Tree-ring studies may help better understand climate variability and extreme climate event frequency and are especially useful in regions where detailed meteorological records lack. We studied the ...effect of droughts and unusually cold periods on
Pinus sylvestris
tree-ring width and wood anatomy. Study sites were selected along an altitudinal gradient on Vitosha Mountain, Bulgaria. Drought conditions caused the formation of narrow tree rings or light rings if the drought occurred in July–August at the lower altitude sites. In years with droughts in June and the first half of July, followed by precipitation in the middle of July, intra-annual density fluctuations (IADFs) were formed. Trees in the zone with optimal growth conditions produced fewer light rings and narrow rings in years with either strongest droughts or unusually cold summers. At the timberline zone, low summer temperature triggered narrow tree rings and light rings. Frost rings were formed when there was a drop in temperatures below the freezing point in the second half of May or at the beginning of June. Our findings show that studies of tree-ring anatomy may contribute to obtain further knowledge about extreme climatic events in the Balkan Peninsula and in other regions where meteorological data lack.
ABSTRACT
The European Mediterranean region is governed by a characteristic climate of summer drought that is likely to increase in duration and intensity under predicted climate change. However, ...large‐scale network analyses investigating spatial aspects of pre‐instrumental drought variability for this biogeographic zone are still scarce. In this study we introduce 54 mid‐ to high‐elevation tree‐ring width (TRW) chronologies comprising 2186 individual series from pine trees (Pinus spp.). This compilation spans a 4000‐km east–west transect from Spain to Turkey, and was subjected to quality control and standardization prior to the development of site chronologies. A principal component analysis (PCA) was applied to identify spatial growth patterns during the network's common period 1862–1976, and new composite TRW chronologies were developed and investigated. The PCA reveals a common variance of 19.7% over the 54 Mediterranean pine chronologies. More interestingly, a dipole pattern in growth variability is found between the western (15% explained variance) and eastern (9.6%) sites, persisting back to 1330 AD. Pine growth on the Iberian Peninsula and Italy favours warm early growing seasons, but summer drought is most critical for ring width formation in the eastern Mediterranean region. Synoptic climate dynamics that have been in operation for the last seven centuries have been identified as the driving mechanism of a distinct east–west dipole in the growth variability of Mediterranean pines.
The precise dating of wooden elements from historical sites is possible with dendrochronological methods. Usually tree-ring cores are extracted with increment borers and then analyzed. A specific ...problem might be the lack of possibility to obtain such cores. This is the case with highly valued objects, as for example icons, paintings and musical instruments. We tested an approach with making high-resolution digital photographs of the back sides of icons in the church “St. Troitsa” in Bansko, Bulgaria. We later combined the images in one single image per icon board and measured the tree-ring widths with the software CooRecorder. The procedure was successful and up to the moment we were able to measure and cross-date 24 series from 7 icons. We consider that fifteen of them were from wood of Norway spruce (Picea abies) or Fir (Abies alba) and the other nine were from Macedonian pine (Pinus peuce). The first years of the dated tree-ring series from icons were between 1658 and 1734, while the last between 1783 and 1816. The used boards were from trees that were cut 30 to 50 years before the icon painting. We found that the boards used in 4 icons were probably from one spruce tree. Our work demonstrates that measurement and precise dating of the sequences of tree rings is possible with the approach of making high-resolution digital images.
Snow avalanches are among the most important disturbances in mountain ecosystems. The effects of avalanches on the endemic Pinus heldreichii and Pinus peuce forests in the Pirin Mountains in Bulgaria ...are poorly understood. These forests are among the few remaining old-growth forests with preserved natural dynamics in Europe. However, the ongoing development of tourist infrastructure at the borders of some of the best-preserved Pinus heldreichii and Pinus peuce forests close to Bansko ski resort leads to increased tourist pressure. Many backcountry skiers and snowboarders venture beyond the resort boundaries, practicing their activities in these forests and avalanche tracks and couloirs within them. The objective of our study was to collect tree-ring cores from Pinus peuce and Pinus heldreichii trees affected by avalanches and verify the specific types of damages and tree responses characteristic for the species and region. Then using the collected data, we aimed at reconstructing the years in which specific areas were affected by avalanches and in this way obtain data on the magnitude of larger events. Our study shows that large magnitude avalanches (LMA) in the vicinity of Bansko ski resort in the Pirin Mountains in Bulgaria occurred dozens of times in the 20th century. On average the period between LMAs ranged between 9 and 20 years with the shortest period between two such events in one couloir being 2 years. Avalanches affected forests high on the couloir banks and left traces in the tree rings related to the mechanical impact that snow avalanches had on the surviving trees. In the studied tree-ring cores of Pinus peuce and Pinus heldreichii the most informative types of responses were sharp growth suppressions, including missing rings, followed by reaction wood and in less cases visible scars and callus tissue. Our data for frequent large avalanches shows that is necessary to address the avalanche risk with high priority especially for the Palashica couloir, which directly threatens the lower parts of the ski runs as well as other facilities in Bansko ski resort.
