Tree growth,mortality, and above-ground biomass accumulation in a holm oak forest under a five-year experimental field drought

A holm oak forest was exposed to an experimental drought during 5 years to elucidate the growth responses of the dominant species Quercus ilex, Arbutus unedo and Phillyrea latifolia. Soil water availability was partially reduced, about 15% as predicted for this area for the next decades by GCM and ecophysiological models, by plastic strips intercepting rainfall and by ditch exclusion of water runoff. The stem diameter increment was highly correlated with annual rainfall in all species, and drought treatment strongly reduced the diameter increment of Q. ilex (41%) and specially of A. unedo (63%), the species showing higher growth rates. Stem mortality rates were highly correlated with previous stem density, but drought treatment increased mortality rates in all species. Q. ilex showed the highest mortality rates (9% and 18% in control and drought plots, respectively), and P. latifolia experienced the lowest mortality rates (1% and 3% in control and drought plots, respectively). Drought strongly reduced the increment of live aboveground biomass during these 5 years (83%). A. unedo and Q. ilex experienced a high reduction in biomass increment by drought, whereas P. latifolia biomass increment was insensitive to drought. The different sensitivity to drought of the dominant species of the holm oak forest may be very important determining their future development and distribution in a drier environment as expected in Mediterranean areas for the next decades. These drier conditions could thus have strong effects on structure (species composition) and functioning (carbon uptake and biomass accumulation) of these Mediterranean forests.     

A new positive relationship between pCO2 and stomatal frequency in Quercus guyavifolia (Fagaceae): a potential proxy for palaeo-CO2 levels

Background and Aims The inverse relationship between atmospheric CO₂ partial pressure (pCO₂) and stomatal frequency in many species of plants has been widely used to estimate palaeoatmospheric CO₂ (palaeo-CO₂) levels; however, the results obtained have been quite variable. This study attempts to find a potential new proxy for palaeo-CO₂ levels by analysing stomatal frequency in Quercus guyavifolia (Q. guajavifolia, Fagaceae), an extant dominant species of sclerophyllous forests in the Himalayas with abundant fossil relatives.Methods Stomatal frequency was analysed for extant samples of Q. guyavifolia collected from17 field sites at altitudes ranging between 2493 and 4497 m. Herbarium specimens collected between 1926 and 2011 were also examined. Correlations of pCO₂–stomatal frequency were determined using samples from both sources, and these were then applied to Q. preguyavaefolia fossils in order to estimate palaeo-CO₂ concentrations for two late-Pliocene floras in south-western China.Key Results In contrast to the negative correlations detected for most other species that have been studied, a positive correlation between pCO₂ and stomatal frequency was determined in Q. guyavifolia sampled from both extant field collections and historical herbarium specimens. Palaeo-CO₂ concentrations were estimated to be approx. 180–240 ppm in the late Pliocene, which is consistent with most other previous estimates.Conclusions A new positive relationship between pCO₂ and stomatal frequency in Q. guyavifolia is presented, which can be applied to the fossils closely related to this species that are widely distributed in the late-Cenozoic strata in order to estimate palaeo-CO₂ concentrations. The results show that it is valid to use a positive relationship to estimate palaeo-CO₂ concentrations, and the study adds to the variety of stomatal density/index relationships that available for estimating pCO₂. The physiological mechanisms underlying this positive response are unclear, however, and require further research.     

秦岭南坡锐齿栎次生林空间结构特征分析

该研究采用坐标定位方法对秦岭南坡不同坡向锐齿栎次生林样地内胸径DBH≥5cm的乔木进行调查,记录树种名称、坐标、胸径、高度、冠幅、生长状况等因子,运用角尺度、大小比数和混交度3个指数分析不同坡向锐齿栎次生林的空间结构,探寻不同坡向锐齿栎林空间结构的形成和差异。结果显示:(1)调查样地内物种多样性丰富,锐齿栎重要值最大,长势良好,占据主要生态空间。(2)两种坡向中,角尺度取值为0.5的个体数均过半,表明随机分布是锐齿栎次生林的主要分布方式。(3)优势木、亚优势木、中庸木、劣态木和绝对劣态木所占比重均为20%左右,表明林木大小差异不明显,在空间结构单元中,林木较稳定,阳坡优势木个体数高于阴坡。(4)两种坡向中,混交度取值大于0.5林木个体分别为84%和73%,表明多数林木个体处于中度、强度和极强度混交状态。研究表明,秦岭南坡锐齿栎次生林聚集度不高、混交良好、分化程度较高,锐齿栎种群优势度明显,林分整体暂时处于相对稳定状态。     

