Kyoji Yoda

The regeneration of pioneer tree species under browsing pressure of Sika deer in an evergreen oak forest

The effects of Sika deer (Cervus nippon) browsing on the regeneration of pioneer species were studied in relation to canopy gaps in a warm temperate evergreen oak forest in Kasugayama, Nara City. Four study sites, three in canopy gaps and one under a closed canopy, were selected and each divided into fenced and unfenced plots. Under the closed canopy, seedlings of all the pioneer species died irrespective of browsing pressure. However, in the canopy gap sites, seedlings of the pioneer species could establish and grow well. The seedling survival ratio in the fenced plots in the canopy gaps was >60% 1 year after germination. However, in the unfenced plots, only <20% of the seedlings survived 1 year, with all dying within 3 years after germination. Thus, the regeneration of pioneer trees in this forest was strongly inhibited by deer browsing. Successful regeneration of a pioneer,Zanthoxylum ailanthoides, occurred for several years even after two major wind disturbances during the past 90 years. This may be due to less browsing pressure from the deer.

Climate and vegetation in China (I). Changes in the altitudinal lapse rate of temperature and distribution of sea level temperature

Changes in the altitudinal lapse rate of temperature (ALRT) and temperature distribution at sea level were studied all over China, using temperature records from 671 meteorological stations during a statistical period from 1951 to 1980.ALRT varied regularly with distance from the eastern and south eastern coast (DC) with a minimum at about 600 km DC and a maximum at 1600–2000 km DC. The ALRT curve pattern was closely related to the mean altitude. The reliability of this trend was verified by calculating ALRT for each latitude group. Values of ALRT did not show any latitidinal trend within a distance group from the coast.An empirical equation was proposed for the relation between the DC and ALRT, and the ALRT for each meteorological station was estimated from the equation. The annual and monthly mean temperatures at sea level were calculated using the ALRT, and distribution maps were constructed. The isotherms ran almost parallel to latitude in January, and roughly parallel to the coastline in July. High temperatures at sea level were remarkable in the Qinghai-Xizang (Tibetan) Plateau, Sichuan Basin, Daxingan Ling and the area surrounding the Tien Shan Mountains.

Climate and vegetation in China II. Distribution of main vegetation types and thermal climate

The authors examined relationships between Kiras warmth index (WI) and four other important thermal indices: the sums of daily mean temperatures above 5°C and 10°C, Thornthwaites potential evapotranspiration (PE) and Holdridges annual biotemperature. The thermal records of 671 meteorological stations evenly located all over China were used to make these comparisons. Close correlations were found within the four relationships, and accordingly WI was used to analyse the thermal distributions of the main vegetation types. Vegetation types around the 671 stations were read from a vegetation map with a scale of 1/4000000. Vegetation types at 269 stations corresponded to the natural or seminatural vegetation, and 29 vegetation types were distinguished by arranging the 269 data into the same or similar types. The geographical distribution of these 29 types and the corresponding main climatic features were described. The relations between WI and distribution of these vegetation types were discussed in detail. As a result, WI values (°C month) corresponding to the vegetation zones could be summarized as follows: (1) arctic or alpine vegetation zone: 0–15; (2) boreal or subalpine vegetation zone: 15-(50–55); (3) cool-temperate vegetation zone: (50–55)–(80–90); (4) warm-temperate vegetation zone: (80–90)–(170–180). These values almost coincided with Kiras values.

Climate and vegetation in China III water balance and distribution of vegetation

Distributions of 29 vegetation types in China as a function of climatic humidity or aridity were analysed using Thornthwaites system, by employing meteorological records from 671 stations in China. The annual potential evapotranspiration and the humidity/aridity indices were calculated for every station, and distribution maps of water deficiency, water surplus and moisture index (Im) were constructed. The Im map showed that arid areas (Im<0) occupied about 56% of the country. The effect of the difference in soil water storage capacity on Thornthwaites indices was examined, and Im values were found to differ little, although some differences were observed in actual annual evapotranspiration, water deficiency and water surplus values. Correlations between Im values and distributions of 29 vegetation types, identified from a vegetation map with a scale of 1/4000000, were investigated. The distributions of desert, steppe, woodland, deciduous forest and evergreen forest corresponded to Im values of below −40, −40–−20, −20-0, 0–60 and over 60, respectively. In addition, climatic factors delimiting the northern distribution of evergreen broadleaf forest were investigated, and it was clarified that the northern limit was restricted by combined hydrothermal conditions, and not by the low temperature in winter.

