Assessment of Plant Species Composition and Diversity in Home garden Agroforestry Practices Across Agro-Ecological Zones of Dara district, Southern Ethiopia

In the highlands of southern Ethiopia, where the air is cool and the slopes are steep, a quiet but vital form of agriculture has sustained communities for generations. It is not the vast, open fields of industrial farming, nor is it the dense, untouched canopy of a wild forest. Instead, it is the home garden: a small, intensely managed plot of land surrounding a family's house. These gardens are a unique blend of nature and human care, where fruit trees, medicinal herbs, vegetables, and staple crops grow side by side. To an ecologist, these gardens are more than just a source of food; they are complex living libraries. They hold a wide variety of plant species, creating a layered world of roots, trunks, and leaves that supports life in ways that simple crop fields cannot. Understanding how these gardens change as you move from the hot, dry lowlands to the cool, misty highlands is crucial. It reveals how farmers adapt their land to the environment and whether these small patches of green can continue to protect biodiversity as the climate shifts and populations grow.

A team of researchers from Dilla University set out to map this hidden diversity across the Dara District, a region that stretches from 900 meters to 2,900 meters above sea level. They wanted to know if the plants found in a garden at the bottom of the valley were the same as those at the top, and how the structure of these gardens changed with altitude. To find the answers, they visited 63 different home gardens, carefully selecting them from three distinct zones: the lowlands, the midlands, and the highlands. In each garden, they did not just count the trees; they looked at the entire community of plants. They measured the width of tree trunks, the height of shrubs, and the density of the grasses and herbs on the ground. They recorded every species they could identify, from the towering eucalyptus to the tiny seedlings pushing through the soil, noting whether each plant was native to Ethiopia or brought in from elsewhere.

The results revealed a landscape rich with life but shaped heavily by human choice. Across all the gardens they studied, the team identified 214 different plant species belonging to 80 distinct families. This is a remarkable variety for such small spaces. However, the makeup of these gardens was not uniform. The most common growth form was not the tree, but the herb. Nearly half of all the plants recorded were herbaceous species—vegetables, medicinal plants, and crops that grow close to the ground and complete their life cycle quickly. Trees made up about a quarter of the plants, with shrubs following closely behind. This suggests that while the gardens are woody, their primary function for the farmers is the rapid production of food and medicine. Furthermore, the gardens are a mix of the local and the foreign. More than half of the species found were exotic, meaning they were introduced from other parts of the world, while the rest were indigenous to Ethiopia. This preference for introduced species highlights how farmers prioritize plants that offer high yields or market value, even as they maintain a significant number of native species.

The location of the garden mattered immensely for the variety of life it held. The midland zone, situated at an intermediate elevation, proved to be the most diverse. Gardens in this middle zone hosted the highest number of species, with an average of nearly 26 different plants in a single plot. They also showed the most balanced mix, where no single species completely dominated the others. In contrast, the lowlands and the highlands were less diverse. The lowlands, with their higher temperatures, and the highlands, with their cooler, potentially frost-prone conditions, supported fewer species. The difference between the lowland and highland gardens was particularly stark; the plants found in one zone were often completely different from those in the other. This high level of turnover means that a garden in the lowlands and a garden in the highlands are essentially different worlds, each holding a unique set of species that the other does not have.

When the researchers looked at the physical structure of the woody plants, they found that elevation influenced size but not necessarily the number of stems. Trees and shrubs in the highlands tended to be larger, with thicker trunks and greater height, likely benefiting from the cooler, moister conditions. However, the total number of tree stems per garden did not change significantly from the lowlands to the highlands. This suggests that farmers plant a similar density of trees regardless of the altitude, but the environment determines how large those trees grow. One species stood out above all the others in terms of its importance to the garden's structure: the enset, a plant related to the banana that is a staple food crop in southern Ethiopia. It was so abundant and widespread that it accounted for more than half of all the woody individuals counted. Alongside it, fruit trees like avocado and native timber trees like Cordia africana played significant roles, but none came close to the dominance of the enset.

Perhaps the most concerning finding of the study relates to the future of these gardens. The researchers counted the plants by their age, looking for seedlings, saplings, and mature trees. They found a population skewed heavily toward the old. There were far more mature trees than young ones, and the number of seedlings was particularly low, especially in the highlands. In the highland zones, for every 1,103 mature trees, there were only 197 seedlings. This imbalance suggests that while the gardens are full of established trees, they are not naturally replacing themselves at a rate that ensures their long-term survival. The conditions in the highlands may be too harsh for young plants to establish, or the management practices there may not be protecting the new growth. Without intervention, the current generation of trees may eventually disappear, leaving a gap that the next generation cannot fill.

The study concludes that home gardens in Dara District are vital reservoirs of biodiversity, holding hundreds of species and providing essential services to rural families. However, their health is not guaranteed. The diversity of these gardens is highest in the midlands, but the structural integrity of the system is threatened by a lack of regeneration, particularly in the highlands. The heavy reliance on a few key species, like the enset, and the dominance of exotic plants over native ones, points to a system driven by immediate human needs. To ensure these gardens continue to thrive, the researchers suggest that farmers and local leaders need to focus on helping young plants survive. This might involve protecting seedlings from grazing animals, planting more native species to balance the exotic ones, and adapting management practices to suit the specific challenges of each altitude. The future of these green oases depends on recognizing that a garden is not just a collection of mature trees, but a living cycle that requires care at every stage, from the first sprout to the towering trunk.