Ground-level ozone (O3) affects vegetation and threatens environmental health when levels exceed critical values, above which adverse effects are expected. Cyprus is expected to be a hotspot for O3 concentrations due to its unique position in the eastern Mediterranean, receiving air masses from Europe, African, and Asian continents, and experiencing a warm Mediterranean climate. In Cyprus, the spatiotemporal features of O3 are poorly understood and the potential risks for forest health have not been explored. We evaluated O3 and nitrogen oxides (NO and NO2) at four regional background stations at different altitudes over 2014−2016. O3 risks to vegetation and human health were estimated by calculating accumulated O3 exposure over a threshold of 40 nmol mol−1 (AOT40) and cumulative exposure to mixing ratios above 35 nmol mol−1 (SOMO35) indices. The data reveal that mean O3 concentrations follow a seasonal pattern, with higher levels in spring (51.8 nmol mol−1) and summer (53.2 nmol mol−1) and lower levels in autumn (46.9 nmol mol−1) and winter (43.3 nmol mol−1). The highest mean O3 exposure (59.5 nmol mol−1) in summer occurred at the high elevation station Mt. Troodos (1819 m a.s.l.). Increasing (decreasing) altitudinal gradients were found for O3 (NOx), driven by summer–winter differences. The diurnal patterns of O3 showed little variation. Only at the lowest altitude O3 displayed a typical O3 diurnal pattern, with hourly differences smaller than 15 nmol mol−1. Accumulated O3 exposures at all stations and in all years exceeded the European Union’s limits for the protection of vegetation, with average values of 3-month (limit: 3000 nmol mol−1 h) and 6-month (limit: 5000 nmol mol−1 h) AOT40 for crops and forests of 16,564 and 31,836 nmol mol−1 h, respectively. O3 exposures were considerably high for human health, with an average SOMO35 value of 7270 nmol mol−1 days across stations and years. The results indicate that O3 is a major environmental and public health issue in Cyprus, and policies must be adopted to mitigate O3 precursor emissions at local and regional scales.
Ecological stoichiometry is an important indicator of biogeochemical cycles and nutrient limitations in terrestrial ecosystems. However, little is known about the response of ecological stoichiometry to plant growth. In this study, carbon (C), nitrogen (N), and phosphorus (P) concentrations were evaluated in plant tissues (trees, shrubs, and herbs), litter, and soil of young (≤ 40-year-old), middle-aged (41–60-year-old), near-mature (61–80-year-old), and mature (81–120-year-old) Quercus secondary forests on the Loess Plateau, China. Vegetation composition, plant biomass, and C stock were determined to illustrate their interaction with stoichiometry. Only tree biomass C significantly increased with stand development. Leaf N and trunk P concentrations generally increased, but branch P decreased with growth stage. Fine roots had the highest C and P concentrations at the middle-aged stage. In contrast, shrubs, herbs, litter, and soil C:N:P stoichiometry did not change significantly during stand development. Leaf N and P were positively correlated with soil C, N, P, and their ratios. However, there was no significant correlation between litter and leaves in terms of C:N:P stoichiometry. A redundancy analysis showed that soil N best explained leaf N and P variance, and tree biomass and C stock were related to biotic factors such as tree age and shrub biomass. Hierarchical partitioning analysis indicated that, compared with soil or litter variables, stand age only accounted for a relatively small proportion of leaf C, N, and P variation. Thus, secondary Quercus ecosystems might have inherent ability to maintain sensitive responses of metabolically active organs to environmental factors during stand aging. The results of this work help to elucidate the biogeochemical cycling of secondary forest ecosystems in tree development, provide novel insights into the adaptation strategies of plants in different organs and growth stages, and could be used to guide fertilization programs and optimize forest structure.
