Larix Principis-rupprechtii Plantation Research Articles

Dynamic Simulation of the Leaf Mass per Area (LMA) in Multilayer Crowns of Young Larix principis-rupprechtii.

Leaf mass per area (LMA) is a key structural parameter that reflects the functional traits of leaves and plays a vital role in simulating the material and energy cycles of plant ecosystems. In this study, vertical whorl-by-whorl sampling of LMA was conducted in a young Larix principis-rupprechtii plantation during the growing season at the Saihanba Forest Farm. The vertical and seasonal variations in LMA were analysed. Subsequently, a predictive model of LMA was constructed. The results revealed that the LMA varied significantly between different crown whorls and growing periods. In the vertical direction of the crown, the LMA decreased with increasing crown depth, but the range of LMA values from the tree top to the bottom was, on average, 30.4 g/m2, which was approximately 2.5 times greater in the fully expanded phase than in the early leaf-expanding phase. During different growing periods, the LMA exhibited an allometric growth trend that increased during the leaf-expanding phase and then tended to stabilize. However, the range of LMA values throughout the growing period was, on average, 40.4 g/m2. Among the univariate models, the leaf dry matter content (LDMC) performed well (adjusted determination coefficient (Ra2) = 0.45, root mean square error (RMSE) = 13.48 g/m2) in estimating the LMA. The correlation between LMA and LDMC significantly differed at different growth stages and at different vertical crown whorls. The dynamic predictive model of LMA constructed with the relative depth in the crown (RDINC) and date of the year (DOY) as independent variables was reliable in both the assessments (Ra2 = 0.68, RMSE = 10.25 g/m2) and the validation (absolute mean error (MAE) = 8.05 g/m2, fit index (FI) = 0.682). Dynamic simulations of crown LMA provide a basis for elucidating the mechanism of crown development and laying the foundation for the construction of an ecological process model.

Effects of Seed Size and Cache Density on the Seed Fate of Quercus wutaishanica Mediated by Rodents.

Animal-mediated seed dispersal is very important for plant population regeneration and the stability of forest ecosystems. Seed size and cache density are important factors for seed dispersal, but we still know little about seed size selection at different cache densities. Here, we conducted field experiments in a Larix principis-rupprechtii plantation in the Liupan Mountains in Ningxia province to investigate the effects of tag-marked Quercus wutaishanica seeds of different sizes and cache densities on predation and the scatter-hoarding behavior of rodents. The results showed lower proportions of intact in situ (IIS) and eaten in situ (EIS) large seeds than small seeds at all levels of cache density, with the exception of IIS seeds at a 6.25 seed·m-2 cache density. A higher proportion of small seeds were eaten after removal (EAR), but a higher proportion of large seeds were scatter-hoarded (SH) by rodents at most cache densities. Furthermore, rodents preferentially removed large seeds farther away for eating or scatter-hoarding. The IIS and EIS proportions of both large and small seeds declined, but the proportion of the two types of seeds that were EAR fluctuated, increasing with increasing cache density. Rodents preferred to increase the proportion of scatter-hoarding of large seeds with increasing cache density, whereas the proportion of scatter-hoarding of small seeds was maximized at a cache density of 6.25 seed·m-2. Both the eaten distance after removal (EDAR) and scatter-hoarded distance (SHD) increased with increasing cache density. These results suggest that large seeds are more likely to be scatter-hoarded and removed to longer distances than small ones. Rodents tended to reduce the seed proportion of EIS seeds and increased the proportion of seeds EAR and SH, and accordingly increased EDAR and SHD with increasing cache density. This study provides some scientific basis for animal-mediated seed dispersal.

