Wissenschaftszentrum Weihenstephan für Ernährung, Landnutzung und Umwelt Lehrstuhl für Renaturierungsökologie Conservation on the edge: habitat conditions and management strategies to maintain amphibious plant communities of temporarily flooded field ponds in north-east Germany Sara Altenfelder Vollständiger Abdruck der von der Fakultät Wissenschaftszentrum Weihenstephan für Ernährung, Landnutzung und Umwelt der Technischen Universität München zur Erlangung des akademischen Grades eines Doktors der Agrarwissenschaften genehmigten Dissertation. Vorsitzender: Univ.-Prof. Dr. J. Schnyder Prüfer der Dissertation: 1. Priv.-Doz. Dr. H. Albrecht 2. Univ.-Prof. Dr. A. Fischer 3. Univ.-Prof. Dr. K. G. Bernhardt Universität für Bodenkultur Wien/ Österreich Die Dissertation wurde am 17.12.2015 bei der Technischen Universität München eingereicht und durch die Fakultät Wissenschaftszentrum Weihenstephan für Ernährung, Landnutzung und Umwelt am 19.02.2016 angenommen. In Erinnerung an Dr. Ingo Holz Contents Summary 1 Zusammenfassung 4 Chapter 1 General Introduction 7 Chapter 2 Effects of water regime and agricultural land use on diversity and species composition of vascular plants of temporary ponds in northeastern Germany 23 1. Introduction 24 2. Materials and methods 25 3. Results 30 4. Discussion 39 Chapter 3 Managing plant species diversity under fluctuating wetland conditions – the case of temporarily flooded depressions 43 1. Introduction 44 2. Methods 47 3. Results 52 4. Discussion 57 Chapter 4 Effects of farming practice on populations of threatened amphibious plant species in temporarily flooded arable fields – implications for conservation management 63 1. Introduction 64 2. Methods 66 3. Results 72 4. Discussion 78 5. Conclusions 81 Chapter 5 General discussion 83 Publications and author contributions 95 Danksagungen 97 References 99 Appendix 117 List of Figures Figure 1: Zonation of the littoral zone at a field pond along a hydrological and soil texture gradient 15 Figure 2: Conceptual diagram of the three dissertation chapters. 16 Figure 3: Aerial picture of the study area 27 Figure 4: Boxplots of number of species (A) and percentage of Isoëto-Nanojuncetea species (B) 34 Figure 5: Effects of farming practices on the total number of species (A) and on the percentage of Isoëto-Nanojuncetea species (B). 35 Figure 6: NMDS ordination plot of all sampling plots (stress 15.3%). 36 Figure 7: NMDS plot of all species (stress 15.3%). 36 Figure 8: NMDS ordination with fitted vectors and smoothed surfaces 38 Figure 9: Position of the seven temporarily flooded depressions (shaded areas) within two arable fields. Aerial picture from Bing (2012). 48 Figure 10: Species richness (a), seedling density (b), evenness (c) and number of Red List species (d) in the soil seed bank of the upper (‘aquatic’) and lower (‘terrestrial’) zone of temporarily flooded depressions in arable fields (Kruskal-Wallis test, P < 0.05). 51 Figure 11: Differences in seedling emergence from soil samples of temporarily flooded depressions in arable fields in response to experimental flooding. 53 Figure 12: Species richness in soil samples from temporarily flooded depressions in arable fields under experimental flooding. 53 Figure 13: Evenness of the species emerging from soil samples of temporarily flooded depressions in arable fields under experimental flooding. 54 Figure 14: Red list species emerging from soil samples of temporarily flooded depressions in arable fields under experimental flooding. 55 Figure 15: Detrended Correspondence Analysis (DCA) of species composition in soil samples responding to experimental flooding from the upper (filled symbols) and lower zone (transparent symbols) of temporarily flooded depressions in arable fields. 56 Figure 16: Changes in the probability of field emergence of the study species a) Myosurus minimus , b) Limosella aquatica and c) Peplis portula in relation to soil tillage, herbicide application and weed cover. 76 Figure 17: Conceptual diagram of steps to identify and maintain suitable habitats and amphibious species of temporary ponds in arable fields. 91 Figure 18: Conceptual diagram of recommended farming practices. 94 List of Tables Table 1: Summary statistics of the measured chemical soil parameters of all seven wetlands. 29 Table 2: Mean constancy (%) of all species 31 Table 3: Annual, perennial and total species numbers 33 Table 4: Results of the vector and smoothed surfaces fitting of the environmental variables. 38 Table 5: Relationship between flooding duration, median Ellenberg indicator value for soil moisture (EIV moisture), water level and wetland zone and the first two DCA axes. P-values are based on 999 random permutations. Bold P- values indicate significant correlations. 