Lise Dalsgaard

Research Scientist

(+47) 974 80 373
lise.dalsgaard@nibio.no

Place
Ås H8

Visiting address
Høgskoleveien 8, 1433 Ås

Abstract

For å verifisere beregningsmetoder og modeller for endringer av karbonlagre i skogsjord brukt i UNFCCC rapporteringen er det behov for data fra jordprøver med gjentak over tid og der prøvetakingsmetoder er konsistente. I Norge finnes ikke denne typen data på nasjonalt / landsdekkende nivå. For å møte behovet for verifisering av beregningsmetodikken brukt i UNFCCC rapporteringen innenfor rammene av eksisterende data med metodisk konsistens over tid, er det i denne undersøkelsen gjennomført ny prøvetaking av jord og vegetasjon i to etablerte forsøksfelt i skog i sør-øst Norge der vi fra før av både har data fra tidligere jordprøveanalyser og tilvekstdata for trær i skogsbestand. De to forsøksfeltene ligger på Nordmoen i Akershus (etablert 1973 og tilplantet 1974) og i Skiptvet i Østfold (etablert 1976 i eksisterende foryngelse med supplerplanting i 1977). Med nye jordprøver, biomassemålinger og vegetasjonsanalyser i 2011 gir dette to tidsserier på hhv. 38 og 34 år med hensyn på endringer i jordkarbon og inngangsverdier i beregningsmodellene. Den eksperimentelle behandlingen i Skiptvet omfatter ulik grad av treslagsblanding av bjørk og gran på de enkelte forsøksrutene, mens på Nordmoen sammenliknes rene bestand av hhv. bjørk, gran og furu. De klimatiske forhold er tilnærmet like, mens jordsmonntypen er ulik med næringsfattig sandjord på Nordmoen og næringsrik leirjord i Skiptvet. Resultatene fra forsøkene er begrenset til å representere klimatiske og vegetasjonsmessige forhold på Østlandet (og forhold tilsvarende de to lokalitetene), og forsøksfeltene er dermed ikke representative eksempelvis for kystnære og kontinentale strøk.

To document

Abstract

There is evidence that recently occurring top dieback of Norway spruce (Picea abies (L.) Karsten) tress in southern Norway is associated with drought stress. We compared functional wood traits of 20 healthy looking trees and 20 trees with visual signs of top dieback. SilviScan technology was applied to measure cell dimensions (lumen and cell wall thickness) in a selected set of trunk wood specimens where vulnerability to cavitation (P50) data were available. The wall/lumen ratio ((t/b)²) was a quite good proxy for P50. Cell dimensions were measured on wood cores of all 40 trees; theoretical vulnerability of single annual rings could be thus estimated. Declining trees tended to have lower (t/b)² before and during a period of water deficit (difference between precipitation and potential evapotranspiration) that lasted from 2004 to 2006. The results are discussed with respect to genetic predisposition.

Abstract

The present study aims to develop biologically sound and parsimonious site index models for Norway to predict changes in site index (SI) under different climatic conditions. The models are constructed using data from the Norwegian National Forest Inventory and climate data from the Norwegian meteorological institute. Site index was modeled using the potential modifier functional form, with a potential component (POT) depending on site quality classes and two modifier components (MOD): temperature and moisture. Each of these modifiers was based on a portfolio of candidate variables. The best model for spruce-dominated stands included temperature as modifier (R2 = 0.56). In the case of pine- and deciduous-dominated stands, the best models included both modifiers (R2 = 0.40 and 0.54 for temperature and moisture, respectively). We illustrate the use of the models by analyzing the possible shift in SI for year 2100 under one (RCP4.5) of the benchmark scenarios adopted by the Intergovernmental Panel on Climate Change for its fifth assessment report. The models presented can be valuable for evaluating the effect of climate change scenarios in Norwegian forests.

