Journal of Forestry Research最新文献

Global warming and frequent extreme drought events lead to tree death and extensive forest decline, but the underlying mechanism is not clear. In drought years, cambial development is more sensitive to climate change, but in different phenological stages, the response relationship is nonlinear. Therefore, the dynamic relationship between tree radial growth and climatic/environmental factors needs to be studied. We thus continuously monitored radial growth of Qinghai spruce (Picea crassifolia Kom.) and environmental factors from January 2021 to November 2022 using point dendrometers and portable meteorological weather stations in the central area of the Qilian Mountains. The relationship and stability between the radial growth of Qinghai spruce and environmental factors were compared for different levels of drought in 2021 and 2022. The year 2022 had higher temperatures and less precipitation and was drier than 2021. Compared with 2021, the growing period in 2022 for Qinghai spruce was 10 days shorter, maximum growth rate (Grmax) was 4.5 μm·d⁻¹ slower, and the initiation of growth was 6 days later. Growth of Qinghai spruce was always restricted by drought, and the stem radial increment (SRI) was more sensitive to precipitation and air relative humidity. Seasonal changes in cumulative radial growth were divided into four phenological stages according to the time of growth onset, cessation, and maximum growth rate (Grmax) of Qinghai spruce. Stability responses of SRI to climate change were stronger in Stage 3 and Stage 4 of 2021 and stronger in Stage 1 (initiation growth stage) and Stage 3 of 2022. The results provide important information on the growth of the trees in response to drought and for specific managing forests as the climate warms.

Changes in annual radial growth is an important indication of climate change. Dendroclimatology studies in northern China have focused on linear statistical analysis, but lacking studies based on the process of ring formation to clarify the radial growth of trees. Tree-ring width standard chronology (STD) was established using samples of Larix principis-rupprechtii collected at 2303 m altitude on Luya Mountain. Using the Vaganov-Shashkin (VS) model to simulate growth and development, the internal physiological mechanism of radial growth is identified. It was concluded that: (1) the growing season of L. principis-rupprechtii was May to September; (2) soil moisture was a significant factor in the early and late growing seasons, and temperature was the dominant factor in its main growth period; and (3) formation of narrow ring widths was closely related to drought stress, the development of wide ring widths will be restricted by increasing future temperatures. The VS model is applicable for radial growth simulation of subalpine coniferous forests and for guiding the cultivation of local tree species in the future.

Biodiversity loss is a significant problem at a global scale and may be amplified by climate change. In recent years, coniferous forests have had substantial dieback across Europe due to drought and subsequent bark-beetle outbreaks. As many studies on the consequences of disturbance and subsequent management have focused on natural stands, management implications for managed spruce stands are not well understood, even though such stands are widespread throughout Europe. In this study, beetle taxonomy, conservation value, and community composition are compared among spruce plantations and four post-disturbance management approaches: standing deadwood, lying deadwood, clear cuts, and long-term succession. Diversity and community composition differed significantly among management categories, while different beetle families responded similarly. Intact spruce stands harbored the lowest beetle diversity while the highest taxonomic diversity and conservation value was on clear cuts and stands with lying or standing deadwood. The proportion of forest specialists was highest in successional forests. In summary, different forest management categories harbored distinct beetle communities at the family-, species-, and ecological guild levels. Therefore, post-disturbance management should consider the landscape scale and include different management types. This enhances landscape heterogeneity and thus overall biodiversity but could also mitigate negative impacts of natural disturbances on ecosystem services.

The regeneration of Tetracentron sinense Oliv. is poor in the understory and in open areas due to the characteristics of natural regeneration of the species on forest edges and in gaps. It is unclear whether different light intensities in various habitats affect eco-physiological characteristics of saplings and their natural regeneration. In this study, the light intensity in T. sinense habitats was simulated by artificial shading (L1: 100% NS (natural sunlight) in the open; L2: 50% NS in a forest gap or edge; L3: 10% NS in understory) to investigate differences in morphology, leaf structure, physiology, and photosynthesis of 2-year-old saplings, and to analyze the mechanism of light intensity on sapling establishment. Significant differences were observed in morphology (including leaf area, and specific leaf area) under different light intensities. Compared to L1 and L3, chloroplast structure in L2 was intact. With increasing time, superoxide dismutase (SOD) and catalase (CAT) activities in L2 became gradually higher than under the other light intensities, while malondialdehyde (MDA) content was opposite. Shading decreased osmoregulation substance contents of leaves but increased chlorophyll. The results suggest that light intensities significantly affect the eco-physiological characteristics of T. sinense saplings and they would respond most favorably at intermediate levels of light by optimizing eco-physiological characteristics. Therefore, 50% natural sunlight should be created to promote saplings establishment and population recovery of T. sinense during in situ conservation, including sowing mature seeds in forest edges or gaps and providing appropriate shade protection for seedlings and saplings in the open.

