Urban forests provide various ecosystem services. However, they also require fairly intensive management, which can be supported with up-to-date tree-level data. Until recently, the data have been collected using traditional field measurements. Laser scanning (LS) techniques provide efficient means for acquiring detailed three-dimensional (3D) data from the vegetation. The objective of this dissertation was to develop methods for mapping and monitoring urban forests at tree level.
In substudy I, a method (MS-STI) utilizing multiple data sources was developed for extracting tree-level attributes. The method combined airborne laser scanning (ALS), field measurements, and tree locations. The field sample was generalized using the non-parametric nearest neighbor (NN) approach. The relative root mean square error (RMSE) of diameter at breast height (DBH) varied between 18.8–33.8%.
The performance of MS-STI was assessed in substudy II by applying it to an existing tree register. 88.8% of the trees were successfully detected, and the relative RMSE of DBH for the most common diameter classes varied between 21.7–24.3%.
In substudy III, downed trees were mapped from a recreational forest area by detecting changes in the canopy. 97.7% of the downed trees were detected and the commission error was 10%. Species group, DBH, and volume were estimated for all downed trees using ALS metrics and existing allometric models. For the DBH, the relative RMSE was 20.8% and 34.1% for conifers and deciduous trees respectively.
Finally, in substudy IV, a method utilizing terrestrial laser scanning (TLS) and tree basic density was developed for estimating tree-level stem biomass for urban trees. The relative RMSE of the stem biomass estimates varied between 8.4–10.5%.
The dissertation demonstrates the applicability of LS data in assessing tree-level attributes for urban forests. The methods developed show potential in providing the planning and management of urban forests with cost-efficient and up-to-date tree-level data.
A mature tree stem generally consists of a column of wood that is composed of a series of annual incremental layers and enclosed in a covering of bark. The dynamic variations of the bark are complex due to its structure and function: the thick outer-bark acts as a protective barrier against the abiotic and biotic environment; while the phloem is where sugar transport occurs. Much of the bark variation is due to the transport of sugars and its related processes. The xylem pathway, which transports water in the opposite direction, is connected to the phloem in parallel along the entire length of the stem. The immediate connection between these two transport pathways suggests a functional linkage.
The purpose of this thesis is to study the dynamic processes that occur within the bark and its interaction with other internal tree processes and the external environment. These interactions have not been thoroughly quantified, especially on an intra-annual (e.g. daily) scale.
The thesis consists of four papers, of which one is a modelling paper and three are experimental studies. Growth is estimated with the model by separating the water-related influences from measured inner-bark, revealing a growth signal – proxy for cambial stem growth. Using this signal, a correlation study to microclimate variables is examined in one paper; and to assumed growth respiration in a second paper. The remaining two papers explore the seasonality of photosynthesis and respiration, and bark stem dynamics during the spring recovery period.
As a conclusion of this thesis, these papers show how inextricably linked individual tree processes and the environmental are to the changes within the bark. The culmination of this thesis opens new opportunities to further understand the dynamics of bark hydraulics and ecophysiological processes by implementing field measurements and state-of-the-art modelling.
Cycling of carbon (C) and nutrients plays pivotal role for functioning of every ecosystem. Biogeochemical cycles of carbon and nitrogen (N) are balanced by a network of inter-actions between plants, litter and soil chemistry, microbial communities, enzyme machinery and climate conditions. This thesis focuses on the role of terpenes in C and N transformations in boreal forest soils. Terpenes are abundant plant secondary compounds. The focus was on certain mono-, di-, and triterpenes.
Soil incubation experiments revealed that terpenes increased the mineralization of carbon but decreased net nitrogen mineralization and net nitrification. Additionally they increased the amounts of carbon and nitrogen in the microbial biomass through enhancement of bacterial growth; however, they inhibited fungal growth. This study suggests that terpenes can act as a C source for some microbial communities. Moreover, terpenes showed inhibitory potential against enzymes, which are involved in C, N, P, S cycling. The mechanism of inhibition seems to be based at least partially on ability of terpenes to bind enzymes.
The field experiment presented the effect of logging residues and wood ash on composition of terpenes and C and N cycling in soil five years after clear-cutting a Norway spruce stand. Logging residue treatment increased the concentrations of certain terpenes in the organic layer. Both, logging residue and wood ash treatments increased net N mineralization and net nitrification. Some changes in terpene concentrations correlated with C and N cycling processes, but the relationship between terpene concentration and C and N cycling processes remained still unclear in the field conditions.
In conclusion, terpenes can affect C and N transformations in boreal forest soil. It is probable that terpenes change N cycling retaining more N in organic forms and potentially decrease nitrogen losses from forest ecosystem.
Increasing rain in winter with climate change may expose boreal forests especially on drained peatlands to winter or spring waterlogging. Information about the response of main forest species on soil waterlogging is important for improving predictions of forest productivity and assessing the demand for ditch-network maintenance. In this study, the aim was to find out the physiological and growth responses of one-year-old Norway spruce (Picea abies (L.) Karst.), silver birch (Betula pendula Roth) and pubescent birch (Betula pubescens Ehrh.) seedlings subjected to one-month waterlogging in late dormancy, and to find out the morphology, physiology and growth of both birch species subjected to one-month waterlogging in the early growing season.
Dormancy waterlogging (DW) led to a reduction of root volume in spruce, but did not affect dark-acclimated chlorophyll fluorescence or biomass of needles, stems and roots. Root biomass and root hydraulic conductance of silver birch were reduced but aboveground organs were not affected by DW. In pubescent birch stomatal conductance and net photosynthesis (Amax) were reduced by DW, however, root morphology and leaf, stem and root biomass was not negatively affected. In conclusion, these tree species tolerated one-month winter waterlogging well.
Growth waterlogging (GW) led to the reduction of stomatal conductance and Amax as well as leaf area in both birch species. Leaf contents of potassium, calcium, magnesium, manganese and boron were reduced in silver birch, whereas only calcium and magnesium contents were reduced in pubescent birch by GW. In pubescent birch, fine cluster roots, the occurrence of leaf trichomes and stem lenticels were increased by GW. However, silver birch did not show such acclimation to waterlogging. In conclusion, GW caused more negative effects to both birch species than DW. The morphological rather than physiological differences may explain why pubescent birch grows better in wet soil than silver birch.