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Chapter 10 Rooting Patterns of Old-Growth Forests: is Aboveground Structural and Functional Diversity Mirrored Belowground? Jurgen Bauhus 10.1 Introduction When we think of old-growth forests, we generally imagine old forests with large trees and possibly a highly diverse forest structure resulting f rom the death of individual trees and the resulting gap- phase dynamics (Oliver and Larson 1996; Franklin et al. 2002). This is also reflected in the definitions of old-growth forests (see Chap. 2 by Wirth et al., this volume), which normally do not refer to belowground structures and processes. This neglect of belowground aspects, although intriguing, is understandable since so little information is available. It is well known that the species richness, and often also the biomass, of inverte- brates, fungi, and bacteria is much higher belowground than aboveground (e.g. Torsvik et al. 1990), yet we know very little about how their diversity and abundance belowground is related to forest age or forest structure. Carbon storage is an important value of old-growth forests, and the carb on stor ed in soils, fore st floor, and belowground biomass often approximates the quantities stored in aboveground biomass (e.g. Trofymow and Blackwell 1998; see Chap. 11 by Gleixner et al., this volume). The turnover of fine roots is believed to be an important driver of soil carbon accumulation, yet little is know about how this process changes with forest age or forest developmental stages found in old- growth forests. Many of the attributes a nd value s of old-growt h forests are related to their aboveground structural diversity (McElhinny et al. 2005). It is therefore i nterest- ing to ask whether this structural diversity in old-growth forests is mirrored belowground, and to what extent belowground structural diversity may contribute to functional diversity. To approach these questions, I willaskfirstlywhich attributes may comprise belowground structural diversity, whereby the term belowground encompasses the substrates colonised by roots, the soil and forest floor layers. C. Wirth et al. (eds.), Old‐Growth Forests, Ecological Studies 207, 211 DOI: 10.1007/978‐3‐540‐92706‐8 10, # Springer‐Verlag Berlin Heidelberg 2009 10.2 What Comprises Belowground Structural Diversity? Since belowground structural diversity has not been defined, I will first reflect on the attributes that commonly are used to quantify structural diversity aboveground. Stand structural diversity is a measure of the numb er of different structural attri- butes present and the relative abundance of each of these attributes, as summarised by McElhinny et al. (2005) for some forest types. These attributes are responsible for variation in the vertical and horizontal structure of forest stands and are thought to be indicative of biodiversity, i.e. related to the provision of fauna l habitat. The range of attributes comprises vertical layering of foliage; variation in canopy density (e.g. caused by gaps); variation in the size and distribution of trees; the height and spacing of trees, and their species diversity and biomass; the cover, height and richness of the understorey including shrubs; and the number, volume and range in decay stages of standing and fallen dead wood (McElhinny et al. 2005). The equivalent belowground attributes that may be important for below- ground biodiversity and ecosystem functioning are listed in Table 10.1. In general terms, these structural elements provide horizontal and vertical heterogeneity in belowground structures. In the following, some of the analogies between below- ground and aboveground structural elements or parameters will be pointed out and discussed, focussing in partic ular on the question of whether the structural diversity created by these elements increases with forest age. Table 10.1 Potential attributes of belowground structural complexity Contribution to: Attribute Quantified as: Vertical structure Maximum rooting depth of structural or fine roots Depth in metres Variation in maximum rooting depth between species Vertical distribution of fine or coarse roots No. of layers, evenness of root distribution in layers/horizons over the profile depth Horizontal variation Size and distribution of roots systems Number, volume Size and number of root gaps Area Quantity and size of belowground coarse woody detritus (stumps, old root channels, etc.) Number, volume and depth Pit and mound topography Area covered by these features 212 J. Bauhus 10.3 Root Gaps and Horizontal Variation in Rooting Density in Old-Growth Forests Old-growth forests are the result of the long-term absence of stand-replacing dis- turbances (see Chap. 2 by Wirth et al., this volume). The old trees may comprise the cohort that developed following the previous stand-replacing disturbance or they may have developed subsequently in gaps created by the death of trees from the distur- bance cohort. In any case, by the time an old-growth developmental phase is reached, the disturbance dynamics, until then, will have been dominated by the formation of gaps in most types of forests. Therefore, gaps are an important feature of old-growth forests. They may occupy 5 15% of the stand area in temperate