ISSN:1054-9811    

DOI:10.1300/J091v06n01_01

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The impact of air pollutants on trees has been a research interest for decades. Nevertheless, uncertainty exists about the potential effects of the pollutant concentrations occurring at present, for example, in Central Europe. This uncertainty results from an incomplete understanding of the mechanisms by which air pollutants and other environmental factors influence woody plants. This review presents examples of the mechanisms of ozone and NO2 impacts at low concentrations on birch and poplar. The question of whether the responses found in the ecophysiology and structural differentiation of the trees reflect acclimation to these pollutants rather than injury is given particular attention. An attempt to interpret the response of carbon allocation to ozone and NO2 by one explanatory model is presented. The capacity of air pollutants to change carbon allocation may affect interspecific competition and, by this, the species composition and the dynamics in the development of forest ecosystems.

ISSN:1054-9811    

DOI:10.1300/J091v06n01_02

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A new sensitive dendrometer system was invented by using a potentiometer and datalogger and applied to the stem of some canopy trees of a stand of deciduous broad-leaf tree species native to Hokkaido, northern Japan. Different types of diameter/age growth curves were observed at the fine level for different species: (1) an ordinary type with smooth and gradual growth; and (2) a slow growth curve mixed with intermittent stair-like periods of rapid growth. Possible reasons for the presence of stair-like rapid growth were examined, including the significance of water availability condition.

ISSN:1054-9811    

DOI:10.1300/J091v06n01_03

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

To provide a more detailed description of the forest light environment useful in interpreting the growth response of herbs and tree seedlings in the forest understory, we present light measurements taken under different sky conditions, seasons and spatial locations both vertically and along transects. Cloudy skies reduced the heterogeneity in both PPFD (photosynthetically-active photon flux density) and R.FR (red to far red ratio, 656-664 pm/ 726-734 nm) in shade and forest gaps. Under cloudy conditions, R:FR was relatively stable across different PPFD. The mean light intensity in some forest sites was higher under cloudy skies than under clear skies because of increased penetration of diffuse light. In areas where overcast conditions are frequent, growth of understory plants may show strong correspondence with the cloudy PPFD and R:FR conditions. Percent canopy opening was stable during the summer but daily sunfleck duration varied considerably because of the shifting solar track. Because of the presence of ground vegetation, light gradient above the forest floor is greatest from 0 to 1 m in the shade. Light environment may become dimmer with increasing heights beyond 1 m as shading from low tree branches imposes a greater influence. Across a forest transect, percent canopy opening showed marginal to five-fold increases from 0 to 1 m indicating higher PPFD on cloudy days. On clear days, plants at 1 m could experience more sunflecks of higher intensity and longer individual duration. Carbon balance of forest understory plants may vary significantly with vertical location and weather conditions.

ISSN:1054-9811    

DOI:10.1300/J091v06n01_04

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

For analyzing and interpreting forest dynamics at community and ecosystem levels, this paper introduces the eco-physiological model and gas exchange chamber. The model considered spatial distributions of light intensity and leaf area of different leaf layers within the tree crown on an individual tree basis. Diurnal and seasonal fluctuations of the transpiration rate from May to October 1989 in a standingFagus crenatatree were measured at intervals of two weeks. The equation variables were defined by multiplying the VPD by the square root of photon-flux density. Estimation of transpiration of a tree was done by multiplying the transpiration rate per unit area by the leaf area at different leaf layers and the light attenuation rate at the same layer. Total stand transpiration was estimated by summing up the transpiration of the trees. The total annual amount of stand transpiration was 3.200 tHiOlhz.The maximum value of mean diurnal transpiration was 2.5 mm in August; and those of May and October were only 1.5 mm. The use of the combinations of the model and gas exchange chamber interrelations helps clarify the unknown functions, productive structures, and relationships among the items within a forest community and its environment.

ISSN:1054-9811    

DOI:10.1300/J091v06n01_05

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Growth characteristics of ash(Fraxinus mandshuricavar.japonicd)and kalopanax(Kalopanax pictus), two mid-succcs-sional species, were monitored in relation to seasonal light in a deciduous broadleaf forest. During the growing, relative light intensity of the gap was 4 to 6 times higher than that under the closed canopy. Seedlings could be found on the mixed hardwood forest floor where relative light intensity was around greater than 7% of full sunlight. When saplings gap openings which had relative light intensities above 20%, they quickly developed lateral branches and increased their foliage volume. The light-photosynthesis curve of seedlings of both species showed a curve typical of the “shade leaf” type even though they grew under sunlight. In contrast, saplings of both species showed the “sun leaf” type of light-photosynthesis curve. This seedling to sapling shift from shade to sun adaptation was also found in other foliage characteristics. This study shows that species can efficiently adjust their leaf and branch characteristics to changing light environments from shade to openings in a forest.

