**4. Long-term vegetation development in glacier forelands as indicated by chronosequences**

To evaluate vegetation dynamics in glacier forelands on a temporally larger scale, chronosequences are commonly employed. Despite some shortcomings (see above) chronosequences are helpful to hypothesize about long-term vegetation development and offer a good baseline to be corroborated or dismissed by long-running permanent plot studies. **Figure 5** exemplifies gradual vegetation changes with time for the chronosequence in the glacier foreland of Goldbergkees. Based on the floristic composition and structural attributes, different successional stages can be identified for both chronosequences surveyed: a pioneer stage, an early Glacier Forelands – Unique Field Laboratories for the Study of Primary Succession of Plants http://dx.doi.org/10.5772/intechopen.69479 137

The permanent plot studies show a very dynamic colonization of recently deglaciated ground. Vegetation dynamics in general are governed by the relative favor or disfavor of a site, which is a function of many different interrelated factors such as elevation, exposure, snow cover duration, continentality, existence of safe sites, seed sources, etc. Despite differences in the absolute values, in general, a swift fill-up of empty niches is taking place during the first decade of the permanent plot study, promoted by the growth of established individuals as well as by a continuous colonization by new individuals. These are invasive populations according to Ref. [50] with young individuals prevailing. A more uniform ("Gaussian") distribution with many species of intermediate age and few young and old ones, which would indicate stable populations (see Ref. [45]), is not yet reached. Several species invest most of the resources in generative reproduction and are able to create persistent diaspore banks. Many of the early colonizers also show ruderal characteristics [51] such as fast increment, the ability for self-pollination, or anemochorous dispersal. Just like their lowland counterparts, alpine ruderals are able to colonize sites with a high disturbance frequency, unlike, however, is their much greater life expectancy [42, 45]. Most of the species encountered in the sample sites are far from their maximum age, explaining the low number of losses in the repeated surveys. If dropouts occur, they are compensated by newly established individuals of the same species, expressed in a general increase of groundcover and individual numbers. One notable exception is *A. alpina* with a life expectancy of only a couple of years. In both glacier forelands, this species is regularly present with diebacks during resurveys. *A. alpina*, however, as self-pollinating species [47] produces a high number of diaspores able for immediate germination and thus a high number of seedlings every year. The short life cycles of *A. alpina* causing a continuous dieback of individuals keep increase of individual numbers moderate compared to more long-lived species such as *O. digyna*, *C. uniflorum*, or *S. bryoides*. Only locally temporary setbacks in the overall vegetation development by disturbances are apparent [17]. Most common is the displacement of meltwater runoff over-pouring the sample sites for a while. The overdose of (cold) water, probably combined with a higher frequency and intensity periglacial processes in the substrate (solifluction, cryoturbation, needle ice, etc.) negatively impacts the life processes of the plants, which is expressed in diebacks of quite a number of individuals of different species in such cases. When the melt-out stops or the runoff is displaced again, progres-

sive developments reemerge.

136 Glacier Evolution in a Changing World

**indicated by chronosequences**

**4. Long-term vegetation development in glacier forelands as** 

To evaluate vegetation dynamics in glacier forelands on a temporally larger scale, chronosequences are commonly employed. Despite some shortcomings (see above) chronosequences are helpful to hypothesize about long-term vegetation development and offer a good baseline to be corroborated or dismissed by long-running permanent plot studies. **Figure 5** exemplifies gradual vegetation changes with time for the chronosequence in the glacier foreland of Goldbergkees. Based on the floristic composition and structural attributes, different successional stages can be identified for both chronosequences surveyed: a pioneer stage, an early

**Figure 5.** Aspects of sample sites along the chronosequence in the glacier foreland of Goldbergkees (the central site out of three per level) illustrate the gradual vegetation change with time. Time since melt-out is 2 years (a), 4 years (b), 15 years (c), 25–30 years (d), 55 years (e), 85 years (f), 120 years (g), and 155 years (h).

successional stage and a later successional stage, which might be further subdivided in a grass-dwarf shrub-phase and a shrub phase. A superordinate species pool characteristic for the siliceous Eastern Alps causes a general similarity between glacier forelands of the Central Eastern Alps (and also for the two presented here); however, the "floristic character of the surroundings" [19] depending on local site conditions (elevation, exposure, topography, etc.) is responsible for some discreetness [17].