Tree mineral nutrition is deteriorating in Europe

The response of forest ecosystems to increased atmospheric CO₂ is constrained by nutrient availability. It is thus crucial to account for nutrient limitation when studying the forest response to climate change. The objectives of this study were to describe the nutritional status of the main European tree species, to identify growth‐limiting nutrients and to assess changes in tree nutrition during the past two decades. We analysed the foliar nutrition data collected during 1992–2009 on the intensive forest monitoring plots of the ICP Forests programme. Of the 22 significant temporal trends that were observed in foliar nutrient concentrations, 20 were decreasing and two were increasing. Some of these trends were alarming, among which the foliar P concentration in F. sylvatica, Q. Petraea and P. sylvestris that significantly deteriorated during 1992–2009. In Q. Petraea and P. sylvestris, the decrease in foliar P concentration was more pronounced on plots with low foliar P status, meaning that trees with latent P deficiency could become deficient in the near future. Increased tree productivity, possibly resulting from high N deposition and from the global increase in atmospheric CO₂, has led to higher nutrient demand by trees. As the soil nutrient supply was not always sufficient to meet the demands of faster growing trees, this could partly explain the deterioration of tree mineral nutrition. The results suggest that when evaluating forest carbon storage capacity and when planning to reduce CO₂ emissions by increasing use of wood biomass for bioenergy, it is crucial that nutrient limitations for forest growth are considered.     

Differential field response of two Mediterranean tree species to inputs of sewage sludge at the seedling stage

Land degradation and desertification is a common feature in Mediterranean landscapes due to extensive and intensive land use and natural or man induced disturbances. The ecosystem may need external inputs to recover its composition and function as soils are often impoverished and vegetal key stone species lost. We evaluated the effects of the application of fresh and air-dried biosolids in the establishment and morphological and physiological performance of seedlings of Pinus halepensis and Quercus ilex under dry Mediterranean field conditions. Seedling survival was not affected by biosolid treatments in any of the studied species both two and ten years after planting. During the first two years, growth was enhanced by the two biosolid treatments in relation to control, although the change in the biomass allocation pattern differed between species. Rooting depth was significantly enhanced by liquid biosolid in Q. ilex and marginally reduced in P. halepensis as well as the exploration of soil. As a consequence, root-to-shoot ratio reduced significantly with dry and liquid sludge due to promoted aboveground growth while maintaining and even reducing belowground fractions. An improvement of the nutritional status, of fertilized seedlings especially of phosphorus, is the explanation for the better field performance. Vector analysis revealed an important phosphorus limitation for both species that was overcome with the application of liquid (both species) and air-dried biosolid (pine). The higher growth of pine seedlings attained in the liquid biosolid treatment was coupled with a significant decrease in foliar δ¹³C, suggesting lower water use efficiency. The significant increase in foliar δ¹⁵N in the biosolid treatments in both species suggested that a large proportion of the total nitrogen uptake came from the applied biosolids. Instead, with regard to the low biosolid application rate used in the study, treatments had an overall positive effect as a restoration tool by improving nutritional status and promoting growth of planted seedlings.     

不同经营措施对黄龙山辽东栎林的影响

以黄龙山林区蔡家川林场的辽东栎群落为研究对象,以未采伐为对照,采取皆伐、间伐30%、间伐15%三种经营措施,在进行自然恢复6年后,对辽东栎林建群种径级结构、群落物种多样性、土壤养分水分状况进行了对比分析,以探讨不同经营措施对黄土高原南部辽东栎(Quercus liaotungensis)林群落多样性的影响.结果表明:不同经营措施实施后建群种径级结构、群落物种多样性、土壤养分水分等指标均与未采伐林地有差异;经过间伐30%的林地,建群种径级结构、群落物种多样性、土壤养分水分等指标均有显著增加;间伐15%林地上述指标均有增加,但不显著;皆伐后的林地相对未采伐林地,建群种径级结构、群落物种多样性、土壤养分水分等指标降低.间伐与皆伐措施后比较,间伐措施的林地建群种个体生长发育良好,林下有大量幼苗,林地物种多样性丰富,土壤养分水分相对优越;皆伐措施的辽东栎建群种个体发育不良,缺乏足够数量的幼苗,林分物种多样性、土壤水分养分相对较差.未来该地区辽东栎林经营管理中,应以近自然经营措施为主,尽量减少对灌草层破坏,完善群落复层结构;间伐强度拟定为30%,尽量间伐劣质木、病虫木,促进群落向异龄方向发展.     