Prescribed burning can alter soil microbial activity and spatially redistribute soil nutrient elements. However, no systematic, in-depth studies have investigated the impact of prescribed burning on the spatial patterns of soil microbial biomass in temperate forest ecosystems in Northeast China. The present study investigated the impacts of prescribed burning on the small-scale spatial heterogeneity of microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) in the upper (0–10 cm) and lower (10–20 cm) soil layers in Pinus koraiensis and Quercus mongolica forests and explored the factors that influence spatial variations of these variables after prescribed burning. Our results showed that, MBC declined by approximately 30% in the 10–20 cm soil layer in the Q. mongolica forest, where there were no significant effects on the soil MBC and MBN contents of the P. koraiensis forest (p > 0.05) after prescribed burning. Compared to the MBC of the Q. mongolica forest before the prescribed burn, MBC spatial dependence in the upper and lower soil layers was approximately 7% and 2% higher, respectively. After the prescribed burn, MBN spatial dependence in the upper and lower soil layers in the P. koraiensis forest was approximately 1% and 13% lower, respectively, than that before the burn, and the MBC spatial variability in the 0–10 cm soil layer in the two forest types was explained by the soil moisture content (SMC), whereas the MBN spatial variability in the 0–10 cm soil layer in the two forests was explained by the soil pH and nitrate nitrogen (NO3 –-N), respectively. In the lower soil layer (10–20 cm) of the Q. mongolica forest, elevation and ammonium nitrogen (NH4 +-N) were the main factors affecting the spatial variability of MBC and MBN, respectively. In the 10–20 cm soil layer of the P. koraiensis forest, NO3 –-N and slope were the main factors affecting the spatial variability of MBC and MBN, respectively, after the burn. The spatial distributions of MBC and MBN in the two forests were largely structured with higher spatial autocorrelation (relative structural variance C/[C 0 + C] > 0.75). However, the factors influencing the spatial variability of MBC and MBN in the two forest types were not consistent between the upper and lower soil layers with prescribed burning. These findings have important implications for developing sustainable management and conservation policies for forest ecosystems.
Accurate assessment of postfire vegetation recovery is important for forest management and the conservation of species diversity. Topography is an important factor affecting vegetation recovery but whether species composition varies with different recovery stages and between valleys and slopes is unclear. Using field data and a space-for-time substitution method, we quantified species richness and diversity to obtain the successional trajectories of valleys and slopes. We surveyed the species of 10 burned areas from 1986 to 2010 in the Greater Khingan Mountains in northeastern China, and found that with increasing postfire recovery time, species richness in both valleys and slopes gradually decreased. However, species richness in valleys was relatively higher. Shrubs recovered rapidly in the valleys, and species diversity maximized approximately 11 years after fire. However, it maximized 17–18 years after fire on the slopes. Numerous shade-tolerant species were present in the valleys 11 years after fire but not until after 18 years on slopes. Larch appeared earlier than 11 years after fire and its recovery was slow in the valleys but appeared quickly on slopes and established dominance early. Our study provides some new insights into vegetation succession after fire at local scales. After fire, the vegetation recovery processes differ with topography and it affects the initial rate of recovery and species composition at different successional stages.
Tropical forests provide several ecosystem services and functions and support approximately two-thirds of the world’s biodiversity but are seriously threatened by deforestation. Approaches to counteract this menace have revolved around afforestation with several or a single tree species. We thus investigated how plantation forests with either a single or several tree species influenced arthropod taxonomic and community composition using pitfall traps to sample selected groups of epigeal arthropods (Araneae, Coleoptera, Orthoptera and Hymenoptera) and with environmental variables assessed simultaneously. Our results revealed 54 taxonomic groups with significantly higher taxonomic richness, activity density, and diversity in the mixed stands than in the monoculture stands. The significant differences in community composition were mainly driven by families including Lycosidae, Formicidae, Staphylinidae, Scotylidae, Hydrophilidae, Gryllidae and Scarabaeidae and were explained by distinct habitat characteristics (canopy openness, litter depth, deadwood volume, and tree height). While the diverse tree communities and heterogeneous vegetation structure offered food and habitat resources for diverse arthropod groups, the allelopathic nature coupled with homogenous stand characteristics of the Tectona grandis stands in the monoculture suppressed the growth of understorey vegetation that could otherwise serve as food and habitat resources for arthropods, which might have led to limited activities and diversity of arthropods in the monoculture plantation stands. The findings thus highlight the need to promote mixed tree plantations in degraded tropical areas, especially when restoring biodiversity is the prime management focus.
