检索结果-南通市图书馆

Tree mortality and biomass loss in drought-aff ected forests of East Texas,USA

在线全文

学校读者我要写书评

暂无评论

Journal of Forestry Research 2021年第1期32卷 67-80页

作者： Mukti Ram Subedi Weimin Xi Christopher B.Edgar Sandra Rideout-Hanzak Ming Yan Department of Biological and Health Sciences Texas A&M University-KingsvilleKingsvilleTX 78363USA Department of Forest Resources University of MinnesotaSt.PaulMN 55108USA Department of Rangeland and Wildlife Sciences and Caesar Kleberg Wildlife Research Institute Texas A&M University-KingsvilleKingsvilleTX 78363USA School of Life Sciences Shanxi Normal UniversityLinfen 041004People’s Republic of China

Changes in tree mortality due to severe drought can alter forest structure,composition,dynamics,ecosystem services,carbon fl uxes,and energy interactions between the atmosphere and land surfaces.We utilized long-term(2000‒2017,3 full inventory cycles)Forest Inventory and Analysis(FIA)data to examine tree mortality and biomass loss in drought-aff ected forests for East Texas,USA.Plots that experienced six or more years of droughts during those censuses were selected based on 12-month moderate drought severity[Standardized Precipitation Evaporation index(SPEI)-1.0].Plots that experienced other disturbances and inconsistent records were excluded from the analysis.In total,222 plots were retained from nearly 4000 plots.Generalized nonlinear mixed models(GNMMs)were used to examine the changes in tree mortality and recruitment rates for selected plots.The results showed that tree mortality rates and biomass loss to mortality increased overall,and across tree sizes,dominant genera,height classes,and ecoregions.An average mortality rate of 5.89%year−1 during the study period could be incited by water stress created by the regional prolonged and episodic drought events.The overall plot and species-group level recruitment rates decreased during the study period.Forest mortality showed mixed results regarding basal area and forest density using all plots together and when analyzed the plots by stand origin and ecoregion.Higher mortality rates of smaller trees were detected and were likely compounded by densitydependent factors.Comparative analysis of drought-induced tree mortality using hydro-meteorological data along with drought severity and length gradient is suggested to better understand the eff ects of drought on tree mortality and biomass loss around and beyond East Texas in the southeastern United States.

关键词： Generalized nonlinear mixed model Endogenous factors Drought index Standardized precipitation evaporation index(SPEI) Above-ground biomass competition index Biomass lost to mortality East Texas

How competitive is the‘pioneer-climax’tree species Nothofagus alpina in pristine temperate forests of Chile?

在线全文

学校读者我要写书评

暂无评论

Journal of Plant Ecology 2019年第1期12卷 144-156页

作者： Rebekka Bögelein Cecilia APérez Philipp Schäferand Frank M.Thomas Faculty of Regional and Environmental Sciences GeobotanyUniversity of TrierBehringstraße 2154296 TrierGermany Present address:Thünen-Institut Institut für WaldökosystemeAlfred-Möller-Straße 116225 EberswaldeGermany Departamento de Ecología de Ecosistemas Instituto de Ecología y Biodiversidad(IEB)Alameda 340SantiagoChile

Aims Nothofagus species are constitutive elements of the temperate forests along the Southern Andes Mountains.The deciduous Nothofagus alpina is a fast-growing,but long-lived opportunistic pioneer spe-cies(‘pioneer-climax species’)and co-occurs with the evergreen N.dombeyi.We tested whether N.alpina is competitively superior to N.dombeyi in mature stands and whether intra-specific competition in N.alpina is stronger than inter-specific competition with N.dombeyi.Methods In a pristine old-growth forest in South-Central Chile,we compared the growth of N.alpina trees in pure stands and in mixture with N.dombeyi to the growth of N.dombeyi and calculated compe-tition indices.We related growth variables to climate data and weather extremes.Important Findings In N.alpina,juvenile basal area increment was signifi-cantly higher in pure than in mixed stands.Contrary to our hypothesis,N.dombeyi exhibited larger radial stem increments than N.alpina in the most recent 40 years.In the most recent two decades,this was caused by high growth rates of large N.dombeyi trees.In both Nothofagus species,stem growth was negatively related to temperature,but N.dombeyi responded more sensitively to weather conditions than N.alpina.In N.alpina,stem increment was negatively related to the intensity of competition,but the size of the competition effects on this species was similar in pure and mixed stands.Thus,compared to N.alpina,the‘pioneer-climax species’concept is even more appropriate for N.dombeyi with its relatively high growth rates even in the early stages of its life.

关键词： competition index dendroecology growth-competition relationship pointer year productivity tree-ring analysis

The growth and production modeling of individual trees of Eucalyptus urophylla plantations

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Forestry Research 2020年第5期31卷 1663-1672页

作者： Joao Victor Nobre Carrijo Ana Beatriz de Freitas Ferreira Marcela Costa Ferreira Mario Cesar de Aguiar Eder Pereira Miguel Eraldo Aparecido Trondoli Matricardi Alba Valeria Rezende Department of Forestry Faculty of TechnologyUniversity of Brası´liaBrası´lia 70910-900Brazil

Individual tree models(ITMs)are classified as growth and production models for projecting current and future forest stands.ITMs are more complex than other growth and production models,show a higher level of detail and,consequently,produce a better modeling resolution.However,the accuracy and efficiency of ITMs have not been properly assessed to date.In this study,we estimated the growth in height,diameter,and individual tree volume of a Eucalyptus urophylla plantation by applying an ITM.We used a continuing forest inventory dataset in which 1554 individual trees within 29 permanent plots were measured in the field over a 6-year period(24 to 72 months).Each individual tree volume was estimated for future tree age.To achieve this,we adjusted the model to predict the height and diameter growth,and the probability of mortality as a function of the competition index.The ITM accuracy was assessed based on the analysis of variance results and,subsequently,the multiple mean comparison test at the 5%significance level.The tree volumes predicted by the ITM for the forest stand aged 72 months,beginning at ages 24,36,48,and 60 months,were compared to the field measured tree volume acquired from the 72-month forest inventory that was used as the reference age.Estimated and observed tree volumes were similar when the estimation was based on the 48-month forest plots.These results might help to reduce financial costs of forest inventory because the ITM produces accurate future predictions of forest stand stocks.Our estimated ITM for Eucalyptus plantations using measurement intervals up to 2 years is recommended because it significantly reduced the projected volume discrepancy compared to the field measurements.

关键词： competition index Forest production Forest site Simulation models Tree mortality

Generalized competition Indices of Primitive θ-Graphs

在线全文

学校读者我要写书评

暂无评论

Journal of Donghua University(English Edition) 2017年第3期34卷 424-429页

作者：孙晓玲高玉斌杜建伟胥兰 School of Science North University of China Taiyuan 030051 China School of Instrument and Electronics North University of China Taiyuan 030051 China

As a generalization of the scrambling index and the exponent,m-competition index has been widely applied to stochastic matrices,food webs and memoryless communication systems in recent years. For a positive integer m,where 1 ≤ m ≤ n,the mcompetition index( generalized competition index) of a primitive digraph D of order n is the smallest positive integer k such that for every pair of vertices x and y,there exist m distinct vertices v_1,v_2,…,v_m such that there exist walks of length k from x to v_i and from y to v_i for 1 ≤ i ≤ m. By analyzing the structure of θ-graphs( theta graphs) and using enumeration investigation methods,the mcompetition indices of primitive θ-graphs are studied and an upper bound is provided. Moreover, some corresponding extremal θ-graphs are characterized.

关键词： competition index m-competition index scrambling index generalized competition index θ-graph