Download Beech forests of Iran

Beech forests of Iran
One of the most abundant and economic hardwood genera in the northern hemisphere
temperate forests is the Fagus (beech) genus. So far 20 beech species have been identified
however, controversies do exist, while all these species are distributed in the northern
hemisphere, only Fagus orientalis Lipsky occurs in Iran. The Iranian beech belt is connected
to the European forests with regarding to plant composition and at this level it has many
similarities with Balkan's beech forests. However, at lower levels, beech forests of Iran are
exclusive based on the presence of sub-tropical elements.
The oldest Fagus fossil found dates back to Cretaceous Period. Many Fagus fossils originate
from the Tertiary found in places such as Greenland, Iceland and Swalbard, where beech trees
no longer exist. The current distribution of F. orientalis (Crimea, Caucasus, western Asia and
Iran) has not been seriously influenced by glaciers and the evolution of the communities has
been more or less since the Teritary. Furthermore, the Iranian beech communities, lying in the
most eastern parts of the distribution range, are very uniform probably due to geographical
separation. There are considerable similarities between the Iranian beech communities and the
northwest American beech communities (F. grandifolia subsp. croliniana), indicating interconnectivity between the north Asian and north American communities. In general, the
eastern beech can be defined as a mountainous species with higher ecological distribution in
comparison with the European beech.
The vertical distribution of beech is highly dependent on climatic conditions so that at a given
latitude and humid climate, beech trees can be found in terrestrial up to alpine vegetation
areas. Although the eastern beech could be found at altitudes ranging from 500m to 2000m,
the optimum growth can only be achieved at altitudes of 900m to 1600m. Generally, the
eastern beech is a semi-hydrophilic species with a high resistance to low temperatures and
freezing, sunburn and other stresses, requiring high quality soils, which grows on deep and
relatively deep, loamy to sandy-loamy, cambisol (forest brown soils) especially the acidic
type as compared with the European beech.
In Iran, pure and mixed beech forests are one of the most important, richest and most
beautiful forests often lying on the northern slopes of Alborz mountain ranges adjacent to the
Caspian Sea coasts. Natural dense sites are found at the altitudes of 1000m to 2100m.
However some communities could be observed down to 600m altitude depending on the local
and microclimatic conditions. The beech trees are found in small groups up to 500m.a.s.l.
while individuals have been reported from 110m up to 2650m. At low altitudes, they occur
mixed with Carpinus betulus while Carpinus orientalis is seen mixed with beech trees at
higher altitudes The best beech stands are found at the altitudes of 900m to 1500m on
northern slopes.
Geology
Geological formation of the Caspian western coasts such as Asalem consist of acidic igneous
rocks (granite), occasionally alkaline diorite, andesite, perfirite, and metamorphic rocks like
quartz schist belonging to the First Period to the Tertiary. In central parts such as Noshahr
(Veisar and Kheiroodkenar forests) the geological formations are dolomite and calcic
sometimes associated with the First Period's red sandstones surrounded by calcic layers of
Jurassic, Cretaceous or Carboniferous. At high altitudes, intrusive igneous rocks often
alkaline are seen. In the eastern Mazandaran (Sangdeh and Neka forests) the geological
formations are often composed by lime and dolomite belonging to Triassic and Jurassic.
However, metamorphic rocks often red quartz schist belonging to the late Tertiary are also
found in some parts. In the most eastern beech forests in Gorgan, the geological formations
mainly include lime, dolomite, sandstones of Devonian or Carboniferous and Jurassic calcic
layers. Metamorphic rocks such as quartz schist are also found in some areas.
Climatic characteristics
According to De Martin method, the climate in the beech sites of Iran is very humid and cold
in lowlands and midlands (up to 1700m) and very humid ultra cold in highlands (up to
2200m). Frost period in lowlands, midlands and highlands are 2 months, 3 months and 5
months respectively. Asalem beech forests in the most western Hyrcanian forests with an
annual precipitation of 2000 mm are the wettest beech forest of the country. Moving toward
the east, this value rapidly drops falling down to half in Gorgan beech forests. Moreover, the
major part of the precipitation in Asalem occurs in the fall and summer whereas that of Gorgan
occurs mostly in fall and winter.
