Relationship between Fruiting Phenology and Climatic Factors in Lower Montane Forest at Doi Suthep – Pui National Park, Chiang Mai Province

Abstract

Background and Objectives: The fruiting phenology of tree species is closely linked to seasonal patterns and climatic factors, both of which play a crucial role in determining the availability of food resources for a wide range of frugivores. These plant-animal interactions are fundamental to maintaining the stability of ecosystem and biodiversity. Amidst on going global climate change, understanding the mechanisms determining fruiting phenology is essential for predicting ecological dynamics and informing effective conservation planning. This is particularly crucial in the lower montane forest, which exhibits unique environmental conditions and is sensitive to climate change impacts, including rising temperatures and erratic rainfall. Nevertheless, understanding of climate change effects on fruiting phenology in Thailand’s montane forests remains insufficient. This research aimed to investigate the timing and magnitude of fruit production in tree species within a permanent lower montane forest plot at Huai Kog Ma, Doi Suthep-Pui National Park, Chiang Mai Province. It also examines the relationship between fruiting phenology and climatic factors, aiming to establish a comprehensive understanding of the environmental drivers shaping fruiting phenology in this lower montane forest ecosystem.

Methodology: A comprehensive review of tree species in the lower montane forest permanent plot was conducted, drawing from databases and literature sources such as the Concise Encyclopedia of Plants in Thailand, the BGO Plant Database, the Useful Tropical Plants Database, and A Field Guide to Forest Trees of Northern Thailand, including a preliminary permanent plot survey to identify species bearing fleshy fruits consumed by wildlife. A diverse set of 32 species from 21 families was selected to ensure broad taxonomic representation. Fruiting phenology was monitored for at least five mature individuals per species using binoculars from October 2016 to December 2018. The average monthly fruiting percentage for each species was then calculated. The relationships between fruiting phenology and climatic factors were analyzed using multiple linear regression in R software.

Main Results: Based on 32 tree species for fruit production monitoring, 18 species were found to bear fruits during the observation period. These species were categorized into three phenological groups. Group 1 comprised species fruiting in the dry season (November–April), including Eurya acuminata, Litsea cambodiana, and Prunus arborea. Group 2 consisted of species fruiting in the rainy season (May–October), including Baccaurea ramiflora, Protium serratum, Saurauia roxburghii, and Syzygium tetragonum. Group 3 comprised species that fruited continuously throughout the year without a specific season, including Acronychia pedunculata, Apodytes dimidiata, Canthiumera glabra, Choerospondias axillaris, Ficus curtipes, Ficus simplicissima, Ficus elmeri, Garcinia celebica, Madhuca floribunda, Melia azedarach, and Heptapleurum heptaphyllum. The timing and quantity of fruit production for each species were influenced by various factors, including tree size, soil nutrient availability, tree density in the area, and climatic conditions. Upon analyzing the relationship between fruiting phenology and climatic factors, it was observed that 8 out of 18 species exhibited a significant correlation with rainfall and temperature. These species can be classified into two distinct groups. The first group comprises four species whose fruiting patterns were significantly correlated with rainfall. Among these, two species—P. serratum and A. dimidiata—demonstrated a positive correlation with rainfall, while two species—F. simplicissima and M. floribunda—exhibited a negative correlation. The second group includes four species whose fruiting was significantly correlated with temperature. Among these, two species—B. ramiflora and F. curtipes—displayed a positive correlation with temperature, while the other two—A. pedunculata and E. acuminata— exhibited a negative correlation. In analyzing the study results in conjunction with climatic data spanning from 2019 to 2022, it was observed that monthly rainfall exhibited significant variability, particularly in the year 2022, during which precipitation experienced a notable increase during the rainy season. Conversely, temperature fluctuations were relatively minor. This observation suggests that the fruiting phenology of species associated with rainfall may also exhibit substantial variability. These findings suggest that species whose fruiting is sensitive to rainfall, particularly F. simplicissima and M. floribunda, may exhibit reduced fruit production under increased precipitation. As both are key food sources for various frugivores, alterations in their fruiting patterns could result in food scarcity, triggering intensified interspecific competition or dietary shifts among wildlife. Such behavioral changes may reduce seed dispersal opportunities for these species, potentially limiting their reproductive success and risking local extinction. If similar effects are experienced by other species. resulting disruption could compromise forest regeneration processes and destabilize the ecological balance of the lower montane forest system.

Conclusion: On going climate change undeniably influences the alterations in the fruiting phenology of those species closely associated with climatic factors. Consequently, it affects frugivores that function as key seed dispersers and disrupts natural ecosystem regeneration processes. The study offers valuable insights into tree species, highly vulnerable to climate change, highlighting the urgent need for conservation strategies aimed at mitigating extinction risks. Such efforts are essential for sustaining ecological balance and promoting the long-term resilience of forest ecosystems under changing environmental conditions.