The Ecology of Helichrysum Splendidum and Festuca Macrophylla in the Menz-Guassa Community Conservation Area and their Future Distribution Under Climate Change in the Central Highlands of Ethiopia
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2024-01
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Addis Ababa University
Abstract
In the Ethiopian highlands, the invasion of Helichrysum splendidum threatens ecosystem services in and around a community-based conservation area, particularly the provisioning of the Festuca macrophylla which is a highly valuable resource for the livelihoods of the local communities and for grazing by livestock and wildlife. The main objective of this research is to investigate factors responsible for a rapid encroachment of Helichrysum splendidum that might lead to and its abundance in the Menz-Guassa Community Conservation Area, Amhara Regional State, Ethiopia.
The study aimed to address four specific objectives. These are: 1) to assess the soil seed bank composition and density (Article I); 2) to investigate the effect of aspect and elevation on the natural regeneration status (Article II); 3) to describe a conservation assessment of the Afroalpine grass (Festuca macrophylla) by habitat suitability modeling (Article III); and 4) to assess habitat suitability of Helichrysum splendidum and Euryops pinifolius under changing climate scenarios for the conservation of Festuca macrophylla (Article IV).
A two-way ANOVA (Analysis of variance), General Linear Model (GLM), SAS statistical software version 9.0.1 (SAS Institute, 2001) for data analysis and the Shannon diversity index to determine soil seedbank diversity and regeneration status (objectives 1 and 2). Then, vegetation was stratified and eight blocks (sampling sites) were selected across a range of elevation and aspect (northeast, northwest, southeast, southwest). Within each block, twenty, 5m x 5m plots
were established (a total of 160 plots). Then, 480 soil samples were collected from five subplots (each measuring 1 m x 1 m) at three depths (0-3 cm, 3-6 cm, and 6-9 cm), which were then sieved and transferred the soil samples to pots in the Glasshouse for the soil seedbank to germinate. After twelve months we identified 74 plant species, representing 55 genera and 23 families that germinated from the soil seedbank. Out of the 74 plant species identified from soil seedbank germination, 11 species are endemic to Ethiopia. Species abundance was negatively correlated with elevation, with fewer species occurring at higher elevation. Meanwhile, species abundance was positively correlated with both northwest and northeast aspect. The highest seed densities were occurred in the upper three centimeters of soil and a gradually decreasing number of species and densities of seeds with increasing soil depth.
For the regeneration data collection, plots were stratified according to two elevational categories (<3350 m/lower and >3350 m/upper elevation) to test whether removal and subsequent regrowth will respond differently at low and high elevations from twenty 5m x 5m plots for a total of 160 plots. Results from the analysis of regeneration status showed that a total of 31 species, representing 27 genera and 16 families were recorded. The families with the highest number of species were Asteraceae (18 species, 22.5%), Fabaceae (3 species, 10%), and Poaceae (3 species, 10%). Of the total families, the dicots constituted 87.5% and monocots 12.5%. Species abundance was negatively correlated with elevation, with fewer species occurring at higher elevation. Meanwhile, species abundance was positively correlated with both northwest and northeast aspect. Germination of H. splendidum decreases over time showing less cover abundance as compared to the number of species before the removal was conducted.
For objective 3, MaxEnt (Maximum entropy model, Version 3.4.1) software was used to run habitat suitability model. Dataset of 119 occurrence points that were compiled, and gathered during fieldwork to run the model. For predicting suitable habitats of Guassa grass, 24 environmental variables were used. The 19 bioclimatic variables and average annual solar radiation data were downloaded from WorldClim (www.worldclim.org) at ~1 km2 (30 arc second) resolution. The model performed highly according to the area under the curve (AUC =0.96), yet nearly 80% of highly suitable Guassa habitat falls outside the range of our training data. It was found that Guassa grass distribution is primarily limited by low mean temperature in the warmest quarter (BIO10, 36.7%), high precipitation in the wettest quarter (BIO16, 21%) and low precipitation in the driest quarter (BIO17, 15.6%).
For the fourth objective, the current and future distribution of Festuca macrophylla, Helichrysum splendidum and Euryops pinifolius were investigated under changing climate scenarios in Ethiopian highlands by using MaxEnt software. Two Representative Concentration Pathways, i.e., the intermediate (RCP 4.5) and extreme (RCP 8.5) were used for the years 2050 and 2070.
Forty-eight, 51 and 53 occurrence data of Festuca macrophylla, Helichrysum splendidum and Euryops pinifolius, respectively, were collected during field visits to the GCCA in 2020. A total of 22 environmental variables including elevation, solar radiation index (SRI), and topographic position index (TPI) were used. Pearson’s correlation was used to test for a collinearity of environmental variables that could produce a robust modeling of current and future suitable habitats of these species.
The results showed that the predicted suitable habitats for the three species, both current and future, were significantly influenced by elevation, topographic position index and Mean temperature of coldest quarter (Bio11). The predicted Festuca macrophylla habitat suitable distribution is limited to the central highlands of Ethiopia under different climate scenarios.
While, the central highlands, northern, western, and north-western Ethiopia were the main habitat suitability distributions for Helichrysum splendidum and Euryops pinifolius in the current and future climate scenarios. These distributions were less suitable, moderately suitable, suitable, and highly suitable habitats. The comparative relative area between the various types of suitable habitat showed a decreasing trend from less suitable to highly suitable habitats, according to the future climatic scenarios.
In conclusion, the existing conservation approach, while admirable and promoting the growth of H. splendidum and the decline of F. macrophylla, calls for interventions to ensure its long-term persistency. The finging of this study urge managers to closely monitor the shifting populations of Guassa grass to determine whether the species is suffering from an extinction debt as a result of climate change's rapid warming at high elevations and altered rainfall patterns in the Ethiopian highlands.
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Keywords
Afroalpine, Conservation Area, Encroachment, Guassa Grass, Regeneration Potential, Species Recovery