forests (e.g. Runkle 1982; Emborg et al. 2000). These gaps contribute greatly to the vertical structural diversity of old-growth forests and also, through the successional processes trig- gered within them (e.g. Busing and White 1997; Rebertus and Veblen 1993), to species diversity. Some canopy species may not be able to regenerate in these gaps and are replaced by more shade-tolerant species (Oliver and Larson 1996; Gilbert 1959). However, the prevalence of gap dynamics in old-growth forests leads to a patchwork of developmental stages, creating horizontal variation in canopy height, tree biomass and necromass and/or species composition (e.g. Emborg et al. 2000; Korpel 1995; Franklin et al. 2002). Whether or not the aboveground structural diversity of old-growth forests attributable to gap formation is mirrored below- ground depends on whether root gaps are created in the process, and on whether belowground structural elements vary with the developmental stage of the patches. This would, for example, be the case if these gap phase s have different levels of fine- or coarse-root biomass, or roots with functional traits or mycorrhizal associa- tions that differ from those found during other developmental stages. First, I will explore the question of whether aboveground gaps create below- ground gaps. Then I will ask to what extent belowground gaps contribute to structural and functional diversity. Aboveground gaps are created when one or more trees participating in the main canopy layer are removed or killed. While the foliage of trees within the crown is confined to a reasonably small projected ground area around the trees, the same is not true for roots. These are far more wide-reaching than the branches (Stone and Kalisz 1991), and so roots tend to overlap much more than crowns. For example, Bu ¨ ttner and Leuschner (1994) found complete spatial overlap of the root systems of the co-occurring species Quercus petraea and Fagus sylvatica. Consequently, when one tree or a small group of trees is removed or killed, the soil beneath them remains partially occupied by the root system of neighbouring trees. Thus, in most cases, ‘‘root gaps’’ do not represent patches with no live roots, but may be characterised as zones of reduced root competition. Runkle (1982) and Brokaw (1982) have defined canopy gaps. These have a certain minimum size, and extend from the top of the canopy through all vegetation layers to a certain height above the ground. We can distinguish between the act ual canopy gap, between the edges of crowns, and the expanded gap between tree 10 Rooting Patterns of Old Growth Forests 213 stems. Since we usually have no zone without roots, it is very difficult and certainly impractical to define a root gap in the field. Thus, attempts to identify root gaps have focussed on the ground areas within the perimeter of aboveground canopy gaps. Also, when root gaps have been studied, the focus was usually on fine roots, which are responsible for belowground competition for soil resources. The picture that emerges from the few available studies of root gaps is far from clear. This is certainly due, in part, to the fact that the results are from different gap sizes and that root measurements are from different soil depths and times since gap creation. Many of these studies are from tropical forests, and, in most cases, only the general gap area was analysed rather than the fine root distribution in relation to distance to the gap perimeter. When fine root biomass between root gaps and intact adjacent areas was compared, a reduction could be observed in most cases (Fig. 10.1). This reduction in fine root biomass was usually not more than 60% (mostly between 20 and 40%). The reduction in live fine roots following canopy creation could be very fast, for example, a 40% reduction in a subtropical wet forest system (Silver and Vogt 1993). However, when medium-term fine root growth between these two areas was compared, root gaps more often showed an increase than a decrease, possibly indicating a reasonably fast recovery of fine root biomass. Unfortunately, very few studies provide information on the process of root gap closure with time. Bauhus and Bartsch (1996) used in-growth cores to compare the fine root growth of Fagus sylvatica at the centre and perimeter of 30 m diameter gaps within an undisturbed ca. 160-year-old forest in the Solling area of Germany. Fine root growth in the stand was 390 g m –2 (0 30 cm soil depth) over a 12-month period (Fig. 10.2). 