False Rings Research Articles

Wood anatomy and growth ring boundaries of Copaifera lucens (Fabaceae)

ABSTRACT The wood anatomy of Copaifera lucens Dwyer was studied with an emphasis on its growth ring boundaries. Growth rings are visible to the naked eye and demarcated by marginal parenchyma bands and, sometimes, by thick-walled fibers in the latewood. Secretory canals are associated with marginal parenchyma bands, but not all marginal parenchyma bands are associated with canals. Paratracheal parenchyma is vasicentric to lozenge-aliform. Rays are 1–4-seriate, heterocellular and non-storied. Vessels are visible to the naked eye, diffuse, predominantly solitary, some in multiples, sometimes filled with gums. Crystals present. Wood anatomical characteristics of C. lucens are in agreement with those previously reported for other species of Copaifera. In addition to what had already been described for C. lucens, we observed gelatinous fibers, and some bifurcate fibers, and extremely rare clustered vessels. The growth ring boundaries are well-defined in mature wood but less distinctive near the pith. There are also partial and confluent (wedging) rings, which are difficult to classify by anatomy only, but which represent false rings and complicate tree-ring analysis in this species.

Respuesta del crecimiento de Pinus oocarpa Schiede a variables climáticas en el noroeste de Lagunas de Montebello, Chiapas, México

Dendrochronological studies are used to reconstruct some climatic variables; in México these studies have focused on central and northern temperate forests where trees present well defined annual rings. Few studies have been carried out in the southern part of the country where annual ring growth is not easily identified and thus makes cross-dating problematic. We analyzed the dendrochronological potential of Pinus oocarpa Schiede for reconstructing climatic variables in the northwest portion of Lagunas de Montebello, Chiapas. We used a selective sampling approach and collected 65 increment cores from 34 trees. While our samples showed a high frequency of false rings (8 to 60 %), we were able to date 30 samples from 22 trees (46 %) using standard dendrochronological techniques and developed total chronologies for total ring width, earlywood, and latewood for a period of 91 years (1925-2015). We found a significant influence of mean precipitation and mean maximum and minimum temperature over the annual ring growth of P. oocarpa in the period 1961-2004. Our results show that winter-spring precipitation (January-May) was the most important for the species’ annual ring growth. However, we found the highest correlation between spring (March-May) precipitation and the earlywood chronology (r = 0.719, P < 0.05). The earlywood chronology also showed potential for reconstructing minimum temperatures (March to May) (r = 0.732, P < 0.05), while the latewood chronology had the potential for reconstructing the maximum temperature (September to January) (r = 0.714, P < 0.05). These results showed that P. oocarpa can be used to reconstruct climatic variables in the Mexican tropics. We recommend that new areas with older trees should be explored in order to increase the depth of chronologies and reconstruct climate records several centuries into the past.

RADIAL GROWTH DYNAMICS OF Khaya ivorensis TREES FROM EXPERIMENTAL PLANTATION

ABSTRACT The objective of this study was to characterize the formation of growth rings in Khaya ivorensis wood, as well as to analyze the variation in the morphology of the vessel elements, aiming to understand the growth of this species in experimental plantations. Disks from the bases of five trees were collected, and after polishing the cross-section, demarcation of the growth rings limits was carried out. The anatomical study of the wood was conducted with the purpose of characterizing the rings, and their width was measured by means of scanned images of the disks. A historical series of data was obtained concerning the diameter of the trees to establish a correlation with the width of the rings measured over the years. The growth rings limits of African mahogany wood are demarcated by a thin layer of marginal parenchyma, and the presence of false rings has been observed. Significant annual growth correlation of 0.62 was observed among the trees, being the radial increment of irregular wood in the first years (wide and narrow rings), and highlighting the 3rd and 11th year of growth in which the largest increases were observed due to a biological adaptation tendency to the environment and the occurrence of thinning carried out in the planting area, respectively.

