Abstract booklet - gtö – Society for Tropical Ecology

68 PARALLEL SESSION HALL III | EAST AFRICAN MOUNTAINPARALLEL SESSION HALL III | EAST AFRICAN MOUNTAIN 69GROWTH STRATEGIES OF EVERGREEN AND DECIDUOUS SPECIES INA TROPICAL MONTANE FOREST IN ETHIOPIAAchim Bräuning 11 University of Erlangen, Erlangen, DE, abraeuning@geographie.uni-erlangen.deTEMPORAL RESOLUTION OF RECENTLY ASSIMILATED CARBONALLOCATION FROM TREE CANOPY TO SOIL CO2 EFFLUX IN TWOCONTRASTING TREE SPECIES OF AN AFROMONTANE FORESTOlga Shibistova 1 , Yonas Yohannes 1 , Masresha Fetene 2 , Birgit Wild 3 ,Margarethe Watzka 3 , Andreas Richter 3 , Georg Guggenberger 1TUESDAY 15:30 Hall H IIISpeaker: Julia KrepkowskiThe growth dynamics of seven tree species belonging to different life forms(evergreen conifer, evergreen broadleaved, deciduous broadleaved) wasstudied in the montane forest of Munessa (2.300 m a.s.l.; Ethiopia) using highresolutiondendrometers. Measurements of stem diameter variations werecollected in 30 minute intervals over two calendar years. In addition, woodanatomical samples were collected in monthly intervals to study cambial activitywith the help of wood anatomical micro-sections. Cambial phenology andlength of the growing season varied considerably between years and life forms.Precipitation and the length of the dry period are the most important climatefactors determining growth activity and the amplitudes of daily stem swellingand shrinkage resulting from transpiration. Wood anatomical micro-sectionsrevealed the formation of growth boundaries. By the help of dendrometerdata, the amount of annually formed wood and of the time of formation ofgrowth boundaries could be determined for each species. The different tree lifeforms show different growth strategies of cambial phenology during the year:evergreen species are able to initiate cambial activity earlier and to interruptgrowth during the short dry season (April-May), if conditions get too dry. Incontrast, deciduous species showed a delayed start of cambial activity whichwas compensated by higher growth rates during the rainy season.1Universität Hannover, Hannover, DE, olgas@ksc.krasn.ru, 2 Addis Ababa University,Addis Ababa, ET, 3 University of Vienna, Vienna, ATUsing a canopy 13C pulse-labeling approach, we studied the temporalresolution of recently assimilated carbon allocation from tree canopy to soil CO 2efflux for the gymnosperm coniferous Podocarpus falcatus and the angiospermdeciduous Croton macrostachyus (a climax and pioneer tree species, respectively)in an Ethiopian Afromontane forest. The current anthropogenic disturbancesof the forest lead to shift in trees abundance to the favor of the pioneer. Wehypothesized that the allocation of recently assimilated carbon is faster and thecontribution of that to soil CO 2 efflux is greater for C. macrostachyus than forP. falcatus. During the labeling, C. macrostachyus assimilated 5.9 g 13C and P.falcatus 6.9 g 13C, corresponding to a tracer uptake efficiency of 61% and 59%.13C excess in leaves declined rapidly following a double exponential functionwith a larger size of the fast pool (64% vs. 50% of the assimilated carbon) havinga shorter MRT (14h vs. 55h) for C. macrostachyus than for P. falcatus. Phloemsap velocity was about 4 times larger for the former. Consequently, in the soilCO 2 efflux the label was recorded earlier under C. macrostachyus (after 24h)then under P. falcatus (after 72h). Within a one year chasing period, 32% of theassimilated 13C appeared in soil CO2 efflux under the pioneer angiosperm,whereas it was only 15% in case of the late-successional gymnosperm.TUESDAY 15:45 Hall H IIIThat different behavior may be related to larger proportion of recentlyassimilated carbon being allocated belowground to enable the water andnutrient uptake by roots mycorrhiza in case of C. macrostachyus. P. falcatus seemsto store more of this carbon in structural components. Continuing degradationof Afromontane forests will probably accelerate the temporal resolution ofcarbon cycling due to an increasing abundance of pioneers.gtöSociety for Tropical Ecology | Gesellschaft für Tropenökologie e.V. Status and future of tropical biodiversity | Frankfurt, 21 - 24 February 2011gtö