Dendrochronological assessment of chestnut (Castanea sativa Mill.) for dating purposes in Central Italy

Chestnut is the most common species used for building construction in Central Italy, but the built chronologies are still floating. This is due to a lack of long master chronologies built for chestnut in these regions and because of the lack of agreement with the very few up to date chestnut curves published for other areas. Chestnut appears to be a suitable species for performing dendrochronological analysis because it forms annual rings, and is a ring-porous species. Nevertheless it shows a very fast growth rate, which results in the presence of only a low number of annual rings even in large beams. To further the understanding of the dendrochronological characteristics that are important for dating purposes, this paper discusses an investigation based an a dendrochronological assessment of living chestnut trees.

In total 89 trees from five stands were sampled in Central Italy. The analysis was performed by testing the quality of single master chronologies and comparing the dendrochronological behaviour of trees of the same stand, the crossdating of chestnut chronologies of different provenances, and the interspecific synchronization with oak, beech and silver fir. These trees are the most widespread species in Central Italy and for which reference chronologies have been recently developed - useful for dating purposes. Chestnut chronologies show rather mean sensitivity values. The mean values of synchronization, according to the mean Gleichläufigkeit (GLK) value, mean correlation value (RBT) and expressed population signal (EPS), among the single curves of the same site are not high. Nevertheless, the number of pointer intervals calculated in the site chronologies can be considered rather high in some periods, and the coincidence of maximum and minimum ring width allows the individual curves to be fitted into the mean site chronology. The results of intraspecific synchronization among chestnut site chronologies are not encouraging. Nevertheless, the degree of visual matching among the chronologies play an important role. The best interspecific synchronization was obtained with oak. No notable correlation was found with beech and silver fir.     

Oak chronology development in the Czech Republic and its teleconnection on a European scale

A prerequisite for successful dating of wooden archaeological finds and historic wooden constructions in a specific territory is the existence of a chronology. In the Czech Republic the species most frequently dated by dendrochronology is oak (Quercus spp.). There are two territories where oak forests can be found (Bohemia and Moravia/Silesia), which are divided by an area without oak – the Highlands (Vyso?ina). The previous oak chronology for the Czech Republic from 2005 was extended in 2010, and currently we have a discontinuous oak chronology (CZGES 2010) ranging from 4682 bc to 2006 ad with a large sample size between 760 ad and the present. When comparing this chronology with European chronologies, the highest degree of similarity has been observed with chronologies for Eastern Austria, most of Germany and the Polish part of South Silesia. When comparing the chronologies for Moravia/Silesia (MORGES 2010) and Bohemia (CECHGES 2010) separately with chronologies from the Pannonian Basin, the Moravian/Silesian chronology manifests higher degrees of similarity. The Czech oak chronology enlarges the European network of chronologies, which is necessary for dendroarchaeological applications mainly.     

Subfossil oaks from riverine sediments of the Seda River in Latvia: The first results of dendrochronological and radiocarbon analysis

The article presents a dendrochronological investigation of subfossil oaks from the riverine sediments of the Seda River in the Lake Burtnieki Undulating Plain, northern Latvia. Thirty-nine oak trunks were investigated for our study. Cross-dating of samples resulted in six floating chronologies spanning 141–636 years. The longest chronology was absolutely dated to AD 652–1287 against regional oak chronologies from Lithuania, Latvia, Belarus and central European Russia. ¹⁴C dating revealed that oaks grew on the site from the last century of the third millennium cal BC to the first half of the second millennium cal AD. We assessed the depositional anomalies from two best-replicated chronologies. The germination of oaks occurred during climate warming, and dying-off phases were triggered by climate cooling and increased precipitation throughout Europe. Our results give new insights into the forest history in northern Latvia and provide a potential to construct absolute-dated millennial oak chronologies in the Baltic countries.     

