Modern forestry is gradually moving towards man-made forests on a large scale. Plantations with advanced forestry system have been introduced with the goal of sustainable forestry development and to ...enhance social, ecological, and economic benefits. Forest plantations with native and exotic species have been established in China and worldwide with shorter rotation cycles than natural forests. In this paper, we discuss the role and perspectives of plantation forests in the Chinese sustainable forest development, the evolution of various plantation programs, the ecological effects of plantations, and the measures to improve plantation forestry. The Chinese government has given substantial importance to nurturing plantation forest resources through various large scale afforestation programs. In 2019, the total area covered by plantations in China reached 79.54 million ha, with a stock volume of 3.39 billion m³ (59.30 m³ per ha); coniferous forests (26.11 million ha, 32.83%) and broad-leaved forests (26.45 million ha, 33.25%) are the dominant types. Plantations have been primarily distributed in the central and southern parts of the country. Plantations with fast-growing and high-yielding tree species facilitated Chinese afforestation activities and improved the administration of forest production, which effectively boosted the forest industry. Plantation forest resources offer many potential productive, economic, and social advantages, though they are also associated with a loss of biodiversity and climate change makes them likely susceptible to disease and insect attack. Appropriate forest management practices during planning, execution, and maintenance of plantations can contribute to the conservation, promotion, and restoration of biodiversity, with the final aim of attaining a balance between having forest plantations and natural forests.
Background
The local pivotal method (LPM) utilizing auxiliary data in sample selection has recently been proposed as a sampling method for national forest inventories (NFIs). Its performance compared ...to simple random sampling (SRS) and LPM with geographical coordinates has produced promising results in simulation studies. In this simulation study we compared all these sampling methods to systematic sampling. The LPM samples were selected solely using the coordinates (LPMxy) or, in addition to that, auxiliary remote sensing-based forest variables (RS variables). We utilized field measurement data (NFI-field) and Multi-Source NFI (MS-NFI) maps as target data, and independent MS-NFI maps as auxiliary data. The designs were compared using relative efficiency (RE); a ratio of mean squared errors of the reference sampling design against the studied design. Applying a method in NFI also requires a proven estimator for the variance. Therefore, three different variance estimators were evaluated against the empirical variance of replications: 1) an estimator corresponding to SRS; 2) a Grafström-Schelin estimator repurposed for LPM; and 3) a Matérn estimator applied in the Finnish NFI for systematic sampling design.
Results
The LPMxy was nearly comparable with the systematic design for the most target variables. The REs of the LPM designs utilizing auxiliary data compared to the systematic design varied between 0.74–1.18, according to the studied target variable. The SRS estimator for variance was expectedly the most biased and conservative estimator. Similarly, the Grafström-Schelin estimator gave overestimates in the case of LPMxy. When the RS variables were utilized as auxiliary data, the Grafström-Schelin estimates tended to underestimate the empirical variance. In systematic sampling the Matérn and Grafström-Schelin estimators performed for practical purposes equally.
Conclusions
LPM optimized for a specific variable tended to be more efficient than systematic sampling, but all of the considered LPM designs were less efficient than the systematic sampling design for some target variables. The Grafström-Schelin estimator could be used as such with LPMxy or instead of the Matérn estimator in systematic sampling. Further studies of the variance estimators are needed if other auxiliary variables are to be used in LPM.
Recent climate warming has fueled interest into climate‐driven range shifts of tree species. A common approach to detect range shifts is to compare the divergent occurrences between juvenile and ...adult trees along environmental gradients using static data. Divergent occurrences between life stages can, however, also be caused by ontogenetic effects. These include shifts of the viable environmental conditions throughout development (‘ontogenetic niche shift') as well as demographic dependencies that constrain the possible occurrence of subsequent life stages. Whether ontogenetic effects are an important driver of divergent occurrences between juvenile and adult trees along large‐scale climatic gradients is largely unknown. It is, however, critical in evaluating whether impacts of environmental change can be inferred from static data on life stage occurrences. Here, we first show theoretically, using a two‐life stage simulation model, how both temporal range shift and ontogenetic effects can lead to similar divergent occurrences between adults and juveniles (juvenile divergence). We further demonstrate that juvenile divergence can unambiguously be attributed to ontogenetic effects, when juveniles diverge from adults in opposite direction to their temporal shift along the environmental gradient. Second, to empirically test whether ontogenetic effects are an important driver of divergent occurrences across Europe, we use repeated national forest inventories from Sweden, Germany and Spain to assess juvenile divergence and temporal shift for 40 tree species along large‐scale climatic gradients. About half of the species‐country combinations had significant juvenile divergences along heat sum and water availability gradients. Only a quarter of the tree species had significant detectable temporal shifts within the observation period. Furthermore, significant juvenile divergences were frequently associated with opposite temporal shifts, indicating that ontogenetic effects are a relevant cause of divergent occurrences between life stages. Our study furthers the understanding of ontogenetic effects and challenges the practice of inferring climate change impacts from static data.