Differentiated responses of daytime and nighttime sap flow to soil water deficit in a larch plantation in Northwest China

Tree transpiration contributes to the forest water budget and its environmental responses differ between daytime and nighttime. Elucidating these divergent responses separately from their biophysical controls is crucial for ascertaining the forest-water relationship in changing environments. To investigate the biophysical controls on daytime and nighttime sap flow (Qd and Qn), the sap flux density, meteorological conditions, soil moisture, and canopy leaf area index (LAI) were simultaneously monitored in a Larix principis-rupprechtii plantation in the Liupan Mountains of Northwest China during the growing seasons (June to September) of three hydrological years (2019, 2021, and 2022). The results showed that the main control factors for Qd and Qn varied depending on the timescale. The variation in Qd was mainly controlled by daytime solar radiation (Rd), vapour pressure deficit (VPDd), relative extractable soil water (REWd) and LAI at a daily scale, but only by Rd at a monthly scale and only by VPDd at an interannual scale. The variation in Qn was mainly controlled by the nighttime vapour pressure deficit (VPDn) and relative extractable soil water (REWn), LAI, and Qd at a daily scale but only by VPDn at monthly and interannual scales. The responses of Qd and Qn to soil water deficit were different and varied by timescale. At the daily scale, the effect of VPDd on Qd became weak, while the effect of VPDn on Qn became strong in drier years (2021 and 2022). At the monthly scale, as the main controlling factor of the monthly variation in Qd (Qn), Rd (VPDn) played a decisive role in the wet (dry) months. At the interannual scale, VPD limited Qd but drove Qn, leading to a decrease in Qd and an increase in Qn with increasing soil water deficit. Overall, our findings revealed the different responses of Qd and Qn to biophysical factors and underscored that Qd and Qn should be explored both separately and synchronously; additionally, our results indicated that the proportion of Qn might increase if soil water stress is increased due to future climate change.

Effect of gap size on the regeneration in Larix principis-rupprechtii plantation.

We conducted a survey on seedlings (height <1 m) and saplings (height ≥1 m, diameter at breast height <5 cm) in 20 gaps of Larix principis-rupprechtii plantations on Guandi Mountains, Shanxi to analyze regene-ration density, growth indicators, and spatial distribution of L. principis-rupprechtii seedlings and saplings under four gap sizes (<60 m2, 60-120 m2, 120-180 m2, and ≥180 m2). The results showed that growth indicators (ground diameter, height) of seedlings and saplings and regeneration density of seedlings were highest in small gaps (14-60 m2). The sapling regeneration density was highest in medium gaps (60-120 m2), and sapling density exceeded seedling density in each size category. L. principis-rupprechtii seedlings and saplings exhibited favorable regeneration in small and medium gaps, while large gaps (120-180 m2) and extra-large gaps (≥180 m2) were unfavorable for L. principis-rupprechtii regeneration. L. principis-rupprechtii seedlings and saplings were mainly distributed within the canopy projection area and along the edge of canopy gap area. Controlling gap size within the range of 14-120 m2 through artificial interventions, such as planting and thinning, could promote the regeneration of L. principis-rupprechtii.

Modeling Free Branch Growth with the Competition Index for a Larix principis-rupprechtii Plantation

Competition among free branches in the tree canopy is an important factor influencing branch length growth. Therefore, there is a need to quantify this competition and to understand the impact of the regression technique on the predictive accuracy of the growth of free branch length (GFBL) model in a Larix principis-rupprechtii plantation. This study focused on an L. principis-rupprechtii plantation in Saihanba Mechanized Forest Farm. Five competition indices based on 2176-branch data points from 76 trees were used to quantify the branch competition, and three regression techniques (nonlinear least squares (NLS), nonlinear mixed-effects model (NLME), and nonlinear quantile regression (NQR)) were used to construct the GFBL model including the branch competition index. The results showed that the Chapman–Richards growth function, including the diameter at breast height (DBH) and depth of branch into crown (DINC), was the optimal equation for describing the GFBL in the studied L. principis-rupprechtii plantation. The branch competition index (CI) was found to be optimal for quantifying the branch competition when used with the maximum value parameter (a0) of the Chapman–Richards growth function. The three parameter estimation methods were compared, and the NLME, which included the CI, was found to have the highest predictive accuracy. The results of this study can act as a reference for improving the management, assessing the management effectiveness, and enhancing the quality of L. principis-rupprechtii plantations.

