Deciduous Broad-leaved Trees Research Articles

The mid-domain effect of mountainous plants is determined by community life form and family flora on the Loess Plateau of China

The mid-domain effect (MDE) explains altitudinal patterns of species diversity of mountainous plants at different elevations. However, its application is limited by the species life form and family flora in different layers of plant communities. To verify the MDE hypothesis at the plant community level, we chose a mountain with representative characteristics of the study area in the east of the Loess Plateau, China, such as obvious elevation (from 1324 to 2745 m) and latitude (from 36° 23′ to 39° 03′) gradients and considerable vegetation types (mainly coniferous and broad-leaved forests). We measured the life forms, families, and species diversity indices of tree, shrub, and herb communities along different elevations. We determined that the family numbers of the herb and shrub communities presented unimodal patterns across an altitudinal gradient, and the highest values occurred at intermediate elevations. The importance values of dominant families in the shrub and tree communities presented unimodal patterns, but the lowest values occurred at intermediate elevations. The species diversity indices of the herb, shrub, and tree communities conformed to unimodal change patterns following an altitudinal gradient, but the greatest diversity occurred at high, low, and intermediate elevations, respectively. At higher elevations, forbs and grasses grew well, whereas sedges grew well at lower elevations. Responses of different tree life forms to the altitudinal gradient were greater for evergreen coniferous tree species than for deciduous coniferous and deciduous broad-leaved tree species. We concluded that the MDE hypothesis of species diversity for mountainous plants is influenced greatly by the community life form and family at the plant community level in a temperate semi-arid region of the Loess Plateau, China. This conclusion tested and modified the MDE hypothesis and may be valuable for fueling prediction of biodiversity models and for the comparison with similar studies in arid and semi-arid mountainous regions.

Root architecture of main tree species and the effects on soil reinforcement in typical black soil region.

To explore root architecture and its effects on soil reinforcement of main tree species in typical black soil region, we measured root spatial distribution characteristics, root fractal characte-ristics, and geometric morphological characteristics of Amygdalus triloba, Caragana microphylla, Betula platyphylla, Acer negundo, Picea koraiensis, Pinus sylvestris var. mongolica, using whole root excavation method and WinRHIZO Pro LA2004 root analysis system. All the examined species are distributed widely in typical black soil region. The vertical uprooting force was determined by in-situ uprooting tests. The results showed that inclined roots were dominant in A. triloba, horizontal roots were dominant in C. microphylla, B. platyphylla, A. negundo and P. koraiensis, and the horizontal and vertical distribution of roots were commensurable in P. sylvestris var. mongolica. Except for the total root surface area of B. platyphylla and the total root length of P. koraiensis, the total root length and root surface area of shrub species were significantly greater than those of arbor species, while deciduous broad-leaved trees were significantly larger than coniferous evergreen trees. The total root volume of B. platyphylla was significantly larger than that of C. microphylla, A. negundo, P. koraiensis and P. sylvestris var. mongolica. The root fractal dimension and abundance of A. triloba, C. microphylla, B. platyphylla were significantly higher than those of P. koraiensis and P. sylvestris var. mongolica. The average maximum uprooting force of A. triloba, C. microphylla, and A. negundo was significantly higher than that of B. platyphylla, P. koraiensis, and P. sylvestris var. mongolica. Due to the role of total root length, total root surface area and the number of inclined roots, root system of A. triloba, C. microphylla and A. negundo showed strong soil reinforcement capacity. A. triloba, C. microphylla and A. negundo could be used as the option-preferred tree species when constructing soil and water conservation vegetation in typical black soil region.

Tree-Ring Based Chronology of Landslides in the Shirakami Mountains, Japan

The N-Ohkawa landslide, and the southern section of the Ohkawa landslide, occurred during the snow-melt seasons of 1999 and 2006, respectively, in the Shirakami Mountains, Japan. This paper examines the response of trees in the Shirakami Mountains to landslides, and also investigates the spatio-temporal occurrence patterns of landslide events in the area. Dendrogeomorphological analysis was used to identify growth suppression and growth increase (GD) markers in tilted deciduous broadleaved trees and also to reveal the timing of the establishment of shade-intolerant tree species. Analysis of the GD markers detected in tree-ring width series revealed confirmatory evidence of landslide events that occurred in 1999 and 2006 and were observed by eyewitnesses, as well as signals from eight additional (previously unrecorded) landslide events during 1986–2005. Furthermore, shade-intolerant species were found to have become established on the N-Ohkawa and southern Ohkawa landslides, but with a lag of up to seven years following the landslide events causing the canopy opening.

