RESEARCH ARTICLE Restoration of Heterogeneous Disturbance Regimes for the Preservation of Endangered Species Steven D. Warren and Reiner Büttner ABSTRACT Disturbance is a natural component of ecosystems. All species, including threatened and endangered species, evolved in the presence of, and are adapted to natural disturbance regimes that vary in the kind, frequency, severity, and duration of disturbance. We investigated the relationship between the level of visible soil disturbance and the density of four endan- gered plant species on U.S. Army training lands in the German state of Bavaria. Two species, gray hairgrass (Corynephorus canescens) and mudwort (Limosella aquatica), showed marked affinity for or dependency on high levels of recent soil disturbance. The density of fringed gentian (Gentianella ciliata) and shepherd’s cress (Teesdalia nudicaulis) declined with recent disturbance, but appeared to favor older disturbance which could not be quantified by the methods employed in this study. The study illustrates the need to restore and maintain disturbance regimes that are heterogeneous in terms of the intensity of and time since disturbance. Such a restoration strategy has the potential to favor plant species along the entire spectrum of ecological succession, thereby maximizing plant biodiversity and ecosystem stability. Keywords: fringed gentian, gray hairgrass, heterogeneous disturbance hypothesis, mudwort, shepherd’s cress cosystems and the species that create and maintain conditions neces- When the European Commission Einhabit them typically evolve in sary for survival. issued Directive 92/43/EEC (Euro- the presence of quasi-stable distur- The grasslands of northern Europe pean Economic Community 1992) bance regimes which are characterized lie within what would be mostly forest requiring all European Union nations by general patterns of perturbation, in the absence of disturbance. Prior to designate a certain percentage of including the types of disturbance and to recent anthropogenic alteration of their landmass as ‘special areas of their frequency, intensity, size, peri- disturbance regimes, the grasslands conservation’ in the NATURA 2000 odicity, and/or duration. Significant were maintained for approximately network, many nations recognized the alteration of the disturbance regimes 1.8 million years by wild ungulate her- ecological value of their military train- has the potential to negatively affect bivores (Pärtel et al. 2005). During the ing areas. As a result, they nominated native biodiversity. The restoration of last millennium, wild ungulates have large tracts of their training lands. For biodiversity is a common goal of res- been largely replaced by domestic her- example, Denmark nominated 45% of toration ecologists around the globe. bivores. More recently, the abandon- its military training landmass, while However, the process is often more ment of traditional grazing practices the Netherlands included 50%, and complicated than it initially appears, and increased use of agricultural fer- Belgium 70% (Gazenbeek 2005). and may well involve the restoration tilization have resulted in a dramatic In Germany, military training areas of the disturbance regime in addition decrease in the spatial extent and bio- provide suitable habitat for a greater to the reintroduction of native spe- diversity of the grasslands ( Jentsch and density of Red List (the European cies ( Jentsch 2007). This can be par- Beyschlag 2003, Butaye et al. 2005, counterpart of U.S. ‘threatened and ticularly important for threatened and Isselstein et al. 2005). endangered’) animal species than pro- endangered species that are dependent During the Cold War, military vided by most other ‘special areas of on a particular disturbance regime to training areas represented some of the conservation’ (Warren et al. 2007). largest tracts of grassland in northern In the post-Cold War era, numerous Ecological Restoration Vol. 32, No. 2, 2014 Europe. Disturbance created by mili- military training areas in Europe have ISSN 1522-4740 E-ISSN 1543-4079 tary training maneuvers provided an been abandoned or have experienced ©2014 by the Board of Regents of the effective surrogate for the disturbance a significantly diminished frequency University of Wisconsin System. under which the grasslands evolved. and intensity of military-related June 2014 ECOLOGICAL RESTORATION 32:2 • 189 disturbance. Many, with extensive Act. It grows erect to 25 cm and occurs FFTA is located approximately and diverse grasslands, have experi- on dry grasslands with soils similar 35 km northeast of HTA and 5 km enced encroachment of woody species to mudwort, but without the addi- southeast of the town of Amberg. It and concomitant reductions in the tional moisture (Rothmaler 1994, comprises approximately 138 ha. Due populations of species that depend on Rosenbauer 1996). Shepherd’s cress to intensive training activities during grasslands maintained by disturbance (Teesdalia nudicaulis) is a small annual the 1960’s, large areas were converted (IUCN 1996, Chojnacka et al. 