Kjersti Holt Hanssen
Research Scientist
Biography
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Kjersti Holt HanssenAbstract
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Kjersti Holt HanssenAbstract
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In a fertiliser experiment in a Norway spruce forest in SE Norway, four treatments were applied in a block design with three replicates per treatment. Treatments included 3 t wood ash ha−1 (Ash), 150 kg nitrogen ha−1 (N), wood ash and nitrogen combined (Ash + N), and unfertilised control (Ctrl). Treatment effects on understory plant species numbers, single abundances of species and (summarised) cover of main species groups were studied. Two years after treatment there were no significant changes for species numbers or abundances of woody species, dwarf shrubs or pteridophytes, nor for Sphagnum spp. in the bottom layer. The cover of graminoids decreased in Ctrl plots. Herb cover increased significantly in Ash + N and N plots due to the increase of Melampyrum sylvaticum. In Ash + N plots, mosses decreased significantly in species number, while their cover increased. Moss cover also decreased significantly in N plots. The species number and cover of hepatics decreased significantly in Ash and Ash + N plots. Hepatics cover also decreased in Ctrl plots. Both the lichen number and cover decreased in Ash + N plots. Single species abundances decreased for many bryophytes in fertilised plots. To conclude, fertilisation had modest effects on vascular plants, while bryophytes were more strongly affected, especially by Ash + N.
Authors
Sigitas Girdziušas Magnus Löf Kjersti Holt Hanssen Dagnija Lazdiņa Palle Madsen Timo Saksa Kaspars Liepiņš Inger Sundheim Fløistad Marek MetslaidAbstract
Since the beginning of the twentieth century, forest regeneration management and policy in the Nordic–Baltic region (Denmark, Sweden, Norway, Finland, Estonia, Latvia and Lithuania) have gone through significant changes. For decades forest as a key natural resource was managed with main focus on timber production. However, several factors influenced shifting forest management, including forest regeneration to meet a wide range of society needs. This review study aims to reveal the historical development of forest regeneration identifying knowledge gaps and supporting decisions that promote sustainable regeneration of future forests. The development of forest regeneration management and policy in the Nordic–Baltic countries is analyzed through reforestation and afforestation practices as well as legislation aspects using a narrative review approach. Trends in forest regeneration practices within the region are identified and explored over a timeframe spanning from 1900 until today. Despite diverse forestry management structures and differing political, social situations, the study shows that forest regeneration development has followed similar patterns over time in all Nordic–Baltic region countries: extensive forestry, clear-cut forestry, retention forestry and currently evolving climate-adaptive forestry. Nevertheless, regional differences among the Nordic–Baltic countries, especially in forest regeneration-related legislation, were identified due to a mixture of international and local driving forces.
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In the Nordic countries Finland, Norway and Sweden, the most common regeneration method is planting after clearcutting and, often, mechanical site preparation (MSP). The main focus of this study is to review quantitative effects that have been reported for the five main MSP methods in terms of survival and growth of manually planted coniferous seedlings of Norway spruce (Picea abies (L.) Karst.), Scots pine (Pinus sylvestris L.) and lodgepole pine (Pinus contorta var. latifolia Engelm.) in clearcuts in these three countries. Meta analyses are used to compare the effects of MSP methods to control areas where there was no MSP and identify any relationships with temperature sum and number of years after planting. In addition, the area of disturbed soil surface and the emergence of naturally regenerated seedlings are evaluated. The MSP methods considered are patch scarification, disc trenching, mounding, soil inversion and ploughing. Studies performed at sites with predominately mineral soils (with an organic topsoil no thicker than 0.30 m), in boreal, nemo-boreal and nemoral vegetation zones in the three Fenno-Scandinavian countries are included in the review. Data from 26 experimental and five survey studies in total were compiled and evaluated. The results show that survival rates of planted conifers at sites where seedlings are not strongly affected by pine weevil (Hylobius abietis L.) are generally 80–90% after MSP, and 15–20 percent units higher than after planting in non-prepared sites. The experimental data indicated that soil inversion and potentially ploughing (few studies) give marginally greater rates than the other methods in this respect. The effects of MSP on survival seem to be independent of the temperature sum. Below 800 degree days, however, the reported survival rates are more variable. MSP generally results in trees 10–25% taller 10–15 years after planting compared to no MSP. The strength of the growth effect appears to be inversely related to the temperature sum. The compiled data may assist in the design, evaluation and comparison of possible regeneration chains, i.e. analyses of the efficiency and cost-effectiveness of multiple combinations of reforestation measures.
