Broad-leaved Forest In Eastern China Research Articles

Effect of species-independent conspecific and heterospecific density dependence is contingent on seedling growth stage, season, and climate conditions

Conspecific negative density dependence (CNDD) and its extension heterospecific positive density dependence (HPDD) are the two most prominent mechanisms used to explain the maintenance of species diversity in forest communities. However, the impact of species identity, growth stage, seasonal and inter-annual variation in precipitation and temperature on conspecific and heterospecific density dependence remains poorly understood. Based on a decade of seedling (dbh < 1 cm) and tree (dbh ≥ 1 cm) census data from a 5-ha subtropical evergreen broad-leaved forest in eastern China, we used generalized linear mixed models with crossed random effects to test whether seedling survival was density dependent and varied by growth stage, species identity, season or interacted with inter-annual variation in seasonal precipitation and temperature. In addition to conspecific and heterospecific seedling and tree density, the height (or age) of the seedlings, habitat variables, seasonal precipitation and temperature and the interactions between conspecific and heterospecific seedling and tree density and seasonal precipitation and temperature were also used as predictors. The results of our long-term, spatially, and temporally explicit study showed that the strength of CNDD and enemy induced HPDD was stronger in summer and at early seedling stages, whereas interspecific facilitation induced HPDD mainly in winter for early and late seedling stages. Additionally, the effects of seasonal temperature and precipitation, and the soil PC1 axis (which correlated positively with soil nutrients and negatively with soil moisture) on seedling survival varied with season, seedling stage, and focal species identity, indicating the potential for niche partitioning among species in this community. However, neither conspecific nor heterospecific neighbor effects varied among focal seedling species, which resulted in a community compensatory trend in young seedlings. Variation in the effect of CNDD and HPDD across seedling stages, seasons, and inter-annual fluctuations of climate conditions highlights the necessity of long-term monitoring of the dynamics of CNDD in tree communities.

Responses of tree seedlings to understory filtering by the recalcitrant fern layer in a subtropical forest.

The recalcitrant understory fern layer is an important ecological filter for seedling regeneration, yet how the fern layer influences seedling regeneration dynamics remains unclear. Here we transplanted 576 seedlings of four dominant tree species, Castanopsis fargesii, Lithocarpus glaber, Schima superba and Hovenia acerba, to the treatments of Diplopterygium glaucum retention and removal under an evergreen broad-leaved forest in eastern China. We monitored the survival, growth and biomass data of these seedlings for 28 months, and then used generalized linear mixed models to evaluate the treatment effects on seedling survival, growth, biomass and root-shoot ratio. Our results showed that fern retention significantly inhibited the seedling establishment of all four species. During the seedling development stage, the seedling relative growth rate of L. glaber decreased under fern retention, which was not the case for the other three species. Root-shootratio of C. fargesii and L. glaber increased significantly under fern retention. Our findings provide new evidence of the filtering effect of a recalcitrant fern understory. Notably, we observed that the response of tree seedlings to the recalcitrant fern understory was more sensitive in the establishment stage. Finally, our work highlights that the filtering effect of the recalcitrant fern understory changes depending on the regeneration stages, and that shade-tolerant species, C. fargesii and L. glaber were even more affected by fern disturbed habitats, suggesting that effective management should attempt to curb forest fern outbreaks, thus unblocking forest recruitment.

The dynamics of conspecific tree and seedling neighbors on seedling survival in a subtropical forest

Negative intraspecific interactions could provide opportunities for heterospecific regeneration, thereby maintaining species coexistence in forest communities. Increasing conspecific tree and seedling neighbor densities often have negative correlations with seedling survival. If and how the strength of interactions change with seedling age remains a knowledge gap. In this study, we followed 2184 newly germinated seedlings belonging to 26 species for five years in a subtropical evergreen broad-leaved forest in eastern China. We tested the density distribution pattern of different aged live seedlings and used generalized linear mixed models to assess the dynamic influence of conspecific tree and seedling neighbors on seedlings survival across years. Our results showed that the density distribution of newly germinated seedlings was more clustered than the other aged live seedlings. Over five years, the clustered density distribution of live seedlings gradually weakened. Particularly, the density distribution of five years old seedlings was statistically random. Meanwhile, the degree of positive correlation between the density of live seedlings and the density of conspecific tree neighbors decreased with seedling age. Correspondingly, the conspecific seedling neighbors had a significant negative correlation with newly germinated seedlings survival in the first year and had a greater effect than conspecific tree neighbor density. As seedlings age, the conspecific tree neighbors had a greater negative relative effect on seedlings survival than the conspecific seedling neighbors. Our findings demonstrate that intraspecific negative interactions are an important mechanism on seedling survival and the magnitude of those interactions change with seedling age. In younger seedlings, intraspecific negative interactions were mainly from conspecific seedling neighbors and weakened as the seedlings aged. In later seedling ages, the interactions from conspecific tree neighbors dominated. Ultimately, these effects reduce species clumping dynamically and provide space for establishment of heterospecifics which would maintain diversity in the forest.

