This page contains text descriptions of each of the ecophysiological variables that make up the *.epc files, used as defaults within the BIOME-BGC model. The variables are described in the order in which they appear in the *.epc files. Each description consists of a header line that identifies the relevant line in the *.epc file, followed by the text description for that line. The header lines contain the units for the parameter followed by the short text description of the parameter as it appears in the *.epc files. Note that all *.epc files have the same parameter lines, in the same order, but that not all lines are relevant to all vegetation types. Lines marked with (*) before the units in a particular *.epc file indicate an irrelevant parameter for that vegetation type, and any numeric value can be substituted in these places without effect. Where units are specified as (DIM), this indicates that the value is dimensionless (e.g. kgC/kgC).
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TEXT
DESCRIPTION
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| (flag) 1 = WOODY 0 = NON-WOODY |
An integer flag specifying the growth
form, where 1 for woody includes both tree and shrub vegetation types,
and 0 for non-woody includes grasses as well as other primarily herbaceous
plants.
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(flag) 1 = EVERGREEN 0 = DECIDUOUS
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An integer flag specifying the leaf habit, where 1 for evergreen includes leaf habits that retain at least some of their foliage year-round, and 0 for deciduous includes leaf habits in which all foliage is absent at some point during a year. Either value for this flag can apply to both woody and non-woody growth forms. |
| (flag) 1 = C3 PSN 0 = C4 PSN |
An integer flag specifying the photosynthetic
pathway, where 1 indicates that the C3 photosynthesis model should be
invoked, and 0 indicates that the C4 model should be invoked. Although
this flag can be set to 0 for any combination of the other parameters,
use of the C4 model should be restricted to grasses and herbaceous plants.
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| (flag) 1 = MODEL PHENOLOGY 0 = USER-SPECIFIED PHENOLOGY |
An integer flag specifying how the phenological control for a simulation will be exercised. A value of 1 invokes the internal phenology routine, while a value of 0 indicates that the user will supply information on the yeardays for the start of new growth and the end of the litterfall period. See below for more details on how to set these parameters for the case of user-specified phenology. |
| (yday) yearday to start new growth
(when phenology flag = 0) (yday) yearday to end litterfall (when phenology flag = 0) |
Two integers specifying the yearday
for the start of new leaf growth, and the yearday for the end of the
litterfall season, respectively. Relevant only when the phenology flag
= 0 (see above). There are several IMPORTANT NOTES about setting these
values: 1) To suppress new leaf growth entirely, for example in the
case of a simulation concerned with bare soil processes, set both of
these values to -1. 2) Yearday values start at 0 and go to 364. Note
that BIOME-BGC does not accept leap-years, i.e. all years are by definition
365 days long. 3) Northern and Southern hemisphere yeardays are treated
differently. In the northern hemisphere, yearday 0 = Jan 1, while in
the southern hemisphere yearday 0 = July 2. This allows the same yearday
values to be used to specify deciduous growth habit in the northern
and southern temperate zones. 4) If the leaf habit flag is set to evergreen
(1), and the phenology model falg is set to user-specified (0), these
values do not have any effect.
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| (prop.) transfer growth period as
fraction of growing season (prop.) litterfall as fraction of growing season |
These two parameters determine the
duration of the transfer growth and litterfall periods, and are defined
as proportions of the period between the start of new growth and the
end of litterfall. These parameters must be set by the user REGARDLESS
of whether internal model phenology or user-specified phenology is specified
in the phenology model flag. These parameters can take any values from
0.0 to 1.0, where a value of 0.0 indicates that all transfer growth
or all litterfall occurs in a single day, and a value of 1.0 indicates
that transfer growth or litterfall occur throughout the growing season.
Transfer growth is the growth derived from carbon and nitrogen resources
stored over the course of the previous growing season. It is the growth
that produces the first flush of new leaves in the spring for deciduous
plants. NOTE that when the leaf habit flag is set for evergreen (1),
both transfer growth and litterfall are assumed to occur at constnat
rates throughout the year, and the specification of these two parameters
has no effect.
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| (1/yr) annual leaf and fine root turnover fraction |
Determines leaf and fine root turnover
for evergreen plants. This is the fraction of the annual maximum leaf
and fine root mass that will be dropped in the following year as litter.
It is the reciprocal of the leaf longevity, so a plant that retains
its leaves an average of two years would have a leaf/fine root turnover
of 0.5. Note that leaf and fine root phenology are assumed to be entirely
synchronized for all vegetation types. ALSO NOTE that when the leaf
habit is specified as deciduous (0), this parameter is always assumed
to be 1.0, and will be reset inside the code if the user specifies any
other value.
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| (1/yr) annual live wood turnover fraction |
Determines livewood turnover to deadwood
for all woody types (deciduous and evergreen). IMPORTANT NOTE about
the definition of livewood and deadwood in BIOME-BGC: Livewood is defined
as the actively respiring woody tissue, that is, the lateral sheathing
meristem of phloem tissue, plus any ray parenchyma extending radially
into the xylem tissue. Deadwood consists of all the other woody material,
including the heartwood, the xylem, and the bark. It has been common
in many tree models, including previous versions of BIOME-BGC, to divide
the woody tissue into two compartments called "sapwood" and "heartwood",
where sapwood is usually defined as the sum of phloem and xylem, with
heartwood defined as the non-conducting woody tissue. The current treatment
ignores the distinction between water-conducting xylem and non-conducting
heartwood.
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| (1/yr) annual whole-plant mortality fraction |
This parameter specifies the fraction of all plant pools that will be removed and sent to the litter compartments over the course of a year. This is one mechanism by which woody material (live and dead) leaves the plant pool and enters the litter pools to be made available for subsequent decomposition. It is the conceptual equivalent of wind-throw, since all plant pools, living and dead, are attenuated at the same rate. This annual proportion is converted internally to a daily rate, and whole-plant mortality is assumed to go on at a constant rate throughout the year. |
| (1/yr) annual fire mortality fraction |
This parameter specifies the fraction of plant pools subject to fire, on average, each year. The current treatment ignores the timing of individual fire events, taking a long-term view of the fire process, in which some fraction of the community is subject to fire each year, at a rate commensurate with the long-term fire frequency. For example, in a system with a stand- replacing fire return interval of 100 yrs, this parameter would be set to 0.01. |
| (ratio) (ALLOCATION) new fine root C : new leaf C |
Sets the ratio of new fine root growth
to new leaf growth. This is a constant, and applies to both current
year growth, and growth resources stored for the next year's transfer
growth.
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| (ratio) (ALLOCATION) new stem C : new leaf C |
Sets the ratio of new stem growth to new leaf growth. Stem growth includes both the live and dead woody components, as described above. This ratio is constant, and applies to both current year growth and growth resources stored for the next year's transfer growth. |
| (ratio) (ALLOCATION) new live wood C : new total wood C |
Sets the ratio of new live wood to new total wood. This ratio is constant, and applies to both current year growth and growth resources stored for the next year's transfer growth. |
| (ratio) (ALLOCATION) new croot C : new stem C |
Sets the ratio of new coarse root
growth to new stem growth. This ratio is constant, and applies to both
current year growth and growth resources stored for the next year's
transfer growth.
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| (prop.) (ALLOCATION) current growth proportion |
Sets the proportion of daily production displayed immediately as new growth, with the remainder stored for the next year's transfer growth. |
| (kgC/kgN) C:N of leaves |
Mass ratio of carbon : nitrogen in
live leaves.
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| (kgC/kgN) C:N of leaf litter, after retranslocation |
Mass ratio of carbon: nitrogen in
freshly fallen leaf litter. This can only be higher than or equal to
the C:N for live leaves, i.e. retranslocation can only be positive or
zero. Retranslocation is the removal of nitrogen from the leaves prior
to litterfall. The model does not consider the possibility of retranslocation
of carbon out of leaves prior to litterfall.
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| (kgC/kgN) C:N of fine roots |
Mass ratio of carbon : nitrogen in fine roots. The model assumes that there is no retranslocation of nitrogen out of fine roots prior to litterfall, so this is the only C:N parameter for fine roots. |
| (kgC/kgN) C:N of live wood |
Mass ratio of carbon : nitrogen for live wood (phloem and ray parenchyma). This will typically be a much smaller value than the average C:N for all woody parts, and is typically found to be close to that for fine roots. |
| (kgC/kgN) C:N of dead wood |
Mass ratio of carbon : nitrogen for dead wood (bark, xylem, heartwood). |
| (DIM) leaf litter labile proportion |
The proportion of leaf litter mass in the labile fraction, usually defined as that fraction soluble in hot water/alcohol. Labile, cellulose, and lignin fractions for leaf litter must sum to 1.0. |
| (DIM) leaf litter cellulose proportion |
The proportion of leaf litter mass in the cellulose fraction, usually defined as that fraction soluble in a mild acid solution, after extraction of the water/alcohol soluble fraction. Labile, cellulose, and lignin fractions for leaf litter must sum to 1.0. |
| (DIM) leaf litter lignin proportion |
The proportion of leaf litter mass in the lignin fraction, usually defined as the remaining fraction after labile and cellulose fractions are removed, as described above. Labile, cellulose, and lignin fractions for leaf litter must sum to 1.0. |
| (DIM) fine root labile proportion |
The proportion of fine root mass in the labile fraction, usually defined as that fraction soluble in hot water/alcohol. Labile, cellulose, and lignin fractions for fine root must sum to 1.0. |
| (DIM) fine root cellulose proportion |
The proportion of fine root mass
in the cellulose fraction, usually defined as that fraction soluble
in a mild acid solution, after extraction of the water/alcohol soluble
fraction. Labile, cellulose, and lignin fractions for fine root must
sum to 1.0.
