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Open AccessArticle

Regeneration in the Understory of Declining Overstory Trees Contributes to Soil Respiration Homeostasis along Succession in a Sub-Mediterranean Beech Forest

1
Forest History, Physiology and Genetics Research Group, School of Forestry Engineering, “Universidad Politécnica de Madrid”, 28040 Madrid, Spain
2
Laboratory of Plant Ecology, Department of Applied Ecology and Environmental Biology, Faculty of Bioscience Engineering, Ghent University, Coupure links 653, B-9000 Ghent, Belgium
3
Plant and Soil Sciences Department, University of Delaware, Newark, DE 19711, USA
4
BC3-Basque Centre for Climate Change, Scientific Campus of the University of the Basque Country, 48940 Leioa, Spain
5
IKERBASQUE-Basque Foundation for Science, María Díaz de Haro 3, 6 solairua, 48013 Bilbao, Spain
*
Author to whom correspondence should be addressed.
Forests 2019, 10(9), 727; https://doi.org/10.3390/f10090727
Received: 12 July 2019 / Revised: 21 August 2019 / Accepted: 22 August 2019 / Published: 24 August 2019
(This article belongs to the Special Issue Dieback on Drought-Prone Forest Ecosystems)
Research Highlights: Tree decline can alter soil carbon cycling, given the close relationship between primary production and the activity of roots and soil microbes. Background and Objectives: We studied how tree decline associated to old age and accelerated by land-use change and increased drought in the last decades, affects soil properties and soil respiration (Rs). Materials and Methods: We measured Rs over two years around centennial European beech (Fagus sylvatica L.) trees representing a gradient of decline in a sub-Mediterranean forest stand, where the number of centennial beech trees has decreased by 54% in the last century. Four replicate plots were established around trees (i) with no apparent crown dieback, (ii) less than 40% crown dieback, (iii) more than 50% crown dieback, and (iv) dead. Results: Temporal variations in Rs were controlled by soil temperature (Ts) and soil water content (SWC). The increase in Rs with Ts depended on SWC. The temperature-normalized Rs exhibited a parabolic relationship with SWC, suggesting a reduced root and microbial respiration associated to drought and waterlogging. The response of Rs to SWC did not vary among tree-decline classes. However, the sensitivity of Rs to Ts was higher around vigorous trees than around those with early symptoms of decline. Spatial variations in Rs were governed by soil carbon to nitrogen ratio, which had a negative effect on Rs, and SWC during summer, when drier plots had lower Rs than wetter plots. These variations were independent of the tree vigor. The basal area of recruits, which was three times (although non-significantly) higher under declining and dead trees than under vigorous trees, had a positive effect on Rs. However, the mean Rs did not change among tree-decline classes. These results indicate that Rs and related soil physico-chemical variables are resilient to the decline and death of dominant centennial trees. Conclusions: The development of advanced regeneration as overstory beech trees decline and die contribute to the Rs homeostasis along forest succession. View Full-Text
Keywords: successional stage; forest decline; tree old-age; old-growth forest; soil carbon; soil nitrogen; rhizosphere; root biomass successional stage; forest decline; tree old-age; old-growth forest; soil carbon; soil nitrogen; rhizosphere; root biomass
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Rodríguez-Calcerrada, J.; Salomón, R.; Barba, J.; Gordaliza, G.G.; Curiel Yuste, J.; Magro, C.; Gil, L. Regeneration in the Understory of Declining Overstory Trees Contributes to Soil Respiration Homeostasis along Succession in a Sub-Mediterranean Beech Forest. Forests 2019, 10, 727.

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