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Veeneiken zijn (veen)restanten van eiken uit moerasbossen op laagveen. Ze vormen interessant materiaal voor dendrochronologisch onderzoek. Er is voor deze eiken inmiddels een chronologie opgebouwd over de jaren 3600 BC tot 563 AD. Onderzoek aan veeneiken in Nederland en Noordwest-Europa en aan twee (pre)historische moerasbossen in Nederland (locaties Zwolle en Ypenburg) wordt gebruikt voor landschap- en klimaatreconstructie

MARKERS INSIDE WOOD – TREE RINGS AS ARCHIVES OF INSECT OUTBREAKS, DRIFT-SAND DYNAMICS AND SPRING FLOODING Trees are long-living organisms that record ecologically relevant information in their xylem that can be accessed by dendrochronology, the study of tree rings. Specific environmental events like frost, fire, floods, burial or wounding may drastically alter the anatomy of tree rings and consequently may leave markers inside trees. These wood-anatomical markers have shown a high potential for studying past environmental events with an annual or even intra-annual temporal resolution. In this thesis, the temporal resolution of wood-anatomical markers was studied to date wounds made by invasive Anoplophora beetles. In addition, the accuracy of dating drift-sand dynamics and spring flooding events was studied using wood-anatomical changes, which were expected to occur after drastic changes in the stem and root environment. It was hypothesised that all these wood-anatomical markers can be used with an intra-annual resolution. Field studies in combination with experiments were used to study tree growth and the formation of wood-anatomical markers in Japanese maple (Acer palmatum Thunb.) and pedunculate oak (Quercus robur L.). It was shown that wounds in Japanese maple can be assigned to three different phases related to tree-ring development: (1) wounds that originated during dormancy are located at the tree-ring boundary; (2) wounds that originated during the growing season are located within the tree ring. If wound-xylem formation was observed locally around the wound (3), it could either imply that the wound originated at the very end of the growing season or just before the onset of radial growth or during dormancy when temperature was high. Dating wounds caused by the formation of exit holes has proved to be very significant in fighting invasive insect outbreaks. By pinpointing the exact year and season when Anoplophora beetles emerged, it can be substantiated whether exit holes in imported trees were formed at the location of import. This knowledge can subsequently be used to draw up customised eradication measures and allocate proper surveillance plans and population dynamics can be reconstructed. Living trees in drift-sand areas may contain burial or exposure signals even if the sand under which they were buried has long since disappeared. Anatomical changes in pedunculate oak trees due to burial are not a result of physical changes in the stem environment that directly affect the cambium. Instead they are most likely the result of adventitious root formation that transforms lower parts of the stem into root, and concomitantly induces a change from stem to root anatomy. As the formation of a wood-anatomical marker caused by burial can be delayed by many years or might be entirely absent, depending on the formation of adventitious root formation, its presence only allows for an estimate on minimum burial age. Flood rings containing anomalously small earlywood vessels in pedunculate oak are formed in response to spring flooding within a narrow time window related to cambial phenology. They can be induced if a flooding event has occurred for at least two weeks during spring. The extreme reduction in vessel size is a consequence of a delay in vessel formation due to anoxic conditions related to flooding. Flood rings however, provide only limited information on the duration of flooding, as the flooding may have lasted for months (during winter) before it is recorded. It is concluded that the origin of wood-anatomical markers largely determines the temporal resolution. Markers induced by wounding or flooding show a high intra-annual temporal resolution and immediate effect on tree functioning, whereas burial might not be recorded three years after the triggering events. The different wood-anatomical markers addressed in this thesis illustrate the relevance of studying the mechanism behind the formation of markers for correct interpretation of the specific triggering factor as well as their temporal resolution. Only with this knowledge it becomes possible to reliably use wood-anatomical markers as archives to understand and reconstruct dynamics in geomorphic, entomologic, pathogenic or climatic factors.

Boktorren die uitvliegen laten sporen na in hun kraamkamer. Promovendus Paul Copini leest die sporen in jaarringen van bomen en kan zeggen wanneer de boktor is geboren. Een oordeel met gewicht.

