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.

Site area

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 Dipterocarpus obtusifolius Teijsm. ex Miq., Dipterocarpus tuberculatus Roxb., Cratoxylum cochinchinense (Lour.) Blume, Diospyros ehretioides Wall. ex G. Don, Garcinia nigrolineata Planch. ex T. Anderson, and Anacardium occidentale L. (Inuthai 2022). A forest’s structure comprises three crown layers as follows the top, middle, and shrub canopies (above 12 m, 6–12 m, and less than 6 m high), respectively. The forest understory is composed of a variety of tree saplings, herbaceous plants, and climbers (Inuthai 2022). The topology of the study site is flat, with loamy sand soil bearing a pH ranging from 5.6–7.5. The climate is characterized by three strong seasons: hot-dry summer (February–April); rainy (May–October); and cool-dry winter (November–January). Rainfall and temperature data for the study area were collected from Northern Meteorological Center, Meteorological Department (Lampang Agromet 2020). Mean monthly rainfall and temperature patterns during the study period are given in Figure 1.

Figure 1. Mean monthly rainfall and temperature during the study period (2018–2020) in Lampang province, Northern Thailand.

Data collection

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.

Statistical analysis

Spearman’s rank correlation coefficient (r_s) between the meteorological factors (rainfall and temperature) and the number of flowering and fruiting species were calculated. The one-way analysis of variance (ANOVA) was conducted to determine whether there was a difference in the number of flowering and fruiting species by seasons and by plant life forms. The pairwise comparisons were performed with the Scheffe post hoc test. The two-way ANOVA was operated to analyze the effect of seasons and plant life forms on the number of flowering and fruiting species. The chi-square test was used to test the relationship between fruit types and periods. All the tests were executed by using the software IBM SPSS statistics v.28.0.1.1 (IBM Co., Armonk, NY, USA).

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%).

Table 1 . List of species, family, life form, flowering period, fruiting period, and fruit type of plants in the deciduous dipterocarp forest at Lampang province, Northern Thailand.

