Growth and Wood Trait Relationships of Alnus glutinosa in Peatland Forest Stands With Contrasting Water Regimes

Human-driven peatland drainage has occurred in Europe for centuries, causing habitat degradation and leading to the emission of greenhouse gases. As such, in the last decades, there has been an increase in policies aiming at restoring these habitats through rewetting. Alder (Alnus glutinosa L.) is a widespread species in temperate forest peatlands with a seemingly high waterlogging tolerance. Yet, little is known about its specific response in growth and wood traits relevant for tree functioning when dealing with changing water table levels. In this study, we investigated the effects of rewetting and extreme flooding on alder growth and wood traits in a peatland forest in northern Germany. We took increment cores from several trees at a drained and a rewetted stand and analyzed changes in ring width, wood density, and xylem anatomical traits related to the hydraulic functioning, growth, and mechanical support for the period 1994–2018. This period included both the rewetting action and an extreme flooding event. We additionally used climate-growth and climate-density correlations to identify the stand-specific responses to climatic conditions. Our results showed that alder growth declined after an extreme flooding in the rewetted stand, whereas the opposite occurred in the drained stand. These changes were accompanied by changes in wood traits related to growth (i.e., number of vessels), but not in wood density and hydraulic-related traits. We found poor climate-growth and climate-density correlations, indicating that water table fluctuations have a stronger effect than climate on alder growth. Our results show detrimental effects on the growth of sudden water table changes leading to permanent waterlogging, but little implications for its wood density and hydraulic architecture. Rewetting actions should thus account for the loss of carbon allocation into wood and ensure suitable conditions for alder growth in temperate peatland forests.

Spectral Pre-Processing and Multivariate Calibration Methods for the Prediction of Wood Density in Chinese White Poplar by Visible and Near Infrared Spectroscopy

Wood density is a key indicator for tree functionality and end utilization. Appropriate chemometric methods play an important role in the successful prediction of wood density by visible and near infrared (Vis-NIR) spectroscopy. The objective of this study was to select appropriate pre-processing, variable selection and multivariate calibration techniques to improve the prediction accuracy of density in Chinese white poplar (Populus tomentosa carriere) wood. The Vis-NIR spectra were de-noised using four methods (lifting wavelet transform, LWT; wavelet transform, WT; multiplicative scatter correction, MSC; and standard normal variate, SNV), and four variable selection techniques, including successive projections algorithm (SPA), uninformative variables elimination (UVE), competitive adaptive reweighted sampling (CARS) and iteratively retains informative variables (IRIV), were compared to simplify the dimension of the high-dimensional spectral matrix. The non-linear models of generalized regression neural network (GRNN) and support vector machine (SVM) were performed using these selected variables. The results showed that the best prediction was obtained by GRNN models combined with the LWT and CARS method for Chinese white poplar wood density (Rp2 = 0.870; RMSEP = 13 Kg/m3; RPDp = 2.774).

Megaherbivores modify forest structure and increase carbon stocks through multiple pathways

Megaherbivores have pervasive ecological effects. In African rainforests, elephants can increase aboveground carbon, though the mechanisms are unclear. Here we combine a large unpublished dataset of forest elephant feeding with published browsing preferences totaling > 120,000 records covering 700 plant species, including nutritional data for 102 species. Elephants increase carbon stocks by: 1) promoting high wood density tree species via preferential browsing on leaves from low wood density species, which are more digestible; 2) dispersing seeds of trees that are relatively large and have the highest average wood density among tree guilds based on dispersal mode. Loss of forest elephants could cause a 5-12% decline in carbon stocks due to regeneration failure of elephant-dispersed trees and an increase in abundance of low wood density trees. These results show the major importance of megaherbivores in maintaining diverse, high-carbon tropical forests. Successful elephant conservation will contribute to climate mitigation at a scale of global relevance.