MARKERS INSIDE WOOD – TREE RINGS AS ARCHIVES OF INSECT OUTBREAKS, DRIFT-SAND DYNAMICS AND SPRING FLOODING Trees are long-living organisms that record ecologically relevant information in their xylem that can be accessed by dendrochronology, the study of tree rings. Specific environmental events like frost, fire, floods, burial or wounding may drastically alter the anatomy of tree rings and consequently may leave markers inside trees. These wood-anatomical markers have shown a high potential for studying past environmental events with an annual or even intra-annual temporal resolution. In this thesis, the temporal resolution of wood-anatomical markers was studied to date wounds made by invasive Anoplophora beetles. In addition, the accuracy of dating drift-sand dynamics and spring flooding events was studied using wood-anatomical changes, which were expected to occur after drastic changes in the stem and root environment. It was hypothesised that all these wood-anatomical markers can be used with an intra-annual resolution. Field studies in combination with experiments were used to study tree growth and the formation of wood-anatomical markers in Japanese maple (Acer palmatum Thunb.) and pedunculate oak (Quercus robur L.). It was shown that wounds in Japanese maple can be assigned to three different phases related to tree-ring development: (1) wounds that originated during dormancy are located at the tree-ring boundary; (2) wounds that originated during the growing season are located within the tree ring. If wound-xylem formation was observed locally around the wound (3), it could either imply that the wound originated at the very end of the growing season or just before the onset of radial growth or during dormancy when temperature was high. Dating wounds caused by the formation of exit holes has proved to be very significant in fighting invasive insect outbreaks. By pinpointing the exact year and season when Anoplophora beetles emerged, it can be substantiated whether exit holes in imported trees were formed at the location of import. This knowledge can subsequently be used to draw up customised eradication measures and allocate proper surveillance plans and population dynamics can be reconstructed. Living trees in drift-sand areas may contain burial or exposure signals even if the sand under which they were buried has long since disappeared. Anatomical changes in pedunculate oak trees due to burial are not a result of physical changes in the stem environment that directly affect the cambium. Instead they are most likely the result of adventitious root formation that transforms lower parts of the stem into root, and concomitantly induces a change from stem to root anatomy. As the formation of a wood-anatomical marker caused by burial can be delayed by many years or might be entirely absent, depending on the formation of adventitious root formation, its presence only allows for an estimate on minimum burial age. Flood rings containing anomalously small earlywood vessels in pedunculate oak are formed in response to spring flooding within a narrow time window related to cambial phenology. They can be induced if a flooding event has occurred for at least two weeks during spring. The extreme reduction in vessel size is a consequence of a delay in vessel formation due to anoxic conditions related to flooding. Flood rings however, provide only limited information on the duration of flooding, as the flooding may have lasted for months (during winter) before it is recorded. It is concluded that the origin of wood-anatomical markers largely determines the temporal resolution. Markers induced by wounding or flooding show a high intra-annual temporal resolution and immediate effect on tree functioning, whereas burial might not be recorded three years after the triggering events. The different wood-anatomical markers addressed in this thesis illustrate the relevance of studying the mechanism behind the formation of markers for correct interpretation of the specific triggering factor as well as their temporal resolution. Only with this knowledge it becomes possible to reliably use wood-anatomical markers as archives to understand and reconstruct dynamics in geomorphic, entomologic, pathogenic or climatic factors.

