Dams are widely recognised as having significant negative consequences for the surrounding natural ecosystems and environment. China’s Three Gorges Dam, being one of the largest in the world, stands ...to inflict more damage than most for numerous reasons. This paper reviews the current knowledge on the impacts of dams and impoundments with regard to reservoir riparian vegetation in order to apply this knowledge to the Three Gorges Project. It also summarises research performed to date on the effects of the Three Gorges Dam on the local riparian zone and vegetation. The known and potential outcomes for local plant communities are examined in terms of their responses to the increased water levels, altered hydrological characteristics and other adverse effects associated with the construction of the dam. Vegetation responses will be diverse and change over time, but will ultimately result in a markedly different landscape and riparian zone within the Three Gorges Reservoir. These changes will take place through a loss of previous vegetation, potential invasion by exotics and result from the significant alteration in hydrological regimes and also erosion and sedimentation processes influencing and creating novel plant communities. Management of the environmental consequences of the Three Gorges Project should take into account factors associated with these processes, in order to facilitate vegetation recovery in the reservoir and to conserve biodiversity of the surrounding ecosystems.
Despite evidence from experimental grasslands that plant diversity increases biomass production and soil organic carbon (SOC) storage, it remains unclear whether this is true in natural ecosystems, ...especially under climatic variations and human disturbances. Based on field observations from 6,098 forest, shrubland, and grassland sites across China and predictions from an integrative model combining multiple theories, we systematically examined the direct effects of climate, soils, and human impacts on SOC storage versus the indirect effects mediated by species richness (SR), aboveground net primary productivity (ANPP), and belowground biomass (BB). We found that favorable climates (high temperature and precipitation) had a consistent negative effect on SOC storage in forests and shrublands, but not in grasslands. Climate favorability, particularly high precipitation, was associated with both higher SR and higher BB, which had consistent positive effects on SOC storage, thus offsetting the direct negative effect of favorable climate on SOC. The indirect effects of climate on SOC storage depended on the relationships of SR with ANPP and BB, which were consistently positive in all biome types. In addition, human disturbance and soil pH had both direct and indirect effects on SOC storage, with the indirect effects mediated by changes in SR, ANPP, and BB. High soil pH had a consistently negative effect on SOC storage. Our findings have important implications for improving global carbon cycling models and ecosystem management: Maintaining high levels of diversity can enhance soil carbon sequestration and help sustain the benefits of plant diversity and productivity.
•Correlation may fail to reveal asymmetric responses of GPP to dry or wet condition.•GPP loss can be underestimated by 45% if the time scale was randomly selected.•Vegetation type, water balance and ...soil textures affected optimal scale variations.
Extreme drought events have caused extensive and severe impacts on terrestrial ecosystem in last decades in China. Given droughts may be more intense and frequent under future climate change, accurate assessment of the drought impact on vegetation primary production can provide reliably scientific supports for the carbon sink potential. Numerous existing studies have used Standardized Precipitation Evapotranspiration Index (SPEI) to discover the drought-production relationships, however, most of them just considered the strongest correlation between production and different time scales (i.e. correlation-based method), which may underestimate the production loss because of the asymmetric responses under dry and wet conditions. In this work, we proposed a new method which assumed that the dominant time scale should correspond to the lowest primary production during each drought year (extreme-based method). Based on six independent Gross Primary Productivity (GPP) products and SPEI dataset, it showed that the extreme-based method was more reasonable and robust (with a larger inter-consistency of 0.50 than that of 0.05 for correlation-based method) to determine at which time scale GPP predominantly responded to extreme droughts. And the GPP loss can be underestimated by 45 ± 26% (mean ± s.d.) if the time scale was randomly selected. Furthermore, spatial analysis suggested that vegetation type, water balance and soil textures mainly affected the spatial heterogeneity of the dominant time scales. In detail, forests, humid biomes, and vegetation planted in loam tended to be more sensitive to longer-term droughts. This study highlighted that optimal time-scale selection using extreme-based assumption can give more accurate estimation of the drought impacts on vegetation primary production.
Rainfall is one of the primary sources of chemical inputs in forest ecosystems, and the basis of forest nutrient cycling. Mixed evergreen and deciduous broadleaved forests are currently one of the ...most threatened ecosystems due to their sensitivity to anthropogenic climate change. As such, understanding the hydrochemical fluxes of these systems is critical for managing their dynamics in the future. We investigate the chemistry of bulk precipitation, stemflow and throughfall in a mixed evergreen and deciduous broadleaved forest in the Shennongjia region of Central China. Mean nutrient concentrations in throughfall and stemflow were higher than in bulk precipitation. Stemflow ion fluxes from deciduous tree species were greater than those for evergreen tree species because of the differences in bark morphology and branch architecture. Throughfall and stemflow chemistry fluctuated dramatically over the growing season. Nitrate nitrogen and ammonium nitrogen were retained, while other elements and compounds were washed off or leached via throughfall and stemflow pathways. Our findings will facilitate a greater understanding of nutrient balance in canopy water fluxes.