Ecoenzymatic Stoichiometry in the Rhizosphere and Bulk Soil of a Larix principis-rupprechtii Plantation in North China

Soil extracellular enzymes play an important role in ecosystem energy conversion and material cycling. Ecoenzymatic stoichiometry can reflect the relationship between the soil’s microbial nutrient cycle and nutrient limitation. However, there have been few studies on the differences in ecoenzymatic stoichiometry and nutrient limitation between rhizosphere soil and bulk soil. This study examined soil nutrients and enzyme activities in rhizosphere soil and bulk soil in a Larix principis-rupprechtii plantation in north China. The results showed that the levels of soil organic carbon (C), total nitrogen (N), and available nutrients in the rhizosphere soil were significantly higher than those in the bulk soil, whereas the total potassium (TK) level was significantly lower. The soil C:N, C:P, and N:P ratios of the rhizosphere soil also exceeded those of the bulk soil. The acid phosphatase (ACP), urease (UE), and β-glucosidase (β-GC) activities in the rhizosphere soil exceeded those in the bulk soil, whereas the activities of N-acetyl-β-D-glucosidase (NAG), aminopeptidase (LAP), and nitrogenase (NA) were lower. The ratios of C, N, and P acquisition activities changed from 1:1.7:1 in the rhizosphere soil to 1:2:1 in the bulk soil. Redundancy analysis showed that the available K and soil water content in the rhizosphere soil were the most important soil factors affecting soil enzyme activities and ecoenzymatic stoichiometry; those in the bulk soil were soil N:P and soil water content. These results suggest that not all soil enzyme activities present rhizosphere effects and that bulk soil is more susceptible to N limitation in Larix principis-rupprechtii plantations. Plant roots play an important role in regulating soil nutrients and soil activities, and future studies should examine the underlying mechanisms in more detail.

Soil nitrogen forms and their coupling relationships during the growing season of a Larix principis-rupprechtii plantation at different growth stages and stand densities

Soil nitrogen forms and their coupling relationships during the growing season of a Larix principis-rupprechtii plantation at different growth stages and stand densities

Effects of two-year nitrogen and phosphorus additions on nutrient release and enzyme activity during leaf litter decomposition in Larix principis-rupprechtii plantation

Effects of two-year nitrogen and phosphorus additions on nutrient release and enzyme activity during leaf litter decomposition in Larix principis-rupprechtii plantation

Short-term responses of soil nutrients and enzyme activities to nitrogen addition in a Larix principis-rupprechtii plantation in North China

Atmospheric nitrogen (N) deposition is among the main manifestations of global change and has profoundly affected forest biogeochemical cycles. However, the threshold of N deposition to soil nutrient contents and enzyme activities has rarely been studied in a forest. In this study, we explored the effects of N deposition on soil nutrients and enzyme activities in a Larix principis-rupprechtii plantation on the northern Yanshan Mountain through multigradient N addition experiments (0, 5, 10, 20, 40, 80, and 160 kg N ha−1 year−1) after fertilization for 2 years. Compared with the controls, N addition first led to a decrease in soil NH4+-N and NO3--N, which then increased significantly. N addition had no significant effects on other soil nutrients. N addition overall elevated soil β-glucosidase activity. N application of &amp;gt;40 kg N ha−1 year−1 significantly reduced soil leucine aminopeptidase activity but had no significant effects on soil acid phosphatase, N-acetyl-β-D-glucosidase, and urease activities. N addition increased the overall stoichiometry ratio of EEA C:N and EEA C:P, but EEA N:P started decreasing after N application of 40 kg N ha−1 year−1. The ratios of C, N, and P acquisition activities changed from 1:1.2:1 under the control conditions to 1:1.1:1 under the N application of 160 kg N ha−1 year−1. N addition increased the overall vector length and had no significant effects on the vector angle. Correlation and redundancy analyses revealed that N addition-induced change in available soil N was the main factor affecting soil enzyme activity and stoichiometry. In general, different enzyme activities had different sensitivities to N addition. Moderate N addition or atmospheric N deposition (e.g., &amp;lt;40 kg N ha−1 year−1) had beneficial effects on soil nutrient cycling and microorganisms in a Larix principis-rupprechtii plantation.

