Seasonal scarcity and the challenge of preserving natural resources

New study shows how predictable income shortfalls can put shared forests under pressure

To the point

• High-resolution data: Researchers combined four years' worth of fortnightly household surveys with 15 years' worth of forestry enforcement records from Pemba in Zanzibar.
• Cash matters: Illegal extraction is particularly sensitive to fluctuations in sectors that generate cash, such as clove production, fishing, trade, transport and manufacturing.
• Predictable pressure: Around 20 per cent of variation in illegal forestry cases can be explained by seasonal economic cycles, with sharp downturns producing much larger increases.
• Policy implications: Conservation efforts may be more effective when combined with measures that reduce seasonal income shortfalls.

Why do people break environmental laws? A new study published in Cell Reports Sustainability suggests that in highly seasonal economies, the answer often lies not in sudden crises, but in predictable scarcity. Researchers from the Max Planck Institute for Evolutionary Anthropology examined how seasonal income fluctuations influence the extraction of natural resources in Pemba, Zanzibar. They found that periods of low earnings lead to increased pressure on shared forest resources.

The study combines unusually detailed data from more than four years of fortnightly household visits, during which production, costs, revenue, consumption, debts, credits and transfers were recorded for 300 households and over 1,200 working adults. This was supplemented by 15 years of government forestry records documenting illegal timber cutting and transport (a total of 745 cases of illegal forestry activity were recorded).

Living with predictable scarcity

The results show that seasonal changes in earnings can routinely shift the number of illegal cases by around 20 per cent per annum. While normal seasonal processes cause median household income to change by about 40 per cent annually. When household earnings rise, illegal activity declines; doubling income is associated with an average 45 per cent reduction in illegal cases. Conversely, seasonal downturns can put considerable pressure on forests.

Seasonal scarcity has been a long-standing challenge for humans. People must strike a balance between their immediate needs for food, fuel, cash and materials, and the long-term state of the resources on which their communities depend. This new study provides an example of this problem in a resource-dependent island economy. "When legal income opportunities shrink, households don't suddenly stop needing food, cash, or building materials," says Jeffrey Andrews of the Max Planck Institute for Evolutionary Anthropology, the study's lead author. "They reallocate effort across the options available to them. In some cases, that means turning to activities that violate rules governing shared resources, and the intensity to which they do so depends on how variable the seasonality is."

The study moves away from simple models of moral failure or normative framings to thinking about compliance in collective action dilemmas as structurally linked to the ways in which households cope when savings, insurance or credit are limited. This helps to explain why illegal extraction increases during predictable economic downturns: the opportunity cost of time decreases, while the immediate value of cash or materials increases.

Cash sectors drive pressure on forests

Illegal forestry is particularly sensitive to fluctuations in cash-generating sectors, such as clove production and fishing, which are two major sources of seasonal income on Pemba.  These sectors, however, are special – cloves have an unpredictable boom and bust cycle, while fishing is a major source of temporary employment for young men. When earnings from these sectors decrease, the effects are felt across the local economy, including in manufacturing, trade, transport and services, as liquidity is reduced.

Forests and other common-pool resources can act as a safety net, helping households to get through difficult periods. However, when many people experience scarcity simultaneously, their individual coping strategies can collectively endanger the shared resource base, creating tensions between immediate household needs, governance institutions, and long-term collective interests.

Climate change may amplify seasonal pressures

The study also examines how changes in rainfall driven by climate change could alter future patterns of illegal extraction. Simulations suggest that changes to the October to December “short rains” could modestly reduce earnings in several sectors, thereby increasing pressure on forests. More broadly, any process that increases the volatility of seasonal income can intensify pressure on shared resources.

The findings suggest that enforcement alone may overlook important drivers of non-compliance. If illegal extraction predictably increases during periods of low seasonal income, interventions timed to coincide with these periods could reduce hardship and environmental pressure. Potential measures include providing short-term credit, setting up savings groups, making seasonal cash transfers, offering support during pre-harvest periods, encouraging livelihood diversification, and making investments that stabilise cash-generating sectors such as fishing and agriculture.

By linking household economics, climate variability and enforcement records, the study provides a framework that could be applied to other seasonal economies. It demonstrates that illegal resource extraction is not solely a response to widespread poverty or long-term economic change, but also to recurring, predictable fluctuations in income. "Seasonality is not background noise," conclude the researchers. "It is a central feature of how people make decisions, how cooperation is maintained, and how pressure on common resources emerges."