Sap flow measurements with some thermodynamic methods,flow integration within trees and scaling up from sample trees to entire forest stands

Sap flow measurement techniques and evaluation of data are reviewed. Particular attention is paid to the trunk segment heat balance (THB) and heat field deformation (HFD) methods based on 30 years experience. Further elaboration of sap flow data is discussed in terms of integrating flow for whole stems from individual measuring points, considering variation of radial patterns in sapwood and variation around stems. Scaling up of data from sets of sample trees to entire forest stands based on widely available biometric data (partially on remote sensing images) is described and evaluated with a discussion of the magnitude of errors, the routine procedure applicable in any forest stand and practical examples.     

Comparative water relations of co-occurring trees in a mixed podocarp-broadleaf forest

AimsAs extreme climatic events including droughts and heat waves become more common in a changing climate, tree mortality has increased across the globe. In order to determine whether certain species have a competitive advantage over others, we explored the water-relations and leaf-gas exchange of four co-occurring species in a forest in northern Aotearoa-New Zealand. We studied the ecologically and culturally significant foundation species,Agathis australis(a conifer), two additional conifers,Phyllocladus trichomanoidesandPodocarpus totaraand the angiospermKnightia excelsa.     

Asymmetric hybridization and gene flow between Joshua trees (Agavaceae: Yucca) reflect differences in pollinator host specificity

The angiosperms are by far the largest group of terrestrial plants. Their spectacular diversity is often attributed to specialized pollination. Obligate pollination mutualisms where both a plant and its pollinator are dependent upon one another for reproduction are thought to be prone to rapid diversification through co‐evolution and pollinator isolation. However, few studies have evaluated the degree to which pollinators actually mediate reproductive isolation in these systems. Here, we examine evidence for hybridization and gene flow between two subspecies of Joshua tree (Yucca brevifolia brevifolia and Yucca brevifolia jaegeriana) pollinated by two sister species of yucca moth. Previous work indicated that the pollinators differ in host specificity, and DNA sequence data suggested asymmetric introgression between the tree subspecies. Through intensive sampling in a zone of sympatry, a large number of morphologically intermediate trees were identified. These included trees with floral characters typical of Y. b. jaegeriana, but vegetative features typical of Y. b. brevifolia. The opposite combination—Y. b. brevifolia flowers with Y. b. jaegeriana vegetative morphology—never occurred. Microsatellite genotyping revealed a high frequency of genetically admixed, hybrid trees. Coalescent‐based estimates of migration indicated significant gene flow between the subspecies and that the direction of gene flow matches differences in pollinator host fidelity. The data suggest that pollinator behaviour determines the magnitude and direction of gene flow between the two subspecies, but that specialized pollination alone is not sufficient to maintain species boundaries. Natural selection may be required to maintain phenotypic differences in the face of ongoing gene flow.     

Successional change of forest pattern along topographical gradients in warm-temperate mixed forests in Mt Kiyosumi,central Japan

Forest patterns along topographical gradients were compared between second- and old-growth forested watersheds in a warm-temperate zone of Mt Kiyosumi, central Japan. Three community types were distinguished depending on the topographical habitat type in each watershed, for example, conifer forest was dominated byAbies firma andTsuga sieboldii on ridge sites, evergreen broad-leaved forest was dominated byQuercus acuta, Q. salicina andCastanopsis cuspidata var.sieboldii on slope sites, and deciduous forest was dominated byEuptelea polyandra andCornus controversa in valley sites. Beta diversity and distinctiveness of each topographical community type increased with progression of secondary succession. Conifers and evergreen broad-leaved trees, which were intermingled with each other on ridges and slopes of the second-growth watershed, were in turn restricted to the ridge and slope habitat type, respectively, in the old-growth watershed. The process of this differentiation can be explained by the continuous regeneration of conifers on ridge sites, and its absence on slope sites due to different light conditions caused by progressive canopy closure of evergreen trees on the slope sites toward the old-growth watershed. In the valley type habitat, frequent soil disturbance, such as landslides and soil creep, hinder the continuous growth of late successional evergreen trees, and thus seral or pioneer deciduous trees can persist in the habitat.     

