A comparison of two techniques for measuring and crossdating tree rings

Crossdating is the core principle of dendrochronology. Our study compared two techniques for measuring and crossdating tree rings using Juniperus virginiana L. (eastern redcedar) as a case study. We used a pseudo 2 × 2 study design comparing the traditional skeleton plot/sliding measuring stage technique to a semi-automatic image analysis program across two technicians. Crossdating was evaluated in COFECHA. Raw measurements of total, earlywood, and latewood widths from the two methods were analyzed using the Verify for Windows program, ANOVA, and correlation matrices. Total ring width and earlywood width were well correlated between techniques and technicians but questionable ring boundaries from image analysis program should be checked under a stereoscope. Juniperus virginiana latewood widths were significantly different between techniques and technicians; therefore, we do not recommend combining latewood measurements from species with limited latewood variability for dendrochronological analysis. A standard definition of the earlywood-latewood boundary that can be replicated across technicians is needed to combine latewood measurements from the sliding measuring stage and image analysis systems.     

RingdateR: A statistical and graphical tool for crossdating

Crossdating is the defining technique of dendrochronology, ensuring that all measurements in a dataset are annually resolved and absolutely dated. This level of accuracy allows for the development of high-resolution environmental reconstructions of climate, disturbance, and productivity not only in trees, but also in other ring-forming organisms including fish, corals, and bivalves. However, crossdating is a laborious process and can be a significant bottleneck in the development of new chronologies, especially when attempting to find matches among undated, dead-collected material. Several software packages have been developed to aid in crossdating, yet efficiently identifying matches among large numbers of dead-collected samples of unknown antiquity remains a gap in functionality. To address this issue we present RingdateR, a new stand-alone and web-based application for statistical and graphical crossdating that shares many key features with established crossdating applications, but has been optimised for crossdating large collections of dead-collected material. The workflow allows users to load undated measurement time series in common file types (e.g. pos, lps, csv, and xlsx) to be matched against one another (i.e. pairwise analyses) or against an existing chronology. RingdateR provides graphical tools to help identify false or missed rings remaining in the matched measurement time series and to evaluate the impact of the newly crossdated measurement time series on chronology statistics. Whilst the decision as to whether a sample is correctly crossdated ultimately lies with careful visual inspection and discretion of the investigator, guidance from RingdateR can greatly expedite the process, especially when building chronologies that involve dead-collected samples.     

Responses of ring widths and maximum densities of Larix gmelinii to climate on contrasting north- and south-facing slopes in central Siberia

An analysis was performed of the climatic responses of the radial growth of Larix gmelinii (Rupr.) Rupr. at two sites—both of which included contrasting north- and south-facing slopes—in Tura, central Siberia, with the development of ring width and maximum-density chronologies for each slope. Both residual and standard chronologies of ring widths were positively correlated with temperature from late May until mid June on all four slopes. By contrast, standard chronologies of ring widths were negatively correlated with precipitation during the winter (from October to April) and in May on the north-facing slope at site 1 and on the south-facing slope at site 2 respectively. The negative correlations with precipitation during the winter and in May on some of the slopes suggested that delayed snowmelt in early spring might inhibit the radial growth of L. gmelinii, and the effects of snow are likely to vary with topography. Both residual and standard chronologies of maximum densities were positively correlated with temperature in early July on all four slopes. Maximum densities were also positively correlated with precipitation during summer of the previous year on all the slopes. These suggest that no major differences exist in terms of responses of maximum density to climatic factors between the north- and south-facing slopes.     

Crossdating Juniperus procera from North Gondar, Ethiopia

The application of dendrochronology in (sub)tropical regions has been limited by the difficulty in finding trees with distinct annual rings that can be crossdated. Here, we report successful crossdating of Juniperus procera trees from North Gondar, Ethiopia. The trees form annual rings in response to a unimodal rainfall regime. The selection of mesic locations ensured that the trees did not respond to intra-seasonal weather anomalies. Crossdating was achieved by comparison of the wood anatomy directly on the surface of the core samples and purpose-adapted skeleton plotting. Wood-anatomical anomalies, such as false and indistinct rings, were regarded as potentially replicated features and used in crossdating. COFECHA yielded site-specific mean series inter-correlations between 0.52 and 0.59. AMS radiocarbon dating during the bomb era indicated that dating uncertainty is ±1 year.     

