Quantitative assessment of total phenol contents of European oak (Quercus petraea and Quercus robur) by diffuse reflectance NIR spectroscopy on solid wood surfaces

Near infrared spectroscopy (NIRS) combined with multivariate analysis techniques was applied to assess phenol content of European oak. NIRS data were firstly collected directly from solid heartwood surfaces: in doing so, the spectra were recorded separately from the longitudinal radial and the transverse section surfaces by diffuse reflectance. The spectral data were then pretreated by several pre-processing procedures, such as multiplicative scatter correction, first derivative, second derivative and standard normal variate. The tannin contents of sawmill collected from the longitudinal radial and transverse section surfaces were determined by quantitative extraction with water/methanol (1:4, by vol). Then, total phenol contents in tannin extracts were measured by the Folin-Ciocalteu method. The NIR data were correlated against the Folin-Ciocalteu results. Calibration models built with partial least squares regression displayed strong correlation - as expressed by high determination correlation coefficient (r2) and high ratio of performance to deviation (RPD) - between measured and predicted total phenols content, and weak calibration and prediction errors (RMSEC, RMSEP). The best calibration was provided with second derivative spectra (r2 value of 0.93 for the longitudinal radial plane and of 0.91 for the transverse section plane). This study illustrates that the NIRS technique when used in conjunction with multivariate analysis could provide reliable, quick and non-destructive assessment of European oak heartwood extractives.

Spatial ecology of a specialist insect herbivore : the leaf-mining moth Tischeria ekebladella on the pedunculate oak Quercus robur

Herbivorous insects comprise a major part of terrestrial biodiversity, and their interactions with their host plants and natural enemies are of vast ecological importance. A large body of research demonstrates that the ecology and evolution of these insects may be affected by trophic interactions, by abiotic influences, and by intraspecific processes, but so far research on these individual aspects has rarely been combined. This thesis uses the leaf-mining moth Tischeria ekebladella and the pedunculate oak (Quercus robur) as a case study to assess how spatial variation in trophic interactions and the physical distribution of host trees jointly affect the distribution, dynamics and evolution of a host-specific herbivore. With respect to habitat quality, Tischeria ekebladella experiences abundant variation at several spatial scales. Most of this variation occurs at small scales notably among leaves and shoots within individual trees. While hypothetically this could cause moths to evolve an ability to select leaves and shoots of high quality, I did not find any coupling between female preference and offspring performance. Based on my studies on temporal variation in resource quality I therefore propose that unpredictable temporal changes in the relative rankings of individual resource units may render it difficult for females to predict the fate of their developing offspring. With respect to intraspecific processes, my results suggest that limited moth dispersal in relation to the spatial distribution of oak trees plays a key role in determining the regional distribution of Tischeria ekebladella. The distribution of the moth is aggregated at the landscape level, where local leaf miner populations are less likely to be present where oaks are scarce. A modelling exercise based on empirical dispersal estimates revealed that the moth population on Wattkast an island in south-western Finland is spatially structured overall, but that the relative importance of local and regional processes on tree-specific moth dynamics varies drastically across the landscape. To conclude, my work in the oak-Tischeria ekebladella system demonstrates that the local abundance and regional distribution of a herbivore may be more strongly influenced by the spatial location of host trees than by their relative quality. Hence, it reveals the importance of considering spatial context in the study of herbivorous insects, and forms a bridge between the classical fields of plant-insect interactions and spatial ecology.

