•C emissions of stem respiration from 16, 25, 41 years old forest were estimated.•Air temperature and moisture are the primary climatic factor affecting RS.•The general model of RS using Q10 may ...underestimated the RS of young trees.•Q10 of RS peaked at a temperature within the range of 0–5°C.•Temperature-corrected Q10 of RS should be considered to estimate C emissions.
Stem respiration is a critical yet unavailable component of forest ecosystem carbon cycle dynamics. It is therefore necessary to study the variation in stem respiration at different time scales, especially regarding the response of the temporal variation in stem respiration to climatic factors. However, stem respiration is commonly measured only a few times a year during the daytime. In this study, we investigated the stem respiration of Larix principis-rupprechtii Mayr at different time scales, including hours, days, months, and seasons, and in forests of different ages as well as its connection with climatic factors using a soil carbon flux system (Li-8100) in North China during the growing season (May to September) and the non-growing season (October) from 2013 to 2015. The maximum daily stem respiration rate (abbreviated as RS) occurred between 14:00 and 18:00, and the minimum occurred between 4:00 and 8:00 (2.01–4.24, 1.71–4.25 and 1.02–1.72 vs. 10.83–2.93, 1.08–2.28 and 0.51–1.17μmolm−2s−1, respectively) for three forestry ages, which was in accordance with single-peak curves. The seasonal respiration was highest in late July and lowest in late October (3.84 vs. 0.27μmolm−2s−1, respectively). Calculation of RS indicated that the annual CO2 efflux per unit area was ranked by forest age as follows: 25 (11.53±2.08tha−1)>16 (7.45±1.02)>41 (4.87±0.66)years of age. The average annual Q10 values were 3.85 (16 years of age), 3.41 (25), and 2.23 (41). The Q10 value of the 16-year-old forest peaked (9.89) during low temperature (0–5°C) and subsequently decreased with increasing air temperature. These results not only clarify the response of RS to climatic factors at different time scales but also reveal the relationship between stem respiration in forests of different ages and their temperature sensitivity. These results suggest that the sensitivity of RS to temperature is negatively correlated with stand age and air temperature. Methodologically, incorporating stand age and air temperature into the conventional method would improve the accuracy of annual stem respiration estimates.
•ES was greater near the crown and the root than at the middle stem positions.•Nitrogen was the primary nutrient element affecting ES.•Sapwood width was the primary wood structure affecting ES.•C ...emissions from older tree was underestimated without the vertical variation in ES.•A model of ES for each stem position was established.
Stem CO2 efflux (ES) plays an essential role in the carbon balance of forest ecosystems. Therefore, it is necessary to study the vertical and seasonal variations in ES in forests with different ages, especially in response to factors associated with temperature, nutrients and wood structure. In this study, we investigated ES and its association with temperature factors using a carbon flux system (Li-8100A) at monthly intervals during the growing season (May to September) and the non-growing season (October) from 2013 to 2015. In addition, we collected data on nutrients and wood structure in August 2016 from 16- (young), 25- (immature), and 41-year-old (mature) Larix principis-rupprechtii Mayr stands in North China. Our analysis showed that the ES values at stem positions near the crown and the root system were generally higher than those in the middle and that the minimum ES values in July occurred at 2.0 m (3.61 μmol m−2 s−1), 3.0 m (2.42 μmol m−2 s−1), and 5.0 m (4.03 μmol m−2 s−1) in the young, immature, and mature forests, respectively. Air temperature and wood temperature influenced the vertical variation in ES, as did stem nitrogen concentration and sapwood width. Compared to the method that uses the vertical ES gradient to determine tree-scale CO2 effluxes for 16-, 25- and 41-year-old L. principis-rupprechtii forests, the method that uses the ES value at the 1.3-m stem position underestimated the CO2 effluxes by 5%, 6%, and 24%, respectively. The ES and Q10 models for each stem position for the three forest ages in this study can be used to accurately estimate tree-scale CO2 effluxes. These results not only clarified the relationships between the vertical variation in ES and temperature, nutrient content and wood structure, but also revealed the likely response mechanisms of ES to these factors. Methodologically, incorporating the vertical variation in ES and the associated drivers into conventional models would improve the accuracy of annual ES estimates.
