Why Study Dipterocarp Forest in Southeast Asia?
Both, the Tube Nosed Fruit Bat (Nyctimene rabori - above) and the Writhed Hornbill (Aceros waldeni - below) depend on fruits from forest trees. Both species are endemic to the Philippines and are critically endangered because of destruction of their habitat.
Legal and illegal logging is responsible for high rates of deforestation throughout Southeast Asia.
Background and Rationale:
The trees from the Dipterocarpaceae family dominate forests in Southeast Asia. Dipterocarps are large trees with dominant crown location. They are known as the “Asian Mahogany” on the international timber market and are very important economically. For this reason, this forest type has been declining rapidly throughout Southeast Asia. Aside from the economic value, dipterocarp forests hold, arguably, even larger environmental value. Of the approximately 510 species, 470 occur in Southeast Asia, many of which are endemic (1). As a dominant forest type, much of the biodiversity depends on dipterocarps. Many species of insects, birds, and bats depend on dipterocarps for pollen or fruits. Loss of dipterocarp forest is responsible for great losses of biodiversity in the region. Deforestation in the recent decades caused serious problems of soil erosion and degradation in water and air quality in Southeast Asia. At the same time, many reforestation and conservation efforts fail because there is lack of knowledge about dipterocarp reproduction patterns.
Dipterocarpaceae are not restricted to Asian tropics. However, only there they exhibit a community wide irregular mass flowering, or general flowering (GF) at interval of two to 10 years. Their seeds are viable only for a few weeks so all conservation and reforestation efforts need to focus on predicting flowering events. During a GF event, majority of the dipterocarp species and even some species of related families, burst into synchronous flowering. The event can involve as many as 200 different species (1). In dipterocarps, synchronization happens among, as well as within species, pointing to an existence of a common cue to which all species respond.
Much research has been done to identify what triggers dipterocarp flowering. Thus far, researchers identified two main climatic triggers. They are severe drought and a drop in night time temperature 30 to 60 days before flowering occurs (2)(3)(4). The two climatic events are related and are strongly associated with El Niño in Southeast Asia. Studies have shown that correlation of El Niño with GF are statistically significant, but not strict (1)(2)(3). However, other studies have shown that neither drought nor a drop in night time temperature precede flowering at all times (3)(4)(5). Majority of the study analyze data for 10 to 15 years, which includes four flowering events, at most. It is difficult to establish any particular pattern, or lack thereof, from such a small period. Therefore, the trigger for the GF event in the dipterocarp forests remains largely a mystery.
The trees from the Dipterocarpaceae family dominate forests in Southeast Asia. Dipterocarps are large trees with dominant crown location. They are known as the “Asian Mahogany” on the international timber market and are very important economically. For this reason, this forest type has been declining rapidly throughout Southeast Asia. Aside from the economic value, dipterocarp forests hold, arguably, even larger environmental value. Of the approximately 510 species, 470 occur in Southeast Asia, many of which are endemic (1). As a dominant forest type, much of the biodiversity depends on dipterocarps. Many species of insects, birds, and bats depend on dipterocarps for pollen or fruits. Loss of dipterocarp forest is responsible for great losses of biodiversity in the region. Deforestation in the recent decades caused serious problems of soil erosion and degradation in water and air quality in Southeast Asia. At the same time, many reforestation and conservation efforts fail because there is lack of knowledge about dipterocarp reproduction patterns.
Dipterocarpaceae are not restricted to Asian tropics. However, only there they exhibit a community wide irregular mass flowering, or general flowering (GF) at interval of two to 10 years. Their seeds are viable only for a few weeks so all conservation and reforestation efforts need to focus on predicting flowering events. During a GF event, majority of the dipterocarp species and even some species of related families, burst into synchronous flowering. The event can involve as many as 200 different species (1). In dipterocarps, synchronization happens among, as well as within species, pointing to an existence of a common cue to which all species respond.
Much research has been done to identify what triggers dipterocarp flowering. Thus far, researchers identified two main climatic triggers. They are severe drought and a drop in night time temperature 30 to 60 days before flowering occurs (2)(3)(4). The two climatic events are related and are strongly associated with El Niño in Southeast Asia. Studies have shown that correlation of El Niño with GF are statistically significant, but not strict (1)(2)(3). However, other studies have shown that neither drought nor a drop in night time temperature precede flowering at all times (3)(4)(5). Majority of the study analyze data for 10 to 15 years, which includes four flowering events, at most. It is difficult to establish any particular pattern, or lack thereof, from such a small period. Therefore, the trigger for the GF event in the dipterocarp forests remains largely a mystery.
Research Objectives:
My objective of this study is to find a correlation between mass flowering in dipterocarps and weather cues based on a long-term flowering and climate data. In order to do this I have gathered 53 years of flowering and weather data from three sub-regions: Peninsular Malaysia, Borneo, and the Philippines. To see if flowering responds to climatic triggers, I chose to analyze six climate variables: precipitation, maximum and minimum temperatures, humidity, cloud cover; and Southern Oscillation Index (SOI). Precipitation, humidity, and cloud cover are related variables and all are predictors of drought. Southern oscillation index (SOI) is a measure of the occurrence of El Niño anomalies. The analysis of correlation between these climate variables and flowering will show if any are responsible for triggering GF events.
