Colin C. Robertson, forester, was the son of James Robertson, headmaster of Haileybury College, and his wife Constance. After completing his schooling at Rugby School in 1902 he came to South Africa and in February 1903 was appointed in the Forestry Division of the Department of Agriculture, Orange River Colony (now the Free State) under the conservator of forests, K.A. Carlson*. The colony and its administration were created towards the end of the Anglo-Boer War (1899-1902) and Robertson's uncle, Sir H.F. Wilson*, was its colonial secretary. During 1903 and part of 1904 he was stationed at Wilgeboom Nek, near Thaba Nchu, from where he sent regular meteorological observations to the Meteorological Commission of the Cape of Good Hope.
In 1905 Robertson was sent to the United States to study forestry at the Yale University Forestry School. As part of his studies he visited Mexico in 1906 to study the cultivation of its pine trees. The next year he was awarded the degree Master of Forestry (MF) with distinction, following the completion of a two year course. He returned to Bloemfontein in September 1907 and the next month was appointed assistant chief of the Forestry Division. He arranged the importation of seedlots of many Mexican pine species, with a view to testing them in the drier regions of the country. His interest in their cultivation eventually led to the publication of his treatise on "The cultivation of Mexican pines in the Union of South Africa, with notes on the species and their original habitat", published in six parts in the Empire Forestry Journal (1932-1934).
Robertson was a member of the Philosophical Society of the Orange River Colony. In 1909 he became a member of the South African Association for the Advancement of Science and that same year presented a paper, "Some suggestions as to the principles of the scientific naturalisation of exotic forest trees", at its annual congress in Bloemfontein. The paper was published in the association's Report for that year (pp. 219-230). In 1916 he became a foundation member of the South African Biological Society.
After the formation of the Union of South Africa in 1910 Robertson was transferred in 1912 to the Department of Forestry in Pretoria as its first research officer. His work was interupted by World War I (1914-1918), during which he did military service in German South West Africa (now Namibia) and in Europe. Soon after his return to South Africa in 1919 he was promoted to chief research officer and professional assistant to the chief conservator of forests, Charles E. Legat*. His duties included the supervision of forestry activities all over the country and Legat found him a prodigious, meticulous and enthusiastic worker.
Robertson published a two-part paper, "Influence of forests on climate and moisture contitions", in the Agricultural Journal of the Cape of Good Hope (1909, Vol. 34, pp. 249-253, 387-393), describing the advantages of aforestation in preventing the loss of soil mosture. A later paper by him, "Prosopia juliflora, the mesquite or algaraba tree, and Prosopia pubescence, the screw bean", appeared in the Agricultural Journal of the Union of South Africa (1914, Vol. 8, pp. 233-239). His description of "The forests of South Africa" was published in the Empire Forestry Journal in 1924. That same year he visited Australia and upon his return wrote an excellent report, The trees of extratropical Australia. A reconnaissance of the forest trees of Australia from the point of view of their cultivation in South Africa. A report of a tour in Australia in 1924 (Cape Town, 1926, 265p). Subsequently his "Notes on artificial extraction of seeds from cones of Pinus longifolia and Pinus patula" was published in the South African Journal of Science (1927, Vol. 24, pp. 320-328).
Following Legat's retirement in 1931 Dr F.C. Geldenhuys, an agricultural economist, was appointed as chief conservator of forests. Serious differences of opinion between Robertson and him led to Roberson's retrenchment. He settled at Winterkloof, outside Pietermaritzburg, in 1933 and the next year married Kathleen Jameson, with whom he had a daughter.