Egbert Beuker

Long‐term effects of temperature on the wood production of Pinus sylvestris L. and Picea abies (L.) Karst. In old provenance experiments

Old provenance experiments with Scots pine and Norway spruce in Finland were used for assessing the long‐term effects of the projected climatic change on forest trees. The northernmost origins showed an increase in wood production when transferred southwards into a climate with an annual mean effective temperature sum close to that which is expected in northern areas as a result of the projected climatic change. A model is constructed with the estimated changes in wood production as a function of the annual mean temperature sum at the original location and the change in the annual mean temperature sum caused by the geographical transfer. The major changes in wood production are expected to occur in the northernmost areas of tree growth.

Seasonal variation in the frost hardiness of Scots pine and Norway spruce in old provenance experiments in Finland

Abstract Temperature is one of the major factors regulating the acclimation of forest trees to winter conditions in the boreal zone. The projected climate warming may therefore affect the overwintering pattern of trees. In this study, old provenance trials with Scots pine ( Pinus sylvestris L.) and Norway spruce ( Picea abies (L.) Karst) were used to simulate the effects of a warmer climate on the seasonal variation in frost hardiness. In both species, there were differences between northern and southern provenances in the timing of bud and needle hardening during autumn. The northern provenances hardened earlier. During the dehardening phase in spring, no significant difference was found between the provenances. For buds of Norway spruce, fluctuations in hardiness that coincided rather well with fluctuations in the ambient temperature were observed during mid-winter. The results of this study do not support the theory that climate warming will increase the risk of frost damage in Scots pine and Norway spruce in boreal areas. Further research is recommended.

Effects of Photoperiod and Thermal Time on the Growth Rhythm of Pinus sylvestris Seedlings

Abstract The effects of photoperiod and thermal time and their interaction on the timing of growth cessation were examined in seedlings of Scots pine (Pinus sylvestris L.) in greenhouses with 20°C day and 10°C night temperatures combined with the natural development of the photoperiod. Sowing was repeated five times during both 1995 and 1996 using origins from different altitudes and latitudes (>60°N) in Sweden and Finland. In this way, gradients in temperature sums at a nearly constant photoperiod and different photoperiods at constant temperature sums were obtained. After the first growing season the timing of growth cessation of seedlings from different origins was flexible, i.e. it was determined by the specific combinations of accumulated temperature sum and night length illustrated by fitted straight lines. The photoperiod at the site of origin was a dominant factor in determining the timing of growth cessation in origins from northern latitudes. Because of predetermined growth, the sowing date did ...

Differences in leaf characteristics between ozone-sensitive and ozone-tolerant hybrid aspen (Populus tremula × Populus tremuloides) clones

The authors analyzed a suite of leaf characteristics that might help to explain the difference between ozone-sensitive and ozone-tolerant hybrid aspen (Populus tremula L. x Populus tremuloides Michx.) clones. An open-field experiment comprising ambient ozone and 1.5x ambient ozone concentration (about 35 ppb) and two soil nitrogen regimes (60 and 140 kg N ha(-1) year(-1)) was conducted over two growing seasons on potted plants of eight hybrid aspen clones. Four of the clones had previously been determined to be ozone sensitive based on impaired growth in response to elevated ozone concentration. Photosynthetic rate, chlorophyll fluorescence, and concentrations of chlorophyll, protein and carbohydrates were analyzed three times during the second growing season, and foliar phenolic concentrations were measured at the end of the second growing season. Nitrogen amendment counteracted the effects of ozone, but had no effect on growth-related ozone sensitivity of the clones. Ozone-sensitive clones had higher photosynthetic capacity and higher concentrations of Rubisco and phenolics than ozone-tolerant clones, but the effects of ozone were similar in the sensitive and tolerant groups. Nitrogen addition had no effect on phenolic concentration, but elevated ozone concentration increased the concentrations of chlorogenic acid and (+)-catechin. This study suggests that condensed tannins and catechin, but not salicylates or flavonol glycosides, play a role in the ozone tolerance of hybrid aspen.

Impacts of Climate Change on Cold Hardiness of Conifers

Due to increased anthropogenic emissions into the atmosphere, concentrations of CO2 and other greenhouse gases have been increasing globally during the past decades. Despite realized and planned control measures, this increase is predicted to continue in the future. Due to the accompanying changes in the physical properties of the atmosphere, the air temperature of the globe is predicted to rise dramatically in the future. According to most meteorological scenarios, the increase of the global mean temperature will be 1 to 4.5°C by the year 2100. However, it is also predicted that the level of warming will be more pronounced in the north than in the south and greater during winter than during summer months (IPCC 1996).

Data quality in field surveys: methods and results for tree condition, phenology, growth, plant diversity and foliar injury due to ozone

Abstract Vegetation-related response variables adopted in the ICP Forests are related to health, growth, phenology, and diversity. Their assessment and measurement is subject to errors, which need to be controlled and documented. To do this, data quality requirements (DQRs) and intercomparison exercises were implemented. During 2009 and 2010, 111–260 field crews took part in different exercises organized across Europe. Results revealed that, while for some variables (e.g., tree diameter, standing basal area, ozone injury, species diversity) DQRs were substantially achieved, problems still exist for other measurements/calculations (tree height, volume and increment, crown base height, crown symptoms identification and description). In some cases, achievement of DRQs was partly due to relaxed DQRs. While the recent progresses in Quality Assurance/Quality Control for field surveys are promising, further effort is necessary to sharpen DQRs, refine standard operating procedures, and reinforce training.

Chapter 9 - Tree Phenology

The chapter describes methodologies for harmonized phenological assessments based on a limited set of development phases: flushing, flowering, secondary flushing, color change, and leaf/needle fall. Manual phenological observations are based on a brief examination in the forest stands. More recently, the use of terrestrial digital image photography for forest phenology monitoring has been adopted. Vegetation indices, such as the normalized difference vegetation index (NDVI) have been used for many years to quantify the phenology of different ecosystems. For satellite-based remote sensing of vegetation phenology, phenological metrics are derived from time series of optical data and represent the only possible assessment of phenology over large and inaccessible regions. All indirect methods using optical vegetation indices from digital camera or NDVI sensors need to be validated against ground observations, for which manual tree phenological observations from the forest monitoring plots are often used. Examples from phenological monitoring in Slovenia, France, United Kingdom, and Finland are presented.