A vegetarian diet is typical of herbivores who digest both the content of plant cells and much of the tough cell wall. In an herbivores stomach, the tough cell wall is digested by microbes after plant parts ferment in their complex stomach. Schaller et al. Pandas are vulnerable when there are large fluctuations in their food supply due to bamboo die-offs. Professors Qin Zisheng and Alan Taylor in matrue arrow bamboo stand.
Bamboo die-off's are natural.
But periodically, each bamboo species flowers, sets seed, and then dies back. The probability of a seed surviving seed-eaters would be greatest when most seeds are produced. But bamboos don't have to die after they produce seed. We don't know, but bamboo seedlings may need their parents to die to establish and grow. Mature bamboos cast deep shade and few plants survive beneath a dense bamboo canopy.