Adaburuaren eta orbelaren euri interzepzioa haritzean (Quercus robur) eta intsinis pinuan (Pinus radiata)

Zuhaitz adaburuaren interzepzioak oihanpera prezipitazio osoaren frakzio bat soilik pasatzea eragiten du, gainerakoa lurrunketaz galtzen baita. Oihanpera pasatzen den ur horren parte bat ere lurzoruko orbelak interzeptatzen du. Espezie arteko konparaketa bat egiteko asmoz, adaburuaren eta orbelaren euri interzepzioa neurtu zen haritzean (Quercus robur) eta pinuan (Pinus radiata), sei euriteetako datuak aintzat hartuz (hiru neguan eta beste hiru udaberrian, haritzak hostoak zituenean). Horrez gain, laborategian bi orbel moten ur-erretentzio ahalmen maximoa (S) neurtu zen. Adaburuaren interzepzioa % 37koa izan zen haritzean eta % 24koa pinuan. Haritzean interzepzioa handiagoa izan zen udaberrian neguan baino, pinuan berdina izan zen bitartean. Azken honetan Hosto Azalera Indizearen (Leaf Area Index, LAI) balio altuago batek interzepzio altuagoa eragin zuen, haritzean erlazio hori behatu ez zelarik neurturiko LAI balioak homogeneoegiak zirelako seguruenik. Orbelaren interzepzioak prezipitazio osoaren % 2,1 eta % 1,5 suposatu zuen haritzean eta pinuan hurrenez hurren. Orbelaren gain eroritako ur kantitatea (throughfall) handitzean, interzepzioa handitu zen, maximo batera heldu arte (2,5 mm kg-1 m2-koa haritzean eta 1,8 mm kg-1 m2-koa pinuan). Adaburu motak, berriz, ez zuen eragin esangarririk izan, haritz azpian, pinu azpian eta klaroetan orbelak antzeko interzepzioa aurkeztu zuelarik. Ur-erretentzio ahalmen maximoa haritzean handiagoa izan zen, 4,7 eta 5,6 mm kg-1 m2 artekoa pinuaren 2,8 eta 3,1 mm kg-1 m2 arteko balioen aurrean. Pinuaren balio horiek antzekoak izan ziren orbel geruzaren sakonera edozein zela ere, baina haritzean, orbel sakonera handiagoarekin balio baxuagoak lortu ziren. Bi espezieen artean behaturiko ezberdintasunek iradokitzen dute harizti naturalak pinu landaketez ordezkatzeak ziklo hidrologikoa aldaraz dezakeela.

Multiple tree-ring proxies (earlywood width, latewood width and δ13C) from pedunculate oak (Quercus robur L.), Hungary

The aim of this study was to analyse the effects of climatic factors (i.e. monthly mean temperature and total precipitation) on radial growth (earlywood width, latewood width, and total ringwidth) and on latewood stable carbon isotope composition in a pedunculate oak (Quercus robur L) stand in northeastern Hungary. Earlywood widths showed the weakest common variance and lack of statistically significant relationship to monthly precipitation and temperature. Latewood width showed the strongest common chronological signal. Correlation analysis with the monthly climate series pointed out the strongest positive/negative correlation with June precipitation for latewood width/stable carbon isotope ratio. These parameters shared the strongest climatic response also for seasonal scale since the highest correlation coefficients, 0.49 and -0.62 for latewood width and stable carbon isotope ratio, respectively, were obtained for both with a 10-month precipitation total (from previous November to current August of the growing season). A combined parameter, derived as difference between latewood width and stable carbon isotope indices showed improved statistical relationship compared to the hydroclimatic calibration target both for local and regional spatial scales. Spatial correlation analysis indicated that the hydroclimatic signal encoded in these moisture sensitive tree-ring parameters from Bakta Forest is expected to be representative for the northeastern Carpathians and for the large part of the Great Hungarian Plain. In addition, the hydroclimatic signal of latewood width chronology was compared to three independent records. Results showed that neither the strength nor the rank of the similarity of the local hydroclimate signals were stable throughout the past two centuries. Future palaeo(hydro)climatological efforts targeting the Carpathian(-Balkan) region are recommended to track carefully the spatial domains for which a given, local, proxy-derived hydroclimate reconstruction might provide useful information.

