On 1 June 1773, Plettenberg presided over a platoon of 30 soldiers charged with the task of salvaging goods and money from the De Jonge Thomas wrecked in a storm in Table Bay.

His successor as Governor of Cape Town was Lieutenant Colonel Cornelis Jacob van de Graaff.

Plettenberg had great interest in the discovery of unknown regions and supported the exploration of southern Africa.

In his time were the voyages of August Frederik Beutler, Carl Joseph Kindermann, Carl Peter Thunberg, Anders Sparrman, Francis Masson, William Patterson, Jan Splinter Stavornius or Stavorinus, Robert Jacob Gordon and François Le Vaillant (Levaillant).

Among others he erected a column for the Dutch East India Company (VOC) on 6 November 1778, the so-called Van Plettenberg Beacon.

Plettenberg was worried about these forests and suggested that a control post be erected to prevent the over-use of the timber.