Supplementary Materials
1. Broadleaved-evergreen biotype
LandClim calculates the biomass of species cohorts, and uses separate allometric relationships to convert the biomass of coniferous and broadleaved-deciduous species to stem diameter (Schumacher et al. 2004). We added a new biomass to diameter conversion for broadleaved-evergreen species based on scaling functions for mature trees and the wood density of Quercus ilex (Pilli et al. 2006), the dominant broadleaved-evergreen species in Italian forests:
(1)
Where a = 0.12817 and is a scaling coefficient based on the density of Q. ilex (0.95 t m-3) and b = 2.5 and is a scaling exponent for mature trees, which is consistent with our means for calculating growth rates and maximum size.
LandClim tracks light availability using leaf area index. Each species is assigned one of five foliage types based on crown density that relate diameter to foliage biomass (Supplemental Table 2; Bugmann 1994; Bugmann 1996). We assumed that the ratio of dry to wet foliage mass, and the specific leaf area of broadleaved-evergreen species are the mean of coniferous and broadleaved-deciduous species (Fyllas et al. 2007).
2. Estimation of life history parameters
LandClim simulates vegetation dynamics on the basis of species-specific life history parameters (Table 2). Plant growth is based on a maximum potential growth rate (rs, tons yr-1) under optimal conditions for each species. Growth is reduced from this maximum by growth reduction functions determined by light availability, drought stress, and growing degree days (Schumacher et al. 2004). We estimated the maximum potential growth rate (rs) using yield tables from Italian forests (Castellani 1982; Federici et al. 2001) to rank the growth rates of commercially-relevant Mediterranean species (e.g. Quercus cerris, Q. ilex) relative to species that were previously parameterized for LandClim. For non-commercial species, we estimated growth rates based on physiological studies from the Mediterranean region (e.g. Baldocchi et al. 2010; Ogaya and Penuelas 2007; Paraskevopoulos et al. 1994; Sanchez-Gomez et al. 2008). We determined maximum potential biomass from height and diameter measurements from a database of Italian big trees (data source: Associazione Ricerche Documentazioni Etologiche e Ambientali, Rome, Italy) following methodology described by Schumacher and Bugmann (2006).
Seedling establishment and growth in LandClim are limited by winter cold and summer warmth using the mean temperature of the coldest month, and the mean annual total of growing degree days, respectively. We estimated temperature constraints for the new Mediterranean species by overlaying spatially-interpolated climatic data from the period 1961-1990 (New et al. 2001) with species distribution maps (EUFORGEN 2009a, b; Meusel et al. 1964; Scholzel et al. 2002), and assigned the minima as two standard deviations below the mean value for the range of each species (Table 2). For species without digitized distribution maps, we generalized temperature tolerances from bioindicator values (Pignatti 2005). We estimated the sensitivity to fire damage to trees based on measurements of stem survival following fire (Fernandes et al. 2008; Gonzalez et al. 2007), and assumed all shrubs have low tolerance to fire. We determined resprouting capacity from a database of fire-related traits of plant species of the Mediterranean Basin (Paula et al. 2009).
Previous LandClim implementations for Central Europe ranked the shade and drought tolerance of each species on a scale of 1 (highly intolerant) – 5 (highly tolerant; Henne et al. 2011; Schumacher and Bugmann 2006). Because the Mediterranean flora includes species that are more adapted to drought stress than those in Central Europe, and because woody species typical of open sunny environments are common in the Mediterranean, we extended both scales to 1 – 6 using bioindicator values (Ellenberg 1996; Pignatti 2005). This strategy provides continuity in the environmental tolerance parameters between Central Europe and the Mediterranean.
3. Estimating the probability of fire spread and browsing mortality
We used the incomplete beta function to relate the probability of fire spread to the LandClim drought index, and the probability of establishment to browsing pressure. The incomplete beta function is defined by the integral (Press et al. 1992):
(2) where α and β are > 0,
(3) and B(α, β) is the value of the beta function:
The parameters α and β define the shape of the function and x is the normalized value of the drought index or browsing intensity.
For all variations in the fire regime, β was constant (i.e. 1.5). For simulations with small infrequent fires, α = 2.5. We increased the probability of fire spread in simulations with large infrequent fires, and small frequent fires by setting α = 2.0. Because fires also occur during dry intervals of wet years, especially when humans increase the number of ignition sources, we set the minimum probability to 0.1 for fire regimes with small infrequent, and large infrequent fires, and to 0.17 for the small frequent fire regime. We used a maximum fire probability of 0.8 for all fire regimes to avoid unrealistically-high fire spread values.
We simulated vegetation dynamics with three browsing intensities: without browsing (x = 0), low browsing (x = 0.25), and moderate browsing (x = 0.5). Each species is assigned a browsing tolerance value (i.e. brTol, Table 2) on a scale of 1 (very intolerant to browsing) to 5 (very tolerant to browsing). A separate cumulative beta probability density function is defined for each browsing tolerance: brTol 1, α = 4, β = 12; brTol 2, α = 2.4, β = 3.5; brTol 3, α = 1.9, β = 1.6; brTol 4, α = 2, β = 1; brTol 5, α = 4, β = 1.
