Response of CO₂ and H₂O fluxes in a mountainous tropical rainforest in equatorial Indonesia to El Niño events

The possible impact of El Niño–Southern Oscillation (ENSO) events on the main components of CO₂ and H₂O fluxes between the tropical rainforest and the atmosphere is investigated. The fluxes were continuously measured in an old-growth mountainous tropical rainforest in Central Sulawesi in Indonesia using the eddy covariance method for the period from January 2004 to June 2008. During this period, two episodes of El Niño and one episode of La Niña were observed. All these ENSO episodes had moderate intensity and were of the central Pacific type. The temporal variability analysis of the main meteorological parameters and components of CO₂ and H₂O exchange showed a high sensitivity of evapotranspiration (ET) and gross primary production (GPP) of the tropical rainforest to meteorological variations caused by both El Niño and La Niña episodes. Incoming solar radiation is the main governing factor that is responsible for ET and GPP variability. Ecosystem respiration (RE) dynamics depend mainly on the air temperature changes and are almost insensitive to ENSO. Changes in precipitation due to moderate ENSO events did not have any notable effect on ET and GPP, mainly because of sufficient soil moisture conditions even in periods of an anomalous reduction in precipitation in the region

Variation in photosynthetic light-use efficiency in a mountainous tropical rain forest in Indonesia

Photosynthetically active radiation (Q)-use efficiency (F) is an important parameter for deriving carbon fluxes between forest canopies and the atmosphere from meteorological ground and remote sensing data. A common approach is to assume gross primary production (P,) and net primary production (P-n) are proportional to Q absorbed by vegetation (Q(abs)) by defining the proportionality constants epsilon(Pg) and epsilon(Pn) (for P-g and P-n respectively). Although remote sensing and climate monitoring provide Q(abs) and other meteorological data at the global scale, information on c is particularly scarce in remote tropical areas. We used a 16-month continuous CO2 flux and meteorological dataset from a mountainous tropical rain forest in central Sulawesi, Indonesia to derive values of epsilon(Pg). and to investigate the relationship between P-g and Q(abs). Absorption was estimated with a 1D SVAT model from measured canopy structure and short wave radiation. The half-hourly P, data showed a saturation response to Q(abs). The amount Of Q(abs) required to saturate P-g was reduced when water vapor saturation deficit (D) was high. Light saturation of P-g was still evident when shifting from half-hourly to daily and monthly time scales. Thus, for a majority of observations, P-g was insensitive to changes in Q(abs). A large proportion of the observed seasonal variability in P-g could not be attributed to changes in Q(abs) or D. Values of epsilon(Pg) varied little around the long-term mean of 0.0179 mol CO2 (mol photon)(-1) or 0.99 g C MJ(-1) (the standard deviations were +/- 0.006 and +/- 0.0018 mol CO2 (mol photon)(-1) for daily and monthly means, respectively). In both cases, c p. values were more sensitive to Q(abs) than to daytime D. These findings show that the current epsilon-approaches fail to predict P-g at our tropical rain forest site for two reasons: (1) they neglect saturation of P-g when Q(abs), is high; and (2) they do not include factors, other than Q(abs) and D, that determine seasonality and annual sums of P-g

Eintrag von atmosphaerischen Spurenstoffen in einen Fichtenbestand im Solling Endbericht

Many forests in Germany suffer from nutrient shortage and toxic compounds as a result of deposition of atmospheric trace substances. It was therefore the aim of our study to quantity deposition rates of atmospheric substances into a spruce forest. The deposition flux of compounds incorporated in rain and fog droplets and the dry deposition of particles and gases was determined by different methods (electronmicroscopy, gradient-flux relation, throughfall analysis canopy rain interaction, cuvette measurements). The results show good internal consistancy so that a rather confident input rate for this forest could be derived for several atmospheric components. (orig.)In Deutschland leiden zahlreiche Waelder an Naehrstoffmangel und toxischen Belastungen als Ergebnis einer Deposition atmosphaerischer Komponenten. Es war daher Ziel dieser Untersuchung, Depositionsraten atmosphaerischer Spurenstoffe in einen Fichtenbestand zu quantifizieren. Die Depositionsraten von Nebel- und Regeninhaltstoffen und die Trockene Deposition von Partikeln und Gasen wurden auf verschiedene Arten bestimmt (Elektronenmikroskopie, Fluss-Gradient-Beziehung, Kronentrauenanalyse, Kronenraufm-Regen-Wechselwirkung, Kuevetten-Messungen). Die Ergebnisse zeigen gute interne Konsistenz, so dass eine ziemlich verlaessliche Eintragsrate fuer mehrere atmosphaerisch Spurenstoffe fuer diesen Wald ermittelt werden konnte. (orig.)Available from TIB Hannover: FR 6979+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman

Effects Of The 2015–2016 El Niño Event On Energy And CO2 Fluxes Of A Tropical Rainforest In Central Sulawesi, Indonesia

