Recent biodiversity loss has emphasized the necessity to critically evaluate the consequences of human alterations of forest ecosystems. Stand diversification via tree species mixtures and the use of ...non‐native trees are two such alterations currently gaining importance as climate change adaptations. However, the effects of local versus regional tree mixing on associated biodiversity and notably the modifying role of tree species growing outside their natural range remain poorly understood.
We assessed how monocultures and mixtures of native and introduced tree species influence the taxonomic and functional diversity of bird communities at stand and landscape scales in north‐west Germany. We focused on the dominant natural tree species (Fagus sylvatica) and economically important conifer species planted outside their natural range (the native Picea abies and non‐native Pseudotsuga menziesii).
We found that bird species richness and functional diversity were generally higher in pure and mixed stands of native F. sylvatica than in pure conifer stands, especially in comparison to non‐native P. menziesii. These differences were particularly strong at the landscape scale. Pure conifer stands harboured only a reduced set of functionally similar bird species. Structural diversity based on tree microhabitat availability emerged as a key predictor of bird diversity.
Synthesis and applications. Our study suggests that tree species mixtures do not necessarily increase bird diversity compared to pure stands of native trees, but can promote bird diversity relative to pure stands of species planted outside their natural range. Moreover, local mixtures, rather than a mosaic of pure stands, may promote bird diversity also at the landscape scale. By contrast, pure stands of tree species planted outside their natural range can increase biotic homogenization of forest birds. Promoting structural diversity of microhabitats via tree retention and ensuring that non‐native trees are planted in mixtures with native trees may alleviate potential limitations of climate change‐oriented management for biodiversity.
Our study suggests that tree species mixtures do not necessarily increase bird diversity compared to pure stands of native trees, but can promote bird diversity relative to pure stands of species planted outside their natural range. Moreover, local mixtures, rather than a mosaic of pure stands, may promote bird diversity also at the landscape scale. By contrast, pure stands of tree species planted outside their natural range can increase biotic homogenization of forest birds. Promoting structural diversity of microhabitats via tree retention and ensuring that non‐native trees are planted in mixtures with native trees may alleviate potential limitations of climate change‐oriented management for biodiversity.
Questions
Non‐native tree species (NNT) may bring about economic benefits, but also threats to ecosystems, mostly if they show expansive trends.
Location
A set of 12,000 permanent plots of the second ...(1986–1996), third (1997–2007) and fourth (2008–2017) Spanish Forest Inventory.
Methods
We quantified changes over time (1986–2017) of the NNT present in forests of peninsular Spain and we assessed how NNT’s traits, propagule pressure and human perception of NNT explain changes in distribution and demography of NNT. We quantified changes in four demographic parameters of every NNT: changes in the occupancy of species (number of plots where the species are present), annual changes in tree density and basal area, and tree growth. To explain the observed species trends, we selected functional traits related to the resource acquisition strategy, and key human drivers.
Results
Most of the NNT expanded their occupancy in the study area and increased their density, basal area, and tree growth through time. Increases in tree density and growth were greater in NNT with greater tolerance for low water potentials, with low specific leaf area, and with high propagule pressure. Increases in basal area were greater with high height of the NNT.
Conclusions
The overall increase in occupancy suggests that there is room for expansion of NNT in Spain. This knowledge will help to predict the dynamics of NNT already present in Spain and identify risks for forest biodiversity.
Most common non‐native tree species (NNT) expanded their range in continental Spain and increased their density, basal area, and growth over the last 30 years. The greatest increase in demographic rates occurred in NNT with high embolism resistance and low specific leaf area, indicating that conservative strategies in carbon and water use are beneficial for tree demographic performance in continental Spain.
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•Almost all forest habitats contained non-native plants, some with high frequency.•Some non-native plants were associated with 1 or 2 habitats, others were widespread.•Some habitats ...already have stable and typical combinations of non-native plants.•Non-native trees often co-occur with other non-native shrubs and herbs.
Even though temperate forests have lower non-native plant species richness and cover in comparison to some other habitats, such as anthropogenically influenced habitats or some grassland habitats, several recent studies from Central Europe suggest that there has been an increase in the numbers and proportions of non-native species in forests. Previous studies on the level of invasion in forest habitats were usually conducted on a relatively coarse scale, often excluding plantations of non-native trees or analyzing them together as a group regardless of the different biological properties of different species. Therefore, a more detailed analysis would be helpful to obtain better insight into the processes taking place in forests, focusing not only on the analysis of the invasion level of different forest types at a finer scale (e.g., in various types of floodplain, beech or coniferous) but also on the character of the non-native plants found there (invasive status, frequencies and habitat preferences). In this study, we aimed to (i) compare the invasion level of various forest habitats (including forests dominated by non-native trees) in Slovakia with regard to different residence times and invasive status of non-native species, (ii) analyze whether forest habitats possess specific non-native species combinations, and (iii) determine the preferences of non-native plants with respect to specific forest habitats and the co-occurrence of other plant species with the most frequent non-native species. Our study confirmed that almost all forest habitats contained at least one non-native species. Native forests at lower elevations and closer to rivers were more invaded, while broadleaved, mixed and especially coniferous forests at higher elevations and ecologically strictly limited forests were less (or un-) invaded. Significant differences between various types of riparian and coniferous forests, emphasized the importance of the more detailed discrimination of the forest habitats in comparison with previous studies. Non-native tree plantations, which are among the most invaded forests, also deserve special attention. Some non-native trees form stable communities with typical native and non-native species, where non-native dominants can act as drivers of further changes in the vegetation composition, facilitating spread of other co-occurring non-native shrubs and herbs. Taking into consideration the potential negative impacts of some non-native plants on species composition, forest microclimate and soil chemistry, it would be advisable for foresters to factor this into forest management because their choice of planted species may both positively and negatively influence the level of invasion in managed forests.