Quercus Robur x sessiliflora

Von G. Maass

Abundance and sizes of European oak species (Quercus petraea (Matt.) Liebl., Quercus robur L.) in dependence of neighborhood and environmental factors

Quercus robur L. (pedunculate oak) and Quercus petraea (Matt.) Liebl. (sessile oak) are two European oak species of great economic and ecological importance. Even though both oaks have wide ecological amplitudes of suitable growing conditions, forests dominated by oaks often fail to regenerate naturally. The regeneration performance of both oak species is assumed to be subject to a variety of variables that interact with one another in complex ways. The novel approach of this research was to study the effect of many ecological variables on the regeneration performance of both oak species together and identify key variables and interactions for different development stages of the oak regeneration on a large scale in the field. For this purpose, overstory and regeneration inventories were conducted in oak dominated forests throughout southern Germany and paired with data on browsing, soil, and light availability. The study was able to verify the assumption that the occurrence of oak regeneration depends on a set of variables and their interactions. Specifically, combinations of site and stand specific variables such as light availability, soil pH and iron content on the one hand, and basal area and species composition of the overstory on the other hand. Also browsing pressure was related to oak abundance. The results also show that the importance of variables and their combinations differs among the development stages of the regeneration. Light availability becomes more important during later development stages, whereas the number of oaks in the overstory is important during early development stages. We conclude that successful natural oak regeneration is more likely to be achieved on sites with lower fertility and requires constantly controlling overstory density. Initially sufficient mature oaks in the overstory should be ensured. In later stages, overstory density should be reduced continuously to meet the increasing light demand of oak seedlings and saplings.

Fungal Planet description sheets: 281–319

Novel species of fungi described in the present study include the following from South Africa: Alanphillipsia aloeicola from Aloe sp., Arxiella dolichandrae from Dolichandra unguiscati, Ganoderma austroafricanum from Jacaranda mimosifolia, Phacidiella podocarpi and Phaeosphaeria podocarpi from Podocarpus latifolius, Phyllosticta mimusopisicola from Mimusops zeyheri and Sphaerulina pelargonii from Pelargonium sp. Furthermore, Barssia maroccana is described from Cedrus atlantica (Morocco), Codinaea pini from Pinus patula (Uganda), Crucellisporiopsis marquesiae from Marquesia acuminata (Zambia), Dinemasporium ipomoeae from Ipomoea pes-caprae (Vietnam), Diaporthe phragmitis from Phragmites australis (China), Marasmius vladimirii from leaf litter (India), Melanconium hedericola from Hedera helix (Spain), Pluteus albotomentosus and Pluteus extremiorientalis from a mixed forest (Russia), Rachicladosporium eucalypti from Eucalyptus globulus (Ethiopia), Sistotrema epiphyllum from dead leaves of Fagus sylvatica in a forest (The Netherlands), Stagonospora chrysopyla from Scirpus microcarpus (USA) and Trichomerium dioscoreae from Dioscorea sp. (Japan). Novel species from Australia include: Corynespora endiandrae from Endiandra introrsa, Gonatophragmium triuniae from Triunia youngiana, Penicillium coccotrypicola from Archontophoenix cunninghamiana and Phytophthora moyootj from soil. Novelties from Iran include Neocamarosporium chichastianum from soil and Seimatosporium pistaciae from Pistacia vera, Xenosonderhenia eucalypti and Zasmidium eucalyptigenum are newly described from Eucalyptus urophylla in Indonesia. Diaporthe acaciarum and Roussoella acacia are newly described from Acacia tortilis in Tanzania. New species from Italy include Comoclathris spartii from Spartium junceum and Phoma tamaricicola from Tamarix gallica. Novel genera include (Ascomycetes): Acremoniopsis from forest soil and Collarina from water sediments (Spain), Phellinocrescentia from a Phellinus sp. (French Guiana), Neobambusicola from Strelitzia nicolai (South Africa), Neocladophialophora from Quercus robur (Germany), Neophysalospora from Cotymbia henryi (Mozambique) and Xenophaeosphaeria from Grewia sp. (Tanzania). Morphological and culture characteristics along with ITS DNA barcodes are provided for all taxa.