How can we regulate an invasive alien species of high commercial value? Black locust (Robinia pseudoacacia L.) has a unique capacity for seed dispersal and high germination. Field surveys indicate that black locust increases its growing area with sprouting roots and the elongation of horizontal roots at a soil depth of 10 cm. Therefore, a method to regulate the development of horizontal roots could be effective in slowing the invasiveness of black locust. In this study, root barrier panels were tested to inhibit the growth of horizontal roots. Since it is labor intensive to observe the growth of roots in the field, it was investigated in a nursery setting. The decrease in secondary flush, an increase in yellowed leaflets, and the height in the seedlings were measured. Installing root barrier panels to a depth of 30 cm effectively inhibit the growth of horizontal roots of young black locust.
Fine roots play key roles in belowground C cycling in terrestrial ecosystems. Based on their distinct functions, fine roots are either absorptive fine roots (AFRs) or transport fine roots (TFRs). However, the function-based fine root dynamics of trees and their responses to forest stand properties remain unclear. Here, we studied the dynamics of AFRs and TFRs and their responses to stand conditions and root density in a subtropical montane mixed forest based on a 2-a root window experiment. Mean (± SE) annual production, mortality, and turnover rate of AFRs were 7.87 ± 0.17 m m−2 a−1, 8.13 ± 0.20 m m−2 a−1and 2.96 ± 0.24 a−1, respectively, compared with 7.09 ± 0.17 m m−2 a−1, 4.59 ± 0.17 m m−2 a−1, and 2.01 ± 0.22 a−1, respectively, for TFRs. The production and mortality of fine roots were significantly higher in high root-density sites than in low-root density sites, whereas the turnover of fine roots was faster in the low root-density sites. Furthermore, root density had a larger positive effect than other environmental factors on TFR production but had no obvious impact on AFR production. Tree species diversity had an apparent positive effect on AFR production and was the crucial driver of AFR production, probably due to a complementary effect, but had no evident impact on TFR. Both tree density and tree species diversity were positively correlated with the mortality of AFRs and negatively related to the turnover of TFRs, suggesting that higher root density caused stronger competition for rooting space and that plants tend to reduce maintenance costs by decreasing TFR turnover. These findings illustrated the importance of root functional groups in understanding root dynamics and their responses to changes in environmental conditions.
Gingko biloba accumulates high levels of secondary metabolites of pharmaceutical value. Ginkgo calli develop a typical browning that reduces its regenerative capacity and thus its usefulness. To elucidate the browning mechanism, histological, transcriptomic, and metabolic alterations were compared between green and browning calli derived from immature ginkgo embryos. Histological observations revealed that browning calli had a more loosely arranged cell structure and accumulated more tannins than in green calli. Integrated metabolic and transcriptomic analyses showed that phenylpropanoid metabolism was specifically activated in the browning calli, and 428 differentially expressed genes and 63 differentially abundant metabolites, including 12 flavonoid compounds, were identified in the browning calli compared to the green calli. Moreover, the expression of flavonol synthase (FLS) and UDP-glucuronosyl-transferase (UGT) genes involved in the flavonoid pathway was more than tenfold higher in browning calli than in green calli, thus promoting biosynthesis of flavonol, which serves as a substrate to form glycosylated flavonoids. Flavonoid glycosides constituted the major coloring component of the browning calli and may act in response to multiple stress conditions to delay cell death caused by browning. Our results revealed the cellular and biochemical changes in browning callus cells that accompanied changes in expression of browning-related genes, providing a scientific basis for improving ginkgo tissue culturability.