The PCAs in **Figure 6** portray the floristic similarity between samples (the closer located within the ordination space, the higher the similarity) as well as changes in groundcover and life form composition during succession for the two chronosequence studies. The pioneer stage includes sites deglaciated for up to 20 years (A- to C-sites on Goldbergkees, B-sites on Lenksteinferner, A-sites on Lenksteinferner are missing as those three selected were still devoid of vegetation in 2007; see **Figure 6**), and vegetation development basically reflects the situation on the permanent plots one decade after deglaciation presented above. Substrate is blocky without any signs of initial soil development. Mineral nutrient supply is guaranteed via sediment input by wind and melting glaciers as well as by dry and wet N-deposition [36–39], creating a first "natural manuring." As already revealed by the permanent plot studies, the chamaephytes *C. uniflorum*, *C. cerastoides*, *S. bryoides*, and *A. alpina*; herbs such as *O. digyna*, *Sagina saginoides*, *V. alpina*, and *Cardamine resedifolia*; the grass *P. laxa*; as well as mosses belong to the early colonizers in both glacier forelands. All of the vascular plants are anemochorous species carried to the glacier foreland by valley winds from the surroundings, where they are able to establish without interspecific competition. Within the first two decades, 20–30 different taxa appear on the new ground. Which species accompany the mentioned early colonizers depends on the seed sources in the surrounding and the local site conditions. In general, the pioneer stage is characterized by a high degree of randomness. Ground cover is low with <2% on the sites sampled. The early successional stage encompasses sites between 20 and 60 years of age (D- and E-sites on Goldbergkees, C- and D-sites on Lenksteinferner; see **Figure 6**). Some species already sparsely present within the pioneer stage gain importance (e.g., *L. alpina*, *G. reptans*, *Gnaphalium supinum*, as well as the grasses *A. rupestris* and *P. alpina*, again predominantly in the viviparous form), and many additional species join the sites. In total, 30 different species of vascular plants were recorded for the early successional stage on Goldbergkees and 31 on Lenksteinferner. Ground cover increases to values around 10% on sites deglaciated for roughly half a century, and dwarf shrubs are the predominant life form (**Figure 6**). Most of the early colonizers are still present with high frequency and/or abundance; on sites older than half a century; however, a continuous influx of additional species segregates the later successional stage (F- to H-sites on Goldbergkees, F- to J-sites on Lenksteinferner) and induces a generally higher dissimilarity between sites than earlier stages (**Figure 6**). One very common species is *Euphrasia minima*, one of the few therophytes involved in primary succession in alpine glacier forelands. Species numbers increase to well over 40, and mean ground cover is around 60%. Increasing ground cover and species richness intensify competition and eliminate some pioneers weak in competition. The later successional stage can be further divided into a grass-dwarf shrub phase (present on Goldbergkees) and a shrub phase (present on Lenksteinferner). In the former, the carpetlike dwarf willows *Salix herbacea* and *Salix retusa* are very common. The shrub phase is characterized by a higher groundcover of more upright-growing shrubs such as *Rhododendron ferrugineum* and different willow species (on Lenksteinferner *Salix appendiculata* and *Salix breviserrata*). In addition, about 120–150 years after deglaciation, the first conifer taxa such as *Juniperus communis* ssp. *nana*, *L. decidua*, or *Picea abies* are present in the sample sites on Lenksteinferner (**Figure 6**).

Glacier Forelands – Unique Field Laboratories for the Study of Primary Succession of Plants http://dx.doi.org/10.5772/intechopen.69479 139

of the surroundings" [19] depending on local site conditions (elevation, exposure, topogra-

The PCAs in **Figure 6** portray the floristic similarity between samples (the closer located within the ordination space, the higher the similarity) as well as changes in groundcover and life form composition during succession for the two chronosequence studies. The pioneer stage includes sites deglaciated for up to 20 years (A- to C-sites on Goldbergkees, B-sites on Lenksteinferner, A-sites on Lenksteinferner are missing as those three selected were still devoid of vegetation in 2007; see **Figure 6**), and vegetation development basically reflects the situation on the permanent plots one decade after deglaciation presented above. Substrate is blocky without any signs of initial soil development. Mineral nutrient supply is guaranteed via sediment input by wind and melting glaciers as well as by dry and wet N-deposition [36–39], creating a first "natural manuring." As already revealed by the permanent plot studies, the chamaephytes *C. uniflorum*, *C. cerastoides*, *S. bryoides*, and *A. alpina*; herbs such as *O. digyna*, *Sagina saginoides*, *V. alpina*, and *Cardamine resedifolia*; the grass *P. laxa*; as well as mosses belong to the early colonizers in both glacier forelands. All of the vascular plants are anemochorous species carried to the glacier foreland by valley winds from the surroundings, where they are able to establish without interspecific competition. Within the first two decades, 20–30 different taxa appear on the new ground. Which species accompany the mentioned early colonizers depends on the seed sources in the surrounding and the local site conditions. In general, the pioneer stage is characterized by a high degree of randomness. Ground cover is low with <2% on the sites sampled. The early successional stage encompasses sites between 20 and 60 years of age (D- and E-sites on Goldbergkees, C- and D-sites on Lenksteinferner; see **Figure 6**). Some species already sparsely present within the pioneer stage gain importance (e.g., *L. alpina*, *G. reptans*, *Gnaphalium supinum*, as well as the grasses *A. rupestris* and *P. alpina*, again predominantly in the viviparous form), and many additional species join the sites. In total, 30 different species of vascular plants were recorded for the early successional stage on Goldbergkees and 31 on Lenksteinferner. Ground cover increases to values around 10% on sites deglaciated for roughly half a century, and dwarf shrubs are the predominant life form (**Figure 6**). Most of the early colonizers are still present with high frequency and/or abundance; on sites older than half a century; however, a continuous influx of additional species segregates the later successional stage (F- to H-sites on Goldbergkees, F- to J-sites on Lenksteinferner) and induces a generally higher dissimilarity between sites than earlier stages (**Figure 6**). One very common species is *Euphrasia minima*, one of the few therophytes involved in primary succession in alpine glacier forelands. Species numbers increase to well over 40, and mean ground cover is around 60%. Increasing ground cover and species richness intensify competition and eliminate some pioneers weak in competition. The later successional stage can be further divided into a grass-dwarf shrub phase (present on Goldbergkees) and a shrub phase (present on Lenksteinferner). In the former, the carpetlike dwarf willows *Salix herbacea* and *Salix retusa* are very common. The shrub phase is characterized by a higher groundcover of more upright-growing shrubs such as *Rhododendron ferrugineum* and different willow species (on Lenksteinferner *Salix appendiculata* and *Salix breviserrata*). In addition, about 120–150 years after deglaciation, the first conifer taxa such as *Juniperus communis* ssp. *nana*, *L. decidua*, or *Picea abies* are present in the sample sites on

