Köhler, Michael

[["dc.bibliographiccitation.firstpage","63"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","Agroforestry Systems"],["dc.bibliographiccitation.lastpage","73"],["dc.bibliographiccitation.volume","88"],["dc.contributor.author","Köhler, Michael"],["dc.contributor.author","Hanf, Andrea"],["dc.contributor.author","Barus, Henry"],["dc.contributor.author","Hölscher, Dirk"],["dc.contributor.author","Hendrayanto, A."],["dc.date.accessioned","2017-09-07T11:45:43Z"],["dc.date.available","2017-09-07T11:45:43Z"],["dc.date.issued","2014"],["dc.description.abstract","We asked how shade tree admixture affects cacao water use in agroforests. In Central Sulawesi, Indonesia, cacao and shade tree sap flux was monitored in a monoculture, in a stand with admixed Gliricidia trees and in a mixture with a multi-species tree assemblage, with both mixtures having similar canopy openness. A Jarvis type sap flux model suggested a distinct difference in sap flux response to changes in vapor pressure deficit and radiation among cacao trees in the individual cultivation systems. We argue that differences originate from stomatal control of transpiration in the monoculture and altered radiation conditions and a different degree of uncoupling of the VPD from the bulk atmosphere inside shaded stands. Probably due to high sap flux variability among trees, these differences however did not result in significantly altered average daily cacao water use rates which were 16 L day−1 in the multi-species assemblage and 22 L day−1 in the other plots. In shaded stands, water use of single cacao trees increased with decreasing canopy gap fraction in the overstory since shading enhanced vegetative growth of cacao fostering transpiration per unit ground area. Estimated transpiration rates of the cacao tree layer were further controlled by stem density and amounted to 1.2 mm day−1 in the monoculture, 2.2 mm day−1 for cacao in the cacao/Gliricidia stand, and 1.1 mm day−1 in the cacao/multi-species stand. The additional transpiration by the shade trees is estimated at 0.5 mm day−1 for the Gliricidia and 1 mm day−1 for the mixed-species cultivation system."],["dc.identifier.doi","10.1007/s10457-013-9656-3"],["dc.identifier.gro","3149064"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/5708"],["dc.language.iso","en"],["dc.notes.intern","Hoelscher Crossref import"],["dc.notes.status","final"],["dc.notes.submitter","chake"],["dc.relation","SFB 990: Ökologische und sozioökonomische Funktionen tropischer Tieflandregenwald-Transformationssysteme (Sumatra, Indonesien)"],["dc.relation","SFB 990 | A | A02: Wassernutzungseigenschaften von Bäumen und Palmen in Regenwald-Transformationssystemen Zusammenfassung"],["dc.relation.issn","0167-4366"],["dc.subject.gro","sfb990_journalarticles"],["dc.title","Cacao trees under different shade tree shelter: effects on water use"],["dc.type","journal_article"],["dc.type.internalPublication","unknown"],["dc.type.peerReviewed","no"],["dc.type.subtype","original_ja"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","563"],["dc.bibliographiccitation.issue","5"],["dc.bibliographiccitation.journal","Tree Physiology"],["dc.bibliographiccitation.lastpage","573"],["dc.bibliographiccitation.volume","35"],["dc.contributor.author","Niu, Furong"],["dc.contributor.author","Röll, Alexander"],["dc.contributor.author","Hardanto, Afik"],["dc.contributor.author","Meijide, Ana"],["dc.contributor.author","Köhler, M."],["dc.contributor.author","Hölscher, Dirk"],["dc.contributor.author","Hendrayanto, A"],["dc.date.accessioned","2017-09-07T11:45:45Z"],["dc.date.available","2017-09-07T11:45:45Z"],["dc.date.issued","2015"],["dc.description.abstract","Oil palm (Elaeis guineensis Jacq.) water use was assessed by sap flux density measurements with the aim to establish the method and derive water-use characteristics. Thermal dissipation probes were inserted into leaf petioles of mature oil palms. In the laboratory, we tested our set-up against gravimetric measurements and derived new parameters for the original calibration equation that are specific to oil palm petioles. In the lowlands of Jambi, Indonesia, in a 12-year-old monoculture plantation, 56 leaves on 10 palms were equipped with one sensor per leaf. A 10-fold variation in individual leaf water use among leaves was observed, but we did not find significant correlations to the variables trunk height and diameter, leaf azimuthal orientation, leaf inclination or estimated horizontal leaf shading. We thus took an un-stratified approach to determine an appropriate sampling design to estimate stand transpiration (Es, mm day(-1)) rates of oil palm. We used the relative standard error of the mean (SEn, %) as a measure for the potential estimation error of Es associated with sample size. It was 14% for a sample size of 13 leaves to determine the average leaf water use and four palms to determine the average number of leaves per palm. Increasing these sample sizes only led to minor further decreases of the SEn of Es. The observed 90-day average of Es was 1.1 mm day(-1) (error margin ± 0.2 mm day(-1)), which seems relatively low, but does not contradict Penman-Monteith-derived estimates of evapotranspiration. Examining the environmental drivers of Es on an intra-daily scale indicates an early, pre-noon maximum of Es rates (11 am) due to a very sensitive reaction of Es to increasing vapor pressure deficit in the morning. This early peak is followed by a steady decline of Es rates for the rest of the day, despite further rising levels of vapor pressure deficit and radiation; this results in pronounced hysteresis, particularly between Es and vapor pressure deficit."],["dc.identifier.doi","10.1093/treephys/tpv013"],["dc.identifier.gro","3149074"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/5719"],["dc.language.iso","en"],["dc.notes.intern","Hoelscher Crossref import"],["dc.notes.status","final"],["dc.notes.submitter","chake"],["dc.relation","SFB 990: Ökologische und sozioökonomische Funktionen tropischer Tieflandregenwald-Transformationssysteme (Sumatra, Indonesien)"],["dc.relation","SFB 990 | A | A02: Wassernutzungseigenschaften von Bäumen und Palmen in Regenwald-Transformationssystemen Zusammenfassung"],["dc.relation","SFB 990 | A | A03: Untersuchung von Land-Atmosphäre Austauschprozesse in Landnutzungsänderungs-Systemen"],["dc.relation.issn","0829-318X"],["dc.subject.gro","sfb990_journalarticles"],["dc.title","Oil palm water use: calibration of a sap flux method and a field measurement scheme"],["dc.type","journal_article"],["dc.type.internalPublication","unknown"],["dc.type.peerReviewed","no"],["dc.type.subtype","original_ja"],["dspace.entity.type","Publication"]]