Effects of Betula platyphylla invasion in North China on soil aggregate stability, soil organic carbon and active carbon composition of larch plantation

In order to better understand the changes of soil carbon sequestration capacity in forest after forest mixing, the effects of broadleaf tree invasion on soil aggregate stability and carbon sequestration were studied. In northern China, the pure Larix principis-rupprechtii plantations and the Larix principis-rupprechtii plantations invaded by Betula platyphylla at various degrees with the same site conditions were selected (Betula platyphylla had mixed degrees of 0.2 and 0.4). The distribution and stability of soil aggregates were analyzed, and soil organic carbon and active carbon components were determined. The distribution of soil macroaggregates (> 0.25 mm) increased with the increase in the mixed degree of Betula platyphylla. The mixture of Betula platyphylla could effectively increased SOC, EOC, DOC and MBC of the original soil and soil aggregates of different diameter classes. The invasion of Betula platyphylla had a positive indirect impact on soil carbon sequestration by affecting the soil physical and chemical properties and the aggregate stability. The invasion of Betula platyphylla had significant positive effects on soil aggregate stability, erosion resistance and soil nutrient status in Larix principis-rupprechtii plantation. Maybe the selection of suitable broadleaf mixed species can improve the soil quality and soil organic carbon sequestration of the Larix principis-rupprechtii plantation in this area.

不同时间尺度下华北落叶松人工林冠层蒸腾与环境因子的关系

PDF HTML阅读 XML下载 导出引用 引用提醒 不同时间尺度下华北落叶松人工林冠层蒸腾与环境因子的关系 DOI: 10.5846/stxb202107151903 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 内蒙古自治区关键技术攻关计划项目(2021GG0033);内蒙古自治区林业和草原局科研能力提升项目;内蒙古自治区自然科学基金项目(2021MS03101) Relationship between canopy transpiration of larch plantation and environmental factors at different time scales Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:在半干旱区连续2年监测华北落叶松(Larix principis-rupprechtii)的树干液流、气象因子和土壤体积含水量,分析不同时间尺度下人工林冠层蒸腾与环境因子的关系。结果表明:不同时间尺度下,华北落叶松人工林冠层蒸腾的季节变化均呈单峰曲线,即先增大后减小的趋势;2016年、2017年日蒸腾量分别为1.58 mm/d和1.71 mm/d,生长季蒸腾总量分别为241.30 mm和260.97 mm。在日尺度下,气温、太阳辐射强度和饱和水汽压差是影响华北落叶松人工林冠层蒸腾主要环境因子;月尺度下,气温、风速、降水和土壤水分是冠层蒸腾的主要影响因子;冠层蒸腾与降水、大气相对湿度的相关关系由日尺度下的负相关到月尺度的正相关,相关性增强。总体来看,随时间尺度由小到大,气温、风速、大气相对湿度、降水、土壤水分对冠层蒸腾的影响作用增大,而太阳辐射强度、饱和水汽压差的作用减弱;在未来增温增雨趋势下,研究区生长季将延长,华北落叶松人工林冠层蒸腾量可能会加大。 Abstract:Canopy transpiration is a major part of forestland water balance and a fundamental datum in understanding the planted forest ecophysiology in dry regions. Quantitatively analyzing variation of canopy transpiration induced by the environmental factors is beneficial for a better estimation forestland water balance and prediction the plantation ecophysiology. But the response mechanism of canopy transpiration to environmental factors may be different in different time scales, so it needs to be further understood. This study was conducted in a 42-year-old Larix principis-Rupprechtii plantation (a density of 1933 trees/hm2) at the middle position of a north facing slope in the Inner Mongolian Daqingshan National Nature Reserve, a semi-arid region of China. Firstly, the sap flow velocity in ten healthy and dominant Larix principis-Rupprechtii trees, soil volumetric water content and meteorological factors including air temperature, precipitation, solar radiation intensity, air relative humidity and wind speed, were observed during two growing seasons (May 1 to September 30) in 2016 and 2017 which precipitation was 435.00 mm and 348.80 mm, respectively. Then, sap flow velocity values which was measured by the thermal diffusion method, were upscaled to the forest canopy level. Finally, the relationship between canopy transpiration and the environmental factors at different time scales was analyzed. The results showed that the seasonal changes of canopy transpiration showed a single peak curve under the different time scales, that was, the trend of increase first and then decrease. In 2016 and 2017, the average value of daily canopy-level transpiration was 1.58 mm/d and 1.71 mm/d, respectively, and the total transpiration in the growing season was 241.30 mm and 260.97 mm, respectively. On the daily scale, air temperature, solar radiation intensity and saturated vapor pressure deficit markedly affected canopy transpiration. At the monthly scale, air temperature, wind speed, precipitation and soil volumetric water content were the main influencing factors of canopy transpiration. The correlation between transpiration and precipitation and air relative humidity increased from negative correlation on the daily scale to positive correlation on the monthly scale. In general, with time scale from small to large, the effects of air temperature, wind speed, air relative humidity, precipitation and soil water content on canopy transpiration increase, while the effects of solar radiation intensity and saturated vapor pressure deficit decrease. With the trend of increasing temperature and rainfall in the future, the growing season of Larix principis-Rupprechtii in the study area will be prolonged, and the canopy transpiration may increase. 参考文献 相似文献 引证文献