2010, forb that is listed as endangered on into barren sand. While large sandy Tschöpe et al. 2011). the Bavarian Red List. It occurs on meadows and open sandy soil can Our hypothesis, based on years sandy, acidic grasslands (Schulze- still be found, the open character is of personal observation on the U.S. Motel 1986, Oberdorfer 1990). currently threatened by shrub inva- Army training areas in Germany, was sion and increasing crown density of that numerous Red List plant species Study Area reforested areas. were favored by the disturbance regime We sampled plant populations at four KTA comprises approximately related to military training activity. active U.S. Army training facilities 1,088 ha and is situated northeast The objective of this effort was to test in the state of Bavaria: Grafenwöhr of the town of Kitzingen. It lies in the hypothesis and determine the Training Area (GTA); Hohenfels a large Pleistocene sand dune area. degree to which it was valid. Assum- Training Area (HTA); Freihölser Mixed layers of sand and gravel depos- ing the hypothesis was supported by Forst Local Training Area (FFTA); its from the nearby Main River and the research data, the information will and Klosterforst Training Area (KTA). former sand dunes characterize the assist restoration ecologists in identi- GTA is approximately 23,000 ha in subsoil. The area has been used for fying and quantifying an appropri- size. It was first used by the Royal military training since before World ate disturbance regime to maintain Bavarian Army in 1910 and has been War I, first by the German Army these threatened and endangered plant used continuously since that time, and, since World War II, by the U.S. species. with control ceded to the U.S. Army Army. Prior to military usage, the area at the end of World War II (Burkhardt was mostly forested with a mixture Methods 1994). The training area is located of hardwood and coniferous forest. between the towns of Vilseck and Approximately 100 ha were cleared for Study Species Grafenwöhr, about 88 km northeast military maneuvers and have remained We evaluated four Red List plant spe- of Nürnberg. The western third of the open since that time. training area is characterized by calcar- cies occurring on U.S. Army training Data Collection areas in the German state of Bavaria. eous soils; the eastern part is composed Gray hairgrass (Corynephorus canes- mainly of sandy soils. It is situated in a Field methods varied based on the cens) is a densely tufted, glaucous low-lying area with numerous streams, species of interest. Gray hairgrass was perennial grass that grows to 30 cm. small lakes and swampy areas. Average found and surveyed at GTA, KTA and It is listed as endangered on the Bavar- annual precipitation is approximately FFTA. We used a plot size of 5 m × 630 mm. 5 m, or 25 m2. One hundred plots ian Red List. It occurs most frequently HTA is approximately 16,000 ha on sandy, acidic grasslands with loose were established; 29 at GTA, 21 at in size. It has been used almost con- sand (Oberdorfer 1990, Rothmaler KTA, and 50 at FFTA in areas where tinuously since it was established in 1994). Mudwort (Limosella aquatica) the species was found. Because the is a small annual forb that prefers 1938 by the German Army (Bur- objective was to ascertain the rela- loamy or clayey soils and occurs most khardt 1994). It is located approxi- tionship, if any, between disturbance commonly in moist areas along the mately 84 km southeast of Nürnberg. and species abundance, the plots were margins of ephemeral water puddles The training area is characterized by equally distributed among areas rep- hilly terrain with softly rounded rock resenting 5 levels of physical ground (Rothmaler 1994, Rosenbauer 1996). formations, karst topography, mixed It can grow to a height of 12 cm and disturbance (i.e. 0–20, 21–40, 41–60, coniferous and deciduous forest, and is listed as endangered on the Bavar- 61–80, and > 81%). A conservative dry valleys. The soils in the training ian Red List. Fringed gentian (Gen- definition of disturbance was used, tianella ciliata, syn. Gentiana ciliata area are mostly clay loams derived labeling as disturbed only the por- and Gentianopsis ciliata), is a small, from weathered limestone or dolo- tion of the plots where recent, defini- tive ground disturbance was evident late-flowering biennial that is listed mite. Dolomitic sands are also pres- ent. Average precipitation is between (e.g., visible vehicle tracks, damaged as endangered on the German Red plants, displaced soil, etc.); the mere List, is on the early warning list for 650 mm and 700 mm per year. Drain- absence of vegetation was considered Bavaria, and requires protection under age is predominantly internal, with Germany’s Federal Nature Protection much of the water entering the karst insufficient to definitively indicate system. recent disturbance. Six transects were 190 • June 2014 ECOLOGICAL RESTORATION 32:2 established at 1m intervals, and per- Table 1. The degrees of freedom (df), mean squares, F-ratios and p-values pendicular to one end of each plot.