Tereza Ponocná | Charles University, Prague (original) (raw)
Papers by Tereza Ponocná
Globální změna klimatu může výrazně ovlivnit fungování jednotlivých ekosystémů, a to především tě... more Globální změna klimatu může výrazně ovlivnit fungování jednotlivých ekosystémů, a to především těch, jejichž výskyt je teplotně podmíněn. Jedním z těchto ekosystémů je ekoton horní hranice lesa, významný vegetační fenomén vysokohorských oblastí, který vzniká postupným ústupem stromové vegetace s rostoucí nadmořskou výškou a klesající teplotou vzduchu. Cílem předkládané disertační práce je vyhodnocení odezvy růstu smrku ztepilého (Picea abies [L.] Karst.) na měnící se klimatické podmínky v oblasti horní hranice lesa a přiléhajících lesů montánní zóny v oblasti střední Evropy. Předkládané výsledky jsou založené na rozsáhlém datovém souboru obsahujícím téměř 1400 jedinců smrku ztepilého. Datový soubor dokládá těsnou závislost růstu stromů na teplotě aktuálního vegetačního období a také na teplotě měsíce října předcházejícího roku vzniku letokruhu. Hlavní rozdíly v odezvě růstu stromů ke klimatickým podmínkám jsou dány nadmořskou výškou, vliv expozice svahu vůči slunečnímu záření nebyl ...
The thesis deals with the influence of thermal conditions on the growth of the trees along the sl... more The thesis deals with the influence of thermal conditions on the growth of the trees along the slopes with differing exposure to solar radiation in the alpine treeline ecotone in the Eastern Giant Mountains. Methodological approach was based on the measuring of the tree top and root zone temperatures, measurement of the dendrometric parameters (tree height, length increment) and radial increment of the Norway spruce (Picea abies). The results show only weak relation between significant temperature characteristics and exposure effect in the alpine treeline ecotone, which correspond to the growth rates of the sampled trees. Slightly higher temperatures were found on the south-facing slopes during the growing seasons in case of the closed canopy forest. Soil and air temperatures in tree groups were a bit higher on the north-facing slopes. In closed-canopy forest there was larger radial increment on south-facing slopes of Lu_ní hora, on the slopes of Malý Šišák there were similar growth...
Trees, 2016
Key message Decadal growth variability of Norway spruce increases with elevation. Recent temperat... more Key message Decadal growth variability of Norway spruce increases with elevation. Recent temperature sensitivity and growth enhancement are limited to trees growing in the zone adjacent to timberline. Abstract Growth trends and climate responses of forest trees along elevational gradients are not fully understood. A deeper insight is, however, fundamental for predicting ecosystem functioning and productivity under future climate change. Supplementary to the effects of elevation and regional provenance on tree growth are sample depth, uneven representation of sample age and varying site conditions. Furthermore, there is only a limited number of studies addressing growth changes along elevational gradients, while at the same time applying tree-ring standardization methods that are sensitive to trend preservation. Here, we introduce 12 novel tree-ring width chronologies of Norway spruce (Picea abies[L.] Karst.) from four elevational belts encompassing montane forests and the local timberline in three regions in East-Central Europe between 15°and 19°E. Each chronology is characterized by sufficient sample replication and a comparable age structure between 1906 and 2010. Tree growth near timberline revealed substantial medium-frequency variability and sharply increasing ring widths since the 1980s. Mediumfrequency growth variability of lower elevation trees was, however, relatively small, and growth rates over the last decade were either stable or even decreased. During the last four decades, Norway spruce from higher elevations exhibited a reduced response to autumn temperatures preceding ring formation. In contrast, trees from the lowermontane zone increased their sensitivity to drought during the same time. Our results emphasize not only different but also instable growth trends and climate responses of forest trees along altitudinal gradients, which should be considered in future forest management strategies. Keywords Climate change Á Mountain forests Á Picea abies Á Radial growth Á Tree rings Á Trend preservation Communicated by G. Piovesan.
International Journal of Climatology, 2014
Tree rings and documentary evidence are the most important palaeoclimatic archives with annual re... more Tree rings and documentary evidence are the most important palaeoclimatic archives with annual resolution that continuously span several centuries. Despite this benefit, local to regional-scale temperature reconstructions and their spatial signatures tend to be irregularly distributed, and the appropriate extent of low-frequency variability captured in these proxy records remains uncertain. Here, the first summer temperature reconstruction from the Czech Sudetes Mountains that extends to 1700 AD was introduced. An ensemble reconstruction approach using 251 new high-elevation spruce ring width samples suggests particularly cold June-July temperatures at the beginning of the 18th century, in the 1740s and around 1820. Markedly warm conditions occurred in the 1790s and during the most recent decades. The reconstructed decadal summer temperature amplitude from 'Little Ice Age Cooling' to 'Recent Anthropogenic Warming' ranges from −3.5 ∘ C between 1700 and 1710 to 1.3 ∘ C in 1999-2009, with respect to the 1961-1990 mean climatology. Comparison of our new reconstruction with existing tree-ring chronologies from the Alps reveals a significant level of coherency that is much higher than the agreement with geographically closer documentary evidence from Central Europe. Our study confirms the importance of independent regional climate reconstructions, which capture the full range of past variability and also fill spatial gaps in large-scale networks.
Agricultural and Forest Meteorology, 2018
While some cold regions show evidence of recent decoupling of tree-ring growth from observed temp... more While some cold regions show evidence of recent decoupling of tree-ring growth from observed temperature rise, i.e. restricted growth increase, similar evidence from other regions is missing. Increasing or diminishing regional coherency in tree growth has also been observed over recent decades. The temporal and spatial extent of the abovementioned processes are poorly known and their drivers are not well understood. Pollution and changing climate have often been discussed as a cause of divergent or convergent growth patterns and deviations of growth from driving climatic variable. We compiled climatic records and robust tree-ring chronologies of treeline Picea abies covering 1920-2010 for four regions in East-Central Europe (Czech Republic, Poland, Slovakia, 50°N, 15-20°E) which experienced differing acid pollution loads. The divergence of these chronologies from Jun-Jul temperatures was compared with temperature and pollution trends. We found a period of low intraregional growth coherency in the 1950s reflecting warmer, less temperature-limiting conditions and land use change. Highly coherent growth in the 1930s, 1970s and 1980s was related to the strong environmental growthlimiting signals of short growing seasons and high acid pollution loads. In all regions, we identified periods with higher (1940-1960s) and lower (1970-1980s) growth than expected based on temperature. In the high-frequency domain, the effect of pollution on growth departure from temperature was limited and detectable exclusively in regions that were most impacted by pollution. In the low-frequency domain, the departures of growth from temperature were caused by combined effects of the changing seasonal window of tree growth sensitivity to climate and pollution load. These results highlight the need to recognize non-stationary noise in the relationship between temperature and tree growth.
Journal of Vegetation Science, 2016
Questions What was the main trigger of treeline ecotone advance – rising temperature or agricultu... more Questions What was the main trigger of treeline ecotone advance – rising temperature or agricultural land abandonment? Were the triggering factors of tree expansion homogeneous or did they differ between upper and lower parts of the treeline ecotone? Location Sudetes Mts., Central Europe (50° N, 15-17° E). Methods Data were gathered from the treeline ecotone formed by Picea abies at elevations ranging from 1250 to 1490 m. The study area experienced a 1 °C temperature increase over the last 100 yr and termination of cattle grazing and grass mowing in the first half of the 20th century. At 38 plots situated at lower (‘timberline’) and middle or upper (‘treeline’ and ‘outpost treeline’) parts of the treeline ecotone, the age structure of all seed origin P. abies was determined. Changes in tree cover and number of trees over the last 60–70 yr were assessed from aerial imagery. The history of agricultural land use for each plot was compiled. Finally, changes in tree establishment were modelled using climatic variables and land-use intensity. Results We found that tree establishment at treeline had occurred with a 30–40-yr lag after the main establishment peak at timberline. Whereas all treeline plots showed gradual increases in tree cover, timberline tree cover first increased, with some plots then undergoing thinning. Enhanced tree establishment was dependent mainly upon agricultural land abandonment. The effect of land-use changes was more important in the lower than in the upper part of the treeline ecotone. Increasing summer temperatures had a negative influence on seedling establishment in the last few decades. Conclusions Treeline ecotone densification was attributable to agricultural land abandonment across the entire treeline ecotone with the most important effect at timberline. More recently, seedling establishment has been limited by the effects of drought and/or absence of suitable microsites. We documented that one or two establishment pulses over 120 yr, together with enhanced growth since the 1980s, were able to trigger treeline ecotone advance.
