Göran Bergqvist

Prediction of basic wood properties for Norway spruce. Interpretation of Near Infrared Spectroscopy data using partial least squares regression

Abstract This work was undertaken to investigate the feasibility of using near infrared spectroscopy (NIR) and partial least squares regression (PLS) as a tool to characterize the basic wood properties of Norway Spruce (Picea abies (L.) Karst.). The wood samples originated from a trial located in the province of Västerbotten in Sweden. In this trial, the effects of birch shelterwoods (Betula pendula Roth) of different densities on growth and yield in Norway spruce understorey were examined. All Norway spruce trees in each shelterwood treatment were divided into three growth rate classes based on diameter at breast height (1.3 m) over bark. Five discs were cut from each tree (i.e. from the root stem, and at 20%, 40%, 60%, and 80% of the total height). The discs from 40% tree height were used (i.e., where the largest variations in annual ring widths and wood density were found). A total of 27 discs were selected. The discs were used for measuring annual ring widths, wood density, average fiber length and the fiber length distributions. Milled wood samples prepared from the discs were used for recording NIR spectra. PLS regression was used to generate prediction models for the wood properties (Y-matrix) and NIR spectra (X-matrix) as well as between the wood properties (Y-matrix) and the fiber length distributions (X-matrix). One set of models was generated using untreated spectra and fiber length distributions. For a second set of models the structure in the X-matrix, which was orthogonal to the matrix described by the wood properties, was eliminated using a soft target rotation technique called orthogonal signal correction (OSC). The PLS model obtained using “raw” untreated NIR spectra and fiber length distributions had a poor modeling power as evidenced by the cumulative Q2 values. For the PLS models based on untreated NIR spectra the cumulative Q2 values ranged from a minimum of 16% (wood density) to a maximum of 46% (no. of annual rings). Orthogonal signal correction of the X-matrix (NIR spectra or fiber length distributions) gave PLS models with a modeling power corresponding to cumulative Q2 values well in excess of 70%. The improvement in predictive ability accomplished by the OSC procedure was verified by placing four of the 27 observations in an external test set and comparing RMSEP values for the test set observations without OSC and with OSC.

Patterns of Stem Damage by Moose (Alces alces) in Young Pinus sylvestris Stands in Sweden

The incidence of recent moose browsing of the main stem on young Scots pine (Pinus sylvestris L.) trees, and correlations with tree or stand characteristics, were examined using data from a large-scale survey in Sweden. On average, 10% of all Scots pine main stems showed one or more types of recent damage, with browsing of the apical leader accounting for about 75% of all damage recorded. Stripping of bark off the main stem occurred most frequently in the southern area, where site productivity is highest. Apical leader browsing was negatively correlated with height of the main stems, length of the apical leader and incidence of pre-commercial thinning, whereas bark stripping and stem breaking were positively correlated with the same variables. All types of recent stem damage correlated positively with the extent of previous stem damage and also with the extent of recent browsing of lateral shoots.

Frequencies and patterns of browsing by large herbivores on conifer seedlings

Browsing by large herbivores on planted and naturally regenerated conifer seedlings (Picea abies and Pinus sylvestris) was recorded in 104 clear‐cuts in east‐central Sweden during 1990 and in 47 clear‐cuts in 1991. The number of seedlings browsed and the browsing patterns were analysed in relation to seedling type. Browsing frequencies were also compared between forest stands with different site productivities and subjected to different management practices. The variation in the number of seedlings browsed in 1990 was explained mainly by seedling category. Among both planted and naturally regenerated seedlings, pine was browsed more than spruce. Two‐year‐old containerized seedlings of spruce was browsed more than 4‐yr‐old bare‐rooted spruce. In 1991, browsing was more equal among species and seedling types. Number of seedlings with their leader browsed and the amount of biomass left after browsing differed significantly between seedling types. Seedlings that had been browsed in 1990 experienced significan...

Large Herbivore Browsing on Conifer Seedlings Related to Seedling Morphology

Large herbivore browsing on conifer seedlings was tested in a field experiment based on the presentation of different seedling types at feeding stations. Altogether 150 feeding stations, each with six different seedling types, were established in ordinary clear - cuts in east - central Sweden. The seedling types used were three each of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.), 1 - year - old and 2 - year - old containerized seedlings, and 2 - year - old bare-rooted seedlings. The planting took place in autumn. After one winter, browsing of the various seedling types was recorded. Number of browsed seedlings, leader browsing, and bite diameter differed between seedling types. Results showed that pine was more browsed than spruce, 2 - year - old seedlings more browsed than 1 - year - old seedlings, and containerized seedlings more browsed than bare - rooted seedlings. Morphological characteristics varied between the six seedling types. Few significant correlations between...

