【正确答案】The special characteristics of forest resources, which justify forest economics as a special field of study, can be summarized as follows:
   Forests can produce a wide variety of goods and services and combinations of them, some of which are not priced in markets. This gives rise to special problems relating to the allocation of resources among uses.
   Timber is an unusually slow-growing crop, often involving investment periods of many decades. This gives rise to special problems in analysing investment, harvesting schedules, risks in carrying forest crops over long periods, and market uncertainty. It also means that forests can be altered only slowly in response to changed economic conditions.
   Forestry usually involves very high capital and carrying costs relative to production because the slow rate of forest growth means that large forest inventories must be carried to sustain a modest harvest. As a result, the costs of forest production are often dominated by the burden of carrying land and capital over time.
   Forests valued for industrial timber are both productive capital and product . This fact distinguishes forests from other forms of capital and gives rise to special analytical problems in selecting the best age to harvest and in designing taxes and regulations.