Published online September 7, 2023
Journal of Ecology and Environment (2023) 47:12
Department of Biotechnology, Faculty of Science and Technology, Thammasat University, Lampang Campus, Lampang 52190, Thailand
Correspondence to:Janejaree Inuthai
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Background: The flowering and fruiting periods play an important role in biological processes. The deciduous dipterocarp forest is an important forest type in Thailand, however the phenological studies are still limited, particularly in different plant life forms. Thus, the present study focused on the flowering and fruiting phenology of herbs, climbers, shrubs, and trees in the deciduous dipterocarp forest at Lampang province of Northern Thailand. Field visits were made to record plant life forms and observe reproductive phenological events at monthly intervals from November 2018 to October 2019 and September to December 2020.
Results: The phenological observations were based on 126 species of 45 families and 102 genera. Flowering and fruiting periods showed similar patterns in herbaceous plants, climbers, and shrubs. Most of these species produced flowers and fruits from the end of the rainy season (October) to the winter season (November–January). Whereas most of flowering and fruiting trees were found from the summer season (March–April) to the beginning of the rainy season (May–June). Most of the dry-fruited species occurred during the dry period (winter and summer seasons), while the majority of fleshy-fruited species dominated in the wet period (rainy season). The statistical analysis supported the phenological patterns of flowering and fruiting in the present study. There were significant negative correlations between the number of flowering and fruiting species and temperature. The number of flowering and fruiting species is significantly impacted by the interaction between seasons and plant life forms.
Conclusions: Plant life form seems to be the important factor that affects the different phenological patterns in the studied plants. The abiotic and biotic factors play major roles in reproductive phenology. However, long-term study and in-depth phenological observations are necessary for better understanding.
Keywords: deciduous dipterocarp forest, flowering, fruiting, Lampang, phenology, Thailand
Phenology is a study of the periodicity of recurring biological phenomena in plants such as leaf drop, leaf flushing, flowering, fruiting, etc. These phenological events are dealing with the relationship between climatic factors and periodic phenomena, for example the response of living organisms to seasonal and climatic changes in the environment (Kachenchart et al. 2008; Nakar and Jadeja 2015). The timing of flowering and fruiting plays an important role in biological processes from organismal to ecological scales (Mohandass et al. 2016). Their patterns ultimately determine the reproductive success in plants (Carvalho and Sartori 2015). The studies on phenology of different plant species have been undertaken from different parts of the world (Mosissa 2019). However, there are only a few phenological studies in Asia, despite this continent has a variety of forest types and climates (Mohandass et al. 2016).
In Southeast Asia, the studies on the flowering and fruiting phenology of trees have tended to focus on the equatorial rain forests (e.g., Corlett 1990; Lord Medway 1972; van Schaik 1986), while the attempts to describe these phenomena in the drier tropical climates, where there are exhibited strongly seasonal of the dry and rainy seasons, are still limited. Therefore, studies on phenology are urgently needed for this region, especially for the dry tropical forests where are considered as the most threatened of the major tropical ecosystems (Janzen 1988).
The dry forests are the majority of forest types in Thailand. One of the most important drier forest types is the deciduous dipterocarp forest (dry dipterocarp forest). It is commonly found in the northern, northeastern, and central parts of the country. Currently, there are restricted data on the phenology of deciduous forests in Thailand (Khemnark 1978). The previous studies on phenological observations in this forest type of country concentrate on tree species (Elliott et al. 1994; Khemnark 1978; Sukwong et al. 1975). There are only a few studies that provide phenological information on all plant species in the deciduous forests of Thailand (Kachenchart et al. 2008; Inuthai 2021). Unfortunately, the results of those phenological studies represent the combination data of whole community, so some specific information about each plant life form might disappear.
