Tree Rings And Climate

Flax and hemp fibres have been increasingly used as reinforcement in polymer composites. First, an overview is given of the technical arguments which convinced designers of consumer goods to use these fibres. In particular, their composites show higher specific stiffness than glass fibre composites in both tension and plate bending and only slightly lower values than carbon fibre composites in plate bending. Moreover, flax and hemp fibres possess a much higher vibration damping capacity, making them excellent candidates for applications in sporting goods or musical instruments. Secondly, the paper describes how designers relate to the non-technical characteristics of these natural fibres. Many concrete examples are given from different application domains in consumer goods: sports, mobility, music and sound, furniture and interior design. The fascination of designers for these bio-based materials combined with the recent introduction in the market of new, composites-oriented preforms of flax and hemp fibres, is rapidly increasing the number and variety of composite products using flax and hemp fibres as reinforcement.

Why are designers fascinated by flax and hemp fibre composites

Tree-ring records can provide valuable information to advance our understanding of contemporary terrestrial carbon cycling and to reconstruct key metrics in the decades preceding monitoring data. The growing use of tree rings in carbon-cycle research is being facilitated by increasing recognition of reciprocal benefits among research communities. Yet, basic questions persist regarding what tree rings represent at the ecosystem level, how to optimally integrate them with other data streams, and what related challenges need to be overcome. It is also apparent that considerable unexplored potential exists for tree rings to refine assessments of terrestrial carbon cycling across a range of temporal and spatial domains. Here, we summarize recent advances and highlight promising paths of investigation with respect to (1) growth phenology, (2) forest productivity trends and variability, (3) CO2 fertilization and water-use efficiency, (4) forest disturbances, and (5) comparisons between observational and computational forest productivity estimates. We encourage the integration of tree-ring data: with eddy-covariance measurements to investigate carbon allocation patterns and water-use efficiency; with remotely sensed observations to distinguish the timing of cambial growth and leaf phenology; and with forest inventories to develop continuous, annually-resolved and long-term carbon budgets. In addition, we note the potential of tree-ring records and derivatives thereof to help evaluate the performance of earth system models regarding the simulated magnitude and dynamics of forest carbon uptake, and inform these models about growth responses to (non-)climatic drivers. Such efforts are expected to improve our understanding of forest carbon cycling and place current developments into a long-term perspective.

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A tree-ring perspective on the terrestrial carbon cycle

The largest part of forest biomass consists of wood. A global estimate of carbon stored in lignified tissues rises up to 400 Pg. Given these quantities, there is a growing interest of implementing wood research in diagnoses and evaluations of the carrying capacity of the global ecosystem and its forests. The question arises how disciplines like wood anatomy could respond to the increasing demands of a trait-based ecology, understood as a paradigmatic shift in addressing global changes. Dendrochronology and ecological wood anatomy, traditionally operating within the paradigm of species-based ecology, developed robust methods to address ecological questions. However, sampling strategies and database design will likely be different when wood traits are to be used to study individual tree performance, including responses to stress.Aiming at optimally involving wood research in trait-based ecology, some trait concepts are analysed. The value of the IAWA standard lists of wood anatomical features as starting points for trait databases is recognized. A summary of the functionality of wood is given to inform the trait-research community of basic aspects of tree performance. The time dimension is highlighted, as well as the foundations for understanding bio-hydraulics, bio-mechanics and metabolism of wood and relevant traits.Guidelines are given for sampling strategies and database concepts. Prospects of time axis construction and system integration are discussed, as well as the importance of standardizing for size.

Wood anatomy and trait-based ecology

Developmental initiation of plant vascular tissue, including xylem and phloem, from the vascular cambium depends on environmental factors, such as temperature and precipitation. Proper formation of vascular tissue is critical for the transpiration stream, along with photosynthesis as a whole. While effects of individual environmental factors on the transpiration stream are well studied, interactive effects of multiple stress factors are underrepresented. As expected, climate change will result in plants experiencing multiple co-occurring environmental stress factors, which require further studies. Also, the effects of the main climate change components (carbon dioxide, temperature, and drought) on vascular cambium are not well understood. This review aims at synthesizing current knowledge regarding the effects of the main climate change components on the initiation and differentiation of vascular cambium, the transpiration stream, and photosynthesis. We predict that combined environmental factors will result in increased diameter and density of xylem vessels or tracheids in the absence of water stress. However, drought may decrease the density of xylem vessels or tracheids. All interactive combinations are expected to increase vascular cell wall thickness, and therefore increase carbon allocation to these tissues. A comprehensive study of the effects of multiple environmental factors on plant vascular tissue and water regulation should help us understand plant responses to climate change.

https://www.mdpi.com/2223-7747/8/3/65/pdf

Environmental Factors Influence Plant Vascular System and Water Regulation

s. Birmensdorf: Swiss Federal Research Institute WSL. Hacke UG, Sperry JS, Pockman WT, Davis SD, MFCulloh KA. 2001. Trends in wood density and structure are linked to prevention of xylem implosion by negative pressure. Oecologia 126: 457–461. IAWA (International Association of Wood Anatomists) Committee. 1989. IAWA list of microscopic features for hardwood identification. IAWA Bulletin, New Series 10: 219 – 329. Jacoby GC, D’Arrigo RD. 1990. Teak (Tectona grandis L.f.), a tropical species of large-scale dendroclimatic potential. Dendrochronologia 8:

PART OF A HIGHLIGHT ON TREE BIOLOGY Fluctuations of cambial activity in relation to precipitation result in annual rings and intra-annual growth zones of xylem and phloem in teak (Tectona grandis) in Ivory Coast

The long-lived pioneer species Pericopsis elata is one of the rare tropical timbers on the list of the Convention on International Trade of Endangered Species, supporting the need for accurate and reliable growth data. In one planted and one natural forest in the Democratic Republic of Congo, respectively four and 37 Pericopsis stem disks were collected. The tree-ring series of planted trees were used to confirm annual tree-ring formation. For the natural forest, a tree-ring chronology with 24 stem disks ranged from 1852 up to 2008. This chronology was compared with time-series of local precipitation, resulting in a significant correlation with the second half of the rainy season (September-November). This seasonal precipitation was related with sea surface temperatures of the West Indian Ocean. Higher precipitation during El Nino years corresponded with higher tree-ring indices but differences were not significant. In addition, pointer years were rare and did not have a consistent link with extreme climatic conditions. The existence of annual tree rings encourages further tree-ring analyses of P. elata and other flagship timber species in order to further document climate-growth responses and to provide the long-term framework that is needed for sustainable management planning.

https://www.mdpi.com/1999-4907/5/12/3087/pdf

Dendrochronological Potential in a Semi-Deciduous Rainforest: The Case of Pericopsis elata in Central Africa

Wood is a renewable material that has been recognized for a long time as a valuable material for construction and engineering. Sound, solid wood can last for centuries. Nevertheless, wood is susceptible to biological and physical degradation. Therefore it needs to be protected properly, all the more when using less durable species. A variety of finishes can be applied. These coatings must meet certain minimum requirements, among which are sufficient penetration, resistance to physical and biological discoloration, and good adhesion. The last is considered the utmost important factor for the overall performance of a coating. Without an adequate anchoring to the wood, the coating will peel off prematurely and, thus, affect the lifetime of the substrate. In this article, the impact of the type of coating used, the wood species, and preweathering of the wood on adhesion are disclosed. In addition, the effect of weathering on the wood-coating system as a whole is looked at as well. The adhesion measurements were obtained with a mechanical torque device developed at VTT in Finland.

Adhesion and weathering performance of waterborne coatings applied to different temperate and tropical wood species

Wood modification aims at the improvement of properties of wood or wood-based materials, mostly to prolong the service life of the product. More specifically, resistance against physical and biological attack needs to be boosted. Given the hygroscopic nature of wood, impacting its moisture dynamical behaviour is an important target to aim at. In this paper several treatments of radiata pine (thermally modified, acetylated and furfurylated) are compared with untreated Scots pine heartwood using a straightforward absorption-desorption laboratory test combined with FDA-PCA analysis. Seemingly acetylated and furfurylated radiate pine behave similarly as pine heartwood, whereas thermally modified material does not. A similar procedure was followed for oak, beech and Scots pine sapwood treated with 3 different siloxane products. The siloxane treaments seem to have some effect, but do not result in sufficient hydrophobation of the solid wood. Based on a detailed study using the results of neutron radiography experiments performed at the NEUtron Transmission RAdiography (NEUTRA) beamline of the Paul Scherrer Institute (PSI) in Villigen, Switzerland on untreated and treated oak, similar results were found.

Moisture dynamics of modified wood

Composite materials reinforced with wood or non-wood natural fibres have the potential to be a lighter and lower-cost alternative construction material. Until better availability and properties and a lower cost price of degradable polymers makes their use more prevalent, the application of natural fibre reinforcements in synthetic polymers is an intermediate step towards products that are completely degradable or compostable after their service life. The inherent degradability of natural fibres makes the circumstances of their composite applications, more specifically the moisture conditions, very important regarding potential development of fungal communities and the related damage. 
For wood and wood-based panels different Use Classes (UC) are defined and for every UC laboratory and field test methods were developed that each determine the (maximum) potential damage caused by the fungi that act in that specific UC. These tests can be used for natural fibre reinforced composites (NFCs) if the specific slower moisture ab- and desorption are taken into account. However the question arises whether the most appropriate way to assess the material resistance is yet developed.
Surface stain or mould fungi develop on NFCs when used in high relative humidity conditions (e.g. UC 2). In UC 3 Basidiomycetes can degrade natural fibres as well as derived composites if the natural fibres reach the critical moisture content. In addition to laboratory tests, a 5 year field test showed that fungal growth is not problematic when moisture traps are not present. Finally a graveyard test (UC 4) only revealed superficial softening after 5 years exposure, confirming the good durability of NFCs. Fungal growth thus seems to be mainly an aesthetical problem. 
Moisture uptake, more than fungal decay, also results in a decrease in mechanical properties, which seems, up to now, relatively unimportant regarding the actual use of such composites. However, if used in structural applications once a better fibre/matrix adhesion leads to enhanced mechanical properties, the damage by moisture and fungi could become critical.

Jan Van den Bulcke

Papers

PART OF A HIGHLIGHT ON TREE BIOLOGY Fluctuations of cambial activity in relation to precipitation result in annual rings and intra-annual growth zones of xylem and phloem in teak (Tectona grandis) in Ivory Coast

Dendrochronological Potential in a Semi-Deciduous Rainforest: The Case of Pericopsis elata in Central Africa

Adhesion and weathering performance of waterborne coatings applied to different temperate and tropical wood species

Moisture dynamics of modified wood

Biological durability of natural fibre reinforced composites