Tropical forests cover only 7% of the earth’s land surface, but harbour almost half of the world’s biodiversity. These forests also provide many ecosystem services, such as the storage of carbon and the regulation of local and regional climate, and many goods such as timber and fruits. Furthermore, tropical forests contribute disproportionately to the global carbon cycle, storing an estimated 25% of the carbon stocks on land and accounting for a third of the terrestrial net primary productivity. Therefore, changes in forest cover or in the net uptake or loss of carbon by forests directly influences the global carbon cycle. Tropical forests are under increasing anthropogenic pressure and are undergoing rapid changes due to deforestation, conversion to other land uses and logging. Additionally, there is evidence that pristine and intact tropical forests are undergoing changes due to the effects of climate change. Concerted increases in biomass and tree growth have been found in studies monitoring intact tropical forests, suggesting that they acted as considerable carbon sinks over the past decades. On the other hand, decreasing or fluctuating forest growth and biomass have also been noted. These different changes have been attributed to different climatic drivers: growth increases have been suggested to arise from growth stimulation by increasing atmospheric CO2 concentrations, while growth decreases have been interpreted to reflect the limiting effects of increased temperature on growth. As monitoring plots usually cover only a few decades, it is still unclear whether these changes are pervasive or whether they simply reflect the effect of short-term climatic fluctuations on tree growth. Assessing whether changes have occurred over centennial scales is thus crucial to understanding whether and how tropical forests are reacting to climatic changes. In this thesis we apply tree-ring analysis on a pantropical study to assess longterm changes in growth of tropical forest trees. Tree-ring analysis was used to measure long-term growth rates of ~1350 trees of different species coming from three sites across the tropics. Trends in growth over the last two centuries were then analysed using an established an a new trend-detection method. Additionally, we applied the long-term growth data from rings to improve the evaluation of forest management practices in Cameroon. All samples were collected and measured within the TROFOCLIM project led by Pieter Zuidema. The project also includes two other PhD theses and sample collection was divided among the three PhD projects and the three sites: in Bolivia (samples collected by Peter van der Sleen), Cameroon (by me) and in Thailand (by Mart Vlam). The main objectives of this thesis were: (1) to assess the potential for using treerings in a wet tropical forest in Central Africa; (2) to project timber yields in the next logging round for four Cameroonian tree species; (3) to evaluate the sensitivity and accuracy of four commonly used methods to detect long-term trends in tree-ring data; and (4) to detect whether growth rates of tropical forest trees have changed over the past ~150 years. In Chapter 2 of this dissertation, we evaluated whether growth rings are formed annually in the wood of tree species growing under very high levels of precipitation (>4000 mm) in an African tropical forest. For this purpose, we assessed whether ring structures are formed in the wood of the 22 commercially exploited tree species and found that ring structures are indeed formed by more than half of these species (in 14 species), though with varying ring clarity. On four species we proved the annual character of ring formation using radiocarbon bomb-peak dating. That rings are formed under such high levels of precipitation is surprising, as these conditions are considered improper to induce ring formation. These results suggest that the potential of tree-rings analysis is more or less similar across the tropics. Based on our results and that of other studies, we estimate that tree rings can be used to measure tree growth and ages for around a quarter to a third of tropical tree species. Worldwide, over 400 million hectares of tropical forests are set aside for timber production. Attaining sustainable use of these forests is very important, in the light of the important role of tropical forests in retaining biodiversity and storing carbon. Ensuring that timber species are not overexploited is key to ensure that forest use is sustainable and entails finding a balance between economic gains and the (ecological) sustainability of logging operations. In Chapter 3, we integrated growth data from tree-rings with logging inventory data to forecast whether timber yields can be sustained in the next harvest round for four timber species in Cameroon. Under current logging practices, future logging yields were predicted to reduce moderately to strongly for all species. These yield reductions are worrisome for forest conservation, as loss of economic value may lead to conversion of forests to other land uses. We recommend that such calculations are needed for more species and argue that these simulations should include the effects of logging and eventual silvicultural measures on the growth and survival of trees. Lifetime tree growth data – as acquired by tree-ring analysis – contains longterm trends in growth that reflect the ontogenetic development of an individual or species, i.e., these data contains an age/size signal in growth. In Chapter 4 we evaluate the sensitivity, accuracy and reliability to detect long-term trends in growth of four methods that are commonly used to disentangle these age/size