Thermal imaging of increment cores: a new method to estimate sapwood depth in trees

The cells in tree sapwood form a network of interconnected conduits which enables the transport of water and nutrients from the tree roots to the canopy. Sapwood depth must be assessed when tree water use is estimated from sap flow velocities. However, current approaches to assess sapwood depth are either not applicable universally, or require expensive instruments, the application of chemicals or laborious field efforts. Here, we present a new method, which estimates sapwood depth by thermal imaging of increment cores. Using a low-cost thermal camera for mobile devices, we show that the sapwood-heartwood boundary is detectable by a sharp increase in temperature. Estimated sapwood depths agree with dye estimates (R-2 = 0.84). We tested our approach on a broad range of temperate and tropical tree species: Quercus robur, Pinus sylvestris, Swietenia macrophylla, Guazuma ulmifolia, Hymenaea courbaril, Sideroxylon capiri and Astronium graveolens. In nearly all species, the methods agreed within 0.6 cm. Thermal imaging of increment cores provides a straightforward, low-cost, easy-to-use, and species-independent tool to identify sapwood depth. It has further potential to reveal radial differences in sapwood conductivity, to improve water balance estimations on larger scales and to quickly develop allometric relationships

Continuous in situ measurements of water stable isotopes in soils, tree trunk and root xylem: Field approval

Rationale New methods to measure stable isotopes of soil and tree water directly in the field enable us to increase the temporal resolution of obtained data and advance our knowledge on the dynamics of soil and plant water fluxes. Only few field applications exist. However, these are needed to further improve novel methods and hence exploit their full potential. Methods We tested the borehole equilibration method in the field and collected in situ and destructive samples of stable isotopes of soil, trunk and root xylem water over a 2.5-month experiment in a tropical dry forest under natural abundance conditions and following labelled irrigation. Water from destructive samples was extracted using cryogenic vacuum extraction. Isotope ratios were determined with IRIS instruments using cavity ring-down spectroscopy both in the field and in the laboratory. Results In general, timelines of both methods agreed well for both soil and xylem samples. Irrigation labelled with heavy hydrogen isotopes clearly impacted the isotope composition of soil water and one of the two studied tree species. Inter-method deviations increased in consequence of labelling, which revealed their different capabilities to cover spatial and temporal heterogeneities. Conclusions We applied the novel borehole equilibration method in a remote field location. Our experiment reinforced the potential of this in situ method for measuring xylem water isotopes in both tree trunks and roots and confirmed the reliability of gas permeable soil probes. However, in situ xylem measurements should be further developed to reduce the uncertainty within the range of natural abundance and hence enable their full potential

Developing knowledge and tools for climate change mitigation and adaptation with multi­functional urban green infrastructure – kick-off symposium of the multidisciplinary project “Maximizing the carbon sequestration in urban trees (CliMax)”

Das interdisziplinäre Forschungsprojekt CliMax ist eine Kooperation des Julius Kühn-Instituts und der Technischen Universität Braunschweig. Das Projekt erforscht die Grundlagen für effizientere Entscheidungshilfen für Städte und Kommunen, mit deren Hilfe nicht nur der Status Quo des Beitrages des Stadtgrüns zur Kohlenstoffsequestrierung geschätzt, sondern auch die Klimawirksamkeit des Stadtgrüns maximiert werden kann. Die Berücksichtigung der Multifunktionalität des Stadtgrüns bezieht dessen positive Effekte in eine Entscheidungsmatrix mit ein und unterstützt dadurch die Integration des Klimaschutzaspektes bei Pflanz- oder Pflegeentscheidungen. Zum Anlass des Auftaktsymposiums berichten wir hier von den Projektvorhaben.The interdisciplinary research project CliMax is a cooperation between the Julius Kühn-Institute and the Technische Universität Braunschweig. It provides information on the status quo of the contribution of urban green spaces to carbon sequestration and aims for the development of decision-support tools for maximizing the climate effectiveness of urban green. Considering the multifunctionality of urban green spaces, such tools must incorporate many effects of urban green space into a decision matrix and thereby support the integration of the climate mitigation aspects in planting or maintenance decisions. On the occasion of the kick-off meeting, we report here on our plans for the project