Groundwater Level Fluctuations Affect the Mortality of Black Alder (Alnus glutinosa Gaertn.)

Szymon Bijak,Adam Grochowina,Mirela Tulik,Joanna Jura-Morawiec

doi:10.3390/f11020134

Abstract

Since the 1990s, a decline of riparian black alder (Alnus glutinosa Gaertn.) has been observed over Europe. The fungus-like eukaryotic pathogen Phytophthora alni subsp. alni is thought to be a causal agent of this process; however, abiotic factors may also be involved. Previous studies suggest that climate conditions and, especially, depletion of groundwater level may be among the most important factors that trigger this phenomenon. We investigated the radial growth and wood vessel diameter of black alder trees of various vigour classes as well as their response to groundwater level changes to search for the link between soil water resources availability and mortality related to alder dieback. Samples were collected in the natural stand located near Sieraków village in the Kampinoski National Park, central Poland, in the area where alder dieback has been recently observed. Based on the crown defoliation level, three vigour classes (healthy, weakened, and dead trees) were distinguished. Cross sections were prepared with a sliding microtome, and Cell P image analysis software was used for the measurements. Tree-ring width (TRW) and vessel diameter (VD) were determined and correlated with the monthly values of precipitation and groundwater level. Alders of the analysed vigour classes exhibited similar patterns of TRW and VD changes over the analysis time. The narrowest tree rings were observed in weakened alders, while the largest vessels were noted in healthy trees. In the case of TRW and VD chronologies, the weakest, and hence insignificant, resemblance was found for healthy and dead trees. TRW and VD of the analysed alders were not correlated with the monthly sum of precipitation, but a negative influence of rainfall in April was observed. In turn, groundwater level had an impact on the radial growth and wood anatomical features of the analysed trees. A negative effect of the highest water table level was found for TRW of weakened and dead trees as well as for VD of healthy and weakened alders. The lowest groundwater level and the amplitude of the water table positively affected VD of the dead trees. Alder decline has a polyetiological nature, and groundwater level fluctuations are one of many factors contributing to disease development.

Highlights

Black alder (Alnus glutinosa Gaertn.) covers Europe as well as large parts of North America andAsia and constitutes an important component of riverine ecosystems, which form a buffer zone along many streams and fulfil a crucial role in the filtration and purification of water [1]
The material was collected in the natural black alder (A. glutinosa Gaertn.) stand located near
We found no significant difference in Tree-ring width (TRW) between distinct vigour classes in the whole common period as well as in the 3, 5 and 10 years prior to dieback (Table 2)

Summary

Introduction

Black alder (Alnus glutinosa Gaertn.) covers Europe as well as large parts of North America andAsia and constitutes an important component of riverine ecosystems, which form a buffer zone along many streams and fulfil a crucial role in the filtration and purification of water [1]. Black alder (Alnus glutinosa Gaertn.) covers Europe as well as large parts of North America and. Forests 2020, 11, 134 the stability of riverbanks and, together with willows, are considered a pioneer species because of their quick initial growth, wind pollination, seed dispersal by wind and water, fast colonisation of naked ground, intolerance of shade, and a comparatively short lifespan [2]. They are tolerant of wet habitats, especially those with spring gain in a river water table. Since the 1990s, in several European countries, a decline of riparian alders has been observed [4,5,6]

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Conclusion