Abstract

Recent methodological advances in quantitative wood anatomy have provided new insights into the climatic responses of radial growth at the scale of cell structure of tree rings. This study considered long-term chronologies of tracheid measurements, indexed by a novel approach to separate their specific climatic responses from signal recorded in cell production (closely reflected in tree-ring width). To fill gaps in understanding the impact of climate on conifer xylem structure, Scots pine (Pinus sylvestris L.) trees > 200 years old were selected within the forest-steppe zone in southern Siberia. Such habitats undergo mild moisture deficits and the resulting climatic regulation of growth processes. Mean and maximum values of cell radial diameter and cell wall thickness were recorded for each tree ring. Despite a low level of climatogenic stress, components of cell chronologies independent of cambial activity were separated to obtain significant climatic signals revealing the timing of the specific stages of tracheid differentiation. Cell expansion lasted from mid-April to July and was impacted similarly to tree-ring width (stimulated by precipitation and stressed by heat), maximum cell size formed late June. A switch in the climatic responses of mean anatomical traits indicated transition to latewood in mid-July. Secondary wall deposition lasted until mid-September, suppressed by end of season temperatures. Generally, anatomical climatic responses were modulated by a less dry May and September compared with summer months.

Global warming will affect growth strategies and how trees will adapt. To compare the response of tree radial growth to climate warming in different slope directions, samples of Pinus armandii Franch were collected and tree-ring chronologies developed on northern and western slopes from the Lubanling in the Funiu Mountains. Correlation analyses showed that two chronologies were mainly limited by temperatures in the previous June–August and the combination of temperatures and moisture in the current May–July. The difference of the climate response to slopes was small but not negligible. Radial growth of the LBL01 site on the northern slope was affected by the combined maximum and minimum temperatures, while that of the LBL02 site was affected by maximum temperatures. With regards to moisture, radial growth of the trees on the north slope was influenced by the relative humidity in the current May–July, while on the western slope, it was affected by the relative humidity in the previous June–August, the current May–July and the precipitation in the current May–July. With the change in climate, the effects of the main limiting factors on growth on different slopes were visible to a certain extent, but the differences in response of trees on different slopes gradually decreased, which might be caused by factors such as different slope directions and the change in diurnal temperature range. These results may provide information for forest protection and ecological construction in this region, and a scientific reference for future climate reconstruction.

In our previous screening of the transcriptome of the causal agent of the devastating pine wilt disease, pine wood nematode (PWN, Bursaphelenchus xylophilus), after treatment with the nematicide fomepizole, Surfeit locus gene sft-4, which encodes a regulatory factor, was found to be downregulated. In situ hybridization results showed that the sft-4 was continuously expressed from egg to adult and was especially high in the reproductive system. Here in a study of the effect of RNA interference (RNAi) of sft-4 and recombinant SFT-4 on PWN activity, treatment with sft-4 dsRNA inhibited feeding, reproduction, oviposition and egg hatching of PWN with the greatest inhibition on reproduction and oviposition, whereas recombinant SFT-4 had the opposite effect. In addition, RNAi of sft-4 changed the female–male ratio and lifespan of PWN. In bioassays of PWNs, with RNAi of sft-4 on seedlings and 2-year-old Pinus thunbergii trees, none of the treated plants developed symptoms during the monitoring period, indicating that virulence of PWNs was either significantly weakened. These results indicate that the influence of sft-4 on PWN pathogenicity may be mainly through regulating reproductive function of PWN and its lifespan.