Developing a Carbon Isotope Chronology for a Coastal Subtropical Tree Species with Variable Subannual Tree-Ring Growth

ABSTRACT Rebenack, C.E.; Cherubini, P., and Anderson, W.T., 2018. Developing a carbon isotope chronology for a coastal subtropical tree species with variable subannual tree-ring growth. Stable carbon isotopes in tree rings are proposed to be used to build a chronology for coastal Pinus elliottii Engelm. var. densa growing along a hydrological gradient in the subtropical Lower Florida Keys. Pinus elliottii var. densa exhibits distinct growth rings; however, cross-dating is difficult because of inconsistent ring growth and the presence of frequent intra-annual density fluctuations (IADFs), or false rings. The δ13C values of earlywood and latewood were used to both identify IADFs and cross-date the trees to build a site chronology (1922–2006). The formation of the IADFs is likely related to moisture availability and the age of the tree, and the presence of IADFs varied among individual trees. A traditionally derived ring-width chronology was compared and contrasted with one developed from the δ13C values of ...

Condition, protection and maintenance of age-old pedunculate oak trees in Feofania forest

Large old trees are significant elements of forests, arboretums, botanical gardens and parks and perform a number of unique functions contributing to ecosystem integrity and biodiversity. At the same time human activities such as compaction of topsoil layers, deterioration of soil permeability and soil aeration drive the decline of large old trees. The human impact is also exacerbated by plants inevitable physiological age-specific changes. The presence of such old trees in urban environments brings great scientific promises enhancing a social, cultural and historical forest value, although these benefits increase responsibility for trees maintaining. Regarding old-growth trees historical, cultural, and environmental significance and their overall vulnerability, the individual-by-individual tree protection measures are required. Pedunculate oak (Quercus robur L.) is among the most widespread long-lived species in Europe, in particular in Ukraine. In Feofania (or Theophania) forest, that is an oak-hornbeam forest located in southern part in Kyiv, the age of the oldest oak trees reaches about 300 years. In this article, we aim to estimate vitality, overall condition, and recreational digression stages of pedunculate oak trees and to develop the recommendations to maintain and extend trees longevity in Feofania forest. We estimate the stages of recreational digression and vitality using an approach of Hensiruk et al. (1987) and Sanitary Regulations in forests of Ukraine (1995) respectively. The dendrochronological analysis is performed on core samples from sixteen age-old pedunculate oaks in order to determine their exact cambial age and to evaluate their growth rates. We use at least two cores per tree extracted at a height from 0.5 m to 1.3 m above ground level with an increment borer. The tree-ring widths are measured using AxioVision (Carl Zeiss) software to the nearest 0.01 mm. To identify false rings we employ stereomicroscope MBS-1. The individual tree-ring series are cross-dated, standardized and checked using the COFECHA program. Then we determine exact cambial age of oak trees as number of tree-rings in individual series. To estimate the age of trees with cores without pith we use a graphical method. The analyze is performed on 42 increment cores containing 7335 annual rings formed in the period from 1746 to 2016. Measured diameter of the age-old oaks ranges from 57.6 cm to 165.2 cm. The longest chronological series contains 271 years. The age of studied trees varies from 202 to 275 years averaging 175 years and radial growth ranges from 1.07±0.400 mm to 2.85±1.487 mm averaging 1.95±0.792 mm. In recent years the reduction of radial growth isn’t observed, although in a long time interval in five studied trees the rings width not exceeds the individual series average value. However, the growth rate reducing could not be regarded as critical for trees vitality because it is above 10 % of the average value yet. The evaluated mean increment coefficient is 5.13±1.482 years in cm that allows to estimate the age of dominant and codominant oaks in the association of Galeobdoloni luteae-Carpinetum in other forests. The estimated vitality is mostly of 6–7 points. Five oaks are in «satisfactory condition», nine oaks are «weakened», one oak is «very weakened» and one tree is «dying». «Weakened» trees are with mechanically damaged stem and are often suffered from leaves defoliation caused by Acrocercops brongniardella and Microsphaera alphitoides. Regarding wood samples maintenance, the «dying» oak stem is found rotted in its center. The recreational digression is at the stage 1–4. For eight oaks it is at the first stage, for four oaks at the second stage, for two oaks at the third stage and for two oaks at the fourth stage with 60 % destruction of the understorey. The number of age-old Q. robur trees is limited, thus measures to care could consider individual tree-specific features. Given trees vitality and stages of recreational digression, we develop the guidelines to preserve and extend trees longevity. We also propose to include four old-growth oaks in the list of monumental plants.