Multi-stemming strategies of Quercus glauca in an evergreen broad-leaved forest: when and where

Abstract Aims Multi-stemming supports plants’ resilience to disturbances and then contributes to soil stabilization and forest function, especially in mountain habitats. Many questions remain about (i) the ontogenetic phase at which multiple stems can occur, (ii) how habitat drivers affect multi-stemming and (iii) whether ontogenetic phase and habitat drivers interact. We asked these questions for Quercus glauca (ring-cupped oak), the dominant species and sprouter across large warm-temperate areas of Asia; its multi-stemmed trees reflect individual survival, population regeneration and forest ecosystem stability. Methods In a 5-ha permanent plot of subtropical evergreen broad-leaved forest in eastern China, we examined the temporal patterns and spatial distribution of multi-stemmed trees of Q. glauca within 99 quadrats of 20 m × 20 m. Important Findings There were three temporal modes for multi-stemming among the Q. glauca trees and most of them appeared to produce multiple stems from an early stage. Environmental disturbances related to slope convexity appear to be the main drivers of multi-stemming of Q. glauca. Moreover, the closer to the ridge, the earlier the multi-stemming occurs. Thus, also for other woody species in other forests and climate zones, ontogeny and environmental drivers promoting disturbance (not only geomorphology, but also extreme weather events, soil drought, fire), as well as soil fertility, need to be considered in combination to better understand multi-stemming and its consequences for community structure.

Can plant phenology explain species coexistence: A case study in the subtropical evergreen broad-leaved forest of Gutianshan,Zhejiang, China

<p indent="0mm">Species coexistence has always been a major research focus in ecology. Classical coexistence theory indicates that plants can achieve species coexistence through spatial niche differentiation, thereby reducing the competition for resources among species. However, whether plants can also promote species coexistence through temporal niche differentiation (such as phenological differentiation) in the subtropical regions has yet to be tested. We take a subtropical evergreen broad-leaved forest in eastern China as an example. Using reproductive phenology data from 2012 to 2017 for 102 species in the Gutianshan 24 ha permanent plot,we analyzed the phenological differences between species with different functional groups. We found that both the first flowering and fruit time had large temporal niche differentiation. The first flowering had greater variation than the first fruiting time, and that the flowering duration varied less than the fruiting duration. There was no overlap between flowering phenology and fruiting phenology. The phenology of different functional groups differed among species, with the first flowering time significantly earlier in trees than shrubs, but the first fruiting time later in trees than shrubs. The first flowering time was significantly earlier for wind-pollinated trees than insect-pollinated trees, and the first flowering time was also significantly earlier for fleshy-fruit species than nonfleshy-fruit species. The results indicate that differences in plant phenology, which create temporal niches, can reduce resource competition among species and promote community coexistence. Considering species coexistence from the perspective of phenology can help us understand how temporal niches alleviate competition for resources.

Effects of litter manipulation on soil respiration under short-term nitrogen addition in a subtropical evergreen forest

Nitrogen (N) availability is rapidly increasing in subtropical ecosystems, where litterfall is also accelerating and may substantially affect belowground carbon (C) storage and soil respiration (Rs). This study aims to detect how litter inputs affect Rs under N addition in a subtropical forest. We conducted a two-factor experiment (N addition and litter manipulation) in a subtropical Schima superba evergreen broad-leaved forest in eastern China. Three levels of N addition included low-N (50 kg N ha−1 yr−1), high-N (100 kg N ha−1 yr−1) and ambient N (0 kg N ha−1 yr−1), and three levels of litter manipulation consisting of litter removal (NL), litter addition (DL) and Control litter input were conducted. Our results showed NL decreased Rs by 41% and 38% under low- and high-N additions, respectively, compared to Control litter input. DL decreased Rs by 24% compared to Control litter input under high-N addition. Furthermore, low- and high-N additions decreased the effect size of NL on Rs, whereas high-N addition decreased the effect size of DL on Rs in the study period, in both rainy and dry seasons. The effect of litter input alteration on Rs under N addition decreased, compared to Rs in Control litter input under N addition. Thus, the increase in Rs under N addition was alleviated, suggesting that soil organic C sequestration may benefit from increasing N deposition in the future. Further study is needed to clarify the effects of litter input alteration on Rs and soil C cycling under long-term N addition in subtropical forests.

