Journal of Forestry Research最新文献

As one of the regions most affected by global climate warming, the Tianshan mountains has experienced several ecological crises, including retreating glaciers and water deficits. Climate warming in these mountains is considered mainly to be caused by increases in minimum temperatures and winter temperatures, while the influence of maximum temperatures is unclear. In this study, a 300-year tree-ring chronology developed from the Western Tianshan Mountains was used to reconstruct the summer (June–August) maximum temperature (T_max6–8) variations from 1718 to 2017. The reconstruction explained 53.1% of the variance in the observed T_max6–8. Over the past 300 years, the T_max6–8 reconstruction showed clear interannual and decadal variabilities. There was a significant warming trend (0.18 °C/decade) after the 1950s, which was close to the increasing rates of the minimum and mean temperatures. The increase in maximum temperature was also present over the whole Tianshan mountains and its impact on climate warming has increased. The T_max6-8 variations in the Western Tianshan mountains were influenced by frequent volcanic eruptions combined with the influence of solar activity and the summer North Atlantic Oscillation. This study reveals that climate warming is significantly influenced by the increase in maximum temperatures and clarifies possible driving mechanisms of temperature variations in the Western Tianshan mountains which should aid climate predictions.

Native grasslands in the Pampas of South America are increasingly being replaced by Eucalyptus and Pinus stands. The short rotation regimes used for the stands require high nutrient levels, with litterfall being a major source of nutrient return. To model the litterfall production using climatic variables and assess the nutrient return in 14-year-old Eucalyptus grandis and Pinus taeda stands, we measured litter production over 2 years, using conical litter traps, and monitored climatic variables. Mean temperature, accumulated precipitation, and mean maximum vapor pressure deficit at the seasonal level influenced litterfall production by E. grandis; seasonal accumulated precipitation and mean maximum temperature affected litterfall by P. taeda. The regression tree modeling based on these climatic variables had great accuracy and predictive power for E. grandis (N = 33; MAE (mean absolute error) = 0.65; RMSE (root mean square error) = 0.91; R² = 0.71) and P. taeda (N = 108; MAE = 1.50; RMSE = 1.59; R² = 0.72). The nutrient return followed a similar pattern to litterfall deposition, as well as the order of importance of macronutrients (E. grandis: Ca > N > K > Mg > P; P. taeda: N > Ca > K > Mg > P) and micronutrients (E. grandis and P. taeda: Mn > Fe > Zn > Cu) in both species. This study constitutes a first approximation of factors that affect litterfall and nutrient return in these systems.

Tree radial growth can have significantly different responses to climate change depending on the environment. To elucidate the effects of climate on radial growth and stable carbon isotope (δ¹³C) fractionation of Qinghai spruce (Picea crassifolia), a widely distributed native conifer in northwestern China in different environments, we developed chronologies for tree-ring widths and δ¹³C in trees on the southern and northern slopes of the Qilian Mountains, and analysed the relationship between these tree-ring variables and major climatic factors. Tree-ring widths were strongly influenced by climatic factors early in the growing season, and the radial growth in trees on the northern slopes was more sensitive to climate than in trees on the southern. Tree-ring δ¹³C was more sensitive to climate than radial growth. δ¹³C fractionation was mainly influenced by summer temperature and precipitation early in the growing season. Stomatal conductance more strongly limited stable carbon isotope fractionation in tree rings than photosynthetic rate did. The response between tree rings and climate in mountains gradually weakened as climate warmed. Changes in radial growth and stable carbon isotope fractionation of P. crassifolia in response to climate in the Qilian Mountains may be further complicated by continued climate change.