Mountain forests are among the most important ecosystems in Europe as they support numerous ecological, hydrological, climatic, social, and economic functions. They are unique relatively natural ...ecosystems consisting of long-lived species in an otherwise densely populated human landscape. Despite this, centuries of intensive forest management in many of these forests have eclipsed evidence of natural processes, especially the role of disturbances in long-term forest dynamics. Recent trends of land abandonment and establishment of protected forests have coincided with a growing interest in managing forests in more natural states. At the same time, the importance of past disturbances highlighted in an emerging body of literature, and recent increasing disturbances due to climate change are challenging long-held views of dynamics in these ecosystems. Here, we synthesize aspects of this Special Issue on the ecology of mountain forest ecosystems in Europe in the context of broader discussions in the field, to present a new perspective on these ecosystems and their natural disturbance regimes. Most mountain forests in Europe, for which long-term data are available, show a strong and long-term effect of not only human land use but also of natural disturbances that vary by orders of magnitude in size and frequency. Although these disturbances may kill many trees, the forests themselves have not been threatened. The relative importance of natural disturbances, land use, and climate change for ecosystem dynamics varies across space and time. Across the continent, changing climate and land use are altering forest cover, forest structure, tree demography, and natural disturbances, including fires, insect outbreaks, avalanches, and wind disturbances. Projected continued increases in forest area and biomass along with continued warming are likely to further promote forest disturbances. Episodic disturbances may foster ecosystem adaptation to the effects of ongoing and future climatic change. Increasing disturbances, along with trends of less intense land use, will promote further increases in coarse woody debris, with cascading positive effects on biodiversity, edaphic conditions, biogeochemical cycles, and increased heterogeneity across a range of spatial scales. Together, this may translate to disturbance-mediated resilience of forest landscapes and increased biodiversity, as long as climate and disturbance regimes remain within the tolerance of relevant species. Understanding ecological variability, even imperfectly, is integral to anticipating vulnerabilities and promoting ecological resilience, especially under growing uncertainty. Allowing some forests to be shaped by natural processes may be congruent with multiple goals of forest management, even in densely settled and developed countries.
Climate changes, their regional patterns, origin, and prediction are currently one of the most important scientific challenges. Tree-rings are among the most widely used proxies for past climate ...variation. However tree-ring width (TRW) from certain tree species and regions often do not contain robust climate signal. Other parameters such as Maximum latewood density (MXD) of conifer tree rings are more sensitive to summer temperatures, but the measurements have high costs. A potential surrogate for MXD is blue intensity (BI), which is based on the measurements of high-resolution images of the wood. The method has been tested and applied for several species. However it has not been tested up to now for Pinus heldreichii Christ (PIHE) and Pinus peuce Griseb. (PIPE). Those species are with limited distribution on the Balkan Peninsula and due to their longevity (frequently more than 500 years with potential to more than 1000 years) may serve as one of the best proxies for past climate variation in SE Europe.
We composed BI chronologies following standard procedures from PIHE and PIPE trees from subalpine locations in the Pirin Mts, Bulgaria. The correlation analysis with climate parameters revealed strong and significant positive correlations of PIHE BI (ΔBI and Latewood BI (LwBI) series) and summer temperatures. The highest were 0.74 (p < 0.05) with July-August average temperatures for the period 1933–1983. The correlation values of ΔBI remained higher than 0.6 for the whole period (1933–2014) and sub-periods both for average monthly and average maximum temperatures. LwBI values of the PIHE chronology had correlation coefficients above 0.52 (highest 0.64) with August and August-July temperatures. The PIPE BI chronologies were also positively correlated with summer temperatures, but showed lower values than PIHE with lower temporal stability. The most stable were the correlations with LwBI average August temperatures, which were above 0.52. Delta BI series displayed high correlations for the 1933–1983 period, but then decreased and this caused overall lower correlations with August temperatures. Our data shows that there is potential to develop long BI chronologies and proxy climate reconstructions from the studied species and in this way complement the knowledge of the past climate of SE Europe.
