Current issue: 54(2)
Differences in vegetation cover estimation by field biologists of the 8th National Forest Inventory in Finland were tested. Eleven observers estimated the canopy coverages of six forests taxa in 25 sample plots, located in one stand. The experiment was arranged after the field work. The coverage of Vaccinium vitis-idaea and the ground layer appeared to be the most difficult to estimate. The mean of the highest estimator was about double that of the lowest one. The least abundant species and the sample plots with the smallest coverages had the largest estimation errors. The most important compositional gradient of the data was natural, even though the test was made in a homogenous area. However, the effect of the observer could be recognized. The differences between observers could be caused by the differences both in visual estimation level and in placing the sampling frame. The results suggest that tests should always be made when several observers are used in vegetation surveys. If calibration is used, it should be made separately for each species.
The PDF includes an abstract in Finnish.
Especially in forest vegetation studies, the light climate below the canopy is of great interest. In extensive forest inventories, direct measurement of the light conditions is too time-consuming. Often only the standard tree stand parameters are available. The present study was undertaken with the aim to develop methods for estimation of the light climate on the basis of readily measurable tree stand characteristics. The study material includes 40 sample plots representing different kinds of more or less mature forest stands of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) H. Karst.).
In each forest stand, a set of hemipherical photographs was taken and standard tree stand measurements were performed. A regression approach was applied in order to elaborate linear models for predicting the canopy coverage. The total basal area of the stand explained 63% of variance in the canopy coverage computed from hemipherical photographs. A coefficient representing the relative proportion of Norway spruce in the stand increased the explanatory power into 75%. When either the stand density (stems/unit area) or dominant age of the stand was included into the model, increment of the explanatory power into 80% was achieved. By incorporating both of the preceding predictors, an explanatory power of 85% was reached.
The PDF includes a summary in Finnish.
The study deals with the relationship between biomass and coverage in ground vegetation of Vaccinium and Calluna forest types. The results show that the biomass of the field layer on both forest types can predict satisfactorily in both coverage values of some the most important species and groups of species. Their total height per plot was used as independent variables. The explaining power of the models constructed for Vaccinium type increased to approximately 57% and for the Calluna type to approximately 74% of the total variation in the amount of dry matter. When the biomass of the bottom layer was predicted using the same kind of variables, the explaining power for the Vaccinium type increased to approximately 35% of the total variation and for the Calluna type approximately 53% of the total variation in the amounts of dry matter. The models for field layer of both Vaccinium and Calluna types were quite well suited for describing the test material. In the case of the bottom layer, the constructed models were not suitable for describing the test material.
The PDF includes a summary in English.