Both forestry theory and practice have proved that amelioration favours the growth of forest stands significantly. The growing stock increases even 10 times, if the amelioration system is well-functioning. Joint Stock Company Latvia State Forests that is managing half of forests in Latvia has started renovation of old amelioration systems aiming to improve the productivity of state owned forests in Latvia. In order to evaluate the impact of the renovation of the old amelioration systems, a tree ring width in 7 pine stands, 5 spruce stands and 3 birch stands was analysed. This study shows that the renovation itself has not affected the productivity of mature pine, spruce and birch significantly 3-4 years after the renovation. Authors have come to a conclusion that the reason for that could be too short observation period or particularities of a stand structure and age.

Litter invertebrate communities in pine forests of different age (cut, six-year-old, 45-, 62-, and 105-year-old) in the Baranivka area of Zhytomyr Polissya (northwestern part of Ukraine) were studied. Samples were collected in April, August, and November 2011. 99% of extracted invertebrates were represented by mites (Acari) and springtails (Collembola). With forest age, the following tendencies were observed: mean absolute density of mites, springtails, and all litter-inhabiting animals increased; relative abundance of mites increased, but relative abundance of springtails decreased; taxonomic richness of invertebrate communities increased. In all samples, the most represented taxon was suborder Oribatida. The most diverse litter invertebrate community was in the 45-year-old forest. Similar compositions of invertebrate community were in the 45-, 62-, and 105-year-old forests as well as the cut and six-year-old ones.

Distribution and status of common juniper (Juniperus communis L.) in Lithuanian Pine stands are investigated in the study. The research was conducted in pure pine stands on sites with normal humidity and poor fertility in South – South Eastern parts of Lithuania. 40 stands were selected for data collection. Temporary rectangular sample plots with area of 10 square m were selected. According to method of underbrush evaluation, diameter root neck level, height and state index was measured for 3 juniper individuals located near the centre of sample plots. The number of sample plots depended on the area of each stand, but it was not lower than 10 in each stand. Average diameter of junipers was 3.03 cm, average height – 2.03 m. It was determined that average density of juniper individuals is 5055 individuals per hectare, and separately in vacciniosum and vaccinio – myrtilosum forest types - 4844 and 5282 individuals per hectare respectively. Average state index of juniper individuals in 6 grade scale was 2.96, which is near to grade 3 (slightly damaged). Results of the study show that distribution, status and dendrometric characteristics of junipers are different in adjacent regions of pine provenance.

The aim of the study is to ascertain how different compositions of stand species affect the work of the harvester in commercial thinning under Latvia’s conditions. The data of the harvester – time-tracking files (*.drf) have been used as a basis for the study, where productivity is expressed as the prepared amount of round timber in cubic meters in a unit of time – an hour (m**3 hE-1). The data were collected from 100 commercial thinning areas which were divided into three types depending on the composition of the species: pure pine stands, pure spruce stands and deciduous tree mixed stands (mixed with coniferous trees). All the data for the study were collected in the forests managed by JSC ‘Latvia`s State Forests’. By summarizing the data, it has been established that in pure pine stands the average volume of the stem to be removed is 0.092 m**3, in mixed stands – 0.085 m**3 and in pure spruce stands - 0.068 m**3. The research demonstrates that the harvester showed its highest productivity while working in pure pine stands – 3.96 m**3 hE-1, the second best result was achieved in the mixed stands – 3.67 m**3 hE-1, but the lowest rate was demonstrated in pure spruce stands – 3.09 m**3 hE-1. Significant differences were observed in the productivity of the harvester between pure pine and pure spruce stands. Comparing the calculations of standard deviations in the harvester productivity, it can be seen that they are the biggest in mixed stands, while the lowest rate is demonstrated in pure spruce stands.

If among engineering phenomena exist nonlinear interconnections, they are expressed with help of corresponding nonlinear functions. Teaching the regression analysis for the engineering science students one of the important topic is method of Least Square Method (LSM) and their application in the nonlinear regression analysis. Based on experience at Latvia University of Agriculture, the illustrated approach of teaching of nonlinear regression topics for undergraduate students in engineering applications is presented. Teaching statistics on regression analysis, students usually have problems with interpretation of the transformed regression model parameters significance. The tasks of teaching using LSM in the nonlinear regression analysis are discussed. On the figure 1 regression dependence are shown between such sizes as age of pine-tree and his height. The main species in Latvia is pine-tree (47% from total Latvia forest area); growth of trees motion is stipulated by tips of growth circumstances (Statistical Yearbook of Latvia, 2005).

The main pine natural woodland habitats (woodland key habitats -WKH) and the importance of their management and monitoring have been described in this paper. The ecological importance of lichen epiphytes in forest ecosystem has been analysed. The lichenoflora and its percental cover features have been described. The exposition of lichen species depending on the cardinal points has been analysed. The paper presents the characteristics of ecological indicators of lichen in the landscape features. The lichenoindicative evaluation and comparison of pine WKH have been carried out.