Soil phosphorus and biomass carbon co-determine plantation soil organic carbon density: a case study in western Beijing, China

Context Studies of afforestation have traditionally neglected the influences of plant microhabitats on the growth and carbon sink capacities of planted forests. Aims We investigated the potential mechanisms related to the relationship of afforestation elevation to soil organic carbon density (SOCD). Methods The carbon density of three plantation ecosystems and barren land soils were evaluated at two elevations in the Donglingshan Mountains of Beijing, with structural equation modelling and variation partitioning analyses used to identify the environmental factors that influenced the carbon densities of plantation ecosystems. Key results Afforestation elevation was related to the vegetation phenology of plantation forests. Specifically, growth periods at higher elevations were delayed relative to those at lower elevations, while different growth periods affected growth rate of diameter at breast height (RDBH), in addition to the carbon and nitrogen contents of ground surface litters. Consequently, lower elevation afforestation reduced the carbon sink capacity of coniferous plantation ecosystems in the study area. Lower plantation elevations were associated with significantly reduced RDBH values of Pinus tabuliformis. Further, biomass carbon density (BCD) and SOCD of Larix principis-rupprechtii plantations were significantly lower due to decreased elevations. Soil nitrogen concentrations, litter nitrogen density (LND), soil phosphorus concentrations, and BCD were the primary drivers of plantation SOCD. Conclusions Overall, different plantation elevations were associated with different vegetation phenologies and RDBH values, which further affected LND and BCD, thereby ultimately affecting variation of SOCD. Implications This study provides important insights into the selection of afforestation plots to maximise plantation carbon sequestration capacities.

Do stand density and month regulate soil enzymes and the stoichiometry of differently aged Larix principis-rupprechtii plantations?