57 Table 6: Number of plots with treatments that had to be changed due to flooding in 2013. 69 Table 7: Accumulated precipitation and deviation on a percentage basis from the long-term average (1981–2010: 521 mm) for the study years and seasons using data from the weather station Angermünde (DWD, 2014). 70 Table 8: Agricultural management (soil tillage, crop competition, fertilization, herbicide application) and abiotic factors (weed cover, flooding, pond) effects on individual densities 75 Table 9: Agricultural management (soil tillage, fertilization, herbicide application) and site (pond) effects on seed densities (seeds per m²) of Myosurus minimus , Limosella aquatica, Peplis portula and Elatine alsinastrum in the soil seed bank. Bold values indicate significance at P < 0.01. 77 1 Summary Thousands of years of historical farming practices formed a highly adapted arable flora that declined during the past decades due to an ongoing intensification of agricultural management. To preserve arable biodiversity, research has focused mainly on terrestrial plant communities, resulting in the implementation of a variety of tools and conservation programmes. Amphibious plant species, many of them rare and threatened, and their communities inhabiting temporarily flooded parts of arable fields have been less well investigated. Therefore, this dissertation aims at studying the effects of water level fluctuations and agricultural management on this species group in order to develop a conservation concept for plant communities at temporarily flooded habitats in arable fields. In a first field study the effects of water level fluctuations, soil properties and agricultural management on the vascular plant communities were examined. The main findings show that fluctuating water levels increased total species richness and the proportion of species belonging to the dwarf rush communities (phytosociological class Isoëto-Nanojuncetea bufonii Br.Bl. et R.Tx. 1943), which harbours many rare amphibious plant species. The species composition was mainly determined by the water regime, whereas soil fertility had a subordinate impact. The effects of farming practices on diversity and species composition were less clear. These results indicate that supporting fluctuation of water levels and keeping the soil nutrient content low would best promote amphibious plant communities in arable fields. As plant species at disturbed habitats like temporary ponds produce persistent seeds, the soil seed bank plays an important role for the conservation of amphibious plant communities. At temporarily flooded depressions, both terrestrial and amphibious plant species contribute to the seed bank, which in turn may harbour the potential for a series of alternating, valuable plant communities. To get a better understanding, how the hydro-period and depth of the water table determine diversity, species composition and conservation value of these communities, a common garden 1 Summary experiment was conducted. Mixed soil samples of the upper and lower littoral zone were kept flooded for short, intermediate or long time periods at differing depths (5, 15, 40 cm) and diversity, number of rare species and species composition of the emerging seedling communities were evaluated. In general, hydro-period most decisively changed species composition and diversity. In all treatments, few rare species emerged, but species composition differed, indicating that all communities along the flooding gradient harbour species of high conservation value. Thus, these findings show that the seed bank has the potential for the conservation of different plant communities in fluctuating ecosystems. Apart from environmental factors like water level fluctuations, the agricultural land use is of great importance for maintaining plant communities in arable fields. Intensified farming practices have led to severe declines of arable plant diversity at terrestrial sites. However, studies on the effects of farming practices like soil tillage, crop competition, fertilization and herbicide application, and their respective combinations on population dynamics of amphibious plant species inhabiting temporarily flooded fields are scarce. Considering the high conservation value of amphibious plant communities, it is highly desirable to understand these processes, in order to develop efficient conservation strategies. Thus, the third main chapter of this dissertation comprises an on-farm experiment with four selected amphibious plant species ( Elatine alsinastrum , Limosella aquatica , Myosurus minimus , Peplis portula ), where aboveground plant establishment and belowground seed densities were determined. The plant emergence of all study species was reduced by herbicide application, whereas soil tillage positively affected