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Home > Research > Research Results > Research Results 2020 > The overstory leaf area determines the amount of water consumed by understory vegetation in dry deciduous forests

Update:December 22, 2020

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The overstory leaf area determines the amount of water consumed by understory vegetation in dry deciduous forests

Article title

Evapotranspiration from the understory of a tropical dry deciduous forest in Cambodia

Author (affiliation)

Shin'ichi Iida (a), Takanori Shimizu (a), Koji Tamai (a), Naoki Kabeya (b), Akira Shimizu (b), Eriko Ito (c), Yasuhiro Ohnuki (d), Sophal Chann (e), Delphis F.Levia (f)

(a) Department of Disaster Prevention, Meteorology and Hydrology, FFPRI, Tsukuba, Ibaraki, Japan.

(b) Kyushu Research Center, FFPRI, Kumamoto, Japan.

(c) Hokkaido Research Center, FFPRI, Sapporo, Hokkaido, Japan.

(d) Tohoku Research Center, FFPRI, Morioka, Iwate, Japan.

(e) Institute of Forest and Wildlife Research and Development, Forestry Administration, Phnom Penh, Cambodia.

(f) Department of Geography & Spatial Sciences and Department of Plant & Soil Sciences, University of Delaware, Newark, DE, United States.

Publication Journal

Agricultural and Forest Meteorology, 295, 108170, December 2020 DOI:10.1016/j.agrformet.2020.108170( External link )

Content introduction

Dry forests, which account for more than 40% of tropical forests, are a type of vegetation that is easily affected by forest development. In Cambodia, dry forests still cover a wide area, but in recent years, development has been proceeding at a rapid pace. Due to Cambodia's domestic conflicts and other matters, there is little scientific information about its forests, which has hindered the development of forest conservation. For example, while dry forests have sparse deciduous trees in the overstory, the ground is covered by dense understory vegetation (Photo), and the amount of water consumed by understory vegetation (evapotranspiration) is still not known.

Therefore, we measured the amount of water consumed by dry forests in Cambodia, and the amount of water consumed by understory vegetation separately. As a result, we found that the proportion of water consumed by understory vegetation tended to be small in months when the leaf area index (Note) of overstory trees was high (Figure 1), but on an annual scale, it accounted for 35% of the entire forest. Furthermore, even in various forests around the world, this proportion tends to change in response to the leaf area index (Figure 2), and we could see that there are differences resulting from differences in climate, vegetation species, mass, and so on.

It has been well known that light conditions on the ground are improved by forest thinning, which promotes the growth of understory vegetation. Most attention so far has been paid to the effects of the thinning of overstory trees from the viewpoint of water conservation in forested watersheds. The importance of the understory vegetation in the forest water cycle, which is clarified in this study, should also be considered to make more suitable plans for forest management in Japan.

 (Note) Leaf area index: The value of total leaf area divided by the area of ground surface occupied by vegetation.

 

Photo:A dry deciduous forest in Cambodia

Photo. A dry deciduous forest in Cambodia. The overstory trees are sparse, while the ground is covered by dense understory vegetation, mainly dwarf bamboo (Vietnamosasa pusilla).

 

Figure1:Relation between the proportion of water consumption

Figure1. Relation between the proportion of water consumption (Evapotranspiration) by understory vegetation in Cambodian dry deciduous forests and the leaf area index of overstory trees. In months when the leaf area index is small, the proportion of water consumption by understory vegetation is large. Data are cited from Iida et al. (2020).

 

Figure2:Relation between the amount of water consumption

Figure2. Relation between the amount of water consumption (Evapotranspiration) by understory vegetation and the leaf area index of overstory trees in forests around the world. When the leaf area index of trees decreases, the proportion of water consumption by understory vegetation increases, but there are large differences among forests. Data are cited from Iida et al. (2020).