Factors That Affect the Mechanical Strength of Archaeological Wood—A Case Study of 18th-Century Wooden Water Pipes from Bóżnicza Street in Poznań, Poland

Large amounts of archaeological wood are often excavated during groundworks in cities and towns. Part of the unearthed artefacts is usually saved, conserved and then presented in museums. However, if the finding contains several similar objects, some of them could potentially be further employed for some other practical purposes. The research aimed to determine the mechanical performance of the remains of wooden water mains excavated at Bóżnicza street in Poznań, Poland and evaluate its potential usefulness for any practical purposes. First, wood density was determined along with its mechanical strength in compression. The density of archaeological wood identified as Scots pine was lower than contemporary pinewood (383 kg × m−3 vs. 572 kg × m−3); therefore, its mechanical properties in compression tests were also lower, as expected, making the wood unsuitable for any practical applications. However, the differences in modulus of elasticity and compressive strength were not justified by the differences in wood density. Further infrared spectroscopy and X-ray diffraction analyses revealed additional differences in chemical composition and cellulose crystallinity between archaeological and contemporary wood. The results indicated the decrease in carbohydrate content and cellulose crystallinity in degraded wood, which, in addition to wood density, apparently contribute to the deterioration in mechanical strength of archaeological wood. The case study of the excavated archaeological wooden pipes shows that they have historical value but are not useful for practical purposes. It also revealed that not only wood density but also its chemical composition and cellulose crystallinity level has a substantial impact on the wood mechanical properties, particularly in compression.

Wood and bark water content and monthly stem growth in Amazonian tree species

ABSTRACT The knowledge of how trees respond to microclimate variability is important in the face of climate changes. The objectives of this study were to examine the variation in wood water content (WWC) and bark water content (BWC) in Amazonian trees, as well as to assess the effect of microclimatic variability on monthly diameter growth rates (DGR). We extracted a core sample from each of 120 trees (28 species) and determined WWC and BWC on a fresh matter basis. DGR was measured monthly during the 12 months of 2007. The effect of microclimatic variability on DGR was analyzed by redundancy analysis. Average BWC and WWC were 53.4% and 34.7%, respectively, with a large variation in stem water content among species (BWC = 36.2−67.1%; WWC = 26.4−50.8%). There was no significant relationship between stem diameter and WWC or BWC, nor between DGR and wood density (p > 0.05). However, wood density was negatively correlated with WWC (r s = −0.69, p < 0.001). The high BWC emphasizes the importance of the bark tissue in Amazonian trees. Contrary to expectations, variability of monthly irradiance, rainfall and temperature had no effect on DGR (p > 0.20). The unresponsiveness of DGR to microclimatic variability, even in an above-average rainy year such as 2007, indicates that other parts of the tree may have greater priority than the stem for carbon allocation during the dry season.

Sources of phenotypic variation of wood density and relationships with mean growth in two Eucalyptus species in Argentina

Aims of the study: To describe the radial patterns of wood density, and to identify their main sources of variation, and the potential tradeoffs with mean tree growth, in two Eucalyptus species. Area of study: Mesopotamian (Corrientes and Entre Ríos provinces) and Pampean region (Buenos Aires province) of Argentina. Materials and methods: Eucalyptus grandis and Eucalyptus viminalis, growing in genetic trials installed in two sites per species were studied. X-ray wood microdensity profiles were developed from core samples. Each profile was proportionally divided in 10 sections. Mean, maximum, minimum and the standard deviation of wood density, for each section were computed. Mean annual growth was used to study the relationships with wood microdensity variables. A linear mixed-effects model computed the significance of different sources of phenotypic variation. Pearson´s correlation computed the relationships between variables. Main results: The pattern of radial variation in E. grandis showed a decrease in wood density from pith to bark, mainly due to the decrease in minimum wood density, while in E. viminalis, wood density increased towards the outer wood. In both species, the standard deviation of the wood density increased along the radial profile from pith to bark. Significant variation in wood density was explained by site, provenance and clone/family effects. In E. grandis mean, maximum and minimum wood density were negatively correlated with mean growth, whereas in E. viminalis correlations were positive but close to zero. Research highlights: Both the pattern of radial variation of wood density and the relationship between wood density and mean growth were different in the studied Eucalyptus species, and they varied within species depending on the site they were growing and genetic provenance.