Fungal Planet description sheets: 281-319

Novel species of fungi described in the present study include the following from South Africa: Alanphillipsia aloeicola from Aloe sp., Arxiella dolichandrae from Dolichandra unguiscati, Ganoderma austroafricanum from Jacaranda mimosifolia, Phacidiella podocarpi and Phaeosphaeria podocarpi from Podocarpus latifolius, Phyllosticta mimusopisicola from Mimusops zeyheri and Sphaerulina pelargonii from Pelargonium sp. Furthermore, Barssia maroccana is described from Cedrus atlantica (Morocco), Codinaea pini from Pinus patula (Uganda), Crucellisporiopsis marquesiae from Marquesia acuminata (Zambia), Dinemasporium ipomoeae from Ipomoea pes-caprae (Vietnam), Diaporthe phragmitis from Phragmites australis (China), Marasmius vladimirii from leaf litter (India), Melanconium hedericola from Hedera helix (Spain), Pluteus albotomentosus and Pluteus extremiorientalis from a mixed forest (Russia), Rachicladosporium eucalypti from Eucalyptus globulus (Ethiopia), Sistotrema epiphyllum from dead leaves of Fagus sylvatica in a forest (The Netherlands), Stagonospora chrysopyla from Scirpus microcarpus (USA) and Trichomerium dioscoreae from Dioscorea sp. (Japan). Novel species from Australia include: Corynespora endiandrae from Endiandra introrsa, Gonatophragmium triuniae from Triunia youngiana, Penicillium coccotrypicola from Archontophoenix cunninghamiana and Phytophthora moyootj from soil. Novelties from Iran include Neocamarosporium chichastianum from soil and Seimatosporium pistaciae from Pistacia vera, Xenosonderhenia eucalypti and Zasmidium eucalyptigenum are newly described from Eucalyptus urophylla in Indonesia. Diaporthe acaciarum and Roussoella acacia are newly described from Acacia tortilis in Tanzania. New species from Italy include Comoclathris spartii from Spartium junceum and Phoma tamaricicola from Tamarix gallica. Novel genera include (Ascomycetes): Acremoniopsis from forest soil and Collarina from water sediments (Spain), Phellinocrescentia from a Phellinus sp. (French Guiana), Neobambusicola from Strelitzia nicolai (South Africa), Neocladophialophora from Quercus robur (Germany), Neophysalospora from Cotymbia henryi (Mozambique) and Xenophaeosphaeria from Grewia sp. (Tanzania). Morphological and culture characteristics along with ITS DNA barcodes are provided for all taxa.

Spatial ecology of an oak-associated herbivore community : A metacommunity of herbivores

Habitat fragmentation is currently affecting many species throughout the world. As a consequence, an increasing number of species are structured as metapopulations, i.e. as local populations connected by dispersal. While excellent studies of metapopulations have accumulated over the past 20 years, the focus has recently shifted from single species to studies of multiple species. This has created the concept of metacommunities, where local communities are connected by the dispersal of one or several of their member species. To understand this higher level of organisation, we need to address not only the properties of single species, but also establish the importance of interspecific interactions. However, studies of metacommunities are so far heavily biased towards laboratory-based systems, and empirical data from natural systems are urgently needed. My thesis focuses on a metacommunity of insect herbivores on the pedunculate oak Quercus robur a tree species known for its high diversity of host-specific insects. Taking advantage of the amenability of this system to both observational and experimental studies, I quantify and compare the importance of local and regional factors in structuring herbivore communities. Most importantly, I contrast the impact of direct and indirect competition, host plant genotype and local adaptation (i.e. local factors) to that of regional processes (as reflected by the spatial context of the local community). As a key approach, I use general theory to generate testable hypotheses, controlled experiments to establish causal relations, and observational data to validate the role played by the pinpointed processes in nature. As the central outcome of my thesis, I am able to relegate local forces to a secondary role in structuring oak-based insect communities. While controlled experiments show that direct competition does occur among both conspecifics and heterospecifics, that indirect interactions can be mediated by both the host plant and the parasitoids, and that host plant genotype may affect local adaptation, the size of these effects is much smaller than that of spatial context. Hence, I conclude that dispersal between habitat patches plays a prime role in structuring the insect community, and that the distribution and abundance of the target species can only be understood in a spatial framework. By extension, I suggest that the majority of herbivore communities are dependent on the spatial structure of their landscape and urge fellow ecologists working on other herbivore systems to either support or refute my generalization.