No.	Scientific name	Family	Life form	Flowering period	Fruiting period	Fruit type
1	Aeschynomene americana L.	Fabaceae	Shrub	Nov–Dec	Nov–Jan	Dry
2	Alternanthera sessilis (L.) R. Br. ex DC.	Amaranthaceae	Herb	Nov–Dec	-	-
3	Alysicarpus vaginalis (L.) DC.	Fabaceae	Herb	Oct	Oct	Dry
4	Amphineurion marginatum (Roxb.) D. J. Middleton	Apocynaceae	Climber	Jun	-	-
5	Anacardium occidentale L.	Anacardiaceae	Tree	Nov–Jun	Mar–Jun	Dry
6	Andrographis paniculata (Burm. f.) Wall. ex Nees	Acanthaceae	Herb	Nov–Jan	Nov–Jan	Dry
7	Antidesma ghaesembilla Gaertn.	Phyllanthaceae	Shrub	Jul	-	-
8	Argyreia osyrensis (Roth) Choisy	Convolvulaceae	Shrub	Nov	Apr	Fleshy
9	Aristolochia tagala Cham.	Aristolochiaceae	Climber	Sep–Nov	Nov–Feb	Dry
10	Asystasia gangetica (L.) T. Anderson	Acanthaceae	Herb	Oct–Feb	Oct–Feb	Dry
11	Barleria cristata L.	Acanthaceae	Shrub	Nov	Nov	Dry
12	Bidens pilosa L.	Asteraceae	Herb	Jan–Dec	Jan–Dec	Dry
13	Biophytum umbraculum Welw.	Oxalidaceae	Herb	Oct–Nov	Oct–Dec	Dry
14	Brucea javanica (L.) Merr.	Simaroubaceae	Shrub	Mar–Oct	Mar–Nov	Fleshy
15	Butea monosperma (Lam.) Taub.	Fabaceae	Tree	Feb–Mar	Feb–Mar	Dry
16	Caesalpinia furfuracea (Prain) Hattink	Fabaceae	Climber	Sep–Oct	Oct–Mar	Dry
17	Calopogonium mucunoides Desv.	Fabaceae	Climber	Oct	-	-
18	Capparis sepiaria L.	Capparaceae	Climber	Apr–May	-	-
19	Capparis zeylanica L.	Capparaceae	Climber	Mar–Apr	Apr–Aug	Fleshy
20	Casearia grewiifolia Vent.	Salicaceae	Tree	Jul	Jun–Sep	Fleshy
21	Catunaregam spathulifolia Tirveng.	Rubiaceae	Tree	-	Nov–Jan	Fleshy
22	Centrosema pubescens Benth.	Fabaceae	Climber	Oct–Jan	Oct–Feb	Dry
23	Chamaecrista pumila (Lam.) K. Larsen	Fabaceae	Herb	Oct	Oct	Dry
24	Chromolaena odorata (L.) R. M. King & H. Rob.	Asteraceae	Herb	Nov–Mar	Dec–Mar	Dry
25	Clausena excavata Burm. f.	Rutaceae	Shrub	Mar–Jun	Jun–Sep	Fleshy
26	Cleome rutidosperma DC.	Cleomaceae	Herb	Aug–Oct	Aug–Oct	Dry
27	Clerodendrum paniculatum L.	Lamiaceae	Shrub	Sep	Oct–Nov	Fleshy
28	Clitoria macrophylla Wall. ex Benth.	Fabaceae	Climber	Sep	-	-
29	Commelina benghalensis L.	Commelinaceae	Herb	Dec–Jan	-	-
30	Corchorus aestuans L.	Malvaceae	Herb	Oct–Jan	Oct–Jan	Dry
31	Cratoxylum cochinchinense (Lour.) Blume	Hypericaceae	Tree	Apr–Sep	Jan–Dec	Dry
32	Cratoxylum formosum (Jacq.) Benth. & Hook. f. ex Dyer subsp. pruniflorum (Kurz) Gogelein	Hypericaceae	Tree	May	Jun–Jul	Dry
33	Crotalaria alata Buch.-Ham. Ex D. Don	Fabaceae	Shrub	Oct–Jan	Oct–Jan	Dry
34	Crotalaria incana L.	Fabaceae	Herb	Nov–Jan	Dec–Jan	Dry
35	Desmodium triflorum (L.) DC.	Fabaceae	Herb	Sep–Nov	Sep–Nov	Dry
36	Desmodium velutinum (Willd.) DC. subsp. velutinum	Fabaceae	Shrub	Nov–Dec	Nov–Jan	Dry
37	Dillenia aurea Sm.	Dilleniaceae	Tree	Apr–Jun	Apr–May	Fleshy
38	Dillenia obovata (Blume) Hoogland	Dilleniaceae	Tree	Feb–Mar	Apr	Fleshy
39	Diospyros ehretioides Wall. ex G. Don	Ebenaceae	Tree	Mar–Apr	Jan–Dec	Fleshy
40	Dipterocarpus obtusifolius Teijsm. ex Miq.	Dipterocarpaceae	Tree	Oct–Dec	Oct–Mar	Dry
41	Dipterocarpus tuberculatus Roxb.	Dipterocarpaceae	Tree	-	-	-
42	Dunbaria bella Prian	Fabaceae	Climber	Nov–Feb	Nov–Feb	Dry