Growth responses of trees and understory plants to nitrogen fertilization in a subtropical forest in China

Abstract. Reactive nitrogen (N) increase in the biosphere has been a noteworthy aspect of global change, producing considerable ecological effects on the functioning and dynamics of the terrestrial ecosystems. A number of observational studies have explored responses of plants to experimentally simulated N enrichment in boreal and temperate forests. Here we investigate how the dominant trees and different understory plants respond to experimental N enrichment in a subtropical forest in China. We conducted a 3.4-year N fertilization experiment in an old-aged subtropical evergreen broad-leaved forest in eastern China with three treatment levels applied to nine 20 m × 20 m plots and replicated in three blocks. We divided the plants into trees, saplings, shrubs (including tree seedlings), and ground-cover plants (ferns) according to the growth forms, and then measured the absolute and relative basal area increments of trees and saplings and the aboveground biomass of understory shrubs and ferns. We further grouped individuals of the dominant tree species, Castanopsis eyrei, into three size classes to investigate their respective growth responses to the N fertilization. Our results showed that the plot-averaged absolute and relative growth rates of basal area and aboveground biomass of trees were not affected by N fertilization. Across the individuals of C. eyrei, the small trees with a DBH (diameter at breast height) of 5–10 cm declined by 66.4 and 59.5 %, respectively, in N50 (50 kg N ha−1 yr−1) and N100 fertilized plots (100 kg N ha−1 yr−1), while the growth of median and large trees with a DBH of &gt; 10 cm did not significantly change with the N fertilization. The growth rate of small trees, saplings, and the aboveground biomass of understory shrubs and ground-cover ferns decreased significantly in the N-fertilized plots. Our findings suggested that N might not be a limiting nutrient in this mature subtropical forest, and that the limitation of other nutrients in the forest ecosystem might be aggravated by the enhanced N availability, potentially resulting in an adverse effect on the development of natural subtropical forest.

Conspecific Leaf Litter-Mediated Effect of Conspecific Adult Neighborhood on Early-Stage Seedling Survival in A Subtropical Forest.

Conspecific adults have strong negative effect on the survival of nearby early-stage seedlings and thus can promote species coexistence by providing space for the regeneration of heterospecifics. The leaf litter fall from the conspecific adults, and it could mediate this conspecific negative adult effect. However, field evidence for such effect of conspecific leaf litter remains absent. In this study, we used generalized linear mixed models to assess the effects of conspecific leaf litter on the early-stage seedling survival of four dominant species (Machilus leptophylla, Litsea elongate, Acer pubinerve and Distylium myricoides) in early-stage seedlings in a subtropical evergreen broad-leaved forest in eastern China. Our results consistently showed that the conspecific leaf litter of three species negatively affected the seedling survival. Meanwhile, the traditional conspecific adult neighborhood indices failed to detect this negative conspecific adult effect. Our study revealed that the accumulation of conspecific leaf litter around adults can largely reduce the survival rate of nearby seedlings. Ignoring it could result in underestimation of the importance of negative density dependence and negative species interactions in the natural forest communities.

Growth synchrony between leaves and stems during twig development differs among plant functional types of subtropical rainforest woody species.