Frequency of partial and missing rings in Acer saccharum in relation to canopy position and growth rate

Locally absent growth rings are known to occur in trees during periods of environmental stress, but little evidence has been available on their frequency in moist temperate forests or on their potential for causing problems in dendroecological studies. In this study, 95 stem disks of Acer saccharum cut from trees representing a wide range of size and age were examined for ring anomalies using three techniques – inspection of disks for partial rings, crossdating of each tree against regional master chronologies, and use of stand history evidence. The number of ring anomalies in Acer saccharum was inversely related to growth rate and vigor. Mean percentage of ring anomalies was 1.3% in dominant canopy trees, 4.6% in trees of the intermediate crown class, and 16.2% in overtopped trees. All of the overtopped trees had partial or missing rings, with a mean of 10 per tree and a range of 2 to 20. Use of crossdating to correct for ring anomalies appeared to be successful in 88% of the canopy trees. However, crossdating results were inconclusive in 32% of the overtopped trees because of low ring width variability, multiple missing rings, and short duration of trouble-free segments. Because overtopped trees are of limited value in reconstructing disturbance history and often cannot be crossdated reliably, we suggest that they normally be excluded from disturbance chronologies.     

Overcoming crossdating challenges to generate ring-width chronologies for Sequoia sempervirens across its native range

We utilize a large dendrochronological dataset for Sequoia sempervirens of 1.29 million rings from 5952 series for 278 trees to generate location and regional ring-width chronologies and to investigate constraints on crossdating. Increment cores were collected at regular height intervals along the trunk via free-hanging ropes with some terrestrial deadwood sampled. Inter-annual chronologies span 86–1687 yr for 47 locations in primary and secondary forests across the native Sequoia range. Shared signals based on declining strength of paired correlations with distance, strong correlations within regions, and groupings of principal components guide chronology creation for northern (1032 yr, 108 trees) and southern (865 yr, 52 trees) regions and four sub-regions. The suite of chronologies provides location-specific references as well as more robust regional indices that reflect distinct signals along a climatically-integrative latitudinal gradient. Secondary forests date to near completion, and we use a subset of data to assess crossdating for trees in primary forests. Among tree and landscape attributes, old age is the most important predictor of undated and missing rings, and undated rings align with periods of reduced biomass production distributed across centuries-long lifespans. Crossdating metrics vary by height above the ground with breast height (BH) and 10 m samples having more undated rings than upper samples. At 10 m, samples have the most missing rings. Buttressing affects the lower trunk as BH series have higher ring widths and lower interseries correlations compared to those up to 70 m. Whole-trunk sampling maximizes success for crossdating old, structurally-complex Sequoia and enables dating of crown damage and assessment of biomass dynamics related to environmental change. Reference chronologies, regional assessments, and crossdating insights collectively guide future study of Sequoia for applications including climatology, fire ecology, and seismology.     

The potential of intra-annual density information for crossdating of short tree-ring series

The crossdating of tree-ring series is typically based on tree-ring width sequences, which is a crude abstraction of the growth signal stored in tree rings. In contrast, intra-annual wood density data allows a much more detailed comparison of wood growth processes and new measurement techniques scale well to measure large amounts of samples. Thus, chronologies of intra-annual densitometric curves can be built. Here, we investigate to what extent intra-annual wood density information can improve crossdating. We evaluate different approaches on a data set of Norway spruce trees (Picea abies) and compare the results to standard methods that are based on ring width or maximum density. Our results show that intra-annual densitometric data indeed increases crossdating success rate notably for short tree ring series that cover less than 25 years.     

