Antti Uotila

Mapping of snow-damaged trees based on bitemporal airborne LiDAR data

The use of multitemporal LiDAR data in forest-monitoring applications has been so far largely unexplored. In this work, we aimed to develop and test a simple method for the detection of snow-induced canopy changes by employing bitemporal LiDAR data acquired in 2006–2010. Our study area was located in southern Finland (62°N, 24°E), where snow-induced damage occurred in 10 permanent Scots pine (Pinus sylvestris)-dominated plots in winter 2009–2010. For the detection of snow-damaged crowns, we developed a ∆CHM method by contrasting bitemporal LiDAR canopy height models (CHMs) and analyzing the resulting difference image, using binary image operations to extract the damaged crowns. Furthermore, we examined the structural and spatial factors that could explain snow damage at the individual tree level. The ∆CHM method developed is based on two threshold parameters, i.e., the required height difference in the contrasted CHMs and the minimum plausible area of damage. When testing the performance of ∆CHM method, we found that the plot-level omission error rates were 19–75%, while the commission error rates were 0–21%. Furthermore, the relative estimation accuracy of the damaged crown projection area (DCPA) ranged from −16.4 to 5.4%. The observed damage could be explained at tree level by stem tapering, relative tree size, and local stand density. To conclude, ∆CHM method developed constitutes a potential tool for the monitoring of structural canopy changes in the dominant tree layer if dense multitemporal LiDAR data are available.

The effect of different levels of green pruning on the diameter growth of Pinus sylvestris L.

It was hypothesized that maximum living crown removal can be determined from experimental data using linear statistical models. Pruning experiments were carried out in four Scots pine (Pinus sylvestris L.) stands. Zero to nine living branch whorls were removed in three stands in southern Finland, and 0–4.5 m of the living crown was removed in a stand in northern Finland. Only dead branch whorls were removed from the control trees. A total of 517 trees were analyzed. Diameter increment was measured five years after pruning. The growth reduction was statistically significant when 40% or more of the living crown was removed by pruning. According to the linear models, green pruning decreased diameter growth by 0 to 33% at defoliation levels below 40%. This loss in diameter growth is, from an economical point of view, compensated by the knotfree timber resulting from pruning 2–3 years earlier.

Two types of the European race of Gremmeniella abietina can be identified with immunoblotting

Gremmeniella abietina, the causative agent of Scleroderris canker in conifers, has been separated into three races: European, North American and Asian. Recent studies have suggested that the European race in Fennoscandinavia may be divided into two types. We show that these types cannot be identified with their protein patterns obtained under denaturing conditions, but the two types can be separated based upon presence or absence of a 26-28 kD immunoreactive double band in western blotting. Polyclonal antibodies, either crude or purified with preparative western blotting, detected this double band in all tested 25 isolates classified as type B or short tree type but not in any of 27 isolates of type A or large tree type. This immunoassay was used to type 10 unclassified isolates. The results indicated that short tree type of the Swedish classification is immunologically identical to the Finnish type B and large tree type is identical to the type A. Thus, in Fennoscandinavia the European race can be divided into two serovars as previously suggested by random amplified polymorphic DNA markers.

Effects of stump and slash removal on growth and mycorrhization of Picea abies seedlings outplanted on a forest clear-cut

The objectives of this study were to investigate impact of stump and slash removal on growth and mycorrhization of Picea abies seedlings outplanted on a forest clear-cut. Four non-replicated site preparation treatments included: (1) mounding (M), (2) removal of stumps (K), (3) mounding and removal of logging slash (HM) and (4) removal of logging slash and stumps (HK). Results showed that height increment of the seedlings was highest in K and lowest in M after the third growing season, and similar pattern remained after the fourth season. Ectomycorrhizal (ECM) colonisation of seedling roots was highest in M (96.6%) and lowest in K (72.3%), and even in HK (76.0%) and HM (76.3%). Morphotyping and sequencing of internal transcribed spacer of fungal ribosomal DNA revealed a total of 13 ECM species. Among those, Thelephora terrestris and Cenococcum geophilum were the most common, found on 27.4% and 26.3% of roots, respectively. The rest of species colonised 26.6% of roots. Richness of ECM species was highest in M (10 species) and lowest in K (three species). Consequently, stump and slash removal from clear-felled sites had a positive effect on growth of outplanted spruce seedlings, but negative effect on their mycorrhization. This suggests that altered soil conditions due to site disturbance by stump and slash removal might be more favourable for tree growth than more abundant mycorrhization of their root systems in less disturbed soil.