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Kjersti Holt HanssenAbstract
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Based on data from long-term experimental fields with Norway spruce (Picea abies (L.) H. Karst.), we developed new stem taper and bark functions for Norway. Data was collected from 477 trees in stands across Norway. Three candidate functions which have shown good performance in previous studies (Kozak 02, Kozak 97 and Bi) were fitted to the data as fixed-effects models. The function with the smallest Akaike Information Criterion (AIC) was then chosen for additional analyses, fitting 1) site index-dependent and 2) age-dependent versions of the model, and 3) fitting a mixed-effects model with tree-specific random parameters. Kozak 97 was found to be the function with the smallest AIC, but all three tested taper functions resulted in fairly similar predictions of stem taper. The site index-dependent function reduced AIC and residual standard error and showed that the effect of site index on stem taper is different in small and large trees. The predictions of the age-independent and age-dependent models were very close to each other. Adding tree-specific random parameters to the model clearly reduced AIC and residual variation. However, the results suggest that the mixed-effects model should be used only when it is possible to calibrate it for each tree, otherwise the fixed-effects Kozak 97 model should be used. A model for double bark thickness was also fitted as fixed-effects Kozak 97 model. The model behaved logically, predicting larger relative but smaller absolute bark thickness for small trees.
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Kjersti Holt HanssenAbstract
The production of ash from wood has greatly increased the last years, because biofuels are increasingly being used for heating and energy production. The ash may either be viewed as a waste problem, or as a resource. Wood ash has a liming effect and contains essential nutrients (P, K, Ca, Mg) which can be exploited for soil fertilisation. With enhanced knowledge about where and how wood ash addition may increase forest growth - without having negative effects on the environment - wood ash may become a renewable nutrient source. We studied the effect of fertilizing a Norway spruce (Picea abies) stand on relatively high site index in SE Norway with ash, nitrogen, or ash + nitrogen. After five years, both current annual increment and standing volume was best in the ASH + N treatment and least in the Control plots. The field trial should be followed for a longer period of time, as the ASH + N treatment still shows an increasing growth trend after five years.
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Several studies have shown the positive effect of nitrogen fertilization on conifer growth. In young Norway spruce (Picea abies) stands, an additional effect of including a mixture of other nutrients has often, but not always, been found. We studied effects of repeated fertilization in 28 stands with young Norway spruce in central Norway. The treatments consisted of plots without nutrient addition (Control), fertilization with 150 kg N ha−1 (150 N), and fertilization with 150 kg N plus addition of P, K, Mg, B, Mn and Cu (150 N + mix), repeated three times with approximately eight years interval. There was a clear positive effect on volume increment of the 150 N and 150 N + mix treatments compared to Control, and the effect was significantly higher for 150 N + mix than for 150 N. Fertilization had a stronger effect in the first fertilization period than in the second, while the third period was intermediate. The effect of 150 N + mix was strongest at plots > 300 m a.s.l. However, this correlation may be due to geological conditions rather than elevation. Further studies are needed to find out under which edaphic conditions a nutrient mixture will increase growth substantially in young spruce stands.
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Tonje Ingeborg Økland Jørn-Frode Nordbakken Holger Lange Ingvald Røsberg Kjersti Holt Hanssen Nicholas ClarkeAbstract
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Kjersti Holt HanssenAbstract
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Nicholas Clarke Silje Skår O. Janne Kjønaas Kjersti Holt Hanssen Tonje Ingeborg Økland Jørn-Frode Nordbakken Toril Drabløs Eldhuset Holger LangeAbstract
Short-term (three to four years) effects of forest harvesting on soil solution chemistry were investigated at two Norway spruce sites in southern Norway, differing in precipitation amount and topography. Experimental plots were either harvested conventionally (stem-only harvesting, SOH) or whole trees, including crowns, twigs and branches were removed (whole-tree harvesting, WTH), leaving residue piles on the ground for some months before removal. The WTH treatment had two sub-treatments: WTH-pile where there had been piles and WTH-removal, from where residues had been removed to make piles. Increased soil solution concentrations of NO3–N, total N, Ca, Mg and K at 30 cm depth, shown by peaks in concentrations in the years after harvesting, were found at the drier, less steep site in eastern Norway after SOH and WTH-pile, but less so after WTH-removal. At the wetter, steeper site in western Norway, peaks were often observed also at WTH-removal plots, which might reflect within-site differences in water pathways due largely to site topography.
