•Douglas fir cannot compete with broadleaves in productive European beech forests.•Abundant Douglas fir regeneration was found on dry and less productive forest sites.•Monitoring of Douglas fir ...regeneration is recommended on dry, nutrient-poor sites.
Douglas fir (Pseudotsuga menziesii) has regenerated naturally in European forests since the middle of the 20th century. Some cases of an invasive character of the species have been reported under specific site conditions, but systematic data on the extent of natural regeneration and spread of Douglas fir across different forest communities are largely lacking. Due to its potential tolerance to increasing summer droughts, Douglas fir has been suggested as a sustainable future tree species for Central European forests. In this study, we investigated natural regeneration of Douglas fir in comparison to native tree species in 39 forest stands in Switzerland belonging to different forest communities. We analyzed the regeneration success of Douglas fir, Norway spruce (Picea abies), silver fir (Abies alba), and European beech (Fagus sylvatica) with respect to ecological site conditions. The proportion of Douglas fir seedlings (<130 cm height) was <5% in the majority of stands; but in four stands, Douglas fir was the most abundant species among seedlings. In most other stands, Norway spruce (occurring in 37 stands/dominant in 10 stands), silver fir (38/2 stands) and beech seedlings (35/10 stands) were more abundant than Douglas fir seedlings. Saplings (≥130 cm height but <12 cm diameter at breast height) of Douglas fir were observed in five stands with proportions between 10% and 23% and in eight stands with proportions of <10%, in particular in stands with a high proportion of Douglas fir seed trees. Beech saplings occurred in 28 stands and were most abundant in eleven stands. Saplings of silver fir (24/3 stands) and Norway spruce (19/6 stands) were less frequent. The abundance of Douglas fir seedlings correlated positively with the proximity to seed trees and light transmission of the canopy, but negatively with understory vegetation cover and litter abundance. Ungulate browsing did not significantly affect the regeneration of any tree species in the study stands. On the Central Plateau, Douglas fir was mainly planted in productive beech forest communities where it is strongly limited due to its low competitiveness compared to beech and other fast-growing deciduous tree species. On dry and less productive sites, where the canopy is not closed, Douglas fir is able to establish successfully. On such sites, a close monitoring of Douglas fir regeneration and the potential implementation of control measures is recommended.
•Site conditions had strong effects on fine root biomass and fine root area index.•FRB and RAI were significantly higher across all stand types on the poor sites.•On the poor sites, FRB significantly ...increased with increasing beech proportion.•No overyielding was observed when FRB was plotted against basal area and/or APA.•Fine root biomass patterns of all species changed along the vertical soil profile.•In contrast to SRA and RAI, SRL was not affected by site but differed among species.
The establishment of broadleaved - conifer mixtures has had positive effects on productivity. However, it is still not clear the degree to which belowground space occupation contributes to these effects and how root traits of the respective species differ between mixed and pure stands. Thus, the aim of this study was to examine how enrichment of beech forests with conifer species impacts fine root biomass and other root traits across variable site conditions.
We studied 20 mature pure and mixed stands of European beech (Fagus sylvatica), Norway spruce (Picea abies), and Douglas-fir (Pseudotsuga menziesii), and determined differences in biomass, spatial distribution, and morphology of fine roots (≤2 mm, to 60 cm soil depth) among beech – conifer mixtures and pure stands of the respective species in two regions with differing site conditions in Northern Germany.
Site conditions had strong effects on fine root biomass (FRB) and fine root area index (RAI). Both FRB and RAI were significantly higher across all stand types on the sites with lower belowground resource availability. On the less favorable sites, FRB significantly increased with increasing beech proportion. In contrast to specific root area (SRA) and RAI, specific root length (SRL) was not affected by site conditions but differed significantly among species. No overyielding was observed when FRB was plotted against basal area and/or area potentially available (APA), which reflects the aboveground horizontal space configuration. Spatial fine root biomass patterns of all species in both monospecific and mixed stands changed along the vertical soil profile at both sites. FRB decreased with increasing soil depth, with the exception of beech in mixed stands.
Our data suggest that both amount and distribution of tree fine roots in pure and mixed stands are highly variable and depend primarily on-site conditions and secondarily on tree species identity. By disentangling soil and species identity effects, we conclude that beech has a remarkable potential for adjusting fine root biomass to cope with unfavorable conditions as compared to spruce and Douglas-fir.