As essential components of soil properties and microbial processes, carbon (C), nitrogen (N), phosphorus (P), and extracellular enzymes play key roles in carbon and nutrient cycling in forest ecosystems worldwide. Forest management should include the development of healthy ecosystems to prevent soil degradation and nutrient loss and support productivity. However, it remains unclear how forest stand density and month impact extracellular soil enzymes, C, N, and P concentrations and their stoichiometry. A total of 486 soil samples were extracted from forest stand plots of different densities and ages, which were sampled continuously during the growing season (May-October). The soil organic C, total N, total P, β-1,4-glucosidase, β-N-acetyl Glucosaminidase, leucine aminopeptidase, and acid phosphatase were quantified. Higher levels of soil organic matter (e.g., C and N) was observed to accumulate in highly dense 27-year-old stands (27a) (2125–2425 trees ha−1). Moderate stand densities (36a, 925–1325 trees ha−1; 48a, 875–1150 trees ha−1) facilitated the procurement of C and N by microorganisms and C and Nsequestration in near-mature and mature forest soils due to an improved environment and more robust microbial activities. The soil contained more N during the mid-growing season, where in July it was ∼ 40 % higher than at the beginning and end of the growing season. Further, the soil microbes that acquired C and N were more robust. Monthly regulation caused the C:N:P acquisition ratio to deviate significantly from 1:1:1. Soil microbes absorbed C and N mid-growing season; however, they tended to absorb N and P at its onset and end. Monthly regulation may serve as a “switch” that adjusts the capacities of soil microbes to acquire C and N in 36a and 48a plantations. The regulation of stand density can promote extracellular enzyme activities through the accumulation and storage of soil organic matter during the growing season.

Natural regeneration of Larix principis-rupprechtii plantations with different densities and its influencing factors

In this study, we analyzed the natural regeneration of Larix principis-rupprechtii pure plantations with stand densities of 128, 240, 320, 400, 480, 560, 640 and 720 trees·hm-2 in the Guandi Mountains and its influencing factors. The results showed that the regeneration index first increased and then decreased with the increases of stand density, and that the regeneration performance of stand with medium density (400-560 trees·hm-2) was significantly better than other stands. Light conditions, herbaceous plants and litter of the understory had a dual effect on the regeneration of L. principis-rupprechtii. Excessive light, herbaceous plant cover or over-thick litter was not instrumental to the regeneration. Soil organic matter promoted stand regeneration by providing soft soil texture, adequate water content, low phosphorus but high nitrogen. The effects of the examined factors on the regeneration index were as follows: soil water content (0.798) &gt; total nitrogen (0.621) &gt; litter thickness (-0.597) &gt; soil porosity (0.504) &gt; soil organic matter (0.493) &gt; total phosphorus (-0.404) &gt; transmitted total light (-0.274) &gt; herbaceous plants cover (-0.021). In the plantation management, stand density could be controlled at about 480 trees·hm-2 by thinning or replanting, while litter could be cleared properly to improve soil condition and to promote natural regeneration of L. principis-rupprechtii.

Dynamic characteristics of soil aggregate stability and related carbon and nitrogen pools at different developmental stages of plantations in northern China

The carbon and nitrogen reserves of forest soil play a key role in combating global climate change. Afforestation is considered an effective measure for increasing carbon and nitrogen reserves in terrestrial forest ecosystems. However, the mechanisms governing how different developmental stages of plantations affect soil carbon and nitrogen stability and storage remain unclear. In this study, we selected three developmental stages of the Larix principis-rupprechtii plantations: medium mature forest (30 yr), near mature forest (40 yr) and mature forest (50 yr). We studied the distribution and stability of soil aggregates at distinct developmental stages, the distribution of carbon and nitrogen pools related to aggregates, and their relationship to environmental factors. We found that with increasing forest age, the soil sand particles became finer. In each developmental stage, the proportion of aggregates >0.25 mm reached more than 85%. The concentrations of carbon and nitrogen in the soil aggregates were lower in the near mature forest (40 a) than in the medium mature forest (30 a), but reached a maximum in the mature forest (50 a). There were significant positive correlations between soil carbon and nitrogen concentrations and soil relative water content (RWC), forest age, and stand density. Soil texture strongly affected the distribution of aggregates. TOC/TN was mainly influenced by aggregate distribution, which was most vulnerable to environmental factors. Environmental factors have a significant negative impact on soil texture, and the path coefficient was −0.812. Environmental factors indirectly affected the concentrations of soil carbon and nitrogen by influencing the distribution and stability of soil aggregates. Therefore, different developmental stages of plantations strongly affected forest carbon and nitrogen pools by changing the soil structure and environmental factors. This study provides a basis for understanding the mechanisms of forest soil carbon and nitrogen storage.