Growth Characteristics of <i>Quercus serrata</i> and <i>Quercus glauca</i> Seedlings in a Restored Urban Forest After Approximately 20 Years Since Construction

To clarify the regeneration processes of two Quercus (Fagaceae) species, Quercus serrata, deciduous broad-leaved tree and Quercus glauca, evergreen broad-leaved tree in an urban forest, 163 research quadrats (163 m2) on the forest floor in a restored deciduous broad-leaved forest, "Inochi- No-Mori" in Kyoto city after approximately 20 years since construction were set up. Growth characteristics, recruitment, mortality and relative height growth rates of seedlings of these two species were investigated. As a result, the recruitment rate of Q. serrata seedlings tends to be higher than that of Q. glauca seedlings, when diffuse site factor was larger than 15.0%, particularly. The relative height growth rate of Q. serrata seedlings in the 15–50-cm height class was relatively high when diffuse site factor was larger than 15.0%. On the other hand, the mortality rate of Q. glauca seedlings in the 15–50-cm height class was very lower than that of Q. serrata seedlings. These results indicate that in order to promote the regeneration of Q. serrata in this site, it is necessary to maintain a light environment with a diffuse site factor amount of larger than 15.0% around the mature Q. serrata trees, by thinning the upper trees and to selectively remove Q. glauca seedlings.

Converting cropland to plantation decreases soil organic carbon stock and liable fractions in the fertile alluvial plain of eastern China

Soil organic carbon (OC) stocks are well known to change as a result of land use change. However, the early responses of soil OC stock and liable fractions to converting cropland to plantation in the fertile alluvial plain remain unknown. Thus, we evaluated the OC stock, liable OC fractions [easily oxidizable carbon (EOC), light fraction organic carbon (LFOC), dissolved organic carbon (DOC) and microbial biomass carbon (MBC)] and carbon management index (CMI) in the 0-60 cm soil profile of an Anthrosols for three pure plantations (i.e., Metasequoia glyptostroboides, Cinnamomum camphora and Bischofia polycarpa) and the adjacent cropland. The marked reductions in OC stock and liable OC content were observed at the 7th year following converting cropland to plantation, and the smallest of these initial losses mostly occurred in Bischofia polycarpa plantation. The distributions of OC stock and liable OC content at the depth of 0–20 cm were changed following converting cropland to plantation. The CMI, EOC and LFOC are more sensitive than OC in response to the land use change, and are taken as the useful early indicators of soil OC dynamic. Although the losses of EOC, LFOC, DOC and MBC were significantly positively correlated with the OC loss, these liable OC fractions were not major part of soil OC loss. We conclude that the soil OC sequestration was significantly decreased in the short-term following converting cropland to plantation in the fertile alluvial plain, and the deciduous broad-leaved tree species (Bischofia polycarpa) for afforestation can mitigate the soil OC loss. Moreover, further research needs to confirm or not the results presented in the study after a long period of time.

Larch or Mongolian pine? Effects of tree species on soil properties and microbial biomass with the consideration of afforestation time

Tree species and afforestation age can affect soil carbon (C) and nitrogen (N) sequestration as well as soil properties through different litter input and microbial activities. However, uncertainty remains because the responses vary under different climates and prior land uses. A site-specific study was conducted to investigate the dissimilarities in plant litter, soil properties, and soil microbial biomass and their influencing factors of different aged (22, 32, and 44 years) larch (Larix principis-rupprechtii) plantations and different aged (19, 30, and 43 years) Mongolian pine (Pinus sylvestris var. mongolica) plantations. In general, afforestation increased soil organic carbon (SOC), soil total nitrogen (STN), soil microbial biomass carbon (MBC), and soil microbial biomass nitrogen (MBN) contents compared with those of sparse grassland. However, there was still room for improvement in these variables compared with local natural secondary forest, which was dominated by white birch (Betula platyphylla, a deciduous broad-leaved tree species). Changes in STN, SOC, MBC, and MBN contents with afforestation age were almost insignificant in larch plantations, while significant increase can be found in STN (only in 10–20 cm soil layer), MBC and MBN in Mongolian pine plantations. The results indicated that larch was superior to Mongolian pine in soil C and N sequestration and soil fertility improvement at an early afforestation stage probably because of the higher C and N inputs from litter and higher N supply in the soil. There is an upper limit of carbon and nitrogen sequestration and soil fertility in the coniferous plantation, and mix planting of broad-leaved trees in coniferous forests may make up for this disadvantage. This study provided a reference for the selection of afforestation tree species in northern China and other areas with similar climatic conditions.