Community dynamics of evergreen broadleaf forests in southwestern Japan. II. Species composition and density of seeds buried in the soil of a climax evergreen oak forest

The species composition and density of seeds in the soil of a climax evergeen oak forest in the Kasugayama Forest Reserve, Nara, Japan were studied by directly extracting seeds from soil samples and using soil samples in planting boxes as the basis of germination tests.A total of 33 species were identified from all seeds collected in 6 stands: 11 evergreen broadleaf, 15 deciduous broadleaf, 2 coniferous, 2 liana, 1 herb, and 2 grass species. Species producing sap fruits and dry fruits accounted for 60% and 40% of the total number of species, respectively. The species composition of all the seeds was independent of the species composition of the forest vegetation. The mean density of the seeds was 22,134 seeds/m2·5 cm.Eurya japonica, of which seeds were found in all soil samples, was the most abundant species, followed byCryptomeria japonica, Ilex micrococca, andBoehmeria longispica. Pioneer species such asMallotus japonicus, Zanthoxylum ailanthoides, andAralia elata were found in all soil samples in spite of the paucity of adult trees in the forest. Seeds of evergreen oaks were relatively aboundant but no viable seeds were found. ViableE. japonica, I. micrococca, Symplocos prunifolia, andB. longispica seeds were abundant.

Regeneration in subalpine coniferous forests. II: Mortality and the pattern of death of canopy trees

Death of canopy trees when gaps are formed was studied in a subalpine coniferous forest, central Japan, which was composed ofAbies, Tsuga, Picea, Betula, andSorbus. Typhoons were considered to be the most important cause of the death of canopy trees. The degree of disturbance in each of 16 plots (20 m×20 m) was represented by the percentage of the total basal area of dead trees to that of living and dead canopy trees (disturbance magnitude; MAG). The mortality of canopy trees increased as their dbh increase in the plots of lower MAG than 90%. The mortality varied among genera, andTsuga was characterized as having lower mortality than that of the other conifers. 418 dead trees were observed. The standing dead trees made up 10.7% of the trees, the stem broken trees 46.7%, and the uprooted trees 42.2%. The stem breaking was most frequent inAbies, and the uprooting was most frequent inTsuga, Picea, andBetula. Undeveloped forests, which have the L-shaped dbh distribution, were destroyed only in high degree (70%<MAG), while developed forests were destroyed in various degrees (30%<MAG<100%). The percentage of uprooted trees in basal area decreased with the development of the forest, from 60% to 10%.

Climate and vegetation in China V. Effect of climatic factors on the upper limit of distribution of evergreen broadleaf forest

In order to clarify correlations between the upper limit of distribution of evergreen broadleaf forest and climatic factors, 62 stands distributed at the upper limit of the forest were collected from various parts of China, and their thermal and precipitation factors were estimated. Among six thermal climatic indices, i.e., warmth index (WI), coldness index (CI) and annual mean (AMT), January mean (JMT), mean minimum (MMT) and minimum (MT) temperatures, the CI at the stands showed the smallest range of variance, and it was therefore considered to be the most significant for interpreting the upward distribution of the forest. However, the distribution of the forest in mountain areas in southwestern China could not be explained by lower temperatures in winter such as CI but by a cumulative temperature such as WI. The continentality and precipitation factors were also important for delimiting the distribution of the forest. In addition, the relation between the distribution of the forest and the MMT was noted, and it was concluded that the MMT was an effective thermal index for explaining the upper limit of distribution of evergreen broadleaf forest in China.

