What does this equation mean?

The dynamics are simple enough to write down, and writing them down exposes an assumption that verbal accounts tend to hide. Let the stock carried into the next period be $S_{t+1} = (1-\delta)\,S_t + H_t - C_t - T_t$. where $S_t$ is the stock held, $H_t$ the harvest added, $C_t$ own consumption, $T_t$ the quantity appropriated by others, and $\delta$ the proportional loss rate to pests, damp and spoilage. The equation is illustrative rather than estimated, and its value is that it separates two subtractions usually conflated. Grain that rots is gone; grain that is taken still exists and has changed owner. A society can be losing a large share of its stock while nobody is being taxed at all, and a low loss rate is what makes a high appropriation rate worth organising. Loss sets the horizon over which any claim on stored food is meaningful: when $\delta$ is high, a granary cannot underwrite an obligation more than a season away, and neither insurance nor extraction can be planned around it.