Assessment of frequent cutting as a plant-community management technique in power-line corridors

Repeated cutting of vegetation at or near ground level in power-line corridors is a common practice for inhibiting tree growth and regeneration. However, few data exist on long-term community responses. In this study, we sampled 20 northern Kentucky power-line corridors and compared their seedling and sapling communities to the edges and interiors of adjacent undisturbed forests. Mean seedling and sapling density in corridors was roughly twice that of adjacent undisturbed forest interiors, suggesting that repeated cutting is not a viable method of inhibiting tree regeneration. Corridor communities were dominated byRobinia pseudoacacia (black locust) andFraxinus americana (white ash), but ordinations indicated strong similaritties among communities in corridors and adjacent forests. Many of the tree species found in adjacent forests, with the exception of a few shade-tolerant species, had highest seedling and sapling densities in corridors. Stump or root sprouting by many species appears to regenerate forests quickly after cutting. However, disturbed soil and detritus accumulations caused by management crews and their equipment may also create a large variety of microsites for seedling establishment. Because repeated cutting selects for dominance by species with highest sprout growth rates, it should not be used as the sole management technique. It may instead be used to alter the vigor, stature, and stored reserves of trees so that herbicides or other methods of tree control can be used more efficiently.     

浅论人为灾害

本文着重对人为灾害进行了讨论，指出了人为灾害的主要特征，即它超越了时间和空间的界限，具有不确定性和惩罚性，并由此将人为灾害划分为随机、次生、潜在三个系统．在以翔实的资料描述人为灾害现状后，提出了防治对策．     

小良热带人工窿缘桉林群落结构分析

本文分析了广东小良24龄的人工窿缘桉林的群落结构。结果表明:该群落种类简单,以矮高位芽植物和大型叶植物为主,但建群种窿缘桉不属此列,反映了其生境差的特点;乔木层植物的密度虽小,但叶面积指数大。灌木、草本层植物密度较大,却无窿缘桉幼苗;组成结构分析表明群落的乔木层结构向着简单化或稳定方向发展,而灌木层和草本层向着复杂的方向发展;该群落总的生物量为217.7t/hm~2,其中树干的积累量最大,生产上可以林分改造组建混交林。     

Timber harvest calculations on a National Forest: A case study

Harvest calculations determine sawtimber flows from public lands and are closely scruntinized by a wide spectrum of forest users. This study examines the reliability of harvest calculations on a single national forest in New Mexico Forest Service determinations of an array of variables were reviewed and evaluated. The study revealed a lack of precision in Forest Service adherence to self-imposed procedural standards governing the calculation process. Timber sales have taken place on lands where such standards prohibit harvesting and these lands have been included in annual harvest calculations. Assumptions required by a mathematical model used by the Forest Service in calculating the harvest were not followed in the subsequent implementation of the harvest level. These factors suggest that the Forest Service could have significantly over-stated annual harvest rate for the first decade. Opportunities exist to improve the calculation, and benefits realized may greatly exceed additional costs of implementation     

清水江流域的生态环境变迁与可持续发展

清水江流域是贵州省少数民族聚居、经济落后的地区。本文通过对该流域森林资源变迁的剖析，提出保护生态环境的措施，以保证流域的可持续发展。     

林火管理经济学的研究与探讨——多种防火要素投入的最佳组合

用经济学的观点分析了多种防火要素投入时的等减灾效益与等成本曲线,研究了多种防火要素之间的相互替代与边际替代率问题,提出了多种防火要素投入时最佳组合的判据。     

非感潮河流水污染带范围的估算

在河流污染带范围随机模拟方法的基础上提出了一个附加概率意义的污染带新定义，然后利用线性回归，分别采用３种曲线拟合和１个方面拟合两种方法，对污染带的范围进行估算，结果表明，能较真实地反映河流污染带的实际情况。     

厌氧—好氧生物滤池处理城镇污水的研究

厌氧－好氧高性能生物滤池是利用附着在塑料模块填料上的微生物系统对城镇污水中的污染物质进行降解处理。厌氧水解池和高负荷生物滤池采用的塑料模块填料具肮空隙率、高附着面积、高布水性能和抗堵塞的优异性能，使出无需回流。当厌氧水解池水力仪时间国４ｈ，生物滤澉水力负荷为３０ｍ＾３／（ｍ＾２．ｄ），城镇污水的ＣＯＤｃｒ去作率达７５％～８５％、ＢＯＤ５去除率达８５％、９５％，ＳＳ去除率达８５％～９０５％，处理后出     

Carbon emissions from land-use change: an analysis of causal factors in Chiapas, Mexico

This study examines the correlation between deforestation, carbon dioxide emissions and potential causal factors of land-use change within an area of 2.7 million ha in Chiapas, southern Mexico between 1975 and 1996. Digitized land-use maps and interpreted satellite images were used to quantify land-use changes. Geo-referenced databases of population and digitized maps of roads and topography were used to determine which factors could be used to explain observed changes in land-use. The study analyzed the relationship between carbon emissions during this period and two types of possible causal factors: “predisposing” factors that determine the susceptibility of a particular area of forest to change (slope, distance to agriculture and roads, land tenure) and “driving” factors representing the pressures for change (population density, poverty). The correlated factors were combined in risk matrices, which show the proportion of vulnerable carbon stocks lost in areas with defined social, economic and environmental characteristics. Such matrices could be used to predict future deforestation rates and provide a verifiable evidence-base for defining baseline carbon emissions for forest conservation projects. Based on the results of the analysis, two matrices were constructed, using population density as the single most important driving factor and distance from roads and distance from agriculture as the two alternatives for the predisposing factors of deforestation.