Effect of forest health and structure to the relative surface temperature captured by airborne thermal imagery : case study in Norway Spruce-dominated stands in Southern Finland

Metsän terveydentilan ja rakenteen vaikutusta ilmalämpökuvauksella hankittuun suhteelliseen pintalämpötilaan tutkittiin kuusikoissa Etelä-Suomessa. Latvuksen pintalämpötilan on tiedetty jo pitkään olevan hyödyllinen kasvillisuuden vesitasapainon tarkkailussa. Viimeaikaiset tutkimukset ovat osoittaneet sen potentiaalin myös kasvillisuuden terveydentilan tarkkailussa. Aineistona olivat ilmalämpökuvasto, ilmalaserkeilausaineisto ja kenttämittaukset tutkimusalueelta. Suhteellinen pintalämpötila korreloi vahvimmin negatiivisesti runkotilavuuden logaritmin, keskipituuden ja pohjapintaalan logaritmin kanssa 254m2 (9-m ympyräkoeala) resoluutiolla. Toisin sanoen, pidemmät ja vanhemmat metsiköt olivat kylmempiä pintalämpötilaltaan. Lisäksi laserkeilauspiirteitä, kuten korkeusprosenttiosuuksia ja latvuston peittävyyttä, verrattiin pintalämpötilaan. Latvuston pintamallin keskihajonta, korkeuspiirteet ja latvuston peittävyys korreloivat vahvimmin negatiivisesti pintalämpötilan kanssa. Korkeampia pintalämpötiloja havaittiin harsuuntuneissa latvuksissa keskimäärin osoittaen, että lämpökuvat voisivat tuoda lisäinformaatiota metsän terveydentilan luokitteluun. Harsuuntuneiden koealojen pintalämpötilat vaihtelivat kuitenkin merkittävästi. Huomattiin myös, että pintalämpötilojen erotus latvuston ja maan välillä oli suurempi harsuuntuneissa koealoissa. Tulosten perusteella voidaan todeta, että metsän terveydentila ja rakenne vaikuttavat ilmalämpökuvauksella hankittuun pintalämpötilaan ja että nämä vaikutukset tulisivat ottaa huomioon metsänterveydentilaa kartoittaessa lämpökuvien avulla.The effect of forest health and structure to the relative surface temperature captured by airborne thermal imagery was investigated in Norway Spruce-dominated stands in Southern Finland. Canopy surface temperature has long been recognized useful in monitoring vegetation water status. Recent studies have shown also its potential in monitoring vegetation health. Airborne thermal imagery, Airborne Light Detection and Ranging (LiDAR) and field measurements were acquired from the area of interest (AOI). The relative surface temperature correlated most negatively with the logarithm of stem volume, Lorey’s height and logarithm of basal area at resolution of 254m2 (9-m radius). In other words, taller and older stands had colder surface temperatures. In addition, LiDAR metrics, such as height percentiles and canopy cover percentage, were compared with surface temperature. Standard deviation of canopy height model, height features (H90, CHM_max) and canopy cover percentage were most strongly negatively correlated with the surface temperature. On average, higher surface temperatures were detected in defoliated canopies indicating that thermal images may provide some additional information for classifying forests health status. However, the surface temperature of defoliated plots varied considerably. It was also found that surface temperature differences between canopy and ground responses were higher in defoliated plots. Based on the results, forest health and structure affect to the surface temperature captured by airborne thermal imagery and these effects should be taken into account when developing forest health mapping applications using thermal imagery

A Novel Method to Simultaneously Measure Leaf Gas Exchange and Water Content

Understanding the relationship between plant water status and productivity and between plant water status and plant mortality is required to effectively quantify and predict the effects of drought on plants. Plant water status is closely linked to leaf water content that may be estimated using remote sensing technologies. Here, we used an inexpensive miniature hyperspectral spectrometer in the 1550–1950 nm wavelength domain to measure changes in silver birch (Betula pendula Roth) leaf water content combined with leaf gas exchange measurements at a sub-minute time resolution, under increasing vapor pressure deficit, CO2 concentrations, and light intensity within the measurement cuvette; we also developed a novel methodology for calibrating reflectance measurements to predict leaf water content for individual leaves. Based on reflectance at 1550 nm, linear regression modeling explained 98–99% of the variation in leaf water content, with a root mean square error of 0.31–0.43 g cm−2. The prediction accuracy of the model represents a c. ten-fold improvement compared to previous studies that have used destructive sampling measurements of several leaves. This novel methodology allows the study of interlinkages between leaf water content, transpiration, and assimilation at a high time resolution that will increase understanding of the movement of water within plants and between plants and the atmosphere