trends from long-term growth trends. We applied these growth-trend detection methods to measured growth data from tree rings and to simulated growth trajectories on which increasing an decreasing trends were imposed. The results revealed that the choice of method influences results of growth-trend studies. We recommend applying two methods simultaneously when analysing long-term trends – the Regional Curve Standardization and Size Class Isolation – as these methods are complementary and showed the highest reliability to detecting long-term growth changes. In Chapter 5, we analysed long-term growth trends in tropical forest trees using a pantropical approach applying the two recommended growth-trend detection methods. We showed that growth rates for most of the 13 tropical tree species, from the three sites across the tropics, decreased over the last centuries. These species-level changes may have important demographic consequences and may eventually lead to shifts in the species composition of tropical forests. We found no strong growth changes when analysing trends aggregated per site or across sites: only weak growth reductions were detected for the Thai site and across sites. These findings contrast growth increases that would be expected if tree growth is stimulated by increased ambient CO2. These growth reductions suggest worsening growth conditions for several tropical tree species, and could result from the negative effect of temperature increases on tree growth, or reflect the effect of large-scale disturbances on these forests. If one image becomes clear from this thesis it is that long-term data are crucial to enhance the management of tropical forests and to quantify changes happening in these forests. Tree-ring analysis provides this long-term perspective for tree growth and is thus a great tool to evaluate changes in the growth of trees, including for tropical species. One of the most important finding of this thesis is that many tropical species show long-term decreases in growth. These results suggest that the commonly assumed growth increases tropical forests, based on measurements over the last couple of decades, may be incorrect. This discrepancy in results could have strong consequences, among others leading to erroneous predictions of the carbon dynamics of tropical forests under future climate change. Combining monitoring plot data (to analyse short-term changes in growth and species composition) with remotely sensed data (to accurately determine forest land cover) and with the long-term growth data from tree rings is probably the best way forward to relate recent findings of short-term changes in tree growth and forest biomass to changes over the past centuries. Such integrative approaches are needed to better quantify and understand the effects of climate change on tropical forests.

Tropical forests cover only 7% of the earth’s land surface, but harbour almost half of the world’s biodiversity. These forests also provide many ecosystem services, such as the storage of carbon and the regulation of local and regional climate, and many goods such as timber and fruits. Furthermore, tropical forests contribute disproportionately to the global carbon cycle, storing an estimated 25% of the carbon stocks on land and accounting for a third of the terrestrial net primary productivity. Therefore, changes in forest cover or in the net uptake or loss of carbon by forests directly influences the global carbon cycle. Tropical forests are under increasing anthropogenic pressure and are undergoing rapid changes due to deforestation, conversion to other land uses and logging. Additionally, there is evidence that pristine and intact tropical forests are undergoing changes due to the effects of climate change. Concerted increases in biomass and tree growth have been found in studies monitoring intact tropical forests, suggesting that they acted as considerable carbon sinks over the past decades. On the other hand, decreasing or fluctuating forest growth and biomass have also been noted. These different changes have been attributed to different climatic drivers: growth increases have been suggested to arise from growth stimulation by increasing atmospheric CO2 concentrations, while growth decreases have been interpreted to reflect the limiting effects of increased temperature on growth. As monitoring plots usually cover only a few decades, it is still unclear whether these changes are pervasive or whether they simply reflect the effect of short-term climatic fluctuations on tree growth. Assessing whether changes have occurred over centennial scales is thus crucial to understanding whether and how tropical forests are reacting to climatic changes. In this thesis we apply tree-ring analysis on a pantropical study to assess longterm changes in growth of tropical forest trees. Tree-ring analysis was used to measure long-term growth rates of ~1350 trees of different species coming from three sites across the tropics. Trends in growth over the last two centuries were then analysed using an established an a new trend-detection method. Additionally, we applied the long-term growth data from rings to improve the evaluation of forest management practices in Cameroon. All samples were collected and measured within the TROFOCLIM project led by Pieter Zuidema. The project also includes two other PhD theses and sample collection was divided among the three PhD projects and the three sites: in Bolivia (samples collected by Peter van der Sleen), Cameroon (by me) and in Thailand (by Mart Vlam). The main objectives of this thesis were: (1) to assess the potential for using treerings in a wet tropical forest in Central Africa; (2) to project timber yields in the next logging round for four Cameroonian tree species; (3) to evaluate the sensitivity and accuracy of four commonly used methods to detect long-term trends in tree-ring data; and (4) to detect whether growth rates of tropical forest trees have changed over the past ~150 years. In Chapter 2 of this dissertation, we evaluated whether growth rings are formed annually in the wood of tree species growing under very high levels of precipitation (>4000 mm) in an African tropical forest. For this purpose, we assessed whether ring structures are formed in the wood of the 22 commercially exploited tree species and found that ring structures are indeed formed by more than half of these species (in 14 species), though with varying ring clarity. On four species we proved the annual character of ring formation using radiocarbon bomb-peak dating. That rings are formed under such high levels of precipitation is surprising, as these conditions are considered improper to induce ring formation. These results suggest that the potential of tree-rings analysis is more or less similar across the tropics. Based on our results and that of other studies, we estimate that tree rings can be used to measure tree growth and ages for around a quarter to a third of tropical tree species. Worldwide, over 400 million hectares of tropical forests are set aside for timber production. Attaining sustainable use of these forests is very important, in the light of the important role of tropical forests in retaining biodiversity and storing carbon. Ensuring that timber species are not overexploited is key to ensure that forest use is sustainable and entails finding a balance between economic gains and the (ecological) sustainability of logging operations. In Chapter 3, we integrated growth data from tree-rings with logging inventory data to forecast whether timber yields can be sustained in the next harvest round for four timber species in Cameroon. Under current logging practices, future logging yields were predicted to reduce moderately to strongly for all species. These yield reductions are worrisome for forest conservation, as loss of economic value may lead to conversion of forests to other land uses. We recommend that such calculations are needed for more species and argue that these simulations should include the effects of logging and eventual silvicultural measures on the growth and survival of trees. Lifetime tree growth data – as acquired by tree-ring analysis – contains longterm trends in growth that reflect the ontogenetic development of an individual or species, i.e., these data contains an age/size signal in growth. In Chapter 4 we evaluate the sensitivity, accuracy and reliability to detect long-term trends in growth of four methods that are commonly used to disentangle these age/size trends from long-term growth trends. We applied these growth-trend detection methods to measured growth data from tree rings and to simulated growth trajectories on which increasing an decreasing trends were imposed. The results revealed that the choice of method influences results of growth-trend studies. We recommend applying two methods simultaneously when analysing long-term trends – the Regional Curve Standardization and Size Class Isolation – as these methods are complementary and showed the highest reliability to detecting long-term growth changes. In Chapter 5, we analysed long-term growth trends in tropical forest trees using a pantropical approach applying the two recommended growth-trend detection methods. We showed that growth rates for most of the 13 tropical tree species, from the three sites across the tropics, decreased over the last centuries. These species-level changes may have important demographic consequences and may eventually lead to shifts in the species composition of tropical forests. We found no strong growth changes when analysing trends aggregated per site or across sites: only weak growth reductions were detected for the Thai site and across sites. These findings contrast growth increases that would be expected if tree growth is stimulated by increased ambient CO2. These growth reductions suggest worsening growth conditions for several tropical tree species, and could result from the negative effect of temperature increases on tree growth, or reflect the effect of large-scale disturbances on these forests. If one image becomes clear from this thesis it is that long-term data are crucial to enhance the management of tropical forests and to quantify changes happening in these forests. Tree-ring analysis provides this long-term perspective for tree growth and is thus a great tool to evaluate changes in the growth of trees, including for tropical species. One of the most important finding of this thesis is that many tropical species show long-term decreases in growth. These results suggest that the commonly assumed growth increases tropical forests, based on measurements over the last couple of decades, may be incorrect. This discrepancy in results could have strong consequences, among others leading to erroneous predictions of the carbon dynamics of tropical forests under future climate change. Combining monitoring plot data (to analyse short-term changes in growth and species composition) with remotely sensed data (to accurately determine forest land cover) and with the long-term growth data from tree rings is probably the best way forward to relate recent findings of short-term changes in tree growth and forest biomass to changes over the past centuries. Such integrative approaches are needed to better quantify and understand the effects of climate change on tropical forests.