Tammen alueellisen levinneisyyden rajoitteet : Tapaustutkimus Länsi-Turunmaalla

Elinympäristön vaikutusta eliölajien esiintymiseen voidaan tutkia habitaattimallinnuksen keinoin. Havainnot lajin esiintymisestä ja puuttumisesta eri kohdissa maisemaa suhteutetaan tilastollisen mallin avulla ympäristötekijöihin, jolloin saadaan kuva lajin elinympäristövaatimuksista. Tällöin oletetaan, että laji esiintyy kaikkialla siellä, missä sen elinympäristövaatimukset täyttyvät. Metapopulaatioteorian valossa näin ei kuitenkaan aina ole: maisemassa voi olla runsaasti lajille soveltuvia mutta asuttamattomia kasvupaikkoja, koska uusien yksilöiden leviäminen ja vanhojen häviäminen eivät välttämättä ole yksittäisten kasvupaikkojen tasolla tasapainossa. Siten myös lajin leviämiskyky vaikuttaa siihen, millaiseksi sen levinneisyyskuvio maisematasolla muodostuu. Tässä työssä keskityn tammen (Quercus robur) alueellisen levinneisyyden mallintamiseen. Tammen suhteellinen harvinaisuus Suomessa sekä sen rooli luonnon monimuotoisuuden merkittävänä tukipilarina tekevät siitä mielenkiintoisen kohdelajin ekologiselle tutkimukselle. Tutkimuskohteekseni valitsin Wattkastin saaren, n. 5 km2:n alueen Länsi-Turunmaalta. Wattkastissa on tutkittu kahdeksan vuoden ajan tammella elävien hyönteisyhteisöjen rakennetta ja kannanvaihteluita, ja saaressa kasvaa yli 1800 luonnonvaraista tammea, joiden tarkat sijainnit tiedetään. Tässä ympäristössä tutkin, rajoittaako tammen alueellista levinneisyyttä ensisijaisesti sopivien elinympäristöjen tilajakauma vai pikemminkin sen leviämiskyky. Yhdistin tammen esiintymiskuviota kuvaavaan habitaattimalliin kokeellisen aineiston, jonka avulla arvioin tammen paikallisen esiintymiskuvion ja tammelle soveltuvien elinympäristöjen tilajakauman vastaavuutta. Kokeellisen aineiston muodostivat 104 Wattkastiin vuonna 2004 istutettua pikkutammea, joiden selviytymisen ja kasvupaikkaolot kartoitin syksyllä 2009. Tutkin yleistetyillä lineaarisilla malleilla puiden menestymiseen siis selviytymiseen ja kuntoon vaikuttavia tekijöitä. Etsin potentiaalisia selittäjiä tammen menestymiselle kasvupaikan ympäristötekijöistä sekä istutetun puun sijainnista suhteessa luontaisiin tammikasvustoihin. Lisäksi tutkin habitaattimallin avulla, selittävätkö ympäristötekijät tammen nykyisen esiintymiskuvion Wattkastissa. Havaitsin, että istutetut puut olivat selviytyneet keskimäärin hyvin ja ettei niiden menestyminen riippunut sijainnista suhteessa luontaisiin tammikasvustoihin. Habitaattimallin selitysaste oli vain 19 %, eli kasvupaikkatekijät selittivät heikosti tammen nykyisen esiintymiskuvion Wattkastissa. Tulosten perusteella tammen paikallinen esiintymiskuvio ei vastaa sille soveltuvien elinympäristöjen jakaumaa maisemassa, joten tammen levinneisyyttä Wattkastissa rajoittaa ilmeisesti sen leviämiskyky. Tulokseni viittaavat siihen, ettei tammen elinympäristön laadussa ole suuria vaihteluita Wattkastin sisällä, koska sopivia kasvupaikkoja on tarjolla tammen nykyesiintymiseen nähden runsaasti. Tämä on tammihyönteistutkimusten kannalta kiinnostava tulos, koska se tarkoittaa, että aiemmat havainnot isäntäpuun sijainnin ja hyönteisten kannanvaihteluiden välisestä yhteydestä edustavat todellisia, tilaan sidottuja populaatioprosesseja eivätkä isäntäpuun välittämiä eroja elinympäristön laadussa. Lisäksi tutkimukseni osoittaa, että yhdistämällä habitaattimallinnukseen kokeellinen lähestymistapa saadaan realistisempi kuva lajin levinneisyyttä rajoittavista tekijöistä kuin tutkimalla pelkästään ympäristötekijöiden vaikutusta lajin esiintymiseen. Jos lajin rajoittunut leviämiskyky on vaikuttanut sen esiintymiskuvion syntyyn, pelkästään ympäristötekijöihin perustuva levinneisyysmalli liioittelee levinneisyyttä. Kokeellisen tutkimuksen avulla on tällaisessa tapauksessa mahdollista paljastaa myös leviämiskyvyn rooli esiintymiskuvion taustalla.