Youth Inclusion in Forest Policy Dialogue: Contemplating HumanForest Relationships through Arts-Based Methods

Awareness of humanforest relationships offers a basis for meaningful forest policy participation. However, weakening connections to forests, particularly among young people, hamper youth inclusion in policy arenas. We consider the use of arts-based methods as knowledge practices that nurture humanforest relationships and may promote inclusive policies. Arts-based methods, such as photography, music, or drama, offer insights and elicit opinions. Within the forest domain, exploiting such methods requires better understanding of how participants perceive them. Here we present two cases where young people (1730 years) unfold their forest relationships. Following prompted retrospective reflections, we qualitatively analyse participant perceptions of the interventions. Case one is an innovation workshop blending art and science, where young research participants joined artists and environmental and forest scientists. Case two is a writing exercise for young research participants, where a hip-hop/rap video about laser scanning and the role of forests in climate change was used to catalyse participants reflections. Analysis applied the tripartite model of attitude comprising cognitive, affective, and behavioural dimensions. The workshop results emphasise benefits of networking and fruitful reflections, coupled with unequal participation concerns. The video experience yielded a range of thoughts and emotions, including excitement and invitingness, but also irritation, doubts over its influence, and no explicit behavioural intentions. The findings suggest that realising the opportunities of arts-based knowledge practices requires time and space for ensuring that young peoples voices are heard. More inclusive participation of youth in formal and informal forest policy dialogue calls for careful facilitation and means to secure continuation

Close-range hyperspectral spectroscopy reveals leaf water content dynamics

Water plays a crucial role in maintaining plant functionality and drives many ecophysiological processes. The distribution of water resources is in a continuous change due to global warming affecting the productivity of ecosystems around the globe, but there is a lack of non-destructive methods capable of continuous monitoring of plant and leaf water content that would help us in understanding the consequences of the redistribution of water. We studied the utilization of novel small hyperspectral sensors in the 1350-1650 nm and 2000-2450 nm spectral ranges in non-destructive estimation of leaf water content in laboratory and field conditions. We found that the sensors captured up to 96% of the variation in equivalent water thickness (EWT, g/m(2)) and up to 90% of the variation in relative water content (RWC). Further tests were done with an indoor plant (Dracaena marginate Lem.) by continuously measuring leaf spectra while drought conditions developed, which revealed detailed diurnal dynamics of leaf water content. The laboratory findings were supported by field measurements, where repeated leaf spectra measurements were in fair agreement (R-2 = 0.70) with RWC and showed similar diurnal dynamics. The estimation of leaf mass per area (LMA) using leaf spectra was investigated as a pathway to improved RWC estimation, but no significant improvement was found. We conclude that close-range hyper spectral spectroscopy can provide a novel tool for continuous measurement of leaf water content at the single leaf level and help us to better understand plant responses to varying environmental conditions.Peer reviewe

Climate change alters disease severity in the Endoconidiophora polonica-Norway spruce pathosystem

Posteri201

Structural Changes in Boreal Forests Can Be Quantified Using Terrestrial Laser Scanning

