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Articles containing the keyword 'forest structure'

Category : Research article

article id 22028, category Research article

Eelis Halme, Matti Mõttus. (2023). Improved parametrisation of a physically-based forest reflectance model for retrieval of boreal forest structural properties. Silva Fennica vol. 57 no. 2 article id 22028. https://doi.org/10.14214/sf.22028

Keywords: forest structure; Sentinel-2; reflectance; hyperspectral; tree distribution

Highlights: Spatial distribution of trees is a key driver for forest reflectance; Knowledge of the ratio of branch to leaf area improves forest reflectance simulation substantially; Different optical properties of the two leaf sides have a notable effect on forest reflectance.

Abstract | Full text in HTML | Full text in PDF | Author Info

Physically-based reflectance models offer a robust and transferable method to assess biophysical characteristics of vegetation in remote sensing. Forests exhibit explicit structure at many scales, from shoots and branches to landscape patches, and hence present a specific challenge to vegetation reflectance modellers. To relate forest reflectance with its structure, the complexity must be parametrised leading to an increase in the number of reflectance model inputs. The parametrisations link reflectance simulations to measurable forest variables, but at the same time rely on abstractions (e.g. a geometric surface forming a tree crown) and physically-based simplifications that are difficult to quantify robustly. As high-quality data on basic forest structure (e.g. tree height and stand density) and optical properties (e.g. leaf and forest floor reflectance) are becoming increasingly available, we used the well-validated forest reflectance and transmittance model FRT to investigate the effect of the values of the “uncertain” input parameters on the accuracy of modelled forest reflectance. With the state-of-the-art structural and spectral forest information, and Sentinel-2 Multispectral Instrument imagery, we identified that the input parameters influencing the most the modelled reflectance, given that the basic forestry variables are set to their true values and leaf mass is determined from reliable allometric models, are the regularity of the tree distribution and the amount of woody elements. When these parameters were set to their new adjusted values, the model performance improved considerably, reaching in the near infrared spectral region (740–950 nm) nearly zero bias, a relative RMSE of 13% and a correlation coefficient of 0.81. In the visible part of the spectrum, the model performance was not as consistent indicating room for improvement.

Halme, VTT Technical Research Centre of Finland, P.O. Box 1000, FI-02044 VTT Espoo, Finland https://orcid.org/0000-0002-7517-6663 E-mail: eelis.halme@vtt.fi
Mõttus, VTT Technical Research Centre of Finland, P.O. Box 1000, FI-02044 VTT Espoo, Finland https://orcid.org/0000-0002-2745-1966 E-mail: matti.mottus@vtt.fi

article id 10010, category Research article

Panu Halme, Jenna Purhonen, Emma-Liina Marjakangas, Atte Komonen, Katja Juutilainen, Nerea Abrego. (2019). Dead wood profile of a semi-natural boreal forest – implications for sampling. Silva Fennica vol. 53 no. 4 article id 10010. https://doi.org/10.14214/sf.10010

Keywords: coarse woody debris; coniferous forest; forest structure; fine woody debris; forest disturbance dynamics; saproxylic

Highlights: We constructed a full dead wood profile of a semi-natural boreal forest; Abundance-diameter distributions were different among tree species; Extensive sampling is needed if focus on large dead wood and rare tree species.

Abstract | Full text in HTML | Full text in PDF | Author Info

Dead wood profile of a forest is a useful tool for describing forest characteristics and assessing forest disturbance history. Nevertheless, there are few studies on dead wood profiles, including both coarse and fine dead wood, and on the effect of sampling intensity on the dead wood estimates. In a semi-natural boreal forest, we measured every dead wood item over 2 cm in diameter from 80 study plots. From eight plots, we further recorded dead wood items below 2 cm in diameter. Based on these data we constructed the full dead wood profile, i.e. the overall number of dead wood items and their distribution among different tree species, volumes of different size and decay stage categories. We discovered that while the number of small dead wood items was immense, their number dropped drastically from the diameter below 1 cm to diameters 2–3 cm. Different tree species had notably different abundance-diameter distribution patterns: spruce dead wood comprised most strikingly the smallest diameter fractions, whereas aspen dead wood comprised a larger share of large-diameter items. Most of the dead wood volume constituted of large pieces (>10 cm in diameter), and 62% of volume was birch. The variation in the dead wood estimates was small for the numerically dominant tree species and smallest diameter categories, but high for the sub-dominant tree species and larger size categories. In conclusion, the more the focus is on rare tree species and large dead wood items, the more comprehensive should the sampling be.