During the development of woody twigs, the growth in leaf may or may not be proportional to the growth in stem. The presence or absence of a synchronicity between these two phenologies may reflect differences in life history adaptive strategies concerning carbon gain. We hypothesized that sun-adapted species are more likely to be less synchronous between growths in total leaf area (TLA) and stem length compared with shade-adapted species, with a bias in growth in stem length, and that shade-adapted species are more likely to be more synchronous between increases in individual leaf area (ILA) (leaf size) and leaf number (LN) during twig development compared with sun-adapted species, giving priority to growth of leaf size. We tested these two hypotheses by recording the phenologies of leaf emergence, leaf expansion and stem elongation during twig development for 19 evergreen woody species (including five shade-adapted understory species, six sun-adapted understory species and eight sun-adapted canopy species) in a subtropical evergreen broad-leaved forest in eastern China. We constructed indices to characterize the synchronicity between TLA and stem length (αLS) and between leaf size and leaf number (αSN) and we derived the α values from logistic functions taking the general form of A = A(max)/[1 + exp(β - αB)] (where A is the TLA or average ILA, B is the corresponding stem length or LN at a specific time, and A(max) is the maximum TLA or the maximum ILA of a twig; the higher the numerical value of α, the less synchronous the corresponding phenologies). Consistent with our hypotheses, sun-adapted species were higher both in α(LS) and α(SN), showing less synchronous patterns in the growths of TLA vs stem length and leaf size vs LN during twig development. Moreover, α(LS) and α(SN) were significantly positively correlated with relative growth rates of LN and leaf size across species, as indicated by both analyses of ordinary regression and phylogenetic generalized least squares. The across-species synchronies during twig development show that the temporal dynamics of the leaf size-twig size spectrum is of adaptive significance in plants. We suggest that temporal dynamics of plant functional traits should be extensively studied to characterize plant life history.

Recovery of saturated hydraulic conductivity along a forest successional series from abandoned land to mature, evergreen broad-leaved forest in eastern China

Saturated hydraulic conductivity (Ks) can be used to indicate changes in soil hydrology resulting from vegetation succession. A constant-head permeameter was used to investigate differences in Ks at five soil depths (10, 20, 40, 60, and 80 cm) along a successional sequence of 155 years in evergreen broad-leaved forest at Tiantong National Forest Park, eastern China. The following six forest successional classes were studied: climax evergreen broad-leaved forest (CE), sub-climax evergreen broad-leaved forest (SE), evergreen broad-leaved mixed coniferous forest (MF), coniferous forest (CF), secondary shrub (SS), and abandoned land (AL). Surface Ks (the geometric mean of Ks at 10 and 20 cm soil depths) significantly increased from AL to CE but declined in CF. The surface Ks value under CE was higher than under other successional stages (CE 271 mm h–1, AL 58 mm h–1, SS 124 mm h–1, CF 90 mm h–1, MF 170 mm h–1, SE 231 mm h–1), and was 4.7 times greater than under AL, 2.2 times greater than under SS, and 3.0 times greater than under CF, but showed no significant difference from SE (P &gt; 0.05). Vertical difference of Ks was detected up to a soil depth of 40 cm along forest successional series. Macroporosity was the main determining factor and played an important role in the process of Ks recovery. The likelihood of overland flow generation was inferred by comparing Ks at soil depths of 10, 20, 40, and 60 cm under the various successional stages at prevailing storm intensities. Overland flow was most likely to occur in the early successional stages. This study suggests that Ks could be restored to climax forest levels along forest successional series, but the recovery time could be as long as 95 years.

Biomass, and carbon and nitrogen pools in a subtropical evergreen broad-leaved forest in eastern China

Subtropical evergreen broad-leaved forest is the most widely distributed land-cover type in eastern China. As the rate of land-use change accelerates worldwide, it is becoming increasingly important to quantify ecosystem biomass and carbon (C) and nitrogen (N) pools. Above and below-ground biomass and ecosystem pools of N and C in a subtropical secondary forest were investigated at Laoshan Mountain Natural Reserve, eastern China. Total biomass was 142.9 Mg ha−1 for a young stand (18 years) and 421.9 Mg ha−1 for a premature stand (ca. 60 years); of this, root biomass was from 26.9 (18.8% of the total) to 100.3 Mg ha−1 (23.8%). Total biomass C and N pools were, respectively, 71.4 Mg ha−1 and 641.6 kg ha−1 in the young stand, and 217.0 Mg ha−1 and 1387.4 kg ha−1 in the premature stand. The tree layer comprised 91.8 and 89.4% of the total biomass C and N pools in the young stand, and 98.0 and 95.6% in the premature stand. Total ecosystem C and N pools were, respectively, 101.4 and 4.6 Mg ha−1 for the young stand, and 260.2 and 6.6 Mg ha−1 for the premature stand. Soil C comprised 23.8–29.6% of total ecosystem C whereas soil N comprised 76.9–84.4% of the total. Our results suggest that a very high percentage of N in this subtropical forest ecosystem is stored in the mineral soil, whereas the proportion of organic C in the soil pool is more variable. The subtropical forest in eastern China seems to rapidly accumulate biomass during secondary succession, which makes it a potentially rapid accumulator of, and large sink for, atmospheric C.

