Sixty individual ring-width series of oak (Quercus robur L.) from six sites in the northwestern Iberian Peninsula, ranging from 50 to 120 years, were grouped using hierarchical cluster analysis with different types of distance measures. Euclidean distances as well as other linkage distances based on statistics used to crossdate tree-ring series (Gleichläufigkeit and coefficient of correlation with its corresponding t-value) were compared. In addition, a new distance measure based on a corrected inversion of the Student’s t is proposed in the present paper, which takes into consideration the number of years used for series comparison. The Euclidean distances, commonly used in ecological analyses, inefficiently identified homogeneous units of trees based on their ring-width patterns. Among crossdating statistics, the correlation coefficient was more effective than Gleichläufigkeit, but the most satisfactory results were obtained when 1/t was used as distance measure. Finally, these methods of cluster analysis have been implemented into a computer program for future use of the dendrochronological community.

We investigated the climatic sensitivity of oak species across a wide elevation range in the southern Appalachian Mountains, an area where greater knowledge of oak sensitivity is desired. We developed three tree-ring chronologies for climatic analyses from oak cores taken from the Jefferson National Forest, Virginia, and Great Smoky Mountains National Park, Tennessee. We statistically compared the three chronologies with monthly climatic data from 1930 to 2005. The results of our analyses suggest that oak species in the southern Appalachian Mountains require a cool, moist summer for above average-growth to occur. The climate signal increased in duration from high to low elevational and latitudinal gradients, indicating a strong moisture-preconditioning signal during the previous fall at our lowest elevation site. A notable finding of this research was the degree of responsiveness in oaks that are growing in forest interior locations where strong climate sensitivity would not be expected because of the effects of internal stand dynamics. Furthermore, the relationships between evapotranspiration rates and the geographic factors of elevation, latitude, and aspect influence the climate signals at the three sites. Our research suggests that oaks located in a warm and xeric climate experience more physiological stress and put forth a more varied climatic response.

Dans le but de progresser dans la compréhension des déterminismes de l'allocation du carbone chez les feuillus, ce travail de recherche a consisté à étudier les effets de l'espèce (chênes, hêtre), du vieillissement, du climat et de la fertilité minérale sur la répartition du carbone assimilé par la photosynthèse entre croissance, stockage de composés de réserves carbonées et reproduction. Les effets du vieillissement ont été étudiés à l'échelle de la révolution forestière au travers de deux chronoséquences. Deux dispositifs d'amendement ont permis d'analyser les effets de la fertilité minérale du sol sur l'allocation du carbone dans l'arbre. Au cours du vieillissement du hêtre, l'allocation de carbone à la croissance, majoritaire pendant la phase juvénile, diminue progressivement au profit du stockage de composés de reserves et de la reproduction. En revanche, cette allocation demeure constante au cours du développement du chêne sessile. L'étude dendroclimatique des variations interannuelles de la croissance radiale montre également que les deux espèces répondent de façon contrastée aux variations climatiques. L'augmentation de la productivité à long terme a été mise en évidence pour les deux espèces. Au contraire du chêne, cette augmentation du niveau de croissance s'accompagne d'une forte variabilité interannuelle de la croissance radiale chez le hêtre. En condition de dépérissement chez le hêtre, l'allocation du carbone à la croissance chute drastiquement au profit de l'allocation aux réserves, permettant aux arbres dépérissants de maintenir des concentrations en composés de réserves glucidiques identiques à celles des arbres sains. Par ailleurs, l'amélioration du niveau de fertilité minérale de la station (par amendement) engendre une augmentation transitoire de la croissance radiale. Des concentrations en composés de réserves carbonées plus élevées chez les hêtres amendés ont été observées 15 ans après le traitement. Ces deux résultats suggèrent l'importance du niveau de réserves dans le maintien de l'intégrité physiologique des arbres adultes. Les résultats de cette étude des facteurs intrinsèques (âge,) et externes (fertilité minérale, climat) de variation de l'allocation du carbone chez le chêne et le hêtre, enrichie des enseignements de la littérature, ont permis de confirmer deux modèles de fonctionnement carboné contrastés. / In order to increase our understanding of carbon allocation in broadleaved species, our research consisted of studying the effects of ageing and soil mineral fertility on the carbon allocation between growth, storage and reproduction for oaks and beech. Ageing was studied over a forest succession using a chronosequences approach. Two liming experiments were investigated in order to study the variation of carbon allocation with soil mineral fertility in contrasting situations. The productivity decline in beech was followed by substantial changes in carbon allocation, with a continuous decrease of carbon allocation to growth, to the benefit of reproduction and storage functions. Conversely, carbon allocation in oak remained stable during its entire development. The dendrochronological analysis of inter-annual variations of radial growth shown also that beech and oaks presented contrasted climate-response of growth. There was clear evidence of a long-term increase with time in radial growth in both species. We also observed a long-term increase of inter-annual variations of growth with time for beech but not for oaks. The declining beech presented a sharp decreasing allocation to growth to the benefit of the carbon storage compounds. Moreover, liming induced an temporary increase of radial growth. However, the increase of carbohydrates in limed beeches was still significant 15 after treatment compare to the controls. These results suggested that the stock of carbohydrates is a key parameter of the physiological integrity for adult beeches. These results concerning the intrinsic (ageing) and external (liming, climate) factors of carbon allocation in oaks and beech enabled to confirm two contrasted models of carbon functioning.

