Terrestrial Ecosystem Response to Environmental Disturbances
Takashi Hirano , Professor
Research Faculty of Agriculture / Graduate School of Agriculture (Department of Bioresource and Environmental Engineering, School of Agriculture)
High school : Toyooka High School (Hyogo)
Academic background : Graduate School of Agriculture, Hokkaido University
- Research areas
- Eco-informatics，Ecosystem meteorology
- Research keywords
- ecosystem monitoring, climate change，carbon cycle， environmental disturbances，CO2 flux
What are you aiming for?
The main substance responsible for the global warming is carbon dioxide (CO2) artificially emitted from fossil fuel combustion and deforestation. It has been found that about 30% of the CO2 emitted into the atmosphere is absorbed and fixed by terrestrial ecosystems that are mainly composed of forests. Although terrestrial ecosystems help to suppress the increase in atmospheric CO2 concentration by absorbing it through photosynthesis, many uncertainties remain about the geological distribution of CO2 absorption, response to environmental change, etc. Therefore, to accurately estimate future CO2 absorption and predict changes in atmospheric CO2 concentration, factors causing changes in CO2 absorption and carbon storage amounts should be correctly understood through accumulating highly accurate and frequent field data from diverse ecosystems. In particular, tropical peatland that stores enormous amounts of carbon as soil organic matter is strongly affected by climate change (mainly El Niño events). The tropical peatland is also the area where large-scale disturbances (deforestation, drainage, fires, etc.) are happening. As carbon stored in peatland is vulnerable to climate change and environmental disturbances, there is the worry that the tropical peat will become a large CO2 emitting source (hot spot) in the near future. We have been monitoring net CO2 exchanges (the difference between CO2 absorption through photosynthesis and CO2 emission through respiration, referred to as CO2 flux) between the atmosphere and the ecosystem in selected disturbed terrestrial ecosystems for long time. We are hoping to clarify the response of terrestrial ecosystems to environmental disturbances and climate change, and accurately evaluate the variation of CO2 absorption through this sort of ecosystem monitoring.
Where and what are you studying?
Fig.1 50-m tall observation tower built in a tropical peat swamp forest
Right now we are conducting long-term continuous measurement (monitoring) of CO2 flux at tropical peat swamp forests in Indonesia and a former larch forest site in the city of Tomakomai, Hokkaido. We were also conducting similar monitoring at Sarobetsu Mire, Northern Hokkaido, until three years ago. We are mainly using the eddy covariance technique to measure CO2 flux. In this method, atmospheric CO2 concentration and wind speed are continuously measured at a high rate on a tower built in the target ecosystem (Fig.1), and the amount of vertical transfer of CO2 (flux) is calculated from the measurements. Currently, CO2 flux monitoring with the eddy covariance technique is conducted at more than 600 terrestrial ecosystem sites around the world.
Fig.2 Depression formed after the peat was burnt off by a fire in 2009 (1.5 m or more in depth)
In Southeast Asia, tropical peatland coexisting with swamp forests (tropical peat swamp forest) covers the lowland areas and has accumulated vast amounts of soil carbon as peat over several thousands of years. In recent years, however, developments involving deforestation and drainage expansion, groundwater level reduction and drought have been rapidly progressing and the risk of peat fires is increasing. We are monitoring of CO2 flux in three tropical peat swamp forests in Indonesia that each have different severity levels of peatland devastation. As a result, it was found that tropical peat swamp forests functioned as a CO2 source (CO2 absorption less than CO2 emission), and that CO2 emissions are increased in El Niño years. Fig.2 shows a depression formed by a peat fire in 2009. During the fire, peat was burnt off and the depression was formed, with a corresponding amount of CO2 being emitted. In Tomakomai, we are conducting ecosystem monitoring of a larch forest destroyed by strong wind of the typhoon in 2004 to evaluate the effect of large-scale natural disturbances on CO2 flux as well as the variation of CO2 flux with the change in vegetation properties after the destruction (Fig.3).
Fig.3 Forest in Tomakomai site (left: larch forest before destruction, middle: one year after destruction (2005), right: ten years after, deciduous
broad-leaved trees such as Japanese white birch (Betula platyphyl) become dominant (2014))
What is your next goal?
It's already been almost fifteen years since we began ecosystem monitoring in Indonesia and Tomakomai. This continuous long-term monitoring allows us to grasp the dynamic response of ecosystems to various environmental disturbances. Currently, our research is focusing on the analysis of data obtained by field observations. We are also involving with international monitoring networks and sharing monitoring data (as a database). In the future, we will further (try to) continue ecosystem monitoring, and proceed with a large-scale evaluation of variations in the terrestrial ecosystem carbon cycle with regard to environmental disturbances, in collaboration with other researchers in the areas of remote sensing and ecosystem modeling.
(1) Hirano T et al., Effects of disturbances on the carbon balance of tropical peat swamp forests. Global Change Biology, 18, 3410-3422 (2012)
(2) Hirano T et al., Carbon dioxide emissions through oxidative peat decomposition on a burnt tropical peatland. Global Change Biology, 20, 555-565 (2014)