Influence of fire severity on the regeneration,recruitment and distribution of eucalypts in the Cotter River Catchment,Australian Capital Territory

Abstract Plant responses to fire are variable between and within species and are influenced by numerous factors including fire severity. This study investigated the effects of fire severity on the regeneration and recruitment of forest eucalypts in the Cotter River Catchment, Australian Capital Territory (ACT). This study also examined the potential for the obligate seeder Eucalyptus delegatensis R.T. Baker (Myrtaceae) to expand into adjacent stands dominated by the facultative resprouter Eucalyptus fastigata H. Deane & Maiden (Myrtaceae) by seed shed and seedling establishment beyond the pre‐fire boundary. Sites were located in areas of either higher or lower fire severity, and transects were placed across the boundary of stands of E. delegatensis and E. fastigata. Species distributions, tree survival and seedling densities and heights were recorded, and the location of each boundary was determined as the region of maximum change in species composition along the transects. Eucalyptus delegatensis was the only eucalypt killed by higher severity fire. However, E. delegatensis seedling density was greater at higher severity sites than lower severity sites. Eucalyptus fastigata seedling density was low across all sites, with other eucalypts producing few, if any, seedlings. There was no evidence that E. delegatensis had increased its range into downslope stands dominated by E. fastigata. Patterns of vegetative recovery and seedling recruitment may be related to a number of factors, including differences in allocation patterns between seeders and sprouters, and the effects of overstory and understory competition. It is unclear what processes impede E. delegatensis seedling establishment beyond the stand boundary, but may involve an inability of E. delegatensis to shed seed sufficiently far downslope; unsuitable conditions for germination beyond the boundary; or, competition from a retained or resprouting overstory, despite the potential for increased dispersal distance soon after fire.     

Germination requirements and responses to leaf litter of four species of eucalypt

We studied how the responses of four species of eucalypt to leaf litter related to their germination responses to light and water availability. Two of the species (Eucalyptus obliqua and E. baxteri) have a mesic distribution, while the other two (E. oleosa, and E. incrassata) are more xerophytic. We studied the effect of litter on emergence of the four species in a glasshouse experiment. Litter did not affect the emergence of E. incrassata and E. oleosa, but enhanced the emergence of E. obliqua and E. baxteri. Litter increased the seedling mortality of all four species. Germination responses to light and water availability were studied in growth cabinets under controlled conditions. The germination of E. obliqua and E. baxteri was substantially lower under fluorescent light than in darkness, but that of E. oleosa and E. incrassata was not affected by the light environment. The germination of E. obliqua and E. baxteri was significantly reduced by reduced water potential (a). Substantial germination of E. oleosa and E. incrassata occurred even at very low a (less than –1.05 MPa). We conclude that both the shade and the humid micro-environment provided by litter may have contributed to the emergence responses of the four species to litter, and these responses may correspond to ecological adaptations to the different environments in which they live.     

太白山南北坡高山林线太白红杉对气候变化的响应差异

气候变化对秦岭植被生长的影响已经引起了人们的广泛关注,在相同的立地条件下,植被对气候变化的响应会因坡向不同而产生差异,秦岭的分水岭太白山尤为典型,为更进一步揭示不同坡向太白红杉(Larix chinensis)对气候变化响应的差异,以树木年代学为依据,利用采自太白山南、北坡相同海拔的太白红杉树芯样本分别建立了树轮年表,并分析了两者的年表特征,探讨了树轮宽度指数与气候因子之间的相关性及逐步线性回归方程。结果表明:太白山南、北坡太白红杉年表的平均敏感度、样本间平均相关系数、样本总体代表性等特征值较高,表明两个不同坡向年表中皆含有丰富的环境信息,相对而言,北坡样地植被对气候的响应较南坡样地敏感;由相关性分析可知,南北坡太白红杉差值年表对气温和降水响应显著的月份有所差异,北坡样地轮宽指数与当年和前一年1—6月平均气温皆为显著正相关关系,而南坡样地轮宽指数仅与当年5—6月平均气温通过显著性检验。南、北坡太白红杉径向生长都明显受到前一年6月降水"滞后效应"的一致影响,但北坡仅与当年8月的降水呈显著正相关,南坡与当年1—4月的平均降水量存在十分显著的负相关;多元线性逐步回归模型显示,气温因子对回归方程的贡献最大值均大于降水因子的贡献最大值,表明气温因子的变化更易引起太白红杉树轮宽度的变化,另外,气温因子对北坡样地回归模型的贡献值比气温因子对南坡样地回归模型的贡献值大,表明北坡样地处树轮宽度指数对气温因子更敏感,并且与相关分析结果一致。     

