INTRODUCTION Forest resources are the most significant natural asset of the state of Latvia. According to data of the 2nd stage of forest resource monitoring for 2014, Latvia has 3575 thousand hectares of forest land comprising 55.3 percent of the total territory of Latvia, while the total timber stock is estimated at 668 million cubic meters (Bumanis et al., 2014). However, from the available data on forest resources it is only possible to theoretically and hypothetically state what proportion of these resources would be useful and economically justified as an energy supply. Each forest stand has a certain amount of undergrowth and understorey – small woody plants (shrubs) which have not been researched much until now. A precise determination of the amount of energy wood in Latvian forests would be of great benefit to the Latvian economy. MATERIAL AND METHODS Research data were collected in forests at the Jelgava Forest District “Forest Research Station”. The research was carried out in two forest subquarters of forest site type Myrtillosa mel. Eight circle-shaped sample plots were established. The area of each single plot was 25 m2. In the sample plots, the understorey and undergrowth trees were cut at the root neck. A sample was prepared from each tree harvested which was then sent for drying. The wood samples were transferred to "Forest and wood products research and development institute Ltd” for moisture determination. Total moisture content of the wood sample was determined according to standard LVS EN ISO 18134-2: 2016. RESULTS In the forest subquarter with a stand composition of 10Pine (66 years old) the sum biomass of undergrowth and understorey was 177.91 kg per sample plot. In the forest subquarter with a stand composition of 9Pine1Birch (88 years old) there was a total understorey tree mass of 180.9 kg but 16.17 kg of undergrowth per plot. This means there was more biomass in understorey than undergrowth in the site investigated. DISCUSSION When the tree stand was 10Pine (66 years old) the amount of dry matter to be extracted from all sample plots was 12.37 t ha-1 on average. In the forest subquarter with a stand composition of 9Pine1Birch (88 years old) the amount of dry mass is 10.24 t ha-1 on average. According to previous research, 7-20 t ha-1 of dry mass was obtained in Sweden, 7 to 12 t ha-1 in Poland, 6 to 14 t ha-1 in Germany and 8 to 12 t ha-1 in Latvia (Lazdina et al., 2010). There are also several researches papers which describe biomass from young hardwood stands on abandoned agricultural land in Canada: the values vary from 0,6 t ha-1 to 82,6 t ha-1 (Lupi et al., 2017). Consequently, a sufficient amount of biomass was obtained in the forest subquarters investigated in our research, which fits with the results of other studies carried out. CONCLUSION The volume of potential energy wood in undergrowth and understorey in Myrtillosa mel. forest site types is significant and it is advisable to use it as a raw material for energy production together with felling residues. However, it is necessary to evaluate the technical and technological capabilities from an economic perspective in each particular case.

The work analyses an impact of a drainage system, established in 1939.on overgrown pine tree stand in longer period of time.For the purposes of study 14 sample plots, established by scientists K. Buss and P. Zalitis during the 50's and the beginning of 60's, were remeasured.Sample plots were organized in the Myrtillosa turf.mel., Vacciniosa turf.mel., and Callunosa turf.mel.forest site types.Stands basal area increased in all compared forest site types, maximal being 41.7 m 2 ha -1 in Myrtillosa turf.mel.forest site type in 2016.Average diameter and average height of a tree in the stand was also bigger in Myrtillosa turf.mel.forest site type plots.The stand volume in Myrtillosa turf.mel. in 2016 was 384.8 m 3 ha -1 , in Vacciniosa turf.mel. it comprised 326 m 3 ha -1 , but in Callunosa turf.mel. it was 259.7 m 3 ha -1 .The average stand volume in 2016 was 323.5 m 3 ha -1 .Analysis of statistical parameters showed the substantial impact by the forest site type on diameter and height of the tree.For the inventory of ground cover vegetation, the point-square method was used.37 plant species from 32 ecological groups were detected at Myrtillosa turf.mel.forest site type plots, 26 species from 23 ecological groups -at Vacciniosa turf.mel., and 23 species from 17 ecological groups -at Callunosa turf.mel.forest site type plots.Ellenberg indicator values, Chekanovsky similarity index and Shannon index for ground cover plants showed the changes of ground cover plant coverage caused by forest drainage.Study results confirm the hypothesis: forest drainage has positive impact on overgrown Scots pine stands dendrometrical parameters and stands growing stock increase.The beneficial effect of hydrotechnical melioration continues even 50 years after reaching the cutting age.

