Current Forestry Reports最新文献

Purpose of Review

The collective virome of forest trees can be considered to include not only plant viruses, but also viral communities harbored by all tree-associated organisms. In this review, we will concentrate on reviewing recent developments in the two fields of forest tree virology that have received the most research input during the last 5 years: (1) current knowledge of virus diseases affecting forest trees and their causal agents and (2) fungal viruses (mycoviruses) and properties that are required for utilizing them for biocontrol purposes.

Recent Findings

The discovery of plant and mycoviruses has been revolutionized during the last few years due to high-throughput sequencing (HTS). This has altered our view of virus diversity and prevalence, but also their host ranges, transmission routes, and host effects. Utilization of HTS has greatly expanded our knowledge of plant virus diversity and disease etiology in forest trees and revealed the commonness of cross-kingdom transmission events between fungi, oomycetes, plants, and arthropods. Research on mycoviruses has also identified several new mycoviruses that restrict the growth or virulence of forest pathogenic fungi.

Summary

Gaining knowledge of the collective virome of forest ecosystems is essential not only for understanding virus evolution and diversity but also for improving our understanding on virus impacts, and our ability for biocontrol-based and environmentally friendly management of viral and fungal diseases that affect economically important plants and beneficial insects, and for preventing possible disease outbreaks in the future. Virus infections play a central role in plant health, but viral symptoms on forest trees remain often unrecognized and may be confused with other biotic or abiotic damages. However, recent studies have revealed previously unknown viruses as causes of forest tree symptoms and suggest that viruses are responsible for far greater economic losses than recognized earlier. However, many knowledge gaps still need to be filled, particularly on the diversity of viruses that infect different species of forest trees, their irregular distribution within the plant, their mode of transmission, epidemiology and choice of hosts also regarding crop plants, their effect on the metabolism of their host tree, and their interaction with other microorganisms. Mycovirus research has already deciphered detailed information on many critical properties that affect utilizing them for biocontrol purposes. Still, more knowledge is needed concerning mycoviral transmission mode and stability in field conditions, the level of host tolerance against mycoviral infection, and the occurrence of interspecies mycovirus transmission in nature, and safety issues related to these topics.

Purpose of Review

We aimed to summarize the evidence linking multi-purpose forest management (MPF) to bird nesting and fledging success in temperate and boreal forests and to identify outstanding research gaps. Forest birds are in decline worldwide, but an ongoing move from production-oriented management towards MPF, integrating biodiversity conservation with other uses, may help counteracting these trends. The effects of MPF on bird diversity and abundance are well-studied, but less is known about effects on bird demographics.

Recent Findings

We retrieved 101 studies, reporting 342 outcomes of MPF for nesting and fledging success. Due to the heterogeneity of the studies, we opted for a systematic mapping approach, accompanied by vote-counting and narrative review. Studies covered 11 types of MPF and 151 bird species. The most frequently studied interventions were overstorey retention and prescribed burning, but research was markedly biased towards temperate North America. Most outcomes (79.5%) were non-significant, and studies often found that breeding success was driven by ecological processes at both broader and finer scales than management interventions. Thus, managing for breeding success likely requires complementary management actions at various scales. Nonetheless, significant positive and negative outcomes of MPF were also found, inclusively affecting species of conservation concern, highlighting the variability and context-dependence of MPF effects.

Summary

In order to foster effectiveness of MPF for forest birds, future research should focus on a set of under-researched interventions and regions, as well as on ecosystem-wide experiments accounting for functional links between bird abundance, demographics, nest predation, and food supply.

Purpose of Review

To describe how general prescriptions to protect temperate and boreal forests against pests have been affecting the conservation of insect diversity, (2) to identify potential conflicts between biodiversity conservation actions and pest control, and (3) to provide future directions to reconcile forest pest management with insect conservation.

Recent Findings

Despite dealing with the same habitats and organisms, forest pest management and insect conservation have been separate disciplines, often pursuing conflicting goals. However, there is a large intersection between the two, as interventions to control pests can have repercussions on biodiversity and vice versa. In several regions, forest pest management is shifting from reactive measures to contain on-going outbreaks to proactive strategies to create forest landscapes that are more resistant and resilient against pests in the long-term. These developments suggest a possible convergence between pest management and insect conservation objectives.