The average annual precipitation and temperature in three altitude classes are shown in
Figure 1.
1400
Percipitation (mm)
1350
1300
1250
1200
1150
1100
1050
Low
Middle
High
Altitude classes
temprature ( C)
14
12
10
8
6
4
2
0
Low
Middle
High
Altitude classes
Fig. 1: Annual mean precipitation and temperature of altitude classes in beech forests.
Pedology
Fagetum communities of Iran occur over two parent rocks namely acidic (igneous and
metamorphic) and calcic (sedimentary and metamorphic). Soils lying on acidic parent rocks
usually have light or balanced texture and complete drainage whereas soils formed over calcic
parent rocks are generally semi-heavy to heavy textured and exhibit gradual or occasionally
slow drainage. method, the soils of this region could be divided into four categories: Acidic
brown, podzolic brown, hydromorphous brown and pseudoglay. Fagetum communities
associated with Vaccinium arctostaphylos have the lightest soils while the communities with
Asperula odorata and Ruscus hyrcanus exhibit the heaviest. The most acidic beech forest
types are associated with Caucasian whortleberry and the most non-acidic ones are associated
with box holly. Fagetum communities of the central areas, where drainage is good, are found
on soils over acidic parent rocks, ridges and high flat lands as well as on deep clay-rich soils.
These soils belong to amphisols with high biological activity in uplayers despite their acidic
condition. C/N ratio does not exceed 20.
The most acidic humus forms are found in Fagetum communities of Asalem, where the
annual rainfall average is the highest. Moving eastwards, the acidity decreases, while the
biological activity increases.
Two humus form order namely mull and Moder and eight humus form groups, including
Verminull, Rhizomull, Leptomoder, Hydromoder, Hydromoder, Mormoder and Lamimoder
have been identified in beech forests so far . In comparison with beech forests of Europe,
especially in upper mineral layers like A1 horizon, pH with an average of 4.9 is slightly lower
than usual.
Thus, seven distinct groups are identified based on beech forest type, local conditions, parent
rocks and soil physio-chemical properties
Fagetum associated with Vaccinium arctostaphylos L.
mainly found at mid and high
altitudes on northeastern and western slopes over acidic (igneous and metamorphic) parent
rocks and light, semi-deep fully drained soils. pH is highly acidic (4-5.5) due to the cold and
humid climate and the organic matter accumulation is high on the surface. These are rich in
phosphorus and magnesium, moderate in nitrogen and highly variable in potassium and
calcium.
Fagetum associated with Ilex spinigera mainly found at mid and high altitudes generally
characterizing low-sloped wet sites over acidic parent rocks and deep, semi-heavy drained
soils which are more or less hydromorphous. The humus is often acidic with pH values
between 4.5-5.5 and accumulated organic matter. These are rich in all minerals except
potassium.
Fagetum associated with Asperula odorata L. syn Galium odoratum Scop Found at the
same altitudes as the two former ones, occur over any parent rocks with deep, semi-heavy to
heavy, drained soils. The soil is less acidic (pH 5-5.5) with less surface organic matter rich in
all minerals except potassium.
Fagetum associated with Ruscus hyrcanus L. Occur at low and mid altitudes on northern
slopes over calcic (sometimes non-calcic) parent rocks with deep heavy-textured but drained
soils. The soil is less acidic (pH 6-6.5) rich in nitrogen, phosphorous, calcium and magnesium
but moderate in potassium. The humus is less acidic and is often eutrophic and mesotrophic
Mulls.
Fagetum associated with Luzula pilos Willd. Mainly found at mid and high altitudes on
northern and northwestern slopes over more acidic and less calcic parent rocks and deep
semi-heavy drained soils. Humus is mostly acidic (pH 4.5 - 5.5) oligotrophic Mull rich in
phosphorous, calcium and magnesium but poor in nitrogen and potassium.