The dispersal-syndrome hypothesis posits that fruit traits are a product of selection by frugivores. Although criticized as adaptationist, recent studies have suggested that traits such as fruit or ...seed size, colour and odour exhibit signatures that imply selection by animal mutualists. These traits imply nutritional rewards (e.g. lipid, carbohydrate), attracting frugivores; however, this remains incompletely resolved. Here, we investigated whether fruit nutrients (lipid, sugar, protein, vitamin C, water content) moderate the co-adaptation of key disperser-group mutualisms. Multivariate techniques revealed that fruit nutrients assembled non-randomly and grouped according to key dispersal modes. Bird-dispersed fruits were richer in lipids than mammal-dispersed fruits. Mixed-dispersed fruits had significantly higher vitamin C than did mammal- or bird-dispersed fruits separately. Sugar and water content were consistently high irrespective of dispersal modes, suggesting that these traits appeal to both avian and mammalian frugivores to match high-energy requirements. Similarly, protein content was low irrespective of dispersal modes, corroborating that birds and mammals avoid protein-rich fruits, which are often associated with toxic levels of nitrogenous secondary compounds. Our results provide substantial over-arching evidence that seed disperser assemblages co-exert fundamental selection pressures on fruit nutrient trait adaptation, with broad implications for structuring fruit-frugivore mutualism and maintaining fruit trait diversity.
•We quantified the stemflow of a mixed evergreen and deciduous broadleaved forest.•Stemflow is more easily initiated by evergreen species than deciduous species.•Evergreen species direct more ...stemflow than deciduous species in subtropical forest.•Small trees are more productive in funneling stemflow than large trees.
Quantification of stemflow is necessary for the assessment of forest ecosystem hydrological effects. Nevertheless, variation of stemflow among plant functional groups is currently not well understood. Stemflow production of co-occurring evergreen broadleaved trees (Cyclobalanopsis multinervis and Cyclobalanopsis oxyodon) and deciduous broadleaved trees (Fagus engleriana and Quercus serrata var. brevipetiolata) was quantified through field observations in a mixed evergreen and deciduous broadleaved forest. The research results revealed that stemflow increased linearly with increasing rainfall magnitude, with precipitation depths of 6.9, 7.2, 10.0 and 14.8mm required for the initiation of stemflow for C. multinervis, C. oxyodon, F. engleriana and Q. serrata, respectively. Stemflow percentage and funneling ratio (FR) increased with increasing rainfall in a logarithmic fashion. Stemflow percentage and FR tended to grow rapidly with increasing rainfall magnitude up to a rainfall threshold of 50mm, above which, further rainfall increases brought about only small increases. For C. multinervis, C. oxyodon, F. engleriana and Q. serrata, FR averaged 19.8, 14.8, 8.9 and 2.8, respectively. The stemflow generating rainfall thresholds for evergreen species were smaller than for deciduous species. Furthermore, stemflow percentage and FR of the former was greater than the latter. For both evergreen species and deciduous species, overall funneling ratio (FRs) decreased with increasing basal area.
We concluded that: (1) although stemflow partitioning represented a fairly low percentage of gross rainfall in mixed evergreen and deciduous broadleaved forests, it was capable of providing substantial amount of rainwater to tree boles; (2) the evergreen species were more likely to generate stemflow than deciduous species, and directed more intercepted rainwater to the root zone; (3) small trees were more productive in funneling stemflow than larger trees, which may provide a favorable condition for the survival and growth of small trees when competing with larger trees.
