Abstract:
In land change science studies, a cover type is defined by land surface attributes, specifically including the types of vegetation, topography and human structures, which
makes it difficult to characterize land cover as discrete classes. One of the challenges in characterizing a land-cover type is to distinguish variability within the class from
actual land-cover transformation. The spread of plant invasions in tropical systems is affected by seasonal variations and disturbances such as agricultural activities and
fires, making it difficult to determine the spread through thematic classifications. In this paper, we estimate the changes in spatial extent and seasonal variation of
bracken fern invasion in Southern Yucata´n from 1989 to 2005 by using a linear mixture model (LMM), a widely used method in the classification of remotely sensed
data. The results show an increase in areas affected by bracken from 40 km2 in 1989 to almost 80 km2 in 2000. Lower estimates of the invasion resulted from data
acquired at the end of the dry season (March–May), when bracken mixes with secondary vegetation or is removed by fires. The accuracy of the maps is estimated
through the use of sketch maps of farmer’s parcels and field data collected from 2000 to 2001. Understanding the spatial distribution and annual variability of bracken
fern cover in the region is critical to determining the relation between disturbances such as fire and forest recovery. Using LMM may enhance this understanding by
giving a more accurate picture of the extent and distribution of bracken fern invasion.
