9.2. Model Development
167
simulates the dynam ics of leaf growth rates, initiation of new leaf growth ,
and leaf plastochrone intervals used to determine both leaf loss and leaf development. The leaf plastochrone interval refers to the time interval between the initiation of two successive leaves (Iacobs 1979).
This chapter describes the process of incorporating the shoo t model
within a more elab orate plant level model for predicting eelgrass bed densities. In other words , this chapter explores the proce ss of "scaling up " the
shoot model to the next hierarchical level. The goal of the plant model is to
initiate growth and development of new shoots and aid the investigation
into the causes of eelgrass declines. The modeling process provides insight
into areas where more research is needed, and provides the researcher with
a means for determining the specific data needed to calibrate the model to
more accurately describe the Great Bay Estuary.
9.2. Model Development
The STELLA model contain s two sectors- a plant-growth sector and a
plant-density sector. The plant-growth sector , in tum, incorporates submodels of shoot growth (Boumans et al.; in press), and root and rhizome
development to explore eelgrass bed dynamics. Each of the sectors and
submodels is described in the following sections.
The use of sub models in STELLA provides a means for highlighting the
major objectives of the model , while still incorporating all necessary features. For example, the main concern with the plant model centers on eelgrass bed development. Shoo t dynamics are not the focus of the model ,
but are still necessary in formul ating plant bed development. Therefore, a
submodel containing the shoo t model maintains the connection between
shoo t development and plant development, but keep s the focus on the
plant level.
Using submodels in this context also maintains a distinction between the
two levels in the hierarchical scheme (with the lower level serving as a submodel of the higher level). This scaling process coincides with current hierarchical theory that nature can be partitioned into "naturally occurring" levels that share similar time and space scales, and each level in the hierarchy
sees the higher levels as constraints and the lower levels as "noise" (Allen
and Starr 1982; O'Neill et al. 1986). Step-by-step instructions for creating
submodels in STELLA are provided in the STELLA help guide.
9.2.1. Plant-Growth Sector
The plant-growth sector (Figure 9.4) represents the resulting growth of the
shoo ts, roots and rhizomes, and reproductive parts , and contains "global inputs " such as temperature and photoperiod. Shoot growth is represented as
the total mass of shoots in the community On units of grams). The shoot
167
simulates the dynam ics of leaf growth rates, initiation of new leaf growth ,
and leaf plastochrone intervals used to determine both leaf loss and leaf development. The leaf plastochrone interval refers to the time interval between the initiation of two successive leaves (Iacobs 1979).
This chapter describes the process of incorporating the shoo t model
within a more elab orate plant level model for predicting eelgrass bed densities. In other words , this chapter explores the proce ss of "scaling up " the
shoot model to the next hierarchical level. The goal of the plant model is to
initiate growth and development of new shoots and aid the investigation
into the causes of eelgrass declines. The modeling process provides insight
into areas where more research is needed, and provides the researcher with
a means for determining the specific data needed to calibrate the model to
more accurately describe the Great Bay Estuary.
9.2. Model Development
The STELLA model contain s two sectors- a plant-growth sector and a
plant-density sector. The plant-growth sector , in tum, incorporates submodels of shoot growth (Boumans et al.; in press), and root and rhizome
development to explore eelgrass bed dynamics. Each of the sectors and
submodels is described in the following sections.
The use of sub models in STELLA provides a means for highlighting the
major objectives of the model , while still incorporating all necessary features. For example, the main concern with the plant model centers on eelgrass bed development. Shoo t dynamics are not the focus of the model ,
but are still necessary in formul ating plant bed development. Therefore, a
submodel containing the shoo t model maintains the connection between
shoo t development and plant development, but keep s the focus on the
plant level.
Using submodels in this context also maintains a distinction between the
two levels in the hierarchical scheme (with the lower level serving as a submodel of the higher level). This scaling process coincides with current hierarchical theory that nature can be partitioned into "naturally occurring" levels that share similar time and space scales, and each level in the hierarchy
sees the higher levels as constraints and the lower levels as "noise" (Allen
and Starr 1982; O'Neill et al. 1986). Step-by-step instructions for creating
submodels in STELLA are provided in the STELLA help guide.
9.2.1. Plant-Growth Sector
The plant-growth sector (Figure 9.4) represents the resulting growth of the
shoo ts, roots and rhizomes, and reproductive parts , and contains "global inputs " such as temperature and photoperiod. Shoot growth is represented as
the total mass of shoots in the community On units of grams). The shoot