Dendrochronological dating of Rebel’s Rest (40FR512), Franklin County,Tennessee, USA

The structure named Rebel’s Rest was a two-story, Reconstruction-era house located on the campus of the University of the South in Sewanee, Tennessee, before being severely damaged by fire in July 2014. The house was constructed of squared timbers and round logs, with later additions built using sawn lumber. Dendrochronological analyses of timbers and logs salvaged from the house reveals wood from four genera: oak (Quercus spp.), tulip poplar (Liriodendron tulipifera L.), American chestnut (Castanea dentata [Marshall] Borkh.), and pine (Pinus spp.). We statistically and graphically crossdated a total of 251 samples (24,410 rings) with regional chronologies from the ITRDB, resulting in three dated chronologies comprised of oak (1645–1874), tulip poplar (1725–1865), and American chestnut (1710–1864). The majority of samples with cutting dates (95.6%) ended in years 1865–1866, confirming the historically reported construction date of 1866 for the initial structure. The cutting date analysis also confirms two rooms as later additions, Room M (1867) and Room B (1875). Based on ring count and the number of chronologies produced, this research represents the largest known dataset from a single historic structure in the Southeastern US.     

Dendrochronological evidence of cockchafer (Melolontha sp.) outbreaks in subfossil tree-trunks from Tovačov (CZ Moravia)

In dendrochronological dating, we encounter the trouble that some samples cannot be dated due to the occurrence of anomalies in the tree-ring series. When dating subfossil wood for the extension of existing master chronologies, this may be an especially unwanted circumstance as subfossil wood is scarce and each sample is valuable. In Moravia (Czech Republic) outbreaks of the cockchafer (Melolontha sp.) used to appear with a disastrous effect on agricultural crops, and, for a dendrochronologist, on samples of wood to be dated. Oak ring width reduction caused by cockchafer induced defoliation can superimpose climate induced growth variations and may complicate dating of historical or subfossil samples. For this study, 33 samples of sub-fossil trunks were assessed; 19 of which were attacked by cockchafer. For comparison, we analysed a total of nine living oak trees from the forest district Strá?nice-Vracov, recently attacked by the cockchafer. Occurrence of the cockchafer was reported there in 1999, 2003 and 2007.We found clear growth patterns with cyclic narrow rings every 4 years. This allowed us to create an artificial curve expressing the recurring cycles of cockchafer outbreaks which assisted us in the detection of the same pattern in subfossil tree growth. The tree-ring series of the attacked living oak stand as well as the 19 individual tree-ring series from subfossil oak trunks could not be dated using standard chronologies and showed a high resemblance to the cockchafer life cycle. Additionally, we found out that the living oak stand was attacked in 1983, 1987, 1991 and 1995 as well. The results support the hypothesis that the periodical reduction observed in tree-rings at regular increments is caused by cockchafer infestation. This evidence is further supported by characteristic anatomical features in early wood. A mean tree-ring series was created from the individual tree-ring series of subfossil oaks even though radiocarbon dating showed completely different ages of samples. This means that the affected tree-ring series cannot be used for dendrochronological dating and dendroclimatological analyses. These series cannot be used without preceding mathematical and statistical modification.     

Castle Pišece,Slovenia – Building history and wood economy revealed by dendrochronology,dendroprovenancing and historical sources

Castle Pišece, located in SE Slovenia near the border with Croatia, is thought to have been built in the 12th/13th century as one in the line of Salzburg fortresses on the then SE border of the Holy Roman Empire. During thorough restoration that started in 2005, its wooden constructions became accessible for dendrochronological investigations. We collected representative samples from floor or ceiling constructions in most of the rooms in the castle. Dendrochronology helped us to identify felling dates of wood and to propose probable years of reconstructions in 1515, 1578, 1644, 1697, 1752, 1758, 1775 and 1878. The dating showed that the constructions in the presumed Romanesque and Renaissance parts of the building were not as old as expected, whereas those in the supposedly Baroque part of the castle were older than assumed. The selection of wood species used for constructions varied over time. Constructions with end dates 1515–1697 were made of oak (Quercus petraea and Q. robur), those dated to 1752 of silver fir (Abies alba), those dated to 1758 of sweet chestnut (Castanea sativa) and those dated to 1878 of common beech (Fagus sylvatica). Comparison of forestry archives and vegetation in the area showed that most of the timber could have originated from nearby forests; only silver fir had to be transported from sites that were at least 20 km away from the castle. Cross-dating of tree-ring series of oak elements with two reference chronologies from Slovenia and two from Austria confirmed the great likelihood that the wood used mostly originated from Slovenia. This indicates that dendroprovenancing, not used in the area before, could also be used SE of the Alps. Both the existing archival documents and dendrochronology indicate that woodworks have taken place every few decades in some periods. The dendrochronological dates can be partly linked to reports on earthquakes (especially the devastating one in 1511), rebellions and year marks carved on the stone plaques.     