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Natural regeneration of Norway spruce (Picea abies (L.) Karst.) is a relatively common practice in Norway on medium to low site indices. However, seedling establishment is often hampered by rapid regrowth of competing vegetation in scarified patches. The aim of our study was to examine the effect of coordinating scarification towards an expected seed-fall, by studying germination and seedling establishment in scarified patches of different age (fresh, one- and two-year-old). The experiment was conducted in two stands in southeast Norway that were clear-cut in 2007. Scarification was applied to subplots in autumn 2008–2010. To simulate seed-fall, seeds were sown in fresh scarification patches in spring 2009–2011, in one-year-old patches in 2010 and 2011, and in twoyear- old patches in 2011. Both germination and seedling survival were negatively affected by the age of the scarified patches. Germination was higher, and mortality lower, at the small fern woodland site, compared with the bilberry woodland site. Sowing in fresh patches also resulted in increased height and root collar diameter of the seedlings compared with sowing in older patches. It is likely that the competing vegetation both on the site and in the scarification patches affected the growth of the seedlings. In conclusion, the age of the scarified patches affected both germination and mortality, as well as early growth of the seedlings.
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Removal of logging residues causes significant nutrient losses from the harvesting site. Furthermore,collection of residues into piles could lead to small-scale differences in establishment conditions for seedlings. We studied the effects of stem-only (SOH) and aboveground whole-tree harvesting (WTH) on Norway spruce (Picea abies) seedling growth and pine weevil (Hylobius abietis) damage at two sites (SE and W Norway). We also compared two planting environments within the WTH plots (WTH-0: areas with no residues, WTH-1: areas where residue piles had been placed and removed before planting). In practice, one-third of the residues were left on site after WTH. After three growing seasons there were no differences for height or diameter increment between SOH and WTH (WTH-1 and WTH-0 combined) treatments. However, relative diameter increment was largest for WTH-1 seedlings and lowest for WTH-0 seedlings. Few seedlings sustained pine weevil attacks at the W Norway site, with no differences among treatments. At the SE Norway site, the percent of seedlings damaged by pine weevils and average debarked area were significantly higher after WTH (82% and 3.3 cm2) compared to SOH (62% and 1.7 cm2). We conclude that WTH may lead to spatial differences in establishment conditions.
Authors
Nicholas Clarke Tonje Ingeborg Økland Kjersti Holt Hanssen Jørn-Frode Nordbakken Katarzyna WasakAbstract
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Kjersti Holt HanssenAbstract
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Feeding by pine weevil (Hylobius abietis L.) causes severe damage to newly planted conifer seedlings in most parts of Scandinavia. We investigated the effect of planting time and insecticide treatment on pine weevil damage and seedling growth. The main objective was to study if planting in early autumn on fresh clear-cuts would promote seedling establishment and reduce the amount of damage caused by pine weevil the following season. The experiment was conducted in southern Sweden and in south-eastern Norway with an identical experimental design at three sites in each country. On each site, Norway spruce seedlings with or without insecticide treatment were planted at four different planting times: August, September, November and May the following year. In Sweden, the proportion of untreated seedlings that were killed by pine weevils was reduced when seedlings were planted at the earliest time (August/September) compared to late planting in November, or May the following year. This pattern was not found in Norway. The average length of leading shoot, diameter growth and biomass were clearly benefited by planting in August in both countries. Insecticide treatment decreased the number of seedlings killed or severely damaged in both Norway and Sweden.