Evergreen broad-leaved forest in Eastern China: Its ecology and conservation and the importance of resprouting in forest restoration

Biogeographical and ecological research on the evergreen broad-leaved forests (EBLF) of the Far East, which have been reduced to remnant fragments over the historical period has, until now, been very limited. To inform forest conservation and management, this paper describes research into major plant community types and underlying environmental gradients of degraded EBLF in Eastern China and examines the importance of resprouting as a key mechanism in secondary succession following forest clearance. Species composition was described from 199 10 m × 10 m plots and analysed using two-way indicator species analysis and canonical correspondence analysis ordination. Some 22 degraded and mature forest community types were identified, while CCA indicated that a primary vegetation gradient was related to distance of sample plot from mature forest, which was closely linked to altitude and slope. The secondary gradient corresponded to successional stage and disturbance. The roles of resprouting and reseeding characteristics in forest regeneration were researched firstly by 10 m × 10 m plots from selected TWINSPAN groups and secondly by 20 m × 20 m plots in representative areas of forest at 1, 20, 43 and 60 years and in an area of mature forest. The importance of resprouting in the regeneration of many EBLF tree and shrub species is demonstrated, a process linked to ideas of the persistence niche. Existing remnant forests should be conserved but forest restoration is also essential and will benefit from understanding of the importance of tree/shrub resprouting, as well as seedling recruitment in forest regeneration. Further work is required on seedbanks, germination success and both inter- and intra-specific competition within Chinese EBLF to assist with successful forest conservation and management.

Leaf nutrient concentration, nutrient resorption and litter decomposition in an evergreen broad-leaved forest in eastern China

While plant mineral nutrition has been well addressed in temperate ecosystems, our knowledge of this topic in subtropical evergreen broad-leaved forests remains weak. We examined various plant leaf traits and litter decomposition rates among three groups—deciduous species (DB) and evergreen broad-leaved species with leaf life span <1.5 years (EBS) and >1.5 years (EBL) in a secondary evergreen broad-leaved forest in eastern China. Relative to DB, EBS and EBL classes contained 33 and 44% less leaf N, and 28 and 45% less leaf P, respectively. N resorption efficiency varied from 27 to 65%, 21 to 52% and 22 to 51% in DB, EBS and EBL, respectively. P resorption efficiency varied from 38 to 77% in DB, 6 to 58% in EBS and 15 to 55% in EBL. P resorption efficiency was greater in DB than in EBS and EBL while N resorption efficiency did not differ among the three classes. N resorption efficiency was not correlated with either leaf N or N:P ratio. In contrast, P resorption efficiency was positively correlated with leaf P. Litter decomposition rates were 2.45, 1.33 and 2.30 year −1 for DB, EBS and EBL, respectively, but the rates did not significantly differ between groups. Litter decomposition rate was positively correlated with specific leaf area (SLA) and initial litter N but not litter P. In conclusion, there were no significant differences between EBS and EBL for any of the leaf traits measured, but these two classes were different from DB. Plants with long leaf life span tend to minimize nutrient loss more by reducing N concentration in leaf litter than by increasing N resorption efficiency.

Eco-physiological modelling of leaf photosynthesis and adaptation analysis of Chinese ivy (Hedera nepalensis var. sinensis) in an evergreen broad-leaved forest in eastern China

The individual plant of Chinese ivy can produce three types of branches (creepy, climbing, and reproductive) during its development, which adapt to different environmental factors. An eco-physiological model was constructed to simulate leaf net photosynthetic rate (PN) of Chinese ivy (Hedera nepalensis var. sinensis) in subtropical evergreen broad-leaved forest based on leaf physiological and mathematical analysis. The model integrated the rate-limiting biochemical process of photosynthesis and the processes of stomatal regulation. Influence of environmental factors (solar radiation, temperature, CO2 concentration, vapour pressure deficit, etc.) on PN was also considered in our model; its parameters were estimated for leaves on three types of branch in the whole growing season. The model was validated with field data. The model could simulate PN of leaf on three types of branches accurately. Influence of solar radiation on leaf PN of three types of branches in different seasons was analyzed through the model with numerical analysis.