Testing the potential of the dwarf shrub Dryas octopetala L. for dating in dendrogeomorphology

Dendrochronology has been applied around the world over decades to reconstruct historical geomorphological events and climatic conditions. Traditionally, this research has been conducted using trees (conifers as well as broad-leaved trees) but, in the last few decades, several shrub and dwarf shrub species have also been shown to be useful for dendrochronological purposes. This study assesses the potential of mountain avens (Dryas octopetala L.) to provide accurately dated information about past debris-flow events. The study site, the Marlt-Graben debris-fan, is located in South Tyrol (Italy). 119 shrubs from three debris-flow tracks were analyzed. The longest radius of each sample was measured and cross-dated to build two chronologies for each debris-flow track, one for each leveé. Correlations between these chronologies and precipitation and temperature data from five climate stations located in the proximity of the study site were calculated. The cross-dating procedure was complex, but a strict grouping of the samples, based on the specific leveés of the tracks, enabled the construction of mean chronologies for each of the individual slopes. Although the development of a mean chronology for the study area was unsuccessful, the cross-dated ages of the single shrubs allowed us to reconstruct debris-flow events by utilizing the minimum age method. The low climate correlations suggest that micro site conditions strongly influence the growth of this dwarf shrub. Although the results of this study suggest that Dryas octopetala may provide useful dendroecological information, additional information about its growth dynamics is required before this potential can be fully realized.     

Historic log structures as ecological archives: A case study from eastern North America

Forests of eastern North America have undergone abrupt transformations over the last several centuries due to changing land use and climate. Researchers look to pre-settlement forests as a guide for forest restoration, though much of our understanding of composition and dynamics in pre-settlement forests is based on spatially restricted sediment records, few and fragmented old-growth stands in a narrow range of site types, and potentially biased historical documentation. Logs from historic structures hold information that may be useful to forest ecology in eastern North America, but before these records can be used, we must first establish where the logs originated, why they were selected over other trees, and what they can and cannot tell us about past forest ecology. Using a case study approach, I collected data from fifteen log structures in the central Appalachian region to compare construction site locations, species used, and mean diameter of logs through time to determine the ecological biases associated with human behavior in log structure construction. Construction site locations changed from valleys to mountains through time and the species used in construction shifted from Quercus alba to a mix of Quercus alba, Liriodendron tulipifera, Pinus strobus, and Castanea dentata over time. The diameter of logs used in construction were generally consistent through time, with an average basal diameter of 31.3 cm (±4.7). Mean age of logs increased through time for Quercus species, regardless of log diameter. These results suggest the species used for structural logs were selected by their abundance at the location of construction but that as construction site locations and resource availability changed through time, the species used in construction changed as well. While there are biases and limitations of dendroecological data from historic structures, the results presented here demonstrate that structural log data provide greater replication during the early European immigration period, representation of upland (valley) forest sites, and establishment of chronologies for species that are not well represented in current tree-ring chronologies (e.g. Castanea dentata, Liriodendron tulipifera). These results suggest structural logs can benefit ecological research by filling the temporal, spatial, and species gaps in tree-ring chronologies not only for the central Appalachian region, but also for other areas in eastern North America.     

Dendrochronological analyses of wood samples from a Late Bronze to early Iron Age site at Lake Luokesa,Lithuania