Light flux and quality are crucial factor for setting endogenous plant circadian rhythms. Evaluating the daily rhythmicity of leaf chlorophyll content is an effective method to monitor the plant physiological endogenous clock in response to environmental signals such as light availability/quality. Here, we used a leaf-clip sensor to monitor diurnal rhythms in the content of chlorophyll and flavonoids such as flavonols and anthocyanins in three green- (Ailanthus altissima, Tilia platyphyllos and Platanus × acerifolia) and two red-leafed (Acer platanoides cv. Crimson King and Prunus cerasifera var. pissardii) tree species, adapted to sun (L) or shade (S). Significant differences in chlorophyll content (Chl) and its variations during the day were observed among treatments in all the analyzed species. S-plants had more Chl than L-plants irrespective of leaf color, and Chl variations were more distinct during the day than in L-plants. In particular, contents were lowest in the morning (9:00) and in the middle of the day (at 12:00 and 15:00), and the highest at dusk (21:00). The less evident trends in Chl variation in L-plants were attributed to a decrease in Chl content in high light, which likely masked any increases in the shaded counterparts during the afternoon. Daily flavonol levels did not vary no notably during the day. In sun-exposed red leaves, anthocyanins partially screened mesophyll cells from incident light, and its levels were similar to the Chl dynamics in the shaded counterparts. This study provides new bases for further work on endogenous rhythms of plant pigments and improves our understanding of plant physiology in the context of day/night rhythmicity.
Larix resources in the Qinghai-Tibet Plateau have important ecological and economic values. However, the lack of genetic diversity background and related research hinders the development of conservation strategies. In this study, genetic diversity and distribution of five Larix species were investigated. Using 19 polymorphic microsatellite markers to study 272 representative individuals from 13 populations, the results show low genetic diversity at the population level, with variation explained mainly by differentiation among populations. The Larix populations were classified into two clades, one formed by eight populations, including three of the species in this study, L. kongboensis, L. speciosa, and L. potaninii var. australis. The other clade consists of five populations, including the other two species in this study, L. griffithii and L. himalaica. Genetic distance of the species was affected by geographical isolation and genetic diversity was mainly affected by altitude. The area suitable for Larix spp. decreased during the Last Glacial Maximum compared to the current distribution according to the niche model, but should increase in future climate scenarios (2050s), expanding westward along the Himalayas. These results provide an important scientific basis for the development of conservation strategies and further the sustainable utilization of Larix resources in the Qinghai-Tibet Plateau.
Genomics research of Populus deltoides, an important timber species that is widely planted worldwide, is an important part of poplar breeding. Currently, the nuclear and chloroplast genome of P. deltoides have been sequenced, but its mitochondrial genome (mitogenome) has not been reported. To further explore the evolution and phylogeny of P. deltoides, the mitogenome of P. deltoides I-69 was assembled using reads from Nanopore and Illumina sequencing platforms and found to consist of 802,637 bp and three circular chromosomes (336,205, 280,841, and 185,591 bp) containing 58 genes (34 protein-coding genes, 21 tRNA genes, and 3 rRNA genes). RNA analysis in combination with several species showed significantly fewer RNA editing sites in the mitogenomes of poplar and other angiosperms than in gymnosperms. Sequence transfer analysis showed extensive mitogenome rearrangements in Populus species, and with evolution from lower to higher plants, tRNA transfer from chloroplasts to mitochondria became increasingly frequent. In a phylogenetic analysis, the evolutionary status of P. deltoides was determined, and the section Populus was supported. Our results based on the first report of a multi-circular conformation of the Populus mitogenome provide a basis for further study of the evolution and genetics of P. deltoides and other Populus species and for breeding programs.
The little layer of tree plantations provides primary nutrients for uptake, buffers changes in soil moisture, and provides habitat and substrate to soil epigeic fauna. However, this layer in eucalypt plantations is often removed to reduce fuel load during the fire season in the Brazilian savanna (Cerrado). Therefore, it is necessary to quantify the effects of changes in litter dynamics on the function of these plantations, on key nutrient cycling processes and on epigeic fauna diversity and abundance. In two adjacent stands (one juvenile and one mature), the consequences of two years of litter removal were quantified as monthly litterfall, leaf and fine wood litter decomposition, epigeic fauna abundance and diversity, soil biogeochemical variables, and tree diameter and basal area increments. Monthly litterfall rates in juvenile and mature stands did not change with litter removal over the study period. Annual litterfall ranged from 4.1 to 4.9 Mg ha−1a−1 in litter removal plots and from 3.9 to 4.8 Mg ha−1a−1 in control plots. Fine wood litter decomposition was slower in litter removal plots compared to controls, while leaf decomposition rates were similar in both. Two years of litter removal in the juvenile stand did not affect topsoil biogeochemical parameters but decreased available phosphorus at 20–40 cm depth relative to controls. In the mature stand, total cation exchange capacity (0–20 cm) was higher in controls (6.4 cmolc dm−3) relative to litter removal plots (6.3 cmolc dm−3), while soil moisture (0–40 cm depth) was lower in litter removal (25.45 m3 m−3) compared to control plots (26 m3 m−3) in the dry season. A non-metric multidimensional scaling ordination revealed an increased homogeneity in epigeic fauna where litter was removed. Litterfall, decomposition, diameter increment, four soil physical parameters and fourteen chemical parameters at 0–20 and 20–40 cm depth explained the differences in soil epigeic fauna composition between litter removal and control plots. Diameter increment decreased with litter removal only in the juvenile stand, which had reached its growth peak. The results indicate that removing excess litter to decrease fuel volume can alter soil biodiversity and edaphic conditions that negatively affect nutrient cycling and tree growth.
