Current issue: 56(4)
An ecophysiological growth process model, called INCA, for simulating the growth and development of a young walnut tree (Juglans regia L.) during three or four years, is presented. This tool, currently under development, aims at integrating architectural and physiological knowledge of the processes involved, in order to give a more rational understanding of the pruning operation. The model describes a simple three-dimensional representation of tree crown, solar radiation interception, photosynthesis, respiration, growth and partitioning of assimilates to leaves, stems, branches and roots. It supports the hypothesis that the tree grows as a collection of semiautonomous, interacting organs that compete for resources, based on daily sink strengths and proximity to sources. The actual growth rate of organs is not predetermined by empirical data, but reflects the pattern of available resources. The major driving variables are solar radiation, temperature, topological, geometrical and physiological factors. Outputs are hourly and daily photosynthate production and respiration, daily dimensional growth, starch storage, biomass production and total number of different types of organ. The user can interact or override any or all of the input variables to examine the effects of such changes on photosynthate production and growth. Within INCA, the tree entities and the surrounding environment are structured in a frame-based representation whereas the processes are coded in a rule-based language. The simulation mechanism is primarily based on the rule chaining capabilities of an inference engine.
There is no doubt that tree survival, growth, and reproduction in North America's boreal forests would be directly influenced by the projected changes in climate if they occur. The indirect effects of climate change may be of even greater importance, however, because of their potential for altering the intensity, frequency, and perhaps even the very nature of the disturbance regimes which drive boreal forest dynamics. Insect defoliator populations are one of the dominating disturbance factors in North America's boreal forests and during outbreaks trees are often killed over vast forest areas. If the predicted shifts in climate occur, the damage patterns caused by insects may be considerably changed, particularly those of insects whose temporal and spatial distributions are singularly dependent on climatic factors. The ensuing uncertainties directly affect depletion forecasts, pest hazard rating procedures, and long-term planning for pest control requirements. Because the potential for wildfire often increases in stands after insect attack, uncertainties in future insect damage patterns also lead to uncertainties in fire regimes. In addition, because the rates of processes key to biogeochemical and nutrient recycling are influenced by insect damage, potential changes in damage patterns can indirectly affect ecosystem resilience and the sustainability of the multiple uses of the forest resource.
In this paper, a mechanistic perspective is developed based on available information describing how defoliating forest insects might respond to climate warming. Because of its prevalence and long history of study, the spruce budworm, Choristoneura fumiferana Clem. (Lepidoptera: Tortricidae), is used for illustrative purposes in developing this perspective. The scenarios that follow outline the potential importance of threshold behaviour, historical conditions, phenological relationships, infrequent but extreme weather, complex feedbacks, and natural selection. The urgency of such considerations is emphasized by reference to research suggesting that climate warming may already be influencing some insect lifecycles.
This paper aims at investigating which factors, in the point of view of the entrepreneur, define the choice of long-distance transport either as floating in bundles, steamship transport or barge transport in the waterway system of Lake Saimaa in 1950s. It defines the usage, kind of fleet, operation and costs of the abovesaid modes of transport. The investigation is mainly based on statistics of Enso-Gutzeit Oyj and the fuel office of the Finnish State Railways.
Location of the industrial enterprise sets the limits for use of the different modes of transport of roundwood. Previous decisions can influence the future choices, for instance, the capital the company has earler invested on the transportation system. Also, the type and amount of timber acquired by the company, transportation distance, time, and means of transport affect the choice of mode of transport. Those factors that direct decision-making, often lead the entrepreneur to stick to the chosen mode of transport.
Floating becomes the more inexpensive the larger the scale of operation is, and if the timber assortment is suitable for floating and water storage. For instance, dry wood is an asset for a wood export agency, and their sales have often time pressures, which rules floating out of their choices. Transportation in vessels has decreased to 4% of all roundwood haulage, but has its function as a supplementary way of transport.
The PDF includes a summary in German.
Different environmental factors were studied to determine which factors influence the species richness, composition and structure of vascular plants in Pinus sylvestris L. forests in a fixed dune landscape in south-western Estonia. In addition to site topographic factors, different environmental parameters were investigated. Thirty-four vascular plant species were recorded in 232 quadrats. The most abundant species was Vaccinium vitis-idaea L., which was in 82.8% of quadrats, followed by Vaccinium myrtillus L. (74.1%), Melampyrum pratense L. (71.1%) and Deschampsia flexuosa (L.) Trin. (69.8%). The multiple response permutation procedure (MRPP) showed considerable differences in species composition at the bottoms of dunes compared with that on the slopes and at the tops of dunes. Indicator species analysis (ISA) determined species exhibited characteristics specific to zone: V. myrtillus had the highest indicator value at the bottoms of dunes; Calluna vulgaris L., at the tops. Soils were Haplic Podzols, and the presence of humus horizon depended on zone. Soil conditions on the dunes were variable and site specific, in general, soils at the bottoms of the dunes were more acidic and moist compared with those of the slopes and tops of the dunes, and the nutrient content decreased toward the dune tops. According to non-metric multidimensional scaling (NMDS) and linear mixed model analyses, species coverage, composition and richness were controlled by site-specific factors such as absolute height, location and aspect of the quadrat on the dune; soil nitrogen, potassium and phosphorus contents; soil pH and moisture; light conditions; and the thickness of the litter horizon.
The effect of climatic factors on wood anatomy of the alien red oak (Quercus rubra L.) growing in three experimental plantations in Latvia was assessed by classical dendrochronological techniques. Two tree-ring proxies – tree-ring width (TRW) and mean area of earlywood vessel lumen (VLA) – were studied on 33 trees. Annual variation of TRW amongst trees was similar (mean r = 0.46), but there was more individuality in VLA (mean r = 0.26); nevertheless, chronologies of both proxies had rather synchronous variation amongst the sites. Annual variation of TRW was affected by factors related to water deficit in late summer, as suggested by the negative effect of temperature and positive effect of precipitation that have intensified during the 20th century, likely due to warming. Although weather conditions during the dormant period did not directly affect TRW, temperature during the autumn-spring period has been the main climatic determinant of VLA likely via influence on overwintering and hence vigour of tree. This suggests that conductive properties of wood and hence the susceptibility to water deficit have been affected by weather conditions before the formation of tree rings. During the 20th century, sensitivity of VLA has shifted from temperature in winter to temperature in autumn likely due to climate change. Still, the positive effect of these factors suggests that warming of climate would increase VLA and hence the risk of embolism and xylem disfunction. Therefore, the importance of availability of water for growth of red oak in Latvia is increasing.
Tree-ring width (TRW) and maximum latewood density (MXD) data of Faxon fir (Abies faxoniana Rehd. et Wils.) were analyzed for five timberline sites in the western Qinling Mountains and northeastern Tibetan Plateau, to investigate their relationships to climate change, especially twentieth century warming. The cross-correlations among TRW chronologies at the low-frequency band were higher, while the higher correlations among MXD chronologies were found at the high-frequency band. Response analysis showed that the tree-ring formation of fir trees was significantly and positively affected by temperature variations, while it was also negatively affected by precipitation. The TRW series captured the warming trends and allowed detecting the recent warming in a long-term context, while the MXD series showed no upward trend. We also found the temperature sensitivity of the TRW series is unstable over space and time. The divergent response between TRW and MXD might be caused by the seasonal variations of warming trends.