Isozymes and DNA markers in gene conservation of forest trees

For long-lived plants that have to cope with high temporal and spatial environmental heterogeneity, genetic diversity is of prime importance for species persistence. Detrimental anthropogenic impact on the gene pool of forest trees calls for conservation of genetic resources. Potentials and limitations of isozymes and DNA markers in forest genetic conservation are reviewed. These markers can contribute to conservation with respect to the delimitations of species and hybrid zones, as well as the assessment of genetic diversity within and among populations. Markers are valuable to identify resource populations, since today‘s genetic diversity in forest trees is predominantly the result of plant history (e.g. glacial refuges, migration). Several suggestions have been put forward to optimize sampling of in situ or ex situ populations on the grounds of marker data. Restraint in this area is recommended. Different types of genetic markers (terpenes, isozymes, nuclear and extrachromosomal DNA polymorphisms) and quantitative traits yield different information about genetic diversity and population differentiation. Hence identification of resource populations should not solely be based upon a certain marker type or on quantitative traits alone. The capability of available markers to predict or assess adaptive potentials in forest tree populations is still very limited. This revised version was published online in August 2006 with corrections to the Cover Date.     

大小兴安岭针叶树倒木上木腐真菌的物种多样性

木腐真菌在森林生态系统中具有丰富的物种多样性, 并在倒木的降解过程中发挥重要的生态功能。针叶树是大小兴安岭森林生态系统的优势树种, 因此研究针叶树倒木木腐真菌物种多样性和影响其物种分布的相关环境因子有助于揭示大小兴安岭森林生态系统物质循环的机理。本研究收集了近16年对大小兴安岭地区冷杉属(Abies)、落叶松属(Larix)、云杉属(Picea)和松属(Pinus) 4类针叶树倒木上1,561份木腐真菌标本的采集信息, 统计了物种种类及其腐朽类型, 并选取具有代表性的地点开展木腐真菌群落多样性及其与环境因子的相关性分析。结果显示, 大小兴安岭针叶树倒木木腐真菌有166种, 隶属于70属, 其中白腐真菌有111种, 占所有种类的66.9%, 褐腐真菌为55种, 占所有种类的33.1%。在4类针叶树倒木上均能生长的真菌种类有19种, 占所有种类的11.5%, 其中柔丝干酪孔菌(Oligoporus sericeomollis)是各类倒木上木腐真菌群落中的优势种。大兴安岭地区落叶松属为优势寄主, 其倒木上生长的木腐真菌种类数和个体数在4类倒木中均为最高; 而小兴安岭地区松属倒木上木腐真菌种类数和个体数比其他3类倒木高, 是该地区的优势寄主。对6个代表性地区木腐真菌群落的研究显示, 有11种真菌在6个地区均有分布, 小兴安岭地区木腐真菌多样性普遍高于大兴安岭地区; 聚类分析显示树种比地理位置对木腐真菌物种分布的影响更大。     

Gas-exchange and sap flow measurements of Salix viminalis trees in short-rotation forest

Simultaneous field measurements of transpiration and sap flow were performed on short-rotation Salix viminalis trees ranging in diameter from 1.5 to 3.5 cm (2-year-old shoots on 8-year-old stumps). Transpiration was measured using an open-top ventilated chamber enclosing the whole foliage of a tree. Sap flow was measured using a tree-trunk heat balance (THB) technique with a constant temperature difference and variable heat input. Both the instantaneous and daily values of water flux measured by the two absolute techniques agreed well with a difference of up to about 5%. In July, the hourly transpiration reached a maximum of about 0.2 kg m^–2 (leaf area) or 0.45 kg tree^–1, whereas maximum daily integrals reached 4 kg tree^–1. The response of sap flow rate to abrupt flux change when inducing emboli by cutting-off the stem was very rapid: the registered signal dropped by 85% within 10 min for a specimen with a projected leaf area of 2 m². For S. viminalis trees, transpiration was linearly correlated with stem cross-sectional area and with leaf area.     

Estimates of forest floor litter frog communities: A comparison of two methods

Estimates of forest leaf litter frog density, mass, richness and diversity given by the widely used 8 m × 8 m large plot method (LPM) were compared with estimates obtained by a newly proposed method (small 2 m × 1 m plots with leaf removal; SPLR). The study site was an undisturbed area of the Atlantic Rainforest of Ilha Grande, an island located in the south of Rio de Janeiro State, Brazil. Twenty‐four LPM (totalling 1536 m² of forest floor) and 90 SPLR (totalling 180 m² of forest floor) were performed. The estimates obtained by the two methods differed markedly, indicating that even using a much smaller sampling area (11.7% of that of LPM), SPLR gave frog density estimates six times higher, and frog mass estimates approximately 2.5 times higher than estimates provided by LPM. The species richness and diversity obtained by the two methods were similar, despite the fact that the total area sampled with SPLR was much smaller. These data suggest that LPM may underestimate the abundance and biomass of leaf litter frogs in a given area.     