Aim: The aim was to examine whether recent mortality can be explained by hydraulic failure linked to water deficit. Location: Western Europe. Time period: 1986–2014. Major taxa studied: Forty-four ...tree species. Methods: We modelled the hydraulic safety margin (HSM) across the ranges of 44 tree species at their driest margin (n = 193,261 plots), defined as the difference between the estimated minimal soil water potential of each plot and the species water stress threshold, which corresponds to the hydraulic failure of the vascular system. Soil water potential was estimated by applying Campbell's equations on the minimal and maximal soil water contents estimated from 1979 to 2010 in the top 289 cm of soil and five soil textures across the species ranges. For each species, we modelled the amount of average mortality derived from plots of the Spanish and French National Forest Inventories to the variation in modelled hydraulic safety margin and environmental drivers across the species ranges using hurdle models. Results: We did not identify any global convergence of modelled HSM within the species distribution ranges, finding instead a rather large variability in modelled HSM for most of the studied species. Fifteen species, out of 25 for which the models were practicable, showed significantly higher mortality in populations with negative HSM in comparison to those showing positive HSM, with positive and negative interaction along the aridity index. Main conclusions: The combination of competition, average climate and modelled HSM explained average tree mortality. Most of the species presented at least one population that had already experienced a negative HSM and many other populations a positive but narrow HSM, suggesting that climate change is likely to push some populations towards a higher risk of hydraulic failure in the drier conditions projected for Western Europe.
Abstract
Disturbed African tropical forests and woodlands have the potential to contribute to climate change mitigation. Therefore, there is a need to understand how carbon stocks of disturbed and ...recovering tropical forests are determined by environmental conditions and human use. In this case study, we explore how gradients in environmental conditions and human use determine aboveground biomass (AGB) in 1958 national forest inventory (NFI) plots located in forests and woodlands in mainland Tanzania. Plots were divided into recovering forests (areas recovering from deforestation for <25years) and established forests (areas consistently defined as forests for ⩾25 years). This division, as well as the detection of year of forest establishment, was obtained through the use of dense satellite time series of forest cover probability. In decreasing order of importance, AGB in recovering forests unexpectedly decreased with water availability, increased with surrounding tree cover and time since establishment, and decreased with elevation, distance to roads, and soil phosphorus content. AGB in established forests unexpectedly decreased with water availability, increased with surrounding tree cover, and soil nitrogen content, and decreased with elevation. AGB in recovering forests increased by 0.4 Mg ha
−1
yr
−1
during the first 20 years following establishment. Our results can serve as the basis of carbon sink estimates in African recovering tropical forests and woodlands, and aid in forest landscape restoration planning.
The timely and accurate monitoring of forest resources is becoming of increasing importance in light of the multi-functionality of these ecosystems and their increasing vulnerability to climate ...change. Remote sensing observations of tree cover and systematic ground observations from National Forest Inventories (NFIs) represent the two major sources of information to assess forest area and use. The specificity of two methods is calling for an in-depth analysis of their strengths and weaknesses and for the design of novel methods emerging from the integration of satellite and surface data. On this specific debate, a recent paper by Breidenbach et al. published in this journal suggests that the detection of a recent increase in EU forest harvest rate—as reported in Nature by Ceccherini et al.—is largely due to technical limitations of satellite-based mapping. The article centers on the difficulty of the approaches to estimate wood harvest based on remote sensing. However, it does not discuss issues with the robustness of validation approaches solely based on NFIs. Here we discuss the use of plot data as a validation set for remote sensing products, discussing potentials and limitations of both NFIs and remote sensing, and how they can be used synergistically. Finally, we highlight the need to collect in situ data that is both relevant and compatible with remote sensing products within the European Union.
