POSSIBLE SPATIAL INDICATORS FOR ENVIRONMENTAL POLICIES ASSESSMENT IN NATURAL PROTECTED AREAS :
TESTING ON A WETLAND TERRITORY : THE CAMARGUE NATIONAL RESERVE

Olivier LEONARD,

Nice Sophia-Antipolis University - UMR. 6012 ESPACE (FR)

Context
Indirect pressures due to urban growth, agricultural practices, population's attempts in terms of good quality landscape and tourism areas, direct pressures (water quality degradation, pedestrian frequentation impacts... ),necessity of a biodiversity conservation... natural areas become real management objects. It's obvious in coastal zone : strong anthropic pressures, need of free areas, use conflicts, particular ecological processes...

Within the natural protected areas like Réserve Nationale de Camargue, it seems very necessary to measure the efficacity of nature conservation and environnmental policies with ecological observation and landscape assessment.

This need seems clear about the ecological objects of "Habitats, Fauna and Flora" Directives . Within the Natura2000 network construction, stakeholders and managers of the natural protected areas which contain Natura2000 sites, have to follow up their territory and to assess if its evolution is good or bad regarding European prerogatives). In this context, the research project EON2000+ :

• Take into account the practices of the managers in terms of habitat monitoring and their needs in terms of methods and data,
• Estimate the interest of earth observation data and geographic information for these subjects,
• Conceive and test environmental, socio-economic and spatial indicators for habitats observation and assessment.

The research works leaded with Montpellier's CEMAGREF Centre (France), have consisted in conceiving and testing spatial indicators, potentially adjusting to follow up a particular wetland sub-aquatic habitat in Camargue (France). The 14 indicators have been defined with a part of the technical staff of Camargue National Reserve, and are based on spatial analysis and images analysis.

The test site

• Camargue is one of the largest area of wetlands in Europe, in which numerous fragile ecosystems interpenetrate. This exceptional biological richness is produced by water and salt inputs on an "amphibious" soil where many species live.
• Camargue National Reserve was the first reserve recognised by the European Council in 1966,
• full protection, so it's a particular test site regarding real diversity of Natura2000 network,
• Briny marine areas and fresh water areas, presenting an international interest as regards the vegetal formations and the habitats which are essential for migratory birds protection.
• Main ecosystems : salt marshs, lagoons, dunes, " sansouires "
• Arles, Nîmes, Marseille : urban areas near to (15-30 kms)

Camargue's natural protected areas (Station Biologique Tour du Valat)

The test habitat
A specific wetland sub-aquatic habitat was chosen by managers : "Herbarium with Zosteres", in Vaccarès Pond. It is a priority habitat regarding to HFFD (code 21), wide and threatened… but just appeared in 1950's ! Here is a part of the nature conservation dilemma !
Partial view of the habitat :

Research aims and methodological proposition
The qualities of a good indicator are well known : a parameter relating to a phenomenon, an elaborated information, with a process of construction, a sense which is synthetic, a helping power to communicate or to take decision.
However, there is a wide diversity of experimentations and much types of indicators exist. Concerning "spatial" indicators and the use of geographic space within the indicator's building processes, it seems that space usually provide indicators with a support for cartographic representation, thematic analysis or segmentation regarding to a parameter.
For example :
- Spectral measures and classifications with earth observation data,
- Land cover statistics,
- Spatial asks and space segmentation with GIS

We could consider that "classic" indicators are "territorial" or "geographical" indicators, because they refer to a surface, provinces or landscape components. But space as geometric, topologic reality is not packaged within this type of indicator. Our proposition was to consider space as a potential component for natural areas monitoring.