Existing streamflow reconstructions based on tree-ring analysis mostly rely on species from upland, mainly montane areas, while lowland species (generally plain) areas are rarely used. This limits the understanding of streamflow change history in the lowlands, which is an important basis for water resource management. This study focused on Populus euphratica stands located along the main stream, eastern and western tributaries in the lower reaches of the Heihe River basin (HRb), in arid northwestern China. We investigated how streamflow regulation interferes with riparian trees in lowlands when they used for streamflow reconstruction. Tree-ring width chronologies were developed and analyzed in conjunction with meteorological and hydrologic observation data. The results show streamflow regulation leads in sharp fluctuations in the streamflow allocation between the eastern tributaries and western tributaries. This resulted in instability of the correlation between streamflow at the two tributaries and at the Zhengyixia hydrologic station, with corresponding fluctuations in radial growth of poplar trees on the banks of the two tributaries and at the station. Streamflow regulation altered the natural patterns of seasonal streamflow below the station, changing the time window of poplar response. This study provides useful insight into tree-ring width based streamflow reconstruction in the lowlands.

Since the launch of the Google Earth Engine (GEE) cloud platform in 2010, it has been widely used, leading to a wealth of valuable information. However, the potential of GEE for forest resource management has not been fully exploited. To extract dominant woody plant species, GEE combined Sentinel-1 (S1) and Sentinel-2 (S2) data with the addition of the National Forest Resources Inventory (NFRI) and topographic data, resulting in a 10 m resolution multimodal geospatial dataset for subtropical forests in southeast China. Spectral and texture features, red-edge bands, and vegetation indices of S1 and S2 data were computed. A hierarchical model obtained information on forest distribution and area and the dominant woody plant species. The results suggest that combining data sources from the S1 winter and S2 yearly ranges enhances accuracy in forest distribution and area extraction compared to using either data source independently. Similarly, for dominant woody species recognition, using S1 winter and S2 data across all four seasons was accurate. Including terrain factors and removing spatial correlation from NFRI sample points further improved the recognition accuracy. The optimal forest extraction achieved an overall accuracy (OA) of 97.4% and a map-level image classification efficacy (MICE) of 96.7%. OA and MICE were 83.6% and 80.7% for dominant species extraction, respectively. The high accuracy and efficacy values indicate that the hierarchical recognition model based on multimodal remote sensing data performed extremely well for extracting information about dominant woody plant species. Visualizing the results using the GEE application allows for an intuitive display of forest and species distribution, offering significant convenience for forest resource monitoring.

Interest in the dynamics of soil respiration (R_s) in subalpine forest ecosystems is increasing due to their high soil carbon density and potential sensitivity to environmental changes. However, as a principal silvicultural practice, the long-term impacts of thinning on R_s and its heterotrophic and autotrophic respiration components (R_h and R_a, respectively) in subalpine plantations are poorly understood, especially in winter. A 3-year field observation was carried out with consideration of winter CO₂ efflux in middle-aged subalpine spruce plantations in northwestern China. A trenching method was used to explore the long-term impacts of thinning on R_s, R_h and R_a. Seventeen years after thinning, mean annual R_s, R_h and R_a increased, while the contribution of R_h to R_s decreased with thinning intensity. Thinning significantly decreased winter R_s because of the reduction in R_h but had no significant effect on R_a. The temperature sensitivity (Q₁₀) of R_h and R_a also increased with thinning intensity, with lower Q₁₀ values for R_h (2.1–2.6) than for R_a (2.4–2.8). The results revealed the explanatory variables and pathways related to R_h and R_a dynamics. Thinning increased soil moisture and nitrate nitrogen (({text{NO}}_{3}^{ - })-N), and the enhanced nitrogen and water availability promoted R_h and R_a by improving fine root biomass and microbial activity. Our results highlight the positive roles of ({text{NO}}_{3}^{ - })-N in stimulating R_s components following long-term thinning. Therefore, applications of nitrogen fertilizer are not recommended while thinning subalpine spruce plantations from the perspective of reducing soil CO₂ emissions. The increased Q₁₀ values of R_s components indicate that a large increase in soil CO₂ emissions would be expected following thinning because of more pronounced climate warming in alpine regions.