Spatial ecology of food webs : herbivore-parasitoid communities on the pedunculate oak

Herbivorous insects, their host plants and natural enemies form the largest and most species-rich communities on earth. But what forces structure such communities? Do they represent random collections of species, or are they assembled by given rules? To address these questions, food webs offer excellent tools. As a result of their versatile information content, such webs have become the focus of intensive research over the last few decades. In this thesis, I study herbivore-parasitoid food webs from a new perspective: I construct multiple, quantitative food webs in a spatially explicit setting, at two different scales. Focusing on food webs consisting of specialist herbivores and their natural enemies on the pedunculate oak, Quercus robur, I examine consistency in food web structure across space and time, and how landscape context affects this structure. As an important methodological development, I use DNA barcoding to resolve potential cryptic species in the food webs, and to examine their effect on food web structure. I find that DNA barcoding changes our perception of species identity for as many as a third of the individuals, by reducing misidentifications and by resolving several cryptic species. In terms of the variation detected in food web structure, I find surprising consistency in both space and time. From a spatial perspective, landscape context leaves no detectable imprint on food web structure, while species richness declines significantly with decreasing connectivity. From a temporal perspective, food web structure remains predictable from year to year, despite considerable species turnover in local communities. The rate of such turnover varies between guilds and species within guilds. The factors best explaining these observations are abundant and common species, which have a quantitatively dominant imprint on overall structure, and suffer the lowest turnover. By contrast, rare species with little impact on food web structure exhibit the highest turnover rates. These patterns reveal important limitations of modern metrics of quantitative food web structure. While they accurately describe the overall topology of the web and its most significant interactions, they are disproportionately affected by species with given traits, and insensitive to the specific identity of species. As rare species have been shown to be important for food web stability, metrics depicting quantitative food web structure should then not be used as the sole descriptors of communities in a changing world. To detect and resolve the versatile imprint of global environmental change, one should rather use these metrics as one tool among several.