Summary

Several reactive measures adopted to control pests can cause negative impacts on non-target insects, although effects are sometimes localized and often context-dependent. Following ecological, economic, and social considerations, pest management has been evolving towards diversifying forests across multiple spatial scales to reduce the severity of outbreaks and the risk of damage. Such strategies concur with multiple conservation goals to increase insect diversity across intensive forest landscapes. Insect conservation has traditionally targeted saproxylic organisms, neglecting the conservation of other insect guilds and seldom assessing side effects on pests. Despite some important knowledge gaps, we propose complementary approaches to combine multiple diversification strategies at the landscape scale to reconcile pest management with insect conservation.

Purpose of Review

The objective quantification of stand density (SD) is necessary for predicting forest dynamics over space and time. Despite the development of various synthetic representations of SD, consensus remains elusive regarding a primary integrated measure due to contrasting data sources, statistical modeling methods, and distinct regional variations in forest structure and composition. One of the most enduring and robust measures of SD is Reineke’s (1933; J. Ag Res. 46, 627-638) stand density index (SDI), which has long formed the basis for the prediction of stand development concerning self-thinning processes in single-species, even-aged stands and stand density management diagrams (SDMDs). Thus, this review tracks the development of different methodologies and necessary data for properly estimating SDI, including its application in complex forests and adaptive management contexts.

Recent Findings

Limitations of SDI in its earliest form have led to important modifications centered on refinement and expanding its application beyond even-aged, single-species stands to multi-cohort, mixed composition stands. Statistical advances for better determination of the maximum size-density boundary line have also been applied to SDI estimates using the ever-expanding availability of remeasured field data including large-scale, national forest inventories. Other innovations include the integration of regional climate information and species functional traits, e.g., wood specific gravity, drought, and shade tolerance.

Summary

In this synthesis, we describe the attributes of SDI that have promulgated its use as a leading measure of SD for nearly 90 years. Recent applications of robust statistical techniques such as hierarchical Bayesian methods and linear quantile mixed modeling have emerged as the best performing methods for establishing the maximum size-density boundary, especially those incorporating ancillary variables like climate.

Purpose of Review

In tandem with China’s rapid urbanisation and economic growth, some negative impacts on the eco-environment and human wellbeing have arisen, such as the urban heat island effect, air pollution and lack of recreational spaces. To address the degradation of urban eco-environment and improve residents’ quality of life simultaneously, China’s central government launched the National Forest City action in 2004, which essentially promotes urban forests as nature-based solutions (UF-NBS) and contributes to achieving sustainable development goals. Whilst this key national action has been implemented for about two decades, it has received limited scholarly attention within and beyond China. This paper is the very first to summarise comprehensively the development of the action, focusing on its rationale, evaluation and management.

Recent Findings

By establishing urban forests as cost-effective solutions to various environmental and social issues, the action integrates novel knowledge and best practices accumulated in Europe and North America into China’s traditional ideology, pertinent to the human-nature relationship in urban landscape design, and further adapts and renovates these to the country’s unique socioeconomic context. It highlights the multi-functionality of urban forests underpinned by a set of key performance indicators covering both qualitative and quantitative aspects of the National Forest City’s planning, construction, management and review. Additionally, it reflects a dynamic interaction within the science-policy-practice continuum hinged on field experiments, knowledge transfer, public engagement, policy agenda and greening actions. Challenges, such as unbalanced geographical distribution and KPIs on ecological integrity and functionality of urban forests, should be addressed for further refining and scaling-up this action.

Summary

China’s National Forest City action promotes UF-NBS as a pathway to sustainable urbanisation, serving as a demonstrative exemplar for other developing and developed countries that may wish to avoid their dependence on traditional development pathways. This paper sheds light on how to implement urban forests as effective and sustainable NBS to addresses global societal challenges.

