Phenology and Growth Habits of Tropical Trees Long-term Observations in the Bogor and Cibodas Botanic Gardens, Indonesia

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The purpose of this research project is to elucidate the aspects of growth patterns of various tropical trees through continued observations of the phenology and growth habits of the trees grown in the Bogor and Cibodas Botanic Gardens, Indonesia. The investigation consists of observations of the frequencies of phenological events, measuring stem elongation and describing leaf longevity during the growth processes. 1) Several types can be detected of stem elongation and leaf replacement patterns. We have described these phenological events based upon the following five different categories: Rank 5 is defined by more than 80% of foliage leaves on the shoots; Rank 4, foliage leaves on 60 to 80% of shoots; Rank 3, foliage leaves on 30 to 60% of shoots; Rank 2, foliage leaves less than 30% of shoots, and Rank 1 without foliage leaves. 2) Longevity of foliage leaves on the shoot is, however, variable. We discerned the ages of shoots based upon the numbers of scale scars, branching patterns and internode length on each shoot. We recognized at least 7 or 8 different shoot ages per branch bearing foliage leaves. However, normally shoots at the ages of 2 to 3 bear foliage leaves, and others have no foliage leaves. What we called "evergreen" in this report includes two patterns of foliage replacement, i.e., 80% of leaves being maintained throughout the season, which we called "Rank 4-5"; whereas what we called "semievergreen" occasionally lose most of the foliage leaves, and are thus categorized as "Rank 2-3". What we called "incompletely deciduous" are trees in which most foliage leaves are lost, but almost simultaneously new foliage leaves appear. There also occur typical "deciduous" trees, and thus they are called "completely deciduous types", although the length of deciduous periods is variable, having a complete leafless period over a week to nearly one month. Differences found in phenophases imply adaptive changes in the replacement patterns of foliage leaves, stem elongation and branching; evergreen to semievergreen; semievergreen to incompletely deciduous; and further to short-term (or long-term) completely deciduous. Leaf longevity of tropical trees tends to be shorter than those of typical temperate trees; on the other hand, regeneration cycles of new foliage leaves are much shorter. 3) There are two patterns of stem elongation, i.e., continuous growth and rhythmic growth. Many trees observed in the Bogor Botanic Garden, most of which are elements of tropical lowland evergreen rain forests, exhibited growth patterns of rhythmic stem elongation and/or discontinuous elongation with frequent resting periods. On the other hand, many species in the Cibodas Botanic Garden, which are elements of tropical lower montane rain forests, exhibited continuous growth habits over several months, with approximately 80% of shoots keeping continuous growth throughout the year. It appears that adaptation to dryness and low temperature may be easier for the species with rhythmic growth than those with continuous growth. 4) Various patterns were observed in the flowering behavior, including flowering once a year to flowering with several-year intervals, although the results showed that continuous flowering throughout the year was the dominant pattern in the study areas. Fruit maturation was more frequent than expected, and there were some species that hardly yielded mature fruits despite high frequencies in flowering. Forty percent of the investigated species flowered regularly, following the calendar year. This implies that the trees respond to slight changes in temperature and dryness under the tropical climate, resulting in the differences in seasonality of flowering. 5) Acclimatization of temperate trees to the tropical climate has been one of the major interests in this study. Various species from Japan and China have been transplanted and cultivated in the Cibodas Botanic Garden. These species revealed several phenophases in response to acclimatization. Exemplified by Rhus succedanea (from Japan), some species exhibited the same phenology as observed in Japan (i.e., annual elongation), while other evergreen shrub species such as Rhododendron mucronatum var. phoeniceum and Camellia japonica showed continuous branch growth. In the case of Nandina domestica, several phenological events (stem elongation, flowering, defoliation, and fruiting) occurred simultaneously on the same individual. Some other species, such as Diospyros kaki, showed different phenological responses among different individuals; defoliation and maturation of fruits were observed in some individuals, while leafing and flowering occurred in some other individuals. Considering a possibility that these groups of species diversified in tropical regions and expanded their distribution to the temperate regions, they may retain and express the intrinsic traits, when they return to their original habitat, i.e., the tropical region, although they are suppressed under the low temperature in Japan.
国立科学博物館の論文

Phenology and Growth Habits of Tropical Trees Long-term Observations in the Bogor and Cibodas Botanic Gardens, Indonesia

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