Summer browsing by moose on Scots pine

Abstract Moose (Alces alces L.) browse Scots pine (Pinus sylvestris L.) mainly during the winter. There is a growing concern also regarding summer browsing by moose on Scots pine. We studied summer browsing on Scots pine during two consecutive years. In a survey of 47 stands in 2003, current summer browsing was found for 20.4% of the Scots pine main stems, and on almost half of them (9.8%) the top shoot was browsed. This indicates that the pine damage causing reduced wood quality was as serious during summer as during the preceding winter. There was significantly more summer browsing on previously browsed pines, compared to a random use, both at tree and stand level, and summer browsing was also spatially clumped within stands. Browsing on top shoots occurred up to a height of 2.8 m, whereas side shoot browsing was recorded for pines with a height up to 4.8 m. In 2004, 11 of the 47 stands were randomly selected for a more detailed study of pines browsed during that summer. The summer browsed trees contained, on average, 114 current shoots tree−1, and 10.5 shoots tree−1 (9.2%) were browsed. In this area, summer browsing may explain a considerable part of the moose-related forest damage recorded. The proportion of pines subjected to summer browsing did not change with availability of pines. Hence, increasing the number of Scots pine trees in young stands may be a way to increase the number of unbrowsed pine trees at a given moose population density.

Browsing by large herbivores on Scots pine (Pinus sylvestris) seedlings in mixture with ash (Fraxinus excelsior) or silver birch (Betula pendula)

Abstract Food selection by large herbivores occurs at a hierarchy of scales, for example landscape, patch or plant. Several hypotheses regarding food plant selection on patch or plant level have been developed. In this cafeteria-type design field experiment, conducted during one winter immediately after planting, we tested the effect of species mixture on browsing by large herbivores (mainly roe deer) on Scots pine seedlings in mixture with seedlings of ash (highly preferred) or silver birch (less preferred). Browsing on Scots pine was not affected by species mixture, neither in terms of the number of browsed pines nor browsing intensity. Instead, browsed biomass was positively and significantly correlated to the total biomass available for browsing. Also, there were differences due to species, with ash being most browsed (44.6%), followed by Scots pine (18.9%) and silver birch (11.6%). Browsed biomass per browsed seedling, however, was largest for Scots pine. In addition, browsed seedlings were initially taller compared to unbrowsed seedlings for all species. The main management implication in this study is that the species mixture did not influence large herbivore browsing on Scots pine seedlings. Hence, removing or discouraging more (or less) attractive browse species in early stages of pine regeneration activities seems unnecessary from the point of large herbivore browsing.

Effects of female body mass and climate on reproduction in northern wild boar

Mammalian life history strategies depend on climate conditions. Hence, reproductive parameters may vary regionally, and knowledge on such patterns are important for sustainable management. Wild boar research has been biased towards south and central Europe. Here we investigate the effects of mothers carcass mass, season and climate (summer temperature and precipitation as well as January temperature) on pregnancy rate and litter size in 601 free-ranging female wild boar from hemiboreal Sweden, close to the north border of wild boar distribution range in Europe. Pregnancy rate was on average 33.4 ± 1.94% (mean ± SE), whereas average litter size of pregnant females was 4.7 ± 0.12. Pregnancy rate was highest during the seasonal reproduction peak in winter and spring, and both pregnancy rate and litter size increased significantly with increasing female body mass. The probability of a female being pregnant exceeded 50% when carcass mass exceeded 58 kg, equivalent to a live mass of 113 kg, and litter size increased by one for each 16 kg increase in female carcass mass. We found no significant effects of temporal variations in climate, and suggest that such variations were not sufficiently large to affect wild boar reproduction. Alternatively, the reproductive strategy of wild boar may be adjusted to prevailing regional climate conditions. In that case, other life history traits, such as mortality, may be more sensitive to short-term climate fluctuations. Wild boar management needs to take temporal variations in reproduction, as well as in resource availability, into consideration when deciding on prudent management actions.