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Key messageLarch trees respond to stand opening with an approximately 4-year delay of growth, and low precipitation in July limits radial growth after a windthrow event.Precise cross-dating of disturbance events is crucial to understanding the functioning of forest stands, and may help explain ongoing ecological processes in a forest. Tree rings are very often used to reconstruct the history of disturbances and to study the response of trees to climatic factors. This study analyzed how quickly European larch can benefit from an abrupt change after catastrophic windthrow events and the extent of trees’ sensitivity to climate. The study is based on cores from 83 larch trees collected in a post-disturbance 100 ha plot established after a catastrophic windstorm in 2004 in the Slovakian High Tatras. Growth release was calculated from the percentage of growth change (PGC) measured in tree rings. The time lag between the disturbance event and release was related to tree diameter at breast height, tree age, and tree’s previous growth. The time lag between the year of the event and the year of growth reaction was 4.6 years on average (median 4 years) in a multi-aged group of trees. The climate analyses employed residual chronology. The new environmental conditions in the post-disturbance area have altered the trees’ growth reaction to climate; in particular, they show sensitivity to water deficit in July.

Question: How many years must elapse for freshly fallen Picea abies stems to be transformed into a substrate for P. abies recruitment? Location: Natural sub-alpine spruce forest, 1200–1300 m a.s.l., western Carpathians, Poland. Methods: Coarse woody debris (CWD) was measured on nine plots with a total area of 4.3 ha. All individuals of P. abies regeneration growing on dead wood were counted and their age was estimated. Decay rate of logs was determined using dendrochronological cross-dating of samples from logs in different decay stages. Results: Although CWD covered only 4% of the forest floor, 43% of the saplings were growing on decaying logs and stumps. The highest abundance of P. abies recruitment occurs on logs 30–60 years after tree death, when wood is in decay stages no. 4-7 (on an 8 degree decay scale). However, much earlier colonization is possible. The first seedlings may germinate on a log during the second decade after tree death and survive for decades. Their slow growth is possibly due to the gradual progressive decomposition of wood. Conclusions: This study confirms the importance of decaying wood for P. abies recruitment. The decaying logs exhibit continuous and favourable conditions for the germination of P. abies seeds throughout their decay process. Logs, irrespective of their decay stage and age, are colonized by young seedlings. This recruitment bank is constantly renewed.

Information about climate–growth relationships is crucial for predicting the potential climatic impact on tree species, especially those growing on the edges of their distribution range, for instance, in high-elevation forests. This study aimed to determine changes in the relationships between tree-ring widths and daily climatic data in high-elevation forests in the Western Carpathians over time. Climate–growth relationships were calculated to obtain the TRWI (tree-ring-width index) chronology (based on 104 trees) and day-wise aggregated data for temperature (mean, minimum, and maximum) and sums of precipitation. The radial growth of stone pine was mostly determined by the mean temperature in the period between mid-June (21st) and the beginning of July (4th) for the critical 14-day window width (r = 0.44). The negative influence of precipitation on the radial growth occurred in summer (r = −0.35) and overlapped with the period of the positive influence of temperature. Dendroclimatic studies based on daily data may define the exact periods (expressed in calendar days) that influence the radial growth of trees much better than the commonly used monthly means. This is particularly important in analysing the growth of trees at high elevations, where the climatic factor strongly limits radial growth.

Key message Based on the first dendroclimatological analyses of the thermo-Mediterranean tree Pyrus bourgaeana , the positive relationship between the growth and climate (i.e., precipitation) has strengthened in recent decades. The combined effect of climate change and habitat destruction and fragmentation threatens many plant populations and even entire communities in Mediterranean ecosystems. The Iberian pear, Pyrus bourgaeana Decne, a characteristic species of Mediterranean ecosystems, is threatened by both habitat and climate changes. We ask whether and how the growth of mature P. bourgaeana in the thermo-Mediterranean zone (i.e., altitude <700 m) has been affected by long-term climate changes during the last century in a fragmented landscape. Dendrochronological methods were used to find growth–climate relationships. We made the first dendroclimatological analyses and constructed a first 103-year tree-ring chronology (1905–2007) of this species. The tree-ring series revealed large growth variability. We found a clear, strong relationship between tree growth and climate, with annual precipitation being the most important climate factor enhancing radial growth. Our results also showed that warm autumns and winters positively affect growth. There was no temporal stability in the relationship between tree growth and climate. The most general trend was in the relationship between annual precipitation and tree growth: the decrease of rainfall in the last decades of the twentieth century was associated with a constant increase of the correlation coefficient. Water accumulated in the soil in autumn and winter proved to be a key factor augmenting tree growth in the following vegetation period. The climate–growth relationship in P. bourgaeana has strengthened in recent decades apparently due to decreased precipitation levels.