43	Dunbaria punctata (Wight & Arn.) Benth.	Fabaceae	Climber	Oct–Nov	Oct–Dec	Dry
44	Ellipanthus tomentosus Kurz	Connaraceae	Tree	Mar	-	-
45	Erythroxylum cuneatum (Miq.) Kurz	Erythroxylaceae	Shrub	Jul–Sep, Dec	Jul–Sep, Dec	Fleshy
46	Eulophia graminea Lindl.	Orchidaceae	Herb	Jan–Mar	Mar	Dry
47	Euphorbia heterophylla L.	Euphorbiaceae	Herb	Sep	Sep	Dry
48	Euphorbia hirta L.	Euphorbiaceae	Herb	May–Feb	May–Feb	Dry
49	Eurycoma longifolia Jack	Simaroubaceae	Shrub	Feb–Jun	May–Jul	Fleshy
50	Evolvulus alsinoides var. decumbens (R. Br.) Ooststr.	Convolvulaceae	Herb	Sep–Oct	-	-
51	Evolvulus nummularius (L.) L.	Convolvulaceae	Herb	Aug–Jan	Aug–Feb	Dry
52	Flemingia stricta Roxb. ex W. T. Aiton	Fabaceae	Shrub	Oct–Mar	Nov–Jan	Dry
53	Garcinia nigrolineata Planch. ex T. Anderson	Clusiaceae	Tree	-	Feb–Jun	Fleshy
54	Geodorum recurvum (Roxb.) Alston	Orchidaceae	Herb	Jul	-	-
55	Harrisonia perforata (Blanco) Merr.	Rutaceae	Shrub	Mar–Jun	Jun–Oct	Fleshy
56	Helicteres lanceolata A. DC. var. gagnepainiana (Craib) Phengklai	Malvaceae	Shrub	Jul–Sep	-	-
57	Helicteres lanceolata A. DC. var. lanceolata	Malvaceae	Shrub	Jul–Oct	-	-
58	Holarrhena pubescens Wall. ex G. Don	Apocynaceae	Shrub	Mar, Jun	-	-
59	Hoya kerrii Craib	Apocynaceae	Climber	May–Jul	Jul–Aug	Dry
60	Hyptis brevipes Poit.	Lamiaceae	Shrub	Nov–Dec	Jan	Dry
61	Hyptis suaveolens (L.) Poit.	Lamiaceae	Shrub	Sep–Feb	Oct–Feb	Dry
62	Ichnocarpus frutescens (L.) W. T. Aiton	Apocynaceae	Climber	Oct–Dec	Jan	Dry
63	Indigofera cassioides Rottler ex DC.	Fabaceae	Shrub	Jan–Feb	Jan–Feb	Dry
64	Indigofera hirsuta L.	Fabaceae	Shrub	Sep–Jan	Sep–Jan	Dry
65	Ipomoea obscura (L.) Ker Gawl.	Convolvulaceae	Climber	Jan–Dec	Dec–May	Dry
66	Ipomoea pes-tigridis L.	Convolvulaceae	Climber	Aug–Oct	Sep–Oct	Dry
67	Jasminum elongatum (P. J. Bergius) Willd.	Oleaceae	Shrub	Jan–Feb	-	-
68	Lantana camara L.	Verbenaceae	Climber	Jun–Feb	Jun–Mar	Fleshy
69	Leea indica (Burm. f.) Merr.	Vitaceae	Shrub	Jul–Aug, Nov	Oct–Jan, Aug	Fleshy
70	Leucas aspera (Willd.) Link	Lamiaceae	Herb	Jan–Feb, Sep–Oct	Dec–Feb	Dry
71	Leucas decemdentata (Willd.) Sm.	Lamiaceae	Herb	Dec	Dec	Dry
72	Lindernia ciliata (Colsm.) Pennell	Linderniaceae	Herb	Sep–Jan	Sep–Dec	Dry
73	Lindernia crustacea (L.) F. Muell. var. crustacea	Linderniaceae	Herb	Sep–Jan	Oct–Jan	Dry
74	Ludwigia hyssopifolia (G. Don) Exell	Onagraceae	Herb	Sep–Nov	Oct	Dry
75	Mammea siamensis (Miq.) T. Anderson	Clusiaceae	Tree	Feb–Mar	-	-
76	Memecylon scutellatum (Lour.) Hook. & Arn. var. scutellatum	Melastomataceae	Shrub	Mar–Jun	Jul–Dec	Fleshy
77	Merremia bambusetorum Kerr.	Convolvulaceae	Climber	Dec–Mar	Jan–Mar	Dry
78	Merremia hirta (L.) Merr.	Convolvulaceae	Climber	Nov	-	-
79	Merremia vitifolia (Burm. f.) Haller f.	Convolvulaceae	Climber	Jan–Apr	Jan–Apr	Dry
80	Mikania micrantha Kunth	Asteraceae	Climber	Oct–Mar	Nov–Mar	Dry
81	Mimosa diplotricha C. Wright ex. Sauvalle	Fabaceae	Herb	Aug–Dec	Nov–Jan	Dry
82	Mimosa pudica L.	Fabaceae	Herb	Jul–Mar	Oct–Mar	Dry
83	Momordica charantia L.	Cucurbitaceae	Climber	Sep–Dec	-	-
84	Murdannia gigantea (Vahl) G. Brückn.	Commelinaceae	Herb	Jul, Nov	Jun–Nov	Dry