Contrasting Hydraulic Efficiency and Photosynthesis Strategy in Differential Successional Stages of a Subtropical Forest in a Karst Region

Understanding the successional process from a disturbed forest to a mature forest is essential for species recovery and conservation initiatives. The resource acquisition and drought tolerance of plants can be instructive to predictions of species abundance and distribution for different forests. However, they have not been adequately tested at different successional stages in karst regions. Here, we selected seven dominant species in an early-succession forest and 17 species in a late-succession forest in a karst region of southwestern China. Resource acquisition-related traits such as hydraulic conductivity and photosynthetic rate, and drought tolerance-related traits, including turgor loss point and wood density, were measured. We found that species in the early-succession forest had a higher hydraulic conductance and photosynthetic rate than those in the late-succession forest, while leaf water potential at turgor loss point and wood density showed nonsignificant differences between the two forests. In addition, we observed a significant negative relationship between photosynthetic rate and drought tolerance in the early-succession forest, which was not identified in late-succession forests. Our study indicates that resource acquisition rather than drought tolerance was the key factor explaining plant distributions in forests at different successional stages in karst regions. We also suggest that the resource acquisition and drought tolerance trade-off hypothesis is not always supported for karst region species. Our study could inform about the design of species replacements in successional forests and provide forest management and restoration guidelines for karst regions.

Tri-trophic interactions of a predator-parasite-host assemblage in New Zealand

<p>Parasites are ubiquitous and the antagonistic relationships between parasites and their hosts shape populations and ecosystems. However, our understanding of complex parasitic interactions is lacking. New Zealand’s largest endemic moth, Aenetus virescens (Lepidoptera: Hepialidae) is a long-lived arboreal parasite. Larvae grow to 100mm, living ~6 years in solitary tunnels in host trees. Larvae cover their tunnel entrance with silk and frass webbing, behind which they feed on host tree phloem. Webbing looks much like the tree background, potentially concealing larvae from predatory parrots who consume larvae by tearing wood from trees. Yet, the ecological and evolutionary relationships between the host tree, the parasitic larvae, and the avian predator remain unresolved. In this thesis, I use a system-based approach to investigate complex parasite-host interactions using A. virescens (hereafter “larvae”) as a model system. First, I investigate the mechanisms driving intraspecific parasite aggregation (Chapter 2). Overall, many hosts had few parasites and few hosts had many, with larvae consistently more abundant in larger hosts. I found no evidence for density-dependent competition as infrapopulation size had no effect on long-term larval growth. Host specificity, the number of species utilised from the larger pool available, reflects parasite niche breadth, risk of extinction and ability to colonise new locations. In Chapter 3, I investigate larvae host specificity in relation to host nutritional rewards (phloem turnover and phloem sugar content) and host defences (bark thickness and wood density). The number of species parasitized was not explained by tree abundance, nutritional rewards or wood density. However, the number of trees parasitised declined significantly with increasing bark thickness indicating host external defences are an important driver of host specificity. Camouflage in animals has traditionally been considered an anti-predator adaptation. Yet the adaptive consequences of camouflage, i.e. increased survivability via predator avoidance, has rarely been tested. In Chapter 4, I show that larvae webbing is visually cryptic to predating kaka, yet did not protect larvae from attack. Instead, cryptic webbing aids larvae thermoregulation suggesting crypsis is non-adaptive. These results support an exciting newly emerging paradigm shift that indicates the evolution of camouflage in animals may be more to do with abiotic conditions than biotic signalling. Males are often the “sicker sex”, experiencing higher pathogen and parasite loads than females. In Chapter 5, I construct the largest host-parasite database to date, spanning 70 animal and 22 plant families, from which I conduct a meta-analysis testing for male biased susceptibility (MBS). Then, I develop a theoretical model that explain MBS as a result of parasite-offspring competition for female resources. I present the first, unified model that explains male-biased susceptibility in animals and plants and provide parameters for model replication, applicable to almost all host-parasite pairings on Earth. This thesis presents the first investigations of the natural history of Aenetus virescens larvae, their relationships with host trees, and the interactions with their avian predator. The results herein support existing theories of parasite aggregation and host specificity from a novel perspective. Furthermore, results support a newly emerging paradigm shift in animal camouflage evolution, and suggest a unified explanation for male biased susceptibility in animals and plants. The results herein help further our understanding of complex antagonistic relationships between parasites and their hosts, presenting novel theories on which future research can be built.</p>