A meta-analysis of changes in soil organic carbon stocks after afforestation with deciduous broadleaved, sempervirent broadleaved, and conifer tree species

Key message Different tree species have dissimilar capacities to sequester soil organic carbon (SOC). Deciduous broadleaved trees show the most stable increase in SOC stock after afforestation than other tree species, while sempervirent conifer trees show the lowest rate of SOC stock change. Sempervirent broadleaved trees show the greatest increase in SOC stock 20 years after afforestation. ContextThe rate at which soil organic carbon (SOC) stock changes after afforestation varies considerably with the tree species. A better understanding of the role of tree species in SOC change dynamic is needed to evaluate the SOC sequestration potential of afforestation programs.AimsThe aim of this paper is to identify the dissimilar rates at which different tree species sequester SOC, following afforestation.MethodsWe complete a meta-analysis with 544 data points from 261 sites in 90 papers. We group tree species into decidious broadleved, sempervirent broadleaved and sempervirent conifer. We use standardization and/or extrapolation methods to standardize soil depths. Statistical analysis test the main effects of tree species and their interactions with previous land use and plantation age on SOC stock change after afforestation.ResultsDeciduous broadleaved trees show a stable increase in SOC stock, and are especially suited for afforestation of grassland or soils with high initial SOC. Sempervirent broadleaved afforestation results in loss of SOC stock in young stands, but greater SOC stock in mature stands. Sempervirent conifer trees show the lowest rate of SOC stock change, but are suitable for nutrient-poor soil.ConclusionThe results emphasize the importance of considering tree species when estimating SOC stock change, in particular when carbon sequestration is an objective of afforestation programs.

Effect of Organic Materials Amendment on Growth of Jujube (Zizyphus jujuba Mill.) and Soil Chemical Properties

Jujube is a deciduous broad-leaved tree belonging to the buckthorn family(Rhamnaceae) and is widely cultivated in Southeast Asia and Southeast Europe, including Korea and China and mainly consumed medicinal herbs or dried jujube. In recent years, consumption of fresh fruits has increased, and organic orchard has also increased. The purpose of this study was to investigate soil chemical changes and growth characteristics of jujube when replacing the total amount of nitrogen fertilizer with organic matter in rain shelter house. In March 2017, after soil testing, bark, animal compost, rice bran, oil cake and chemical fertilizers (NPK) were treated based on nitrogen content. After treatment of organic materials, by March 2020, the pH increased and organic matter, phosphoric acid and cation content in soil increased. After harvest of jujube, the yield of compost treatment was the highest and the NPK treatment was the lowest. The length, hardness and weight of fruit were greater in the NPK treatment, but the diameter and sugar content were not significantly different from the organic material treatments except rice bran. Therefore, when the cultivation of the jujube, nitrogen fertilizer was totally replaced with organic material, there was the effect of improving soil chemistry, such as an increase in the organic content of the jujube orchard and an increase in the yield of jujube but no clear effect on fruit quality. Yield of jujube by organic materials treatment.