Bosnian pine (Pinus heldreichii Christ, also known as Pinus leucodermis Antoine) is a relict species found in isolated locations in the mountains of the Balkan Peninsula and Southern Italy. The ...forests are of high conservational value because they are extremely rich in rare and endemic species of plants and fungi. Yet, the natural history and disturbance regime of P. heldreichii ecosystems is not well understood. Fire traces show that fires played a major role, but there is very limited historical data. Therefore proxy methods to reconstruct past events have to be used. The analysis of tree rings provides such an opportunity. To our knowledge, there have been no attempts to use tree ring cores from P. heldreichii trees to date fire events. Our aim was therefore to test if tree ring cores collected with an increment borer could successfully be used to date fires and verify other tree ring indicators caused by the fire events. We tested an approach that was based on extracting multiple cores from fire-scarred trees and nearby standing trees without injuries. A total of 136 cores from 99 trees were collected from which we dated all 34 cores with fire scars. We found the exact fire years for 29 of the samples, and the remaining 5 samples were approximately dated. Up to 83% of all sampled trees had additional growth reactions, mostly suppressions lasting 5–10 years after the fire years.
AIM: To evaluate the climate sensitivity of model‐based forest productivity estimates using a continental‐scale tree‐ring network. LOCATION: Europe and North Africa (30–70° N, 10° W–40° E). METHODS: ...We compiled close to 1000 annually resolved records of radial tree growth for all major European tree species and quantified changes in growth as a function of historical climatic variation. Sites were grouped using a neural network clustering technique to isolate spatiotemporal and species‐specific climate response patterns. The resulting empirical climate sensitivities were compared with the sensitivities of net primary production (NPP) estimates derived from the ORCHIDEE‐FM and LPJ‐wsl dynamic global vegetation models (DGVMs). RESULTS: We found coherent biogeographic patterns in climate response that depend upon (1) phylogenetic controls and (2) ambient environmental conditions delineated by latitudinal/elevational location. Temperature controls dominate forest productivity in high‐elevation and high‐latitude areas whereas moisture sensitive sites are widespread at low elevation in central and southern Europe. DGVM simulations broadly reproduce the empirical patterns, but show less temperature sensitivity in the boreal zone and stronger precipitation sensitivity towards the mid‐latitudes. MAIN CONCLUSIONS: Large‐scale forest productivity is driven by monthly to seasonal climate controls, but our results emphasize species‐specific growth patterns under comparable environmental conditions. Furthermore, we demonstrate that carry‐over effects from the previous growing season can significantly influence tree growth, particularly in areas with harsh climatic conditions – an element not considered in most current‐state DGVMs. Model–data discrepancies suggest that the simulated climate sensitivity of NPP will need refinement before carbon‐cycle climate feedbacks can be accurately quantified.
Where are Europe's last primary forests? Sabatini, Francesco Maria; Burrascano, Sabina; Keeton, William S. ...
Diversity & distributions,
October 2018, Letnik:
24, Številka:
9/10
Journal Article
Recenzirano
Odprti dostop
Aim: Primary forests have high conservation value but are rare in Europe due to historic land use. Yet many primary forest patches remain unmapped, and it is unclear to what extent they are ...effectively protected. Our aim was to (1) compile the most comprehensive European-scale map of currently known primary forests, (2) analyse the spatial determinants characterizing their location and (3) locate areas where so far unmapped primary forests likely occur. Location: Europe. Methods: We aggregated data from a literature review, online questionnaires and 32 datasets of primary forests. We used boosted regression trees to explore which biophysical, socio-economic and forest-related variables explain the current distribution of primary forests. Finally, we predicted and mapped the relative likelihood of primary forest occurrence at a 1-km resolution across Europe. Results: Data on primary forests were frequently incomplete or inconsistent among countries. Known primary forests covered 1.4 Mha in 32 countries (0.7% of Europe's forest area). Most of these forests were protected (89%), but only 46% of them strictly. Primary forests mostly occurred in mountain and boreal areas and were unevenly distributed across countries, biogeographical regions and forest types. Unmapped primary forests likely occur in the least accessible and populated areas, where forests cover a greater share of land, but wood demand historically has been low. Main conclusions: Despite their outstanding conservation value, primary forests are rare and their current distribution is the result of centuries of land use and forest management. The conservation outlook for primary forests is uncertain as many are not strictly protected and most are small and fragmented, making them prone to extinction debt and human disturbance. Predicting where unmapped primary forests likely occur could guide conservation efforts, especially in Eastern Europe where large areas of primary forest still exist but are being lost at an alarming pace.
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