Mixed-species plantations have been suggested as ecologically and economically viable alternatives to monocultures. We examined the growth response of coastal Douglas-fir (Pseudotsuga menziesii var. ...menziesii (Mirb.) Franco) and western redcedar (Thuja plicata Donn ex D. Don in Lamb.) to different species mixtures (Douglas-fir : western redcedar mixtures of 1:0, 1:1, 1:3, and 0:1) and planting densities (500, 1000, and 1500 stems·ha
−1
) in a dry maritime forest on eastern Vancouver Island, Canada. Twenty-two years postplanting, species mixture significantly affected diameter and height growth (p < 0.001), with stand diameter and height generally decreasing with increasing redcedar composition. Inherent variation in soil productivity across the plantation (carbon:nitrogen ratio) equally constrained stand growth. The widest spacing had larger diameter than the closest spacing (p = 0.025) but the least stand basal area compared with the other spacing treatments (p = 0.003–0.031). Stand volume was significantly affected by mixture × density interaction (p = 0.024) and generally declined with increasing proportion of redcedar and decreasing stand density. In the first decades after plantation establishment, inherent species growth traits and soil fertility were most important in dictating stand productivity. Because of the differences in resource utilization of both species, stand dynamics may change as competition for light and soil resources increases. Evaluation of silvicultural recommendations regarding mixtures of both species will continue with plantation development.
Catalytic pyrolysis of Douglas fir with MgO and biomass-derived activated carbon catalysts (MAC) was investigated for the first time. The effects of MAC to Douglas fir ratio, experimental ...temperature, and MgO to activated carbon ratio on product distributions were studied. The bio-oil yields varied from 45.7 to 58.5 wt% under various experimental conditions. The main bio-oil products from the catalytic pyrolysis of Douglas fir were phenols, furans, aldehydes, and ketones. Methane, hydrogen, carbon dioxide, and carbon monoxide were the dominant gas products. The bio-oil yields, the selectivities of phenols and furans, and the proportion of target gas products were increased with the addition of catalysts compared to Douglas fir pyrolysis without catalysts, but the effect of MAC to Douglas fir ratio was negative for the bio-oil yield. The alkylation of methoxy phenols was promoted by MgO. According to the different experimental results, the maximum production of bio-oils was acquired at the experimental condition of 500 °C, MAC to Douglas fir ratio of 1:2, and MgO to activated carbon ratio of 0.2. This work could provide a novel and viable way for the conversion of Douglas fir into high bio-oil yield and relieve the stress of energy shortages and environmental pollution.
•Fast catalytic pyrolysis of Douglas fir with MgO and activated carbon was studied.•Up to 58.5 wt% of pyrolysis products belonged to phenolic-rich bio-oils.•High selectivity of phenolic products was achieved.•The alkylation of methoxy phenols was promoted by MgO.
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•A new catalyst of bifunctional activated carbon with iron (AC/Fe) was developed.•Fe/AC exhibited excellent catalytic performance with newly created strong acid sites.•Fe/AC resulted ...in high selectivity of jet fuel range hydrocarbons.•Increasing catalyst ratio and temperature favored high selectivity of mono-aromatics.•Synergy promoted dehydroxylation of phenol to form aromatics via H-transfer reaction.
Low-cost and high-efficiency catalysts are vital to the conversion of solid wastes into biofuels or chemicals. In this study, a bifunctional activated carbon catalyst modified with Fe (Fe/AC) was obtained and applied to the catalytic co-pyrolysis of Douglas fir (DF) and low-density polyethylene (LDPE) using a facile fixed bed reactor. The effects of Fe loading amount, catalyst to feedstock ratio, and pyrolysis temperature on the product yields and distributions were studied. Results showed that the highest yield of bio-oil (53.67%) was achieved using 10Fe/AC at a pyrolysis temperature of 500 °C with a catalyst to feedstock ratio of 1. The main chemical compositions of the obtained catalytic bio-oil were aromatics, alkanes, and phenols. Increasing the temperature (450–600 °C) and catalyst to feedstock ratio (0.5–2) enhanced the selectivity of aromatics at the expense of phenols and alkanes. Compared to the AC catalyst, Fe/AC exhibited excellent performance on aromatics production (especially mono-aromatics) due to the newly created acid sites. The catalytic synergistic effect over 10Fe/AC significantly promoted the formation of aromatics through hydrogen transfer reactions which facilitated the dehydroxylation and demethoxylation of phenols. The present work provides a promising approach of converting biomass and plastic wastes directly into jet fuel range hydrocarbons by using green inexpensive carbon-based catalysts.
We tested the “home-field advantage” hypothesis, i.e., that leaves decay faster under the parent tree species in European beech, Douglas fir, and Turkey oak stands in a mountain forest in Italy. The ...fate of leaves in buried litterbags was monitored for one year to document their carbon (C) and nitrogen (N) dynamics, chemical structure, and associated microbial community.