Urban heat island (UHI) attenuation is an essential aspect for maintaining environmental sustainability at a local, regional, and global scale. Although impervious surfaces (IS) and green spaces have ...been confirmed to have a dominant effect on the spatial differentiation of the urban land surface temperature (LST), comprehensive temporal and quantitative analysis of their combined effects on LST and surface urban heat island intensity (SUHII) changes is still partly lacking. This study took the plain area of Beijing, China as an example. Here, rapid urbanization and a large-scale afforestation project have caused distinct IS and vegetation cover changes within a small range of years. Based on 8 scenes of Landsat 5 TM/7ETM/8OLI images (30 m × 30 m spatial resolution), 920 scenes of EOS-Aqua-MODIS LST images (1 km × 1 km spatial resolution), and other data/information collected by different approaches, this study characterized the interrelationship of the impervious surface area (ISA) dynamic, forest cover increase, and LST and SUHII changes in Beijing’s plain area during 2009–2018. An innovative controlled regression analysis and scenario prediction method was used to identify the contribution of ISA change and afforestation to SUHII changes. The results showed that percent ISA and forest cover increased by 6.6 and 10.0, respectively, during 2009–2018. SUHIIs had significant rising tendencies during the decade, according to the time division of warm season days (summer days included) and cold season nights (winter nights included). LST changes during warm season days responded positively to a regionalized ISA increase and negatively to a regionalized forest cover increase. However, during cold season nights, LST changes responded negatively to a slight regionalized ISA increase, but positively to an extensive regionalized ISA increase, and LST variations responded negatively to a regionalized forest cover increase. The effect of vegetation cooling was weaker than ISA warming on warm season days, but the effect of vegetation cooling was similar to that of ISA during cold season nights. When it was assumed that LST variations were only caused by the combined effects of ISA changes and the planting project, it was found that 82.9% of the SUHII rise on warm season days (and 73.6% on summer days) was induced by the planting project, while 80.6% of the SUHII increase during cold season nights (and 78.9% during winter nights) was caused by ISA change. The study presents novel insights on UHI alleviation concerning IS and green space planning, e.g., the importance of the joint planning of IS and green spaces, season-oriented UHI mitigation, and considering the thresholds of regional IS expansion in relation to LST changes.
The growth and physiological characteristics of four Magnoliaceae plants (
,
, and two varieties of
(Jiaohong 1 and Jiaohong 2)) were investigated. Four Magnoliaceae plants were subjected to various ...concentrations of NaCl for 60 days: 0 mM, 60 mM, 120 mM, 180 mM, and 240 mM. The leaf water content (LWC), relative growth rate of plant height and stem diameter, photosynthetic pigments, and photosynthetic rate (
) decreased during the NaCl treatments, indicating slowed growth and photosynthesis. Malondialdehyde (MDA), Na
, superoxide dismutase (SOD) activity, peroxidase (POD) activity, ascorbic acid (AsA) content, and soluble sugar content all increased while K
decreased. Ascorbate peroxidase (APX) activity, glutathione (GSH), soluble protein, and proline first increased after decreasing with increasing NaCl concentration. Principal component 1 (PC1) had larger loading values for growth and photosynthesis indices, while principal component 2 (PC2) exhibited larger loading values for antioxidant substances and osmotic adjustment substances; the correlation analysis showed that PC1 and PC2 had negative correlations. The four Magnoliaceae plants exhibited largely variable growth and physiological activities in response to NaCl.
exhibited greater reductions in growth and photosynthesis and greater decreases in antioxidant enzyme activities and osmotic adjustment substances, which indicated poor tolerance to salt stress. Among the four Magnoliaceae plants, Jiaohong 1 exhibited the greatest salt tolerance, followed by Jiaohong 2,
, and
.
Tree shape can affect microclimate, which may directly influence fruit growth and development. Open center and round head are two tree canopy shapes that are generally used in Camellia oleifera Abel. ...cultivation. To study the effects of the two canopy shapes on the microclimate and fruit quality parameters inside the canopy and investigate the correlations between microclimate and oil yield characteristics, microclimates in different developmental periods and fruit quality parameters at maturity at different positions in the two canopy shapes were determined. In this study, the open-center shape increased the light intensity and temperature, and reduced the relative humidity within the canopy, and the microclimate was more uniformly distributed within the open-center canopy. Fruit quality parameters of open-center canopied trees were also significantly increased and had more uniform distributions, especially the oil yield parameters. The content ratio of the dry seed, oil content ratio of the fresh fruit, and oil yield increased by 43.55%, 59.30% and 79.01%, in the lower layer, respectively, and 27.33%, 41.75%, and 55.43%, in the inner canopy, respectively, compared to those of round-head canopied trees. For both canopy shapes, oil yield parameters had positive correlations with light intensity and temperature, but negative correlations with relative humidity, and the correlation coefficients between light intensity and temperature at different developmental stages and oil yield parameters in round-head canopies were greater than in the open-center canopies. Additionally, regression equations between the single microclimatic factor in different developmental periods and oil yield parameters could be used to estimate the latter in the two canopy shapes. The optimum light conditions for open-center and round-head canopy shapes were 916–1893 and 1108–1259 μmol·m2·s−1, respectively. Overall, the open-center canopy had a more desirable microclimate and a more uniform microclimate distribution, especially the light intensity, which contributes to high uniform fruit quality parameters. Thus, an open-center canopy is the desirable shape in C. oleifera production.