Tree rings of 184 archaeological wood samples from two Late Bronze to early Iron Age lake sites at Lake Luokesa (Luokesai e?eras), Lithuania, Moletai district, were analyzed. Despite severe difficulties with synchronization, Pinus (pine), Quercus (oak) and Alnus (alder) yielded some cross-datable series. The general picture is that the settlers chose small trees as timber, which they used in their natural round shape. The trees did not grow in homogeneous even-aged stands, but show very different ages and growth levels. Despite the generally low numbers of tree rings in the individual samples, the strong archaeological framework allowed cross-dating of some series and the building of chronologies for single structures. Based on these attempts, a 90 year long first floating chronology of the settlement structures is presented. Luokesa Site 2 (L2) was mainly built within the relative year 53. Luokesa Site 1 (L1) was certainly in use from the relative year 74 onwards. All fences at L1 show their main building activity in the relative year 81, four years after the main building activities in the village itself. It can be concluded that the settlement L1 was in use for at least 16 years. Because of the lack of a standard dendrochronological curve for the Baltic region, wiggle-matching was applied to obtain an absolute date for both settlements. The data clearly show that all samples relate to the Late Bronze–early Iron Age. The period where all wiggle matching results overlap is the period between 625 and 535 bc (the 2σ ranges are given). Based on the dating, duration and timber characteristics of the occupation, comparisons with Polish early Iron Age sites are made, which indicate a close resemblance in terms of wood use and settlement concept.     

Evaluating the potential for dendrochronological analysis of live oak (Quercus virginiana Mill.) from the urban and rural environment—An explorative study

Live oak (Quercus virginiana Mill.) is a long lived, broadleaf, evergreen species native to the lower Coastal Plain of the southern and southeastern United States and is frequently planted in the urban environment. However, live oak has received limited attention for its potential for dendrochronological analyses possibly because its growth-ring boundaries may be less defined due to the absence of a distinct dormancy period. The objective of this explorative study was to determine whether live oak rings in both urban and historic trees could be accurately identified and measured for dendrochronological applications. One hundred urban live oaks were assessed as well as four cross-sectional specimens from historic sites in the southeastern United States. Age of all cored live oak ranged from 7 to 29 (average = 16.8 rings), while cross-sections were taken from trees with an average age of 175 years. A chronology was created from cores that had the highest interseries correlations (n = 27), resulting in an average interseries correlation of 0.654. The analysis of live oak cross sections revealed that the rings on live oak are very faint and barely discernible, delimited mainly by a faint row of earlywood vessels with no or barely visible terminal parenchyma. Rings on these sections were erratic (i.e., fading out along the circumference) and non-concentric (i.e., a particular ring could be both wide and narrow at certain points along the circumference) so that any attempt to measure the rings on opposing radii would have produced meaningless results. However, based on the results of this study, we conclude that the dendrochronological analysis of live oak is possible with careful sample preparation and analysis and that results would be reliable, even for urban trees. Results of this study suggest that urban tree-ring series with higher interseries correlations were more vigorous than those with lower values, suggesting that urban environmental stresses related to individual sites may decrease the usefulness of crossdating techniques for evaluating annual rings on younger, urban trees.     

Dendrochronological potential of the Azorean endemic gymnosperm Juniperus brevifolia (Seub.) Antoine

Tree-ring inter-annual pattern variation is crucial in dendrochronology, allowing the identification of possible limiting factors on growth. Thus, trees exposed to subtropical or tropical climates without a marked seasonality may show a low degree of interannual variation, impeding a straightforward dendroclimatological approach. Meanwhile, subtropical regions, and areas in transitional climates such as the Azores archipelago, are widely unexplored in terms of dendroclimatology, providing opportunities to work with endemic trees, including the dominant Azorean tree Juniperus brevifolia (Seub.) Antoine. To evaluate the dendrochronological potential of J. brevifolia, we analyzed tree-ring patterns, crossdating capabilities, and correlation with climate parameters. We sampled 48 individual trees from two natural populations (São Miguel and Terceira islands) using an increment borer. Besides, a Trephor tool was used to obtain wood microcores for micro-anatomical analysis. Although the transition between early and latewood was evident, partially indistinct ring boundaries and wedging rings were present in some cases, affecting the crossdating process, but not impeding the establishment of reliable ring-width chronologies. Following detrending, master chronologies were built and correlated with monthly temperature and precipitation data using the treeclim R package. The climate-growth relationships indicated negative correlations with late summer temperature in both populations. Considering our results and the importance of J. brevifolia as a dominant tree in the Azores natural forests, we conclude that it shows an acceptable potential for dendrochronological research. Thus, this study provides baseline information to help fill the knowledge gap regarding the climate-growth relationship of Azorean trees.     

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.     