Purpose of Review

Because tree seeds have been considered a low-risk pathway for the spread of plant pathogenic fungi, their international movement is not subject to strict phytosanitary regulation. However, recent studies have provided scientific evidence that the biosecurity risk of seed trade may not be as negligible as assumed. This review summarises current knowledge about seed trade activity across the world and seed-borne plant pathogenic fungi and highlights knowledge gaps that need to be filled to mitigate the risk of spreading tree pathogens via seeds.

Recent Findings

Several outbreaks of severe tree diseases in natural forests and plantations worldwide have been linked to fungal pathogens spread by seed trade. Indeed, recent studies based on modern sequencing technologies have shown that tree seeds harbour highly diverse fungal communities, including well-known pathogens and fungal taxa belonging to unknown species. While it has become clear that even apparently healthy seeds can carry potentially pathogenic fungi, the likelihood of seed-borne pathogens being introduced and becoming established, spreading and causing impact in the new environment is still unclear which challenges the assessment of the phytosanitary risk posed by seed trade.

Summary

Our analyses show that large amounts of tree seeds have been traded among countries and continents. Based on published literature, the risk of spreading pathogenic fungi via tree seed movement is high. However, the role of the taxonomically and functionally diverse fungal communities associated with seeds is still poorly understood. In particular, more research is needed to assess the likelihood of seed-borne fungi being transmitted to the seedlings and spreading and causing impact in the new environment.

Purpose of Review

The aim of this review is to provide an overview of the functional role of large wood in the functioning of fluvial ecosystems, ranging from the scale of microhabitats to entire catchments. To this purpose, this review is structured according to the major ecosystem processes occurring at different spatial scales, ranging from the microhabitat scale, e.g. the internal processes of organic matter breakdown by microbes, to the catchment scale, e.g. the catchment-scale-processes of water flow, sediment transport, and nutrient fluxes.

Recent Findings

Recent research increasingly shows that dead wood drives a complex of multi-scaled processes. The role of large wood as a channel structuring entity and a driver of hydromorphological functioning is well known, but the importance of large wood at higher spatial scales has not been fully acknowledged. This encompasses the importance of large wood in enhancing multiple channel — floodplain interactions by creating a dynamic exchange of matter (water, sediments, nutrients) and energy. It also strengthens the water retention and storage capacity of rivers, attenuating floods and droughts and plays an important role in sediment, nutrient and organic matter interception, and processing. All these attributes contribute to ecosystem complexity and functioning, as well as providing valuable ecosystem services. Furthermore, large wood also acts as an important dispersal vector which, together with the multiple scale processes, promotes biodiversity.

Summary

Recognising the multiple scale spatial and temporal processes acting in, around, and induced by large wood can strongly support future fluvial management, especially regarding the re-introduction and way of installing of large wood in rivers. As large wood management is context-dependent, research should focus on catchment specific processes.

Abstract

Purpose of Review

The successful application of thermal infrared (TIR) remote sensing in the agricultural domain, largely driven by the arrival of new platforms and sensors that substantially increased thermal data resolution and availability, has sparked interest in thermography as a tool for monitoring forest health. In this review, we take a step back to reflect on what physiological responses are reflected in leaf and canopy temperature and summarise research activities on TIR remote sensing of stress responses in forest environments, highlighting current methodological challenges, open questions, and promising opportunities.

Recent Findings

This systematic literature review showed that whilst the focus still remains on satellite imagery, Uncrewed Aerial Vehicles (UAVs) are playing an increasingly important role in testing the capabilities and sensitivity to stress onset at the individual tree level. To date, drought stress has been the focal point of research, largely due to its direct link to stomatal functioning at leaf level. Though, research into thermal responses to other stressors, e.g. pathogens, is also gaining momentum.

Summary

Disentangling stress-induced canopy temperature variations from environmental factors and structural influences remains the main challenge for broader application of TIR remote sensing. Further development and testing of approaches for thermal data analysis, including their applicability for different tree species and sensitivity under different climatic conditions, are required to establish how TIR remote sensing can best complement existing forest health monitoring approaches.