Climatic signals in tree rings of <Emphasis Type="Italic">Burkea africana</Emphasis> and <Emphasis Type="Italic">Pterocarpus angolensis</Emphasis> from semiarid forests in Namibia

Tree-ring studies contribute worldwide to the understanding of climate and its relation to tree growth. Long tree-ring chronologies serve as climate proxies for the reconstruction of past, pre-instrument climate and its recent change. In tropical regions, the availability of exactly dated tree-ring chronologies is limited. The dendroclimatic potential of two dominant species from dry forests in northern Namibia was examined in the study presented in this paper. Both species (Burkea africana Hook and Pterocarpus angolensis DC) were sampled at two sites (ca. 900 km apart), and the response to several climatic variables, including ENSO indices, is studied. All specimens showed distinct growth rings and cross-dating between radii was successful for all trees. Species-specific mean curves were built for both sites. The mean curves of different species of the same site synchronised significantly, allowing the construction of a site-specific chronology. Synchronisation between sites was not possible, but spectral analysis of the chronologies implied that both show similar long-term (6.7 year) oscillation patterns. B. africana is more sensitive to rainfall variation than P. angolensis at both sites. Growth response to rainfall was positive, but a time-lag in the reaction occurred between the sites, corresponding to the time-lag of the beginning of the rainy season. Air temperature showed a negative correlation with stem increment at both sites. The response at the westernmost site to two ENSO indices indicates a tree growth decrease during El Niño years, which are generally dry in southern Africa.     

升温突变对川西道孚林线川西云杉和鳞皮冷杉生长的影响

高山林线作为理想的全球气候变化监测器,是研究植被与气候变化关系的重要场所。利用川西道孚县高山林线川西云杉（Picea likiangensis var.balfouriana）和鳞皮冷杉（Abies squamata）的年轮宽度资料,基于树木年代学的方法,构建差值年表并通过升温突变前后（1995年前后）年轮指数与气候要素的相关分析,探讨了该区林线主要针叶树种的年轮响应变化,为研究青藏高原地区树木与气候响应关系提供研究基础。结果表明：（1）年尺度上,1995年气温突变前后川西云杉和鳞皮冷杉年轮指数和生长弹性时间变化趋势均不显著,没有发生显著的响应分歧现象。（2）月尺度上,升温突变前川西云杉年轮指数与前一年11月月均最高温、5-7月月均温、6月月均最高温、7月月均最低温呈显著正相关;鳞皮冷杉则与前一年11月月均温、11月月均最高温和12月月均温呈显著正相关;表明升温突变前林线树木生长分别受夏季和冬季温度控制;升温突变后川西云杉年轮指数与前一年11月月均温呈显著负相关,和当年2月降水量及7月月均最低温呈显著正相关;而鳞皮冷杉则与当年5月月均温和5月月均最低温呈显著负相关,与5月降水的正相关性达到最大;表明升温突变后林线川西云杉生长依然受夏季温度控制,而鳞皮冷杉生长则受到春季干旱胁迫的影响。未来气候若随着升温出现干暖化,则林线鳞皮冷杉可能会发生明显的响应分歧现象。     

Ensuring a representative sample of earlywood vessels for dendroecological studies: an example from two ring-porous species