Climate and vegetation in China. IV, Distribution of tree species along the thermal gradient

The aim of this study was to examine correlations between vegetational zones and thermal climate on the basis of analysis of the thermal distribution of main-component trees in each zone. The whole and main thermal distribution ranges for 73 tree species were obtained from their distributions along the warmth index (WI) gradicnt. Cluster analysis using the WI values at the upper and lower limits of the main distribution ranges as parameters gave seven species groups. The geographical distributions of the species in each group were described. Moreover, the frequency distribution curves of the seven species groups were determined along the WI grandient, and four borderlines (lines I, II, III and IV) were found among them. The WI values at the lines I, II and IV were 50, 90, 175°C month, respectively, and corresponded to boundaries between the subarctic and cool-temperate zones (I), the cool-and warm-temperate zones (II) and the warmtemperated and subtropical/tropical zones (IV), respectively. Line III corresponded to a WI of 135°C month. The WI values at the forest limit and at the lower limit of the subarctic forest were estimated, and their averages were 15.2 and 49.6°C month, respectively. In conclusion, thermal climatic zones in China could be divided by the following WI values: alpine (arctic) zone, WI<15; subarctic zone, 15–50; cool-temperate zone, 50–90; warm-temperate zone, 90–175; subtropical/tropical zone >175°C month.

Density effects and self-thinning in even-aged pure stands ofEucalyptus camaldulensis Dehn

The competition density effect and changes of mean total tree weight (w) and stand density (ρ) during course of self-thinning were examined in even-aged pure stands ofEucalyptus camaldulensis Dehn. which were planted in the tropical monsoon region. The level of competition was controlled by changing the initial stand density from 625 trees ha−1 to 40,000 trees ha−1. Hozumis model was used to describe thew-ρ trajectory with aging of each stand and thew-ρ relation between stands of different densities at each time. The higher density produced trees of smaller mean tree sizes. The higher the density, the sooner self-thinning began. The growth curve ofE. camaldulensis followed the logistic growth curve where both maximum size and intrinsic growth rate change with time. Mean intrinsic growth rate was maximized at initiation of growth after lag time and then gradually decreased as time progressed. Hozumis model was considered to be the best model with wide applicability for describing and comparing the growth characteristics during the course of self-thinning among different species, especially in tropical forest plantations, in which many diverse species were used for reforestation.

Carbon-cycling changes during regeneration of a decinduous broadleaf forest after clear-cutting II. Aboveground net production

Growth and death rates of aboveground plant parts were measured in a mature forest and four different-aged deciduous broadleaf forests regeneratede after clear-cutting, with special reference to rates for woody parts (stems and branches) of different diameters (ø) in rerms of the pipe model theory (Shinozaki et al., 1964). The total biomass increment of woody parts of trees higher than 1.3 m varied within a range of 2.1-4.6 ton ha−1 yr−1, the increase beingdue largely to the growth of canopy trees exposed to direct sunlight. Biomass increments of small (ø<1 cm) and medium (1≤ø<5 cm) woody parts were negligibly small except in the youngest forest, and changes in aboveground woody biomass with forest age after clear-cutting mainly resulted from accumulation of large (5 cm<ø) woody parts of canopy trees. Biomass loss of trees due to death and grazing increased with forest age from 4.0 to 8.3 ton ha−1 yr−1. Recovery of leaf and small wood falls was observed at the early stage of regeneration, while large wood falls increased during regeneration. Flower and fruit fall was markedly higher in the mature forest than in the other four forest types. Mortality of woody parts became higher with forest age and was 20, 5.0 and 0.46% yr−1 for small, medium and large parts, respectively, at the mature stage. Aboveground net production of the forest was in therange 7.6-13.3 ton ha−1 yr−1 with the undergrowth vegetation lower than 1.3 m being 0.4-1.4 ton ha−1 yr−1. Production recovered rapidly at an early stage of regeneration and was highest in mature forest.