Abstract

Boreal forests contain 30% of the global forest carbon with the majority residing in soils. While challenging to quantify, soil carbon changes comprise a significant, and potentially increasing, part of the terrestrial carbon cycle. Thus, their estimation is important when designing forest-based climate change mitigation strategies and soil carbon change estimates are required for the reporting of greenhouse gas emissions. Organic matter decomposition varies with climate in complex nonlinear ways, rendering data aggregation nontrivial. Here, we explored the effects of temporal and spatial aggregation of climatic and litter input data on regional estimates of soil organic carbon stocks and changes for upland forests. We used the soil carbon and decomposition model Yasso07 with input from the Norwegian National Forest Inventory (11275 plots, 1960–2012). Estimates were produced at three spatial and three temporal scales. Results showed that a national level average soil carbon stock estimate varied by 10% depending on the applied spatial and temporal scale of aggregation. Higher stocks were found when applying plot-level input compared to country-level input and when long-term climate was used as compared to annual or 5-year mean values. A national level estimate for soil carbon change was similar across spatial scales, but was considerably (60–70%) lower when applying annual or 5-year mean climate compared to long-term mean climate reflecting the recent climatic changes in Norway. This was particularly evident for the forest-dominated districts in the southeastern and central parts of Norway and in the far north. We concluded that the sensitivity of model estimates to spatial aggregation will depend on the region of interest. Further, that using long-term climate averages during periods with strong climatic trends results in large differences in soil carbon estimates. The largest differences in this study were observed in central and northern regions with strongly increasing temperatures.

To document

Abstract

Top dieback in 40–60 years old forest stands of Norway spruce [Picea abies (L.) Karst.] in southern Norway is supposed to be associated with climatic extremes. Our intention was to learn more about the processes related to top dieback and in particular about the plasticity of possible predisposing factors. We aimed at (i) developing proxies for P50 based on anatomical data assessed by SilviScan technology and (ii) testing these proxies for their plasticity regarding climate, in order to (iii) analyze annual variations of hydraulic proxies of healthy looking trees and trees with top dieback upon their impact on tree survival. At two sites we selected 10 tree pairs, i.e., one healthy looking tree and one tree with visual signs of dieback such as dry tops, needle shortening and needle yellowing (n = 40 trees). Vulnerability to cavitation (P50) of the main trunk was assessed in a selected sample set (n = 19) and we thereafter applied SilviScan technology to measure cell dimensions (lumen (b) and cell wall thickness (t)) in these specimen and in all 40 trees in tree rings formed between 1990 and 2010. In a first analysis step, we searched for anatomical proxies for P50. The set of potential proxies included hydraulic lumen diameters and wall reinforcement parameters based on mean, radial, and tangential tracheid diameters. The conduit wall reinforcement based on tangential hydraulic lumen diameters ((t/bht)2) was the best estimate for P50. It was thus possible to relate climatic extremes to the potential vulnerability of single annual rings. Trees with top dieback had significantly lower (t/bht)2 and wider tangential (hydraulic) lumen diameters some years before a period of water deficit (2005–2006). Radial (hydraulic) lumen diameters showed however no significant differences between both tree groups. (t/bht)2 was influenced by annual climate variability; strongest correlations were found with precipitation in September of the previous growing season: high precipitation in previous September resulted in more vulnerable annual rings in the next season. The results are discussed with respect to an “opportunistic behavior” and genetic predisposition to drought sensitivity.

To document

Abstract

Soil organic carbon (C), accumulated over millennia, comprise more than half of the C stored in boreal and temperate forest landscapes. We used the Norwegian national forest inventory and soil survey network (n = 719, no deep organic soils) to explore the validity of a deterministic model representation of this pool (Yasso07). We statistically compared simulated and measured soil C stocks and related differences (measured – simulated) to site factors (drainage, topography, climate, vegetation, C-to-N ratio, and soil classification). Median C stocks were 5.0 kg C·m−2 (model) and 14.5 kg C·m−2 (measurements). Soil C differences related to site factors (r2 of 0.16 to 0.37). For Brunisols, Gleysols, and wet Organic soils, differences related primarily to topographic wetness. For Regosols, Podzols, and Dystric Eluviated Brunisols, they related to climate, profile depth, and, in some cases, drainage class and site index. We argue that soil moisture regimes in our study area overrule tree productivity effects in the determination of soil C stocks and present conditions for soil formation that the model cannot (and does not explicitly) account for. These are processes such as humification and podsolization that involve eluviation and illuviation of dissolved organic C (DOC) with sesquioxides to form spodic B horizons and carbon enrichment due to hampered decomposition in frequently anoxic conditions.