No description available.

Optimum brood cover for wild turkeys is composed of herbaceous cover <0.5 m tall that conceals poults from predators and allows travel underneath. On tracts of hardwoods where early succession stages and young forest cover are scarce, a lack of understory development can limit turkey populations. Additionally, retaining oak on these sites after logging or habitat enhancement is important to provide future timber value and hard mast. I compared the effects of silvicultural practices (multiple fires [F], shelterwood cutting [S], shelterwood cutting with one fire [SF], retention cutting [R], retention cutting with multiple fires [RF], retention cutting with herbicide application [RH], and retention cutting with herbicide application and multiple fires [RHF]) with controls (C) on wild turkey brood habitat and oak regeneration in upland central hardwood stands. I measured structure and food resources to quantify the quality of wild turkey brood cover. Shelterwood and retention cuts increased photosynthetically active radiation. However, herbaceous, vine, and bramble groundcover did not increase. Woody regeneration was greater following canopy reduction and understory disturbance compared to C. Disturbance (fire or herbicide) was required to maintain vegetation at the ideal height for wild turkey broods. Soft mast production increased after canopy reduction with and without fire. Invertebrate biomass did not increase following any treatment, but availability exceeded the dietary requirements of a wild turkey brood. I also counted stem density of oak and competitor regeneration in response to these treatments. Seedlings <12.7 cm were ephemeral. S and SF had a greater density of oak stems >1.4 m than C and F. However, S and SF also had the greatest density of oak >1.4 m prior to treatment. Canopy reduction increased oak competitors, but prescribed fire reduced competitors. I recommend canopy reduction, followed by repeated low-intensity prescribed fire to maintain low groundcover to enhance brood habitat for wild turkeys in mature closed-canopy upland hardwood stands.