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| (DIM) fine root lignin proportion |
The proportion of fine root mass
in the lignin fraction, usually defined as the remaining fraction after
labile and cellulose fractions are removed, as described above. Labile,
cellulose, and lignin fractions for fine root must sum to 1.0.
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| (DIM) dead wood cellulose proportion |
The proportion of dead wood mass in the cellulose fraction, usually defined as that fraction soluble in a mild acid solution, after extraction of the water/alcohol soluble fraction. Cellulose and lignin fractions for dead wood must sum to 1.0. |
| (DIM) dead wood lignin proportion |
The proportion of dead wood mass
in the lignin fraction, usually defined as the remaining fraction after
labile and cellulose fractions are removed, as described above. Cellulose
and lignin frastions for dead wood must sum to 1.0.
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| (1/LAI/d) canopy water interception coefficient |
The proportion of daily rainfall that can be intercepted and retained on the canopy per unit of projected leaf area index. |
| (DIM) canopy light extinction coefficient |
The Beer's law extinction coefficient
for attenuation of radiation in the canopy, using a projected leaf area
basis, and accounting for leaf clumping effects.
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| (DIM) all-sided to projected leaf area ratio |
The ratio between the all-sided area and the projected area for leaves. Projected area for this and all other uses in BIOME-BGC is the projected area of the leaf laid flat with its two longest dimensions parallel to the measurement surface, while all-sided area is the total leaf surface area. |
| (m2/kgC) canopy average specific leaf area (projected area basis) |
Projected area per unit of leaf carbon
mass, averaged over the canopy.
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| (DIM) ratio of shaded SLA:sunlit SLA |
Ratio between specific leaf area
for leaves in the shaded canopy fraction and specific leaf area for
leaves in the sunlit canopy fraction.
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| (DIM) fraction of leaf N in Rubisco |
The fraction of total live leaf nitrogen
occurring in the Rubisco enzyme.
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| (m/s) maximum stomatal conductance (projected area basis) |
The maximum stomatal conductance
to water vapor, expressed on a projected leaf area basis. This is the
conductance under saturating light, low VPD, leaf water potential near
0.0, and moderate temperatures. Reciprocal of minimum stomatal resistance.
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| (m/s) cuticular conductance (projected area basis) |
The conductance of the leaf cuticle
to water vapor, expressed on a projected area basis. Assumed constant
under all environmental conditions.
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| (m/s) boundary layer conductance (projected area basis) |
Leaf boundary layer conductance to water vapor, expressed on a projected area basis. This is also refered to as the aerodynamic conductance. It is defined as the conductance for water vapor entering the atmosphere from a free water surface on the leaf surface (a raindrop on the leaf). It is assumed constant under all environmental conditions, although it is in reality a strong function of wind speed. A constant windspeed of 1 m/s is assumed in defining values of this parameter for various leaf morphologies. |
| (MPa) leaf water potential: start
of conductance reduction (MPa) leaf water potential: complete conductance reduction |
These two parameters set the endpoints
for a linear control on stomatal conductance due to leaf water potential.
The first parameter sets the leaf water potential at which conductance
reduction begins, and the second parameter sets the water potential
at which stomatal conductance is reduced to 0.0. In the range between
these values, reduction of stomatal conductance is a linear function
of leaf water potential.
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| (Pa) vapor pressure deficit: start
of conductance reduction (Pa) vapor pressure deficit: complete conductance reduction |
These two parameters set the endpoints for a linear control on stomatal conductance due to the water vapor pressure difference (VPD) between the interior of the leaf and the air adjacent to the leaf. The first parameter sets the VPD at which conductance reduction begins, and the second parameter sets the VPD at which stomatal conductance is reduced to 0.0. In the range between these values, reduction of stomatal conductance is a linear function of VPD. |