Yield and crown structure characteristics in a red oak (Quercus rubra L.) stand: Case study

The paper provides the results of a detailed analysis of timber volume and several important crown variables of red oak (Quercus rubra L.) based on an experimental plot in eastern Hungary. At the age 32 years the crop trees belonged to different height classes. If the volume of the mean tree from height class I was considered as 100%, the volume of the mean tree of class II was 59%, and the mean tree of class III was only 36%. It appeared that there was a significant correlation between crown indices and yield. For this reason, diameter at breast height showed a positive linear correlation with crown diameter (R2= 0.6211). Additionally, there was also positive linear relationship between crown diameter and volume (R2= 0.6908). The variation of crown indices is height even within the same stand and indicates the importance of following a selective thinning operation method.

Red Oak (Quercus rubra L.) Fruits as Potential Alternative for Cocoa Powder: Optimization of Roasting Conditions, Antioxidant, and Biological Properties

Cocoa powder is a basic ingredient in the manufacture of chocolate, one of the most appreciated sweet products in the world for its sensory and nutritional properties. Furthermore, it displays a central nervous system stimulant effect. This study aimed to investigate acorn-derived powder as an alternative to cocoa powder, in order to obtain a chocolate that does not contain stimulants of the nervous system. Both the chocolate technological process and acorns roasting process (180 °C/25 min, 200 °C/20 min and 220 °C/15 min) were optimized to obtain acorn powder with an organoleptic profile as close as possible to that of cocoa powder. The chocolate sensory evaluation was performed by means of the hedonic test. Furthermore, the aqueous extracts obtained from the resulting powder were evaluated for total polyphenol content, and in vitro antimicrobial and antiproliferative properties. The results point out a high content of phenolic compounds (500.78–524.01 mg GAE/100 g); protection against microbial contamination based on the ability to inhibit a Gram-positive bacterium (Bacillus cereus) was also noticed. The aqueous acorn extracts were also able to reduce the cell viability of HFL-1 (human fetal lung fibroblast) and DLD-1 (colorectal adenocarcinoma) lines. This study suggests red oak (Quercus rubra) fruits as a potential alternative to cocoa powder in the manufacture of chocolate.

Temperate tree seedlings have similar drought vulnerability despite having different hydraulic drought responses in adults

Climate change is projected result in higher frequencies of drought events across the world and lead to reduced performance in many temperate tree species. However, many studies in this area focus specifically on adult tree drought responses and overlook how trees in other age classes might differ in their vulnerability. Evidence shows that seedling drought response can differ from that of adults and furthermore that demographic performance in the seedling age class will have disproportionately strong effects on the assembly dynamics of future forests, together suggesting that understanding seedling drought responses will be critical to our ability to predict how forests will respond to climate change. In this study, we measured four indices of hydraulic response to drought (leaf water potential, photosynthetic capacity, non-structural carbohydrate concentration, and hydraulic conductivity), as well as interaction effects with shade treatments, for seedlings of two temperate tree species that differ in their adult drought response: isohydric Acer saccharum and anisohydric Quercus rubra . We found a strong isohydric response in A. saccharum seedlings that included conservation of leaf water potentials (> -1.8 MPa) and reductions in non-structural carbohydrate concentrations consistent with reduction of stomatal conductance. Quercus rubra seedlings were able to survive to more negative water potentials, but only rarely, and they showed a similar reduction in photosynthetic capacity as was found for A. saccharum . Our results suggest that, although Q. rubra seedlings display some anisohydric responses to drought, they are more isohydric than adults. Both species seem to be relatively similar in their vulnerability to drought despite the differences predicted from adult drought response, and our results suggest that seedlings of both species will be similarly vulnerable to future drought events.