The analysis of time series of wood cell anatomical features (such as the earlywood vessels of ring-porous trees) is a successful approach to understand the effect of environmental factors on tree growth and thus constitutes a valuable source of information about past environmental conditions. However, despite the rising interest in analyzing wood anatomical time series, little or no attention has been paid to establish an adequate sample of cells in order to minimize the risk of missing a valuable environmental signal. In order to contribute to such methodological bases, this paper is aimed at (1) identifying a representative sample of earlywood vessels within a tree, which encode the same climatic information, and (2) assessing if it is preferable to obtain the sample of vessels along one or two radii. Four individuals of sessile oak (Quercus petraea (Mattuschka) Liebl.) and sweet chestnut (Castanea sativa Mill.) were harvested and all their earlywood vessel lumina were measured along two 40-mm wide radial strips. Measured vessels were selected stepwise while increasing the tangential width of the wood section from 1 to 40 mm, analyzing at each step (1) the common signal of chronologies and (2) the correlation to the main climatic variables controlling growth. Additionally, both radii in each tree were analyzed together and separately. The results showed that a total tangential width of 10 mm was enough to stabilize the climatic signal with improvement when distributed along two different radii, but a slightly larger tangential width was required to reach an optimal common signal. We suggest that, at least for the case of these two species growing at this specific climatic context, two 5-mm increment cores ensure a representative vessel selection.     

Climatic Signals in Tree Rings of Heritiera fomes Buch.-Ham. in the Sundarbans,Bangladesh

Mangroves occur along the coastlines throughout the tropics and sub-tropics, supporting a wide variety of resources and services. In order to understand the responses of future climate change on this ecosystem, we need to know how mangrove species have responded to climate changes in the recent past. This study aims at exploring the climatic influences on the radial growth of Heritiera fomes from a local to global scale. A total of 40 stem discs were collected at breast height position from two different zones with contrasting salinity in the Sundarbans, Bangladesh. All specimens showed distinct tree rings and most of the trees (70%) could be visually and statistically crossdated. Successful crossdating enabled the development of two zone-specific chronologies. The mean radial increment was significantly higher at low salinity (eastern) zone compared to higher salinity (western) zone. The two zone-specific chronologies synchronized significantly, allowing for the construction of a regional chronology. The annual and monsoon precipitation mainly influence the tree growth of H. fomes. The growth response to local precipitation is similar in both zones except June and November in the western zone, while the significant influence is lacking. The large-scale climatic drivers such as sea surface temperature (SST) of equatorial Pacific and Indian Ocean as well as the El Niño-Southern Oscillation (ENSO) revealed no teleconnection with tree growth. The tree rings of this species are thus an indicator for monsoon precipitation variations in Bangladesh. The wider distribution of this species from the South to South East Asian coast presents an outstanding opportunity for developing a large-scale tree-ring network of mangroves.     

西藏东部主要建群树种径向生长对极端干旱的响应差异

不同坡向、不同海拔树木生长对极端干旱事件的响应可能不同,然而这方面的认识不足。为此,选取西藏东部珠角拉山阴、阳坡的建群树种川西云杉 (Picea likiangensis var. rubescens) 和大果圆柏 (Juniperus tibetica),在不同海拔高度建立了树轮宽度年表,分析了径向生长的气候响应,以及对极端干旱事件的抵抗力和恢复力。结果表明:阳坡大果圆柏和阴坡川西云杉的树木生长对气候的响应存在相似性,均与前一年3-6月、11-12月气温显著正相关,与当年4-5月气温显著负相关,与当年4-5月降水和帕尔默干旱指数 (PDSI, Palmer Drought Severity Index) 显著正相关 (P <0.05)。阳坡大果圆柏的抵抗力显著低于阴坡川西云杉。随着海拔升高,阴坡川西云杉树木个体的抵抗力和恢复力均显著提高,而阳坡大果圆柏树木个体抵抗力、恢复力在不同海拔无显著区别。结合混合效应模型表明树木抵抗力主要受当年4-5月平均最高气温限制,树木恢复力主要受干旱事件后四年4-5月平均最高气温限制 (P <0.01),说明生长季高温引起的极端干旱是树木径向生长下降的主要原因。     

Tree regeneration responses in a lowland Nothofagus-dominated forest after bamboo dieback in South-Central Chile