Authors
Tonje Ingeborg Økland Jørn-Frode Nordbakken Holger Lange Ingvald Røsberg O. Janne Kjønaas Kjersti Holt Hanssen Nicholas ClarkeAbstract
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Nicholas Clarke Hugh Cross Toril Drabløs Eldhuset Kjersti Holt Hanssen Ari Hietala O. Janne Kjønaas Holger Lange Jørn-Frode Nordbakken Tonje Ingeborg Økland Ingvald Røsberg Silje SkårAbstract
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Nicholas Clarke Kjersti Holt Hanssen Jørn-Frode Nordbakken Tonje Ingeborg Økland Katarzyna WasakAbstract
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Nicholas Clarke Kjersti Holt Hanssen Jørn-Frode Nordbakken Tonje Ingeborg Økland Katarzyna WasakAbstract
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Nicholas Clarke Kjersti Holt Hanssen Janka Dibdiakova Jørn-Frode Nordbakken Tonje Ingeborg ØklandAbstract
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Tonje Ingeborg Økland Jørn-Frode Nordbakken Holger Lange Ingvald Røsberg O. Janne Kjønaas Kjersti Holt Hanssen Nicholas ClarkeAbstract
Whole-tree harvest (WTH), i.e. harvesting of forest residues (twigs, branches and crown tops) in addition to stems, for bioenergy purposes may lead to biodiversity loss and changes in species composition in forest ground vegetation, which in turn also will affect soil properties. Effects of clear-cut harvesting on ground vegetation have been investigated at two Norway spruce sites in southern east and western Norway, respectively, differing in climate and topography. Experimental plots at these two sites were either harvested conventionally (stem-only harvest, SOH), leaving harvest residues spread on the site,or WTH was carried out, with the residues collected into piles at the site for six - nine months prior to removal. Vegetation plots in the eastern site were established and analysed before WTH and SOH in 2008 and reanalysed after harvesting in 2010, 2012 and 2014. In the western site vegetation plots were established before WTH and SOH in 2010 and reanalysed after harvesting in 2012 and 2014 (and planned for 2016). All vegetation plots are permanently marked. Pre-as well as post-harvesting species abundances of all species in each vegetation plot were each time recorded as percentage cover (vertical projection) and subplot frequency. Environmental variables (topographical, soil physical, soil chemical, and tree variables) were recorded only once; before WTH and SOH. Effec ts of WTH and SOH on ground vegetation biodiversity and cover are presented.
Authors
O. Janne Kjønaas Nicholas Clarke Toril Drabløs Eldhuset Ari Hietala Hugh Cross Kjersti Holt Hanssen Tonje Ingeborg Økland Holger Lange Jørn-Frode Nordbakken Ingvald RøsbergAbstract
Tree harvest and different harvesting methods may affect the soil carbon (C) pool in forest ecosystems. In con- ventional stem-only timber harvesting (SOH), branches and tops that are left in the forests may contribute to the build-up of the soil carbon pool. In whole-tree harvesting (WTH), inputs of organic matter from branches and tops are strongly reduced. We established field experiments at Gaupen, SE and Vindberg, SW Norway, to study the short-term effects of SOH and WTH on processes affecting the accumulation and loss of soil C. Logging residues on the WTH plots were collected in piles that were removed after 6 months, rendering two sub treatments (WTH- pile and WTH-removal areas). We weighed selected trees and logging residues, surveyed understorey biomass production, quantified pre-harvest soil C and nutrient pools down to 30 cm. Soil respiration was measured and soil water sampled monthly during the growing season, while temperature and moisture were measured continuously. Organic and mineral horizons were incubated at different temperatures to estimate potential C and N mineraliza- tion, and deep sequencing of the ITS2 barcode region of fungal DNA was performed on the samples. Litterbags were deployed in the SOH plots. The logging residues amounted to 2.2-2.4 kg C m-2 At Gaupen, the mean in situ soil respiration rates increased following harvest with all treatments, but were significantly higher in WTH-pile and SOH relative to the WTH- removal areas in the first year as well as the fourth year of treatment. The former rates included aboveground decomposing needles and twigs but excluded coarser branches. The observed increase in the WTH-removal areas may be related to decomposing roots, as well as to increased C mineralization partly due to the higher soil tem- peratures following harvest. Soil temperature was the single most important factor explaining the variability in soil respiration rates over all treatments. At Vindberg, a decrease in soil respiration was observed with all treatments in the second and third years following harvest. At both sites, decomposition of logging residues from needles was more rapid relative to twigs and fine roots. The decomposing residues released a substantial amount of nitrogen which was gradually reflected in the soil water at 30 cm soil depth. A considerable increase in the NO3-N concen- tration also in the WTH-removal areas in the second year following harvest suggests an increase in N availability from decomposing fine roots and/or soil organic matter. The increased N availability in the WTH-removal areas was supported by results from short term lab incubations of undisturbed soil from the forest floor. The changes in the WTH-removal areas were also reflected in the soil fungal diversity: saprophytic ascomycetes on decaying plant material showed a striking increase in all treatments. For the WTH-removal areas, this may, again, be related to the increased input of root litter; however, the decrease in mycorrhizal basidiomycete species and the vigorous increase of ascomycetes following harvest may also affect the C mineralization of soil organic matter.