Vegetation evolution in response to climate change and rapid sea-level rise during 8.2–7.0 cal ka BP: Pollen evidence from the northwest coast of Bohai Bay, north China

To understand vegetation dynamics and their response to climate changes and sea-level rise (SLR) on the northern coast of the Bohai Sea during a marine transgression period (8.2–7.0 cal ka BP), we obtained two sedimentary cores (HG01 and HG02) with high-resolution accelerator mass spectrometry carbon-14 (14C) data from the coastal plain of Bohai Bay in northeastern China. A general warming and wetting trend from 8190 to 7920 cal a BP was indicated by the greater abundance of deciduous broadleaved forest, which showed that the Asian summer monsoon was stronger over this period. The abundance of deciduous broadleaved trees was relatively high, which revealed that the climate was relatively warm and wet and that the Asian summer monsoon was strong, during the periods of 7920–7690 cal a BP and 7230–7020 cal a BP. Broadleaved tree abundance decreased over the intervening period—from 7610 to 7230 cal a BP—suggesting a declining monsoon, and relatively cool, dry climate. The abrupt cooling event from 7460 to 7230 cal a BP may have been a global event, closely related to the decrease in solar activity and rapid SLR before 7460 cal a BP. The results also showed that the large number of halophytes mainly Chenopodiaceae, sharply increased at times, mirroring four SLR fluctuation periods: 7940–7860 cal BP, 7760–7700 cal BP, 7560–7460 cal BP, and 7230–7130 cal BP. SLR in Bohai Bay occurred during warm and wet climate periods, and the phased SLR observed during ~7.9–~7.1 cal ka BP may have been the local manifestation of a global event.

Intraspecific variation in spring leaf phenology and duration of leaf expansion in relation to leaf habit and leaf size of temperate tree species

Spring leaf phenology has been intensively studied in temperate deciduous broad-leaved tree species, but the phenology of evergreen broad-leaved tree species has seldom been focused on. Evaluation of the difference in spring leaf phenology between coexisting deciduous and evergreen species is essential to predict their responses to climate change. In this study, spring leaf phenology was investigated for the 12 deciduous and 12 evergreen broad-leaved species coexisting in a warm-temperate forest in Japan, based on the predictions that selection pressure for earlier leaf production in spring results in less intraspecific variation in phenology at a given timing (SDmax) and a shorter duration of leaf expansion in deciduous than in evergreen species. In contrast to this prediction, SDmax did not differ between deciduous and evergreen species and was not related to leaf area or LMA. On the other hand, the duration of leaf expansion was longer in evergreen than in deciduous species, and was positively correlated with LMA. The leaves of greater LMA required longer periods of leaf expansion, probably due to a higher cost of and/or more conservative leaf development in the face of herbivory. As a consequence, the timing of full leaf expansion was delayed not only by later budburst (approximately two weeks) but also by a longer duration of leaf expansion (approximately two weeks) in evergreen than in deciduous broad-leaved species, which would probably influence the productivity of newly emerging leaves in spring.

Evaluating the terrestrial carbon dioxide removal potential of improved forest management and accelerated forest conversion in Norway.

As a carbon dioxide removal measure, the Norwegian government is currently considering a policy of large-scale planting of spruce (Picea abies (L) H. Karst) on lands in various states of natural transition to a forest dominated by deciduous broadleaved tree species. Given the aspiration to bring emissions on balance with removals in the latter half of the 21st century in effort to limit the global mean temperature rise to "well below" 2°C, the effectiveness of such a policy is unclear given relatively low spruce growth rates in the region. Further convoluting the picture is the magnitude and relevance of surface albedo changes linked to such projects, which typically counteract the benefits of an enhanced forest CO2 sink in high-latitude regions. Here, we carry out a rigorous empirically based assessment of the terrestrial carbon dioxide removal (tCDR) potential of large-scale spruce planting in Norway, taking into account transient developments in both terrestrial carbon sinks and surface albedo over the 21st century and beyond. We find that surface albedo changes would likely play a negligible role in counteracting tCDR, yet given low forest growth rates in the region, notable tCDR benefits from such projects would not be realized until the second half of the 21st century, with maximum benefits occurring even later around 2150. We estimate Norway's total accumulated tCDR potential at 2100 and 2150 (including surface albedo changes) to be 447 (±240) and 852 (±295)MtCO2 -eq. at mean net present values of US$ 12 (±3) and US$ 13 (±2) per ton CDR, respectively. For perspective, the accumulated tCDR potential at 2100 represents around 8years of Norway's total current annual production-based (i.e., territorial) CO2 -eq. emissions.

