Ecological land classification: A survey approach

A landscape approach to ecological land mapping, as illustrated in this article, proceeds by pattern recognition based on ecological theory. The unit areas delineated are hypotheses that arise from a knowledge of what is ecologically important in the land. Units formed by the mapper are likely to be inefficient or irrelevant for ecological purposes unless he possesses a sound rationale as to the interactions and controlling influences of the structural components of ecosystems. Here is the central problem with what have been called objective multivariate approaches to mapping based on grid units and the sometimes arbitrary attributes thereof; they tend to conceal the importance of ecological theory and the necessity for theory-based supervision of pattern recognition. Multivariate techniques are best used iteratively to verify and refine map units initially recognized and delineated by theoretical considerations. These ideas are illustrated by an example of a reconnaissance survey in the Northwest Territories of Canada.     

Changes in flood-plain vegetation and land use along the Missouri River from 1826 to 1972

Changes in vegetation and land use since 1826 were evaluated along the 800 kilometer portion of the Missouri River flood-plain that extends across the State of Missouri using County Land Office Survey records for 1826 and aerial photos for 1937, 1958, and 1972. The combined results show a decline in flood-plain forest coverage from 76% in 1826 to 13% in 1972; cultivated land increased from 18% to 83% during the same time. Uncultivated-unforested areas increased from 6% in 1826 to 27% in 1937, then declined to 1% in 1972; these changes occurred coincident with extensive bank-stabilization and channelization activities initiated in 1912 by the U.S. Army Corps of Engineers. Riverbank stabilization activity since that time may account for the increased rate of decline in flood-plain forests from 0.25% per year between 1826 and 1937 to 1.6% per year between 1937 and 1972.The overall species composition of the 1826 flood-plain forests was found to be most similar to mature forest stands evaluated in 1972; similar frequencies in 1826 and 1972 occurred for hackberry (Celtis occidentalis; 80% in 1826, 83% in 1972), elm (Ulmus spp.; 80% and 83%), and sycamore (Platanus occidentalis; 57% and 50%). Pawpaw (Asimina triloba), found only in mature flood-plain forests in 1972, was recorded along 54% of the 1826 section lines.These combined data indicate (1) that pre-settlement flood-plain forests were extensive and included frequent, mature stands, (2) that in certain areas substantial portions of the flood-plain were in cultivation prior to extensive riverbank stabilization and channelization, and (3) that increased flood-plain forest clearing occurred coincident with increased bank-stabilization activities.     

我国的森林火灾状况和对策研究

讨论了我国森林火灾的状况, 并对森林火灾的时间变化、区域分布、气候因素、人为因素及地形因素影响等特点进行了论述, 在此基础上提出了相应的林火对策     

浅谈伊犁地区山地天然林资源的保护和发展

伊犁地区林牧区生态系统的保水功能受到畜牧业生产活动的影响已明显下降,尤其是山地天然林资源的生态总体质量和生态功能都同步处于下降趋势。伊犁地区的生态建设重点应放在山地天然林分布区。保护和大力发展山地天然林资源是伊犁地区生态产业发展的核心内容。大力营造山地人工林,是目前条件下保护和发展山地森林资源的最有效手段。每年营造山地人工林不少于0 3×104hm2,才能够基本保持山地森林生态系统在资源总量和生态效能上的稳定,才能够基本维持伊犁地区以往良好的生态形象。建议自治区人民政府继续启动实施天山、阿尔泰山百万亩山林再造工程。     

NITROGEN AND PHOSPHORUS CONCENTRATIONS IN FOREST STREAMS OF THE UNITED STATES1

ABSTRACT: Seventy to eighty percent of the water flowing in rivers in the United States originates as precipitation in forests. This project developed a synoptic picture of the patterns in water chemistry for over 300 streams in small, forested watersheds across the United States. Nitrate (NO₃^?) concentrations averaged 0.31 mg N/L, with some streams averaging ten times this level. Nitrate concentrations tended to be higher in the northeastern United States in watersheds dominated by hardwood forests (especially hardwoods other than oaks) and in recently harvested watersheds. Concentrations of dissolved organic N (mean 0.32 mg N/L) were similar to those of NO₃～, whereas ammonium (NH₄⁺) concentrations were much lower (mean 0.05 mg N/L). Nitrate dominated the N loads of streams draining hardwood forests, whereas dissolved organic N dominated the streams in coniferous forests. Concentrations of inorganic phosphate were typically much lower (mean 12 mg P/L) than dissolved organic phosphate (mean 84 mg P/L). The frequencies of chemical concentrations in streams in small, forested watersheds showed more streams with higher NO₃^? concentrations than the streams used in national monitoring programs of larger, mostly forested watersheds. At a local scale, no trend in nitrate concentration with stream order or basin size was consistent across studies.     