Phenological patterns vary at different levels of analysis (Boyle and Bronstein 2012). Different life forms such as herbs, shrubs, trees, and climbers are correlated with different patterns of flowering and fruiting phenology (Croat 1975; Nakar and Jadeja 2015). Each plant life form demonstrates a particular association with particular climatic conditions (Ramírez and Briceño 2011). The phenological data differ depending on whether only trees and shrubs, only herbaceous plants, or one or more populations are studied (Carvalho and Sartori 2015). Thus, each species may have its own phenological strategy, that might remain undetected if only the whole community is considered (Boyle and Bronstein 2012; Medeiros et al. 2007).
Phenology of trees has been studied extensively around the world (Anderson et al. 2005; Bhat 1992; Handayani 2016; Kurten et al. 2018; Mishra et al. 2006; Mosissa 2019; Singh and Kushwaha 2006; Yap 1982), while phenology of herbs, shrubs, and climbers is not well studied, with few exceptions (Croat 1975; Morellato and Leitão-Filho 1996; Nakar and Jadeja 2015). This confirms that the study on phenology of each plant life form, particularly in the deciduous forests of Thailand, is greatly needed.
Therefore, the present study attempts to fill in the knowledge gaps and increase the phenological information of plants in the dry forest of Thailand. The specific objective is to investigate the flowering and fruiting phenology of herbs, climbers, shrubs, and trees in the deciduous dipterocarp forest at Lampang province, Northern Thailand.
The present study was conducted in the tropical deciduous forest of Thammasat University, Lampang Campus, Lampang province, Northern Thailand (18º19´1.6˝ N Latitude, 99º23´52.2˝ E Longitude; elevation, 257–267 m above sea level). The study area covers about 45,000 m2. The natural vegetation is the deciduous dipterocarp forest and dominated by
Field visits were made at monthly intervals from November 2018 to October 2019 and September to December 2020. The survey was carried out by walking through the entire study area to collect all the reproductive plant species and record their phenological phenomena. Plant life forms were observed and classified as follows: herbaceous plants (including terrestrial orchids), climbers, shrubs, and trees. All plant specimens were identified using the taxonomic literature, e.g., Flora of Thailand, Thai Forest Bulletin, Flora of China, Handbook, including the appropriate taxonomic websites (e.g., Balslev and Chantaranothai 2018; eFloras 2022; Koyama et al. 2016; Pooma et al. 2017; Puff et al. 2021; Thaithong et al. 2018; Utteridge and Bramley 2014). International Plant Names Index (IPNI 2023), World Flora Online Plant List (2021), and Tem Smitinand’s Thai Plant Names, Revised Edition (Pooma and Suddee 2014) were used for scientific names and author abbreviations. The phenological data were recorded through surveys by documenting its period of flowering and fruiting. Binocular observations were made to check the overlapping of events. Graphs of flowering and fruiting activities were performed for each plant life form, together with a graph of combination data of all plant species. Fruit types recorded were either fleshy or dry, then a graph was generated for showing the result. The voucher specimens were organized following the procedure defined by Bridson and Forman (1998) and have been deposited in the Biotechnology Laboratory of Thammasat University, Lampang Campus, Thailand.
Spearman’s rank correlation coefficient (
The present study revealed 126 species of vascular plants belonging to 45 families and 102 genera (Table 1). Most of them were collected from 2018 to 2019. Only five species were added to the database based on the collection in 2020. Species-rich families were Fabaceae (26 species), Malvaceae (11 species), Convolvulaceae (8 species), Lamiaceae and Apocynaceae (7 species each). Among 126 taxa, 38 species were herbaceous plants (30.16%), 32 species were climbers (25.40%), 39 species were shrubs (30.95%), and 17 species were trees (13.49%).