One of the main ideas of non-native tree species introduction into forest stands is to replace declining native species. The same is also valid for industry; the wood of native species should be ...replaced by a wood of the same or even better quality. Douglas-fir is often compared to other coniferous tree species based on its production. This study compared Douglas-fir wood properties with European commercial species, namely Norway spruce, Scots pine, and European larch. Trees representing different sites and ages were tested for wood density, shrinkage, and compression strength. In all cases, Douglas-fir outclassed spruce and pine in density and strength. The difference was striking, especially for spruce, where the density was surpassed by Douglas-fir by more than 100 kg.m−3 (above 25%). In the case of compression, the strength of Douglas-fir was up to 12.3 MPa higher (above 33%) compared to spruce. The only species that obtained higher figures was larch. Wood shrinkage was comparable to European softwoods. Therefore, Douglas-fir wood can be regarded as an excellent and promising substitute for the European processing industry.
•Douglas-fir represents promising non-native species for Europe.•It should be a substitute, especially for Norway spruce in industry.•We tested some of the properties important for applications.•In contrast to previous studies, tested species grew together in the same stand.•Douglas-fir exceeded not only spruce but also Scots pine.
Climate change poses severe pressures to European conifer forests. Using non‐native tree species, such as Douglas fir (Pseudotsuga menziesii), is one proposed strategy to circumvent adverse effects ...for forest management. However, novel forest health risks can impair the cultivation of non‐native trees. In 2022, we observed large Douglas fir trees (approximately 40–50 years old, diameter at breast height (dbh) 21–41 cm) that had recently died in spring or summer 2022 in three forest stands in Eastern Austria. Intensive resin flow, blue‐staining of the sapwood and the absence of bark‐ and wood‐boring insects indicated a fungal infection. Isolations from blue‐stained sapwood of the dead trees consistently yielded cultures of the opportunistic pathogen Diplodia sapinea. In a greenhouse wound inoculation experiment, seven D. sapinea isolates obtained from Douglas fir caused phloem necrosis, blue‐staining of sapwood and mortality and thus displayed pathogenicity towards seedlings of both Ps. menziesii and its common host, Scots pine (Pinus sylvestris). Diplodia sapinea produced significantly longer areas of blue‐stain as well as higher and faster mortality in Ps. menziesii compared to P. sylvestris. We conclude that D. sapinea substantially contributed to the death of seven of the 13 examined large Douglas fir trees. While this fungus has been described as a pathogen of young Douglas fir trees before, this is the first report that it can potentially kill large individuals of this conifer species under drought conditions. Thus, our results indicate that D. sapinea could represent a severe threat to the cultivation of Ps. menziesii in European forestry.
The management of non-native tree species in European forests has a long history, but the information on the current number and geographic distribution of these species in European forests is ...incomplete and scattered across various datasets. This study aims to perform an inventory of the most frequent non-native tree species growing in European forests and analyse their current extent, geographic distribution and geographic origin. Our results show that at least 150 non-native tree species are currently growing in European forests and provenance trials. The genera represented by largest number of species are Eucalyptus, Pinus, Acacia and Abies. Species growing at the largest areas are Robinia pseudoacacia (2.44 million ha), Eucalyptus globulus (1.46 million ha), Picea sitchensis (1.16 million ha) and Pseudotsuga menziesii (0.83 million ha). In total, non-native tree species in Europe are found in an area of approximately 8.54 million ha, or 4.0% of the European forest area, and the five most abundant species account for up to 77% of this area. The largest number of these 150 species were introduced from North America (71), followed by Asia (45) and Australia (20). North American species occupy by far the largest area.