A decline in soil quality is a major factor contributing to the degradation of forest ecological function. Vegetation plays a vital role in maintaining soil quality; however, the influence of ...plantation length on soil quality remains unclear. In this study, we collected soil samples in Northern China using a space-for-time substitution method. Soil were collected from control grassland; a clear-cutting site; 16-year-old (young, first, and second generation), 28-year-old (immature, first, and second generation), and 44-year-old (mature, first generation) Larix principis-rupprechtii Mayr stands in May, July, and September 2016. We measured soil physical and chemical properties, microbial communities, and enzymatic activities. We selected soil bulk density, non-capillary porosity, volume humidity, soil organic carbon and activity of polyphenol oxidase to calculate a soil quality index (SQI) for each site. Our data indicated that clear-cutting greatly decreased soil quality of Larix principis-rupprechtii forests but returning the harvesting residues to the forest floor could reduce the negative impact of clear-cutting on soil quality. The soil quality improved significantly by prolonging the cultivation cycle and it took about 39 years for the first-generation forest to restore soil quality to the level of the control plot. Our study confirms that SQI provides a comprehensive measurement of soil quality with the identification of a minimum data set. Comparing SQI with other soil quality indicators would help us to optimize the method for assessing soil quality.
In Hebei Province of North China, forest was recovered with natural recruitment in plantations with large area of clear-cutting Chinese pine (
Pinus tabuliformis
). This study was aimed to ...demonstrate the dynamic characteristics of recruits during the natural recruitment. Both plot survey and the spatial point-pattern analysis were performed. Five developmental stages of natural recruitment were selected and studied, including 1 year before and 2, 5, 8, and 11 years after clear-cutting. Different slope aspects were also included. Natural recruitment was always dominated by Chinese pine with a proportion of higher than 90%. For plots of 1 year before clear-cutting on east- and north-facing slopes, recruit densities were 7886 and 5036 stems/hm
2
, the average heights were 0.78 (±0.85) and 1.06 (±1.15) m, and the average diameters at breast height (DBH) were 3.21 (±1.38) and 2.91 (±1.38) cm, respectively. After clear-cutting, recruit density was initially increased, then it was gradually declined with time; however, the variation of average DBH was contrary to that of recruit density. Both of them were no longer varied between 8 and 11 years after clear-cutting. The average height of recruits continued to increase after clear-cutting. For the plots of 11 years after clear-cutting on east- and north-facing slopes, average heights of recruits reached 2.00 (±1.14) and 2.24 (±1.20) m, respectively. The statuses of recruits on north-facing slopes were better than those on east-facing slopes after clear-cutting. Meanwhile, recruits on east-facing slopes were always aggregated at small scales, while spatial pattern of recruits varied with time on north-facing slopes. Moreover, forest was recovered more quickly by natural recruitment than by artificial afforestation after clear-cutting. The structural diversity was higher in naturally regenerated forests than in plantations of the same age. Our results demonstrated that clear-cutting of Chinese pine plantations recovered by natural recruitment has the potential to be an effective approach for establishing multifunctional forest.
China has extensive areas of forest plantations that sequester and store large quantities of carbon. However, the rate of carbon sequestration by Chinese arborvitae (Platycladus orientalis Linn. ...Franco) is unknown. This research looks at carbon stocks and fluxes in forest vegetation, soil and litter seven years after thinning Chinese arborvitae in order to evaluate the effect of thinning levels on carbon sequestration. At 22 years, the plots were reduced from 5900 to 4100 and 3000 trees per hectare in three replicates. Carbon stocks of above-ground tree materials were lowest in the heaviest thinned plots and highest in the control plots. Above-ground shrub carbon pools were the opposite, i.e., largest in the heaviest thinned plots and lowest in the controls. Soil and litter carbon stocks were not affected by thinning treatment. Results suggest that thinning may positively affect vegetation carbon sequestration in the short term, an important observation for forest managers using thinning to optimize carbon sequestration capacity.
•We surveyed the use of urban green spaces by young urban residents.•Low-intensity activities such as walking were the most common activities.•Living context, quality of vegetation, and accessibility ...affect the use significantly.•Physical activities can be encouraged by increase the link of existing green spaces.
Urban green spaces hold great potential for promoting an active life style that allows urban residents to achieve important health benefits. The type of urban green space that is most effective to reach these goals is still unclear. In this study we used an online survey to investigate the ways in which young, urban residents in Beijing, China use urban green spaces for physical activities. We analyzed the factors that affect the residents’ satisfaction levels when participating in physical activities in urban green spaces by using ordinal logistic regression. Responses from the 1062 survey participants indicated that low-intensity activities (e.g., walking, sightseeing) were the most common activities. The living context, quality of vegetation, and accessibility of urban green spaces had a significant effect on residents’ satisfaction levels. For a compact city like Beijing, we recommended plans that focus on increasing the link among existing urban green spaces and improve the maintenance of residential green spaces in order to increase the use of urban green spaces for physical activities.
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