The phenological record of individual species was presented in Table 1. From observation of the present study, the results showed that flowering and fruiting periods seemed to have quite a similar pattern in herbaceous plants, climbers, and shrubs (Figs. 2-4). Flower formation of those three life forms showed a peak during the end of the rainy season to the beginning of the winter season (October–November). They included 26, 16, and 17 species of herbs, climbers, and shrubs, respectively. However, climbers and shrubs also showed another small flowering peak in the rainy season (June). The lowest flowering periods of herbaceous plants, climbers, and shrubs were found in the summer season to the beginning of the rainy season (March–May). Whereas tree species showed the opposite trend. The highest number of flowering trees was recorded with six species during the summer season (March–April) and the beginning of the rainy season (May) (Fig. 5). The peak periods for fruiting phenology were observed in the rainy season (October and June) for herbaceous plants (26 species) and trees (8 species), and presented in the winter season (January and November–December) for climbers (16 species) and shrubs (18 species). The lowest fruiting periods were recorded in the summer season for herbaceous plants, in the rainy season for climbers and trees, and from the summer to rainy seasons for shrubs.
The diagram in Figure 6 demonstrated the trend of flowering and fruiting periods of all plant life forms throughout the year. The results showed that flowering and fruiting periods pointed to the peaks in the winter season (November and December, respectively). Then, the number of flowering and fruiting species steadily declined in the summer season and reached the lowest amounts in April and May, respectively. Afterward, the number of flowering and fruiting species gradually increased again in the rainy season.
The highest of flowering and fruiting of the whole species occurred in the winter season. They contained 59 species of flowering in November and 57 species of fruiting in December. Whilst the lowest flowering and fruiting periods happened at the end of the summer season and the beginning of the rainy season, based on 21 species in April and 17 species in May, respectively. Interestingly, the highest and lowest numbers of fruiting were observed in a month after the highest and lowest flowering.
The results of the statistical study revealed that there was no statistically significant relationship between the number of flowering and fruiting species and rainfall. While there were strong negative correlations between temperature and the number of flowering (
The number of flowering and fruiting species was compared between the winter, summer, and rainy seasons using a one-way ANOVA. The number of flowering species varied significantly by seasons at the 0.05 level,
A one-way ANOVA was also conducted to determine the differences in the number of flowering and fruiting species among various plant life forms. Groups of herbs, climbers, shrubs, and trees were compared. The number of flowering species varied significantly among the various types of life forms at the 0.05 level,
The effect of seasons and plant life forms on the number of flowering and fruiting species was studied using a two-way ANOVA. As shown in Table 7, the results demonstrated statistically significant interactions between the effects of seasons and plant life forms on the number of flowering (
The fruit types of fruiting species were shown in Table 1. There were 104 species that produced fruits during the study period. Among these taxa, 73 species (70.19%) were dry fruits, and 31 species (29.81%) were fleshy fruits. Dry-fruited species showed a peak in the winter season (January), while the lowest number was found from the end of summer season to the beginning of rainy season (April–May) (Fig. 7). On the other hand, fleshy-fruited species showed a peak in the rainy season (May–June), and the lowest of fruiting occurred in the winter season (December). To assess the association between the fruit types (dry and fleshy) and the periods (wet and dry), a chi-square test of independence was used. The result revealed that they were strongly associated (chi-square = 35.423;
There was a first record on the diversity of plants among four selected sites in the deciduous forest at Lampang Campus of Thammasat University, which included an overview of flowering and fruiting phenology (Inuthai 2021). However, the author reported the information in terms of the combination data of whole community. Thus, the phenological pattern is quite similar to Figure 6 in the present study. As mentioned above, each species has its phenological strategy (Boyle and Bronstein 2012; Medeiros et al. 2007), so if only the whole community is considered, much essential information might be lost. Therefore, the present study attempted to go deeper into details for filling in the missing data and completing the phenological information of plants in the area.
The results from the present study indicated that herbaceous plants produced many flowers during the rainy to winter seasons (October–November). The highest peak of fruiting was observed in the winter season (December). This is similar to previous reports from other tropical forests in Southeast Asia (Bhat and Murali 2001; Nakar and Jadeja 2015; Sivaraj and Krishnamurthy 1989). Flowering and fruiting were found in numerous species from the end of the rainy season to the beginning of the winter season, then the number of species gradually dropped during the summer season. This is probably due to the seasonal changes. The diminished rainfall from the wet to dry periods (rainy to winter and summer) probably forces water stress on plants. Several herbaceous plants struggle to survive in the dry period, thus some of them disappear from their habitats during this time (Inuthai 2021).