85	Murdannia nudiflora (L.) Brenan	Commelinaceae	Herb	Oct	Oct	Dry
86	Ochna integerrima (Lour.) Merr.	Ochnaceae	Shrub	Mar–Jun	Mar–Aug	Fleshy
87	Olax psittacorum (Lam.) Vahl	Olacaceae	Climber	May	Jun	Fleshy
88	Oldenlandia corymbosa L.	Rubiaceae	Herb	Aug–Dec	Aug–Dec	Dry
89	Paederia pilifera Hook. f.	Rubiaceae	Climber	Dec–Mar	Jan–Apr	Dry
90	Parinari anamensis Hance	Chrysobalanaceae	Tree	Oct–Jun	Oct–Nov	Fleshy
91	Passiflora foetida L.	Passifloraceae	Climber	Apr–Aug	Jan, Apr–Sep	Fleshy
92	Phyllanthus urinaria L.	Phyllanthaceae	Herb	-	Sep–Dec	Fleshy
93	Phyllanthus virgatus G. Forst.	Phyllanthaceae	Herb	Jun–Sep, Nov–Dec	Jul–Dec	Fleshy
94	Phyllodium pulchellum (L.) Desv.	Fabaceae	Shrub	Sep, Nov	Nov–Feb	Dry
95	Polygala elongata Klein ex Willd.	Polygalaceae	Herb	Aug–Oct	Sep–Oct	Dry
96	Praxelis clematidea (Griseb.) R.M. King & H. Rob.	Asteraceae	Herb	Jan–Dec	Jan–Dec	Dry
97	Premna herbacea Roxb.	Lamiaceae	Shrub	Jun	Jun–Sep	Fleshy
98	Pueraria phaseoloides (Roxb.) Benth.	Fabaceae	Climber	Nov	Nov	Dry
99	Rotheca serrata (L.) Steane & Mabb.	Lamiaceae	Shrub	Aug–Oct	Aug–Nov	Fleshy
100	Sauropus androgynus (L.) Merr.	Phyllanthaceae	Shrub	Jul–Jan	-	-
101	Senna hirsuta (L.) H. S. Irwin & Barneby	Fabaceae	Shrub	Nov–Dec	Nov–Dec	Dry
102	Sida acuta Burm. f.	Malvaceae	Shrub	Jan, Oct, Dec	Oct–Jan	Dry
103	Sida cordata (Burm. f.) Borss. Waalk.	Malvaceae	Shrub	Nov–Feb	Nov–Feb	Dry
104	Sida cordifolia L.	Malvaceae	Shrub	Oct–Feb	Oct–Mar	Dry
105	Sida rhombifolia L. subsp. rhombifolia	Malvaceae	Shrub	Nov	-	-
106	Sindora siamensis Teijsm. ex Miq. var. siamensis	Fabaceae	Tree	Apr–May	May–Jan	Dry
107	Smilax luzonensis C. Presl	Smilacaceae	Climber	Apr–Jun	Jul–Oct	Fleshy
108	Solena heterophylla Lour.	Cucurbitaceae	Climber	Jun–Sep, Nov–Jan	Jan–Apr	Fleshy
109	Spermacoce ocymoides Burm. f.	Rubiaceae	Herb	Sep–Feb	Oct–Feb	Dry
110	Streptocaulon juventas (Lour.) Merr.	Apocynaceae	Climber	Aug–Sep	Oct	Dry
111	Strychnos nux-blanda A. W. Hill	Loganiaceae	Tree	-	Oct–Jul	Fleshy
112	Stylosanthes humilis Humb., Bonpl. & Kunth	Fabaceae	Herb	Jun–Feb	Dec–Feb, Sep–Oct	Dry
113	Telosma pallida (Roxb.) Craib.	Apocynaceae	Climber	Jun–Aug	-	-
114	Tephrosia vestita Vogel	Fabaceae	Shrub	Oct–Dec	Oct–Jan	Dry
115	Thunbergia fragrans Roxb.	Acanthaceae	Climber	Sep–Feb	Oct–Feb	Dry
116	Toxocarpus villosus (Blume) Decne.	Apocynaceae	Climber	Oct–Feb	Jan–Feb	Dry
117	Tridax procumbens L.	Asteraceae	Herb	Jan–Dec	Jan–Dec	Dry
118	Triumfetta pilosa Roth	Malvaceae	Herb	Sep–Feb	Oct–Feb	Dry
119	Urena lobata L.	Malvaceae	Shrub	Dec	Dec	Dry
120	Urena rigida Wall. ex Mast.	Malvaceae	Shrub	Nov–Feb	Dec–Feb	Dry
121	Uvaria cherrevensis (Pierre ex Finet & Gagnep.) L. L. Zhou, Y. C. F. Su & R. M. K. Saunder	Annonaceae	Shrub	Jun–Sep	Jul–Sep, Dec	Fleshy
122	Vangueria pubescens Kurz	Rubiaceae	Shrub	May	Jun–Oct	Fleshy
123	Ventilago denticulata Willd.	Rhamnaceae	Climber	Oct–Nov	Jan–Apr	Dry
124	Waltheria indica L.	Malvaceae	Shrub	Feb, Jun–Jul	-	-
125	Ziziphus oenoplia (L.) Mill. var. oenoplia	Rhamnaceae	Climber	Aug–Nov	Oct–Dec	Fleshy
126	Zornia gibbosa Span.	Fabaceae	Herb	Oct	Oct	Dry