ISSN:1054-9811    

DOI:10.1300/J091v06n01_06

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Forest trees are usually classified into broad ecological groups (e.g., pioneers vs. mature-phase species) based on the importance of natural disturbance for their regeneration. These classifications only tie into account a small component of the plant's life-cycle, usually seeds and seedlings, and therefore may over-simplify the role of natural disturbance in the evolution of life-history traits. We present a conceptual model for the study of plant demography within heterogeneous environments, and illustrate its use by reviewing how natural disturbance influences the demography of several lowland tropical tree species at Los Tuxtlas, Mexico. Our model assumes that habitat patches such as treefall gaps in tropical forests can affect a plant at all stages of its life-cycle, and reveals many potential life history patterns in relation to forest dynamics. We propose that only detailed demographic studies of whole life histories and genetics of tree populations, as well as forest disturbance regimes, will allow us to elucidate convergent life histories and the existence of discrete ecological groups among tropical forest trees.

ISSN:1054-9811    

DOI:10.1300/J091v06n01_07

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The distribution ofPhyllostachys pubescens, introduced to Japan from China in 1736, has been expanding. The expansion was studied in Tanabe Town, Kyoto Pref., Central Japan. Long term expansion was traced using a topographic map, a land-use map and aerial photographs. Within the research region (21.35 km2), the number and total area of bamboo sites increased from 24 and 0.16 km2in 1953 to 174 and 3.04 km2in 1985. By contrast, the total area of tree sites decreased from 12.2 km2in 1953 to 8.5 km2in 1985. The average area of bamboo sites also increased from 0.67 ha in 1953 to 1.75 ha in 1985. The average rates of the current expansion, measured by censusing current and old culms in the front of 10 unmanaged bamboo sites, were 2.1 m yr-1. Stand structure was detailed in a transitional area from a pure stand ofP. pubescensto a mixed broadleaved forest. Stand structure was simpler in the area dominated byP. pubescens.Culms off!pubescenswere larger in the pure stand, and variations in DBH and height were smaller for the bamboo than for the trees in each sample site.P. pubescenshad a greater average crown length and higher canopy position. These traits allowP. pubescensto invade adjacent forests, form a uniform monolayer of foliage, and dominate competing vegetation. There was no evidence of seedling regeneration under the bamboo. More than two-thirds of the Japanese forest is secondary growth or young plantations of conifers, and in most of these, canopy height is lower than that ofP. pubescens.The continuous area increment in bamboo from 1953 to 1985, positive current expansion rate in the front of unmanaged bamboo stands and the advantageous stand structure of bamboo suggest that the range expansion ofP. pubescensin the secondary forest will continue in the future.

ISSN:1054-9811    

DOI:10.1300/J091v06n01_08

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In order to clarify mechanisms of canopy recruitment ofFagus japonicastems of sprout origin, age structure and growth dynamics were studied for stems within beech stools in two stands of old growth forests on the Pacific side of central Japan. The DBH vs. height and age relationships of the beech stems showed continuous distribution from small-young, understory stems to large-old, canopy ones. There were one to seven definable periods of suppression prior to canopy recruitment inF japonica.Prior to canopy recruitment number and length of release episodes were fewer and shorter than those of suppression.E japonicastems of sprout origin can endure suppression for a long time. Continuous emergence and the alternation of fast and slow growth inF. japonicastems suggest the sprouting ability for the beech canopy can play an important role in the successful closure of canopy openings. Canopy stems showed patterns of suppression and release that were often synchronous with other canopy stems within the same beech stool. Minor disturbances such as single crown falls can play an important role in the maintenance of the multi-stem structure of beech stools in old growth forests.

ISSN:1054-9811    

DOI:10.1300/J091v06n01_09

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

We observed seed (or diaspore) dispersal of six species (4 species of Betulaceae, 2 species of Aceraceae) for 5 years in a species-rich deciduous broad-leaved forest (Ogawa Forest Reserve, central Japan), and explained the observed patterns with a mechanistic model of dispersal. The model involves three parameters which can be biologically interpreted; terminal seed velocity(F), tree height(H), and amount öf dispersed seed per reproductive individual(Q).The relationship between dispersed seed density and distance from a single seed source were explained well by the model. Two dimensional distribution of seed density dispersed from multiple seed sources was approximated by the model. We evaluated the dispersal success in reaching safe sites as the gap area covered by a given seed density, and discussed the adaptive meaning of the dispersal traits based on the model and empirical data. WhileFdid not vary greatly among the species,Qshowed greater variation among the species in this forest. The species with largeQdescended more slowly(H/F)in this forest. The traits which were related to the enlargement of dispersal area tended to compensate for the low survival-of seedlings.

ISSN:1054-9811    

DOI:10.1300/J091v06n01_10

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor