Martti Lindgren

Extensive tree health monitoring networks are useful in revealing the impacts of widespread biotic damage in boreal forests

We surveyed the regional distribution of conifer defoliation in Finland with an extensive monitoring network during 1995–2006 (EU Forest Focus Level I). The average defoliation in the whole Finland was 10.3% in pine and 19.9% in spruce. The sharp changes were often related to abiotic and biotic factors. The mean age of the stand explained more than one half of the between-plot variance in defoliation. In a variance component analysis, the main effect of years was negligible, while most of the random variation was due to plot main effect and plot × year interaction. About one fifth of the defoliation could be attributed to abiotic or biotic damage, and there were strong local correlations, e.g., between the changes in defoliation and degree of pine sawfly (Diprionidae) damage. There were clear temporal and spatial patterns in the incidence of the most important causes [Scots pine: Scleroderris canker (Gremmeniella abietina), pine shoot beetles (Tomicus sp.), and pine sawflies (Diprion pini, Neodiprion sertifer); Norway spruce: rust fungi (primarily Chrysomyxa ledi)]. Our results suggest that extensive monitoring networks can reveal useful information about the widespread outbreaks of pest organisms (insects and fungi) already in their increase phases, giving some time for management decisions. In a changing climate, large-scale, regular monitoring of tree health, including abiotic and biotic causes, is more important than ever before.

Effects of natural winter browsing and simulated summer browsing by moose on growth and shoot biomass of birch and its associated invertebrate fauna.

Plant responses to mammalian herbivores can be manifold. Browsing by large mammals such as moose may change plant growth and morphology, which, in turn, will change the food quality and availability for e.g. invertebrate herbivores sharing the same forage plant. Furthermore, the intensity and timing of herbivory may affect plant responses and future herbivore attack. In a field experiment, we tested whether simulated summer browsing and natural winter browsing by moose affects growth and morphology of birch Betula pendula, and whether possible changes had effects on abundance and defoliation by herbivorous invertebrates. The simulated summer browsing treatment was applied in two intensities (50% and 100% defoliation of long shoots) during two different periods of the growth season (mid-June and mid-July). Simulated summer browsing delayed the timing of budburst, reduced height and diameter growth and resulted in reduced defoliation by invertebrate herbivores indicating an induced defence. Winter browsing by moose reduced diameter growth, leaf biomass of short shoots but increased height growth, the abundance of aphids and defoliation by insect herbivores. The effects of herbivory on the timing of budburst, leaf biomass of long and short shoots and the abundance of aphids were more pronounced when the birches were both browsed in winter and artificially stripped. The timing of the artificial leaf stripping treatment was important for nearly all tested variables. Concluding, summer and winter browsing by moose can have opposing or additive effects on plant morphology and growth. Therefore, also indirect effects of mammalian herbivory on invertebrate communities feeding on the same plant may differ, depending on the browsing intensity, the season of browsing and even the timing of browsing within the same season.

The effect of stand density on the susceptibility of Pinus sylvestris to Gremmeniella abietina

The susceptibility of a 20‐year‐old Scots pine stand to Scleroderris canker caused by Gremmeniella abietina was monitored in relation to stocking density. The data included five densities varying from 800 to 5 000 trees/ha. The degree of damage, as indicated by the proportion of brown needles and the number of dead trees, correlated positively with the stand density. The proportion of dead trees was low at densities below 1 100 trees/ha, but increased linearly with increasing density.

Soil Acidity Parameters and Defoliation Degree in Six Norway Spruce Stands in Finland

Soil acidity parameters (pH, basesaturation, exchangeable Al) in the organic and mineralsoil layers and in soil water (pH, dissolved organiccarbon, total Al, Al3+ and molar Ca/Al ratios) insix Norway spruce stands in different parts of Finlandwere compared. An attempt was also made to relate thedegree of defoliation in the tree stand to N and Sdeposition and soil parameters. No relationship was foundbetween soil acidity parameters and defoliation in thesix stands. Defoliation was positively correlated withstand age and the C/N ratio of the organic layer, andnegatively with the cation exchange capacity. The plotlocated on a so-called sulphate soil on the west coast ofFinland had very low soil pH values, and extremely highAl and SO42- concentrations and molar Ca/Alratios of well below 1.0 in soil water. Despite the highnatural acidity in the soil on this plot, defoliation inthe spruce stand was the lowest (mean 8.6%) of all sixplots. The results of this study indicate that soilacidity is not a major factor affecting stand conditionin these spruce stands, and that the variation in soilacidity parameters is closely related to climatic factorsand natural soil formation processes.

Forest Condition in Relation to Environmental Factors

A decrease in forest vitality was observed over large areas in Central Europe in the late 1970’s. The deterioration in tree condition not only occurred in highly polluted areas close to industrial regions, but also in areas located at considerable distances from emission sources. The hypotheses put forward to explain the phenomenon claimed that the causal agents were either acidic deposition and the dissolution of soil aluminium (Ulrich et al 1979, Sverdrup et al 1994), gaseous pollutants (Krause et al 1986, Prinz et al 1985), nitrogen deposition (Nihlgard 1985) or nutrient deficiencies (Schulze 1988). It has subsequently been accepted that forest damage is a highly complex phenomenon, the effects of pollutants being connected to climatic factors, local growth conditions, selection of provenances, abiotic and biotic damage or to the history of forest use (Fuhrer 1990, Innes 1993, Landman and Bonneau 1995). According to one point of view, the direct effects of pollutants on forest condition can only be demonstrated in the environments of industrial areas (Skelly and Innes 1994, Kandier and Innes 1995).

Relationships between crown condition, tree nutrition and soil properties in the coastal Picea abies forests (Western Finland)

The state of health of 30 Norway spruce (Picea abies L. Karst.) stands located on the uplifting coast of western Finland was examined in 1992. Relationships between crown condition, elemental concentrations of the needles, organic layer properties and soil type were studied using sitewise data. The site scores along the first axis of the Principal Component Analysis for certain needle and organic layer variables were used as the site fertility index. The spruces in the study area showed a higher level of defoliation and this occurred in younger stands than elsewhere in southern Finland. Defoliation and discoloration correlated positively with stand age, and negatively with the site fertility index. Low N and Cu concentrations of the needles were found in older stands where spruces were highly defoliated and discolored. Boron concentrations of the needles were highest in these stands. Total N of organic layer and extractable S concentrations were negatively correlated with stand age, defoliation and discol...

Forest Condition in Finland — Concluding Remarks

Forest condition has been a matter of considerable public concern since the beginning of the 1980’s when the reports of widespread forest decline and damage in central Europe were immediately associated with anthropogenic pollution of the environment. Industrial activities have, especially since the 1940’s, emitted increasing amounts of a wide range of air pollutants, and increased the concentrations of greenhouse gases in the atmosphere.