From 1897-1953 the French maintained varying levels of control over Cambodia (except for a short period when the Japanese invaded during World War II). Finally, July 3, 1953, the French gave Cambodia (and Vietnam and Laos) full independence.
During the long French protectorate period, the French did little to improve the Cambodian economy. Shortly after Cambodia became a protectorate of France, the French found that Cambodia had no hidden riches. Therefore, the French did not put a lot of money into developing the Cambodian economy. The French had a small amount of train track laid down and built some roads. But none of these things directly had much of an impact on the economy. However if Cambodians wanted to make efficient use of these new roads and tracks they would need to industrialize more.
Because the French did not industrial Cambodia, the French Protectorate period had resulted in little impact on the environment
The French did not really help the Cambodians settle any more land than they already had. Also, the French did not promote immigration of French people to Cambodia. Most of the French in Cambodia were higher up in society and lived in higher class towns that were already settled.