JAPANESE JOURNAL OF ECOLOGY

Stand structure, tree growth and mortality in a coastal Kashiwa oak (.Quercus dentata) forest in northern Hokkaido were investigated from 1995 to 2001. The stand structure was strongly affected by sand dune topography, and trees were more dwarfed at higher elevation. The topography also affected the growth of trees and the local tree mortality. Height growth was negatively correlated with relative stem height, calculated as (stem height in 1995)/(height of canopy surface) to evaluate the local stand structure. This result suggests that the height growth of canopy trees was severely restricted by the sea breeze. Relative diameter growth rate of stems was affected not only by initial diameter, but also by projected crown area and relative stem height. The latter two variables would strongly influence the light conditions surrounding the trees. No recruiting by seedlings or root collar sprouting was observed. About 10% of stems died during the study period, and about 37% of the dead stems were severely damaged by Clethrionomys rufocanus bedfordiae. Tree mortality due to other factors was positively correlated with local initial density and relative altitude in the study plot. Thus a higher density and higher position resulted in higher mortality. Relative stem height of the trees that died was less than that of the trees that survived. This result suggests that one-sided competition for light also plays an important role in the stand dynamics of coastal Kashiwa oak forest. The effect of tree position in the study plot might be related to the recovery ability of the damaged crown. This means that trees at a higher position on dunes are unable to recover from severe crown damage.

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The lucidophyllous forests at Shiratori, Kurino and Tatera in Kyushu, Japan, were investigated in order to clarify differences in species composition and species richness between closed canopy stands (mature phase) and canopy gap stands (gap phase). The mature phase was mainly characterized by the presence of many epiphytes which were component species of lucidophyllous forest (elements of Camellietea japonicae). The gap phase was primarily characterized by the presence of summergreen trees, summergreen shrubs, summergreen climbers and others which composed Rosetea multiflorae, Fico-Mallotetalia, Fagetea crenatae and Artemisietea principis. The gap phase was differentiated not only by the above species, but also by the component species of lucidophyllous forest. In the gap phase, the species richness of all occurring species and that of component species, except for epiphytes of lucidophyllous forest, were higher than those in the mature phase. Canopy gaps play an important role in the maintenance of species richness of component species of lucidophyllous forest as well as the process of lucidophyllous forest regeneration.

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The adequate ground level for planting of seeds of the gray mangrove, Avicennia marina (Forsk.) Vierh, in the intertidal zone is an important factor for successful afforestation of desert coasts. Seeds germinated at all levels in the intertidal zone except near the high tide line, and all seedlings grew steadily during the first year. However, most of the seedlings that had become established at the low and high tide levels died during the second year, and only trees that grew at the mid-tidal level with a mean tidal difference of 30.6-63% of the mean survived. For three years thereafter, there was no further mortality at this level. Therefore, the appropriate ground level for plantation of seeds is the area with a mean tidal difference of 30.6-41.4 %. The increased seawater salinity under the soil at the level with a mean tidal difference of 43.2-63% probably inhibited trees from growing smoothly. Although more than 90% of seeds germinated during the 8-year afforestation project, a large number of seedlings were killed during the second year due to deposition of seaweed and flotsam. High-density planting of seedlings (at a 25-cm interval) could increase their survival under this type of pressure, because a dense patch of seedlings has more resistance to covering with seaweed and flotsam than a single seedling.

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Since the commercial cultivation of genetically modified (GM) crops began in the late 1990s, the planting area for such crops has markedly increased, especially in the USA, Canada, Argentina and China. The current predominant GM crops are both herbicide-tolerant and insecticidal (Bt) crops, the latter accounting for about 25% of the total area worldwide. Some researchers have suggested that transgenic insecticidal crops may have negative effects on non-target insects such as the monarch butterfly, green lacewing and ladybird beetle. However, subsequent studies have shown that these negative effects occur only in the laboratory under non-choice conditions, and that non-target insects are scarcely affected under field conditions. When considering the environmental effects of GM crops, it is important to well understand the above facts. This review summarizes research reports on the effects of transgenic insecticidal crops on non-target natural enemies and soil microfauna. To date, none of the reports have described deleterious effects on non-target arthropods in the field or under field-cage conditions. GM crops expressing new types of insecticidal proteins such as lectins, protease inhibitors and vegetative insecticidal proteins are scheduled for commercial cultivation, and these crops will need to be evaluated cautiously for their ecological safety prior to field cultivation. As secondary insect pests that GM crops cannot control may become important pests, it will be necessary to study the complex interaction of transgenic crops, insect pests and their natural enemies in agro-ecosystems. Studies on soil microfauna have a number of methodological problems, such as which species or groups should be monitored, and how long the census period should continue. Most studies on the ecological impact of GM crops have been published by scientists who have created the crops themselves. In future, therefore, more reports by independent ecological researchers will be needed in order to provide more reliable data for citizens who are concerned about the safety of GM crops.

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