Terrestrial laser scanning (TLS) has been adopted as a feasible technique to digitize trees and forest stands, providing accurate information on tree and forest structural attributes. However, there is limited understanding on how a variety of forest structural changes can be quantified using TLS in boreal forest conditions. In this study, we assessed the accuracy and feasibility of TLS in quantifying changes in the structure of boreal forests. We collected TLS data and field reference from 37 sample plots in 2014 (T1) and 2019 (T2). Tree stems typically have planar, vertical, and cylindrical characteristics in a point cloud, and thus we applied surface normal filtering, point cloud clustering, and RANSAC-cylinder filtering to identify these geometries and to characterize trees and forest stands at both time points. The results strengthened the existing knowledge that TLS has the capacity to characterize trees and forest stands in space and showed that TLS could characterize structural changes in time in boreal forest conditions. Root-mean-square-errors (RMSEs) in the estimates for changes in the tree attributes were 0.99–1.22 cm for diameter at breast height (Δdbh), 44.14–55.49 cm2 for basal area (Δg), and 1.91–4.85 m for tree height (Δh). In general, tree attributes were estimated more accurately for Scots pine trees, followed by Norway spruce and broadleaved trees. At the forest stand level, an RMSE of 0.60–1.13 cm was recorded for changes in basal area-weighted mean diameter (ΔDg), 0.81–2.26 m for changes in basal area-weighted mean height (ΔHg), 1.40–2.34 m2/ha for changes in mean basal area (ΔG), and 74–193 n/ha for changes in the number of trees per hectare (ΔTPH). The plot-level accuracy was higher in Scots pine-dominated sample plots than in Norway spruce-dominated and mixed-species sample plots. TLS-derived tree and forest structural attributes at time points T1 and T2 differed significantly from each other (p < 0.05). If there was an increase or decrease in dbh, g, h, height of the crown base, crown ratio, Dg, Hg, or G recorded in the field, a similar outcome was achieved by using TLS. Our results provided new information on the feasibility of TLS for the purposes of forest ecosystem growth monitoring

Structural Changes in Boreal Forests Can Be Quantified Using Terrestrial Laser Scanning

Terrestrial laser scanning (TLS) has been adopted as a feasible technique to digitize trees and forest stands, providing accurate information on tree and forest structural attributes. However, there is limited understanding on how a variety of forest structural changes can be quantified using TLS in boreal forest conditions. In this study, we assessed the accuracy and feasibility of TLS in quantifying changes in the structure of boreal forests. We collected TLS data and field reference from 37 sample plots in 2014 (T1) and 2019 (T2). Tree stems typically have planar, vertical, and cylindrical characteristics in a point cloud, and thus we applied surface normal filtering, point cloud clustering, and RANSAC-cylinder filtering to identify these geometries and to characterize trees and forest stands at both time points. The results strengthened the existing knowledge that TLS has the capacity to characterize trees and forest stands in space and showed that TLS could characterize structural changes in time in boreal forest conditions. Root-mean-square-errors (RMSEs) in the estimates for changes in the tree attributes were 0.99–1.22 cm for diameter at breast height (Δdbh), 44.14–55.49 cm2 for basal area (Δg), and 1.91–4.85 m for tree height (Δh). In general, tree attributes were estimated more accurately for Scots pine trees, followed by Norway spruce and broadleaved trees. At the forest stand level, an RMSE of 0.60–1.13 cm was recorded for changes in basal area-weighted mean diameter (ΔDg), 0.81–2.26 m for changes in basal area-weighted mean height (ΔHg), 1.40–2.34 m2/ha for changes in mean basal area (ΔG), and 74–193 n/ha for changes in the number of trees per hectare (ΔTPH). The plot-level accuracy was higher in Scots pine-dominated sample plots than in Norway spruce-dominated and mixed-species sample plots. TLS-derived tree and forest structural attributes at time points T1 and T2 differed significantly from each other (p < 0.05). If there was an increase or decrease in dbh, g, h, height of the crown base, crown ratio, Dg, Hg, or G recorded in the field, a similar outcome was achieved by using TLS. Our results provided new information on the feasibility of TLS for the purposes of forest ecosystem growth monitoring

Terrestrial Laser Scanning Reveal Connection Between Changes in Tree Stem Dimensions and Crown Structure

Peer reviewe

Tree Water Status Affects Tree Branch Position

Physiological processes cause movements of tree stems and branches that occur in a circadian rhythm and over longer time periods, but there is a lack of quantitative understanding of the cause-and-effect relationships. We investigated the movement of tree branches in a long-term drought experiment and at a circadian time scale using time-series of terrestrial laser scanning measurements coupled with measurements of environmental drivers and tree water status. Our results showed that movement of branches was largely explained by leaf water status measured as leaf water potential in a controlled environment for both measured trees (R2 = 0.86 and R2 = 0.75). Our hypothesis is that changes in leaf and branch water status would cause branch movements was further supported by strong relationship between vapor pressure deficit and overnight branch movement (R2 = [0.57–0.74]). Due to lower atmospheric water demand during the nighttime, tree branches settle down as the amount of water in leaves increases. The results indicate that the quantified movement of tree branches could help us to further monitor and understand the water relations of tree communities