Abstract
Background and aims – There is increasing recognition that plant traits mediate environmental influenceon species distribution, justifying non-random community assembly. We studied the influence of local scale edaphic factors on the distribution of functional traits in a tropical rainforest of Cameroon with the aim to find correlations between the main edaphic gradient and community functional trait metrics (weighted mean trait, functional divergence and intraspecific variation). Methods – Within the Korup Forest Dynamics Plot (50 ha), we randomly selected 44 quadrats of 0.04 ha each, collected soils and analysed 11 topography and soil variables. Leaves were harvested from all 98 tree species found in the quadrats to calculate community trait metrics [quadrat-level weighted mean (qk) and functional divergence (FDivk)] for leaf area (LA), specific leaf area (SLA), leaf phosphorus (LPC), leaf nitrogen concentration (LNC) and nitrogen to phosphorus ratio (N:P ratio). We examined relationships between the main edaphic gradient with qk, with FDivk and with intraspecific variation and interpreted correlations as the effects of abiotic filtering and competitive interaction. Key results – Soil fertility was the main edaphic gradient and was significantly correlated with qk for LPC, LNC and LA and with FDivk for LPC, N:P ratio, LA and SLA, confirming the influence of abiotic filtering and competitive interaction by the soil fertility gradient, respectively. For a given trait, quadrats were either over-dispersed or under-dispersed, accounting for 7–33 % of non-random trait distribution along the soil fertility gradient. Trends in intraspecific traits variation were consistently lower than quadrat-level mean traits along the soil fertility gradient. Conclusions – This study demonstrates the influence of soil fertility gradient on local scale community trait distribution and its contribution to non-random community assembly.
Highlights
Understanding the distribution of plant species and structural types along gradients at different spatial scales is a major goal in community ecology (HilleRisLambers et al 2012)
The slopes of intraspecific trait variation ranged from -8.33 to 3.94 but these variations changed between the traits and were either in the same direction or in the opposite directions relative to the quadrat-level mean trait
When the quadrat-level mean trait values were substituted by Dim. 1 (i.e. principal component analysis (PCA) scores related to quadrats), the results obtained for intraspecific trait variation were similar to the one above
Summary
Understanding the distribution of plant species and structural types along gradients at different spatial scales is a major goal in community ecology (HilleRisLambers et al 2012). Functional traits have shown to mediate species response to environmental gradients, shift plant strategies within and among communities, and inform on community assembly processes (Keddy 1992, Díaz & Cabido 1997, Lavorel & Garnier 2002, Westoby et al 2002, McGill et al 2006). Functional traits can inform on intraspecific variation, species coexistence and prevailing environmental conditions. (Cornwell & Ackerly 2009). This knowledge about traits has led to the identification of different trait-response strategies for leaf (Wright et al 2004), wood (Chave et al 2009) and whole plant (Reich 2014, Díaz et al 2015)
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