Soil pedestals have long been used as qualitative indicators of soil splash erosion. In rangelands, plant-capped pedestals, generally grass tussocks, have also been used to quantitatively estimate soil loss since the first half of the twentieth century. In agricultural lands, forests, and badlands, stone-capped pedestals have been used as qualitative and semi-quantitative indicators of active, ‘extreme’ erosion. Little work has been reported on using capstone pedestal data for quantifying soil loss. We postulate that three distinct capstone pedestal types may be present in any given location and that a detailed analysis of a pedestal height histogram may be used to recognize their populations. This analysis can subsequently inform if soil loss can be reliably estimated and if so, which of the existing methods using pedestal height data will provide more accurate results. The three proposed capstone pedestal types are: (1) neo-pedestals formed underneath surface stones exposed by (partial) removal of the soil surface cover; (2) endo-pedestals formed underneath stones that were buried in the soil but have been exposed by erosion; and (3) phoenix-pedestals formed underneath stones from collapsed pedestals. In the pedestal height histogram of any given location, a skew to smaller heights may indicate the existence of endo- and/or phoenix-pedestals, which may be revealed as a bi-(or tri) modal distribution when using a smaller bin size. This concept was applied to a case study where soil loss had been monitored for control plots and mulched plots during a 5-year period following wildfire in a eucalypt plantation. We measured pedestal heights and used methods to quantitatively assess soil loss from soil pedestal data in the available literature. Soil pedestal data at the end of the 5-year period under or overestimated soil loss in the control treatment, with results ranging from 60 to 115% of measured soil loss, depending on the method. It is postulated that phoenix- and endo-pedestals may be a driving factor behind the observed discrepancies. We discuss how future research may provide more insight into dominant processes, and how frequency distributions may be used to select the best methods for estimating soil loss from pedestals.

Understanding the relationship between forest management and water use efficiency (WUE) is important for evaluating forest adaptability to climate change. However, the effects of thinning and understory removal on WUE and its key controlling processes are not well understood, which limits our comprehension of the physiological mechanisms of various management practices. In this study, four forest management measures (no thinning: NT; understory removal: UR; light thinning: LT; and heavy thinning: HT) were carried out in Pinus massoniana plantations in a subtropical region of China. Photosynthetic capacity and needle stable carbon isotope composition (δ¹³C) were measured to assess instantaneous water use efficiency (WUE_inst) and long-term water use efficiency (WUE_i). Multiple regression models and structural equation modelling (SEM) identified the effects of soil properties and physiological performances on WUE_inst and WUE_i. The results show that WUE_inst values among the four treatments were insignificant. However, compared with the NT stand (35.8 μmol·mol⁻¹), WUE_i values significantly increased to 41.7 μmol·mol⁻¹ in the UR, 50.1 μmol·mol⁻¹ in the LT and 46.6 μmol·mol⁻¹ in HT treatments, largely explained by photosynthetic capacity and soil water content. Understory removal did not change physiological performance (needle water potential and photosynthetic capacity). Thinning increased the net photosynthetic rate (A_n) but not stomatal conductance (g_s) or predawn needle water potential (ψ_pd), implying that the improvement in water use efficiency for thinned stands was largely driven by radiation interception than by soil water availability. In general, thinning may be an appropriate management measure to promote P. massoniana WUE to cope with seasonal droughts under future extreme climates.

Extreme climate has increasingly led to negative impacts on forest ecosystems globally, especially in semiarid areas where forest ecosystems are more vulnerable. However, it is poorly understood how tree growth is affected by different drought events. In 2006–2009, the larch plantations in the semiarid areas of Northwest China were negatively affected by four consecutive dry years, which was a very rare phenomenon that may occur frequently under future climate warming. In this study, we analyzed the effect of these consecutive dry years on tree growth based on the data of the tree rings in the dominant layer of the forest canopy on a larch plantation. We found that the tree-ring width index (RWI) in dry years was lower than that in normal years, and it experienced a rapidly decreasing trend from 2006 to 2009 (slope = − 0.139 year⁻¹, r = − 0.94) due to water supply deficits in those dry years. Drought induced legacy effects of tree growth reduction, and consecutive dry years corresponded with greater growth reductions and legacy effects. Growth reductions and legacy effects were significantly stronger in the third and fourth consecutive dry years than that of single dry year (p < 0.05), which might have been due to the cumulative stress caused by consecutive dry years. Our results showed that larch trees experienced greater tree growth reduction due to consecutive dry years and their legacy effect, and the trees had lower recovery rates after consecutive dry years. Our results highlight that consecutive dry years pose a new threat to plantations under climate warming, and thus, the effect of climate extremes on tree growth should be considered in growth models in semiarid areas.