Climate forcing of tree growth in dry Afromontane forest fragments of Northern Ethiopia: evidence from multi-species responses

Zenebe Girmay Siyum,Motuma Tolera Feyissa,J O Ayoade,M A Onilude

doi:10.1186/s40663-019-0178-y

Zenebe Girmay Siyum, Motuma Tolera Feyissa + Show 2 more

Open Access

https://doi.org/10.1186/s40663-019-0178-y

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Abstract

BackgroundClimate-induced challenge remains a growing concern in the dry tropics, threatening carbon sink potential of tropical dry forests. Hence, understanding their responses to the changing climate is of high priority to facilitate sustainable management of the remnant dry forests. In this study, we examined the long-term climate-growth relations of main tree species in the remnant dry Afromontane forests in northern Ethiopia. The aim of this study was to assess the dendrochronological potential of selected dry Afromontane tree species and to study the influence of climatic variables (temperature and rainfall) on radial growth. It was hypothesized that there are potential tree species with discernible annual growth rings owing to the uni-modality of rainfall in the region. Ring width measurements were based on increment core samples and stem discs collected from a total of 106 trees belonging to three tree species (Juniperus procera, Olea europaea subsp. cuspidate and Podocarpus falcatus). The collected samples were prepared, crossdated, and analyzed using standard dendrochronological methods. The formation of annual growth rings of the study species was verified based on successful crossdatability and by correlating tree-ring widths with rainfall.ResultsThe results showed that all the sampled tree species form distinct growth boundaries though differences in the distinctiveness were observed among the species. Positive and significant correlations were found between the tree-ring widths and rainfall, implying that rainfall plays a vital role in determining tree growth in the region. The study confirmed the formation of annual growth rings through successful crossdating, thus highlighted the potential applicability of dendroclimatic studies in the region.ConclusionsOverall, the results proved the strong linkage between tree-ring chronologies and climate variability in the study region, which further strengthens the potential of dendrochronological studies developing in Ethiopia, and also has great implications for further paleo-climatic reconstructions and in the restoration of degraded lands. Further knowledge on the growth characteristics of tree species from the region is required to improve the network of tree-ring data and quality of the chronology so as to successfully reconstruct historic environmental changes.

Highlights

Climate-induced challenge remains a growing concern in the dry tropics, threatening carbon sink potential of tropical dry forests
P. falcatus formed distinct ring boundaries, which are characterized by narrow bands of tracheids with slightly thickened cell walls towards the latewood
Variations in tree-ring widths were observed within tree species and among tree species

Summary

Introduction

Climate-induced challenge remains a growing concern in the dry tropics, threatening carbon sink potential of tropical dry forests. Most studies undertaken on tropical forest dynamics paid much attention to inventories from permanent plots and plant physiological experiments (Lewis et al 2009) Even though such monitoring plots provided much of the evidence for understanding tropical forest dynamics, they have shortfalls in that they accounted only for short time horizons and limited areas (Lewis et al 2009; Zhou et al 2013). This hindered understanding of the long-term responses and feedback of tropical forests to global changes (including climate change)

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