A new method for dating tree-rings in trees with faint, indeterminate ring boundaries using the Itrax core scanner

Eastern Australia is known to experience multi-decadal periods of flood and drought. Subtropical Southeast Queensland is one region where these devastating extreme events occur regularly yet a full understanding of their frequency and magnitude cannot be determined from the short duration (<100 years) climate data available for the region. Tree-rings are a potential source of long-term (>100 years) proxy rainfall information but locating suitable forest stands is difficult due to extensive land clearing by European settlers. Another factor deterring the use of trees as proxy data sources is that longer-lived species frequently contain anomalous rings, particularly faint rings, hindering their use for paleoclimate study. Here we present a method which overcomes the problems of identifying faint ring boundaries in trees by using X-radiographs and density patterns developed on the Itrax core scanner. We analysed 39 tree cores from 20 trees at a site in D'Aguilar National Park located just north of Brisbane city in Queensland, Australia. Each core had a 2 mm lath cut perpendicular to its rings which was then passed through an Itrax core scanner. The tree-ring boundaries were identified on the image by both the visual features in the radiograph and the change in density observed between rings. From this information we developed a tree-ring chronology. The chronology was checked using bomb-pulse radiocarbon dating on five trees to confirm the annual nature of the rings, and to correct dating errors in the chronology due to false rings which are common in this species. Climate response function analysis showed Austral annual rainfall (June–May) was the dominant environmental variable driving tree growth. Finally, a 69-year statistically significant reconstruction of Brisbane precipitation was produced showing that this non-destructive Itrax ring identification technique together with age validation by bomb-pulse radiocarbon dating is useful for dendroclimatological studies of trees with faint ring boundaries.

Moisture-driven xylogenesis in Pinus ponderosa from a Mojave Desert mountain reveals high phenological plasticity.

Future seasonal dynamics of wood formation in hyperarid environments are still unclear. Although temperature-driven extension of the growing season and increased forest productivity are expected for boreal and temperate biomes under global warming, a similar trend remains questionable in water-limited regions. We monitored cambial activity in a montane stand of ponderosa pine (Pinus ponderosa) from the Mojave Desert for 2 consecutive years (2015-2016) showing opposite-sign anomalies between warm- and cold-season precipitation. After the wet winter/spring of 2016, xylogenesis started 2months earlier compared to 2015, characterized by abundant monsoonal (July-August) rainfall and hyperarid spring. Tree size did not influence the onset and ending of wood formation, highlighting a predominant climatic control over xylem phenological processes. Moisture conditions in the previous month, in particular soil water content and dew point, were the main drivers of cambial phenology. Latewood formation started roughly at the same time in both years; however, monsoonal precipitation triggered the formation of more false rings and density fluctuations in 2015. Because of uncertainties in future precipitation patterns simulated by global change models for the Southwestern United States, the dependency of P.ponderosa on seasonal moisture implies a greater conservation challenge than for species that respond mostly to temperature conditions.

