Old Trees, Thin Harvests: The Age Structure Behind Zanzibar’s Declining Clove Crop

It’s easy to read Zanzibar’s clove statistics year by year and see nothing but noise — a good season followed by a bad one, prices up one year and crashing the next. Looked at across a full century instead, the pattern is not noise. It’s a long, close-to-monotonic decline from a nineteenth-century peak, and the underlying driver is one that doesn’t change from season to season: the age of the trees producing the crop.

A hundred and fifty years of numbers

By the end of the 1800s, Zanzibar supplied roughly ninety percent of the world’s cloves, according to AramcoWorld’s history of the trade — the direct result of Sultan Said bin Sultan’s 1830s policy requiring three clove trees planted for every coconut palm, itself a response to the loss of slave-trade revenue. Production held near that scale into the twentieth century. The Citizen’s retrospective on the industry cites annual output of roughly 16,000 tonnes in the 1970s, falling to around 10,800 tonnes in the early 1980s, then to about 3,500 tonnes by 1990 — a collapse that followed the 1964 revolution and the nationalization of plantations under the new government. From 2015 to 2020, output swung between 1,690 and 8,277 tonnes depending on the year; more recently, production came in at 7,840.8 tonnes in 2021 and fell to 4,734 tonnes in 2022, per Zanzibar government figures reported by The Citizen. By 2025, the same outlet’s retrospective piece put current annual output at roughly 5,550 tonnes — a fraction of the nineteenth-century peak — and reported that export earnings had fallen by approximately 76% year-on-year, from close to $28.8 million to around $6.3 million.

Why age, specifically, is the constraint

Clove trees are slow assets. They take six to ten years to yield a meaningful harvest and up to twenty years to reach full maturity, according to the historical account in The Citizen’s 2025 piece on the industry’s 200-year arc — which also identifies aging tree stock, alongside emerging crop disease affecting hundreds of thousands of trees, as a current structural constraint on output, separate from any given year’s weather or price.

A controlled agronomic study specifically on Zanzibar clove trees — comparing young trees (3–4 years old) against mature ones (45 years old), published via PMC in 2020 — found that flowering buds from the young trees actually produced a higher essential-oil yield (16.73%) than buds from the 45-year-old trees (14.93%). That’s a counterintuitive but important data point: productivity per bud does not simply keep rising with tree age. Combined with the historical record of a government replanting programme dating to the 1960s that was, by most accounts, never sustained at the pace needed to keep the tree stock young, the picture that emerges is of an aging orchard base whose average productivity has been quietly eroding for decades — independent of whatever the buying price happens to be in any given year.

A pricing system with weak replanting incentives

The Zanzibar State Trading Corporation, the sole official buyer since 1966, operates under a government policy of paying farmers 80% of the prevailing market price for cloves — a structure that, by design, leaves smallholders capturing less than the full value of their crop even before considering the cost of replanting a tree that won’t yield significantly for six to ten years. Research compiled in a 2022 WIDER working paper on the determinants of Zanzibar’s clove exports has linked persistent low farmgate prices under this monopsony structure to reduced farmer incentive to invest in replanting — a feedback loop where an aging tree stock depresses output, low buyer prices reduce the return on replanting that stock, and the orchard keeps aging. Some growers, faced with declining yields from old trees and thin margins, have reportedly cut clove trees for firewood and charcoal instead — a small but telling sign of how the economics can invert at the smallholder level.

None of this is a story that resolves in a single season. Unlike a price swing driven by one buyer’s decisions in one year, an aging tree stock is a multi-decade problem, and the data suggests Zanzibar has been living with it, in slow motion, since at least the 1980s.