Relationship between the activity concentration of 137Cs in the growing shoots of Quercus serrata and soil 137Cs, exchangeable cations, and pH in Fukushima, Japan

Incorporation of radiocesium by plants via root uptake appears to be affected by some of the exchangeable cations in the soil and/or pH of the soil. However, few studies have examined the relationship between 137Cs in trees and soil properties in the area surrounding the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) after the accident in March 2011. To elucidate the relationships between the root uptake of 137Cs by deciduous broadleaved trees and soil properties, we measured the activity concentration of 137Cs in the growing shoots of coppiced konara oak (Quercus serrata) grown after the FDNPP accident and the amounts of total 137Cs; exchangeable (ex-) 137Cs, ex-K, ex-Mg, and ex-Ca; and pH (H2O) in soils collected from 34 forest stands in Fukushima between December 2016 and May 2017. Ex-137Cs showed a positive linear relationship with the activity concentration of 137Cs in the growing konara oak shoots, whereas ln-transformed ex-K, ex-Mg, ex-Ca, and pH (H2O) showed negative linear relationships with ln-transformed 137Cs activity concentrations in the growing shoots. However, only ex-137Cs and ex-K were identified as significant factors determining the activity concentration of 137Cs in konara oak according to multiple regression methods and a model selection using Akaike information criterion; ex-K had a stronger influence on the activity concentration of 137Cs in konara oak than ex-137Cs. In the present study, we demonstrated that soil ex-K negatively and non-linearly alters 137Cs activity concentration in deciduous broadleaved trees. We also noted that the relationship between 137Cs in deciduous broadleaved trees and soil ex-K in forests without K fertilization was similar to the relationships between 137Cs in other plants and ex-K in K-fertilized lands reported in previous studies of the FDNPP accident.

Interactive climate factors restrict future increases in spring productivity of temperate and boreal trees.

Climate warming is currently advancing spring leaf-out of temperate and boreal trees, enhancing net primary productivity (NPP) of forests. However, it remains unclear whether this trend will continue, preventing for accurate projections of ecosystem functioning and climate feedbacks. Several ecophysiological mechanisms have been proposed to regulate the timing of leaf emergence in response to changing environmental cues, but the relative importance of those mechanisms remains unclear. Here, we use 727,401 direct phenological observations of common European forest trees to examine the dominant controls on leaf-out. Using the emerging mechanisms, we forecast future trajectories of spring arrival and evaluate the consequences for forest carbon dynamics. By representing hypothesized relationships with autumn temperature, winter chilling, and the timing of spring onset, we accurately predicted reductions in the advance of leaf-out. There was a strong consensus between our empirical model and existing process-based models, revealing that the advance in leaf-out will not exceed 2weeks over the rest of the century. We further estimate that, under a 'business-as-usual' climate scenario, earlier spring arrival will enhance NPP of temperate and boreal forests by ~0.2Gt per year at the end of the century. In contrast, previous estimates based on a simple degree-day model range around 0.8Gt. As such, the expected NPP is drastically reduced in our updated model relative to previous estimates-by a total of ~25Gt over the rest of the century. These findings reveal important environmental constraints on the productivity of broad-leaved deciduous trees and highlight that shifting spring phenology is unlikely to slow the rate of warming by offsetting anthropogenic carbon emissions.

Sap flow characteristics in growing and non-growing seasons in three tree species in the semiarid Loess Plateau region of China

Year-round observation suggests that sap flow in growing season represents species-specific transpiration characteristics and sap flow of deciduous broadleaved species in non-growing season is related to daily changes in stem diameter. Year-round observation is necessary to investigate species-specific characteristics of sap flow and its possible contribution in non-growing season. The middle Loess Plateau in China is characterized by temperate climate and vegetation cover of generally drought-tolerant deciduous broadleaved and some evergreen coniferous trees. In this study, Granier-type thermal dissipation probes were applied to measure year-round xylem sap flow in three species from April 2017 to April 2018. Solar radiation, air temperature, relative air humidity, precipitation, and soil moisture were monitored continuously. The results showed that the peak time of sap flux density (Fd) in the diurnal courses of Robinia pseudoacacia was later than that of Quercus liaotungensis and Platycladus orientalis. The peak time of Fd for R. pseudoacacia was significantly postponed during the period with higher soil moisture when compared with that at lower soil moisture, whereas the peak time was reached slightly earlier in the other two species. Sap flow during the non-growing season was relatively higher in P. orientalis than in the two broadleaved species. The diurnal course of Fd in non-growing season showed high values at nighttime and low values in daytime, opposite to that in growing season. Daily variation in stem diameter was inverse of the change in sap flow in the two broadleaved species, whereas the daily change in stem diameter of P. orientalis was very small and showed no clear relation with sap flow. The results suggest that changes in transpiration characteristics with soil moisture conditions vary with tree species; sap flow in deciduous broadleaved trees in non-growing season is small and closely related to daily changes in stem diameter.