Population genetics of the wood-rotting basidiomycete Armillaria cepistipes in a fragmented forest landscape

Armillaria cepistipes is a common wood-rotting basidiomycete fungus found in most forests in Central Europe. In Switzerland, the habitat of A. cepistipes is fragmented because of the presence of major geographical barriers, in particular the Alps, and past deforestation. We analysed the impact of habitat fragmentation on the current spatial genetic structure of the Swiss A. cepistipes population. A total of 167 isolates were sampled across an area of 41 000 km² and genotyped at seven microsatellite and four single nucleotide polymorphism (SNP) loci. All isolates belonged to different genotypes which, according to the Bayesian clustering algorithm implemented in Tess, originated from a single gene pool. Our analyses indicate that the overall A. cepistipes population shows little, but significant (F_ST = 0.02), genetic differentiation. Such a situation suggests gene flow is strong, possibly due to long-distance dispersal of airborne basidiospores. This hypothesis is supported by the fact that we could not detect a pattern of isolation by distance. Gene flow is partially restricted by the high mountain ranges of the Alps, as indicated by a signal of spatial autocorrelation detected among genotypes separated by less than about 80–130 km. In contrast, past deforestation seems to have no significant effect on the current spatial population structure of A. cepistipes. This might indicate the existence of a time lag between the current spatial genetic structure and the processes that have induced this specific structure.     

Causes of spatial patterns of dead trees in forest fragments in Illinois

Natural disturbances introduce spatial heterogeneity into forests by causing non-random mortality of trees. We examined whether wind was the primary cause of spatial patterns of dead trees at fragment- and individual tree-levels in three fragments of temperate deciduous forests in Illinois, USA. Dead trees and wind-caused types of mortality were expected to be higher at forest edges, on windward aspects, in poorly-drained soils, and adjacent to existing canopy gaps. The extent of wind-related mortality was determined by comparing spatial and temporal patterns of dead trees, as well as characteristics of trees downed by single windstorms versus all dead trees. At the fragment-level, we used randomly located quadrats of 25×25 m to sample edge and interior areas of Trelease Woods, Brownfield Woods, and Hart Woods in 1995-1996 and again in 1999-2000. We noted type of mortality (standing dead, snapped-off, or uprooted trees), and measured DBH ( 10 cm) and direction of fall of each dead tree. The same measures were made for trees felled by two single storms in 1994. At the individual tree-level, domino effects were evaluated by comparing openness surrounding target treefalls vs. an equal sample size of living trees. The study provided limited evidence that wind caused spatial patterns of dead trees. Instead, spatial patterns of dead trees in the fragments accumulated from domino effects at the individual tree-level in two of the three fragments. Dead trees were more associated with preexisting gaps. Contrary to our predictions at the fragment-level, the frequency of dead trees was not greater at edges, on windward aspects, or in poorly drained soils. This study demonstrated the complexity of spatial patterns of dead trees in forest fragments. The significant domino effects indicated that the occurrence of dead trees was not random, but determined by previous disturbances.     

Habitat associations of Sterculiaceae trees in a Bornean rain forest plot

Questions: 1. Are trees in a Bornean tropical rain forest associated with a particular habitat? 2. Does the strength of habitat association with the species‐specific optimal habitat increase with tree size? Location : A 52‐ha plot in a mixed dipterocarp forest in a heterogeneous landscape at the Lambir Hills National Park, Sarawak, East Malaysia. Methods : Ten species from the Sterculiaceae were chosen as representative of all species in the plot, on the assumption that competition among closely related species is more stringent than that among more distantly related taxa. Their habitat associations were tested using data from a 52‐ha plot by a torus‐translation test. Results : The torus‐translation test showed that eight out of the ten species examined had significant association with at least one habitat. We could not find negative species‐habitat associations for rare species, probably due to their small sample sizes. Among four species small trees were less strongly associated with habitat than large trees, implying competitive exclusion of trees in suboptimal habitats. The other four species showed the opposite pattern, possibly owing to the smaller sample size of large trees. A habitat had a maximum of three species with which it was significantly positively associated. Conclusions : For a species to survive in population equilibrium in a landscape, habitats in which ‘source’ subpopulations can be sustained without subsidy from adjacent habitats are essential. Competition is most severe among related species whose source subpopulations share the same habitat. On the evidence of source subpopulations identified by positive species‐habitat association, species‐habitat association reduces the number of confamilial competitors. Our results therefore indicate that edaphic niche specialization contributes to coexistence of species of Sterculiaceae in the plot, consistent with the expectations of equilibrium hypotheses.     