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Kjersti Holt HanssenAbstract
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Tonje Ingeborg Økland Jørn-Frode Nordbakken Holger Lange Ingvald Røsberg O. Janne Kjønaas Nicholas Clarke Kjersti Holt HanssenAbstract
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Tonje Ingeborg Økland Jørn-Frode Nordbakken Holger Lange Ingvald Røsberg O. Janne Kjønaas Kjersti Holt Hanssen Nicholas ClarkeAbstract
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Nicholas Clarke Toril Drabløs Eldhuset Kjersti Holt Hanssen Ari Hietala O. Janne Kjønaas Holger Lange Jørn-Frode Nordbakken Tonje Ingeborg Økland Ingvald RøsbergAbstract
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Nicholas Clarke Toril Drabløs Eldhuset Kjersti Holt Hanssen Ari Hietala O. Janne Kjønaas Holger Lange Jørn-Frode Nordbakken Tonje Ingeborg Økland Ingvald RøsbergAbstract
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O. Janne Kjønaas Nicholas Clarke Toril Drabløs Eldhuset Kjersti Holt Hanssen Ari Hietala Holger Lange Jørn-Frode Nordbakken Tonje Ingeborg Økland Ingvald RøsbergAbstract
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O. Janne Kjønaas Nicholas Clarke Toril Drabløs Eldhuset Ari Hietala Hugh Cross Tonje Ingeborg Økland Jørn-Frode Nordbakken Holger Lange Ingvald Røsberg Kjersti Holt HanssenAbstract
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Tonje Ingeborg Økland Jørn Frode Nordbakken Holger Lange Ingvald Røsberg Janne O. Kjønaas Kjersti Holt Hanssen Toril Drabløs Eldhuset Nicholas ClarkeAbstract
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The relative volume growth effects of thinning after whole-tree harvesting (WTH) compared to a conventional stem-only harvest (CH) in young stands of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) were analyzed, using a series of four pine and four spruce field experiments. The series was established in the years 1972–1977, and thinning was performed only once. Results are shown periodically and cumulatively. All sites were included for 20 (19) years in pine and 25 years in spruce. The total experimental period varied between 19 and 35 years for individual sites. Four models assuming additive or multiplicative effects gave only slightly varying results. The inclusion of standing volume after thinning as a covariate was effective in spruce independent of whether the covariate was treated as multiplicative or additive. A logarithmic model with a multiplicative effect of the covariate was preferred in further presentations. Results for pine stands after 20 years indicated a nonsignificant loss of 5% with confidence limits (p = 0.05) of ±6–7%, while the spruce stands showed a significant growth loss of 11% with confidence limits of ±4–5% after 25 years. The difference between the species in relative growth effects was significant, and amounted to 8% for a cumulative 20-year period. No indications of trends in response were found during a 20-year period in pine and a 25-year period in spruce. An analysis of growth effects in the first years showed that basal area increment in spruce was significantly reduced already in the first growing season after thinning.
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In this report, the oral and poster contributions of the scientific conference “Forest Management and Silviculture in the North – Balancing Future Needs” have been compiled. The conference was arranged 6-8 September 2011 in Stjørdal, Norway, gathering more than 50 delegates from seven countries. The conference was hosted by the Norwegian Forest and Landscape Institute and was initiated jointly by IUFRO WP 1.01.01 Boreal forest silviculture and management and the SNS network group Sustainable forest management in northern Fennoscandia (NORFOR).