Oak trees and soil interactions in Mediterranean forests: a positive feedback model

Questions: What is the spectrum of variability of chemical elements in a Mediterranean forest ecosystem across the different compartments? Do co‐existing tree species with different leaf chemical composition and nutrient cycling distinctly modify soil conditions? Could these species‐specific, tree‐generated soil changes create a potential positive feedback by affecting long‐term species distribution? Location: Mixed oak forests of southern Spain, Los Alcornocales Natural Park. Methods: We sampled and chemically analysed five different ecosystem components: leaves, leaf fall, litter and superficial (0–25 cm) and sub‐superficial (25–50 cm) soil beneath the canopies of evergreen Quercus suber and deciduous Q. canariensis trees. We used multiple co‐inertia analysis (MCoA) to conjointly analyse the patterns of variability and covariation of eight macro‐ and micronutrients determined in each of the sampled ecological materials. We implemented a path analysis to investigate alternative causal models of relationships among the chemical properties of the different ecosystem components. Results: Variability in the concentration of chemical elements was related to the nature of their biogeochemical cycles. However, the rank of element concentration was consistent across ecosystem components. Analysis of co‐inertia (MCoA) revealed that there was a common underlying multivariate pattern of nutrient enrichment in the ecosystem, which supported the hypothesis of a separation in biogeochemical niches between the two co‐existing oak species, with Q. canariensis having richer plant tissues and more fertile soil directly under each tree than Q. suber. The feasibility of a potential tree–soil positive feedback model was the only statistically validated among several alternative (non‐feedback) models tested. Conclusions: In the studied Mediterranean forests, oak species distinctly modify soil fertility conditions through different nutrient return pathways. Further investigation is needed to address whether these tree‐generated soil changes could affect seedling establishment and ultimately influence species distribution.     

Fire history of a prairie/forest boundary: more than 250 years of frequent fire in a North American tallgrass prairie

Questions: Most modern fire‐prone landscapes have experienced disruptions of their historic fire regimes. Are the primary tallgrass prairies of the Flint Hills reflective of a history of continuous fire occurrence? Did fire frequency, severity, size and seasonality change in connection with changes in land use? Has fire occurrence been related to drought conditions? Location: Edges of Cross Timbers forest stands at the Tallgrass Prairie Preserve (TGPP) in the Flint Hills of Osage County, Oklahoma, USA. Methods: Cross‐sections of 76 Quercus stellata were collected from Cross Timbers stands at or near the grassland edge in the TGPP. Dendrochronological methods were used to identify years of formation for tree rings and fire scars. Superposed epoch analysis was used to evaluate the effect of drought conditions on fire occurrence. Results: Fires were recorded in 46.6% of the years between 1729 and 2005. In 41 cross‐sections at one site, the mean fire interval between 1759 and 2003 was 2.59 years, with fire interval decreasing from a mean fire interval of 3.76 years in the early part of the record to 2.13 years in modern times. No extended periods without fire were recorded in the study area. Drought conditions had no significant effect on fire occurrence. Conclusions: In contrast with many fire‐prone landscapes worldwide, the prairies of the Flint Hills have experienced no recent fire suppression or exclusion. Changes in fire frequency mark transitions in land use, primarily from being traditionally used by Native Americans to being managed for cattle production.     

The effect of Quercus castaneifolia extract on pathogenic enteric bacteria

The family of Enterobacteriaceae is a major group of gram negative bacteria, some of these microorganisms are pathogen and could cause disease mainly gastroenteritis. Recently, due to drug resistant nature of these bacteria specially in developing countries treatment of the patient considered as important investigate. Quercus castaneifolia is a native plant of Yasuj province in Iran, which the people who living in this area consume the fruit of this plant for treatment of enteric disease. Hence, the present study was conducted to evaluate the effect of fruit of Q. castaneifolia extract on pathogenic enteric bacteria viz., E. coli, Salmonella typhimurium, Shigella dysenteriae and Yersinia enterocolitica.Antimicrobial susceptibility and minimal inhibitory concentration (MIC) of the extracts were assessed by gel diffusion method and modification of E-test respectively. All the experiments were performed in triplicate and the statistical analysis was carried out on the results. The results obtained from this study indicated that alcoholic extract was shown antimicrobial effect on the microorganisms tested. In addition, S. dysentriae was more sensitive with zone of inhibition 18 mm and MIC value was 2.5 × 10⁻⁴ whereas, E. coli was less sensitive with zone of inhibition 12 mm and MIC value 1 × 10⁻². Salmonella typhimurium and Yersinia enterocolitica showed relatively intermediate susceptibility to the extract with zone of inhibition of 14 mm and MIC value 5 × 10⁻³. Overall, Q. castaneifolia may be considered for treatment of the patients suffering from enteric disease.