Impact Assessment of Ozone Absorbed through Stomata on Photosynthetic Carbon Dioxide Uptake by Japanese Deciduous Forest Trees: Implications for Ozone Mitigation Policies

Photosynthesis by trees is expected to contribute to preventing climate change including global warming. However, the current levels of tropospheric ozone (O3) reduce the uptake of photosynthetic carbon dioxide (CO2) by forest trees in Japan, which is a concern. Furthermore, it is unknown how much O3 should be reduced to prevent plants’ O3-induced damage. The objective of the present study was to assess the negative effects of the current levels of O3 absorbed via stomata and the impact of its mitigation on the CO2 uptake by trees in Japanese forests. Impact assessment, targeted in 2011–2015, was performed for four deciduous broad-leaved trees: Fagus crenata, Quercus serrata, Q. mongolica var. crispula, and Betula platyphylla var. japonica. The assessment was based on species-specific cumulative stomatal O3 uptake (COU) and species-specific responses of annual photosynthetic CO2 uptake to COU. Annual COU differed between the four trees; the average COU of F. crenata, Q. serrata, Q. mongolica var. crispula, and B. platyphylla var. japonica across Japan was 41.7, 26.5, 33.0, and 29.1 mmol m−2, respectively, and the reductions in CO2 uptake by the four trees were 14.0%, 10.6%, 8.6%, and 15.4%, respectively. Further analysis revealed that reducing the atmospheric O3 concentration by approximately 28%, 20%, 17%, and 49% decreased the O3-induced reductions in photosynthetic CO2 uptake to 5% in F. crenata, Q. serrata, Q. mongolica var. crispula, and B. platyphylla var. japonica, respectively. In the near future, implementing mitigation measures for the O3 damage in plants is expected to enhance the photosynthetic capacity of Japanese forest tree species.

Environmental and physiological controls on diurnal and seasonal patterns of biogenic volatile organic compound emissions from five dominant woody species under field conditions

Biogenic volatile organic compounds (BVOCs) play essential roles in tropospheric chemistry, on both regional and global scales. The emissions of large quantities of species-specific BVOC depend not only on environmental (temperature, T; photosynthetically active radiation, PAR), but also physiological parameters (i.e. net photosynthetic rate, Pn; transpiration rate, Tr; stomatal conductance, gs and intercellular CO2 concentration, Ci). Here, isoprene, monoterpene and sesquiterpene emissions were determined from five dominant mature woody tree species in northern China, which are two evergreen conifers (Pinus tabuliformis and Platycladus orientalis) and three broad-leaved deciduous trees (Quercus variabilis, Populus tomentosa and Robinia pseudoacacia). A dynamic enclosure technique combined with GC-MS was used to sample BVOCs and analyse their fractional composition at daily and annual scales. The diurnal data showed that both isoprene and monoterpene emissions increased with increasing temperature, and reached their maximum emission rates in the peak of growing season for both coniferous and broad-leaved species. The emissions of individual compound within the monoterpenes and sesquiterpenes were statistically correlated with each other for all species. Furthermore, some oxygenated monoterpene emissions were highly correlated to sesquiterpenes in all tree species. Linking BVOC emissions to environmental and leaf physiological parameters exhibited that monoterpene emissions were linearly and positively correlated to the variation of T, PAR, Pn and Tr, while their relationship to gs and Ci is more complex. Collectively, these findings provided important information for improving current model estimations in terms of the linkage between BVOC emissions and plant physiological traits. The data presented in this study can be used to update emission capacity used in models, as this is the first time of reporting BVOC emissions from five dominant species in this region. The whole-year measurement of leaf-level BVOCs can also advance our understanding of seasonal variation in BVOC emissions.