Ekens (Quercus robur) nordgräns sägs gå vid Dalälven, Limes Norrlandicus – den biologiska Norrlandsgränsen. Ludvikabygden skiljer sig naturgeografiskt och topografiskt från övriga Dalarna och tillhör Mälarens avrinningsområde. Trakten runt sjön Väsman har ett varmare klimat och fler soltimmar än den övriga bygden. För mellan 5.000-8.000 år sedan vandrade eken in i Sverige efter den senaste istiden. Det tog 3.000 år för den att sprida sig över hela Sverige som då hade en medeltemperatur 2-3? högre än idag.Ekens vegetationsperiod – när dygnsmedeltemperaturen överstiger 5? – är ca 7 månader för att ekollonen skall bli groningsdugliga och därmed kunna föröka sig naturligt. I Ludvikatrakten är vegetationsperioden ca 6 månader. Dalarnas skogar består av ? 1% ek. Årsmedeltemperaturen har i Mellansverige ökat ungefär 1? de senaste 30 åren. I framtiden får vi räkna med temperaturhöjningar på mellan 2-6? beroende på hur stort utsläpp som sker till atmosfären. Detta innebär att vi på dessa breddgrader får ett klimat liknande det i Centraleuropa med längre odlingssäsong. Det innebär också ökande skador på skog och växtlighet samt fler och mer extrema väderväxlingar.Syftet med den här undersökningen är att se om etablering av ek har skett i Ludvikatrakten de senaste decennierna samt vilka faktorer som kan påverka detta. Två separata områden om vardera 1,0 ha undersöktes. På område 1 i nordvästsluttning registrerades 20 exemplar av ek. På område 2 i västsluttning registrerades 28 exemplar av ek. Gamla ekar är en nyckelbiotop för sällsynta insekter och kryptogamer. Ek är stormfast p g a dess djupa rotsystem. Blandskog motverkar parasit-, insektsangrepp och rotröta samt gynnar biologisk mångfald och etablering av fältskikt. Ekens virke är dessutom eftertraktat då det är hårt och slitstarkt.

Isoprene is the most abundant volatile organic compound (VOC) emitted from vegetation, mainly trees. Because it plays an important role in tropospheric chemistry leading to formation of pollutants and enhancing the lifetime of the greenhouse gas methane, concern about the response of isoprene emissions to the rise in atmospheric CO2 concentration and global climate change has been increasing over the last few years. The consequences of predicted climate change will have complex repercussions on global isoprene emission. The increasing atmospheric CO2 per se will have direct effects on terrestrial vegetation since CO2 is the substrate of photosynthesis. Because photosynthesis is limited by CO2 at current ambient concentrations, an increase in CO2 is expected to increase leaf biomass (i.e. isoprene emitting surface). Predicted warmer climate, extended drought periods, the possible shift in plant species in favour of isoprene emitters and the increase in length of growing season, may cause an increase in global isoprene emissions with profound perturbations of air quality and the global carbon cycle. The aim of this thesis was to investigate the effect of environmental variables such as light, temperature, drought and leaf-to-air vapour pressure deficit (VPD), and the short- and long-term effect of atmospheric [CO2] on isoprene emission from temperate and tropical tree species. Both leaf and whole ecosystem level fluxes were studied. At the leaf scale, a short-term experiment with leaves of potted two-year old trees of Quercus virginiana was carried out, exposing plants to two drying-rewatering cycles. Leaf isoprene emission fell, but the process was considerably less sensitive to water stress than photosynthesis and stomatal conductance. In drought conditions, the large reduction in photosynthesis caused the percentage of fixed carbon lost as isoprene to increase as plants became more stressed, reaching peaks of 50% when photosynthesis was almost zero. Isoprene emissions also showed a strong negative linear relationship with pre-dawn leaf water potential (psi-leaf). In another experiment carried out at the large enclosed facility of Biosphere 2 (B2L, Arizona, USA), studying isoprene emission from leaves of three-year-old plants of Populus deltoides grown at three CO2 atmospheric concentrations (430, 800 and 1200 mu mol mol-1 CO2) in non-stressed conditions, instantaneous increases in atmospheric [CO2] always resulted in a reduction of isoprene emission and a stimulation of photosynthesis. Moreover, in the long-term, the CO2 inhibition effect for isoprene emission became a permanent feature for plants growing under elevated [CO2]. Again, isoprene emission was less responsive to drought than photosynthesis. Both water-stress and high VPD strongly stimulated isoprene emission and depressed photosynthetic rate as a result of stomatal closure and the resulting decreases in intercellular [CO2] (Ci). This also led to a dramatic increase in the proportion of assimilated carbon lost as isoprene. The effect of atmospheric elevated [CO2] and its interaction with high VPD and water stress on ecosystem gross isoprene production (GIP) and net ecosystem exchange of CO2 (NEE) in the Populus deltoides plantations was also studied. Although GIP and NEE showed a similar response to light and temperature, NEE was stimulated by elevated CO2 by 72% and depressed by high VPD, while GIP was inhibited by elevated CO2 by 58% and stimulated by high VPD. Similar to what was observed at leaf level, under water stress conditions GIP was stimulated in the short term and declined only when the stress was severe, whereas NEE started to decrease from the beginning of the experiment. This contrasting response led the percentage of assimilated carbon lost by the ecosystem as isoprene to increase as water stress progressed from 2.5% and 0.6% in well-watered conditions to 60% and 40% for the ambient and the elevated CO2 treatments, respectively. Again, we found water limitation and high VPD off-set the inhibitory effect of elevated CO2, leading to increased isoprene emissions. The effect of a mild water stress on GIP and gross primary production (GPP) was also observed in the model tropical rainforest mesocosm of B2L. Although GPP was reduced by 32% during drought, GIP was not affected and correlated very well with both light and temperature. The percentage of fixed C lost as isoprene tended to increase during drought because of the reduction in GPP. Consumption of isoprene by soil was observed in both systems. The isoprene sink capacity of litter-free soil of the agroforest stands showed no significant response to different CO2 treatments, while isoprene production was strongly depressed by elevated atmospheric [CO2]. In both mesocosms, drought suppressed the sink capacity, but the full sink capacity of dry soil was recovered within a few hours upon rewetting. In summary, elevated CO2 increased biomass production and photosynthesis while depressing isoprene production. However, both drought and VPD may off-set the CO2 effect and lead to enhanced isoprene emission. We conclude that the overall effect of global climate change could be of enhancing global isoprene emissions while depressing the soil sink, and that the soil uptake of atmospheric isoprene is likely to be modest but significant and needs to be taken into account for a comprehensive estimate of the global isoprene budget.

