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This is basic to resource management as well as to impact assessment. Airborne 
and satellite remote sensing may help to identify, classify and describe the 
building blocks of our environment. Ecosystems can be defined as any area of 
nature that includes living organisms and non-living substances to produce an 
exchange of materials between living and non-living parts (Odum, 1961). The 
non-living parts of an ecosystem are collectively known as ’physiography’, 
consisting of both landform and climate. Plants, animal and human communities 
comprise the living portions of the ecosystems (Hills, 1970). Because of the 
relative stability landform features are frequently used to classify ecosystems. 
During the last decade only have there been attempts in Canada to 
survey and provide resource data in a multidisciplinary and integrated fashion— 
the Canada Land Inventory System and the Bio-physical Land Classification System 
(Lacate et al, 1970) are examples of this. However, in addition to these integrated 
surveys, single disciplinary resource monitoring will still be required. For 
adequate monitoring of environmental phenomena at least monthly or seasonal surveys 
are needed over large areas. In Canada very few regularly repeated airborne surveys 
have been carried out and ERTS-1 imagery is the only source of information which 
has been gathered with reasonable frequency (18-day interval) and resolution (about 
80 meters on the ground). ERTS covers all areas; data is provided rapidly for areas 
that are of immediate interest and a file of information is built up for areas which 
may be of future concern. Many of the following discussions are therefore related 
to ERTS-1 applications which are usually combined with selected airborne surveys. 
The bio-physical land classification system is an ecological survey which 
uses the relatively stable landforms as a basis for ecosystem mapping. Such a 
survey provides information related to the ecological limitations and is a prere 
quisite to integrated resource management (Jurdant et al, 1974). Four different 
levels are identified in the system: land region, land district, land system and 
land type. ERTS remote sensing can contribute to the mapping, description and 
monitoring of these units as it builds up a file of information on environmental 
dynamics covering large areas on the earth’s surface; the data may include snow 
cover, snow melt, freezing and thawing of lakes, phenology of vegetation, etc. 
Such information, collected over a period of time, may assist in the delineation 
of areas with ecologically significant uniform climate. For example, the melting 
of snow and lake ice (Fig. 1) correlates strongly with land region (ecoregion) 
boundaries which were obtained after extensive field work. These climatically 
defined larger units (mapping scale usually 1 : 1 , 000,000 or smaller) can be 
broken down into the next level (land district; scale of mapping 1:500,000 to 
1:1,000,000) on ERTS imagery. While satellite imagery can help in the mapping 
of land systems, the description of land systems will have to be based on a 
description of land types (ecosystems). For the analysis and description of 
these building blocks airphoto interpretation is essential and cannot be replaced 
at the present time. In areas where relatively simple relationships exist 
between vegetation and soils and where little disturbances have occurred, such as 
by fire, satellite mapping of land systems may become effective. Such areas 
include Arctic and sub-Arctic environments, as well as large wetlands. In the 
more complex areas, such as the Boreal zone of the Precambrian Shield, most 
mapping and monitoring will have to be carried out on airborne imagery (Thie et al, 
1974).