals were found in 1st hieght class in Belesa Mean height 6.13 +- 0.19 m

23. Population structure of all woody plants based on height-class distribution at both sites. No significance differences between plots High number of individuals in the first height class (0-2 m), 30% Better represented in consecutive three height classes (2- 10 m) Steadily decreasing towards the upper height classes Mean height 4.77 m

24. Relationship between seedlings and matured & saplings that plots with the larger number of trees had also a higher number of seedlings was only fulfilled in plot five Mosebit. In other plots there were no clear relation between trees and regeneration.

25. conclusion This is the the first study in these two districts to identified the composition of the species and its structures�.and contribute We found that, a relatively high number of species than privies studies in the same region, A few studies in the ANRS Metema (e.g Eshete 2002, Asfaw 206 , ) and Tach armachiho districts (Eshete 2002) have almost similar results (24 and 32 species in Metema and 27 species in Tach armachiho districts) Lesser density of Boswellia papyrifere was found in Jawi and Belesa. density and basal area of all woody plants and B.papyrifera shows a significant differences from other studies. It may be attributed a high human induce factors in both sites