Annals of Forest Science最新文献

Key message

A novel periodic site index is introduced for the quantification of dynamic forest site productivity. The measure is age-independent, sensitive to environmental changes and efficient for the estimation and prediction of stand height and stand volume increment.

Context

Accurate and up-to-date prediction of site productivity is crucial for the sustainable management of forest ecosystems, especially under environmental changes.

Aims

The aim of this study was to introduce a novel concept: a periodic site index based on growth-effective age for the quantification of dynamic forest site productivity.

Methods

The growth-effective age based periodic site index is estimated from repeated or multi-temporal measurements of stand dominant height. Furthermore, a recursive procedure to update the underlying site index model is presented by using repeated measurements of stand dominant height. The database used in this study comprised repeated measurements of 945 Norway spruce (Picea abies L.) experimental plots at 508 different locations in Southwest Germany.

Results

The evaluation shows that periodic site index is statistically superior to the conventional site index, based on chronological stand age, for estimating stand height and stand volume increment. The analysis of temporal differences between growth-effective stand age and chronological stand age and between periodic site index and conventional site index in the period 1900 to 2020 reveals trends referring to stand age and site productivity, which corroborate earlier regional studies on forest growth trends due to environmental changes.

Conclusions

The periodic site index is a better indicator for site productivity than conventional site index. Under conditions of environmental changes, conventional site index is biased, whereas the growth-effective age based site index provides an unbiased estimate of stand height development. With the more widespread application of remote sensing techniques, such as airborne laser scanning, the availability of multi-temporal stand height data will increase in the near future. The novel concept provides an adaptive modeling approach perfectly suited to these data for an improved estimation and prediction of forest site productivity under environmental changes and can straightforwardly be applied also to uneven-aged and multi-species stands.

Key message

Data acquisition of remote sensing products is an essential component of modern forest inventories. The quality and properties of optical remote sensing data are further emphasised in tree species-specific inventories, where the discrimination of different tree species is based on differences in their spectral properties. Furthermore, phenology affects the spectral properties of both evergreen and deciduous trees through seasons. These confounding factors in both sensor configuration and timing of data acquisition can result in unexpectedly complicated situations if not taken into consideration. This paper examines how the timing of data acquisition and sensor properties influence the prediction of tree species proportions and volumes in a boreal forest area dominated by Norway spruce and Scots pine, with a smaller presence of deciduous trees.

Context

The effectiveness of remote sensing for vegetation mapping depends on the properties of the survey area, mapping objectives and sensor configuration.

Aims

The objective of this study was to investigate the plot-level relationship between seasonality and different optical band configurations and prediction performance of common boreal tree species. The study was conducted on a 40-ha study area with a systematically sampled circular field plots.

Methods

Tree species proportions (0–1) and volumes (m³ ha⁻¹) were predicted with repeated remote sensing data collections in three stages of the growing season: prior (spring), during (summer) and end (autumn). Sensor band configurations included conventional RGB and multispectral (MS). The importance of different wavelengths (red, green, blue, near-infrared and red-edge) and predictive performance of the different band configurations were analysed using zero–one-inflated beta regression and Gaussian process regression.

Results

Prediction errors of broadleaves were most affected by band configuration, MS data resulting in lower prediction errors in all seasons. The MS data exhibited slightly lower prediction errors with summer data acquisition compared to other seasons, whereas this period was found to be less suitable for RGB data.

Conclusion

The MS data was found to be much less affected by seasonality than the RGB data. Spring was found to be the least optimal season to collect MS and RGB data for tree species-specific predictions.

Key message

Winter reddening of young Douglas-fir (Pseudotsuga menziesii Mirb. Franco), triggered by large thermal fluctuations in late winter, is a critical problem for European forestry. A literature review identified certain climatic conditions that are characteristic of ‘reddening’ years, including warm daily temperatures, high daily temperature amplitude, low relative humidity, moderate wind speeds, as well as the occurrence of freeze-thaw cycles with cold night temperatures.