Tree-ring distinctness,dating potential and climatic sensitivity of laurel forest tree species in Tenerife Island

Macaronesian laurel forests are the only remnants of a subtropical palaeoecosystem dominant during the Tertiary in Europe and northern Africa. These biodiverse ecosystems are restricted to cloudy and temperate insular environments in the North Atlantic Ocean. Due to their reduced distribution area, these forests are particularly vulnerable to anthropogenic disturbances and changes in climatic conditions. The assessment of laurel forest trees’ response to climate variation by dendrochronological methods is limited because it was assumed that the lack of marked seasonality would prevent the formation of distinct annual tree rings. The aims of this study were to identify the presence of annual growth rings and to assess the dendrochronological potential of the most representative tree species from laurel forests in Tenerife, Canary Islands. We sampled increment cores from 498 trees of 12 species in two well-preserved forests in Tenerife Island. We evaluated tree-ring boundary distinctness, dating potential, and sensitivity of tree-ring growth to climate and, particularly, to drought occurrence. Eight species showed clear tree-ring boundaries, but synchronic annual tree rings and robust tree-ring chronologies were only obtained for Laurus novocanariensis, Ilex perado subsp. platyphylla, Persea indica and Picconia excelsa, a third of the studied species. Tree-ring width depended on water balance and drought occurrence, showing sharp reductions in growth in the face of decreased water availability, a response that was consistent among species and sites. Inter-annual tree-ring width variation was directly dependent on rainfall input in the humid period, from previous October to current April. The four negative pointer years 1995, 1999, 2008 and 2012 corresponded to severe drought events in the study area. This study gives the first assessment of dendrochronological potential and tree-ring climate sensitivity of tree species from the Tenerife laurel forest, which opens new research avenues for dendroecological studies in Macaronesian laurel forests.     

Parameter-specific hydroclimatic sensitivity of a low-elevation network of living and historical tree-ring series from north-eastern Austria

Compared to the alpine regions of Austria, the eastern part of the country is overall warmer and drier with some tree species growing at the dry limit within their ecological range. This suggests that tree rings may be a valuable proxy for hydroclimatic variability. In this study, we develop ring-width, earlywood-width and latewood-width chronologies obtained from drought sensitive living trees and historical timber from one of the driest and warmest regions of Austria, the Weinviertel. For this, samples of four different tree species − fir (Abies alba Mill.), spruce (Picea abies (L.) Karst.), oak (Quercus petraea Liebl., Q. robur L., Q. cerris L.), and pine (Pinus sylvestris L., P. nigra Arnold) were collected from 88 sites (23 forest stands and 65 historical constructions). 1589 samples (oak: 592 samples, pine: 577, spruce: 212, fir: 208) were dated. Dendro-provenancing was required to ensure that only regional material has entered the chronologies. According to the analyses, historical pine and oak wood were nearly 100% regional, while spruce and fir wood were imported to a great extent with only 44% spruce and 35% fir confirmed to be regional. Because site conditions of historical wood samples are unknown but can have a significant influence on tree growth, changes to site replication over time were important in the assessment of chronology reliability. We also controlled for potential artificial increases in sample depth when more than one construction element is made from a single trunk.We assessed the pine (1584-2011 AD) and oak (1244-2011 AD) chronologies’ potential for reconstructing past hydroclimatic variability by means of response functions in a 17-months window from previous June to current October with climate data from three weather stations (Vienna, Retz, Brno) from 1897 to 2010 AD. The highest seasonal response coefficients are for oak and pine ring width (∼0.43) with respect to aggregated March to July precipitation totals and Thornthwaite climatic water balance. These chronologies reveal a high potential for estimating past changes in regional-scale moisture availability during the earlier growing season.     

Precision dating of Cook’s Mill,a Civil War era structure in West Virginia

Dendroarchaeology can provide critical understanding of a structure built during key historic periods, such as the American Civil War (1861–1865), when historical documentation is likely to be sparse or incomplete. Cook’s Mill is located in Greenville, West Virginia and extensive information derived from deeds, court records, wills, and oral history places the present mill’s original construction in 1857. The American Civil War began shortly after its construction and military conflict in the area led to the burning of several key structures, one of which was an unknown mill in Greenville (formerly Centerville). Written history suggests the mill is original and survived the American Civil War, however we used dendroarchaeology to confirm its precise date of construction. We collected 46 samples from the mill and 6 cross sections from a nearby exhumed bridge for dendrochronological dating. The mill was constructed with white oak (Quercus alba) and tulip poplar (Liriodendron tulipifera) logs and the bridge samples were white oak. We visually and statistically crossdated 32 white oak samples from the mill and bridge by comparing them to a local chronology developed for this study and two regional oak chronologies from the International Tree-Ring Data Bank. Based on terminal ring attributes and cutting date years we were able to provide a suggested construction date of the spring or early summer of 1868. This date suggests Cook’s Mill was the mill burned during military conflict in the area and that the current structure was subsequently rebuilt following the conclusion of the war.     