My objective of this study is to find a correlation between mass flowering in dipterocarps and weather cues based on a long-term flowering and climate data. In order to do this I have gathered 53 years of flowering and weather data from three sub-regions: Peninsular Malaysia, Borneo, and the Philippines. To see if flowering responds to climatic triggers, I chose to analyze six climate variables: precipitation, maximum and minimum temperatures, humidity, cloud cover; and Southern Oscillation Index (SOI). Precipitation, humidity, and cloud cover are related variables and all are predictors of drought. Southern oscillation index (SOI) is a measure of the occurrence of El Niño anomalies. The analysis of correlation between these climate variables and flowering will show if any are responsible for triggering GF events.
Deforestation is attributed to severe soil erosion and landslides in Southeast Asia.
Expected Results:
I expect to see a correlation between drought and flowering in all three regions. In Southeast Asia, drought is followed by a rainy season, a condition that is very favorable for sapling recruitment. Therefore, dipterocarps respond to drought in order to insure that by the time the seeds are set the conditions are favorable for them to grow. Drought conditions correspond to low precipitation, low humidity, higher maximum temperatures, and clear skies. I expect to see a negative relationship between cloud over, precipitation, humidity and flowering; and a positive relationship between flowering and maximum temperatures. Minimum temperatures are associated with clear skies during drought. Therefore minimum temperatures should have a negative correlation with flowering. El Niño anomalies signify a particularly heavy drought in Southeast Asia. Therefore, I also expect to see a negative relationship between SOI and flowering.
I expect to see a correlation between drought and flowering in all three regions. In Southeast Asia, drought is followed by a rainy season, a condition that is very favorable for sapling recruitment. Therefore, dipterocarps respond to drought in order to insure that by the time the seeds are set the conditions are favorable for them to grow. Drought conditions correspond to low precipitation, low humidity, higher maximum temperatures, and clear skies. I expect to see a negative relationship between cloud over, precipitation, humidity and flowering; and a positive relationship between flowering and maximum temperatures. Minimum temperatures are associated with clear skies during drought. Therefore minimum temperatures should have a negative correlation with flowering. El Niño anomalies signify a particularly heavy drought in Southeast Asia. Therefore, I also expect to see a negative relationship between SOI and flowering.
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,(1) Appanah, S. 1993. Mass Flowering of Dipterocarp Forests in the Aseasonal Tropics. Journal of Biosciences 18:457-474.
(2) Ashton, P. S., T. J. Givnish, et al. (1988). "Staggered Flowering in the Dipterocarpaceae - New Insights into Floral Induction and the Evolution of Mast Fruiting in the Aseasonal Tropics." American Naturalist 132(1): 44-66.
(3) Numata, S., M. Yasuda, T. Okuda, N. Kachi, and N. S. M. Noor. 2003. Temporal and spatial patterns of mass flowerings on the Malay Peninsula. American Journal of Botany 90:1025-1031.
(4) Sakai, S., R. D. Harrison, K. Momose, K. Kuraji, H. Nagamasu, T. Yasunari, L. Chong, and T. Nakashizuka. 2006.Irregular droughts trigger mass flowering in aseasonal tropical forests in Asia. American Journal of Botany 93:1134 1139.
(5) Brearley, F. Q., J. Proctor, Suriantata, L. Nagy, G. Dalrymple, and B. C. Voysey. 2007a. Reproductive phenology over a 10-year period in a lowland evergreen rain forest of central Borneo. Journal of Ecology 95:828-839.
,(1) Appanah, S. 1993. Mass Flowering of Dipterocarp Forests in the Aseasonal Tropics. Journal of Biosciences 18:457-474.
(2) Ashton, P. S., T. J. Givnish, et al. (1988). "Staggered Flowering in the Dipterocarpaceae - New Insights into Floral Induction and the Evolution of Mast Fruiting in the Aseasonal Tropics." American Naturalist 132(1): 44-66.
(3) Numata, S., M. Yasuda, T. Okuda, N. Kachi, and N. S. M. Noor. 2003. Temporal and spatial patterns of mass flowerings on the Malay Peninsula. American Journal of Botany 90:1025-1031.
(4) Sakai, S., R. D. Harrison, K. Momose, K. Kuraji, H. Nagamasu, T. Yasunari, L. Chong, and T. Nakashizuka. 2006.Irregular droughts trigger mass flowering in aseasonal tropical forests in Asia. American Journal of Botany 93:1134 1139.
(5) Brearley, F. Q., J. Proctor, Suriantata, L. Nagy, G. Dalrymple, and B. C. Voysey. 2007a. Reproductive phenology over a 10-year period in a lowland evergreen rain forest of central Borneo. Journal of Ecology 95:828-839.
