Ecosystem Thermal Buffer Capacity as an Indicator of the Restoration Status of Protected Areas in the Northern Ethiopian Highlands

摘要

Restoration status of forest rehabilitation areas can be assessed by comparing their ecosystem characteristics with those of a reference system, most often what is considered the natural climax vegetation. However, comprehensive measurements needed for a traditional vegetation description are often hard or impractical in complex (sub)tropical ecosystems. Therefore, an alternative approach is the identification of simple indicators of ecosystem integrity. The use of such indicators can speed up the availability of resource inventories and thus contribute to the accelerated implementation of successful rehabilitation practices. Thermal buffer capacity (TBC) of ecosystems has been previously proposed as an overall indicator of ecosystem integrity. In this article, sequential surface-temperature measurements are proposed as a method for TBC assessment of different land-use types. Surface temperatures of seven land units in central Tigray (northern Ethiopia), each with a uniform land-use type (degraded and bushy grazing land, enriched and non-enriched rehabilitation area, and forest), were measured with a hand-held infrared thermometer in the rainy and the dry season. Surface-temperature models were derived by means of quadratic regression. Cross-correlation functions were calculated for all possible pairs of land-unit tune- series data. Instantaneous heat-up rates, average TBC, and accumulated heat load were calculated. Repeated-measures analysis of variance was used to test the effect of aspect and protection status on TBC. Kruskal-Wallis one-way analysis of variance by ranks for small samples was used to test the significance of differences in heat-up rates and heat load among land-use groups. Time lags between land-unit surface temperatures are caused by differences in aspect rather than land-use type. Protection status and aspect have a significant effect on the average TBC. Results clearly demonstrate a differentiation between protected (low heat-up rate) and non-protected areas (high heat-up rate). Overall ranking suggests that the remnant forest has the highest TBC of all surveyed land-use types, followed by-the enriched protected area. Results of this study show that TBC quickly responds to area closure and can therefore be used to monitor the development of protected areas. It is strongly recommended that a detailed monitoring strategy for protected areas on the basis of this technology be devised, validated, and finally transferred to the local communities.