Tree-Ring Research of Mexican Beech (Fagus GrandifoliaSubsp.Mexicana) A Relict Tree Endemic to Eastern Mexico

Mexican beech (Fagus grandifolia subsp. mexicana) has been classified as an endangered species because of its restricted distribution. The current distribution of Mexican beech, which is considered a Miocene relict, is limited to Tropical Montane Cloud Forests (TMCF) in the mountains of the Sierra Madre Oriental in eastern Mexico. We used dendroclimatic techniques to evaluate the effects of climate variability on the growth of Mexican beech within three forest fragments. The independent chronologies developed for the three sites were 152–178 years long. Cross-sections helped to assess the quality of the crossdating and detect false rings. Over the last 180 years, Mexican beech trees have lower mean radial growth than rates exhibited by other Fagus species. Mexican beech growth appears to be influenced by growing-season temperatures, especially mean maximum temperature. The response appears to be positive at the beginning of the growing season but becomes negative later. These results suggest that the persistence of Fagus-dominated forests in Mexico is dependent on local-scale climatic conditions of the TMCF. Mexican beech forests are associated with micro-climatic conditions that will control the fate of these forests in the face of on-going climate change.

False Ring Formation in Bald Cypress (Taxodium distichum)

False rings are intra-annual bands of high density xylem cells that form in response to an environmental condition that a causes a tree to form two bands of latewood cells during a single growing season. We examined whether precipitation and/or stream flow measurements coincided with false ring formation in adult bald cypress trees (Taxodium distichum (L.) Rich.). We collected increment cores from bald cypress growing along the Blackwater and Nottoway Rivers in Virginia, U.S.A. The frequency and timing of false rings was quantified for each core. Annual synchronicity of false ring formation occurred, indicating a common environmental trigger. At both sites, false ring formation in bald cypress appeared to be more common during years with late summer precipitation and associated high late summer stream flow. In years when moisture is available late in the growing season, dormant bald cypress trees resume earlywood formation and a false ring is formed. Therefore, false rings in bald cypress wood can serve as a proxy record of seasonal historical stream flow and precipitation.

Ductoagathoxylon jimsarensis gen. nov. et sp. nov., a gymnospermous stem from the Wuchiapingian (upper Permian) Wutonggou Formation in the Junggar Basin, northern Bogda Mountains, northwestern China

A silicified stem, Ductoagathoxylon jimsarensis Wan, Yang, Liu et Wang gen. nov. et sp. nov., is described from the Wuchiapingian (late Permian) Wutonggou Formation from the Dalongkou section, Jimsar County, Xinjiang Uygur Autonomous Region, northwestern China. It is composed of a pith, and primary and secondary xylem. The stem is characterized by a solid, heterocelluar pith with grouped secretory ducts and cells, an end- to mesarch primary xylem, and an Agathoxylon-type secondary xylem. Based on the Agathoxylon-type secondary xylem and the occurrence of secretory ducts and cells in the pith, it is suggested that Ductoagathoxylon is of a coniferous affinity. It provides additional evidence for the biodiversity of the Wuchiapingian Subangaran flora in northwestern China. Growth rings and false rings in D. jimsarensis and other previously reported fossil woods from the Wutonggou Formation in the Junggar Basin indicate both seasonal and intra-seasonal growth variations caused by environmental stress and precipitation seasonality. The fossil stem records suggest varying climatic and environmental conditions between the Dalongkou section in the northern Bogda Mountains and the Tarlong-Taodonggou sections, about 70km to the south, in the southern Bogda Mountains during the Wuchiapingian.

Scots pine tree ring structure modifications and relation with climate

In this study we assessed the tree ring structure modifications and the relation with climate in Scots pine from Aleșd region (Romania). Tree rings structures were analysed based on microscopic sections obtained from the core sample. The analysis on the area of the incomplete lignified cells (IC) and the lignified cells (CL) was made. The results show a high frequency of false rings, and unlignified cells. The tree ring with the highest unlignified cells part could be observed in the years 2007 and 1989. A reduced number of the unlignified cells were formed in the year 1998. An anomaly was analyzed in the tree ring structure of the year 1986. The temperature below 10 °C in the second period of the growing season has stopped the process of lignification of the wood cell walls. This study confirms the influence of temperature on the formation of the Scots pine tree rings. Key words: Scots pine, anatomical structure, radial growth, tree rings, temperature.