Two flowering peaks of climber community were observed in the present study: a major peak in the winter season (November) and a minor one in the rainy season (June). Flowering activity declined during the summer season. This result conforms with the previous studies in a semideciduous forest in Brazil (Morellato and Leitão-Filho 1996) and the Barro Colorado Island (Croat 1975). They suggested that the herbaceous vines are seasonal with a flowering peak in the late wet season to early dry season, while the June peak represents species that appear to be triggered by wet rather than dry conditions. The peak period for fruiting phenology in the present study was observed in the winter season (January), which was a part of the dry period. This is consistent with the finding by Morellato and Leitão-Filho (1996), who reported that most climber species produce fruits during the dry period. This circumstance is probably the fact that many species of lianas have wind-dispersed fruits even though they may flower in the rainy season (Croat 1975).
The results showed two peaks of flowering in shrub species, viz. one in the winter season (November), and another in the rainy season (June). This phenology seems to have a similar pattern with climbers. The peak of fruiting period was found in the winter season (November–December). The results conform to the study of aromatic species including shrubs in India, where flowering and fruiting are seen mostly in December (Pandey and Tripathi 2010), and the phenological study of woody species in an arid environment of the Brazilian Chaco (Carvalho and Sartori 2015). The minor peak of flowering in the rainy season may be explained by the moisture stress in shallow-rooted plants during the dry period. This stress is perhaps adequately high to inhibit flower initiation and may experience a period of protective dormancy during the dry months (Murali and Sukumar 1994). Then, the first rains in May might act as a cue to flowering that lead to the peak in June.
The flowering of trees in the present study peaked in the summer season which conforms to the various studies on phenology of tree species in the dry deciduous forests (Bhat 1992; Murali and Sukumar 1994; Nanda et al. 2009; Nanda et al. 2014; Yap 1982). This is possibly due to the influences of the high temperature, low humidity, low soil moisture, and daylight changes during the dry period, which help in bud break and flower opening (Borchert et al. 2005; Frankie et al. 1974; Mohandass et al. 2016; Njoku 1958). In the present study, the peak period of fruiting in tree species was in the rainy season (June), which is similar to the phenological studies of trees in the dry deciduous dipterocarp forest in Thailand (Elliott et al. 1994; Sukwong et al. 1975) and other studies (Mohandass et al. 2016; Nanda et al. 2014).
Numerous tree species in the present study produced fruits during the summer season and the beginning of the rainy seasons. The different seasons of fruiting time might be due to whether they are wind-dispersed or animal-dispersed species. Elliott et al. (1994) suggested that wind-dispersed species expose the peak in the period of highest mean wind speed in April, whereas animal-dispersed species happen in July to August during the migration time of animals and birds from the evergreen forests to the deciduous forests to take advantage of increase food resources during the rainy season. Wind-dispersed species in the present study, such as
The results showed that many tree species had phenological patterns that synchronized flowering and fruiting in the dry months. Thus, flowering and fruiting during the summer season provide the selective advantages. Wright and van Schaik (1994) and Nanda et al. (2009) mentioned that flowering in the dry period is a response to the rapid resource-use rate, which more efficient to transfer assimilates directly into growing organs rather than having to store and translocate them later. Moreover, the timing of flowering peak during the dry season attracts more pollinators. This is because many trees are leafless during dry period, thus flowers are more visible and available to pollinators (Bawa et al. 2003; Elliott et al. 1994; Janzen 1967; Mohandass et al. 2016; Wright and Calderon 1995). This conforms to the observation in the present study that a large amount of leaf fall happened during January to April, corresponding with the dry period.
The statistical analysis supported the phenological patterns of flowering and fruiting in the present study. There were significant negative correlations between the number of flowering and fruiting species and temperature. Moreover, the number of flowering and fruiting species varied significantly by seasons, particularly between the winter and summer seasons. These results matched the circumstances that the flowering and fruiting species were more common in the winter season, when temperatures were at their lowest, and less common in the summer season when they were at their highest. Furthermore, the interactions between seasons and plant life forms have significant effects on the number of flowering and fruiting species. There was also statistically significant difference in the number of flowering and fruiting species depending on seasons or types of life forms.
