Topography imposes an abiotic filter on tree growth in restored areas

Topography is a key abiotic factor for plant performance and, despite the well-known effects of topographic features on tree growth and traits in mature and secondary forests, less attention has been paid to early-stage restoration areas. We aimed to test whether and how elevation, slope, and slope aspects affect tree growth rates, and morpho-physiological traits in restoration. In this scenario, we asked which traits correlate with tree growth? How do species adjust their growth and traits to topography? And how does intraspecific variation change with topography? This study was carried out on a hill of ca. 70 m, with a former history of use for pasture. Six tree species were monitored over a one-year sampling interval. Principal component analysis, simple regressions, and ANOVA tests were applied. More growth was observed in the north-facing aspect. Traits related to photoprotection (non-photochemical quenching, and total carotenoids) were the ones that most correlated with growth rates, most notably stem diameter, which suggests that strategies for dealing with photoinhibition are crucial for tree growth in degraded pastures. Four out of six species showed a great differentiation between slope aspects. Physiological traits were more plastic and responsive to topography than was specific leaf area. While significant relationships between species and topographic features were an indication that intraspecific variation is influenced by topography, the direction of changes in intraspecific variation was not common to all species (except for total chlorophyll). The results indicate that species selection processes for restoration in degraded pastures should consider the interaction between functional traits (including pigments, and chlorophyll a fluorescence) and local topography.

Automated summary

Topography plays a crucial role in plant performance, particularly in early-stage restoration areas. This study aims to investigate the effects of elevation, slope, and slope aspects on tree growth rates and morpho-physiological traits. The results show that north-facing slopes promote better tree growth, and traits related to photoprotection are strongly correlated with growth rates. Different tree species have varying responses to topography, and physiological traits are more responsive to topographic changes than specific leaf area. Species selection for restoration should consider the interaction between functional traits and local topography.