Many ecological processes of interest in global change studies, such as productivity, biogeochemical cycling, and water and energy exchange, operate at a number of scales. To date, many global models on ecosystem processes are based on direct extrapolations of process understanding at the point scale and ignore landscape scale phenomena. This joint task deals with the effects of the mechanisms of changes in landscape patterns on ecosystem functioning, and how these effects are expressed in the larger scale (landscape and higher) functioning. This linkage is essential to improve our understanding of, and ability to predict the impacts of global change.

Making a model or data base spatially interactive for upscaling requires more than giving spatial coordinates to the landscape elements: the inclusion of processes which couple different parts of the landscape or that act at the scale above the individual elements is critical. Examples of such processes include cross-scale disturbances (e.g. fire, grazing, pests) and species migration. Critical questions to be addressed in this Task are:

When can indicators of ecosystem functioning be simply aggregated as an area-weighted sum of local values, and when, on the contrary, do distribution and patchiness of landscape elements affect these summations?

For a given landscape what are the dominant mechanisms causing such non-linearity, and how do they change over time?

The work will rest on two hypotheses: First, for any landscape, there are a small number of critical (keystone) cross-scale processes that cause departures from the linear aggregation model. Second, these processes have characteristic time and spatial scales that are embodied in the spatial and temporal attributes of the landscape components.

The questions can be addressed with a series of analyses of increasing ecological complexity. At the first level, simple aggregation, values for a process over a landscape are calculated as the average by area of patch values. Predictions using this linear model will be compared with the next level of analysis, in which the size distribution of patches is considered in addition to the abundances. At this level, ecosystem processes causing patch size distribution effects will need to be considered. At the third level, the analysis will consider such scale attributes as patch size and age distributions, as well as the spatial organization of landscape elements (e.g. adjacency, interspersion, and connectivity). Temporal components may also have to be added to account for hysteresis at the landscape scale. For example, the neighborhoodÕs disturbance history as well as the changes in present environment may determine the present ecosystem trajectory through time. The goal of this step-wise approach is to understand and classify the conditions under which assessments at each of those levels will suffice to explain and predict landscape or regional processes.

Objectives

To determine the effects of mechanisms that cause changes in landscape patterns (complexity) on ecosystem functioning, such as biogeochemical cycling and primary productivity.

To examine the influence of spatially dynamic processes on regional-to-landscape function

To predict how the interactive effects of global change drivers on the relationship between landscape complexity and ecosystem functioning.

To develop heuristic models that examine the interactions of cross-scale processes with patch scale dynamics

Implementation

The implementation of this Task will begin with a review of the considerable existing work on upscaling techniques of ecosystem processes to the landscape and regional scales. This review will identify 1) systems that have already been shown to exhibit non-linearity vs. additivity, 2) circumstances where an area-weighted average is an inadequate technique for aggregation, and 3) the spatially interactive processes that are responsible for non-linearities.

Comparative studies will then be used to relate aspects of landscape complexity to integrated measures of landscape processes. The analyses will require 1) selection of techniques for classification of different landscape patterns, 2) synoptic estimates of ecosystem processes such as net primary productivity, gas emissions, or movement of nutrients, and 3) identification of the landscape key attributes (components and processes) that are responsible for the changes in patterns and function. Metrics including aspects of pattern (e.g., patch size, shape, number, location) and functioning (e.g., source/sink relationships) will be developed. These metrics will be combined with process measurements, carried out along IGBP transects and at intensive test sites, to determine which and how many metrics are needed to best predict aggregated process values at the landscape or regional scale. This Task will make use of a highly interactive, ongoing electronic workshop, in which data, mathematical and simulation modules are exchanged to stimulate discussion and debate.

Improved estimations of the effects of global change on ecosystem functioning at the landscape scale will then be obtained by driving models of ecosystem functioning with projections of changes in land-use, disturbances, and migration. Such linked models should also examine how past land-use and disturbance legacies affect current ecosystem processes and future trajectories of land cover change. Predicted changes in pattern and function will be used to estimate the regional contribution to various indicators of global functioning such as BGC feedbacks through changes in NPP and NEP. A focus of the analysis will be to detect dynamic responses such as time lags, threshold effects, or the amplification of responses.

Concurrent to the development of this main approach, a modelling sub-group will be convened to examine the interactions of cross-scale processes with patch scale dynamics, using a set of generic landscape models. These models will incorporate the plant functional type responses from task 2.2.1, disturbance models from task 2.2.2, and dispersal and migration rules from task 2.2.3. The short-term aim of this activity is to analyze systematically the interactions between landscape and patch scale processes. The longer term aim will be to develop a set of generic landscape response modules for use in regional assessments and DGVMs.

Milestones

1998: Electronic workshop for review of metrics of landscape complexity and processes that introduce non-linearities at the larger scale. Collate data bases from case studies and GCTE transect data sets.

1999: Workshop to refine the implementation plan, establish the design of modeling studies, standardize the methodology of analyses, and identify the initial networks of research groups and projects.

1999: Develop models and implement with data from transects and test sites

August 1999: workshop (IALE international conference, Snowmass USA, 29/7 - 3/8)

2000 (venue to be determined): Activity workshop: Synthesis of landscape functioning and generic landscape models.