From the antiquity, the hilly landscape around the city of Axum in northern Ethiopia has been terraced and extensively used for agriculture purposes. Impacts of the “ard” plough on protruding and/or buried boulder at a depth less than the tillage depth produce scratches on their sides or their top. The spatial relationship among plough marks and rock surface orientations gives information on the ploughing direction, whereas the relative height from the present ground surface to the top of the marks and information on the age of cultivation can be used to assess soil loss rates. Parameters to define plough mark orientation were defined and measured in the field on boulders with plough marks within a study terrace located in an archaeological area with an approx of 2040 year age. These parameters are height from the ground, dip, slope and frequency. 相似文献
Maple sugar and maple syrup have long been important non-timber forest products in North America. We examined the historical and the scientific literature to determine the long-term sustainability of the industry in an economic, an ecological, and a cultural context. During the 18th and 19th centuries, maple sugar was an inexpensive substitute for cane sugar and a cash crop that fit into the work schedule of the northern farmer. Maple syrup replaced maple sugar as the mainstay of the industry at the end of the 19th century as increasingly cheaper cane sugar and other sweeteners undercut the sugar market. Active government intervention and support have made Quebec the major bulk supplier of maple syrup today. Quebec alone produces approximately 80% of the world’s supply of maple products. A series of good sap years and production in excess of demand, however, has recently reduced the price of bulk syrup and the profit of producers in Quebec. Producers in the United States have focused on the more lucrative and price stable retail syrup market.
Farming practices in the late 18th and early 19th centuries tended to clear away sugar maple on the more fertile, level sites and preserve sugar maple as a source of fuel wood, sugar and syrup on the less accessible, marginal sites. The crude tapping procedures employed at the same time often killed the trees. Widespread grazing in the 20th century and more recently diameter-limit cutting of even-aged stands have hindered the regeneration of the sugarbush. An emphasis on monocultures and global warming currently threatens the sustainability of the sugarbush. On the whole, however, the maple products industry has probably increased sugar maple’s representation in the forest. From a cultural standpoint, the industry represents a positive work experience that unites families, connects one to the land, and provides a sense of continuity with the past. 相似文献