Effects of thinning on soil aggregation, organic carbon and labile carbon component distribution in Larix principis-rupprechtii plantations in North China

The forest ecosystem is the ecosystem with the largest terrestrial carbon pool in the world. Afforestation, cutting and tending mutually affect the forest carbon source and the carbon sink. However, few studies have explored the effects of larch plantation management on soil aggregate stability and soil aggregate carbon storage. The effects of the four thinning intensities (unmanaged control (CK), 15% reduction, mild thinning (LT), 30% reduction, intermediate thinning (MT), and 50% reduction, severe thinning (HT)) on soil aggregate stability and carbon storage were investigated in Larix principis-rupprechtii plantations in North China. The results showed that soil aggregates with a particle size of >2 mm or 1–2 mm under all thinning intensities were the most abundant. At the same time, organic carbon and labile carbon were mainly distributed in >0.25 mm soil aggregates. The MT treatment corresponded with the highest organic carbon and labile carbon levels. The distribution of soil macro aggregates was greatly affected by stand density, while the distribution of micro aggregates was most affected by nutrient-related factors. Forest thinning reduces the stability of soil aggregates, though intermediate thinning can improve the carbon sequestration potential of soil aggregates. These findings will provide essential evidence for carbon sequestration of soil aggregates in plantations after thinning, and provide reference for those formulating plantation management strategies in North China.

Assessing the Impact of Soil Moisture on Canopy Transpiration Using a Modified Jarvis-Stewart Model

In dryland regions, soil moisture is an important limiting factor for canopy transpiration (T). Thus, clarifying the impact of soil moisture on T is critical for comprehensive forest—water management and sustainable development. In this study, T, meteorological factors (reference evapotranspiration, ETref), soil moisture (relative soil water content, RSWC), and leaf area index (LAI) in a Larix principis-rupprechtii plantation of Liupan Mountains in the dryland region of Northwest China were simultaneously monitored during the growing seasons in 2017–2019. A modified Jarvis—Stewart model was established by introducing the impact of RSWC in different soil layers (0–20, 20–40, and 40–60 cm, respectively) to quantify the independent contribution of RSWC of different soil layers to T. Results showed that with rising ETref, T firstly increased and then decreased, and with rising RSWC and LAI, T firstly increased and then gradually stabilised, respectively. The modified Jarvis—Stewart model was able to give comparable estimates of T to those derived from sap flow measurements. The contribution of RSWC to T in different soil layers has obvious specificity, and the contribution rate of 20–40 cm (13.4%) and 0–20 cm soil layers (6.6%) where roots are mainly distributed is significantly higher than that of 40–60 cm soil layer (1.9%). As the soil moisture status changes from moist (RSWC0–60cm ≥ 0.4) to drought (RSWC0–60cm &lt; 0.4), the role of the soil moisture in the 0–20 cm soil layer increased compared with other layers. The impacts of soil moisture that were coupled into the Jarvis—Stewart model can genuinely reflect the environmental influence and can be used to quantify the contributions of soil moisture to T. Thus, it has the potential to become a new tool to guide the protection and management of forest water resources.