Question: Have past windstorm events influenced the structure and composition of mountain forests in the Tatra Mountains? Can severe and infrequent wind disturbances lead to dynamic coexistence of two tree species with different ecological requirements? Location: Subalpine mixed spruce-larch forest at 1200-1300 m a.s.l. in the Slovakian Tatra Mountains. A forested site affected by catastrophic large-scale windthrow on 19 November 2004. Methods: Sixty-seven spruce and 30 larch cross-sections from the oldest cohorts were collected in a regular pattern in a 100-ha plot. Tree-ring series were analysed to reconstruct growth releases associated with past windthrows. A boundary-line release criterion was applied to detect disturbance year. Spatial patterns of release signals were statistically detected with Mantel's test. We compared reconstructed years of disturbance events with historical records. Results: Releases in both species showed three main pulses. More than 85% showed major or moderate releases in 1865-1879, 48% in 1915-1924, and 25% in 1940-1949. All of these disturbance events affected the whole 100-ha area. Releases were spatially patterned in the first disturbances, but distributed randomly in the last. Releases co-occurred in time with enhanced production of compression wood, suggesting disturbances were of wind origin. Reconstructed dates of windthrows were confirmed using historical data on storms. Conclusions: At least three windthrows of major and moderate severity took place in the last 150 years on southern slopes of the Tatra Mountains. This disturbance regime may contribute to coexistence of spruce and larch through differences in vulnerability and response to heavy windstorms.

Life history theory posits that an increased investment in reproduction should result in decreased vegetative investment. Switching resources from growth to reproduction are also expected in species experiencing selection pressure for high variation of seed crops. In this study, we tested whether the reproductive effort of trees, measured as the number of fruits produced, is related to their radial growth increment. We examined a population of Sorbus aucuparia, a fleshy-fruited tree species with highly variable interannual individual fruit production growing in the subalpine zone and under strong selection pressure from pre-dispersal seed predators. We used 12-year data to test the relationship between fruit crop and radial growth increments in current, previous and subsequent years, and found no trade-off between growth and reproduction. For almost all trees, there was no correlation between fruit crop and radial growth increment in the same year or next year. Only a few trees showed a positive correlation between fruit crop and previous-year growth. In the statistics, we took advantage of the high variability of individual fruit crops in high production years. In four heavy crop years, we compared the radial growth increments of trees with heavy crops with those of trees with low fruit crops. Current and next-year radial growth did not differ between trees with low and high fruit crops. In all those years, however, trees having heavy fruit crops had higher previous-year growth increments. We suggest that the harsh subalpine weather conditions account for the lack of a trade-off between growth and reproduction in the studied population.

Question: How many years must elapse for freshly fallen Picea abies stems to be transformed into a substrate for P. abies recruitment? Location: Natural sub‐alpine spruce forest, 1200–1300 m a.s.l., western Carpathians, Poland. Methods: Coarse woody debris (CWD) was measured on nine plots with a total area of 4.3 ha. All individuals of P. abies regeneration growing on dead wood were counted and their age was estimated. Decay rate of logs was determined using dendrochronological cross‐dating of samples from logs in different decay stages. Results: Although CWD covered only 4% of the forest floor, 43% of the saplings were growing on decaying logs and stumps. The highest abundance of P. abies recruitment occurs on logs 30–60 years after tree death, when wood is in decay stages no. 4–7 (on an 8 degree decay scale). However, much earlier colonization is possible. The first seedlings may germinate on a log during the second decade after tree death and survive for decades. Their slow growth is possibly due to the gradual progressive decomposition of wood. Conclusions: This study confirms the importance of decaying wood for P. abies recruitment. The decaying logs exhibit continuous and favourable conditions for the germination of P. abies seeds throughout their decay process. Logs, irrespective of their decay stage and age, are colonized by young seedlings. This recruitment bank is constantly renewed.