Globální změna klimatu může výrazně ovlivnit fungování jednotlivých ekosystémů, a to především tě... more Globální změna klimatu může výrazně ovlivnit fungování jednotlivých ekosystémů, a to především těch, jejichž výskyt je teplotně podmíněn. Jedním z těchto ekosystémů je ekoton horní hranice lesa, významný vegetační fenomén vysokohorských oblastí, který vzniká postupným ústupem stromové vegetace s rostoucí nadmořskou výškou a klesající teplotou vzduchu. Cílem předkládané disertační práce je vyhodnocení odezvy růstu smrku ztepilého (Picea abies [L.] Karst.) na měnící se klimatické podmínky v oblasti horní hranice lesa a přiléhajících lesů montánní zóny v oblasti střední Evropy. Předkládané výsledky jsou založené na rozsáhlém datovém souboru obsahujícím téměř 1400 jedinců smrku ztepilého. Datový soubor dokládá těsnou závislost růstu stromů na teplotě aktuálního vegetačního období a také na teplotě měsíce října předcházejícího roku vzniku letokruhu. Hlavní rozdíly v odezvě růstu stromů ke klimatickým podmínkám jsou dány nadmořskou výškou, vliv expozice svahu vůči slunečnímu záření nebyl ...
The thesis deals with the influence of thermal conditions on the growth of the trees along the sl... more The thesis deals with the influence of thermal conditions on the growth of the trees along the slopes with differing exposure to solar radiation in the alpine treeline ecotone in the Eastern Giant Mountains. Methodological approach was based on the measuring of the tree top and root zone temperatures, measurement of the dendrometric parameters (tree height, length increment) and radial increment of the Norway spruce (Picea abies). The results show only weak relation between significant temperature characteristics and exposure effect in the alpine treeline ecotone, which correspond to the growth rates of the sampled trees. Slightly higher temperatures were found on the south-facing slopes during the growing seasons in case of the closed canopy forest. Soil and air temperatures in tree groups were a bit higher on the north-facing slopes. In closed-canopy forest there was larger radial increment on south-facing slopes of Lu_ní hora, on the slopes of Malý Šišák there were similar growth...
Trees, 2016
Key message Decadal growth variability of Norway spruce increases with elevation. Recent temperat... more Key message Decadal growth variability of Norway spruce increases with elevation. Recent temperature sensitivity and growth enhancement are limited to trees growing in the zone adjacent to timberline. Abstract Growth trends and climate responses of forest trees along elevational gradients are not fully understood. A deeper insight is, however, fundamental for predicting ecosystem functioning and productivity under future climate change. Supplementary to the effects of elevation and regional provenance on tree growth are sample depth, uneven representation of sample age and varying site conditions. Furthermore, there is only a limited number of studies addressing growth changes along elevational gradients, while at the same time applying tree-ring standardization methods that are sensitive to trend preservation. Here, we introduce 12 novel tree-ring width chronologies of Norway spruce (Picea abies[L.] Karst.) from four elevational belts encompassing montane forests and the local timberline in three regions in East-Central Europe between 15°and 19°E. Each chronology is characterized by sufficient sample replication and a comparable age structure between 1906 and 2010. Tree growth near timberline revealed substantial medium-frequency variability and sharply increasing ring widths since the 1980s. Mediumfrequency growth variability of lower elevation trees was, however, relatively small, and growth rates over the last decade were either stable or even decreased. During the last four decades, Norway spruce from higher elevations exhibited a reduced response to autumn temperatures preceding ring formation. In contrast, trees from the lowermontane zone increased their sensitivity to drought during the same time. Our results emphasize not only different but also instable growth trends and climate responses of forest trees along altitudinal gradients, which should be considered in future forest management strategies. Keywords Climate change Á Mountain forests Á Picea abies Á Radial growth Á Tree rings Á Trend preservation Communicated by G. Piovesan.