It is hypothesized that plant submergence tolerance could be assessed from the decline of plant biomass due to submergence, as biomass integrates all eco-physiological processes leading to fitness. ...An alternative hypothesis stated that the consumption rate of carbohydrate is essential in differing tolerance to submergence. In the present study, the responses of biomass, biomass allocation, and carbohydrate content to simulated long-term winter submergence were assessed in four tolerant and four sensitive perennials. The four tolerant perennials occur in a newly established riparian ecosystem created by The Three Gorges Dam, China. They had 100% survival after 120 days’ simulated submergence, and had full photosynthesis recovery after 30 days’ re-aeration, and the photosynthetic rate was positively related to the growth during the recovery period. Tolerant perennials were characterized by higher carbohydrate levels, compared with the four sensitive perennials (0% survival) at the end of submergence. Additionally, by using a method which simulates posterior estimates, and bootstraps the confidence interval for the difference between strata means, it was found that the biomass response to post-hypoxia, rather than that to submergence, could be a reliable indicator to assess submergence tolerance. Interestingly, the differences of changes in carbohydrate content between tolerant and sensitive perennials during submergence were significant, which were distinct from the biomass response, supporting the hypothesis that tolerant perennials could sacrifice non-vital components of biomass to prioritize the saving of carbohydrates for later recovery. Our study provides some insight into the underlying mechanism(s) of perennials’ tolerance to submergence in ecosystems such as temperate wetland and reservoir riparian.
Evergreen and deciduous broad‐leaved tree species can coexist across the globe and constitute different broad‐leaved forests along large‐scale geographical and climatic gradients. A better ...understanding of climatic influence on the distribution of mixed evergreen and deciduous broad‐leaved forest is of fundamental importance when assessing this mixed forest's resilience and predicting potential dynamics of broad‐leaved forests under future climate change. Here, we quantified the horizontal distribution of this mixed forest in mountains in relation to climate seasonality by compiling vegetation information from the earlier records and our own field sampling on major subtropical mountains of China. We found that the probability of occurrence of this forest in subtropical mountains was positively associated with the latitude but not the longitude. The occurrence probability of this forest was observed at high‐temperature but not precipitation seasonality mountains. Temperature seasonality was five times more important than precipitation seasonality in explaining the total variation of occurrence of this mixed forest. For its distribution, our results shed light on that temperature seasonality was generally a more powerful predictor than precipitation seasonality for montane mixed forest distribution. Collectively, this study clearly underscores the important role of temperature seasonality, a previously not quantified climatic variable, in the occurrence of this mixed forest along geographical gradients and hence yields useful insight into our understanding of climate–vegetation relationships and climate change vulnerability assessment in a changing climate.
Mixed evergreen-deciduous broadleaved forest is the transitional type of evergreen broadleaved forest and deciduous broadleaved forest, and plays a unique eco-hydrologic role in terrestrial ...ecosystem. We investigated the spatio-temporal patterns of throughfall volume of the forest type in Shennongjia, central China. The results indicated that throughfall represented 84.8% of gross rainfall in the forest. The mean CV (coefficient of variation) of throughfall was 27.27%. Inter-event variability in stand-scale throughfall generation can be substantially altered due to changes in rainfall characteristics, throughfall CV decreased with increasing rainfall amount and intensity, and reached a quasi-constant level when rainfall amount reached 25 mm or rainfall intensity reached 2 mm h−1. During the leafed period, the spatial pattern of throughfall was highly temporal stable, which may result in spatial heterogeneity of soil moisture.
Ongoing global climate change is predicted to increase the frequency and magnitude of extreme weather events, impacting population dynamics and community structure. There is, however, a critical lack ...of case studies considering how climatic perturbations affect biotic interactions. Here, we document how an obligate seed dispersal mutualism was disrupted by a temporally anomalous and meteorologically extreme interlude of unseasonably frigid weather, with accompanying snowstorms, in subtropical China, during January–February 2008. Based on the analysis of 5892 fecal samples (representing six mammalian seed dispersers), this event caused a substantial disruption to the relative seed dispersal function for the raisin tree Hovenia dulcis from prestorm 6.29 (2006) and 11.47 (2007), down to 0.35 during the storm (2008). Crucially, this was due to impacts on mammalian seed dispersers and not due to a paucity of fruit, where 4.63 fruit per branch were available in January 2008, vs. 3.73 in 2006 and 3.58 in 2007. An induced dietary shift occurred among omnivorous carnivores during this event, from the consumption fruit to small mammals and birds, reducing their role in seed dispersal substantially. Induced range shift extinguished the functionality of herbivorous mammals completely, however, seed dispersal function was compensated in part by three omnivorous carnivores during poststorm years, and thus while the mutualism remained intact it was enacted by a narrower assemblage of species, rendering the system more vulnerable to extrinsic perturbations. The storm's extended effects also had anthropogenic corollaries – migrating ungulates becoming exposed to heightened levels of illegal hunting – causing long‐term modification to the seed dispersal community and mutualism dynamics. Furthermore, degraded forests proved especially vulnerable to the storm's effects. Considering increasing climate variability and anthropogenic disturbance, the impacts of such massive, aberrant events warrant conservation concern, while affording unique insights into the stability of mutualisms and the processes that structure biodiversity and mediate ecosystem dynamics.
PDF