Most of the dry-fruited species were found during the dry period (winter and summer seasons), while the majority of fleshy-fruited species occurred in the wet period (rainy season). A chi-square result showed a significant relationship between the fruit types and the periods. The present study corresponds with a previous report from a dry tropical forest in Ghana (Lieberman 1982). The author mentioned that dry fruits (frequently wind-dispersed) are more common during the dry season, whereas fleshy fruits (generally animal-dispersed) are most abundant during the wet season. In addition, dry fruits especially explosive-dispersed fruits are improved to dehiscing during the dry period when relative humidity is low (Murali and Sukumar 1994).
In the present study, herbaceous plants and climbers were triggered by conditions of drought, whereas shrubs and trees did not respond so quickly to the changes in the environment. It is perhaps to the fact that shrubs and trees are less exposed to the environment than other life forms. Most of the herbaceous plants, climbers, and shrubs flowered at the end of the rainy season, continuing until the beginning of the winter season. This phenomenon is probably because of the declining photoperiod (Singh and Kushwaha 2006). The flower blooming at the same time among herbs, climbers, and shrubs may increase the visits of shared pollen vectors. Many pollinators help to increase the possibility of better fertilization (Staggemeier et al. 2010). Climbers, which were usually found on the tree crowns, were able to flower in a period of low reproductive activity of trees. Both plant life forms might compete for the same habitat to show their flowers and consequently to be found by pollinators. So, a shift of flowering time of climbers and trees is expected to reduce competition for pollen vectors among species (Morellato and Leitão-Filho 1996). In addition, statistical results revealed that the mean numbers of flowering trees varied significantly from herbs, shrubs, and climbers. Conversely, there were no differences among groups of herbs, climbers, and shrubs.
The present study revealed the diversity of flowering and fruiting patterns among different plant life forms based on 126 species in the deciduous dipterocarp forest at Lampang province of Northern Thailand. The present study confirms that different life forms cause different phenological patterns. Most of the herbaceous plants, climbers, and shrubs flowered from the end of the rainy season to the beginning of the winter season, while trees produced a peak of flowering during the summer season to the beginning of the rainy season. The fruiting periods showed a peak in the rainy season for herbaceous plants and trees, while climbers and shrubs usually presented their fruits in the winter season. These phenological patterns seem to be related to abiotic (e.g., rainfall, temperature, photoperiod, etc.) and biotic (e.g., pollinator, animal disperser, animal migration, etc.) factors. However, long-term study and in-depth phenological observations are needed for better understanding. The present study would be helpful for comparison to the other phenological studies in the dry forests, which are decreasing year by year due to human activities. Moreover, knowing the behavior of flowering and fruiting plants will be able to help with conservation planning in the future.
I would like to express my sincere gratitude to Dr. Naiyana Tetsana, Forest Herbarium, Department of National Parks, Wildlife and Plants Conservation, Bangkok, Thailand, for her hospitality and suggestions in botanical identification. My sincere thanks to Miss Visuda Keawnunchai, a scientist, Department of Biotechnology, Faculty of Science and Technology, Thammasat University, Lampang, Thailand for her assistance during the field surveys and data collection. My appreciation to Assistant Professor Dr. Jumpot Intrakul, Department of Mathematics and Statistics, Faculty of Science and Technology, Thammasat University, Lampang, Thailand for his advice in statistical analysis. I am deeply grateful to the editor and anonymous reviewers for all their valuable comments and suggestions to improve the manuscript.
CI: Confidence interval
ANOVA: Analysis of variance
All data generated or analyzed during this study are included in this published article.
The author declares that they have no competing interests.
Janejaree Inuthai, PhD is an Assistant Professor at the Department of Biotechnology, Faculty of Science and Technology, Thammasat University, with research interests on bryology, plant taxonomy, and plant ecology.