0 1 2 3 4 5 150 140 120 100 80 60 40 >40 Fine-root biomass or growth in gaps relative to intact forest (%) Frequency biomass growth Fig. 10.1 Reduction or increase in fine root (<2 mm diameter) biomass or growth observed in root gaps associated with canopy gaps in different forest ecosystems, where fine root biomass was compared to that of intact adjacent forest. Note that the time since gap creation differs between studies (Bauhus and Bartsch 1996; Silver and Vogt 1993; Ostertag 1998; Denslow et al. 1998; Wilczynski and Pickett 1993; Cavelier et al. 1996; Sanford 1990; Battles and Fahey 2000) 214 J. Bauhus At a distance of 5 m from the edge trees into gaps fine root production over the same period declined to 15 130 g m –2 , whereas in the centre of gaps it was negligible. Similarly, Mu ¨ ller and Wagner (2003) found the greatest fine root growth in gaps only 2.2 m from the edge of the gap in a 35-year-old spruce (Picea abies) forest, while no live fine roots were found beyond 7.4 m from the gap edge. These studies show that root gaps can persist for a substantial period of time, if gaps are not, or only slowly, recolonised by other vegetation, as was the case in the two studies cited above. However, fine root biomass may recover rapidly when gaps are large enough to be recolonised by fast-growing understorey or shrub species (Bauhus and Bartsch 1996). Jones et al. (2003) showed that belowground gaps in Pinus palustris forests closed quickly because understorey vegetation compensated for the absence of pine fine roots, in particular in gaps with higher soil moisture and nitrate concentrations than in the surrounding forest. Campbell et al. (1998) also found a rapid recovery of non-tree roots in small experimental gaps in mixed boreal forests in Que ´ bec. Whether the speed of recolonisation depends on the contrast in soil nutrient and water availability between the root gaps and surrounding soil, such that the root gaps represent rich patches, is not clear (e.g. Ostertag 1998). Higher concentrations of nitrate and phosphate in soils of root gaps as compared to undisturbed areas might facilitate colonisation by pioneer species (Denslow et al. 1998). Once saplings have established in gaps, fine root growth in them might be higher than in the undisturbed surrounding forest (Battles and Fahey 2000). The occurrence of fine root gaps is related to the horizontal distribution of fine root mass of individual trees. Models of fine root distribution of single trees indicate that the biomass over the entire soil profile is greatest near the stem and decline s with distance from the tree (Nielsen and Mackenthun 1991; Ammer and Wagner 2005). However, other studies have indicated that the spatial distribution of roots around stems does not follow such a symmetrical pattern but may be related more to soil nutrient availability (Mou et al. 1995). Large-crowned trees have more fine root 0 100 200 300 400 500 600 0510 Distance from egde (m) Fine-root ingrowth (g m –2 ) Fig. 10.2 Fine root biomass production over a 16 months period determined by the ingrowth core method in an undisturbed European beech forest (0 m) and at different positions (5 and 10 m from the edge) within 30 m diameter gaps (0 30 cm soil depth) (after Bauhus and Bartsch 1996) 10 Rooting Patterns of Old Growth Forests 215 biomass and a greater maximum extent of the root system than small trees with little foliage. Therefore, the reduction in fine root biomass following the removal or death o f individual trees will be greatest in the immediate vicinity of the stump. Owing to the lack of studies on this topic, we know neither what size of above- ground gap is required to create a root gap in stands of different tree dimensions, nor what reduction in fine root density is required to have a situation one might call a root gap. However, some studies have quantified the distance from the gap edge at which fine root growth ceases (Bauhus and Bartsch 1996; Jones et al. 2003). In addition to a significant reduction in fine root density or growth, root gaps should be characterised by changes in the level of resources such as soil moisture and nutri- ents, which would allow colonisation of the gap area by vegetation that previously could not become established under competition from trees occupying the area. A number of studies have demonstrated that belowground ecosystem processes can change dramatically in gaps (Denslow et al. 1998; Parsons et al. 1994), supporting the notion that the structural diversity in old-growth forests also leads to functional diversity. For example, reduced root competition by mature trees and increased precipitation in gaps lead to higher levels of soil moisture in gaps (e.g. Bauhus and Bartsch 1995; Ritter and Vesterdal 2006). Depending on the microcli- matic and soil conditions in gaps, this may or may not lea d to increased decompo- sition of organic matter (e.g. Bauhus et al. 2004). Increased mineralisation of nutrients and, owing to reduced uptake, increased availa bility of nutrients can lead to high losses via leaching (Bartsch et al. 2002; Ritter and Vesterdal 2006; Parsons et al. 1994) or in gaseous forms (Brumme 1995). Both processes commonly are associated with changes in soil microflora (e.g. Bauhus et al. 1996), which is often reflected in increased nitrification rates (e.g. Parsons et al. 1994). Von Wilpert et al. (2000) documented a rapid and very high increase in seepage water nitrate concentrations at a soil depth of 180 cm following the removal of a single Picea abies tree in a pole-sized stand. Their results showed that such dramatic changes in nutrient transformation processes, equivalent in magnitude to changes following clearfelling, can occur even in very small gaps, probably as a result of the rapid turnover of mycorrhizal fungi. Therefore, although most gaps in old-growth forests are small, and only a few gaps are large (Runkle 1982; Butler-Manning 2007), it can be assumed that most, if not all, gaps leave a belowground signal in the form of