Abstract:
Climate change and forest degradation are major threats to forest ecosystems. The climatic changes can affect the mineralization rate in soils and therefore change the amount of available nitrogen components for plants. Thus these changes can influence foliar C/N-ratio. Previous studies used an elevation gradient to test the influence of climatic changes on ecosystems, and showed that foliar C/N-ratio is positively correlated with elevation. Changes in foliar C/N-ratio may affect the feeding behavior of insect herbivores and therefore influence leaf area loss (LAL). LAL is used as an indicator of herbivory and therefore may consequently also be related to ant abundance because ants prey on insect herbivores. Ants in return, are also affected by the abiotic
changes with increasing elevation and therefore sensitive to climate change. However, forest degradation is
currently the greater threat to ecosystems.
Degradation can lead to changes in the nutrient uptake of plants and therefore to changes in foliar C/N-ratio. Moreover it can reduce ant
abundance as ants are sensitive to the conversion of forests. We nalyzed the causal effects of abiotic factors (elevation and degradation) on biotic factors (foliar C/N-ratio and ant activityabundance) and the relationships between the biotic factors and LAL with linear mixed-effect models in a path model. We found a significant positive correlation between foliar C/N-ratio and
elevation, and a significant negative correlation between ant activity-abundance and elevation. Foliar carbon-content had a significant negative correlation with degradation. Our results revealed no
significant relationships with LAL, but LAL correlated
negatively with foliar C/N-ratio in the shrub layer. The results of our study point out that foliar C/N-ratio and ant activityabundance
change with elevation and thus respond to climatic changes. Moreover
our results indicate that foliar C/N-ratio can be connected to LAL, but that influences such as the abundance and distribution of insect herbivores along elevation should be examined closely. Our finding that
foliar C/N-ratio, ant activity-abundance and LAL were unaffected by degradation indicates that the studied degraded forests are still suitable habitats for insect herbivores and ants.