Effects of stand density on soil respiration and labile organic carbon in different aged Larix principis-rupprechtii plantations

BackgroundThe carbon pools of forest soils play a vital role in global carbon sequestration and emissions. Forest management can regulate the sequestration and output of forest soil carbon pools to a certain extent; however, the kinetics of the effects of forest density on soil carbon pools require further investigation.MethodsWe established sample plots with stand density gradients in three different aged Larix principis-rupprechtii plantations and quantified the soil respiration, soil organic carbon (SOC), soil dissolved organic carbon (DOC), microbial biomass carbon (MBC), light fraction organic carbon (LFOC), and readily oxidized carbon (ROC).Results and conclusionsDuring the growth and development of plantations, stand density is an essential factor that impacts soil respiration and its associated elements. Moderate density was observed to promote both the soil and heterotrophic respiration rates and the sequestration of MBC and LFOC, whereas it inhibited the sequestration of ROC. The soil, heterotrophic, and autotrophic respiration rates of older forest stands were relatively rapid, whereas the contents of SOC, MBC, LFOC, DOC, and ROC were higher and more sensitive to changes in stand density. The MBC, LFOC, and ROC in soil labile organic carbon were closely related to both the soil and heterotrophic respiration, but not the SOC. Among them, the LFOC and MBC played the roles of “warehouse” and “tool” and were significantly correlated with soil and heterotrophic respiration. The ROC, as a “raw material”, exhibited a significantly negative correlation with the soil and heterotrophic respiration. When the soil and heterotrophic respiration rates were rapid, the ROC content in the soil maintained the low level of a “dynamically stabilized” state. The stand density regulated heterotrophic respiration by affecting the soil labile organic carbon, which provided an essential path for the stand density to regulate soil respiration.

Multivariate path analysis of factors influencing Larix principis-rupprechtii plantation regeneration in northern China

Forest regeneration is a critical indicator of the overall health of forest ecosystems, and is considered to be a vital process in which old and senescent trees are replaced by young ones. The seed-to-seedling transition entails seedlings’ emergence from seeds and their establishment, this phase being the most vulnerable to mortality effects from biotic and abiotic factors. Larix principis-rupprechtii is a typical tree species in northern China, where the natural regeneration of artificial forests dominated by this species is very limited. This study explored the limiting factors affecting the natural regeneration of Larix principis-rupprechtii forests via field surveys of large-scale sampling plots. Redundancy analysis and structural equation models were developed and applied to determine the relative importance of direct and indirect factors affecting the regeneration of Larix principis-rupprechtii plantations. We found a negative relationship between the regeneration index and stand structure, for which the path coefficient was –0.54, the strongest correlation. Conversely, the regeneration index was positively correlated with the herb index, soil index, and elevation, having path coefficients of 0.06, 0.07, and 0.32, respectively. The soil index was negative correlated with both elevation and herb index, with path coefficients of –0.31 and –0.53, respectively, while stand structure was negatively correlated with the herb index and positively correlated with elevation (respective path coefficients: –0.62 and 0.29). Stand density and tree height to crown base were the main factors representing stand structure and, accordingly, the most important factors influencing forest regeneration of the species. At a stand density of ca. 200 trees·hm−2, the number and quality of seedling regeneration were robust. In later stages of stand management and thinning, the proper adjustment of stand density and timely pruning interventions can promote this tree’s natural regeneration to achieve the sustainable development of forest resources.

Changes of light response indicators and its impact factors of Larix principis-rupprechtii on Saihanba Forest Farm, China.

We examined the differences of maximum light use efficiency (LUEmax), most effective light intensity (PARe), light compensation point (LCP) and light saturation point (LSP) in diffe-rent vertical positions and different phenological periods of tree crown in Larix principis-rupprechtii plantation in Saihanba Mechanical Forest Farm of Hebei Province. We analyzed the main influencing factors for all the variables. The results showed that LUEmax increased with the increasing crown depth, and that PARe, LCP and LSP decreased with the increasing crown depth. Such a result indicated that upper crown had higher utilization efficiency to strong light and that the lower crown was more efficient to adapt to weak light environment. During the leaf development in the growth period, the LUEmax approximately increased except in July, while the changes of other photosynthe-tic-light factors showed a tendency of unimodal curve. Environmental factors were significantly correlated with the indices of light response, mainly due to the stress reaction of leaf stomata to surrounding environment. Understanding the spatial and seasonal changes of the photosynthetic-light indicators was important for formulating scientific management measures, optimizing stand structure, improving local microenvironment and maximizing forest productivity.