Climate effect on tree-ring widths of Fagus orientalis in the Caspian forests, northern Iran

ABSTRACTThis study aims at understanding the impacts of climate factors on the annual growth variations of oriental beech (Fagus orientalis Lipsky) at the Kheyrud Forest Research Station located in the Caspian forests of northern Iran. To this end, 18 disc samples were randomly taken from altitudes of 1038 to 1152 m above sea level. Tree rings were measured using TSAP-win software and a LINTABII machine. Since false and missing rings are typical in beech trees, skeleton plots were created to enhance crossdating accuracy. Chronologies were observed for a total of 15 samples. Meteorological data for rainfall and air temperature were recorded at the Nowshahr Meteorological Station, located near the study sites. Results showed a significant correlation between mean annual air temperature and radial growth (R = 0.54). Within the growing season, August temperatures reveal a significant correlation with tree ring (R = 0.41) while the highest association was observed in the previous December (R = 0.44) and the least association was found in February (R = 0.31). Excluding March (R = 0.33), there appeared to be no significant correlation between precipitation accumulated during and prior to the growing season and tree ring. In addition to oriental beech, there are many other species important to this region that may be sensitive to increasing temperatures.

Climatic fluctuations trigger false ring occurrence and radial-growth variation in teak (Tectona grandis L.f.)

The objective of this study was to examine the interaction of extreme growth years in teak (Tectona grandis) with climatic conditions of current, antecedent and subsequent years, in order to explain the nature and the effects of climatic variability on teak growth in northeastern Thailand. A 33-year tree-ring index was constructed and extreme growth years during the period 1976-2008 were identified. A superposed epoch analysis (SEA) was used to study the interaction of climatic data and extreme growth years. Extreme growth years were derived from eight wider and seven narrower annual rings identified using the Cropper’s method. Seventeen false rings were detected using the threshold value ≥ 80% of false ring occurrence for all samples in each growth year. False ring occurrence was associated with narrow ring width formation and triggered by increasing maximum and mean temperatures at the beginning of the rainy season (May to August). In the third year after false ring formation, we observed a pattern of wet year occurrence when annual rainfall and relative humidity in September to December were higher than in adjacent years. Moreover, in the sixth year before false ring formation, a wet year was observed when relative humidity in September to December was higher than in adjacent years. Wider ring width index occurring in a particular year was found to be triggered by a decrease in maximum and mean temperatures in May to August of the current year, suggesting that wet years promote teak growth. The third year after the formation of wider rings was characterized by a low annual rainfall. Our results showed that drought years trigger false ring and narrow ring formation, while wet years trigger wide ring formation in teak. A cycle of wet years between the sixth year prior to, and the third year after, the formation of false rings was also observed, as well as the occurrence of drought in the third year since the formation of wide rings. False ring, narrow ring and wide ring occurrences appear to be good indicators of a 3-6 year climate fluctuation pattern, similar to that of the El Niño-Southern Oscillation (ENSO) cycle in this region.

Influence of regional rainfall and Atlantic sea surface temperature on tree-ring growth of Poincianella pyramidalis, semiarid forest from Brazil

A tree-ring width chronology was developed from samples of thirteen Poincianella pyramidalis trees from the Caatinga semiarid region of northeastern Brazil, where the climate is characterized by marked seasonality in precipitation levels. Although a thin continuous marginal parenchyma band represents the limit of seasonal xylem production, and in spite of the presence of false rings, cross-dating is possible. In this sense, an interseries correlation of 0.572 was found indicating a considerable degree of consistency in the variability found among trees. Precipitation between January and July has a direct influence on growth, while a five month dry season interrupts the active division of cambial cells. A significant positive correlation was also found between sea surface temperatures (SSTs) in the tropical Atlantic and tree growth, but with a lag of six months. As the rainfall regime of northeastern Brazil presents a great deal of inter-annual variability due to fluctuations in global factors such as the SSTs of the tropical Atlantic and the intertropical convergence zone, the close relationship observed between P. pyramidalis tree growth and regional climate fluctuations appears as a logical plant-environment interaction that can be used as a reliable parameter for dendroecological inferences on tree growth dynamics and the reconstructions of past droughts in the Caatinga region.