Boreal forests commonly suffer from nitrogen deficiency due to low rate of nitrogen mineralization. Biochar may promote soil organic matter decomposition and accelerate nitrogen mineralization. In this study, Illumina NovaSeq sequencing combined with functional annotation of prokaryotic taxa (FAPROTAX) analysis was used to investigate the effect of biochar pyrolysis temperatures, the amount of applied biochar, and the period since the biochar application (2- and 3-year) on soil bacterial communities. The results show that biochar pyrolysis temperatures (500 °C and 650 °C) and the amount of applied biochar (0.5 kg m−2 and 1.0 kg m−2) did not change soil properties. Nevertheless, the interaction of biochar pyrolysis temperature and the amount had significant effects on bacterial species richness and evenness (P < 0.05). The application of biochar produced at 500 °C had a lower abundance of Actinobacteria and Verrucomicrobia, while that produced at 650 °C had a higher abundance of Conexibacter and Phenylobacterium. When biochar produced at 650 °C was applied, applying 0.5 kg m−2 had a higher abundance of Cyanobacteria, Conexibacter, and Phenylobacterium than that of 1.0 kg m−2 (P < 0.05). Functionally, the abundance of the aromatic compound degradation group increased with the extension of application time and increase of pyrolysis temperature. The time since application played an important role in the formation of soil bacterial communities and their functional structure. Long-term studies are necessary to understand the consequence of biochar on bacterial communities in boreal forests.
Sexual dimorphism of plants shapes the different morphology and physiology between males and females. However, it is still unclear whether it influences belowground ecological processes. In this study, rhizosphere soil of male and female Populus deltoides and bulk soil were collected from an 18-year plantation (male and female trees mix-planted) and grouped into three soil compartments. Soil carbon (C), nitrogen (N) and phosphorus (P) levels were determined, and soil bacterial communities were analyzed by high-throughput sequencing. The results showed the less total carbon and total organic carbon, the more nutrients (available phosphorus, nitrate nitrogen and ammonium nitrogen) available in the rhizosphere soils of female poplars than soils of males. However, α-diversity indices of the rhizosphere bacterial communities under male plants were significantly higher. Principal component analysis showed that the bacterial communities were significantly different between the male and female soil compartments. Further, the bacterial co-occurrence network in soil under male trees had more nodes and edges than under females. BugBase analysis showed the more functional bacteria taxa related to biofilm formation and antioxidation under males. The results indicate that soils under male poplars had more diverse and more complex co-occurrence networks of the rhizosphere bacterial community than soils under female trees, implying that male poplars might have better environmental adaptability. The study provides insight into the different soil-microbe interactions of dioecious plants. More details about the influencing mechanism of sexual dimorphism on rhizosphere soil bacterial communities need to be further studied.