Tri-trophic interactions of a predator-parasite-host assemblage in New Zealand

<p>Parasites are ubiquitous and the antagonistic relationships between parasites and their hosts shape populations and ecosystems. However, our understanding of complex parasitic interactions is lacking. New Zealand’s largest endemic moth, Aenetus virescens (Lepidoptera: Hepialidae) is a long-lived arboreal parasite. Larvae grow to 100mm, living ~6 years in solitary tunnels in host trees. Larvae cover their tunnel entrance with silk and frass webbing, behind which they feed on host tree phloem. Webbing looks much like the tree background, potentially concealing larvae from predatory parrots who consume larvae by tearing wood from trees. Yet, the ecological and evolutionary relationships between the host tree, the parasitic larvae, and the avian predator remain unresolved. In this thesis, I use a system-based approach to investigate complex parasite-host interactions using A. virescens (hereafter “larvae”) as a model system. First, I investigate the mechanisms driving intraspecific parasite aggregation (Chapter 2). Overall, many hosts had few parasites and few hosts had many, with larvae consistently more abundant in larger hosts. I found no evidence for density-dependent competition as infrapopulation size had no effect on long-term larval growth. Host specificity, the number of species utilised from the larger pool available, reflects parasite niche breadth, risk of extinction and ability to colonise new locations. In Chapter 3, I investigate larvae host specificity in relation to host nutritional rewards (phloem turnover and phloem sugar content) and host defences (bark thickness and wood density). The number of species parasitized was not explained by tree abundance, nutritional rewards or wood density. However, the number of trees parasitised declined significantly with increasing bark thickness indicating host external defences are an important driver of host specificity. Camouflage in animals has traditionally been considered an anti-predator adaptation. Yet the adaptive consequences of camouflage, i.e. increased survivability via predator avoidance, has rarely been tested. In Chapter 4, I show that larvae webbing is visually cryptic to predating kaka, yet did not protect larvae from attack. Instead, cryptic webbing aids larvae thermoregulation suggesting crypsis is non-adaptive. These results support an exciting newly emerging paradigm shift that indicates the evolution of camouflage in animals may be more to do with abiotic conditions than biotic signalling. Males are often the “sicker sex”, experiencing higher pathogen and parasite loads than females. In Chapter 5, I construct the largest host-parasite database to date, spanning 70 animal and 22 plant families, from which I conduct a meta-analysis testing for male biased susceptibility (MBS). Then, I develop a theoretical model that explain MBS as a result of parasite-offspring competition for female resources. I present the first, unified model that explains male-biased susceptibility in animals and plants and provide parameters for model replication, applicable to almost all host-parasite pairings on Earth. This thesis presents the first investigations of the natural history of Aenetus virescens larvae, their relationships with host trees, and the interactions with their avian predator. The results herein support existing theories of parasite aggregation and host specificity from a novel perspective. Furthermore, results support a newly emerging paradigm shift in animal camouflage evolution, and suggest a unified explanation for male biased susceptibility in animals and plants. The results herein help further our understanding of complex antagonistic relationships between parasites and their hosts, presenting novel theories on which future research can be built.</p>