Nowadays forestry sector uses forest site type descriptions developed from beginning of 20th century till 1980's and descriptions are obtained for pre-mature and mature stand age. There is less information about ground cover vegetation for full rotation cycle. In this research has been gathered information about ground cover vegetation succession in first 5 years after clear cut in mature Scots pine stand. The chronosequence method was used. The Brown-Blanquet and the point-square methods for accounting of ground cover plants were used. The ecological values of Ellenberg for describing the environmental status and the coefficient of Tschekanovsky for estimation of the difference between plant communities in forest young growths of different age were used. The biological diversity of species in this research compared to mature stand also is increasing. Ellenberg's ecological indicator values as light and nitrogen are also increasing: nitrogen value has increased the most - by 2.62 units. There are registered changes in vascular plants, mosses, lichens and trees projective covering's proportion. The most significant changes in individual species occurrence are between the second and third year's (Tschekanovsky coefficient = 0.19). Five years after clear cut the Tschekanovsky coefficient between the mature stand and five years old clearing is 0.18. In the 4th and 5th year after the clear cut there increase the projective cover of Monocotyledonae plants (families Graminaea and Cyperaceae) forming higher vertical structure and overtaking the dominance from another groups. The results obtained in this research promote further research in different stand age.

Biolocation is a method which allows estimating the biophysical anomalies on the Earth surface, underground and air by considering of changes in condition of dowsing rod or other indicator in hands of dowser.The first results of study, carried out in Forest Quarter 42 of the Jelgava Forest District of the Scientific Research Forests near the City Jelgava in Latvia, suggest that only weak correlation between pine tree diameter and distance till anomalies belts and points of those intersections exists. However, in both cases there a slightly increase of tree diameter by biggest distance from biophysical anomaly was obtained which may suggest that anomaly belts hinder the growth of pines.The results of analyze of the distances till closest belt and point of intersection suggest that belts and intersections of biophysical anomalies have no significant influence on tree quality. However, a slightly trend of improving of tree quality can be observed by the increase of distance from the closest belt of biophysical anomalies.Although there were not found clearly evidence of connection between wooden faults and distance till closest biophysical anomaly, such faults as sloping stem and sinuous stem are more abundant by closest distance to anomaly belt, but such faults as large branches or many branches are more abundant by trees growing in bigger distance from anomaly.The abundance of certain wooden faults shows an opposite character by analyzing the impact of distance till closest point of intersection of biophysical anomalies. The trees with sinuous stem are more abundant by the bigger distance from the points of intersection.

The forest typology in Latvia started in the beginning of 20th century when the first forest site types were defined according to the specific growth conditions and the tree stand parameters. These parameters were obtained for age of mature forest stand. However, till up to now, there is little knowledge about the ground cover vegetation succession during all the forest rotation cycle.To clarify this scientific question there was the chronosequence method used, when we take the forest stands of the same forest site type and dominant tree species at different ages. For the beginning we took forest stands of the first 5 years after the clearcut. Six sample plots with size of 10 m2 per each forest-stand-clearcut were established.-The point-square method by accounting of ground cover plants was used. Twenty sticks df 1 mm thick metallic needle were made in each square to estimate the taxonomic structure and abundance of plant species. The ecological values of Ellenberg were used to describe the environmental status of each site. The coefficient of Tschekanovsky was used to estimate the difference between plant communities in forest young growths of different age. The forest site type investigated was the Hylocomiosa site type with Scots pine (Pinus sylvestris L.) as a dominant tree species. This forest site type is dominant in forests of Latvia, taking 22% of total forest area.The results suggest considerable changes in taxonomic structure and abundance of ground cover plants in first years after the clearcut. The results obtained and further research will be valuable supplement for practical forest inventory allowing describing the characteristic ground cover vegetation in Hylocomiosa forest site type not only in mature forest age but during all forest rotation cycle.

Most of the ground cover vegetation descriptions given for characteristic of certainforest site types are made for mature forest stands. However the site typeestimation for the practical forest inventory needs knowledge about the vegetationin every age class of forest. The clearcut as an artificial forest disturbance causesdramatically changes in plant community. Especially fast changes proceed duringthe first years after the clearcut. Due to increase of temperature and nutrientavailability there proceeds several processes causing significant changes in groundcover vegetation. In 2015 a research was started to clarify the changes in groundcover vegetation in Hylocomiosa forest site type. This forest site type is mostabundant in Latvian forests taking around 22%. The dominant tree species inHylocomiosa is Scots pine (Pinus sylvestris L.) although the silver birch (Betulapendula Roth), Norway spruce (Picea abies (L.) Karsten) and aspen (Populustremula L.) can form a tree stand there. The chronosequence method was used byproviding the inventory at 5 tree stands dominated by pine. Six sample plots ateach forest stand with size of 10 m2 were established. The point-square method byusing of 1mm thick and 1m high metallic needle was used for registration of plantsat each square of sample plot. The inventory showed significant changes of speciescomposition and projective cover of moss species and caulescent plants. Theresults of calculation of the Ellenberg’s ecological values and Tschekanovskycoefficient suggest of appearance of plants with another attitude to the ecologicalfactors.

