A problem with this scheme is that the categories are not mutually exclusive. Colwell et al.
(1980) suggested a more hierarchical framework (Table 1). Although this classification is mutually
exclusive and totally exhaustive, it falls short by not providing a link between change event and causal
agent. Finnish researchers (Hame, 1986) took a more mechanistic view and grouped the possible sources
of temporal inconsistency in multidate imagery as shown in Table 2. Hobbs (1990) focused more on
ecological aspects and differentiated between seasonal vegetation responses, interannual variability, and
directional change. The latter may be caused by intrinsic vegetation processes (e.g., succession), landuse
conversion, other human-induced changes (e.g., pollution stress), and alterations in global climate
patterns (e.g., global warming).