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.

Figure 2. Flowering and fruiting periodicity expressed as the number of herbaceous plants (including terrestrial orchids) in the deciduous dipterocarp forest at Lampang province.

Figure 3. Flowering and fruiting periodicity expressed as the number of climbers in the deciduous dipterocarp forest at Lampang province.

Figure 4. Flowering and fruiting periodicity expressed as the number of shrubs in the deciduous dipterocarp forest at Lampang province.

Figure 5. Flowering and fruiting periodicity expressed as the number of trees in the deciduous dipterocarp forest at Lampang province.

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.

Figure 6. Flowering and fruiting periodicity of herbs, climbers, shrubs, and trees combined in the deciduous dipterocarp forest at Lampang province.

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 (r_s = –0.774, p = 0.003), and fruiting species (r_s = –0.947, p < 0.001) (Table 2).

Table 2 . Results of the Spearman’s correlation of flowering and fruiting with rainfall and temperature.

	Rainfall			Temperature
	Flowering	Fruiting		Flowering	Fruiting
rs	–0.123	–0.232		–0.774	–0.947
p-value	0.704	0.469		0.003	<0.001

r_s: Spearman’s correlation; p < 0.01.

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, F(2, 9) = 4.664, p = 0.041 (Table 3). Scheffe’s post hoc test for multiple comparisons indicated that the mean numbers of flowering species were significantly different between the winter and summer seasons (p = 0.05; 95% confidence interval [CI] = 0.03, 47.97) (Table 4). However, there were no statistically significant differences in the mean numbers of flowering species between the winter and rainy seasons (p = 0.106), or between the rainy and summer seasons (p = 0.645) (Table 4). Moreover, there was a significant difference in the number of fruiting species among seasons at the 0.05 level, F(2, 9) = 6.585, p = 0.017 (Table 3). According to Scheffe’s post hoc analysis, there were significant differences in the mean numbers of fruiting species between the winter and summer seasons (p = 0.033; 95% CI = 2.32, 51.68), as well as between the winter and rainy seasons (p = 0.030; 95% CI = 2.46, 45.21) (Table 4). However, there was no significant difference in the mean numbers of fruiting species between the summer and rainy seasons (p = 0.912) (Table 4).

Table 3 . Results of one-way ANOVA for the number of flowering and fruiting species among different seasons.

Source of variation	Sum of squares	Degree of freedom	Mean square	F-value	p-value
Flowering
Between groups	944.083	2	472.042	4.664	0.041
Within groups	910.833	9	101.204
Total	1,854.917	11
Fruiting
Between groups	1,413.833	2	706.917	6.585	0.017
Within groups	966.167	9	107.352
Total	2,380.000	11

Table 4 . Results of Scheffe’s post hoc test for multiple comparisons of the number of flowering and fruiting species in different seasons.