Comparison of Two Approaches for Determining Fire Dates From Tree Scars

Knowledge regarding the historic role of fire in forest ecosystems is often derived by dating fire scars. Fire history studies in boreal and western coniferous forests have used either complete or partial cross sections cut from fire-scarred trees. The occurrence of missing or false rings presents an obstacle to the accurate dating of individual fires. Two different techniques of dating partial cross sections of fire-scarred ponderosa pine (Pinus ponderosa Laws) were compared using the same samples. Method I involves the tabulation of raw dates followed by a subsequent adjustment based on synchronization with fire dates from adjacent trees. Method II uses correlations with master chronologies based on analysis of increment cores taken in the same region as the sampled fire scar sections. Method I is prone to error since the assumption that fire dates differing by a few years may actually be from the same year cannot be independently verified. Method II provides a higher degree of certainty with regard to the accuracy of individual dates because the cross dating of local patterns of ring widths circumvents the problem of absent or false rings. Eight samples from the Horse Pasture Plateau in Zion National Park, Utah, were dated by both methods. Agreement on dates derived by the two methods for 39 separate fire years was limited to only 26 percent. The average error of Method I was 1.0 year. Fire history studies using Method I are accurate enough for most managerial recommendations and some ecological interpretations, but they may lack the precision necessary to correctly identify fire years or differentiate small changes in fire frequency. The dendrochronological approach of Method II is preferable because of its greater reliability, especially in ecosystems where short fire intervals are common or where fires occur in consecutive years. FORESX SCI. 28:856861. ADDITIONAL

Automated quantification of intra-annual density fluctuations using microdensity profiles of mature Pinus taeda in a replicated irrigation experiment

Key message We developed a new automated method to use wood microdensity profiles to detect and quantify intra-annual wood density fluctuations in earlywood of pine trees. Abstract We developed a new, automated method to use X-ray wood microdensity profiles to detect and quantify intra-annual density fluctuations within the earlywood region (IADFe) of each annual growth ring. The method quantifies the number and area of IADFe by detecting variations in wood density beyond the limits of ''normal'' values observed during periods without environmental stress. As a case study, we examined the effect of water availability and water stress associated with the formation of IADFe in irrigated and non-irrigated 11-year-old lob- lolly pine trees. As expected, non-irrigated trees formed significantly more IADFe than irrigated trees. Strong relationships were observed between IADFe formation (as a proportion of total earlywood area or as the number of IADFe formed each year) and the minimum monthly Pal- mer Drought Severity Index for the earlywood growing season (February to July). When compared against visual detection, the number of IADFe detected optically was significantly fewer than the number detected with densitometry. This difference likely comes from the higher resolution and more objective criteria that confidently detected and counted more very small IADFe than was possible optically at 109 magnification. The method to detect and quantify IADFe described in this study can allow climate analysis in long-lived species prone to pro- ducing intra-annual growth zones and false rings.

Kinetics of tracheid development explain conifer tree-ring structure.

Conifer tree rings are generally composed of large, thin-walled cells of light earlywood followed by narrow, thick-walled cells of dense latewood. Yet, how wood formation processes and the associated kinetics create this typical pattern remains poorly understood. We monitored tree-ring formation weekly over 3yr in 45 trees of three conifer species in France. Data were used to model cell development kinetics, and to attribute the relative importance of the duration and rate of cell enlargement and cell wall deposition on tree-ring structure. Cell enlargement duration contributed to 75% of changes in cell diameter along the tree rings. Remarkably, the amount of wall material per cell was quite constant along the rings. Consequently, and in contrast with widespread belief, changes in cell wall thickness were not principally attributed to the duration and rate of wall deposition (33%), but rather to the changes in cell size (67%). Cell enlargement duration, as the main driver of cell size and wall thickness, contributed to 56% of wood density variation along the rings. This mechanistic framework now forms the basis for unraveling how environmental stresses trigger deviations (e.g. false rings) from the normal tree-ring structure.