phy, etc.) is responsible for some discreetness [17].

138 Glacier Evolution in a Changing World

Lenksteinferner (**Figure 6**).

**Figure 6.** Principal component analyses (PCAs) based on species data for the chronosequence studies in the glacier forelands of Goldbergkees (above) and Lenksteinferner (below). The pies indicate life form composition and total ground cover for all samples. Where necessary (A, B, and C on Goldbergkees, B on Lenksteinferner) pies are zoomed for better reading.

Succession on new ground is commonly reflected by an increase of species numbers and ground cover, at least until a certain point [52] (see **Figure 6**). Species diversity of a particular successional stage is not so much triggered by elevation, rather by the vegetation belt in which it is located. For instance, on Goldbergkees sites being deglaciated for one and a half century are located within the alpine belt and exhibit less species than the same-aged sites on Lenksteinferner which are—despite higher absolute elevation—located close to the treeline ecotone allowing for an association of subnival, alpine, and subalpine elements. While the increase of species numbers shows a more negative logarithmic behavior, the development of ground cover is positive logarithmic, i.e., despite a swift increase of species numbers during the pioneer and early successional stages, ground cover values lag behind during the first decades (see **Figure 7**)—a pattern already observable during the first decade of the permanent plot study. Approximately half a century after deglaciation, a speedup in ground cover becomes apparent. This increase is not always continuous; rather disturbances such as mudflows, relocation of glacial runoff, avalanches, etc. can throw back succession to an earlier stage, as displayed by the decrease in both species numbers and ground cover values on the 90-year-old G-sites on Lenksteinferner (see **Figure 7**).

Primary succession in glacier forelands is a process that always occurred when glaciers receded, whether in postglacial times, after the LIA, or today with recent climate warming. While the general processes of primary succession were basically always the same, the circumstances controlling these processes may differ between today and the past. Recent studies, at least, found primary succession within glacier forelands of the Alps to be accelerated,

**Figure 7.** Development (mean out of three samples) of species numbers (blue open circles) and ground cover (green closed circles) along the chronosequences in the glacier forelands of Goldbergkees (left) and Lenksteinferner (right).

most likely due to climate warming (e.g., Refs. [24, 53]). As a complete list of species present in the foreland of Lenksteinferner was already published for the early twentieth century [19], this glacier foreland offers the great opportunity to compare these historic data with those collected roughly one century later (i.e., those presented here). Ref. [54] employed these two spatiotemporally different data sets to address the question whether primary succession of plants in glacier forelands today differs from the past concerning the dynamics of colonization, the plant species involved, and their respective biological traits. The main outcome of this study was that even if additional species occur and the colonization apparently is faster today compared to the past, fundamental differences concerning the floristic inventory, the biological traits, or the colonization strategies of the early colonizers due to climate change do not exist. This is apparently a consequence of a compensation of climate warming during the twentieth century by the shift of the glacier terminus to a higher elevation. The vertical shift of the glacier snout of Lenksteinferner between the early twentieth and early twenty-first century amounts approximately 300 m in elevation. Assuming a mean adiabatic temperature lapse rate of −0.57 K/100 m, mean annual temperatures between the two elevational levels differ by 1.7 K [54]. This value corresponds quiet well to the magnitude of climate warming between the two sampling dates, and therefore, almost identical thermal conditions can be assumed for the recent glacier foreland (at higher elevation but affected by climate warming) and the one at the beginning of the last century (at lower elevations but under colder climate). As a shift in elevation of glacier termini during recession is a common issue, such compensation effects can be assumed to be a widespread determinant for succession in glacier forelands of the Alps (and elsewhere). Glaciers which terminate in flat glacial valleys (e.g., Morteratsch glacier in the Swiss Engadine [53]) may react differently, as compensation effects of elevation change by climate warming are lacking and the increasing temperatures may immediately affect plant colonization and vegetation dynamics in glacier forelands, allowing thermophilous species of lower elevations to participate in primary succession.
