The proposed method of forest ecosystem monitoring will be employed from the standpoint of monitoring intensity: 1) extensive monitoring - EM (I) and 2) intensive monitoring - IM (II)

I) Extensive monitoring - EM: helps assess to what extent the results of intensive monitoring obtained through the cited case studies can be generalized for the same habitat type, geological parent rock, vegetation features and similar. It involves relatively rapid and cheap measurements of basic structural parameters on permanent sample plots of 1 ha (100 x 100 m). The measurement methodology is described in detail below. Data obtained by EM will serve to help understand the dynamics of forest stands on a broader spatial level in relation to IM.

II) Intensive monitoring - IM: can be perceived as a set of individual case studied (CS) for a given monitoring indicator. It should serve as a representative research object for all the plots under extensive monitoring. The results obtained with intensive monitoring will provide a basis for ecological modelling and future projections as they comprise a broad range of monitoring activities (from tree to stand level). Plots for intensive monitoring will be selected according to the following criteria: naturalness (natural variability without direct anthropogenic impact), scope of ecological gradient (it must encompass the ecological gradient of species and habitats), and the possibility of valid generalisation on extensive monitoring plots.

Figure 1 Position of plots for extensive monitoring in Croatia established in the period 1979 - 1985 as part of the MAP programme (red dots), and the proposed new areas in old growth stands. The layout of a permanent sample plot sized 100 x 100 m.

Figure 2 Research area of each particular case study in the spatial-temporal dynamics of Ecosystem A. Mutual relationship of case studies within Activity B.

High heterogeneity of old-growth forests is an aggravating circumstance, especially with regard to the age range, where there are trees of different dimensions and ages. Accordingly, it is impossible to single out certain parts of old-growth forests as homogeneous mosaics of equal age. As the study of dynamics requires a change in monitoring indicators during a time period, this hinders the implementation of certain case studies.

In order to successfully analyze the dynamics of an old-growth ecosystem in terms of particular monitoring indicators, we will employ ecological modelling methods.

Research will be focused on the evaluation of impacts of natural disturbances on the dynamics of growth and development, mortality, deadwood dynamics, regeneration and the analysis of carbon and nitrogen cycling.

Intensive monitoring (IM) comprises the following case studies:

Figure 3 Carbon cycle methodology

Activity 2.1. Establishing plots for intensive monitoring

Activity 2.2. Analyzing the dynamics of natural disturbance regimes

CS 1. Dendroecological reconstruction of natural disturbance dynamics

CS 2. Canopy gap characteristics

Activity 2.3. Analyzing the dynamics of old-growth ecosystem structure

CS 1. Analyzing the structure and dynamics of tree growth and development

CS 2. Analyzing the dynamics of mortality

CS 3. Analyzing the dynamics of deadwood accumulation and decomposition rate

CS 4. Analyzing old-growth forest regeneration

Activity 2.4. Analyzing the carbon cycle

CS 1. Assessing carbon stock in live biomass

CS 2. Assessing carbon stock in deadwood

CS 3. Assessing carbon stock in soil organic matter (in the forest floor and mineral part of the soil)

CS 4. Analyzing carbon flows by monitoring the production of biomass and waste (leaf biomass and fruit), forest floor and deadwood decomposition

Activity 2.5. Analyzing indicators of biological diversity

CS 1. Analyzing biological diversity of the flora

CS 2. Analyzing biological diversity of deadwood-bryophytes