The country's 6 million acres of forests constitute a valuable source of raw material. Information on the volume of the annual tree harvests has not been published. Substantial quantities of lumber and, increasingly, of lumber products and furniture have been exported, although at the expense of domestic consumption. In a program to conserve and rebuild this important resource, which was severely overexploited during World War II, a strict limitation was placed in the early 1950s on the annual volume of timber cut. A further reduction in the amount of timber felling was decreed for the 1971-75 period. Through a more efficient utilization of the timber and the expansion of wood processing, including the manufacture of plywood, chipboard, and furniture, the value of the output, nevertheless, increased substantially. Exports of lumber and wood products accounted for 13.4 percent of total exports in 1970, but this ratio is scheduled to decline to 6 percent in 1975, not because of a reduction in the volume of these exports but as a result of a planned expansion of other industrial and food product exports. ELECTRIC POWER Electrical power development has proceeded at a rapid pace. The installed generating capacity of 7.3 million kilowatts in 1970 was four times larger than the capacity available a decade earlier. Eighty-four percent of the installed capacity in 1970 was in thermal power plants, and the remaining 16 percent, in hydroelectric stations. Hydroelectric capacity development had been relatively more rapid, with a sixfold increase during the decade. The production of electrical energy increased even faster than installed capacity because newly built plants operated at greater efficiency. The output of 35 billion kilowatt-hours in 1970 was 4.6 times greater than output in 1960. Power output is scheduled to reach 58 billion to 60.8 billion kilowatt-hours in 1975. These figures imply an average annual increase in power production of 10.5 to 11.7 percent, compared with an average increase of 16.5 percent in the 1960-70 period. Thermal power plants accounted for 92 percent of the output in 1970, and hydroelectric stations, for only 8 percent. Output per unit of thermal capacity was more than double that of hydroelectric generators. The total hydroelectric power potential that could be economically developed has been estimated at 24 billion kilowatt-hours per year. The Romanian power grid is connected to the power grids of Bulgaria, Czechoslovakia, and Yugoslavia. This tie-in makes possible a more efficient use of available power through mutual exchanges to equalize the load and provides some insurance in the event of regional power failures.