The amount and decay stages of dead wood and the residence time of logs was studied in old-growth spruce-dominated stands in the Tatra and Babia Góra in the western Carpathian Mountains in Central Europe. The DBH of living trees and snags as well as the dimensions of logs (with a minimum diameter of 10 cm) were measured on nine sample plots with a pooled area of 4.3 ha. For the logs, the decay stage was identified according to an eight-level decay classification. Dendrochronological cross-dating was applied to 107 wood samples of logs to determine the time since death. The average volume of living trees was 454 m 3 /ha and the volume of coarse woody debris (CWD) averaged 191 m 3 /ha. The noted volume of CWD was higher than volumes reported from previous studies in the Carpathian Mountains. On average, CWD made up 30% of the total volume (living plus dead) and varied between 49% and 21% for the stands. The average age of logs for decay class 1 was 13 years and 24, 28, 38, 45, 38, and 60 years for decay classes 2-7, respectively. Considerable variation of time since death between decay classes was probably due to a variable time while dead trees remained standing as snags.

1. Fires are nowadays small, yet frequent, in temperate Central European conifer forests, but little is known about the fire history in this region. This is likely due to the lack of intact forests that contain old trees and dead wood from which fire history may be reconstructed. An exception is the Białowieża Primeval Forest (BPF) in Poland for which we were able to reconstruct the fire history in detail. 2. From 886 tree ring samples collected in a 13-ha conifer-dominated area, we reconstructed fire events and tree establishment back to the mid 1600s. From 1653 to the late 1700s fires were very frequent, with mean point (single tree) fire intervals of 18 years and mean stand scale fire intervals of 6 years. After 1781, the intervals between the fires increased dramatically, and since 1874 no major fire was recorded. 3. Tree establishment underwent substantial changes, closely tracking shifts in fire frequency. When fires were frequent, Pinus sylvestris establishment occurred only sporadically. Later, less frequent fires promoted massive establishment of both P. sylvestris and Picea abies. At present, only P. abies and a few deciduous trees regenerate. 4. Synthesis. We present the first high-resolution fire history in the Central European temperate lowland forest area. The discovery of old P. sylvestris trees and stumps with fire scars in many conifer-dominated parts of BPF show that fire was a major component in the past dynamics of this forest. We also show that historically, fires were recurring at very close intervals, supporting an open, Pinus-dominated forest. These result contrasts with the written history of BPF, which focus on a few, large fires from the past. Human influence on the fire regime was probably substantial, although the disentangling of climatic and human impacts needs further studies. We propose that fire should be increasingly taken into consideration in models of disturbance, vegetation development and forest openness in the whole Central European lowland forest region.

This is a study of the colonization pattern of herbs and dwarf shrubs on rotten logs in subalpine spruce forests (Plagiothecio Piceetum) in the Tatra Mountains. On four study plots (total area 1.43 ha.) all dead logs were measured and the decomposition stage was estimated using the 8-degree scale. For each log the cover of all vascular species, bryophytes and lichens was determined according to the methods of classical phytosociology. Constancy and an index of coverage were calculated for all vascular species growing on logs. The total volume of logs was relatively high (93 m3 ha(-1)) and constituted 22% of the volume of living trees. Logs and stumps covered 411 m2 ha(-1). These values are similar to those known from natural spruce forest from Carpathians and Scandinavia. The 8 stages of decomposition were equally represented, which indicates a constant supply of dead wood to the forest floor over time. The colonization of dead wood starts with lichens, followed by bryophytes and finally herbs and tree saplings. The first vascular plant colonists of dead logs appear at decay stage nr. 3 at least 20 years after tree death. The most suitable condition for most of the herb species corresponds to decay stage nr. 6 ca. 50 years after tree death. The herb cover is distinctively dominated by Vaccinium myrtillus. Simultaneously with herb species, tree seedlings colonize the logs. Constancy and abundance of Norway spruce saplings increases with advanced decomposition. It seems that the herb cover of logs does not hinder the regeneration of spruce.