Should we Leave Nature Unattended or Assist through Enrichment to Foster Climate Change Mitigation? Exclosure Management in the Highlands of Ethiopia.

In order to foster the potential of exclosures to sequester carbon, it is understood that they are increasingly assisted through enrichment planting. To study the impact of the enrichment planting on carbon sequestration process, five exclosures with enrichment planting and five pure naturally regenerated exclosures were selected. Along parallel transects, 20 × 20 m plots were laid at 100 m intervals where all woody vegetations were counted and measured for their diameter and total height. For soil sampling, five subplots at the center and four at each corner of the plots were established. The samples were collected at a depth of 0-0.2 m, and this procedure was repeated for each plot. In this case, when good management practices were implemented (such as Wukro exclosures), significant differences in organic soil carbon above the ground and the total carbon between naturally regenerated and enriched exclosures (P < 0.05) were found. The mean estimates of the above ground carbon, soil carbon, and total carbon were respectively 8.08, 31.04, and 39.12 ton/ha for natural regeneration vs. 7.94, 31.00, and 38.93 ton/ha for enriched regeneration. Lower altitudes had significantly higher soil organic carbon (P < 0.05) than the higher altitudes. However, the slope had an insignificant effect on carbon distribution. Enriched exclosures performed more poorly in carbon sequestration. This was possibly due to the disturbances caused by mass plantation and poor post plantation follow up, since improved performance (P < 0.05) was seen in one enriched exclosure with better management practices.

Topographic variables to determine the diversity of woody species in the exclosure of Northern Ethiopia.

Exclosures are established with the objective of rehabilitating degraded lands and restoring of woody vegetation. Various studies have been conducted to evaluate the success of exclosure on restoring woody species diversity. However, works focusing on the effect of topographic factors on woody species diversity are scarce. Understanding the factors that determine woody species diversity is important for management purposes. Therefore, this paper analyzes the effect of altitude, slope, and aspect as topographic variables on woody species diversity in Dawsura exclosure in northern Ethiopia. Data on species identity, abundance, slope, elevation and aspect were recorded from 58 sampling plots. Different diversity indices were used to analyze the data and one-way ANOVA and linear regression was conducted. There were a total of 34 woody species represented 15 families, of which 62% and 38% were trees and shrubs respectively. Altitude (r2 = 0.63, p = 0.000 and r = 0.794, p < 0.01) and slope (r2 = 0.57, p = 0.002 and r = 0.68, p < 0.01) correlated significantly and positively with Shannon diversity, whereas aspect (r2 = 0.12, p = 0.378 and r = 0.27, p > 0.05) did not correlate significantly with Shannon diversity. Woody species diversity at moderate (1.44) and high (1.85) altitudes was significantly different from that of low (0.86) altitude areas (p = 0.0013). Furthermore, significantly higher woody species diversity was recorded at steep slope (1.88) and moderately steep slope (1.62) areas as compared to the gentle slope (0.95) areas. No significant variation was observed in woody species diversity among the aspect categories (p > 0.05). The study concludes that woody species diversity is largely regulated by slope and altitude than aspect in the exclosure. We suggest other environmental and anthropogenic variables should be taken into consideration in future studies on woody species diversity.