Postdoctoral Project 2

The results highlighted recent important changes in forest productivity, which were investigated through ecological indicators of vegetation density (Normalized Difference Vegetation Index – NDVI) (1), above-ground live biomass (AGB) (2) and net primary productivity (NPP) (3). In terms of vegetation density (1), the results showed general greening (increasing NDVI) trends of forests nationally (65% of all NDVI changes), which were dominated by widespread positive NDVI trends in the Carpathians region. This general ecological dynamic suggests a possible enhancement in vegetation productivity in the country’s high-altitude areas. Contrasting browning (decreasing NDVI) trends were found for 35% of Romanian forestlands marked by NDVI changes, especially in the Extra-Carpathians (lowland) region, which indicates that in these cases forests were probably degraded or devitalized. However, the statistical significance of both greening and browning trends is limited across the country, which means that NDVI dynamics should be interpreted with caution.

Regarding biomass (2), a quantitative measure of forest productivity (t/ha/yr), findings revealed increasing (positive) and decreasing (negative) AGB trends that account for ~70% and 30%, respectively, of the countrywide AGB changes. However, it was found that about half (~48%) of all positive AGB trends are statistically significant, while negative AGB trends have a statistical confidence on only one-fifth (~21%) of their spatial footprint in Romania. Regionally, the AGB change pattern is not marked by obvious contrasting trends between Carpathian and Extra-Carpathian regions.

In terms of forest NPP (3), exploring the changes of this quantitative ecological indicator (t C/ha/yr) showed, surprisingly, almost exclusively increasing trends (99.6%) at the national level, statistically significant on a large scale across the country (~73% of all countrywide positive trends). These NPP changes reflect an intensification of carbon fluxes between countrywide forests and the atmosphere, and an increase in carbon storage capacity of Romanian forests, after 1987.

The analysis of the climate impact on forest vegetation state, performed through eco-climatic statistical correlations, revealed that recent warming is one of the driving forces of the general increases in forest productivity, probably due to lengthening of the vegetation growing season and to the increase in phenological (photosynthetic) activity. However, a generally moderate intensity of eco-climatic relationships was detected in Romania, which indicates an additional role of other non-climatic environmental factors (in the forest ecological dynamics) that were not explored in this research, but which could open new research directions in future ecological studies.

All these results of the project may be useful to various forestry stakeholders and policymakers operating regionally or centrally in Romania. For example, the various data resulting from this extensive countrywide research may be of interest, at regional level, to County Forestry Directorates, which work towards the sustainable management (protection, conservation, development, capitalization and rational use) of countrywide forests. At central level, the results can be a valuable informational support for current and future government strategies aimed at protecting and developing the national forest sector or at adapting forest ecosystems to the effects of current and future climate change.