Old-growthness attributes and climate and anthropic factors of the Third Spanish National Forest Inventory's plots.

This dataset depicts several metrics that report on the old-growthness attributes of the plots in the Third Spanish National Forest Inventory (1997-2007), as well as a series of climate, topographic, landscape and anthropic factors.Only naturally forested plots were selected, excluding both plantations and <i>dehesas </i>(a multifunctional, agrosylvopastoral system with grasslands used for grazing accompanied by low densities of trees, usually from the <i>Quercus</i> genus). In addition, plots dominated by typically planted species like <i>Pinus radiata </i>or any of the species from the <i>Eucalyptus</i> genus, or in general by any non-native species, were also discarded, even if they were not reported as being plantations. Plots with basal area of less than 5 m²/ha were also discarded, even if they were not reported as <i>dehesas</i>.The old-growthness attributes selected were:<i>Basal area of large trees</i>Total basal area of trees whose DBH were above a certain threshold. The thresholds differed across species to avoid biases created by the distinct natural physical attributes of the multiple species considered.<i>Number of DBH classes</i>Number of 5 cm DBH classes of the trees present in the plot, including regeneration. Classes started at 2.5 cm.<i>Number of height classes</i>Number of 2 m height classes of the trees present in the plot, including regeneration. Classes started at 0 m.<i>Volume of standing deadwood</i>Volume of standing dead trees present in the plot with a DBH value higher than the mean DBH of the plot, to avoid accounting for tree mortality caused by competition in early stages of stand development.<i>Basal area of trees with microhabitats</i>Total basal area of the trees recorded as presenting damages of certain types and magnitudes. These damages were considered as proxies of possible microhabitats.<i>Number of shade-tolerant species</i>The number of shade-tolerant species in each plot. The distinction between shade-tolerant and shade-intolerant differed across different habitats and was based on the values assigned by Niinemets &amp; Valladares (2006).<i>Aggregated index</i>The six indicators were aggregated into an index. To weigh the different indicators, we used a statistical approach that assigned each indicator a weight corresponding to its overall contribution to the variation in the data. A principal component analysis (PCA) was performed, which was then rotated to assess the contribution of each indicator to the total unit of variance of each factor of the PCA. Finally, the individual contribution of each indicator to the factors was then weighed by the proportion of the explained variance of each factor to the dataset following the method in OECD/European Union/EC-JRC (2008).<br>Ten factors were calculated for every plot:<i>Climate and topographic variables:</i>· Annual precipitation: calculated as the mean annual precipitation in the period 1950-1999; data from <i>Atlas Climático Digital de la Península Ibérica</i> (Ninyerola et al. 2005).· Mean annual temperature: calculated as the average mean annual temperature in the period 1950-1999; data from <i>Atlas Climático Digital de la Península Ibérica</i> (Ninyerola et al. 2005).· Solar radiation: potential amount of solar radiation received by a plot calculated as a function of the latitude, slope, orientation and topographic shade; data from <i>Atlas Climático Digital de la Península Ibérica</i> (Ninyerola et al. 2005).· Topographic wetness index: proxy of soil moisture and groundwater availability, calculated as a function of both the slope and the upstream contributing area (Kopecký et al. 2020).· Rockiness: measuring the percentage of the area of the plot covered by rocks in five categories (0 %; 0-25 %, 25-50 %, 50-75 %, 75-100 %), provided by the SNFI.· Slope: maximum steepness of each plot calculated in degrees, provided by the SNFI.<i>Landscape variables</i>· Edge effects: measuring the edge effects caused by fragmentation, calculated as the percentage of non-forest cover in an area of a circle with a radius of 5 km around the plot; data from the MFE50 (https://www.miteco.gob.es/ca/biodiversidad/servicios/banco-datos-naturaleza/informacion-disponible/mfe50.html).<i>Anthropic variables</i>· Accessibility: human accessibility to the plot, calculated as the linear length of all roads ―including both paved and unpaved roads in all road categories― in a 500 m radius around the plot; data from the map Redes de Transporte (https://www.idee.es/csw-inspire-idee/srv/spa/catalog.search?#/metadata/spaign_IGR_Transporte).· Managed vs. unmanaged plots: a plot was considered as managed if it was reported as showing signs of having suffered recent substantial management practices (recently cut stumps, debris from recent logging, etc.) either in the 2nd edition (1986-1996) or the 3rd edition (1997-2007) of the SNFI.· Protected vs. unprotected areas: all protection figures were included regardless of their protection level; data on protection level from the map Espacios Naturales Protegidos (https://www.miteco.gob.es/es/biodiversidad/servicios/banco-datos-naturaleza/informacion-disponible/enp_descargas.html).<br>