Though riparian areas generally have a shallow water table and higher soil moisture compared to upslope areas, climatic seasonality may trigger water repellency in tropical riparian forests, which, if persistent, could negatively affect essential ecosystem functions related to water resources protection such as reduced overland-flow, sediment transport, and nutrient filtration. The objective of this study was to answer the following: can tropical riparian forests develop water repellency? If so, does water repellency affect infiltration on a seasonal basis? For this, water repellency and infiltration were measured in a grid of 72 points during a dry and a wet month of a tropical riparian forest with a shallow water table in a region with highly marked climatic seasonality. Water repellency and infiltration were significantly different between the wet and dry months. Water repellency affected negatively infiltration in the dry month, its effect in the wet month was insignificant. As a result, a higher infiltration capacity was observed over the wet period. Previous research has claimed that the development and persistence of repellency in soils could promote other hydrological processes such as overland flow. The findings shown here demonstrate that such phenomenon does not persist longer than the dry season.
Many tree planting programmes have long been initiated to increase forest cover to mitigate the effects of global climate change. Successful planting requires careful planning at the project level, including using suitable species with favourable traits. However, there is a paucity of improvement data for tropical tree species. An experimental common garden of Shorea leprosula was established to study traits related to growth performance which are key factors in planting success. Seedlings of S. leprosula were collected from nine geographical forest reserves. To study the effects of genetic variation, seedlings were planted in a common environment following a randomized complete block design. From performance data collected 2017‒2019, one population showed the highest coefficient for relative height growth, significantly higher than most of the other populations. Interestingly, this population from Beserah also exhibited the lowest coefficient for scale insect infestation. This study provides preliminary results on growth performance and susceptibility to scale insect infestation in S. leprosula and the first common garden experiment site conducted on dipterocarp species. It lays a foundation for future genome-wide studies.
Cork oak forests in Morocco are rich in resources and services thanks to their great biological diversity, playing an important ecological and socioeconomic role. Considerable degradation of the forests has been accentuated in recent years by significant human pressure and effects of climate change; hence, the health of the stands needs to be monitored. In this study, the Google Engine Earth platform was leveraged to extract the normalized difference vegetation index (NDVI) and soil-adjusted vegetation index, from Landsat 8 OLI/TIRS satellite images between 2015 and 2017 to assess the health of the Sibara Forest in Morocco. Our results highlight the importance of interannual variations in NDVI in forest monitoring; the variations had a significantly high relationship (p < 0.001) with dieback severity. NDVI was positively and negatively correlated with mean annual precipitation and mean annual temperature with respective coefficients of 0.49 and − 0.67, highlighting its ability to predict phenotypic changes in forest species. Monthly interannual variation in NDVI between 2016 and 2017 seemed to confirm field observations of cork oak dieback in 2018, with the largest decreases in NDVI (up to − 38%) in December in the most-affected plots. Analysis of the influence of ecological factors on dieback highlighted the role of substrate as a driver of dieback, with the most severely affected plots characterized by granite-granodiorite substrates.
Airborne laser scanning (ALS) and terrestrial laser scanning (TLS) has attracted attention due to their forest parameter investigation and research applications. ALS is limited to obtaining fine structure information below the forest canopy due to the occlusion of trees in natural forests. In contrast, TLS is unable to gather fine structure information about the upper canopy. To address the problem of incomplete acquisition of natural forest point cloud data by ALS and TLS on a single platform, this study proposes data registration without control points. The ALS and TLS original data were cropped according to sample plot size, and the ALS point cloud data was converted into relative coordinates with the center of the cropped data as the origin. The same feature point pairs of the ALS and TLS point cloud data were then selected to register the point cloud data. The initial registered point cloud data was finely and optimally registered via the iterative closest point (ICP) algorithm. The results show that the proposed method achieved high-precision registration of ALS and TLS point cloud data from two natural forest plots of Pinus yunnanensis Franch. and Picea asperata Mast. which included different species and environments. An average registration accuracy of 0.06 m and 0.09 m were obtained for P. yunnanensis and P. asperata, respectively.
The important contributions of urban trees and green spaces to for example, climate moderation and public health have been recognized. This paper discusses guidelines and norms that promote the benefits of viewing green, living amongst green, and having easy access to green spaces for recreational use. Having trees and other vegetation in sight from one’s home, place of work, or school has important mental health and performance benefits. Local tree canopy cover is positively associated with cooling and other aspects of climate moderation. With public green spaces in proximity to one’s home stimulates regular use of these areas and results in positive impacts on mental, physical, and social health. After analyzing existing guidelines and rules for urban green space planning and provision, a new, comprehensive guideline is presented, known as the ‘3–30–300 rule’ for urban forestry. This guideline aims to provide equitable access to trees and green spaces and their benefits by setting the thresholds of having at least 3 well-established trees in view from every home, school, and place of work, no less than a 30% tree canopy in every neighbourhood; and no more than 300 m to the nearest public green space from every residence. Current implementation of this new guideline is discussed, as well as the advantages and disadvantages of using this evidence-based but also clear and simple rules.