Forests in the wet tropics harbour an incredible biodiversity, provide many ecosystem services and regulate climatic conditions on regional scales. Tropical forests are also a major component of the global carbon cycle, storing 25% of the total terrestrial carbon and accounting for a third of net primary production. This means that changes in forest structure and forest cover in the wet tropics will not only affect biodiversity and ecosystem services, but also have implications for the global carbon cycle and – as a result – may speed up or slow down global warming. Deforestation rates are still high in the tropics and have profoundly affected the extent of forests in many countries. Additionally, there are indications that undisturbed and pristine tropical forests are changing. The most notable changes found by the monitoring of permanent forest plots are an increase of tree growth and forest biomass per unit of surface area over the last decades. If this is indeed the case, it would entail that the world’s tropical forests are potentially absorbing a significant fraction of human caused CO2emissions and as such are mitigating global warming. However, increased tree growth and forest biomass have not been found in all studies. Furthermore, it is unknown whether the observed changes in intact forests are part of a long-term change, or merely reflect decadal scale fluctuations. These uncertainties lead to an ongoing debate on whether tree growth and forest biomass have increased in tropical forests and – if so – to what extent. In addition, there is also a scientific discussion on the factor(s) that could underlie the potential changes in tree growth and forest biomass. Possibly, they are caused by an internal driver, like the lasting effect of large scale disturbances in the past, or by external drivers. Possible external factors affecting tropical forest dynamics are (1) climate change (temperature and precipitation), (2) increased nutrient depositions and (3) increased atmospheric CO2concentration. In this thesis, I investigated the environmental changes that could have formed the basis for changes in tropical tree growth. I used two relatively new tools in tropical forest ecology: tree-ring measurements and stable isotope analyses. Tree-ring widths were measured to obtain long-term information on tree growth. Stable isotopes in the wood of tree rings were analysed to provide information on the environmental and physiological drivers of tree growth changes. This thesis is part of a larger project on the long-term changes in intact forests in the wet tropics (the TroFoClim project, led by Pieter Zuidema) and also includes the PhD theses of Mart Vlam and Peter Groenendijk. In this project, ~1400 trees of 15 species were examined that were collected in three forest sites distributed across the tropics (in Bolivia, Cameroon and Thailand). For the assessment of long-term changes in growth and stable isotopes, it is important to understand shorter term fluctuations due to forest dynamics (i.e. gap formation), because these interfere with changes on a longer temporal scale. The formation of a gap in a closed canopy forest, after the death of a tree, can cause considerable environmental changes in the surrounding area, e.g. in light, nutrient and water availability. This can strongly affect the growth rates of the remaining trees. However, in most studies the environmental drivers of changes in tree growth after gap formation are not considered. In CHAPTER 2 I measured carbon isotope discrimination (Δ13C) in annual growth rings of Peltogyne cf.heterophylla, from a moist forest in North-eastern Bolivia, and evaluated the environmental drivers of growth responses after gap formation. Growth and Δ13C was compared between the seven years before and after gap formation. Forty-two trees of different sizes were studied, half of which grew close (

Forests in the wet tropics harbour an incredible biodiversity, provide many ecosystem services and regulate climatic conditions on regional scales. Tropical forests are also a major component of the global carbon cycle, storing 25% of the total terrestrial carbon and accounting for a third of net primary production. This means that changes in forest structure and forest cover in the wet tropics will not only affect biodiversity and ecosystem services, but also have implications for the global carbon cycle and – as a result – may speed up or slow down global warming. Deforestation rates are still high in the tropics and have profoundly affected the extent of forests in many countries. Additionally, there are indications that undisturbed and pristine tropical forests are changing. The most notable changes found by the monitoring of permanent forest plots are an increase of tree growth and forest biomass per unit of surface area over the last