It supposes to treat space as the object, the target of the indicator's building process :

• describe and characterize some geometric or topologic aspects as fragmentation, patch's sizes, orientation, lengthening, partition…
• consider that these spatial characteristics and their variation according to the time, correspond to a spatial variation and that this spatial variation is due to a internal or external process which potentially change the state of conservation of the habitat. So, we have to consider spatial processes as fusion, division, distortion…

A great number of indicators is possible and also, many spatial indicators could be conceived. So, it was absolutely necessary to lead an interactive work with managers and technicians of the territory.
Spatial variations : potential marks for the change of the state of conservation of the habitat ?
Structuring questions have been asked and a progressive way was followed to form indicators :

This simple sequence has permitted to identify which are the stakes relating to sub-aquatic vegetation conservation, which are the potential factors of change for this habitat and how it could appear in terms of spatial variation. Finally, 14 spatial indicators have seemed pertinent... and available in terms of data !

Realisation : working images
In order to create work images about two dates (1992 and 1998), aerial pictures taken in 1992 (IGN), were scanned and rectified with ER Mapper tools for ArcView. For 1998, very high resolution numeric aerial picture (IGN BD-Ortho). We have become difficulties with these data in terms of quality (eddies, missing habitat or not present for both dates). So, three test zones were chosen in order to test proposed indicators.

The habitat was mapped by photo-interpretation on the three zones, for 1992 and 1998. When it was impossible to mapped the habitat in the same place and for the two dates, some fictive images were created with the help of 1992 data. This point seemed not to be a real problem too, because it was realized with a pedagogic and demonstrative intention.

Realisation : spatial indicators
It was necessary to use a method which allows us to identify and describe targeted spatial variations, with a "spatial analysis" approach and images analysis functionalities. For these reasons, we have chosen mathematic morphology method. It was funded in 1965 by J.SERRA et G.MATHERON, for mining and medical applications. Then, it has expanded within of CMM (ENSMP ).
According to a simple approach, we can say that this method allows :

• To describe forms and "make them speak",
• To describe shapes or images, which have a spatial variation or a deployment in space, with a qualitative or a quantitative approach,
• To analyse general morphologic properties or structural organisation.

An example of application
It's possible to explain the possible interest of this method with a simple example : the roughness of the out-line of a little or wide spot of sub-aquatic vegetation - or "roughness of the out-line". It seems to the managers that the indented, slick or out-lined appearance of the sub-aquatic herbarium, could be an important information concerning the state of health of the herbarium, even if it's difficult to say if an indented aspect is better than a slick one. So, describe the external aspect of the herbarium could represent a following up hypothesis about the state of conservation of the targeted habitat and "roughness of the out-line" could be one of the potential indicators for this job. If it's an important information for managers, how can we describe this information and translate it ? It looks difficult with a vector GIS approach (only with AML, scripts…). However, mathematical morphology gives some simple tools based on images transformations.

The opening is a morphological transformation based on erosion-dilatation sequences. This operation induces a simplification of the out-line. The more the opening size is great, the more the little shapes disappear. It is the reason why it allows the description of the roughness of a spot :

 

How does it work (Micromorph® software ) ?

In order to be more explicit, the variation of the surface of the spot is reported on a graphic after each opening operation. So, the graphic shows with a synthetic way a complex spatial information :

The first opening sizes contain the most interesting information about out-line morphological characteristics. The operation is leaded until the whole of the spot disappear (110 opening size here), that is to say the main and global shape. One type of morphologic transformation can be a way to process several spatial indicators.
For example, opening transformations have been also used for a"granulometry" indicator, but with a different target and with another working image.

What about GIS and geomatics ? A tools's chain
One of the important aims of the EON2000+ project, is the experimentation of an observation and following-up information system for natural areas. Within this work, many geomatic tools and methods have been used : vector data, earth observation data, images analysis, photo-interpretation... If you conceive GIS not only like software and hardware tools, but also like human and work organization, the information system within the territorial structure which is responsible of a natural area (for example Reserve Nationale de Camargue), could be organised with such an observation and assessment aim.

So, a geographic datas chain and a tools's chain must be defined, where mathematic morphology and images analysis could be very pertinent tools and investigation ways... if it is called by thematic hypothesis and expert knowledge about targeted natural area !