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

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.

Growth and Wood Trait Relationships of Alnus glutinosa in Peatland Forest Stands With Contrasting Water Regimes

“…Yet, our results showed a growth decline in the rewetted stand after the extreme flooding in 2011 ( Figures 2 – 4 ). Negative effects of waterlogging on alder growth have been previously reported in other studies ( Rodríguez-González et al, 2010 ; Tulik et al, 2020 ) and the rewetting action that took place in 2003 at our study sites leading to a sudden and permanent flooding of an adjacent stand caused the death of all alder trees there ( Bönsel, 2006 ). The negative effects of waterlogging, which are especially detrimental when occurring during the growing season ( Kozlowski, 1997 ) as occurred in July 2011 in our study stands, are related to physiological dysfunctions caused by soil anaerobiosis, such as root hypoxia and growth inhibition ( Kozlowski, 2002 ).…”

“…Only those anatomical traits more related to growth, such as the number of vessels (both absolute and per unit area) and the theoretical hydraulic conductivity (which is tightly related to the number of vessels, Supplementary Figure 9 ; Tyree and Zimmerman, 2002 ) responded to changing water regimes in a similar way as ring width. Tulik et al (2020) studied vessel size adjustments to changing water table levels in alder trees of different health conditions and found a general decrease in vessel size under higher water table levels. Another study on flash-flood impacts on tree species anatomy found that the vessel size of alder decreased after wounding and identified alder as a particularly sensitive species to flash floods.…”

“…It is a pioneer species that can fix atmospheric nitrogen, thanks to its symbiosis with the bacterium, Frankia alni ( McVean, 1956 ; Claessens et al, 2010 ); it is a peat forming species ( Barthelmes, 2009 ), and it is of economic value for timber production ( Claessens et al, 2010 ). Even though it is a waterlogging-tolerant species ( Glenz et al, 2006 ; Niinemets and Valladares, 2006 ), several studies have reported the negative effects of prolonged flooding and water level fluctuations on alder radial growth ( Laganis et al, 2008 ; Douda et al, 2009 ; Rodríguez-González et al, 2010 ; Tulik et al, 2020 ) and high water table levels are known to decrease the wood quality of alder ( Barthelmes, 2009 ). Previous attempts at rewetting drained alder forests that led to sudden changes in the water table and permanent waterlogging caused severe tree damage and ultimately trees and forests die-off ( Bönsel, 2006 ).…”

“…Anatomical structures may be negatively affected by waterlogging even in flood-tolerant species due to a reduction of cambial activity ( Kozlowski, 1984 ). Indeed, vessel size has been shown to respond negatively to high water table levels in alder after flooding ( Tulik et al, 2020 ). Studies on other flood-tolerant species, such as Quercus robur L. have also reported a decrease in the vessel size in response to flooding ( Tumajer and Treml, 2016 ), as well as the appearance of “flood rings” after spring flooding, characterized by having especially narrow earlywood vessels caused by the cessation of earlywood vessel development ( Copini et al, 2016 ).…”

Distribution, productivity and natural regeneration of black alder (Alnus glutinosa (L.) Gaertn.) in Ukrainian Polissya

“…At the end of the twentieth century, a new disease caused by Phytophthora alni was detected in alder trees, the symptoms of which are black spots on the leaves and small yellowish leaves (BRASIER et al, 1995). The disease onset may be associated with fl uctuations in groundwater levels, especially during the growing season (TULIK et al, 2020). Besides, alder forests are also characterized by a high fungal species diversity.…”