The Balearic Islands: a reservoir of cpDNA genetic variation for evergreen oaks

Aim To analyse the role of the Balearic Islands as a refuge area for evergreen Quercus (cork oak: Quercus suber L., holm oak: Q. ilex L., kermes oak: Q. coccifera L.), by using molecular, historical and palaeobotanical data. Location The Western Mediterranean Basin (Balearic Islands, eastern Iberia, Provence, Sardinia, Corsica, Sicily, Malta, Italy, Northern Africa). Methods We sampled 108 populations and used the PCR‐RFLP technique with five universal cpDNA primers to define haplotypes in the sampled populations. Diversity, differentiation parameters and spatial analysis of the populations, using a spatial version of amova , were linked to the geological history of the Western Mediterranean Basin in order to explain the present spatial pattern of the evergreen Quercus populations in the Balearics. Results Evergreen Quercus cpDNA shows a complex structure, with remnants of ancient diversity in the Balearics. Balearic populations of holm oak are related to Iberian populations, while for cork and kermes oaks, we found both Tyrrhenian and Iberian haplotypes. Main conclusions The complex spatial patterns of cpDNA in Balearic evergreen Quercus appears explicable in terms of a combination of physical (vicariance and long distance dispersal) and biological (introgressive hybridization) factors. The Balearics constitute a glacial refuge area and a reservoir of genetic variation with traces of ancient diversity from Messinian–Pliocene stages.     

Dendroecological investigations on Swietenia macrophylla King and Cedrela odorata L. (Meliaceae) in the central Amazon

The width of the increment zones in the xylem of Swietenia macrophylla King and Cedrela odorata L. was investigated by dendroecological methods in a primary forest near Aripuanã, Mato Grosso, Brazil (10°09′S, 59°26′W). The annual period of cambial cell division and its intra-annual variation were determined by dendrometer measurements of 30 trees of each species. Tree-ring width chronologies for Swietenia and Cedrela were developed from cross-dated increment curves of 33 out of 47 Swietenia and 51 out of 64 Cedrela trees. Simple correlations were computed between the radial growth increment and monthly precipitation for the period 1890–2000. In Swietenia, cambium activity occurred throughout almost the whole year, but in Cedrela it was restricted to the rainy period from September of the previous year to June of the current year. Tree-rings were formed annually in the juvenile and adult wood of Cedrela, while in Swietenia the annual formation of tree-rings was restricted to the adult wood. Consequently the age of the Swietenia trees could be dated by the tree-rings in good approximation, while age dating of the Cedrela trees was exact. Correlation analyses revealed a significant relationship between the precipitation at the beginning and at the end of the growth season and the width of the increment zones in the adult xylem of Swietenia. In contrast, the width of the growth increment in the xylem of Cedrela was significantly correlated with the precipitation in March and May of the previous growth period.     

The Geographic Distribution of a Tropical Montane Bird Is Limited by a Tree: Acorn Woodpeckers (Melanerpes formicivorus) and Colombian Oaks (Quercus humboldtii) in the Northern Andes