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Gunnhild Søgaard Inger Sundheim Fløistad Aksel Granhus Kjersti Holt Hanssen Harald Kvaalen Tore Skrøppa Arne SteffenremAbstract
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Helja-Sisko Helmisaari Kjersti Holt Hanssen Staffan Jacobson Mikko Kukkola Jukka Luiro Anna Saarsalmi Pekka Tamminen Bjørn TveiteAbstract
The aim of this study was to determine the effect of whole-tree harvesting (WTH) on the growth of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) as compared to conventional stem harvesting (CH) over 10 and 20 years. Compensatory (WTH+ CoF) and normal nitrogen-based (CH + F or WTH+ F) fertilisation were also studied. A series of 22 field experiments were established during 1977–1987, representing a range of site types and climatic conditions in Finland, Norway and Sweden. The treatments were performed at the time of establishment and were repeated after 10–13 years at 11 experimental sites. Seven experiments were followed for 25 years. Volume increment was on average significantly lower after WTH than after CH in both 10-year periods in the spruce stands. In the pine stands thinned only once, the WTH induced growth reduction was significant during the second 10-year period, indicating a long-term response. Volume increment of pine stands was 4 and 8% and that of spruce stands 5 and 13% lower on the WTH plots than on CH during the first and the second 10-year period, respectively. For the second 10- year period the relative volume increment of the whole-tree harvested plots tended to be negatively correlated with the amount of logging residue. Accordingly, the relative volume increment decreased more, the more logging residue was harvested, stressing the importance of developing methods for leaving the nutrient-rich needles on site. If nutrient (N, P, K) losses with the removed logging residues were compensated with fertiliser (WTH+ CoF), the volume increment was equal to that in the CH plots. Nitrogen (150–180 kg ha−1) or N+ P fertilisation increased tree growth in all experiments except in one very productive spruce stand. Pine stands fertilised only once had a normal positive growth response during the first 10-year period, on average 13m3 ha−1, followed by a negative response of 5m3 ha−1 during the second 10-year period. The fertilisation effect of WTH+ F and WTH+ CoF on basal area increment was both smaller and shorter than with CH+ F.
Authors
Kjersti Holt HanssenAbstract
The pine weevil (Hylobius abietis) is an important pest to conifer seedlings in large parts of Europe. To get an objective measure of the extent of damages related to pine weevils in South-Eastern Norway, a survey was implemented in the autumn of 2010 in nine counties. Altogether, 155 stands regenerated by planting in 2009 or 2010 were examined. The percentage of seedlings killed from pine weevil attacks varied between 0 and 63 % in the surveyed fields. On average, 7 % of the seedlings were killed by pine weevils, while 23 % had bark wounds. In addition, 3 % of the seedlings were killed by other causes. Few of the registered field variables were correlated to the degree of damage, but there was a tendency towards higher mortality at the largest clear cuts, in hilly areas, and for dry soil types. The present survey shows that in unscarified stands in SE Norway pine weevils are the most important cause of seedling mortality. A total seedling mortality of at least 10% should be expected the first two years.
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The use of logging residues for bioenergy is encouraged in many countries, due to an increasing demand for renewable energy. However, there is concern that removal of logging residues may cause a long-term reduction in soil nutrient availability, reducing forest growth in the remaining stand. To quantify the growth response of Norway spruce and Scots pine to whole-three harvesting at first thinning a series of eight field experiments was set up in SE Norway in the seventies. Results after 25 years showed that whole-tree thinning lead to a decrease in forest growth. The effect was present more or less immediately after thinning, and was still present after 25 years. The average reduction in growth was around 10 % after 25 years in the spruce stands, while in the pine stands a non-significant average growth reduction of 4 % was found. The results are generated under experimental conditions, and in practice a share of the residues is left on site, decreasing the nutrient loss.