Growth Rate and Climatic Response ofMachaerium scleroxylonIn a Dry Tropical Forest In Southeastern Santa Cruz, Bolivia

Machaerium scleroxylon (morado) is an important timber species from the lowland tropical dry forests in Bolivia. We followed a dendrochronological approach to (i) evaluate the responses of radial growth to climatic variables and atmospheric circulation patterns, and (ii) quantify the growth rate in order to estimate the Minimum Logging Diameter (MLD), age, and optimal cutting rotation. We measured tree-ring width in wood discs taken from ten randomly selected mature individuals. We used previous histological analyses to distinguish and visually crossdate tree rings. Despite the existence of false rings, lenses and wedging rings, the species showed defined annual ring boundaries, thus enabling a tree-ring chronology analysis. Correlations between residual ring-width indices and monthly climatic variables (temperature and rainfall) and atmospheric circulation patterns (El Niño-Southern Oscillation) index were calculated. Growth showed a significant positive correlation with monthly rainfall and a negative correlation with mean temperature during the late rainy season (i.e. from December up to March). A positive correlation found between the ring width and ENSO indices indicates that the growth of M. scleroxylon was significantly affected by atmospheric circulation patterns. Growth rate is slow in morado, suggesting a MLD of 50 cm and an optimal cutting cycle longer than 40 years depending on each site.

Determining the annual periodicity of growth rings in seven tree species of a tropical moist forest in Santa Cruz, Bolivia

To determine the annual periodicity of growth rings in seven tree species from a tropical moist forest in Santa Cruz, Bolivia, a fire scar was used as a marker point to verify the annual nature of tree rings. The number of tree rings formed between the 1995 fire scar and the collection of the cross sections in 2002 was visually identified. The seven species showed annual growth rings. In most cases, boundaries between rings were marked by the presence of marginal parenchyma and wall-thicked fibers formed at the end of the growing season. Growth lenses and false rings were recorded in some species. Tree rings can be carefully used in Santa Cruz forests to determine rates of growth. This information is crucial for defining forest management practices in tropical regions.

False Ring Formation in Eastern Hemlock Branches: Impacts of Hemlock Woolly Adelgid and Elongate Hemlock Scale

Herbivores can alter plant physiology through the induction of abnormal wood formation. Feeding by some insects induces the formation of false rings, a band of thick-walled latewood cells within the earlywood portion of the tree ring that reduces water transport. Hemlock woolly adelgid (Adelges tsugae Annand) and elongate hemlock scale (Fiorinia externa Ferris) are invasive insects that both feed on eastern hemlock [Tsuga canadensis (L.) Carrière]. Adelges tsugae has a greater effect on tree health than F. externa, but the mechanism underlying their differential effect is unknown. We explored the effects of these herbivores by assessing growth ring formation in branches of trees that had been experimentally infested for 4 yr with A. tsugae, F. externa, or neither insect. We measured false ring density, ring growth, and earlywood: latewood ratios in the two most recently deposited growth rings. Branches from A. tsugae-infested trees had 30% more false rings than branches from F. externa-infested trees and 50% more than branches from uninfested trees. In contrast, branches from F. externa-infested trees and control trees did not differ in false ring formation. Radial growth and earlywood: latewood ratios did not differ among treatments. Our results show that two invasive herbivores with piercing-sucking mouth parts have differing effects on false ring formation in eastern hemlock. These false rings may be the product of a systemic plant hypersensitive response to feeding by A. tsugae on hemlock stems. If false rings are responsible for or symptomatic of hemlock water stress, this may provide a potential explanation for the relatively large effect of A. tsugae infestations on tree health.