The three litter types lost C continuously at a similar rate, regardless of the species they were buried under. On the other hand, the N losses varied among litter types, and beech even gained a small but significant amount of N in the first 3–6 months. Differences between the litters were evident in the alkyl region of the nuclear magnetic resonance spectra and smaller in the aromatic and aryl acids regions. By the end of the experiment, all litters had lost substantial quantities of carbohydrates, lignin, proteins, and lipids, particularly oak litter. The richness and diversity of bacterial and fungal communities increased with time. Litter type had the greatest impact on microbial community composition in the first months of decomposition; afterwards, the stand type had a greater influence on the assemblage of decomposer microorganisms.
Overall, this study provides little evidence in support of the home-field advantage hypothesis, which could be valid only for oak. Instead, our findings indicate that the chemical composition of litter is the main factor affecting the early stages of litter decomposition. Tree species and soil properties within the stand play an important role in the advanced stages of decomposition since these factors control the assemblage and functions of the soil microbial community.
•In a mountain forest in Italy, we found little evidence that leaves decay faster under their parent trees.•In early stages, the nature of the litter prevailed over the type of tree cover as driving factor of litter decay.•Three types of litter investigated showed different decay pathways, as highlighted by NMR.•Type of tree cover impact on microbial communities became increasingly evident as decay progressed.
•Douglas fir is introduced to European forests as an adaption to climate change.•We studied the impact of increasing shares of Douglas fir on vascular plants.•Douglas fir admixture promotes ...nitrogen-tolerant disturbance indicators.•Generalist species increase with increasing Douglas fir canopy fractions.•The share of typical beech forest species decreases.
Introduction of drought-tolerant exotic tree species is seen as an important adaptation measure of forest management to climate change in Central Europe. Douglas fir (Pseudotsuga menziesii) is particularly favored in this context, because it is adapted to summer droughts due to the climate in its natural distribution range in temperate western North America and it is also fast-growing and the wood is readily marketable. In Germany, there are plans to grow Douglas fir on a large scale in mixed forests with other tree species on acidic soils. Potential ecological consequences have not yet been sufficiently scrutinized. Here, we analyze effects of Douglas fir introduction into forests of European beech (Fagus sylvatica), which would naturally predominate Central Europe’s forests. We analyzed vascular plant diversity and species composition of the ground vegetation in a gradient with increasing Douglas fir canopy fraction that ranged from pure beech (0% Douglas fir) via mixed stands (25%, 50%, 75% Douglas fir) to pure (100%) Douglas fir forest. Species richness, Shannon diversity, and Simpson diversity increased with increasing Douglas fir canopy fraction. However, this increase was primarily driven by an increase of nitrogen-tolerant disturbance indicators, whereas the share of forest species that were predominant in pure beech forests decreased. Beech forest species declined gradually with increasing Douglas fir canopy fraction, but these declining species were fewer than the number of species increasing due to Douglas fir introduction. Cover of ∼30% of species remained constant when Douglas fir was introduced. Strong changes in the ground vegetation were observed at Douglas fir canopy fractions > 40 – 50% and the original character of the ground vegetation was completely lost beyond a threshold of 75%. Therefore, we discourage from high Douglas fir proportions beyond these thresholds in production forests and from any introduction of Douglas fir where nature conservation is a priority.
•CAM was significantly associated with greater decreases in residual basal area and tree density.•Ponderosa pine importance value was not significantly associated with CAM.•CAM did not influence ...spatial heterogeneity.•Novel tools may be required to meet composition and heterogeneity goals for forest restoration.
In response to large, severe wildfires across the western US, federal initiatives have been enacted to increase the pace, scale, and quality of ecological restoration in fire dependent forests. To address uncertainty and controversy in agreement among specific restoration prescriptions on national forest land, several initiatives adopt a collaborative adaptive management (CAM) strategy wherein monitoring data can inform stakeholder input into future management actions. It is unclear, however, how such approaches may change restoration outcomes. Here we assess the extent to which CAM strategies impact restoration outcomes that were implemented as part of the Collaborative Forest Landscape Restoration Program (CFLRP) in ponderosa pine-dominated forests of the Colorado Front Range. We assessed stand-level desired conditions across 24 projects over a 7-year period to determine how restoration treatments contribute to desired conditions, and compared treatment outcomes over implementation time to assess whether the CAM processes contribute towards treatments better approximating restoration. We found that restoration treatments improve aspects of forest structure related to stand density. However, meeting objectives related to forest composition and horizontal structural complexity goals were not met. Additionally, CAM processes were effective at improving outcomes related to forest density over implementation time, but novel tools and approaches may be required so that outcomes related to forest composition and horizontal structural complexity are more congruent with restoration objectives. Evaluating the success and challenges of CAM provides insight to improve collaborative and large-scale restoration.
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