Seasonal Dynamics of Tropical Forest Vegetation in Ngoc Linh Nature Reserve, Vietnam Based on UAV Data

Abstract

Seasonal dynamics in tropical forests are closely related to the variation in forest canopy gaps. The canopy gaps change continuously in shape and size between the rainy and dry seasons, leading to the variation in the vegetative indicators. To monitor the variation of the canopy gaps, UAVs were used to collect datas in the mentioned tropical forests at an altitude of over 1,000m in Ngoc Linh Nature Reserve, Vietnam with a post-processing image resolution of about 8cm, which allows the detection of relatively small gaps. The analysis results at 10 squares of 1 ha showed a decrease in the area of ​​ canopy gaps from the rainy season in September 2019 to the dry season of May 2020. The mixed broad-leaved or broadleaf forest dominates with a greater variation, when the area of ​​the gaps decreases significantly. The variation in forest canopy gaps and vegetative indicators are closely related to the high differentiation of terrain, the seasonal and the dry season climatic characteristics. The fluctuation of the vegetation cover affects the habitats of the species under the forest canopy such as animals, birds and soil fauna. This is one of the scientific bases that contributes to the management and conservation of flora and fauna biodiversity, especially in mountainous tropical forests such as Ngoc Linh Nature Reserve.

Seasonality in the equatorial tropics: Flower, fruit, and leaf phenology of montane trees in the highlands of Southwest Uganda

“…This view is consistent with the hypothesis that flower induction in tropical trees is determined primarily by internal factors and secondarily by environmental factors that affect the seasonal development of vegetative structures (Borchert, 1983; Wright, 2018). It is also recognized in various contexts around the world that many plant adaptations appear to precede rather than follow key environmental factors—for example, in many monsoon environments deciduous trees develop new leaves and start to transpire in an apparent anticipation of the rains, so despite a correlation the rains and the cues of leaf growth are distinct (Dang Hoi & Dung, 2021; Elliott et al, 2006; Nanda et al, 2015; Singh, 2005). Teasing out what is causal and what is merely correlated due to common seasonal patterns will require multiple years of data with adequate variation in and among the key variables.…”

Differences in the vegetation dynamic patterns of three tropical secondary forests in South Sulawesi, Indonesia

“…The other was a primary tree species (P. obovatum) with a diameter of 74.81 cm, which was uprooted by strong winds. The death of these six trees created a canopy gap large enough to encourage seedlings of a climax species to grow to ≥5 cm in diameter (see Hoi and Dung 2021), giving rise to marked population dynamics and species composition. Accordingly, it takes about seven years for the Lowland forest to stabilize its population dynamics and species composition after experiencing the death of these six large canopy trees.…”

How have RPAS helped monitor forests and what can we apply in forest restoration monitoring?

“…Additionally, they involved the development of algorithms for classification through AI, followed by statistical tests to measure the quality of the indicators of interest. Examples of these indicators include tree canopy, canopy gaps (Hoi & Dung 2021), and crown delineation (Safonova et al 2021).…”