森林野外火火区上的浮力流动与降雨的相互作用模型

本文是在《森林野外火火区上的浮力流动及其与一些环境气象因素关系的数值模拟》的基础上进行的。上文求解了无降雨时的气体流动情况,本文在此基础上加入了降雨模型,形成了能体现降雨与气流相互作用的程序。本文算出了不同大小的雨滴的下落过程,并能估计出多大的雨滴可落入燃烧区。     

STORMFLOW AND SEDIMENT LOSS FROM INTENSIVELY MANAGED FOREST WATERSHEDS IN EAST TEXAS1

ABSTRACT: Five small (4 ha) forested watersheds in East Texas were instrumented in December 1980 to determine the effect of forest harvesting, mechanical site preparation, and livestock grazing on stormflow, peak discharge rate, and sediment loss. After three pretreatment years, four of the watersheds were treated as follows: (1) clearcutting followed by roller chopping; (2) clearcutting following by shearing and windrowing; (3) clearcutting following by shearing, windrowing, and continuous grazing; and (4) clearcutting followed by shearing, windrowing, and rotational grazing. Clearcut harvesting and all site preparation treatments significantly increased stormflow, peak discharge, and sediment losses over the undisturbed condition. Roller chopping and shearing/windrowing had little impact on sediment loss from these watersheds and appears to be a sound forest conservation practice for gently sloping watersheds (> 8 percent). As applied, livestock grazing had minimal impact on stormflow and peak discharge. The moderately stocked continuously grazed treatment had little impact on sediment loss, but the high stocking density of the rotational grazing treatment increased sediment losses over the undisturbed condition. Sediment losses from these intensively managed forest watersheds, even though significantly greater than from undisturbed conditions, were within the range of sediment losses from undisturbed watersheds in the Southeast, below the range of losses from mechanically prepared watersheds elsewhere, and well below potential losses from pasture and cropland.     

Carbon sequestration,biological diversity,and sustainable development: Integrated forest management

Tropical deforestation provides a significant contribution to anthropogenic increases in atmospheric CO₂ concentration that may lead to global warming. Forestation and other forest management options to sequester CO₂ in the tropical latitudes may fail unless they address local economic, social, environmental, and political needs of people in the developing world. Forest management is discussed in terms of three objectives: carbon sequestration, sustainable development, and biodiversity conservation. An integrated forest management strategy of land-use planning is proposed to achieve these objectives and is centered around: preservation of primary forest, intensified use of nontimber resources, agroforestry, and selective use of plantation forestry. The information in this document has been wholly funded by the US Environmental Protection Agency. It has been subjected to the agency's peer and administrative review and approved for publication of an EPA document. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.     

Control of landscape diversity by catastrophic disturbance: A theory and a case study of fire in a Canadian boreal forest

A landscape may be envisioned as a space partitioned by a number of ecosystem types, and so it conforms to a neo-Clementsian model of succession. A corollary is that intermediate disturbance rates should maximize landscape (beta) diversity. This was confirmed using eight boreal forest landscapes in northwestern Ontario, Canada, where intermediate rates of forest fire were associated with highest landscape diversity. Because current measures of evenness subsume a richness measure, it is not, as yet, feasible to assess the relative contributions of evenness and richness to biological diversity, and thus it was not possible to determine the roles of numbers of habitat types and relative amounts of habitat types in the above situation. Both theory and observations suggest that forest fire control in fire-prone landscapes increases landscape diversity, but that it is lowered by fire control in landscapes of intermediate to low diversity.     

SEDIMENT AND WATER YIELDS FROM MANAGED FORESTS ON FLAT COASTAL PLAIN SITES1

ABSTRACT: Sediment losses and water yields were measured for five years on nine forested watersheds in the Gulf Coastal Plain of Arkansas. After one year of pretreatment measurements, three watersheds were clearcut and mechanically site prepared, three were selectively harvested, and three control watersheds were left undisturbed. Sediment losses and water yields were similar for the selectively harvested and cohtrol watersheds during all four post-treatment years. However, clearcutting with mechanical site preparation significantly increased sediment losses and water yields above levels measured on other watersheds. Increased sediment losses persisted for two years, while water yields increased for one year. Although sediment losses from clear-cutting were greater than for other treatments, actual losses averaged only 264 kg/ha and 63 kg/ha for the first and second post-treatment years, respectively. The relatively low sediment losses are attributed to the flat terrain and the relatively low flow discharge rates that typify these sites.