Tree-ring width (RW), density, elemental composition, and stable carbon and oxygen isotope (δ¹³C, δ¹⁸O) are widely used as proxies to assess climate change, ecology, and environmental pollution; however, a specific pretreatment has been needed for each proxy. Here, we developed a method by which each proxy can be measured in the same sample. First, the sample is polished for ring width measurement. After obtaining the ring width data, the sample is cut to form a 1-mm-thick wood plate. The sample is then mounted in a vertical sample holder, and gradually scanned by an X-ray beam. Simultaneously, the count rates of the fluorescent photons of elements (for chemical characterization) and a radiographic grayscale image (for wood density) are obtained, i.e. the density and the element content are obtained. Then, cellulose is isolated from the 1-mm wood plate by removal of lignin, and hemicellulose. After producing this cellulose plate, cellulose subsamples are separated by knife under the microscope for inter-annual and intra-annual stable carbon and oxygen isotope (δ¹³C, δ¹⁸O) analysis. Based on this method, RW, density, elemental composition, δ¹³C, and δ¹⁸O can be measured from the same sample, which reduces sample amount and treatment time, and is helpful for multi-proxy comparison and combination research.

Urbanization has profound impacts on ecological environments. Green spaces are a vital component of urban ecosystems and play a crucial role in maintaining ecological balance and enhancing sustainability. This study aimed to investigate the community composition characteristics of butterflies in urban green spaces within the context of rapid urbanization. Simultaneously, it explored the status and differences in butterfly taxonomic diversity, functional diversity, and functional traits among different types of urban green spaces, regions, and urban gradients to provide relevant insights for further improving urban green space quality and promoting biodiversity conservation. We conducted a year-long survey of 80 green spaces across different urban regions and ring roads within Hefei City, Anhui Province, with monthly sampling intervals over 187 transects. A total of 4822 butterflies, belonging to 5 families, 17 subfamilies, 40 genera, and 55 species were identified. The species richness, Shannon, Simpson, functional richness, and Rao's quadratic entropy indices of butterflies in urban park green spaces were all significantly higher than those in residential and street green spaces (P < 0.05). Differences in butterfly diversity and functional traits among different urban regions and ring roads were relatively minor, and small-sized, multivoltine, and long flying duration butterflies dominated urban green spaces. Overall, these spaces offer more favorable habitats for butterflies. However, some residential green spaces and street green spaces demonstrate potential for butterfly conservation.

Litterfall is the largest source of nutrients to forest soils of tropical rainforests. However, variability in litterfall production, nutrient remobilization, and changes in leaf nutrient concentration with climate seasonality remain largely unknown for the central Amazon. This study measured litterfall production, leaf nutrient remobilization, and leaf area index on a forest plateau in the central Amazon. Litterfall was measured at monthly intervals during 2014, while nitrogen, phosphorus, potassium, calcium and magnesium concentrations of leaf litter and canopy leaves were measured in the dry and rainy seasons, and remobilization rates determined. Leaf area index was also recorded in the dry and rainy seasons. Monthly litterfall varied from 33.2 (in the rainy season) to 87.6 g m^‒2 in the dry season, while leaf area index increased slightly in the rainy season. Climatic seasonality had no effect on concentrations of nitrogen, calcium, and magnesium, whereas phosphorous and potassium responded to rainfall seasonality oppositely. While phosphorous increased, potassium decreased during the dry season. Over seasons, nitrogen, potassium, and phosphorous decreased in leaf litter; calcium increased in leaf litter, while magnesium remained unaffected with leaf aging. Regardless, the five nutrients had similar remobilization rates over the year. The absence of climate seasonality on nutrient remobilization suggests that the current length of the dry season does not alter nutrient remobilization rates but this may change as dry periods become more prolonged in the future due to climate change.

Abstract

Evapotranspiration is an important parameter used to characterize the water cycle of ecosystems. To understand the properties of the evapotranspiration and energy balance of a subalpine forest in the southeastern Qinghai–Tibet Plateau, an open-path eddy covariance system was set up to monitor the forest from November 2020 to October 2021 in a core area of the Three Parallel Rivers in the Qinghai–Tibet Plateau. The results show that the evapotranspiration peaked daily, the maximum occurring between 11:00 and 15:00. Environmental factors had significant effects on evapotranspiration, among them, net radiation the greatest (R² = 0.487), and relative humidity the least (R² = 0.001). The energy flux varied considerably in different seasons and sensible heat flux accounted for the main part of turbulent energy. The energy balance ratio in the dormant season was less than that in the growing season, and there is an energy imbalance at the site on an annual time scale.