The bamboo Chusquea quila (Poaceae:Bambuseae) is the most abundant understory species ofNothofagus-dominated forests at low elevations inthe Chilean Lake District. Species of this genus strongly inhibit theestablishment and growth of tree species, especially those of the genusNothofagus. At intervals of many years, this bambooflowerssynchronously and dies, creating large-scale disturbances. The mainobjective of this study was to determine the influence of bamboo dieback ontreeregeneration, especially of shade-intolerant species. The forest studiedis a remnant stand of old-growth forest dominated by emergent individualsof N. obliqua and Eucryphiacordifoliawhich project about 10 m above a main canopy formed byAextoxicon punctatum, Laureliaphilippiana, and Podocarpus saligna. Treeseedlings that established prior to bamboo dieback were recorded in six gapsdensely covered by bamboo. After the dieback event in the early 1990's,recruitment, height growth and survivorship were monitored in four gaps duringtwo growing seasons. After the synchronous mass flowering and death ofChusqueaquila, both reorganization of advance regeneration and new seedlingrecruitment were observed in gaps. The advance regeneration consisted mainly ofthe shade-tolerant species A. punctatum,L. philippiana, and Amomyrtus luma.These species together with E. cordifolia accounted forover 90% of the total individuals in gaps. During the following twoseasons, c. 40% of the advance regeneration either died or was damaged.Root suckers of E. cordifolia and L.philippiana were taller and grew faster than the seedlings of otherspecies. Nothofagus obliqua was unable to establishadvanceregeneration in gaps formerly dominated by bamboo. New recruitment resulted inthe synchronized establishment of treeseedlings, especially less shade-tolerant species such as N.obliqua, Aristotelia chilensis,Rhaphithamnus spinosus, and E.cordifolia. These species recruited into the gaps almost entirelyduring the first season right after the bamboo dieback. However, by the end ofthe second season, these species had a lower density due to a combination oflower recruitment rate, shortened recruitment period, and greater mortalityratecompared to the shade-tolerant species. New bamboo seedlings grew fasterand were more abundant than tree seedlings, except for root suckers (bothnew establishment and advance regeneration) of E.cordifolia which is more likely to successfully recruit into thecanopy. Seedlings of N. obliqua compete poorly with bambooseedlings; its successful recruitment may require bamboo flowering coincidentwith a mast seed year for the tree species.     

宝天曼自然保护区不同针叶树径向生长对气候的响应

树木年轮资料能够提供区域内过去长时间的环境和气候信息,成为获取过去气候变化信息的重要手段之一。利用采自宝天曼自然保护区的两种针叶树种油松和华山松树木年轮样本分别建立了油松和华山松树轮宽度标准年表PT和PA,并将油松和华山松样本合并建立了联合树种的区域年表(RC)。3种年表分别与不同气候要素(月平均气温、月平均最高气温、月平均最低气温、月降水量)及其不同月份组合进行相关分析,结果表明,油松年表PT和华山松年表PA都包含较高的气候信息,且都和生长季不同月份温度显著负相关和降水显著正相关。其中,油松和华山松都与当年4月和5月降水显著正相关,油松还与当年5月的平均最高温度和上年11月最低温显著负相关,与当年3月平均最低气温显著正相关;华山松与上年10月和当年4月的平均最高温度显著负相关,与上年12月和当年7月平均最低温度显著正相关;联合年表RC包含了单个年表PT和PA共同的气候信息,与当年4—5月降水和3月最低温显著正相关,与当年7月最低温和4、5月最高温显著负相关。不同年表与生长季(3—8月)内气候要素月份组合的相关分析也表明联合年表RC包含和单物种年表PT、PA相似的气候信息并加强了PT、PA受当年生长季气候变化影响的公共信号。可见,同一地区的多树种联合年表一定程度上能体现出区域性树木生长对气候变化响应的生态生理特征,为同地区建成多树种联合年表来探讨当地区域性气候变化提供了可行性的理论基础和一定的参考作用.     