Halme, Department of Biological and Environmental Science, University of Jyväskylä, P.O. Box 35, FI-40014 University of Jyväskylä, Finland; School of Resource Wisdom, University of Jyväskylä, P.O. Box 35, FI-40014 University of Jyväskylä, Finland E-mail: panu.halme@jyu.fi
Purhonen, Department of Biological and Environmental Science, University of Jyväskylä, P.O. Box 35, FI-40014 University of Jyväskylä, Finland E-mail: jenna.e.i.purhonen@jyu.fi
Marjakangas, Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology, N-7491 Trondheim, Norway E-mail: emma-liina.marjakangas@ntnu.no
Komonen, Department of Biological and Environmental Science, University of Jyväskylä, P.O. Box 35, FI-40014 University of Jyväskylä, Finland; School of Resource Wisdom, University of Jyväskylä, P.O. Box 35, FI-40014 University of Jyväskylä, Finland E-mail: atte.komonen@jyu.fi
Juutilainen, Department of Biological and Environmental Science, University of Jyväskylä, P.O. Box 35, FI-40014 University of Jyväskylä, Finland E-mail: kjuutilainen@yahoo.com
Abrego, Department of Agricultural Sciences, University of Helsinki, P.O. Box 27, FI-00014 University of Helsinki, Finland E-mail: nerea.abrego@helsinki.fi

article id 1207, category Research article

Olli-Pekka Tikkanen, Irina A. Chernyakova. (2014). Past human population history affects current forest landscape structure of Vodlozero National Park, Northwest Russia. Silva Fennica vol. 48 no. 4 article id 1207. https://doi.org/10.14214/sf.1207

Keywords: boreal forests; forest fires; recovery; forest structure; landscape change

Highlights: In large scale (0–20 km), the proportion of spruce in forest stands was positively affected by distance from old villages. This relationship was non-linear with a threshold distance of 15 km; In small scale (0–5 km), old villages affected tree species composition and age structure of forests. Effect on age structure was the strongest on stands growing on mineral soils.

Abstract | Full text in HTML | Full text in PDF | Author Info

The information about location and size of past human settlements can give new insights into the analysis of landscape structures. Vodlozero National Park (NP) is one the largest strictly protected areas in Northwestern Europe. We mapped the location of historic villages, which were abandoned in 1958, and studied the effect of past human activity in the forest landscape in two different scales using forest survey data. We assessed the possible change in age, volume and tree species composition from the edge of open fields up to the distance of 5 km from villages. We made a larger landscape analysis using a grid of forest stands covering the whole northern part of the NP. The past human activity was clearly visible in the present forest landscape. Distance from villages affected age, volume and tree species composition of the forest stands. This effect was the strongest within the first two kilometers from the villages. At the level of whole northern NP, the proportion of spruce markedly increased after approximately 15 km from the nearest old village. The changes in the forests surrounding the villages were most likely the result of the intensive use of wood for different commodities needed in households and farming, in addition to short rotation slash and burn agriculture. If the occurrence of forest fires was more frequent closer to villages than in more remote areas, it can well explain the observed pattern in the abundance of spruce in the larger landscape that is less tolerant to fire than pine.

Tikkanen, Department of Biology, University of Eastern Finland, P.O. Box 111, FI-80101 Joensuu, Finland (Current: School of Forest Sciences, University of Eastern Finland, P.O. Box 111, FI-80101 Joensuu, Finland) & Interdisciplinary Research and Educational Center of Cross-border Communication CARELICA, Institute of History, Political and Social Sciences, Petrozavodsk State University, 33 Lenin Prospectus, 185910 Petrozavodsk, Republic of Karelia, Russia E-mail: Olli-Pekka.Tikkanen@uef.fi
Chernyakova, Interdisciplinary Research and Educational Center of Cross-border Communication CARELICA, Institute of History, Political and Social Sciences, Petrozavodsk State University, 33 Lenin Prospectus, 185910 Petrozavodsk, Republic of Karelia, Russia E-mail: irina.chernyakova@onego.ru

article id 501, category Research article

Jiaojun Zhu, Yutaka Gonda, Takeshi Matsuzaki, Masashi Yamamoto. (2003). Modeling relative wind speed by optical stratification porosity within the canopy of a coastal protective forest at different stem densities. Silva Fennica vol. 37 no. 2 article id 501. https://doi.org/10.14214/sf.501