Season	Mean	Flowering				Mean	Fruiting
		Winter	Summer	Rainy			Winter	Summer	Rainy
Winter	51.00	-	24.000*	17.167		54.67	-	27.000*	23.833*
Summer	27.00		-	6.833		27.67		-	3.167
Rainy	33.83			-		30.83			-

-: not applicable.

-*p < 0.05.

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, F(3, 44) = 9.560, p < 0.001 (Table 5). According to Scheffe’s post hoc test, the mean numbers of flowering species were significantly different between herbs and trees (p < 0.001; 95% CI = –16.45, –4.72), shrubs and trees (p = 0.012; 95% CI = –12.95, –1.22), and climbers and trees (p = 0.027; 95% CI = –12.28, –0.55), respectively (Table 6). However, there were no significant differences between the mean numbers of flowering species between herbs and climbers (p = 0.249), herbs and shrubs (p = 0.400), and climbers and shrubs (p = 0.991) (Table 6). Moreover, there was no statistically significant difference in the number of fruiting species across the various categories of life forms (p = 0.53) (Table 6).

Table 5 . Results of one-way ANOVA for the number of flowering and fruiting species among different plant life forms.

Source of variation	Sum of squares	Degree of freedom	Mean square	F-value	p-value
Flowering
Between groups	700.229	3	233.410	9.560	<0.001
Within groups	1,074.250	44	24.415
Total	1,774.479	47
Fruiting
Between groups	227.229	3	75.743	2.769	0.053
Within groups	1,203.750	44	27.358
Total	1,430.979	47

Table 6 . Results of Scheffe’s post hoc test for multiple comparisons of the number of flowering and fruiting species in different plant life forms.

Plant life form	Mean	Flowering					Mean	Fruiting
		Herb	Climber	Shrub	Tree			Herb	Climber	Shrub	Tree
Herb	13.67	-	4.167	3.500	10.583**		12.08	-	4.000	2.333	5.917
Climber	9.50		-	0.667	6.417*		8.08		-	1.667	1.917
Shrub	10.17			-	7.083*		9.75			-	3.583
Tree	3.08				-		6.17				-

-: not applicable.

*p < 0.05, **p < 0.001.

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 (F(6, 36) = 2.649, p = 0.031) and fruiting (F(6, 36) = 2.782, p = 0.025) species, respectively. Seasons and plant life forms both demonstrated statistically significant effects on the number of flowering and fruiting species (p < 0.05), according to a simple main effects analysis.

Table 7 . Results of two-way ANOVA of the effect of seasons and plant life forms on the number of flowering and fruiting species.

Effect	Degree of freedom	Flowering			Fruiting
		F-value	p-value		F-value	p-value
Season	2	7.306	0.002		11.369	<0.001
Plant life form	3	13.277	<0.001		4.472	0.009
Season × plant life form	6	2.649	0.031		2.782	0.025
Model	12	26.680	<0.001		24.869	<0.001

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; p < 0.001; Table 8). As shown in Figure 7, the dry fruits appeared to demonstrate a positive trend toward the dry period, whereas the fleshy fruits were more frequently detected during the wet period.

Table 8 . The accumulated number of fruiting events of dry- and fleshy-fruited species during the dry and wet periods.

Fruit type	Period
	Dry	Wet	Total
Dry	193	94	287
Fleshy	54	91	145
Total	247	185	432

Values are presented as number only.

Dry period: winter and summer seasons; Wet period: rainy season.

Figure 7. Fruiting periodicity of dry- and fleshy-fruited species in the deciduous dipterocarp forest at Lampang province.

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 Butea monosperma (Lam.) Taub., Dipterocarpus obtusifolius Teijsm. ex Miq., which fruiting times obviously appeared during the summer season and the beginning of the rainy season. Another possibility of fruiting in the rainy season, perhaps because rainfalls are necessary for seed germination and seeding survival of plants.

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

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All data generated or analyzed during this study are included in this published article.

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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.