root gaps, which contribute to the functional diversity of old-growth ecosystems. These patches, with their higher soil moisture and greater nutrient availability, can be colonised by species that were either absent or present in low abundance in undisturbed parts of old-growth stands. These different species might in turn support a different soil microfauna and micro flora than would dominate under undisturbed conditions, thus contributing to belowground biodiversity. While it is likely that roots gaps are formed when aboveground gaps are created, it is not clear whether the vegetation patches of different ages that developed subsequently in gaps also differ in their belowground biomass. There are indica- tions that fine root growth of saplings in gaps exceeds that of the surrounding stand matrix (Battles and Fahey 2000). For fine roots, the biomass of even-aged stands may be indicative of that found for similar stand developmental phases in patches of 216 J. Bauhus old-growth forests. However, owing to the onerous nature of such a task, few studies have compared different age classes of the same species on compara ble sites and at the same soil depth. Where this has been done for the same ecosystem (Idol et al. 2000), it was shown that fine root growth, mortality and decomposition in 4-year-old stands was as high, if not higher, than in 10-, 29-, or 80- to 100- year-old stands of an oak-hickory forest.Wheredataonfinerootbiomassfrom the literature have been compiled, such analyses do not reveal clear temporal patterns of fine root biomass with stand age, and even show contradictory trends for differe nt spe cies. In their analysis of published studies, Leuschner and Hertel (2003) showed that the fine root biomass of Fagus sylvatica appeared to decline with age, whereas fine root biomass in Picea abies stands increased with stand age. It is conceivable that in spruce stands, owing to the low quality of litter and associated accumulation of forest floor mass with age (Meiwes et al. 2002), nutrients become more growth-limiting with age, hence necessitating the mainte- nance of more fine roots for nutrient capture in older stands compared to young stands. This age-dependent increase in fine root biomass has also been observed in Abies amabilis forests in the Washington Cascades in the United States (Grier et al. 1981), or for a chronosequence of a tropical montane Quercus forest in Costa Rica, ranging from an early-successional stage to old-growth (Hertel et al. 2003). In both cases, this increase in fine root biomass also coincided with an increase in forest floor thickness and greater fine root biomass in the forest floor layer but not in the mineral soil, lending support to the idea that the increase may be linked to the immobilisation of nutrients. Cavelier et al. (1996) reported that fine root biomass in the surface mineral soil of early-successional stages from a tropical montane cloud forest did not differ from that in a mature forest. However, the fine root biomass (<5 mm) growing in a root mat above the mineral soil surface on logs and branches was higher in the 20-ye ar-old and the mature forest than in the young secondary forest. They assumed that, in this extremely moist environment, fine root density saturation and oxygen limitation in the surface mineral soil leads to an expansion of the root system ‘‘aboveground’’. The increasing heterogeneity of the micro- topography with stand age facilitated this process. However, this pattern of increasing fine root biomass with age cannot be generalised, as demonstrated for fine root biomass in chronosequences of the species Fagus sylvatica, Picea abies, and Quercus cerris (Cla us and George 2005). In these cases, fine root biomass peaked at around 20 30% of the mature age of each species, and at levels of 150 200% of the fine root biomass at stand maturity. In their study, however, two of three sites had almost no forest floor, whereas at the third site, differences in fine root biomass resulted from differences in forest flo or thickness. The pattern observed in the latter study mirrors the temporal dynamics commonly observed for foliage biomass or leaf area index, suggesting that, for these stands, the ratio of foliage biomass to fine root biomass is maintained at a similar level with stand age. This may be a more general pattern in situations where nutrient and water availability do not decrease with age. However, Uselman et al. (2007) found that the fine root production and turnover increases with forest age from 77 years to over 850 years in a successional sequence at 10 Rooting Patterns of Old Growth Forests 217 Mt. Shasta, California, while the aboveground litterfall declines. Owing to the paucity of published data on fine root biomass in chronosequences, it remains speculative whether age-related increases in fine root biomass or production are related to decreasing nutrient or water availability. Therefore, it is also not possible to state whether the spatial heterogeneity in fine root density associated with patches of different ages is higher in old-growth forests than in younger, regrowth stands. At sites where an accumulation of forest floor material with stand age occurs, it is likely that gaps, and subsequent development of