By describing the triggering environmental and stand factors, we propose three hypotheses for the physiological processes leading to winter reddening, namely (i) hydraulic failure due to winter drought stress, (ii) photo-oxidative stress in shade-acclimated trees, and (iii) early cold deacclimation during warm periods.

i) Low soil temperature, by reducing root water uptake, combined with anticyclonic conditions, by increasing water losses, can induce hydraulic failure in the xylem. Hydraulic failure may be further accelerated by night frosts.

ii) Winter reddening can occur when low temperature and high irradiance coincide, disrupting photostasis. Overwhelming of winter photo-protection may lead to photodamage and subsequent reddening.

iii) Warm periods, by inducing cold deacclimation, make trees susceptible to frost damage.

Finally, the three processes may interact under atypical anticyclonic conditions in late winter (e.g. cold or dry soils, warm days, high irradiance and/or freezing nights). Indeed, trees under water stress would develop a higher sensitivity to freezing night and photooxidative stress. We therefore proposed mitigation actions to avoid exposing trees to stressful conditions based on e.g. stand characteristics, understorey vegetation and planting.

Key message

The elapsed times to deplete starch concentrations and to reach a null hydraulic safety margin were related to tree seedling mortality under experimental drought. Starch concentration showed an accelerated decline across all species during the early stages of dehydration, while the concentrations of soluble sugars and total nonstructural carbohydrates remained stable. Concomitant carbohydrate depletion and hydraulic failure drive seedling mortality under drought.

Context

Current upsurges of drought events are provoking impacts on tree physiology, resulting in forest mortality. Hydraulic dysfunction and nonstructural carbohydrate (NSC) depletion have been posited as the main mechanisms leading to plant mortality under drought.

Aims

This study explores the dynamics of the two mortality-inducing processes during drought stress using an experimental approach with 12 evergreen tree species.

Methods

Seedlings were subjected to drought until 100% mortality was observed. Midday (Ψ_MD) and predawn (Ψ_PD) water potentials, xylem pressure leading to a 50% loss of hydraulic conductivity (Ψ₅₀), along with NSC concentrations in different organs (leaves, stems, and roots) were measured regularly during drought.

Results

Total NSC concentrations and soluble sugar pools did not decline during drought. However, starch pools showed strong reductions early during drought stress as Ψ_PD decreased, and the time leading to starch depletion emerged as a strong mortality predictor. Ψ₅₀ alone did not provide an accurate estimate of mortality, while the elapsed time to reach a null hydraulic safety margin (Ψ_MD—Ψ₅₀ = 0) was related to seedling mortality.

Conclusion

Adopting a dynamic approach by estimating the times to consume both starch reserves and hydraulic safety margins is highly relevant to improve predictions of tree mortality under the current context of increasing global drought.

Key Message

Understanding the impact of extreme drought on the canopy fuel moisture content (CFMC) is crucial to anticipate the effects of climate change on wildfires. Our study demonstrates that foliage mortality, caused by leaf embolism, can substantially diminish CFMC during drought on Pinus halepensis Mill. and Quercus ilex L. It emphasizes the importance of considering plant hydraulics to improve wildfire predictions.

Context

Canopy fuel moisture content (CFMC), which represents the water-to-dry mass ratio in leaves and fine twigs within the canopy, is a major factor of fire danger across ecosystems worldwide. CFMC results from the fuel moisture content of living foliage (live fuel moisture content, LFMC) and dead foliage (dead fuel moisture content, DFMC) weighted by the proportion of foliage mortality in the canopy (α_Dead). Understanding how LFMC, α_Dead, and ultimately CFMC are affected during extreme drought is essential for effective wildfire planning.

Aims

We aimed to understand how plant hydraulics affect CFMC for different levels of soil water deficit, examining its influence on both LFMC and α_Dead.

Methods

We conducted a drought experiment on seedlings of two Mediterranean species: Aleppo pine (Pinus halepensis Mill.) and Holm oak (Quercus ilex L.). Throughout the drought experiment and after rewatering, we monitored CFMC, LFMC, and α_Dead along with other ecophysiological variables.

Results

LFMC exhibited a significant decrease during drought, and as leaf water potentials reached low levels, α_Dead increased in both species, thereby reducing CFMC. Distinct water use strategies resulted in species-specific variations in dehydration dynamics.

Conclusion

Our findings demonstrate that as drought conditions intensify, foliage mortality might become a critical physiological factor driving the decline in CFMC.