Oak (Acorn)–Weevil Interactions across an Extensive Latitudinal Gradient in Eastern North America

Recent studies have explored how nut weevils (Curculio and Conotrachelus spp. (Coleoptera: Curculionidae) prey on the fruits (acorns) of oak (Quercus spp.). However, few, if any, have examined these interactions over both an extensive geographic area and over several years. Here, we observed patterns of infestation in acorns of both red oak (Quercus rubra) and white oak (Quercus alba) over an eight-year period along a latitudinal transect, extending as far as 900km, across much of the shared range of these two oak species. Although weevil prevalence did not differ significantly between the two oak species, in red oak, infestation prevalence increased significantly with latitude. In contrast, an opposite pattern was evident in white oak, with the highest infestation prevalence occurring at lower latitudes. One controlled measure of cotyledon damage was significantly lower in acorns of red oak than those of white oak, which may in part be due to larger acorn size at the lower latitudes. Future investigations in this system should focus on the distribution of weevil species (with DNA barcoding) across this range and geographic variation in chemical gradients that likely determine patterns of weevil damage in individual acorns.

Forest inventory-based assessments of the invasion risk of Pseudotsuga menziesii (Mirb.) Franco and Quercus rubra L. in Germany

In Europe, some non-native tree species (NNT) are classified as invasive because they have spread into semi-natural habitats. Yet, available risk assessment protocols are often based on a few limited case studies with unknown representativeness and uncertain data quality. This is particularly problematic when negative impacts of NNT are confined to particular ecosystems or processes, whilst providing valuable ecosystem services elsewhere. Here, we filled this knowledge gap and assessed invasion risks of two controversially discussed NNT in Germany (Quercus rubra L., Pseudotsuga menziesii (Mirb.) Franco) for broad forest types using large scale inventory data. For this purpose, establishment success of natural regeneration was quantified in terms of cover and height classes. The current extent of spread into protected forest habitats was investigated in south-west Germany using regional data. Establishment was most successful at sites where the NNT are abundant in the canopy and where sufficient light is available in the understory. Natural regeneration of both NNT was observed in 0.3% of the total area of protected habitats. In forest habitats with sufficient light in the understory and competitively inferior tree species, there is a risk that Douglas fir and red oak cause changes in species composition in the absence of management interventions. The installation of buffer zones and regular removal of unwanted regeneration could minimize such risks for protected areas. Our study showed that forest inventories can provide valuable data for comparing the establishment risk of NNT amongst ecosystem types, regions or jurisdictions. This information can be improved by recording the abundance and developmental stage of widespread NNT, particularly in semi-natural ecosystems.

How do invasive trees impact shrub layer diversity and productivity in temperate forests?

• Key message Invasive tree species alter taxonomic diversity and functioning of forest shrub layers: Prunus serotina increases shrub layer biomass two to three times but decreases its biodiversity, Robinia pseudoacacia slightly increases shrub layer biomass and has no effect on its biodiversity, while Quercus rubra both biomass and biodiversity of the shrub layer. • Context Although the impact of invasive trees on understory biodiversity is known, very little data exist about their influence on shrub layer biodiversity and productivity. • Aims To assess impacts of Prunus serotina Ehrh., Quercus rubra L., and Robinia pseudoacacia L. on shrub layer aboveground biomass, species composition, and alpha diversity. • Methods We measured stand structures in a set of 168 study plots established in Wielkopolski National Park (W Poland), and we compared biomass and diversity metrics using generalized mixed-effects linear models. • Results We found the lowest aboveground biomass of shrub layers in Q. rubra forests. P. sylvestris forests invaded by P. serotina had two to three times higher aboveground biomass than non-invaded forests. R. pseudoacacia forests had 27.8% higher shrub layer biomass than Quercus-Acer-Tilia forests. We found negative impacts of Q. rubra and negligible impacts of R. pseudoacacia on shrub layer alpha diversity metrics. However, the effect of Q. rubra was similar to native F. sylvatica. P. serotina negatively affected functional diversity, but its effects were lower in rich P. sylvestris forests than in poor P. sylvestris forests. • Conclusion The introduction of alien tree species alters ecosystem services and species diversity of shrub layers. The direction and magnitude of these alterations are alien species-specific and context-dependent. Therefore, their management should account for their impacts.