Authors
Holger Lange Nicholas Clarke O. Janne Kjønaas Wenche Aas Kjell Andreassen Rasmus Astrup Susanne Eich-Greatorex Toril Eldhuset Kjersti Holt Hanssen Tonje Ingeborg Økland Ingvald Røsberg Trine A SognAbstract
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Authors
Svein Solberg Andreas Brunner Kjersti Holt Hanssen Holger Lange Erik Næsset Miina Rautiainen Pauline StenbergAbstract
In this study we demonstrate how airborne laser scanning (ALS) can be applied to map effective leaf area index (LAI(e)) in a spruce forest, after being calibrated with ground based measurements. In 2003 and 2005, ALS data and field estimates of LAI(e) were acquired in a Norway spruce forest in SE Norway. We used LI-COR's LAI-2000 (R) Plant canopy analyzer ("LAI-2000") and hemispherical images ("HI") for field based estimates of LAI(e). ALS penetration rate calculated from first echoes and from first and last echoes was strongly related to field estimates of LAI(e). We fitted regression models of LAI(e) against the log-transformed inverse of the ALS penetration rate, and in accordance with the Beer-Lambert law this produced a linear, no-intercept relationship. This was particularly the case for the LAI-2000, having R-2 values > 0.9. The strongest relationship was obtained by selecting ALS data from within a circle around each plot with a radius of 0.75 times the tree height. We found a slight difference in the relationship for the two years, which can be attributed to the differences in the ALS acquisition settings. The relationship was valid across four age classes of trees representing different stages of stand development, except in one case with newly regenerated stands which most likely was an artifact. Using LAI(e) based on HI data produced weaker relationships with the ALS data. This was the case even when we simulated LAI-2000 measurements based on the HI data. (C) 2009 Elsevier Inc. All rights reserved.
Abstract
Manipulation of the canopy cover and site preparation are the most important silvicultural measures to enhance the conditions for natural regeneration of Norway spruce (Picea abies (L.) Karst.). During the early regeneration phase however, seedling mortality may be high, so it is important to study how different combinations of stand-level treatments and site preparation methods affect seedling establishment. We studied emergence, 1st winter and 2nd summer mortality for naturally regenerated spruce seedlings in a field experiment that combined four harvest treatments (shelterwoods of high (SH), medium (SM) and low (SL) residual basal area, and a 50 x 50 m clear-cut (CC)) and two site preparation methods (patch scarification and inverting). The CC had significantly fewer seedlings the 1st fall than the SL and SH (p = 0.0377), and in all harvest treatments, fewer seedlings emerged in inverted than in patch scarified spots (p = 0.0351). Mortality was also lower with patch scarification than inverting (1st winter: p = 0.0565, 2nd summer: p = 0.0377), but was not affected by harvest treatment (1st winter: p = 0.9211, 2nd summer: p = 0.1896). On average, mortality from 1st to 2nd fall reached 38% and 27% after inverting and patch scarification, respectively. First winter mortality accounted for approximately two thirds of the accumulated mortality, regardless of the harvest treatment and site preparation method.
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The relationships between measures of forest structure as derived from airborne laser scanner data and the variation in quantity (Q) and vitality (V) of young trees in a size-diverse spruce forest were analyzed. A regeneration success rate (Q), leader length (V), relative leader length (V), and apical dominance ratio (V) were regressed against 27 different laser-derived explanatory variables representing three different spatial scales. The resulting 81 different models for each response variable were ranked according to their Akaike information criterion score and significance level. Each laser variable was then associated with four categories. These were scale, return, fraction, and type. Within the scale category, laser variables were grouped according to the spatial scale from which they originated. Similarly, within the return, fraction, and type categories, the variables were grouped according to if they originated from first or last return echoes; if they originated from lower, middle, or upper fraction of the range of laser heights or values derived from the full range of laser pulses, and if they were canopy height or canopy density metrics. The results show that the laser variables were strongest correlated with the quantity of small trees and that these variables could be attributed to large-scale, last return, lower fraction, and density metrics. The correlations with the vitality responses were weaker, but the results indicate that variables derived from a smaller scale than for the quantity were better in order to explain variation in leader length, relative leader length, and apical dominance ratio. (C) 2007 Elsevier B.V. All rights reserved.