decades. If this is indeed the case, it would entail that the world’s tropical forests are potentially absorbing a significant fraction of human caused CO2emissions and as such are mitigating global warming. However, increased tree growth and forest biomass have not been found in all studies. Furthermore, it is unknown whether the observed changes in intact forests are part of a long-term change, or merely reflect decadal scale fluctuations. These uncertainties lead to an ongoing debate on whether tree growth and forest biomass have increased in tropical forests and – if so – to what extent. In addition, there is also a scientific discussion on the factor(s) that could underlie the potential changes in tree growth and forest biomass. Possibly, they are caused by an internal driver, like the lasting effect of large scale disturbances in the past, or by external drivers. Possible external factors affecting tropical forest dynamics are (1) climate change (temperature and precipitation), (2) increased nutrient depositions and (3) increased atmospheric CO2concentration. In this thesis, I investigated the environmental changes that could have formed the basis for changes in tropical tree growth. I used two relatively new tools in tropical forest ecology: tree-ring measurements and stable isotope analyses. Tree-ring widths were measured to obtain long-term information on tree growth. Stable isotopes in the wood of tree rings were analysed to provide information on the environmental and physiological drivers of tree growth changes. This thesis is part of a larger project on the long-term changes in intact forests in the wet tropics (the TroFoClim project, led by Pieter Zuidema) and also includes the PhD theses of Mart Vlam and Peter Groenendijk. In this project, ~1400 trees of 15 species were examined that were collected in three forest sites distributed across the tropics (in Bolivia, Cameroon and Thailand). For the assessment of long-term changes in growth and stable isotopes, it is important to understand shorter term fluctuations due to forest dynamics (i.e. gap formation), because these interfere with changes on a longer temporal scale. The formation of a gap in a closed canopy forest, after the death of a tree, can cause considerable environmental changes in the surrounding area, e.g. in light, nutrient and water availability. This can strongly affect the growth rates of the remaining trees. However, in most studies the environmental drivers of changes in tree growth after gap formation are not considered. In CHAPTER 2 I measured carbon isotope discrimination (Δ13C) in annual growth rings of Peltogyne cf.heterophylla, from a moist forest in North-eastern Bolivia, and evaluated the environmental drivers of growth responses after gap formation. Growth and Δ13C was compared between the seven years before and after gap formation. Forty-two trees of different sizes were studied, half of which grew close (

Boktorren die uitvliegen laten sporen na in hun kraamkamer. Promovendus Paul Copini leest die sporen in jaarringen van bomen en kan zeggen wanneer de boktor is geboren. Een oordeel met gewicht.

Veeneiken zijn (veen)restanten van eiken uit moerasbossen op laagveen. Ze vormen interessant materiaal voor dendrochronologisch onderzoek. Er is voor deze eiken inmiddels een chronologie opgebouwd over de jaren 3600 BC tot 563 AD. Onderzoek aan veeneiken in Nederland en Noordwest-Europa en aan twee (pre)historische moerasbossen in Nederland (locaties Zwolle en Ypenburg) wordt gebruikt voor landschap- en klimaatreconstructie

Distinct zones of growth were usually only found in tropical deciduous trees with a periodically resting cambium. Reversedly a periodically resting cambium proved not to produce always distinct zones. All possible combinations of cambial activity and the formation of zones were shown to occur in the tropics. The zones could be distinguished in cross-sections by a) radial compression of the fibres formed before the new burst of cambial activity, b) a thin circular layer of parenchyma, c) a thin layer of libriform fibres, d) alternating widths of layers of libriform fibres and parenchyma, e) layers alternating in vessel diameter or arrangement. Most species formed either marked zones in east and west Java or less marked or irregular zones in the more even climate of west Java. Only a few species formed no growth zones at all in the more even climate.Young trees often did not form growth zones or only temporary ones, so that the zones were not a direct indication of age. Imported evergreen trees (except leafy trees with individually flushing branches) from cooler climates had no zones or vague ones. Renewed growth in leafy trees was always induced by substances or stimuli conducted from the sprouting leaf buds (and later from leaves) or from flowers (in leafless trees).