Occurrence and impact of the root-rot biocontrol agent Phlebiopsis gigantea on soil fungal communities in Picea abies forests of northern Europe

The aim of this study was to assess belowground occurrence, persistence and possible impact of the biocontrol agent Phlebiopsis gigantea (Fr.) Jülich on soil fungi. Sampling of soil and roots of Picea abies (L.) H. Karst. was carried out at 12 P. gigantea-treated and five nontreated control sites representing 1- to 60-month-old clear-cuts and thinned forest sites in Finland and Latvia. The 454-sequencing of ITS rRNA from fine roots, humus and mineral soil resulted in 8626 high-quality fungal sequences. Phlebiopsis gigantea represented 1.3% of all fungal sequences and was found in 14 treated and nontreated sites and in all three substrates. In different substrates, the relative abundance of P. gigantea at stump treatment sites either did not differ significantly or was significantly lower than in nontreated controls. No significant correlation was found between the time elapsed since the tree harvesting and/or application of the biocontrol and abundance of P. gigantea in different substrates. In conclusion, the results demonstrate that P. gigantea occasionally occurs belowground in forest ecosystems but that stump treatment with the biocontrol agent has little or no impact on occurrence and persistence of P. gigantea belowground, and consequently no significant impact on soil fungi.

High infection rate of residual conifer stumps by Heterobasidion species in an area with assumed low infection pressure

Abstract The study was made in order to assess the infection rate of conifer stumps by Heterobasidion species in transition zone between southern boreal and middle boreal areas. Majority of surveys of stump infection rate have been made in areas where the fungus is already a considerable problem; typically the effective temperature sum in these areas exceeds 1200 degree days (d.d.). In the study, the incidence of stump infection was surveyed by intensive sampling of cut stump surfaces in the Central Finland in area where the temperature sum is 1100 d.d. and sporadic observations of damages caused by H. annosum s.l. have been made. Residual stumps were surveyed in total of 31 sites where majority of stumps had been harvested. Of those, 24 (75%) were infected. The stump infection rate was less than 20% on most sites. On average, 13% of spruce stumps were infected. The frequency of infected stumps varied considerably between the studied stands. The infection percentage of residual stumps in stump harvesting areas was corresponding to that obtained from earlier studies. Our results demonstrate that although the stump harvesting effectively decreases the number of infected stumps, the stumps left after summer cutting on the clear-cut area may be an additional infection pathway. No clear linear trend between mean temperature and proportion of infected stumps could be found.

Soil temperatures during prescribed burning and the occurrence of Rhizina undulata Fr.

Rhizina undulata is a postfire fungus. The ascospores germinate after heating over 35°C. The prescribed burning of one forest compartment was done in the purpose to investigate the effects of forest fire to atmosphere at Hyytiala Forestry Field Station in Southern Finland. The soil temperature measurements were one part of that research. One year after burning, the ascocarps of R. undulata appeared offering the possibility to use temperature data for studying the ecology of the species. The soil temperature was measured with 21 iButton sensors. Before and during the burning, all sensors were at 7 cm depth in the burned area. After burning, 10 sensors were moved to the unburned control area. The ascocarps were inventoried from 40 systematically located 10 m 2 plots. On average 6 ascocarps were found in one plot. Ascocarps were present on 75% of plots. Most ascocarps were found on spots for seeding with bare mineral soil visible. The fungus has not killed germlings of pine but 43% of planted seedlings were dead. The temperature during the burning reached 35°C in 10 points. In 4 points, the temperature was over 60°C, which could be too high temperature for spores to survive. It seems that the ascospores could exist in the soil in 2 to 10 cm depth if they can germinate. The temperatures after burning did not reach 35°C in 7 cm depth. More measurements are needed to show if the temperature in the surface of burned area reached critical point after burning.