Fagetum associated with Sanicula europaea L. Often found at mid altitudes occur on
northwestern and western slopes over various parent rocks with deep, semi-heavy, drained
soils. The humus is mostly mesotrophic and oligotrophic Mull with a pH of 4.5-5.5. The soil
is rich in nitrogen, calcium and magnesium, poor in potassium and highly variable in
phosphorous.
Fagetum associated with Mercurialis perennis L. Often found at mid altitudes occur on
northwestern and western slopes over calcic parent rocks with deep, heavy but fully drained
soils. The humus is eutrophic and mesotrophic Mulls with a pH of 5-6 rich in nitrogen.
Silviculture characteristics
Beech forests accounts for approximately 17.6% of the total forest area, 30% of the standing
volume and 23.6% of the stem number in Hyrcanian forests in Iran. The average beech
volume per ha ranges between 480 and 740 cubic meters in pure stands and 600 and 700
cubic meters in mixed stands. Moreover, one third of the total volume of the existing trees fall
into the large size trees ( dbh >55 cm) comprising two thirds of the total stand volume.
Observations and experience indicate that seeding occurs every 4 to 6 years in these beech
forests. A dual seeding cycle has been suggested to exist for beech trees in Iran; minor one
with a few amounts of seeds happens every one to five years and major one with the highest
amount of seed occurs every 4 to 5 years.
Silvicultural studies indicate that the Hyrcanian Fagetum communities are heterogeneous
regarding their silvicultural characteristics both in pure and mixed stands. Group forms are
observed in stands.
These even-aged young or old tree groups resemble an uneven-aged structure at a larger scale.
The results show that at 0.25 to 0.5 ha areas, even-aged structure can be distinguished despite
the irregularity and heterogeneity of the number distribution in diameter classes. At wider
levels with more than 0.5 ha area, the number distribution in diameter classes exhibits
uneven-aged structure. The mosaics of even-aged and uneven-aged spots are horizontally
distributed adjacent to each other at different sizes. Although the curves and structure greatly
deviate from the normal curves in selectively managed forests, there still exists a kind of
irregular heterogeneous structure with trees in different levels and vertical spaces.
Based on the same study, beech trees growing in 200m2 to 500 m2 area gaps exhibit
qualitatively and quantitatively better reproduction. The naturally occurring gaps in the forest
are not regularly shaped mainly having oval shapes. Studies have indicated that although the
best beech quantitative growth is observed in large holes (> 0.1 ha), young trees with the best
forms are found in medium-sized (200 m2 to 500 m2) gaps. Therefore, it seems that the group
selection system with removing of 2-4 main trees could be suggested as a sustainable
management method for the Iranian beech stands.
Over the past decade, even-aged uniform methods particularly shelterwood system, have been
extensively employed for forest management. However, these methods have not been very
successful in the North Iranian forests due to a number of technical and potential problems.
The presence of livestock in all forests and failure in preventing their entrance into the
regeneration area, improper felling, incorrect marking, dependence on natural advanced
regeneration and improper utilization practices are among the main technical problems.
Unfavorable annual regeneration, inappropriate climates such as wet falls (harmful for ripen
seeds on the trees), mild winters with low snowfall (decreasing the shelf time of the seeds),
cold springs and late frost (harmful to germination, shootings health and seed trees blooming)
could be noted as the main potential problems. Furthermore, frequent droughts, inappropriate
beds with acidic humus forms, under-humid or over-humid site conditions, soil compaction
due to the livestock presence, steep slopes unfavorable for seeds establishment and
germination, the naturally irregular structure of the stands and their incompatibility with the
even-aged uniform methods also greatly influence the conditions.
These altogether have led the authorities of the Forests and Rangelands Organization to adopt
sustainable stand management policies with emphasis on the close to nature silviculture
system and the employment of uneven-aged uniform methods.