Key Message

As the number and extent of wildfires are increasing due to climate change and human impacts, the demand for effective risk reduction strategies is growing. Due to limited resources or management capabilities in Slovakia, appropriate multistakeholder participation could help decrease the risk of wildfires while continuing to implement the principles of sustainable forest management. Thus, we recommend improving relationships with responsible stakeholders and increasing their knowledge.

Context

Although the frequency of wildfires has declined in Slovakia, the total burned area per year and the average burned area per fire have increased rapidly, mainly due to traditional land management and increasing numbers of natural disasters resulting from climate change.

Aim

The objective of this study is to assess the participation and management of stakeholders in the region of Podpoľanie, which is the region of Slovakia that is most prone to wildfires. In particular, this study investigates the questions of who is accountable, in what networks, and with regard to what issues with the goal of enhancing efforts to combat wildfires.

Methods

This single-country case study features an exploratory sequential mixed-methods design. While stakeholders’ participation was explored via face-to-face interviews and interest-influence matrices, stakeholders’ prioritization was assessed via an online survey and the quantitative mapping of stakeholders’ involvement, power, interest, and knowledge.

Results

We separately identified primary stakeholders (e.g., fire departments and state-owned forest enterprises) and secondary stakeholders (e.g., municipalities and community members). Tasks related to efforts to combat wildfires were largely in compliance with legal regulations and other mandates. Nonetheless, some stakeholders (e.g., governmental organizations involved in nature protection or nonstate forest owners and the associated enterprises) lacked the knowledge, experience, or responsibility necessary to perform these tasks.

Conclusion

These stakeholders should be informed and monitored closely to achieve outcomes that can benefit a variety of stakeholders. We recommend a plan that involves improving the relationships among primary and secondary stakeholders, increasing their knowledge, and promoting effective participation to decrease the risk of wildfires in the region.

Key Message

We present data from a new delimited 1-ha forest plot on the Sierra Nevada de Santa Marta in Colombia and describe its tree diversity, composition, and structure. This data can be used in regional analyses and help to refine remote sensing models. Future censuses will provide data on the demographics of rare, endangered, and endemic trees that can be used for their conservation. Dataset access is at https://doi.org/10.15472/ftwol2. Associated metadata are available at https://metadata-afs.nancy.inra.fr/geonetwork/srv/fre/catalog.search#/metadata/a4a7855f-4cb2-459b-a1a2-287bd1e6d587.

Key message

A Soil Monitoring Law to improve soil health across all land uses has been proposed by the European Commission. As forests soils have different chemical and physical properties as well as biogeochemical dynamics compared to agricultural land, they also face different challenges in maintaining and restoring soil health. Examples are soil acidification, eutrophication by atmospheric deposition, responses to climate change, and loss of biodiversity. Therefore, we propose forest soil specific health descriptors and thresholds based on experience and knowledge from existing long-term monitoring programs.

Key message

A validation convention can be established for forest management optimization models. It consists of (1) the delivery of face validation, (2) performing at least one other validation technique, and (3) an explicit discussion of how the optimization model fulfills the stated purpose. Validation by potential users or external experts is of high importance.

Context

Optimization modeling has long assisted the management of forest ecosystems, but the credibility of these models has always been debated with criticisms concerning data quality, failures to include relevant processes in the scope of models, and the inclusion of unrealistic assumptions. Validation is widely considered to be crucial to establishing the credibility of models in general, but how to validate optimization models in particular represents a permanent question generally in operations research.

Aims

We aim to synthesize practical recommendations for the development of validation frameworks in the optimization modeling for forest management.

Methods

We selected a sample of 46 studies devoted to optimization models to be applied in practice, analysed the contents with respect to validation, and provided a critical review.

Results

We (1) clarified the meaning and usage of different validation-related terms that are commonly encountered in the literature, (2) identified and categorised the various methods and frameworks that are used to demonstrate model credibility, and (3) derived organizing principles that helped to suggest improvements in validation frameworks.

Conclusions

A practical validation convention can be established and we suggest the convention to consist of three stages. By providing structured and consistent information about validation processes, researchers in forest management optimization can better demonstrate the credibility of their work to readers and potential users.