The influence of short-range rapidity correlations on the fluctuation of the number of charged particles in a given rapidity interval of observation is investigated. It is shown that for pp collisions at LHC energies, the fluctuations of the particle number from a given string cluster are, due to the presence of short-range correlations between particles, significantly larger than the Poisson ones. The value of the scaled and robust variance of the multiplicity for pp collisions is calculated at three initial energies: 0.9, 2.76, and 7 TeV, both with and without taking into account the processes of string fusion and formation of string clusters. A comparison with experimental data is performed and it is shown that the results obtained taking into account the formation of string clusters agree well with the experimental values, in contrast to the case where string fusion processes are not taken into account.