Keywords: coastal protective forest; optical porosity; Pinus thunbergii; vertical forest structure; wind speed

Abstract | View details | Full text in PDF | Author Info

Wind speed and optical stratification porosity (OSP) were measured at various heights inside a coastal protective forest thinned to different stem densities to assess whether any characteristics of the wind profile in the coastal protective forest could be predicted from OSP. OSP was defined as vertical distribution of the proportion of sky hemisphere not obscured by tree elements inside a forest stand, and was determined for various heights using hemispherical photographic silhouettes on a computer processing system. The distribution of OSP in the coastal forest follows the Lambert-Beer’s law with an extinction coefficient (v). The relative wind speed within the canopy can be described using an exponential form with an attenuation coefficient (a). Variation in relative wind speed was very closely correlated with the distribution of OSP within the canopy. While below the canopy, i.e., in the trunk space, relative wind speed was little correlated with the distribution of OSP because the distribution of OSP was relatively constant there. Therefore, the linear relationships between relative wind speed and OSP and between the two coefficients v and a were established within the canopy. The results suggest that OSP can be used to predict the wind profile in case of the application within the canopy of the coastal forest.

Zhu, Qingyuan Station of Forest Ecology, Institute of Applied Ecology, the Chinese Academy of Sciences, No. 72 Wenhua Road, Shenyang 110016, P.R. China; Faculty of Agriculture, Niigata University, Niigata 950-2181, Japan E-mail: jiaojunzhu@iae.ac.cn
Gonda, Faculty of Agriculture, Niigata University, Niigata 950-2181, Japan E-mail: yg@nn.jp
Matsuzaki, Faculty of Agriculture, Niigata University, Niigata 950-2181, Japan E-mail: tm@nn.jp
Yamamoto, Faculty of Agriculture, Niigata University, Niigata 950-2181, Japan E-mail: my@nn.jp

article id 554, category Research article

Seppo Rouvinen, Timo Kuuluvainen, Juha Siitonen. (2002). Tree mortality in a Pinus sylvestris dominated boreal forest landscape in Vienansalo wilderness, eastern Fennoscandia. Silva Fennica vol. 36 no. 1 article id 554. https://doi.org/10.14214/sf.554

Keywords: dead wood; disturbance dynamics; spatial pattern analysis; mortality agent; forest structure; temporal variation

Abstract | View details | Full text in PDF | Author Info

Tree mortality and its causes and spatial pattern were examined along four transects (width 40 m, length 2550–3960 m), with a total length of 12 190 m and area of 48.8 ha, in a Pinus sylvestris L. dominated, boreal forest landscape. Tree mortality was determined within a time window of 3 years by identifying those trees (dbh ≥ 10 cm) along the transects that fitted into one of the three categories: 1) current mortality: trees that had died during the year of survey (1998), 2) recent mortality: trees that had died during the year (1997) before the survey year, and 3) predicted mortality: trees that were expected to die during the year (1999) following the survey year. Long-term tree mortality was studied on 10 plots (20 m x 100 m) by dating 87 dead trees using dendrochronological methods. The mean current mortality was 1.4 m3 ha–1 (3.7 trees ha–1). Both the recent and predicted mortalities were also 1.4 m3 ha–1. Mortality was, on the average, higher on peatlands than on mineral soils. The highest mortality was found within an area recently flooded by beavers. Over half of the examined trees (52%) were judged to die without any visible signs of an external abiotic cause. At the landscape scale, tree mortality was continuous although somewhat aggregated in space. Of the 66 dated standing dead Pinus trees, 23 (35%) had died during the 19th century and two during the 18th century, demonstrating that dead Pinus can remain standing for long periods of time before falling. Our results show that autogenic mortality of individual trees or small groups of trees was the predominant mode of disturbance in this Pinus dominated landscape.

Rouvinen, University of Joensuu, Faculty of Forestry, P.O. Box 111, FIN-80101 Joensuu, Finland E-mail: seppo.rouvinen@forest.joensuu.fi
Kuuluvainen, University of Helsinki, Department of Forest Ecology, P.O. Box 27, FIN-00014 University of Helsinki, Finland E-mail: tk@nn.fi
Siitonen, Finnish Forest Research Institute, P.O. Box 18, FIN-01301 Vantaa, Finland E-mail: juha.siitonen@metla.fi

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