Black locust (
L.) was introduced in Poland over 200 years ago, and its distribution area now covers the whole country, with the highest concentration of occurrence in the western part. Breeding of ...this species has been started in Poland for about 20 years, albeit on a limited scale, and two selected seed stands, 34 plus trees and two seed orchards have been registered. So far, selection efforts have not been coupled with the recognition of variation in the genetic structure of local populations. To fill the knowledge gap on genetic diversity, we selected the seven qualitatively best populations of
for our study. To clarify the origin of the Polish population of
, a sample from a seed stand in eastern Germany and from a seed orchard with Hungarian clones from the Oborniki Śląskie Forest District was added. In this study, three microsatellites were used to evaluate genotypes: Rops15, Rops16 and Rops18, with the Rops15 locus (motif AG) showing hypermutability. Moderate or high variability was observed in all microsatellite loci examined, with a total of 27 alleles identified. In all stands, the average observed number of alleles per locus was higher than the average effective number of alleles per locus. Three main clusters have been identified in the genetic structure of the population, one of which is represented by the population from the Regional Directorate of State Forests in Zielona Góra. The second group comprised the populations from Mieszkowice, the populations Pińczów and Wołów, and the population from Germany. The last one included population from Strzelce and Oborniki Śląskie, where the population from Hungary is represented. This may be of great importance for practice. Perhaps it is worth postulating the separation of two seed regions. Under most scenarios, climate change is projected to change the distribution of forest types and tree species in all biomes. It can be assumed that the importance of black locust in times of climate change is likely to increase.
Purpose of Review
Non-native tree species (NNT) raise a range of different associations and emotions—to many citizens they are just an exotic curiosity in parks, to many conservationists they are an ...evil to native ecosystems that should be eradicated, to a rising group of foresters they are part of the solution to climate change and an increasing timber demand, and to others they are already daily forestry business. In this review, where we also summarise the findings of the recent COST Action FP1403 (NNEXT) ‘Non-native tree species for European forests: experiences, risks and opportunities’, we highlight opportunities and challenges in the light of climate change, ecological risks and legislative limits of growing non-native tree species in Europe.
Recent Findings
Few NNT in Europe show invasive behaviour and are listed as prohibited species or as species to be monitored. A larger number of NNT is utilised in productive forestry and forest restoration due to their superior growth, valuable timber properties and good performance under harsh growing conditions. Current species distribution, experiences with success and failures and environmental concerns differ profoundly across Europe, with Western Europe overall revealing higher shares in NNT and showing a stronger interest of forestry related stakeholder groups to continue planting NNT.
Summary
Many more NNT are already used in forestry than previously thought, but relatively few species have major importance in terms of area, mainly in western European countries. Diversification, mixing and avoidance of invasion in relation to NNT are necessities that are relatively new on the agenda. In contrast, provenance research of major NNT has been going on for many decades and now provides important information for climate change adaptation. Despite the limitations to the use of NNT either through legal restrictions or forest certification that differ considerably across Europe, the careful integration of a range of tested NNT also into future forest management planning shows a high potential for climate change adaptation and mitigation.
The paper analyzes the elements of the stand structure and proposes
silvicultural measures to improve conditions in the stand of black locust
(Robinia pseudoacacia L.) and common hackberry (Celtis ...occidentalis L.) aged
28 years in Subotica-Horgos sands. The research was performed on three
permanent experimental plots on which selective thinning (T1 and T2) was
performed experimentally in two plots, while one was left as a control plot
(C).Initially, 528 trees for tending per hectare were selected in the
studied age, of which 448 black locust and 80 common hackberry trees per
hectare were selected on T1, and 320 black locust and 208 common hackberry
trees per hectare on T2.In experimental plots T1 and T2 at least one
competing tree was cut down to each tree for tending, and a total of 912 and
1072 trees were cut down per hectare with a total volume of 53-55 m3?ha?1.In
this way, a basis was created for the assessment of the growth response of
trees to selective thinning in the upcoming period.
Key message
Douglas-fir growth correlates with the climate, the soil moisture regime, and the soil nutrient status, reflecting a broad physiological amplitude. Even though planting this non-native ...tree species is suggested as a viable strategy to improve adaptiveness of European forests to a more extreme climate and to assure future productivity, the expected temperature increase may induce a decline in forest stand productivity for Douglas-fir in already warm and dry regions.
Context
Tree species selection is one of the most important forest management decisions to enhance forest productivity and stand stability on a given site. Douglas-fir (
Pseudotsuga menziesii
(Mirb.) Franco var.
menziesii
), a non-native species from north-western America, is seen as an important additional species option for adapting Central European forests to a changing climate.
Aims
This study assesses Douglas-fir forest productivity derived from site conditions. We investigate climatic and physico-chemical soil characteristics and productivity of 28 mature Douglas-fir stands growing on siliceous, as well as carbonate bedrock material in southern Germany and north-eastern Austria.
Methods
The importance of climatic and physico-chemical soil characteristics was analyzed with the machine learning method
Random Forests
.
Results
The results show that Douglas-fir growth correlates with climate, soil moisture, and soil nutrient availability derived from ten climatic and physico-chemical soil parameters.
Conclusion
The broad pH optimum between 4.5 and 7.2 reflects the broad physiological amplitude of Douglas-fir, and no significant differences were detectable between carbonate and siliceous bedrock. We also conclude that climate change may induce a forest stand productivity decline, because lower productivity with the highest mean summer temperature across our study range was observed at the warmest sites in Eastern Austria.
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