Synthesis and establishment of <Emphasis Type="Italic">Tuber melanosporum</Emphasis> Vitt. ectomycorrhizae on two <Emphasis Type="Italic">Nothofagus</Emphasis> species in Chile

Axenically germinated seedlings of two species of Southern beech (Nothofagus obliqua, N. glauca) from Chile were inoculated with spores of the Périgord black truffle (Tuber melanosporum). Ectomycorrhizal development was monitored for 6 months in the greenhouse and compared to the performance of the natural host species Quercus ilex and Quercus robur. Seedling survival and mycorrhization showed major differences in both Nothofagus species: T. melanosporum readily formed ectomycorrhizae with seedlings of N. obliqua, although at a lower rate than with Q. ilex but at a proportion very similar to Q. robur; survival and colonization rates were high, and seedling growth was not visibly affected by the high soil pH required by T. melanosporum. In contrast, more than 50% of N. glauca seedlings died after inoculation, and mycorrhiza formation was very sparse. In both species, no colonization by adventive ectomycorrhizal fungi could be observed, whereas both species of Quercus showed minor colonization by another fungus, probably Inocybe or Hebeloma. Our results show that it is possible to infect N. obliqua with the Périgord black truffle under greenhouse conditions, which opens up the possibility of cultivating this truffle as a secondary crop during reforestation with N. obliqua in Chile.     

Patterns of phytophagous insect herbivory and abundance on juvenile regrowth of Eucalyptus subgenera coexisting in southeastern Tasmania

Abstract Eucalypts from the subgenus Monocalyptus tend to be more abundant and dominate species from the subgenus Symphyomyrtus where they occur together in the mixed species stands of southeastern Australia. The differential impacts of herbivory by phytophagous insects has been postulated as a causal mechanism in the creation and maintenance of such stands. This research aimed to quantify phytophagous insect abundance and herbivory in mixed species juvenile regrowth of Eucalyptus globulus, E. viminalis (Symphyomyrtus), E. obliqua and E. pulchella (Monocalyptus} southwest of Hobart, Tasmania. Monocalyptus experienced a higher level of herbivory than Symphyomyrtus. However, mean damage levels were relatively low at less than 11% throughout. Furthermore, due to the positively skewed nature of herbivory data the mean was an inappropriate measure of central tendency; median damage levels ranged from 4.9% to 8.4%. Patterns of herbivory tended to be different for each eucalypt species: E. obliqua was particularly prone to chewing damage, E. pulchella and E. globulus suffered higher levels of distortion while E. viminalis was least affected by insect attack. Even though some trends in insect community structure seemed apparent at the level of eucalypt subgenus, closer examination revealed patterns of abundance were characteristic of each Eucalyptus species. The composition of foliar damage corresponded with the prominence of particular insect groups. Sucking insects tended to dominate the fauna except on E. obliqua where chewing insects in general, and chrysomelids in particular, were most prevalent. Both the distribution and magnitude of herbivory suggested that phytophagous insects had a negligible effect on competition between coexisting juvenile eucalypts and were unlikely to be responsible for the dominance of Monocalyptus or the maintenance of mixed species stands.     

The effect of high pH and P on the development of lime-chlorosis in two seedling populations ofEucalyptus obliqua L'Hérit

Summary Glasshouse experiments have shown that the application of an acidulating agent to a calcareous soil can increase growth and alleviate severe chlorosis in an acidic population ofE. obliqua. In contrast, a calcareous population showed only a slight response to this treatment and maintained adequate growth and a low frequency of chlorosis on both control and treated calcareous soils. Foliar analyses of seedlings of the acidic population showed that alleviation of chlorosis was concomitant with a reduction in the levels of P, Ca and K, and an increase in uptake of Fe. However, the total Fe content of foliage was poorly correlated with the occurrence of severe chlorosis. Although this evidence suggested that the differential susceptibility ofE. obliqua to lime-chlorosis can be reduced by increasing the availability of Fe, the greater concentration of Fe in chlorotic seedlings indicated that lime-chlorosis may also be due to an inactivation of Fe within the plant (i.e. by P). This hypothesis was partly confirmed by a water culture experiment which showed that a combination of relatively high pH and high external levels of P could induce severe chlorosis in seedlings of the acidic population. In contrast, it appears that the calcareous population has a more efficient mechanism for absorbing Fe and holding it in an available form, even when external concentrations of P are high. It is suggested that plants which have an efficient mechanism for the uptake of Fe at relatively high pH and are less susceptible to the detrimental effects of P have been selected for on these alkaline calcareous soils.