The influence  of the very strong 2015–16 El Niño event on local and regional meteorological   conditions,  as  well as  on  energy and CO2   fluxes in  a  mountainous primary  tropical  rainforest  was investigated  using ERA-Interim  reanalysis  data as well as meteorological  and eddy covariance  flux measurements   from  Central Sulawesi  in Indonesia. The El Niño event led to a strong increase of incoming monthly solar radiation and air temperature, simultaneously with the increasing Niño4 index. Monthly precipitation first strongly decreased  and then increased  reaching  a maximum  in 3–4 months after El  Niño culmination.  Ecosystem  respiration  increased  while gross  primary  production showed only a weak response  to the El  Niño event resulting  in a positive  anomaly  of net ecosystem CO2 exchange (reduced CO2 uptake). The changes of key meteorological parameters and fluxes caused  by the strong  El Niño event of 2015–16  differed from the effects  of moderate  El Niño events  observed  during  the period  2003-2008,  where net ecosystem CO2 exchange  remained largely unaffected. In contrast to earlier moderate  El Niño events, the strong El Niño 2015–16 affected mostly the air temperature  resulting  in a weakening of the net carbon  sink at the rainforest site in Central Sulawesi, Indonesia

Quantification Of Leaf Emissivities Of Forest Species: Effects On Modelled Energy And Matter Fluxes In Forest Ecosystems

Climate  change  has distinct regional and local differences in its impacts on the land sur face. One of the important parameters determining the climate change signal is the emissivity (ε) of the sur face. In forest-climate interactions, the leaf sur face emissivity plays a decisive   role.  The accurate  determination  of leaf emissivities  is crucial for  the appropriate  interpretation  of measured  energy and matter fluxes between the forest and the atmosphere. In this study, we quantified the emissivity of the five broadleaf tree species Acer pseudoplatanus, Fagus sylvatica, Fraxinus excelsior, Populus simonii and Populus candicans. Measurements of leaf sur face temperatures were conducted under laboratory conditions in a controlled-climate chamber within the temperature range of +8 °C and +32°C. Based on these measurements, broadband  leaf emissivities ε (ε for the spectral range of 8-14 µm) were calculated. Average ε8-14 µm was 0.958±0.002 for all species with very little variation among species. In a second step, the soil-vegetation-atmosphere  transfer model ‘MixFor-SVAT ’ was applied to examine the effects of ε changes on radiative, sensible and latent energy  fluxes of the Hainich  forest in Central Germany.  Model experiments  were driven by meteorological data measured at the Hainich  site. The simulations  were  forced with the calculated ε value as well as with minimum and maximum values obtained from the literature.  Significant  effects  of ε changes were detected.  The strongest  effect was identified for the sensible heat flux with a sensitivity of 20.7 % per 1 % ε change. Thus, the variability of ε should be considered in climate change studies

A modelling approach for simulation of water and carbon dioxide exchange between multi-species tropical rain forest and the atmosphere

An one-dimensional process-based SVAT model (Mixfor-SVAT) was developed to describe energy, water and carbon dioxide exchanges between vegetation canopy and the atmosphere at a local scale. Simulation of the energy, water and CO(2) fluxes in Mixfor-SVAT is based on aggregated description of the physical and biological processes on the leaf, tree (plant) and stand levels that allows to apply this model for prediction of atmospheric fluxes for the different vegetation types from grasslands and agricultural crops to vertically structured mono-specific and mixed forest stands represented by one or by many different tree species, as well as for description of the flux partitioning among different canopy sub-layers and different tree species. Upper boundary conditions of the model are measured or predicted meteorological parameters (air temperature and humidity, wind speed, CO(2) concentration, precipitation rate and global radiation) at some height above a plant canopy within the atmospheric surface layer. For simulation of exchange processes within a multi-specific forest stand Mixfor-SVAT uses both averaged and species specific biophysical parameters of the trees describing their structure (e.g. height, crown shape, stem diameter, root depth) and biological properties (e.g. leaf stomatal conductance, photosynthesis and respiration rates, etc.). Mixfor-SVAT assumes that trees of the different species are evenly distributed over some homogeneous ground surface area and that there are no differences in biophysical properties between the same tree species. Mixfor-SVAT was applied to a natural tropical rainforest in Central Sulawesi, Indonesia. The modelled H(2)O and CO(2) fluxes were compared with results of eddy covariance flux measurements above the forest canopy for the period from October 2003 to February 2005. All necessary biophysical parameters of vegetation and soil were obtained during several intensive field campaigns in 2004-2006. Comparisons showed a good agreement between modelled and measured H(2)O and CO(2) fluxes especially for smoothed daily flux trends. However, a large number of spikes in measured data series caused by some instrumental errors, sensor wetting, changes in the footprint or fast changes in turbulence conditions resulted in some reduction of correlation between modeled and measured fluxes (e.g. r(2) = 0.62 for CO(2) and r(2) = 0.64 for H(2)O fluxes under friction velocity u > 0.3 ms(-1)). The developed Mixfor-SVAT model could be applied for solutions of the different theoretical and applied tasks, e.g. to describe the response of H(2)O and CO(2) budgets of the different forest ecosystems to environmental and land use changes in different time scales, or to recover the long-term records of H(2)O and CO(2) fluxes in the cases of data loss or not reliable measured fluxes. (c) 2007 Elsevier B.V. All rights reserved