International Journal of Climatology, 2014
Tree rings and documentary evidence are the most important palaeoclimatic archives with annual re... more Tree rings and documentary evidence are the most important palaeoclimatic archives with annual resolution that continuously span several centuries. Despite this benefit, local to regional-scale temperature reconstructions and their spatial signatures tend to be irregularly distributed, and the appropriate extent of low-frequency variability captured in these proxy records remains uncertain. Here, the first summer temperature reconstruction from the Czech Sudetes Mountains that extends to 1700 AD was introduced. An ensemble reconstruction approach using 251 new high-elevation spruce ring width samples suggests particularly cold June-July temperatures at the beginning of the 18th century, in the 1740s and around 1820. Markedly warm conditions occurred in the 1790s and during the most recent decades. The reconstructed decadal summer temperature amplitude from 'Little Ice Age Cooling' to 'Recent Anthropogenic Warming' ranges from −3.5 ∘ C between 1700 and 1710 to 1.3 ∘ C in 1999-2009, with respect to the 1961-1990 mean climatology. Comparison of our new reconstruction with existing tree-ring chronologies from the Alps reveals a significant level of coherency that is much higher than the agreement with geographically closer documentary evidence from Central Europe. Our study confirms the importance of independent regional climate reconstructions, which capture the full range of past variability and also fill spatial gaps in large-scale networks.
Agricultural and Forest Meteorology, 2018
While some cold regions show evidence of recent decoupling of tree-ring growth from observed temp... more While some cold regions show evidence of recent decoupling of tree-ring growth from observed temperature rise, i.e. restricted growth increase, similar evidence from other regions is missing. Increasing or diminishing regional coherency in tree growth has also been observed over recent decades. The temporal and spatial extent of the abovementioned processes are poorly known and their drivers are not well understood. Pollution and changing climate have often been discussed as a cause of divergent or convergent growth patterns and deviations of growth from driving climatic variable. We compiled climatic records and robust tree-ring chronologies of treeline Picea abies covering 1920-2010 for four regions in East-Central Europe (Czech Republic, Poland, Slovakia, 50°N, 15-20°E) which experienced differing acid pollution loads. The divergence of these chronologies from Jun-Jul temperatures was compared with temperature and pollution trends. We found a period of low intraregional growth coherency in the 1950s reflecting warmer, less temperature-limiting conditions and land use change. Highly coherent growth in the 1930s, 1970s and 1980s was related to the strong environmental growthlimiting signals of short growing seasons and high acid pollution loads. In all regions, we identified periods with higher (1940-1960s) and lower (1970-1980s) growth than expected based on temperature. In the high-frequency domain, the effect of pollution on growth departure from temperature was limited and detectable exclusively in regions that were most impacted by pollution. In the low-frequency domain, the departures of growth from temperature were caused by combined effects of the changing seasonal window of tree growth sensitivity to climate and pollution load. These results highlight the need to recognize non-stationary noise in the relationship between temperature and tree growth.
Journal of Vegetation Science, 2016
Questions What was the main trigger of treeline ecotone advance – rising temperature or agricultu... more Questions What was the main trigger of treeline ecotone advance – rising temperature or agricultural land abandonment? Were the triggering factors of tree expansion homogeneous or did they differ between upper and lower parts of the treeline ecotone? Location Sudetes Mts., Central Europe (50° N, 15-17° E). Methods Data were gathered from the treeline ecotone formed by Picea abies at elevations ranging from 1250 to 1490 m. The study area experienced a 1 °C temperature increase over the last 100 yr and termination of cattle grazing and grass mowing in the first half of the 20th century. At 38 plots situated at lower (‘timberline’) and middle or upper (‘treeline’ and ‘outpost treeline’) parts of the treeline ecotone, the age structure of all seed origin P. abies was determined. Changes in tree cover and number of trees over the last 60–70 yr were assessed from aerial imagery. The history of agricultural land use for each plot was compiled. Finally, changes in tree establishment were modelled using climatic variables and land-use intensity. Results We found that tree establishment at treeline had occurred with a 30–40-yr lag after the main establishment peak at timberline. Whereas all treeline plots showed gradual increases in tree cover, timberline tree cover first increased, with some plots then undergoing thinning. Enhanced tree establishment was dependent mainly upon agricultural land abandonment. The effect of land-use changes was more important in the lower than in the upper part of the treeline ecotone. Increasing summer temperatures had a negative influence on seedling establishment in the last few decades. Conclusions Treeline ecotone densification was attributable to agricultural land abandonment across the entire treeline ecotone with the most important effect at timberline. More recently, seedling establishment has been limited by the effects of drought and/or absence of suitable microsites. We documented that one or two establishment pulses over 120 yr, together with enhanced growth since the 1980s, were able to trigger treeline ecotone advance.