Together, the heat island effect and air pollution pose a threat to human health and well-being in urban settings. Nature-based solutions such as planting trees are a mitigation strategy to improve outdoor temperatures (thermal comfort) and enhance air quality in urban areas. In this study, outdoor thermal comfort, and particulate matter levels were compared between treeless and treed areas to provide a better understanding of how street trees improve thermal comfort and air quality. Street trees decreased the physiological equivalent temperature from 46.3 to 44.2 °C in summer but increased it from 36.4 to 37.5 °C in autumn. Air temperature and relative humidity contributed more in summer while wind speed contributed more in autumn. Particulate matter concentrations were negatively correlated with physiological equivalent temperature in summer but not in autumn. The presence of trees decreased concentrations of fine particulate matter in hot summer conditions but increased in hot autumn conditions. The presence of trees increased coarse particulate matter in very hot summer conditions in summer and in hot autumn conditions. Overall, the layout of trees in urban street canyons should consider the trade-off between outdoor thermal comfort and air quality improvement.
As a cultural concept reflecting the relationship between humans and forests, forest culture plays an active role in sustainable forest management. Forest parks provide a wide range of ecosystem services essential for the sustainable development of society, and the relationships between forest culture, green construction and management of forest parks have practical significance. This study aimed to understand the interaction and process of forest culture influencing green construction and management in forest parks with the models Knowledge-Attitude-Practice (KAP) and Theory of Planned Behavior (TPB) by proposing a theoretical model. Four hypotheses were tested using data collected from 193 forest park employees in Heilongjiang Province, China. Our results show that forest culture had a significant influence on green construction and forest management. In addition, subjective norm and perceived behavioral control directly impacted behavior in green construction and management of the forest park, whereas attitude did not have an impact. Subjective norm had a direct effect on attitude. Results between constructs show that forest culture had an indirect effect on planning and construction, and on ecological and economic management. Consequently, it supported three of four hypotheses within the proposed model in determining the influence of forest culture on green construction and management.
Basic wood density is an excellent indicator of quality, it is correlated with numerous physical, physiological and mechanical characteristics of a species and is a good descriptor of wood quality and important indicator of tree performance in community ecology. An accurate method is thus needed to estimate wood density. The standard way is to calculate the ratio of the oven-dried mass of a wood sample divided by its green volume, but wood characteristics within and between growth rings are highly variable; the density can vary in the longitudinal and the radial directions. The present study investigates the longitudinal and radial fluctuations in the basic density of Abies cephalonica Loud and Pinus halepensis Mill. Four logs were cut from four different trees for each species and 16 discs were formed (two discs from each log, one at the base and one at the top). Each disc was cut into cubes where their distance from the pith was measured and then sorted into 2 cm wide concentric zones. The results revealed a mild decreasing trend in basic density from the foot of the trunk upward for both species. The pith in both species also seems to have a relatively high density, which in the immediate next growth rings decreases only to resume increasing toward the bark.
Oil palm plantations have dramatically expanded in tropical Asia over the past decades. Although their establishment has been projected to increase nitrous oxide (N2O) emissions, earlier reports have shown inconsistent results. This study analyzed these previously published data to compare N2O emissions in oil palm plantations to reference forests. A linear mixed-effects model was used to examine the significance of the effect of establishing oil palm plantations on N2O emissions, rather than to calculate mean effect sizes because of limitations in the data structure. The results indicated that N2O emissions were significantly greater from oil palm plantations than from reference forests, as expected. This is the first study to report the effect of oil palm plantations on N2O emissions by synthesizing previously published data. To quantify the size of this effect, additional studies with frequent and long-term monitoring data are needed.
