Functional diversity along disturbance and environmental gradients in Ethiopian moist Afromontane forest

Abstract

Considering multiple measures to fully capture functional diversity is important. However, the effects of disturbance gradients on diversity have been controversial, as species diversity alone may not fully capture these effects. This study aimed to evaluate trait-based diversity across disturbance gradients in the moist Afromontane forest of Ethiopia, Yayu Coffee Forest Biosphere Reserve (YCFBR). Vegetation data and relevant traits related to plant-life strategies, competition, and responses to disturbances were collected. A multiple regression model was used to test the response of functional diversity to disturbances and environmental gradients. The results revealed functional diversity in plant communities, including dendrogram-based functional diversity for plot-based (FDp), functional richness (FRic), functional evenness (FEve), functional divergence (FDiv), functional dispersions (FDis), and community-weighted mean of maximum tree height (CWM.Hmax), showed decreasing patterns with increasing disturbance intensity in the YCFBR. Additionally, the findings highlighted that FDis and Hmax are the most vulnerable functional traits to anthropogenic factors and are less tolerant in disturbed ecosystem environments. Therefore, reducing disturbances is crucial to maintaining higher levels of these functional diversities. For example, the results showed that the CWM.Hmax declined from 27.25 m to 15 m, indicating a shift towards shorter plant species. In contrast, the community-weighted mean of woody density (CWM.WD), the community-weighted mean of specific leaf area (CWM.SLA), and the community-weighted mean of seed mass (CWM.SM) increased significantly with an increase in disturbance intensity. For instance, CWM.SM and CWM.SLA changed from 5 to 14.25 (g) and 90 to 130 (cm2/g), respectively. These indices may serve as indicators of ecosystem resilience at disturbed forest ecosystem sites. Furthermore, the regression results indicated that FDp, FRic, FEve, FDiv, FDis, CWM.WD, and CWM.Hmax showed increasing patterns with increasing species richness, which suggests that protecting and promoting species diversity can contribute to maintaining high levels of functional diversity. The mixed effects model revealed that anthropogenic disturbance and elevational gradients had significant effects on functional diversity in the YCFBR. Therefore, when managing and conserving biodiversity in heterogeneous environments, both anthropogenic factors and environmental variables need to be considered. Species with low SLA and SM are recommended for the restoration of disturbed ecosystems. Overall, this study demonstrates that trait-based functional diversity is useful for predicting the adaptation potentials of species in heterogeneous environments and disturbance gradients.