Long-Term Changes of Softwood Floodplain Forests—Did the Disappearance of Wet Vegetation Accelerate the Invasion Process?

Katarína Mikulová,Tomáš Bacigál,Jozef Šibík,Mária Šibíková,Ivan Jarolímek

doi:10.3390/f11111218

Katarína Mikulová, Tomáš Bacigál + Show 3 more

Open Access

https://doi.org/10.3390/f11111218

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Abstract

Objectives: We followed the long-term changes of softwood floodplain forests strongly altered by water regime changes and examine the behaviour of neophytes in this environment. Here we ask: (1) How did the composition of neophyte and native species change? (2) How did the presence of species that prefer wetter conditions change? (3) What traditionally distinguished type of softwood floodplain forests (a wetter one or a more mesophilous one) do neophytes prefer? (4) What environmental factors affect the native species richness and the occurrence and cover of neophytes? Materials and Methods: Historical and recent phytosociological relevés of the association Salicetum albae of the Slovak part of the inland delta of the Danube River were used (177 plots together). For each plot, the number and cover of neophytes and number of native species were measured, and the Shannon-Wiener diversity index, the stand structure (cover of tree, shrub and herb layer) and the mean of Ellenberg indicator values were calculated and compared among time periods. Temporal trends of the soil moisture characterized by indicator values calculated for each plot were determined using a Linear Model. The synoptic table of traditional vegetation types was done to show preferences of neophytes for particular softwood forest types. The effect of site conditions on native species richness and occurrence of neophytes was determined using the Generalized Linear Model. Results: The relative number and cover of neophyte species increased and the absolute number of native species decreased over time; the vegetation of the area has changed from variable hygrophilous and mesophilous to homogenised mesophilous; most non-native species prefer the mesophilous vegetation of the floodplain forests; the wetter parts of the floodplain more successfully resisted invasions. Conclusions: The vegetation of the researched area has considerably changed over time to become less diverse and less hygrophilous, and has more invasive species. To preserve floodplain forests, natural hydrological and connectivity patterns should be adequately protected.

Highlights

The floodplains of large rivers create space for the development of various riparian ecosystems [1]. these ecosystems previously covered wide stretches along rivers, today only a fraction of them remain
The relative number and cover of neophyte species increased and the absolute number of native species decreased over time; the vegetation of the area has changed from variable hygrophilous and mesophilous to homogenised mesophilous; most non-native species prefer the mesophilous vegetation of the floodplain forests; the wetter parts of the floodplain more successfully resisted invasions
The species composition of the softwood floodplain forests of the Danube inland delta significantly changed over time (Figure 2)

Summary

Introduction

The floodplains of large rivers create space for the development of various riparian ecosystems [1]. These ecosystems previously covered wide stretches along rivers, today only a fraction of them remain. The physical processes play a substantial role in diaspore dispersal, the creation of new ecotopes and the establishment of the cottonwood and willow tree stands [4,5]. These processes are often disrupted by intensive human activities concentrated along rivers [4]. Intensive forestry, water extraction and recreational activities significantly contribute to reducing the stability of river ecosystems as well [4]

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