Table 1.

Five principles (P1–P5) for understanding change in drylands, after ref. 4, with conclusions from this study

Principle	Dryland development principles and key implications	Conclusions from drought episode analysis
P1	Human–environmental systems are coupled, dynamic, and coadapting, so that their structure, function and interrelationships change over time. Understanding dryland desertification and development issues always requires the simultaneous consideration of both human and environmental drivers, recognizing that there is no static equilibrium to aim for.	The episodes cannot be understood without analyzing the links between the human and environmental subsystems. The two subsystems have shown some coevolution in the way that human learning has caused and responded to change, although there remain dysfunctional aspects to these changes.
P2	A limited suite of slow variables are critical determinants of human–environmental system dynamics. A limited suite of critical processes and variables at any scale makes a complex problem tractable.	In early episodes, pastoralists and institutions alike were only monitoring and responding to fast variables (rainfall and pasture production, not long-term climatic cycles and pasture condition; market prices, not long-term trends and variability), and have only gradually come to focus on the underlying controlling variables.
P3	Thresholds in key slow variables define different states of human–environmental systems, often with different controlling processes; thresholds may change over time. The costs of intervention rise nonlinearly with increasing land degradation or the degree of socioeconomic dysfunction; yet high variability means great uncertainty in detecting thresholds, so managers should invoke the precautionary principle.	There were critical thresholds observable in both human and environment subsystems, management that was viable under good climatic and market conditions collapsed when both declined; the thresholds of rainfall or stock numbers at which such collapses happen were made more sensitive by the effects of antecedent management on pasture condition (and debt levels). The eventual impacts of high stock numbers, while triggered by drought, were generally a result of slow declines in the resilience of vegetation, coupled in some cases with threshold declines in soil fertility and water holding capacity.
P4	Coupled human–environmental systems are hierarchical, nested, and networked across multiple scales. Human–environmental systems must be managed at the appropriate scale; cross-scale linkages are important in this, but are often remote and weak in drylands, requiring special institutional attention.	Understanding the interplay between effects at different scales in space, time, and institutional process is crucial to future solutions. Management and learning at the individual pastoralist scale turns out to be too fine-scaled, particularly in time, while tactical responses at the national level are too ponderous (and often counterproductive). Policy needs to focus on creating a context of regional institutions and knowledge support rather than intervening directly.
P5	The maintenance of a body of up-to-date LEK is key to functional coadaptation of human–environmental systems. The development of appropriate hybrid scientific and LEK must be accelerated both for local management and regional policy.	There was no lack of LEK and learning within some individuals' lifetimes, but this was acting against many institutional and economic pressures and mismatched particularly with the time scale of variability. The climatic drivers of importance were those associated with long-term (quasi-decadal) oscillations. This cycle (≈19 years) is too short to be regarded as invariant for a manager's lifetime, but too long for one manager to build up repeated experience of changes. The necessary collective learning requires an alliance of industry, science, and public institutions and is now further hindered by climate change.