Supplemental Table 1. List of trees and shrubs included in simulations.
Abies alba
Acer campestre
Acer monspessulanum
Acer platanoides
Acer pseudoplatanus
Arbutus unedo
Carpinus betulus
Castanea sativa
Cistus salvifolius
Corylus avellana
Erica arborea
Fagus sylvatica
Fraxinus excelsior
Fraxinus ornus
Ilex aquifolium
Laurus nobilis
Olea europea
Ostrya carpinifolia
Phillyrea angustifolia
Phillyrea latifolia
Pinus halepensis
Pistacia lentiscus
Pistacia terebinthus
Quercus cerris
Quercus coccifera
Quercus ilex
Quercus petraea
Quercus pubescens
Quercus robur
Quercus suber
Rhamnus alaternus
Tilia cordata
Tilia platyphyllos
Ulmus glabra
Supplemental Table 2a. Life history parameters for Mediterranean species not included in previous LandClim versions, and other important species mentioned in text.
Species r K maxAge matu ED MD vegP spAge
(t yr-1) (t) (yr) (yr) (m) (m) (yr)
Abies alba 0.08 17.6 700 70 50 160 0 0
Arbutus unedo 0.07 0.7 400 20 30 -1 1 75
Cistus salvifolius 0.005 0.005 70 10 40 170 0 0
Erica arborea 0.06 0.1 100 10 30 100 1 50
Fraxinus ornus 0.07 2.7 200 20 40 140 1 50
Laurus nobilis 0.06 0.5 300 20 30 -1 1 50
Olea europea 0.04 10.0 700 10 30 -1 1 75
Ostrya carpinifolia 0.1 2.0 150 30 55 180 1 30
Phillyrea latifolia 0.03 0.2 300 10 30 -1 1 50
Phillyrea angustifolia 0.03 0.2 50 10 30 -1 1 50
Pinus halepensis 0.07 2.7 275 20 90 300 0 0
Pistacia lentiscus 0.04 0.4 300 10 30 -1 1 50
Pistacia terebinthus 0.04 0.4 300 10 30 -1 1 50
Quercus cerris 0.09 11.6 600 60 30 -1 1 75
Quercus coccifera 0.03 1.4 450 20 30 -1 1 75
Quercus ilex 0.03 8.9 600 20 30 -1 1 75
Quercus pubescens 0.07 2.4 500 60 30 -1 1 50
Quercus suber 0.03 8.3 400 20 30 -1 1 75
Rhamnus alaternus 0.005 0.01 100 10 30 -1 1 50
r: maximum above-ground biomass growth rate; K: maximum above-ground tree biomass; maxAge: maximum longevity; matu: age for seed production; ED: effective seeding distance; MD: maximum seeding distance; vegP: species capable (1) or not capable (0) of resprouting following disturbance; spAge: maximum age for vegetative reproduction. Data sources are listed in the text.
Table 2b.
Species BioT folType shTol minDD mint drTol brTol FireTol
(d) (°C)
Abies alba NE 5 6 641 -6 3 1 3
Arbutus unedo BE 4 1 1792 2 5 3 1
Cistus salvifolius BE 4 1 1792 2 6 4 1
Erica arborea BE 4 3 1554 2 5 5 1
Fraxinus ornus D 2 4 1639 0 5 3 2
Laurus nobilis BE 5 6 1800 0 1 3 1
Olea europea BE 4 1 2031 6 6 3 3
Ostrya carpinifolia D 2 5 937 -7 4 4 2
Phillyrea latifolia BE 4 4 2074 1 4 5 1
Phillyrea angustifolia BE 4 1 2174 2 6 5 1
Pinus halepensis NE 4 1 2303 2 6 3 3
Pistacia lentiscus BE 4 1 2031 2 6 4 1
Pistacia terebinthus D 4 1 1554 0 6 4 1
Quercus cerris D 2 3 1554 -1 4 2 3
Quercus coccifera BE 4 3 1963 1 5 4 3
Quercus ilex BE 4 6 1773 1 5 3 3
Quercus pubescens D 3 3 1011 -99 5 2 3
Quercus suber BE 4 5 2635 6 5 3 5
Rhamnus alaternus BE 4 5 1792 2 6 3 1
BioT: NE denotes needle-leaved evergreen, BE broad-leaved evergreen, and D deciduous species. folType: Foliage type; shTol: shade tolerance (1 = very intolerant, 6 = very tolerant). To expand the range for the Mediterranean species, we added 1 to the values used by Schumacher (2004), but the implementation is the same in the model for like species. minDD: minimum annual degree-day sum; mint: minimum temperature for establishment; drTol: drought tolerance (1 = very intolerant, 6 = very tolerant); brTol: browsing tolerance (1 = very tolerant, 5 = very intolerant); FireTol: sensitivity to fire damage of trees that have reached the canopy.
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