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Authors
Kjersti Holt HanssenAbstract
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Authors
Michelle de Chantal Kjersti Holt Hanssen Aksel Granhus Urban Bergsten Mikaell Ottosson-Löfvenius Harald GripAbstract
We studied first winter frost-heaving damage to one-year-old Picea abies (L.) Karst. seedlings planted in gaps made by group fellings (large circular gaps, ca. 500 m(2)) and single-tree selection cuttings (small irregularly shaped gaps, ca. 175 m 2), as well as in uncut forest. One-month-old seedlings were planted on manually exposed LF, Ae, and B horizons that emulated various intensities and depths of scarification. The three experimental sites were located in multistoried Pinus sylvestris L. or P. abies forests on sandy loam or silt loam in southeastern Norway. Altogether, 5% of seedlings sustained frost heaving damage on the LF horizon, compared with 20% on the Ae horizon and 45% on the B horizon. On average, 31% of the seedlings in large gaps incurred frost-heaving damage compared with 20% in small gaps and 19% in uncut forest. Exposed roots and poorly anchored or uplifted seedlings were recurring classes of damage, especially on the B horizon and in large gaps. The above- versus below-ground biomass ratio of seedlings was higher on the B than on the Ae horizon in uncut forest and large gaps, inferring broken roots. Therefore, to reduce the risk of frost-heaving damage, shallow soil preparation and smaller gap sizes should be used.
Abstract
The relationships between measures of forest structure as derived from airborne laser scanner data and the variation in quantity of young trees established by natural regeneration in a size-diverse spruce forest were analyzed. A regeneration success rate (RSR) was regressed against 27 different laser-derived explanatory variables. The 27 different models were ranked according to their Akaike information criterion score. Each laser variable was then associated with two categories. These were return and type. Within the return and type categories, the variables were grouped according to if they originated from first or last return echoes and if they were canopy height or canopy density metrics. The results show that the laser variables strongest correlated to the quantity of small trees could be attributed to last return and density metrics.
Authors
Michelle de Chantal Kjersti Holt Hanssen Aksel Granhus Urban Bergsten Mikaell Ottosson-Löfvenius Harald GripAbstract
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In a balanced experiment based on 20 field plots located in a 21 km(2) Scots pine forest in southeast Norway covering age classes from newly regenerated to old forest, leaf area index (LAI) was determined in field by a LAI-2000 instrument and hemispheric photography. Based on a fortualized framework, i.e., the so-called Beer-Lambert law, gap fraction derived from small-footprint airborne laser scanner data was regressed against field-measured LAI. LAI was strongly (R-2 =0.87-0.93), positively, and linearly related to the log-transformed inverse of the gap fraction derived from the laser scanner data. This was as expected according to the Beer-Lambert law, as was the absence of an intercept, producing a directly proportionality of the two variables. We estimated an extinction coefficient for the first return echoes to be 0.7, fortunately fairly stable across age classes, and this is likely to be a parameter specific for the applied laser scanner system under the given flight and system settings, such as flying altitude and laser pulse repetition frequency. It was demonstrated that airborne laser was able to detect defoliation in terms of estimated changes in LAI, by three repeated laser data acquisitions over the area where severe insect attacks were going on in between the acquisitions. (c) 2006 Elsevier Inc. All rights reserved.
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Abstract
Establishment, survival and height growth of sown and naturally regenerated Picea abies (L.) Karst. seedlings were examined in a 6 yr period in eight stands on bilberry woodland in south- east Norway. Five harvesting treatments (shelterwoods of high, medium and low density, 253/25 m patch-cut, 503/50 m clear-cut) and three scarification alternatives (unscarified, patch scarification, inverting) were combined in a split-plot design. Establishment, survival and plant height after 6 yrs were positively affected by scarification. Significant differences between patch scarification and inverting were not observed, although mortality tended to be lower, and seedlings slightly taller, after patch scarification. Establishment after natural seedfall was least successful on the clear-cut, but more or less equal at the other stand treatments. Height growth increased with decreasing overstorey retention, while there was a tendency towards lower survival on the clear-cuts and patch-cuts. Natural regeneration in the unscarified plots was unsuccessful after 6 yrs, while the different combinations of harvesting and scarification treatments usually gave sufficient regeneration.
Authors
Kjersti Holt HanssenAbstract
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