John Croumbie Brown was a grandson of the renowned Scottish theologian Rev. John Brown (1722-1787) and was trained as a missionary. In 1833 he was sent to St. Petersburg, Russia, by the London Missionary Society and spent four years there. In 1844 the same society asked him to go to Cape Town to assist another of its congregations to become self-supporting. He stayed for four years. During this time he demonstrated an interest in, and familiarity with, the natural sciences by presenting a variety of public lectures on scientific topics. His first lecture, in association with the Cape Town Mental Improvement Society, was "On the discoveries of modern astronomy" in November 1844. This was followed, from May 1845 onwards, by a series of lectures on chemistry, in association with the recently established Institute for the Diffusion of Useful Knowledge (which had incorporated the Mental Improvement Society). Finally, in May 1847, he started a series of lectures in association with the same Institute, "On the physiology and structure of the human frame". The two series of lectures were published in book form in Cape Town in 1846 and 1848 respectively.
Back in Scotland Brown settled as a pastor in Aberdeen in 1849. Here he delivered a further series of scientific lectures which were so much appreciated that he was presented with a microscope. He also studied botany, and in April 1853 was appointed lecturer in botany in the Joint Medical School (King's College), Aberdeen. He received the degree Doctor of Laws from the same School in 1858.
In 1862, after the death of Dr. C.W.L. Pappe*, Brown accepted the post of Colonial Botanist at the Cape, arriving in April 1863. The post included an appointment as professor of botany at the South African College, Cape Town, though he had only one student in 1864. He undertook a tour of observation through the colony during 1863, delivering public lectures on botany and endeavouring to promote an interest in the subject among the general population. He discouraged deforestation and veld burning, arguing that these led to the loss of soil mosture. He advised the government on forestry matters, and added various memoirs on forestry, as well as a list of South African trees, shrubs, and arborescent herbs, to his annual report for 1866. In his reports he also gave attention to various agricultural matters, such as diseases in fruit trees, rust, manuring, the cultivation of various crops, experimental farms, irrigation, and Cape wines. He is furthermore credited with the first official record in South Africa of "krimpsiekte" (poisoning by plants of the family Crassulaceae) in goats, in his report for 1863. He visited various localities where water might be stored, travelling at his own expense, and collected information on the hydrology of the country. Throughout he showed a profound interest in the welfare of the farming community. However, he did not contribute much to botany, though he did organise the collection and distribution of local plants and seeds.
Brown's post was abolished at the end of 1866 for financial reasons and he returned to Scotland in January 1867. His work was severely criticized by H. Bolus*, who described him as incompetent. Others pointed out that he had contributed little if anything to botanical knowledge. However, in 1865 W.H. Harvey*, in the preface to Volume 3 of the Flora Capensis, thanked Brown "for his unremitting kind attention to the interests of this work, and for the zeal which he has shown, since his appointment, in endeavouring to promote the study of botany in all parts of the Colony, and among the neighbouring extra-colonial missionaries". The government also seriously considered his recommendations and acted upon some of them. Hence he failed as a scientific botanist, but did much to promote public interest in the subject, as well as sound methods in agriculture, forestry, and veld management.
Brown continued his studies on the forestry and hydrology of the Cape Colony in Scotland, publishing several important works. The first of these, Hydrology of South Africa, was published in London in 1875. In Part 3 of this work the author deals extensively with the aridity and water supply of South Africa, as affected by vegetation and forests. His Water supply of South Africa and facilities for the storage of it (Edinburgh, 1877) contains summaries of all available meteorological observations, an exhaustive treatment of the climate of South Africa, and a discussion on how to alleviate the effects of the aridity of the Cape by building dams to collect run off, stopping veld burning, and conserving and expanding forests. In 1881 he published an article on "Forests in South Africa" in the Transactions of the Royal Scottish Arboricultural Society, and in 1887 a book, Management of Crown forests at the Cape of Good Hope under the old regime and under the new. In this work he pointed out that over-exploitation and fire clearing have led to deforestation of large areas and reduced rainfall. Many of his unpublished manuscripts on South African agriculture, forestry and botany were brought to South Africa by his grandson, Dr. Eric A. Nobbs*, and were later deposited in the Faculty of Forestry at the University of Stellenbosch.
Brown was a prolific writer. In addition to his publications relating to South Africa and religious writings he wrote books on Forests and moisture... (1877); forestry in France (1875, 1878), Finland (1883), England (1883), Norway (1884), Northern Russia (1884), the Urals (1884), and Poland (1885); forest schools in Spain (1886), and Germany (1887); forest economy (1884); the pine trees of Europe (1890); and on the people of Finland in archaic times (1891). He also translated the Narrative of an exploratory tour to the north-east of the Colony of the Cape of Good Hope... by T. Arbousset*, from French into English. The translation was published in Cape Town in 1846. His "List of Natal trees" was published as an appendix to J. Chapman's* Travels into the interior of South Africa... in 1868 (Vol. 2, pp. 464-465).
Brown was elected a Fellow of the Royal Geographical Society and a Fellow of the Linnean Society, mainly on the strength of his reports on his work at the Cape.