Abstract

Reliable methods are required to predict changes in soil carbon stocks. Process-based models often require many parameters which are largely unconstrained by observations. This induces uncertainties which are best met by using repeated measurements from the same sites. Here, we compare two carbon models, Yasso07 and Romul, in their ability to reproduce a set of field observations in Norway. The models are different in the level of process representation, structure, initialization requirements and calibration- and parameterization strategy. Field sites represent contrasting tree species, mixture and soil types. The number of repetitions of C measurements varies from 2 to 6 over a period of up to 35 years, and for some of the sites, which are part of long-term monitoring programs, plenty of auxiliary information is available. These reduce the danger of overparametrization and provide a stringent testbed for the two models. Focus is on the model intercomparison, using identical site descriptions to the extent possible, but another important aspect is the upscaling of model results to the regional or national scale, utilizing the Norwegian forest inventory system. We suggest that a proper uncertainty assessment of soil C stocks and changes has to include at least two (and preferably more) parametrized models.

Abstract

Reliable methods are required to predict changes in soil carbon stocks. Process-based models often require many parameters which are largely unconstrained by observations. This induces uncertainties which are best met by using repeated measurements from the same sites. Here, we compare two carbon models, Yasso07 and Romul, in their ability to reproduce a set of field observations in Norway. The models are different in the level of process representation, structure, initialization requirements and calibration- and parameterization strategy. Field sites represent contrasting tree species, mixture and soil types. The number of repetitions of C measurements varies from 2 to 6 over a period of up to 35 years, and for some of the sites, which are part of long-term monitoring programs, plenty of auxiliary information is available. These reduce the danger of overparametrization and provide a stringent testbed for the two models. Focus is on the model intercomparison, using identical site descriptions to the extent possible, but another important aspect is the upscaling of model results to the regional or national scale, utilizing the Norwegian forest inventory system. We suggest that a proper uncertainty assessment of soil C stocks and changes has to include at least two (and preferably more) parametrized models.

Abstract

Aims Beech (Fagus sylvatica L.) is an important species in natural and managed forests in Europe. This drought-sensitive species dominates even-aged stands as well more natural stands composed of a mixture of tree species, age and size classes. This study evaluates the extent that heterogeneity in spacing and tree diameter affect the seasonal availability and use of water. Methods Two stands were evaluated: 1) a heterogeneous forest remnant (NAT) with trees up to ca. 300 years old, a mean top height of 28.4 m, and a total of 733 stems ha-1 with stem diameters averaging 18 cm and 2) an even-aged 80-year old stand (MAN), with a height of 25 m, and a total of 283 stems ha-1 with diameters averaging 38 cm. Stem sap flow, Js (g m-2 s-1), was continuously measured in 12 (MAN) and 13 (NAT) trees using 20 mm long heat dissipation sensors. Individual tree measures of sap flow were correlated using non-linear statistical methods with air vapour pressure deficit (D, hPa) and global radiation (Rg, J m-2 day-1), along with contraints imposed by reductions in soil water content (SWC). Soil water content was measured as volumetric % using time domain reflectometry. Important findings The daily integrated Js (Js-sum) for trees growing in the evenly spaced MAN stand and trees in canopy and closed forest positions in NAT stand decreased as the availability of soil moisture was reduced. In the heterogeneous NAT stand, SWC in a recently formed canopy gap remained high throughout the vegetation period. Based on regression models, the predicted relative decrease in Js-sum for dry relative to moist soil water conditions in the closed forest (at mean daily D = 10 hPa) was 7-11% for trees near the gap and 39-42% for trees in the closed forest. In MAN the reduction in Js-sum was 29% in dry relative to moist conditions. Js-sum in the outer 20 mm of the xylem in NAT was lower than that in MAN and the rate of decline in Js with xylem depth was less in NAT than in MAN. In MAN, Js-sum in deep and outer xylem was negatively affected at low soil moisture availability; in NAT this was the case for only the outer xylem indicating that deep roots could be important in supplying water at times of low soil moisture in the upper soil.

Abstract

This study is a part of a larger project designed to find out the causes of top dieback symptoms in Norway spruce in SE Norway. Because sapwood tracheids constitute a water transport system while parenchyma serves as a reserve tissue (Sellin, 1991), the separation and quantification of the sapwood and heartwood may contribute to understanding of the healthy tree functioning. As the extent of sapwood is related to tree vitality, it reflects the tree growth, health and effect of environmental factors (Sandberg & Sterley, 2009). Therefore, the sapwood cross-sectional area is widely used as a biometric parameter indicating the tree vitality, although its estimation and evaluation is prone to scaling errors....