**3.0 CONCEPTUAL ECOLOGICAL MODELS**  (Scott and Eckert)

A c onceptual ecological model i s presented in Figure 1 to summarize how natural and human drivers interact with key structural an d functional elements of ecos ystems that span the US/Mexico border

- region

. This model focuses on natural resource assets of concern to resource managers and the public , as well as how illegal border activities, border security infrastructure and enforcement interact with natural disturbance processes to influence border ecos yst ems. The model further links select ecos ys tem structural and functional attributes to specific phys ical and biological metrics, which can be used to monitor change in resource condition over time.

An e cosystem is a spatially defined unit of the Earth that includes all organisms, along with all components of the phy sical environment within its boundaries (Christensen et al. 1996). Ecosystem structure includes the types, amounts, and spatial arrangement of phy sical and biological elements of an ecosy stem

. Ecosystem functioning refers to flows of energy and materials through biological and phy sical components of an ecos ys tem. Functional processes include stream flow and related channel change processes, hillslope runoff and erosion, nutrient cycling, and the production, retention and decompo sition of organic material (Díaz and Cabido 2001). A complete list of ecos ys tem structural and functional elements is provided in Appendix 1. A driver is any natural or human

- induced factor that directl y or indirectl y causes a change in an ecos ys tem (Carpenter et al. 2006). Important phy sical and biological drivers include climate change , extreme weather events , land conversion, diseases and invasive species. Ecos ys tems and resource conditions are not static. They c hange within a natural range of variation , while maintaining structural and functional integrity , in response to natural drivers like climate variability . This natural range of variation is represented in Figure 1 by the shifting edges and dashed arrows a ssociated with ecos ys tem elements as well as resource condition metrics. Any long

- term ecological resource monitoring effort must be done with an understanding of the natural range of variation in an ecos ys tem.
Figure 2 depicts the conceptual ecological model in the context of project design and implementation. M onitoring design draws upon key ecos ys tems and ecos ystem elements to identify

study areas and define study design. Specific m onitoring protocols developed and refined in the context of monitorin g design for the measurement of specific resource metrics . Monitoring implementation produces quantitative data on resource condition. These data will need to be managed and archived so that they can be anal yzed and used to report on the direction and ma gnitude of change in resource condition over time. The project design process is consistent with an adaptive management framework whereby monitoring is used to evaluate and refine the effectiveness of management actions on resource condition.Figure 1. A c onceptual ecological model representing US/Mexico border ecosystems and related physical and biological metrics

(orange ellipse) , which could be used to monitor change in resource condition over time . Ecosystem structur al and functional elements (green ellipse ) interact dynamically with natural and human drivers (blue ellipses) of ecosystem change. Ecosystem elements and condition metrics vary over time in response to natural drivers (dashed arrows). REGIONAL CLIMATE & NA TURAL DISTURBANCES DIRECT BORDER FENCE EFFECTS RECREATION & UNDOCUMENTED ALIENS BORDER SECRUITY

I NFRASTRUCTURE ENFORCEMENT ACTIVITIES LIVESTOCK GRAZING WI LDLAND FIRE INVASIVE SPECIES (e.g., Pre cipitation, te mp erature
, drought & storms) **NA TURAL**  **DRIVERS HUMAN**  **DRIVERS**

**ECOSYSTE M**  **STRUCTURAL**

**AND FUNCTIONAL**  **ELEMENTS**

**RESOURCE CO**  **NDITION METRICS**  CATCHMENT CHARACTERISTICS

HYDROLOGIC GEOMORPHIC BIOGEOCHEMICAL HABITAT STRUCTURE, ARRANGEMENT & CONNECTIVITY

VEGETATION CHARACTERISTICS POPULATION DYNAMICS SPECIES OF CONCERN CULTURAL

CHANGE IN HILLSLOPE RUNOFF AND EROSION CHANGE IN EROSION OF CHANNEL BED AND BANKS

CHANNEL AGGRADATION CHANGE IN FLOODING CHANGE IN W ILDLAND FIRES CHANGE IN DIVERSITY OF NATIVE SPECIES CHANGE IN COVER OF NATIVE VEGETATION CHANGE IN COVER OF NON

- NATIVE VEGETATIONFigure 2. The relationship of monitoring design, implementation, and data management, analysis and reporting to border

ecosystems and selected resource condition metrics.

**RESOURCE CONDITION**  **METRICS HUMAN**  **DRIVERS NA**  **TURAL DRIVERS** 

**ECOSYSTEM ST** 

**RUCTURAL AND FUNCTIONAL**  **ELEMENTS MONITORING**  **DESIGN**

EXPERIMENTAL DESIGN STUDY AREAS

**MONITORING PROT** 

**OCOLS**

**DA TA**  **A NAL**  **YS IS AND**  **REPORTING DA**  **TA M**  **ANA GEMENT**  **AND ARCHIVING**

ASSESSMENTS OF RESOURCE CONDITION MEASUREMENT OF RESOURCE

METRICS