Population dynamics of coniferous and broad-leaved trees in a Japanese temperate mixed forest

The growth and survival of coniferous and broad-leaved trees were followed over a 5-yr period in a temperate old-growth mixed forest in Japan, and dynamic features of the forest were studied in relation to the life history of the dominants, the coniferous Abies homolepis and the broad-leaved Fagus crenata. During this period, the gap formation rate was 31m² ha^?1yr^?1, the mortality of trees > 2m high was 1.7%/yr, and the rate of loss in basal area 1.4%/yr. These values were much higher than the recruitment, 0.3%/yr, and the total growth of surviving and new trees, 0.6%/yr, owing to the inhibition of regeneration by understorey dwarf bamboo (Sasa borealis). A transition matrix model based on DBH size classes predicts that the basal area of the forest will decrease by 14% in 50 yr, but that the DBH distribution of trees > 10 cm diameter will change little. Equilibrium DBH distributions assuming recruitment being equal to mortality, were quite different between broad-leaved and coniferous trees, reflecting different survivorship curves of the two dominants. The composition and structure of the forest may change depending on the pattern and frequency of disturbances, or episodic events, notably the synchronous death of Sasa borealis.     

阔叶红松林倒木贮量的变化规律

研究了长白山阔叶红松林倒木贮量的动态变化规律。阔叶红松林倒木贮量包括其现有倒木及其年输入量等贮量的变化规律。阔叶红松林现有倒木贮量开始为１６．２５ｔ／ｈｍ＾２,以后随时间减少,到１００ａ后分解掉其干重的８５％左右,３００ａ后所剩无几。例木年输入量平均约为０．６ｔ／ｈｍ＾２,其贮量是随时间而增加,２００ａ后稳定在３１ｇ／ｈｍ＾２,可保持到该群落的顶级时期。倒木总贮量的变化在初期呈增加趋势,而后随着现     

Mating system of Carapa procera (Meliaceae) in the french guiana tropical forest

The mating system of the tropical rainforest tree Carapa procera was studied for a population located within a sylvicultural trial in French Guiana. We used the mixed-mating model with the genotypes of 47 open-pollinated progenies at ten polymorphic loci, obtained through isozyme analysis. Seeds were collected on both logged and unlogged (control) plots, which were interspersed. A high multilocus outcrossing rate (0.78) was found for the global population. and there was indirect evidence for nonrandom mating for outcrosses. It is argued that this may be due to some kind of positive assortative mating, probably biparental inbreeding. Correlation of selfing between sibs was not significantly different from zero. and the proportion of full-sibs among outcrossed sib-pairs was significant but low (0.16). We found significant differences between outcrossing rates when computing separate estimates for the 14 trees located on logged plots (tm = 0.63) and the 33 trees located on undisturbed plots (tm = 0.85). It is argued that the decrease in density is probably not the only cause of the decrease in outcrossing rate on logged plots. Lastly, several points concerning the reliability of the estimation are outlined. In particular. the downward bias due to ignoring null alleles during genetic interpretations of zymograms is quantified in a few cases by simulating artificial populations.     

红松阔叶林倒木贮量动态的研究

在森林倒木研究的基础上探讨长白山红松阔叶林倒木贮量的动态,涉及红松阔叶林倒木分解及其贮量的动态规律。研究表明,倒木分解,除心腐木外,均由表及里进行;倒木分解速率在其它生态条件相同时因树种、直径和部位而异。红松阔叶林倒木贮量动态包括现有倒木贮量和倒木年输入量两个分解动态过程,现有倒木贮量在头100年其干重迅速减少,其中椴树比红松尤速,前者分解91%,后者为72%.林地倒木贮量动态与倒木年输入量分解动态相似,但前者在分解初期贮量增加较大,因为部分现有倒木未完全分解;100年后趋于一致,并恒定于16～17t·hm^-2,直至群落的顶极阶段结束.