Species distributions are limited by a complex array of abiotic and biotic factors. In general, abiotic (climatic) factors are thought to explain species’ broad geographic distributions, while biotic factors regulate species’ abundance patterns at local scales. We used species distribution models to test the hypothesis that a biotic interaction with a tree, the Colombian oak (Quercus humboldtii), limits the broad-scale distribution of the Acorn Woodpecker (Melanerpes formicivorus) in the Northern Andes of South America. North American populations of Acorn Woodpeckers consume acorns from Quercus oaks and are limited by the presence of Quercus oaks. However, Acorn Woodpeckers in the Northern Andes seldom consume Colombian oak acorns (though may regularly drink sap from oak trees) and have been observed at sites without Colombian oaks, the sole species of Quercus found in South America. We found that climate-only models overpredicted Acorn Woodpecker distribution, suggesting that suitable abiotic conditions (e.g. in northern Ecuador) exist beyond the woodpecker’s southern range margin. In contrast, models that incorporate Colombian oak presence outperformed climate-only models and more accurately predicted the location of the Acorn Woodpecker’s southern range margin in southern Colombia. These findings support the hypothesis that a biotic interaction with Colombian oaks sets Acorn Woodpecker’s broad-scale geographic limit in South America, probably because Acorn Woodpeckers rely on Colombian oaks as a food resource (possibly for the oak’s sap rather than for acorns). Although empirical examples of particular plants limiting tropical birds’ distributions are scarce, we predict that similar biotic interactions may play an important role in structuring the geographic distributions of many species of tropical montane birds with specialized foraging behavior.     

First dendrochronological studies of Quercus protoroburoides

Quercus protoroburoides Donchev and Bouzov ex Tashev and Tsavkov (Rila oak) is a species with extremely limited and localized distribution. It is found only on several locations on slopes above Rila Monastery in Rila Mountains (Bulgaria) at elevations between 1500 m and 1750 m a.s.l. The trees are in small groups or scattered, usually situated on ridges slightly higher than the local population of sessile oak (Quercus petraea (Matt.) Liebl.) and above mixed fir-beech forests. The species was first discovered and described in 1968 by Boris Buzov, but was officially validated in 2017 by Tashev and Tsavkov. Up to this moment there were no dendrochronological studies of the species and there is general lack of data on how climate affects its growth. Our aim was to contribute to filling this knowledge gap. In our study we analyzed 42 series (22 trees) from Q. protoroburoides from two locations (Drushlyavitsa and Brichebor) and compared them to cores from Q. petraea from the same region. The Rila oak trees varied in age from 30 to 170 years. Nearly half of them were about 50 years old. The composed tree-ring chronology spans from 1856 to 2019 with more than 5 included series after 1870. The sessile oak trees were generally older and the chronology spanned from 1743, having more than 4 series after 1786. The climate-growth analysis with local and gridded data revealed positive effects on growth of previous August and current April-June precipitation, positive correlations with previous May-June temperatures and negative with August temperatures. Most of the pointer years with low growth were characterized by extreme climate conditions, such as summer droughts, unusually cold summers or delayed start of the vegetation period due to late frost events at the end of May or early June. Our data indicate that Q. protoroburoides and Q. petraea trees at this unusually high location for oaks are sensitive to climate conditions including summer droughts.     

Influence of human impact and bedrock differences on the vegetational history of the Insubrian Southern Alps

Vegetation history for the study region is reconstructed on the basis of pollen, charcoal and AMS¹⁴C investigations of lake sediments from Lago del Segrino (calcareous bedrock) and Lago di Muzzano (siliceous bedrock). Late-glacial forests were characterised byBetula andPinus sylvestris. At the beginning of the Holocene they were replaced by temperate continental forest and shrub communities. A special type of temperate lowland forest, withAbies alba as the most important tree, was present in the period 8300 to 4500 B.P. Subsequently,Fagus, Quercus andAlnus glutinosa were the main forest components andA. alba ceased to be of importance.Castanea sativa andJuglans regia were probably introduced after forest clearance by fire during the first century A.D. On soils derived from siliceous bedrock,C. sativa was already dominant at ca. A.D. 200 (A.D. dates are in calendar years). In limestone areas, however,C. sativa failed to achieve a dominant role. After the introduction ofC. sativa, the main trees were initially oak (Quercus spp.) and later the walnut (Juglans regia). Ostrya carpinifolia became the dominant tree around Lago del Segrino only in the last 100–200 years though it had spread into the area at ca. 5000 cal. B.C. This recent expansion ofOstrya is confirmed at other sites and appears to be controlled by human disturbances involving especially clearance. It is argued that these forests should not be regarded as climax communities. It is suggested that under undisturbed succession they would develop into mixed deciduous forests consisting ofFraxinus excelsior, Tilia, Ulmus, Quercus andAcer.