Spruce bud scale (Physokermes piceae Schrnk.) affects tree growth directly and indirectly. Direct injury appears in the form of tissue damage, as insects suck sap from tree phloem. Indirect injury appears as “honeydew”, which results in negative effects on tree growth. Plant sap is saturated with various carbohydrates called photosynthates that are difficult for scaly insects to digest. Therefore it is secreted in excrements, which are subsequently a food source for the black sooty mold (Apiosporium pinophilum Fuckel). The fungus covers needles blocking stomata, causing decreased transpiration and photosynthesis. An inexplicable wither of Norway spruce was reported in Latvia during 2010 due to black sooty mold. However, spruce bud scale was not evident. In 2011, mass propagation of spruce bud scale was observed following the 2010 Norway spruce loss. One objective of this research was to determine if Kraft tree growth classes could be applied to establish the factors responsible for tree foliage damage. Six 21 - 40 year old (second age class) Norway spruce stands were evaluated. Two circular sample plots with a 7.98 m radius, and a 200-m2 area were randomly established per each forest stand hectare. Diameter at breast height (dbh, 1.3 m), and height of approximately 30 trees was measured to model a trend. For all trees, Kraft class, and foliage damage level caused by spruce bud scale and black sooty mold were determined. Significant differences were not observed in tree damage levels among stands, however significant differences among damage levels in different Kraft classes were detected (F = 3.45 > Fcrit. = 2.80, α = 0.05 > P = 0.02) found. Overall damage intensity was 29.3 %. Total forestry loss was 1153 LVL (1640 EUR) for all surveyed stands (10 ha), and 115 LVL (164 EUR) per hectare.

The outstanding and character of forest fires are predicted by the interaction of the meteorological conditions, topography as well the site and forest stand peculiarities. In Latvia since 1990 there have been at an average 850 forest fires every year.The forest site type Sphagnosa is characterising by at least 30 cm thick peat layer and with unfortunate soil moisture and aeration regime. The Sphagnosa forests take 1.4% from the total forest area of Latvia. The forest stand is formed by unproductive pine (Pinus sylvestris L.) with site index V with some birch admixture. Because of strong suffering during the forest fires, already two or three years after the burning the trees dry up and fall down.There is a natural regeneration with pubescent birch (Betula pubescens Ehrh.) permissible in Sphagnosa forest site type, because after the fire there begins the paludification process in the burned area and the birch increases the water transpiration thus improving the growth conditions for the natural regeneration of pine.The research is carried out in 2010 in the Forestry Rietumvidzeme of the Joint stock company "Latvian state forests". The purpose of research was to evaluate the process of natural regeneration after the subsurface fire in the Sphagnosa forest ecosystem 2, 6, 10 and 16 years after the burning by comparing of different areas burned in the past.Two years after the forest fire all old trees dried up in the burned area. The main tree species of young growth are: birch with 5200 +/- 478 trees per hectare, average height 0.29 +/- 0.026 m; pine - 800 +/- 289 trees per hectare, average height 0.04 +/- 0.010 m. The stand composition is 9Birch (2) (years)1Pine (1) (year) with 6000 +/- 558 trees per hectare.Six years after the forest fire the main tree species are: birch with 5540 trees per hectare, average height 1.15 +/- 0.076 m; pine - 2670 +/- 249 trees per hectare, average height 0.41 +/- 0.031 m and stand composition 7Birch 3Pine (6) (years). The total number of trees per hectare is 8210 +/- 529.Ten years after the forest fire the main tree species are: pine with 3430 +/- 622 trees per hectare, average height 0.93 +/- 0.092 m; birch 2230 +/- 211 trees per hectare, average height 1.36 +/- 0.069 m. The stand composition is 6Pine 4Birch (10 years) with the 5660 +/- 614 trees per hectare. Sixteen years after the forest fire the main tree species in forest stand is pine. The tree stand composition is 8Pine 2Birch (16) (years) with the total number of 7310 +/- 876 trees per hectare, from which 5490 +/- 779 trees per hectare are pines with the average height of 1.99 +/- 0.142 m. The number of birch is 1830 +/- 408 trees per hectare with the average height of 1.96 +/- 0.117 m.There was no significant differences found between the total number of trees in burned areas of different ages in Sphagnosa forest site type (F-fact.=0.5283p=0.05). During the inventory in the young growth areas there have been damages found caused by pine bud moth (Blastesthia turionella Hb.) in sixteen years old burned area in amount of 3.1% and the damages of pine resin-gall moth (Petrova resinella L.) in ten years old burned area in amount of 2.6% and in sixteen years old burned area in amount of 6.3%. There were only the branches and buds of branches damaged.The fire as a natural disturbance promotes forming of gaps in the layer of tree stand canopies, thus supporting favourable conditions for the natural regeneration of forest. At the age of 16 years the average height of pine and birch is almost similar reaching for pine 1.99 +/- 0.142 m and for birch - 1.96 +/- 0.117 m.