Throughout the history, growing stock has been one of the main indicators of the condition of forests. Together with the increment, fellings, forest area and the allowable cut, it forms a basic group of indicators used in monitoring the development of forests. These indicators serve as a basis for estimating the amount of biomass and carbon in a specific forest. The information about how these indicators have been changing through time is of vital importance.
In the last decades, the growing stock per hectare and the increment have been on a constant rise. According to the 2007 reports of the Slovenia Forest Service, the annual growing stock volume was 269 m3/ha, and the increment was 6.61 m3/ha. In the last 60 years, they increased by approximately 110%. The quantity of fellings depends not only on natural resources but also on socio-economic factors, which is why it has been changing through decades. According to the Slovenia Forest Service report, the quantity of fellings in 2007 was 3,242,070 m3.
In the Global Forest Assessment 2005, published by FAO, the following definitions of subindicators are listed:
Growing stock: Volume of all living trees with bark that have more than a certain diameter (X cm) at breast height (or above any irregularities in the form of the trunk). It includes the stem from ground level or stump height up to a given top diameter (Y cm), and may also include branches above the minimum diameter (W cm). In Slovenia, the minimum (X) is 10 centimetres, so all trees thicker than 10 cm are counted as growing stock. The minimum diameter (Y) is 5 centimetres. Branches are not included in the growing stock.
Increment: The average annual volume of increment over the reference period of all trees measured to a minimum diameter breast height (or above any irregularities in the form of the trunk). It includes the increment on trees which have been felled or died during the reference period.
Growing stock and increment are calculated based on the measurements of trees at permanent sample plots taken during the Forest Management Plan renewal. In some forests (if the site’s annual production capacity is less than 4 m3 per hectare), the growing stock and increment volume are estimated based on ocular assessment. The bases for determining the increment are two consecutive measurements within a given period (10 years).
Fellings: Average annual volume of all trees, living or dead, measured overbark to a minimum diameter that are felled during the given reference period, including the volume of trees or parts of trees that are not removed from the forest.
The method of taking inventory of fellings and the method of acquiring data on the growing stock and increment are defined in the Rules on the forest management and silviculture plans: Rules on the forest management and silviculture plans, Official Gazette of the Republic of Slovenia, no. 5/1998 and Rules amending the Rules on forest management and silviculture plans, Official Gazette of the Republic of Slovenia, no. 7/2006.
Slovenia Forest Service, 2008.
|conifers||m3 pro hectare||68.03||90.8||95.73||100.4||100.15||111.95||121.25||123.26||125.5|
|deciduous||m3 pro hectare||58.02||65.33||75.79||85.21||92.29||119.74||136.01||138.86||143.34|
Slovenia Forest Service, 2008.
|conifers||m3 pro hectare||1.71||2.05||2.31||2.45||2.43||2.73||2.87||2.89||2.93|
|deciduous||m3 pro hectare||1.38||1.46||1.76||2.26||2.49||3.33||3.61||3.63||3.68|
Slovenia Forest Service, 2008.
The growing stock and increment values have increased significantly in the majority of Slovenian forests with the use of more suitable methods of identification. However, due to poor baseline data on the condition of growing stock and increment, the prognoses for their development and consequently the prognoses for the development of the allowable cut in Slovenian forests for the following decades, outlined in the Slovenian Forest Development Programme, are inadequate.
How was the indicator measured?
To calculate the growing stock and increment volume at the level of individual forest management units, data acquired at permanent sample plots (major part) and by means of ocular assessment (minor part) are used. In the protective forests and forests with a special purpose where interventions are not allowed, mostly the ocular assessment method is used.
In all other types of forests (multi-purpose forests and forests with a special purpose where interventions are allowed), the abovementioned indicators are measured based on permanent sample plots that are distributed on the surface into a systematic grid with different degrees of density (from 200x200 m onwards). In each plot, the stand type is determined which serves as a basis for the stratification. Average values are calculated for each level of thickness (5 cm).
The basis for determining the increment are two consecutive measurements within a given period.
The manner of keeping an inventory of fellings is determined by the Regulation on the forest management and silviculture plans. The basis for keeping an inventory of fellings are the fieldwork data sheets for fellings where the trees intended for fellings are recorded according to the tree types, thickness levels, types and causes of fellings, the follow-up of works related to the decisions in the administrative procedure according to Articles 17 and 19 of the Act on Forests, and the inventory of unauthorised fellings. For each previous year, the data on fellings at the level of sections (E4 form), management class, ownership and forest management unit (in the EVP table) are entered into at least one copy of the Forest Unit Management Plan by the end of February. The 2007 values are lower because a new way of taking inventory of felled trees was introduced.
For forests where growing stock and increment are determined by means of permanent sample plots (500 m2), the fellings and the quantity of unexploited trees for the entire management period are independently evaluated based on the measurements taken at sample plots (Veselič 2005).
Data for Slovenia:
• name of the original database: Annual reports of the Slovenia Forest Service
• institution acting as the administrator of the database: Slovenia Forest Service
• description of the data source: Annual reports of the Slovenia Forest Service on forests
• data are shown for the period: growing stock and increment 1947 – 2007, fellings 1991 -2007
Data for Europe:
• name of the original database: Global Forest Assessment 2005, Global Forest Assessment 2000,
• institution acting as the administrator of the database: UN FAO, Department of Forestry
• description of the data source: Data and analyses in the report were calculated based on reports from individual countries.
o Slovenia Forest Service, Central Database of Forest Management Unit Plans, March 2007
o Veselič, Ž., Matijašić, D., 2002. Forest Management Unit Plans for the period 2001-2010, Journal of Forestry, Volume 60, Issue 10 (Dec. 2002), pp. 461-489.
o Slovenian national forest development programme, Official Gazette of the Republic of Slovenia, no. 14/1996 of 8-3-1996.
o National Forest Programme, draft. March 2007,
o Rules on the forest management and silviculture plans, Official Gazette of the Republic of Slovenia, no. 5/1998 of 23-1-1998, pp. 256 – 282.
o Rules amending the Rules on forest management and silviculture plans, Official Gazette of the Republic of Slovenia, no. 70/2006 of 6-7-2006, pp. 7293-7298.
o National Environmental Action Plan (NEAP), Official Gazette of the Republic of Slovenia, no.. 83-3953/1999, p. 12765.
o Global Forest Resources Assessment 2005, UN FAO, Department of Forestry, 2006.
o Global Forest Resources Assessment 2000, UN FAO, Department of Forestry, 2001.
o Veselič, Ž., 2005. Illegal logging in Slovenia, Slovenia Forest Service