Highland Soils and Fungal Residue: A Survey of Kaffa and Harar?

Highland Soils and Fungal Residue surveys the agricultural conditions and fungal ecology of the Kaffa and Harar regions—the heartland of buna cultivation—from the fifteenth century through the early colonial period. The Kaffa highlands, rising above 1500 meters in the forested southwest, and the limestone plateaus of Harar to the northeast, provided the narrow climatic window in which Coffea arabica thrived as both wild plant and managed crop. The soils of both regions, derived from volcanic basalt and volcanic ash in Kaffa and limestone-derived clay in Harar, retained moisture through the dry seasons and offered the acidic profile the plant demanded. Yet this same environment harbored fungal pathogens that would prove catastrophic once the plant's range began to contract.

The arrival of the Harar Wilt in 1543 marked not the introduction of a novel pathogen but rather the explosive spread of fungal species—likely several distinct rust fungi of the genus Hemileia, though contemporary accounts remain too vague to permit certain identification—that had coexisted with wild buna stands for centuries in a condition of equilibrium. Wild-coffee forests in Kaffa, scattered across terrain too steep and inaccessible for systematic cultivation, had evolved alongside these fungi. The fungal load remained low where plants were dispersed and surrounded by competing vegetation. Intensified cultivation, particularly the clearance of understory plants and the establishment of denser buna stands in terraced plots around Ta'izz in Yemen and in managed groves near Harar city, altered this balance. Merchant accounts from the 1530s describe the profitability of buna exports from Red Sea ports; by 1550, letters from Portuguese traders report fields already failing.

The mechanism of the fungal advance remains incompletely documented. Several scholars propose that the Harar Wilt represented a single catastrophic infection event, possibly introduced through seed or plant material carried along newly intensified trade routes. Others, notably Alemayehu in his 1987 study Highland Pathogens and the Limits of Monoculture, argue for a more gradual process of fungal adaptation to cultivated hosts, with the wilt representing the threshold moment when multiple fungal species achieved simultaneously high virulence. The distinction has material consequences: a single introduction event would suggest human agency in spreading the blight, while an adaptation model suggests the plant's own expansion created the conditions for its undoing.

What is certain is that by the 1570s, systematic buna cultivation had largely ceased in both Kaffa and Harar. The terraced plantations around Ta'izz in Yemen, established with great expense in the 1550s and 1560s to supply the Ottoman market, failed irreversibly by 1575. Contemporary Yemeni tax records show declining export volumes, then the cessation of buna as a taxed commodity. The wild forests of Kaffa, harder to document, experienced less sudden collapse but steady retreat. By 1620, when the Portuguese geographer and missionary Gonçalo Estêvão surveyed the region, he found buna cultivation restricted to scattered high-altitude plots tended by individual households and monastic communities, primarily at Debre Libanos and similar refuge sites.

The ecological consequence persisted for generations. Soil surveys conducted by Italian agronomists during the colonial period of the 1880s and early 1900s noted that plots formerly devoted to buna showed persistent fungal spore loads in the upper soil horizons, detectable through inoculation experiments. Whether this represented dormant fungal matter capable of re-infecting new plantings, or merely residual spores of saprophytic fungi no longer pathogenic, remained unclear. The result was the same: any attempt to re-establish large-scale buna cultivation in the same locations faced immediate and severe disease pressure. This fungal legacy in the soil itself, not merely in wild host populations, appears to have been the primary obstacle preventing even local merchants from rebuilding the crop after the initial wilt had passed.

The persistence of buna in isolated highland communities—maintained through careful seed selection, cultivation at marginal elevations where fungal pressure remained low, and rotation between scattered plots—allowed the plant and its preparation to survive as a cultural practice rather than a commodity. This dispersed, localized preservation, while it prevented the extinction of Coffea arabica in its native region, also made the plant inaccessible to large-scale cultivation or trade, a condition that persists to the present day.