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R.A. Diaz-Varela et al. 2010. Quantitative assessment of temporal dynamics in altitudinal-driven ecotones
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seven morphological spatial pattern classes: edge, core, perforated, islets, bridge, loop and
branch. We ran the software using the default parameters for the computation of MSPA,
considering an edge width of 20 m.
3. Results
For the period analysed, tundra remained mostly stable while forest and scattered tree classes
experienced more intense dynamics, as indicated by kappa values of Table 1. From the
contingency matrix shown in this table, we observed that tundra also experienced some
expansion colonising rocky areas and bare soils while in other areas it was colonised by
scattered trees. The increase of dense forest occurred at the expenses of areas occupied by
scattered trees in 1954.
The totals and altitudinal distribution of the outpost is shown in Fig. 3. The forest line was
located between 1350 and 1950 m, rarely reaching more than 2000 m. The tree line showed a
slightly elevated position (around 100-150 m higher) on the slopes, while the tundra line lay
clearly much higher, with maxima up to 2600 m.
Figure 4 shows the altitude distribution, along with the horizontal and vertical increments of
outpost altitudinal shifts, distinguishing positive (advance) and negative (retreats) altitude
increments. A total of 225, 352 and 645 paths showing positive altitudinal shifts were recorded
for forest line, tree line and tundra line respectively, with median values of 26, 17 and 15 m of
decadal altitude increment respectively. Retreats were far less common than advances for the
three ecotones under analysis. Putting together advances and retreats gives an overall view of
the altitudinal shifts: the forest, tree and tundra lines showed a net advance, with medians of 25,
13 and 11 m of altitude shifts respectively. Altitude plays a major role in the occurrence and
magnitude of the shifts. Advances of forest line took place mainly from 1300 to 1700 m. The
altitude advance magnitude shows a clear trend to decrease with the rise in altitude. Thus, shifts
that started from lower positions attained the most important advances, up to 600 m, while those
starting near the top of the altitudinal limit for the class reached much lower values (e.g. less
than 20 m on average in the interval 1900-2000). This tendency is less clear in the case of tree
line, which showed more regular behaviour along its altitudinal range and altitudinal shifts
which were generally lower than 200-300 m. The tundra line advance also shows the same trend
to decrease its magnitude proportional to the altitude gradient, starting from large shifts (400-
800 m) occurring at the lower locations (1600-1900 m) to small ones (less than 50 m) near its
altitudinal limit (2700-2800 m). Retreat paths showed less clear patterns in terms of variation of
magnitude along the altitudinal gradient.
Similarly to land cover dynamics, the spatial pattern of tundra experienced little variation (cf.
Fig. 5, being characterised by a high amount of core and little proportion of edge and other
morphological classes, though there is some increase of branches and islets reflecting the
expansion and colonisation of new areas. Scattered trees and forest classes experienced an
increase in core and decrease in edge and branches, as a result of their expansion they became
more compact.
4. Discussion
The application of the method on multi-date land cover datasets (1954 and 2003) in a study
area of the Southern Alps, allowed the monitoring of spatiotemporal dynamics of forest,
woodland and tundra formations and pointed out significant upward shifts of their ecotones,
formalised as forest, tree and tundra lines.
Forest Landscapes and Global Change-New Frontiers in Management, Conservation and Restoration. Proceedings of the IUFRO Landscape Ecology
Working Group International Conference, September 21-27, 2010, Bragança, Portugal. J.C. Azevedo, M. Feliciano, J. Castro & M.A. Pinto (eds.)
2010, Instituto Politécnico de Bragança, Bragança, Portugal.