Environmental and climatic dependences of stable isotope ratios in tree rings on different temporal scales

This work examines stable isotope ratios of carbon, oxygen and hydrogen in annual growth rings of trees. Isotopic composition in wood cellulose is used as a tool to study past climate. The method benefits from the accurate and precise dating provided by dendrochronology. In this study the origin, nature and the strength of climatic correlations are studied on different temporal scales and at different sites in Finland. The origin of carbon isotopic signal is in photosynthetic fractionation. The basic physical and chemical fractionations involved are reasonably well understood. This was confirmed by measuring instantaneous photosynthetic discrimination on Scots pine (Pinus sylvestris L.). The internal conductance of CO2 was recognized to have a significant impact on the observed fractionation, and further investigations are suggested to quantify its role in controlling the isotopic signal of photosynthates. Isotopic composition of the produced biomass can potentially be affected by variety of external factors that induce physiological changes in trees. Response of carbon isotopic signal in tree ring cellulose to changes in resource availability was assessed in a manipulation experiment. It showed that the signal was relatively stable despite of changes in water and nitrogen availability to the tree. Palaeoclimatic reconstructions are typically based on functions describing empirical relationship between isotopic and climatic parameters. These empirical relationships may change depending on the site conditions, species and timeframe studied. Annual variation in Scots pine tree ring carbon and oxygen isotopic composition was studied in northern and in central eastern Finland and annual variation in tree ring latewood carbon, oxygen and hydrogen isotopic ratio in Oak (Quercus robur L.) was studied in southern Finland. In all of the studied sites at least one of the studied isotope ratios was shown to record climate strongly enough to be used in climatic reconstructions. Using the observed relationships, four-century-long climate reconstructions from living Scots pine were created for northern and central eastern Finland. Also temporal stability of the relationships between three proxy indicators, tree ring growth and carbon and oxygen isotopic composition was studied during the four-hundred-year period. Isotope ratios measured from tree rings in Finland were shown to be sensitive indicators of climate. Increasing understanding of environmental controls and physiological mechanisms affecting tree ring isotopic composition will make possible more accurate interpretation of isotope data. This study also demonstrated that by measuring multiple isotopes and physical proxies from the same tree rings, additional information on tree physiology can be obtained. Thus isotopic ratios measured from tree ring cellulose provide means to improve the reliability of climate reconstructions.

Monimuotoisuudelle arvokkaat ontot puut kaupunkialueilla – onttojen runkojen esiintymistodennäköisyyteen vaikuttavat tekijät

Tutkimuksen tavoitteena oli selvittää lahosta puuaineesta riippuvaiselle lajistolle tärkeiden onttojen puiden ominaisuuksien vaikutusta pääkaupunkiseudun jalojen puistopuiden onttouden esiintymistodennäköisyyteen. Tutkimuksessa mitattavia ominaisuuksia olivat puiden läpimitta, puulaji, pituus sekä kasvupaikan valoisuus ja metsäisyys. Tutkittavia puulajeja olivat lehmus (Tilia cordata), vaahtera (Acer platanoides), tammi (Quercus robur), saarni (Fraxinus excelsior) ja jalavat (Ulmus glabra ja U. laevis). Tutkimuskohteina olivat pääkaupunkiseudulla sijaitsevat 14 viheraluetta, jotka vaihtelivat metsäisistä puustokeskittymistä valoisiin ja intensiivisesti hoidettuihin puistoihin. Onttouden esiintymisen riippuvuutta muista muuttujista tutkittiin korrelaatioanalyysillä sekä logistisilla regressioanalyyseillä, joissa huomioitiin myös puiden jakaantuminen viheraluiden välillä. Puulajilla ja puun läpimitalla oli vaikutusta onttouden esiintymistodennäköisyyteen. Kasvupaikan valoisuudella oli merkitystä rungon onttoutumisessa ainakin lehmukselle ja vaahteralle. Metsäisyys liittyy valoisuuteen ja näiden muuttujien vaikutus rungon onttoutumistodennäköisyyteen on kietoutunut toisiinsa. Pituudella ei todennäköisesti ollut merkitystä onttoutumiseen. Tulosten perusteella etenkin pääkaupunkiseudun lehmukset sekä vaahterat ovat herkkiä onttoutumaan ja täten ne muodostavat monimuotoisia elinympäristöjä. Valoisuuden ja metsäisyyden vaikutus onttoutumiseen on vahvasti sidoksissa puiden hoitoon ja hoitotoimilla on siis suuri vaikutus onkaloiden syntyyn.