Problems developing tall oak seedlings of high abundance have become a concern throughout many eastern hardwood forests. The decline in oak seedling recruitment into canopy positions is often attributed to the increasing abundance of shade tolerant midstory species, especially red maple (Acer rubrum L.). Studies have shown that increasing light to the understory by way of a midstory removal has the ability to favor oak seedlings over competitors. The majority of studies to date have examined northern red (Quercus rubra L.) and cherrybark oak (Quercus pagoda Raf.) on productive sites, but relatively little is known about the effects of midstory removal on white (Quercus alba L.) and black (Quercus velutina L.) oaks, which are valuable species commercially and for wildlife. This study tests the effect of a midstory removal on oak seedlings and red maples six years after treatment implementation. In addition to seedling growth, survival, and competitiveness, the study also illustrates the changes in canopy structure and light transmittance resulting from the midstory removal. Basal clipping response of white oak seedlings following six years under a midstory removal is also examined as a method for regenerating more vigorous oaks. Results from this study support implementation of midstory removal as a method for improving oak regeneration.

Thesis (Ph. D.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 175-186). Available also in a digital version from Dissertation Abstracts.

Bottomland hardwood forests present a unique opportunity to examine the ecological response to hydrologically altered river and floodplain systems. These ecosystems, under natural conditions, are floodplain forests directly linked to the river. However, with major alterations to the river-floodplain system, bottomland hardwood forests can now provide insight into the loss of river connectivity and history of the flood pulse. This study reviewed the age distribution and growth of Quercus lyrata Walt. and the anatomical response of Quercus spp. to high magnitude floods in the 19th and 20th century in an old-growth Mississippi River floodplain forest in southeastern Missouri. Tree-ring samples collected from 43 trees at Big Oak Tree State Park contain physiological signatures (`flood rings') associated with growing season floods in the 20th century, and similar signatures are present in years corresponding to historical floods of the 19th century. The duration of 20th century Mississippi River growing season floods were examined to compare the occurrence of flood rings and the duration and intensity of floods on the Mississippi River at New Madrid, Missouri. Patterns in the occurrence of flood rings are developed as a response to alterations to the Mississippi River, river floodplain, and park hydrologic system.