Holm Oak and Holm Oak Forests: An Introduction
7
lodrys O. Schwarz. It can grow up to 27 m high but rarely reaches 15 m. Two
main forms exist: Q. ilex ssp. ilex and Q. ilex ssp. ballota (Desf.) Sampaio
(= Q. ilex ssp. rotundifolia), sometimes considered to be different species
(Q. ilex L. and Q. rotundifolia Lam. Schwarz 1964, respectively). Both forms
can interbreed, but their main distribution ranges are separated, with the
ssp. ilex in coastal areas and the ssp. ballota mostly in interior areas. The
morphological differences between the leaves of both forms are probably related to the constraints of their respective environments. In this book we will
deal with the ssp. ilex.
Holm oak is a hardwood tree that grows slowly, forming dense canopies.
Its leaves are small and coriaceous, the upper side is dark green, while the
lower side is covered by white hairs. Stomata are relatively small (length is
22-27 ~m) and limited to the abaxial surface of the leaf, hidden under a
dense cover of stellate hairs. There are between 100 and 500 stomata mm- 2 • A
fine adjustment of holm oak stomata allows a hydrostable behaviour (Larcher 1995). The upper epidermis and cuticle are much thicker than their
lower counterparts. We must consider these characteristics as a part of a conservative strategy in order to maintain a low cuticular transpiration and a
high resistance to desiccation (Chap. 10).
Holm oak is a shade-tolerant tree, becoming dominant in late successional
stages. Photosynthesis is conducted throughout the year (Eckardt et al. 1978).
Leaf chlorophyll content is very high. A LAI of 4.5 m 2 m- 2 could be near optimal (Sala et al. 1994). LAI seems to be poorly sensitive to water availability.
In closed-canopy stands, leaves are mostly concentrated in the uppermost
meter of the canopy (Chap. 9).
Wood is dense and its structure is diffuse semiporous, with a 50- to
150-~m porus diameter (Marchal 1995). Vessels are irregularly distributed
and have slightly decreasing diameters towards the outer part of the growth
ring. There are many relatively narrow and quite short vessels compared with
the ring-porous woods found in deciduous oaks. Annual rings can be difficult to recognize because false tree-rings are frequent and pluriseriate medullar rays obscure the growth pattern (Gene et al. 1993). As a result, few data
are available on radial growth rate. Wood hardness and density have made
holm oak wood useful for making carts, tool handles, jack planes and other
carpentry tools, gear teeth, parquets, etc. As a result of its vessel characteristics, holm oak has slow midday peak velocities of water flow, ranging from
1 to 6 m h- I (0.3-1.7 mm S-I). The cavitation of one vessel in that organization causes much less damage than in ring-porous trees.
Holm oak has deep roots. In only one year, the unbranched taproot of a
holm oak seedling can reach 60-80 cm. In adult holm oaks, there is also a
complex system of spreading lateral roots that can extend many meters,
growing from a thick, sometimes massive root crown, particularly in coppices as a result of tissue accumulation during successive resprout production. There are few data on aboveground/underground biomass ratio, but a
7
lodrys O. Schwarz. It can grow up to 27 m high but rarely reaches 15 m. Two
main forms exist: Q. ilex ssp. ilex and Q. ilex ssp. ballota (Desf.) Sampaio
(= Q. ilex ssp. rotundifolia), sometimes considered to be different species
(Q. ilex L. and Q. rotundifolia Lam. Schwarz 1964, respectively). Both forms
can interbreed, but their main distribution ranges are separated, with the
ssp. ilex in coastal areas and the ssp. ballota mostly in interior areas. The
morphological differences between the leaves of both forms are probably related to the constraints of their respective environments. In this book we will
deal with the ssp. ilex.
Holm oak is a hardwood tree that grows slowly, forming dense canopies.
Its leaves are small and coriaceous, the upper side is dark green, while the
lower side is covered by white hairs. Stomata are relatively small (length is
22-27 ~m) and limited to the abaxial surface of the leaf, hidden under a
dense cover of stellate hairs. There are between 100 and 500 stomata mm- 2 • A
fine adjustment of holm oak stomata allows a hydrostable behaviour (Larcher 1995). The upper epidermis and cuticle are much thicker than their
lower counterparts. We must consider these characteristics as a part of a conservative strategy in order to maintain a low cuticular transpiration and a
high resistance to desiccation (Chap. 10).
Holm oak is a shade-tolerant tree, becoming dominant in late successional
stages. Photosynthesis is conducted throughout the year (Eckardt et al. 1978).
Leaf chlorophyll content is very high. A LAI of 4.5 m 2 m- 2 could be near optimal (Sala et al. 1994). LAI seems to be poorly sensitive to water availability.
In closed-canopy stands, leaves are mostly concentrated in the uppermost
meter of the canopy (Chap. 9).
Wood is dense and its structure is diffuse semiporous, with a 50- to
150-~m porus diameter (Marchal 1995). Vessels are irregularly distributed
and have slightly decreasing diameters towards the outer part of the growth
ring. There are many relatively narrow and quite short vessels compared with
the ring-porous woods found in deciduous oaks. Annual rings can be difficult to recognize because false tree-rings are frequent and pluriseriate medullar rays obscure the growth pattern (Gene et al. 1993). As a result, few data
are available on radial growth rate. Wood hardness and density have made
holm oak wood useful for making carts, tool handles, jack planes and other
carpentry tools, gear teeth, parquets, etc. As a result of its vessel characteristics, holm oak has slow midday peak velocities of water flow, ranging from
1 to 6 m h- I (0.3-1.7 mm S-I). The cavitation of one vessel in that organization causes much less damage than in ring-porous trees.
Holm oak has deep roots. In only one year, the unbranched taproot of a
holm oak seedling can reach 60-80 cm. In adult holm oaks, there is also a
complex system of spreading lateral roots that can extend many meters,
growing from a thick, sometimes massive root crown, particularly in coppices as a result of tissue accumulation during successive resprout production. There are few data on aboveground/underground biomass ratio, but a