Forest types

Prior to creating the FMG, we developed a classification of forest types at stand level, based on analysis of National Forest Inventory (NFI) data ( ICONA, 1994 ; DGCN, 2005 ), comprehensive bibliographic review, and expert knowledge (enrolling 20-odd working groups). The classification was based on two attributes: i) tree species composition and related density variables (number of trees per hectare, basal area and crown cover), and ii) site quality, based on ecological variables, which determines species adaptation, vitality and potential productivity.

The combination of forest types (species composition and site quality at stand level) with other relevant indicators reveals the stand’s vocation and; from there, the main objectives and appropriate FMG to assign (Fig. S1).

Concerning species composition ( Fig. 1 ), we elaborated a classification of pure (when one species accounts for at least the 80% of total basal area) and mixed forests (stands with more than one species, none of which dominate more than 80% of total basal area). Data from 11,859 NFI plots highlighted the huge importance of mixed stands, which represented 46% of total forest cover in Catalonia.

Concerning site-quality classifications, experts determined that only two or three quality classes need to be differentiated for most species, based on the premise that it is only rational to set different site qualities when they lead to different goals and management schemes.

The process of defining site-quality classes for each species based on ecological variables involved two stages. First, we led expert-panel group sessions to establish the number of classes needed and identify the key ecological variables related to site quality, including their relative importance and ranges. Second, we ran statistical analyses on the relationship between growth indicators obtained from the NFI and certain ecological variables readily identifiable by managers ( i.e . Vericat et al. , 2013 ). This process resulted in site quality charts that serve to assign a quality class based on environmental variables.

Forest management guidelines (FMG)

Silvicultural models and FMG were also developed based on NFI data and other field-base data, combined with complete bibliographic review of growth and yield models ( i.e . Bravo et al ., 2011 ) and literature on the main species ( i.e . Serrada et al ., 2008 ), and expert knowledge (same working groups were involved). As an example, see Beltrán et al. (2012) who described the case of Pinus sylvestris FMG elaboration. Further work was done with the NFI data to fill the gap in growth models for certain minor species.

Initially, we established a set of scenarios combining site quality, fire risk, stand structure and different objectives. Then, draft silvicultural schemes were developed for each scenario in an iterative elaboration process starting with a design of the different stand stages. Stand parameters were calculated at each stage based on site index, mortality and growth models, allometric relationships, and competition indexes.

Inside the iterative process, we led an economic and silvicultural evaluation of each proposed scheme. Treatments and products obtained were valuated, and the behaviour of the whole management cycle was assessed using a common framework. Strength tests were carried out by varying the price increase rate and the production output obtained. The working groups discussed and validated the schemes to help settle on the final silvicultural models. Fig. 1 schematizes the process followed to construct the FMG.

We further integrated wildfire prevention into the guidelines. To do this, we developed keys for ranking crown fire hazard based on the main forest stand variables that play a significant role in crown fires ( Piqué et al ., 2011 ). In addition, based on these fire risk assessment keys, we elaborated specific silvicultural models with the main objective of reducing crown fire hazard at stand level (results not shown).

ORGEST consists in a set of FMG covering almost every conifer and broadleaf species-dominated forest in Catalonia (including pure and mixed forests), which together represent over 90% of Catalonia’s forest area. The Forest Ownership Centre has published the ORGEST FMG as manuals through its open-access website (see ags.ctfc.cat/?p=649 for the links).

For each species-dominated forest considered, ORGEST offers site quality charts and different guidelines for various management scenarios. They were built considering 2–3 site quality classes (depending on species), high or low risk of large wildfires in the area, even- or multi-aged forest structure, and different objectives such as timber production, non-wood forest products, wildfire prevention, or enhancing forest vitality and resilience.

Site quality charts developed for the main species ( Piqué et al ., 2014 ) allow forest managers to quickly and objectively assign the most likely site quality class at stand level through readily identifiable ecological factors.

Fig. 2 shows an example of a site quality chart for P. sylvestris , where A is best site quality class (the species is well adapted and shows good growth) and C is poorest class.

ORGEST introduces silvicultural models and FMG for pure forests, including even- and multi-aged stands ( Fig. 3 ), but also guidelines for mixed forests based on previous models for pure forests “reference models”, and specific silvicultural models for crown fire prevention (results not shown).

The silvicultural models for even-aged stands give a table with typical forest variables (dominant height, mean diameter, density, basal area, volume, etc.) plotting time–course evolution, including extracted basal area and volume when silvicultural treatments are applied ( Fig. 3 ). Silvicultural models for multi-aged stands give a reference distribution of basal area and density among diametrical classes grouped as small, medium and large trees, and an expected evolution until the next selection felling should be done. Extracted basal area and volume data are also included ( Fig. 3 ).

Moreover, the FMG also include a complete and applied description of all treatments (clearing, thinning, regeneration cutting, selection felling, etc.) and a code of best forest practices in order to ensure correct implementation of the silvicultural models.

Both the forest types classification and FMG provide forest administrators and managers with technical information for achieving management objectives and more efficient allocation of public funds in forest management.

Forest types provide information that helps reduce inventory costs and may ease strategic planning at larger scales (promoting certain objectives depending on forest types). The site quality charts based on ecological factors enable site quality to be classified fast, despite the current stand conditions used. The ORGEST approach enables stand-level-adaptable forest management, which is vital in our context due to the huge diversity of species, structures, site qualities and objectives involved at stand level.

In summary, the methodology used, combining expert knowledge, NFI data analysis, existing growth and production models, and in-field validation with stakeholder participation has proven to be very useful not just for establishing the forest types and FMG but also in driving acceptance of the guidelines by practitioners and forest technicians. We anticipate that our methodology could be replicated to other forested regions and that the silvicultural models and FMG could be directly applied in other areas with similar conditions, mainly within the Mediterranean basin.