National Forest Inventories (NFIs) collect and provide a large amount of information regarding the forest volume, carbon stocks, vitality, biodiversity, non-wood forest products and their changes. ...Forest stands variables data are paramount to understanding their composition, especially on those related with understory characteristics and the coverage of species according to canopy layers; they are essential to assess biodiversity and to support forest management. At the same time, these inventories allow the development of harmonized forest descriptions beyond the national scale. This study aims to develop a homogeneous characterization of the Iberian Peninsula’s forests, in order to classify and identify the forest types. For this purpose, harmonized data from NFIs of Portugal and Spain were used to assess the composition of species, dominance and the percentage of cover for each species in a vertical space defined by seven canopy layers. Using the “K-means” clustering algorithm, a set of clusters was identified and georeferenced using forest polygons from land use and cover maps of both countries. The interpretation and description of the clusters lead to the establishment of 28 forest types that characterize all of the Iberian Peninsula forests. Each forest area has been described through one of the forest types and their relation with other ecological characteristics of the stands was analyzed. Shrubs formations are generally widely distributed in the forest area of the Iberian Peninsula, however their abundance in terms of cover is lower in comparison with tree species. Around 71% of the forest types are dominated by trees, mainly species from the genera Pinus and Quercus, and 21% are dominated by shrub formations with species of Ulex spp., Cytisus spp., and Cistus spp. The Quercus ilex s.l. L. and Pinus pinaster Aiton are the common species of importance for both NFIs. The results represent a powerful and homogenous multi-use tool describing the Iberian Peninsula’s forestlands with applications on landscape analysis, forest management and conservation. This information can be used for comparisons at larger scales, allowing cross-border analysis in relation to various aspects, such as hazards and wildfires, as well as management and conservation of forest biodiversity. The developed method is adaptable to an updated dataset from more recent NFIs and to other study areas.
•Broad-scale forest surveys are suitable tools for monitoring plant invasions in forests.•Acacia dealbata and Acacia melanoxylon showed annual spread rates of 0.1% and 0.08%.•Acacia species are ...increasing their dominance, becoming the dominant species in the regeneration.•Acacia species exhibit an early stage of invasion, so future spread is expected.•Environmental factors and connectivity are the major spread constraints.•Disturbances and biotic factors also influence forest invasibility.
Invasive species currently pose a major environmental challenge. Understanding their development and the factors associated with their expansion is the first step towards developing effective control measures. This work proposes the use of detailed spatio-temporal information from forest monitoring systems to assess the demographic rates, spatio-temporal patterns and spread determinants of invasive plants in forest ecosystems. For this purpose, we selected two of the most widespread non-native plants in Europe: Acacia dealbata and Acacia melanoxylon. Focusing on the forested area of northwest Spain and based on the comparison of two cycles of the Spanish National Forest Inventory, this study analyzes the dynamics of Acacia species between 1998 and 2008 in regards to changes in their spatial distribution, dominance, abundance, diametrical (dbh) structure and regeneration. In addition, the forested area was classified into forest types to identify the forests which are more susceptible to invasion. Finally, through general linear models, this study analyzes the relative importance of abiotic and biotic factors determining the spread of Acacia species over the studied period. The results confirm a rapid expansion in the presence of Acacia species in the forests of NW Spain, with annual spread rates around 0.1%. These two species are increasing their dominance across most forest types in the study area, where they are becoming the dominant species in the regeneration of some of them. Environmental factors and connectivity between Acacia populations are identified as the main factors associated with their spread into new areas. Additionally, the combination of disturbances and biotic factors associated with stand structure (total basal area, richness and tree cover) appear to determine the vulnerability or resistance of some forest to their spread. The early stage of invasion detected highlights the potential of Acacia species to continue spreading. This aspect, in conjunction with the high degree of disturbances (mainly fires) in this region, could be critical in determining the configuration of future forest landscapes in NW Spain. This study demonstrates the value of considering broad-scale periodic forest surveys to monitor biological invasions in forests ecosystems. The spatially-explicit data obtained from these surveys can contribute not only to furthering our knowledge with regard to invasion biology but also to developing more efficient conservation and management strategies.
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