  The combination of a large superconducting gap, low transition temperature,
and quasi two-dimensionality in strongly underdoped high temperature
superconductors severely constrains the behavior of the ab-plane superfluid
density \rho with temperature T. In particular, we argue that the contribution
of nodal quasiparticles to \rho(T) is essential to account both for the
amplitude of, and the recently observed deviations from, the Uemura scaling. A
relation between T_c and \rho(0) which combines the effects of quasiparticle
excitations at low temperatures and of vortex fluctuations near the critical
temperature is proposed and discussed in light of recent experiments.