Difference of the initial growing speed from seedlings and from epicormic shoots in deciduous broad-leaved trees

Difference of the initial growing speed from seedlings and from epicormic shoots in deciduous broad-leaved trees

Life form dynamics of the tree layer in evergreen and deciduous broad-leaved mixed forest during 1996–2017 in Tianmu Mountains, eastern China

In the forest areas of eastern China, there is a change from forest dominated by deciduous broad-leaved trees to forest dominated by evergreen broad-leaved trees as the latitude or altitude decreases. Different life forms have different survival strategies to deal with climate change, and studying the life form dynamics of the tree layers in the mixed forest in eastern China, with increasing temperature, can help us understand how the forest responds. This study was performed in a 1 ha plot in evergreen and deciduous broad-leaved mixed forest in Tianmu Mountain National Nature Reserve. Based on the data from two surveys (1996 and 2017), the changes in life form composition and biodiversity over the past 21 years were analyzed. We obtained the following results: (1) The proportion of evergreen trees increased from 55.0% in 1996 to 67.5% in 2017, and the dominance of evergreen species was enhanced. (2) The diversity of both life forms increased, and the tree species were more abundant. (3) The average annual recruitment rate of the evergreen species was 2.1% greater than their mortality rate, and the average annual recruitment rate of the deciduous species was 0.5% less than their mortality rate. (4) The competition among the trees in the small-diameter class (10 cm ≤ DBH < 20 cm) was fierce for many tree species. The proportion of the evergreen species in the small-diameter class was high. The life forms making up the mixed climax forest community has changed over the past 21 years, with the proportion and dominance of evergreen trees increasing significantly.

Vegetation succession and climate change during the early pleistocene (2.2-1.8 Ma) in the Nihewan Basin, northern China

The Nihewan Formation, northern China is ideal for studying environmental changes during the early Pleistocene. In conjunction with palaeomagnetic measurements, pollen and grain-size analyses were conducted on 120 samples from a ~24 m long section (2.2-1.8 Ma) of core NHA from the Nihewan Basin, in order to reconstruct past vegetation and climatic changes. The pollen assemblages were dominated by Pinus, indicating that the vegetation was primarily pine forest and that the climate was relatively warm and wet. From 2.15-1.92 Ma, deciduous broad-leaved tree pollen significantly increased to >10% of the total, showing that more broad-leaved trees grew in the study area during the warmest and wettest period in the study section. From 1.92-1.78 Ma (coeval with the Olduvai event), Pinus and broad-leaved tree pollen types decreased. The percentages of Picea (>20%), Artemisia and Chenopodiaceae increased, indicating that spruce forests expanded, the openness of the forested areas increased and the climate became cold and dry. The vegetation changes reconstructed during the Olduvai period indicates that the climate in the Nihewan Basin was cold and dry, relating to global cooling facilitated by the uplift of the Tibetan Plateau and the strengthening of the winter monsoon.

Factors limiting the distribution of deciduous broadleaved trees in warm-temperate mountainous riparian forests

We examined differences in the responses of deciduous and evergreen broadleaved trees to fluvial disturbance and light environment near a river-facing forest edge in order to identify the factors limiting the distribution of deciduous trees, which are important components of warm-temperate mountainous riparian forests. Deciduous trees tended to be distributed on lower terraces of less than 2-m relative elevation from the water level, which corresponded with sites suffering from strong bank erosion due to high flood frequency. On the other hand, evergreen trees showed an opposite trend of distribution, indicating that high flood frequency associated with strong erosion-dominated soil disturbances might be a constraint for their establishment and/or survival. Furthermore, crowns of deciduous trees tended to be in the canopy layer at the forest edge, with fewer individuals observed beneath the canopy of evergreen trees, even at the forest edge. In contrast, evergreen trees were concentrated in the understory of the forest interior. These observations suggested that the light environment is the predominant factor affecting the establishment and survival of deciduous trees in warm-temperate mountainous riparian forests; however, the river-facing forest edge beneath the evergreen canopy is not a suitable habitat for deciduous trees. We concluded that erosion-dominated soil disturbance on lower terraces provides suitable habitats for deciduous trees by facilitating their reaching the canopy layer by limiting the establishment and/or survival of evergreen trees.