even-aged groups in these gaps, contribute to a diversification of forest floor conditions and thus rooting patterns. Ponge and Delhaye (1995) demonstrate how relationships between stand developmental phases and forest floor development in an old-growth European beech forests influence earthworm communities. The presence of different age classes or age-related vegetation communities may also influence the distribution of soil microflora and microfauna, which can be age- and species-specific. The coarse root biomass of individual trees is closely related to their size. As trees become older and taller they need to be firmly anchored, and they need to support an increasingly far-reaching network of fine roots. Coarse root biomass of individual trees is therefore commonly predicted through allometric relationships to measures such as tree diameter at breast height (e.g. Bolte et al. 2004) or by using root-shoot ratios (Mokany et al. 2006). The relationship between aboveground and root biomass declines with tree biomass and stand age (Mokany et al. 2006). However, the declining trend in these relationships is confined largely to young ages and small values for stand biomass. Above 30 years or 100 t ha –1 , root:shoot ratios remain surprisingly constant. This means that, for most situations, below- ground biomass is closely related to the age or biomass of stands and patches. Therefore, old-growth forests, which are often characterised by a high spatial heterogeneity of aboveground biomass (Korpel 1995; Butler-Manning 2007), should also have a high spatial heterogeneity of belowground biomass. However, it is not yet clear what relevance this spatia l heterogeneity of belowground biomass has for ecosystem function (cf. Chap. 11, Gleixner et al., this volume). The below- ground equivalent of large old trees, which are an important feature of old-growth, is their large root systems. Analogous to dead wood in the crowns of old living trees, with its particular importance to species such as woodpeckers or xylobiotic arthro- pods, the large root systems may generate large coarse dead roots, which provide belowground habitat and substrate. Eventually, when the aboveground part dies, stumps and structural roots will constitute a large input of woody material. The function of these large dead roots will be discussed further below. Trees also act as conduits for the input of precipitation and chemical elements into forest ecosystems. Depending on the architecture of tree crowns, different proportions of these factors enter the system in the form of crown drip and stem flow. For smooth-barked species with mostly steep-angled branches such as Fagus sylvatica, the proportion of stem flow is so high that the soil at the base of trees exhibits significantly different chemical characteristics than soil further away from the stem. Usually it is substantially more acidified (Koch and Matzner 1993). The quantity of stem flow increases with tree crown size so that the channelling effect 218 J. Bauhus for inputs and the resulting changes in soil chemical conditions is more pronounced for soil at the base of large trees as compared to small trees. Consequently, this phenomenon will also lead to higher spatial belowground heterogeneity in old- growth forests comprising species, where stem flow forms an important part of their input fluxes. When tree species have different influences on nutrient cycles and soils (for the underlying mechanisms see Binkley and Giardina 1998), this can lead to long-lasting spatial patterns in soils (e.g. Boettcher and Kalisz 1990; Fujinuma et al. 2005). We can assume that these patterns are more profound in old-growth forests, where trees are long-lived and tend to maintain these different influences for long periods of time. 10.4 Pit-and-Mound Topography in Old-Growth Forest In addi tion to root gaps, small scale gap-phase disturbance in old-growth forests may also lead to heterogeneity in soil conditions, when trees are blown over and their root plates are tipped up (Liechty et al. 1997). Since the risk of windthrow increases wi th tree height, this phenomenon is more common in taller, older forests than in young forests. In addition, the volume of the pits created by uprooting and the size of the mound resulting from the decay of the root plate are strongly related to tree size (Putz 1983; Clinton and Baker 2000). The importance of this phenome- non differs with forest type, depending on the typical root development of the dominant species, which is often influenced by soil thickness and the soil water regime. In mixed species forests in the Carpathian Mountains and boreal forests in Central Russia, the surface area covered by pits and mounds ranged from 6.5 to 25% (Ulanova 2000). The latter case is obviously the result of a catastrophic windthrow event. In northern hardwood , and hemlock-hardwood old-growth forests in Michigan, the surface area in pit-and-mound topography shaped by recent windthrow events was 27% and 33%, respectively (Liechty et al. 1997). Both pits and mounds can be associated with important ecosystem functions. The uprooting of trees bares mineral soil, which may be required for the regenera- tion of species with small seeds or that otherwise have difficulty in germinating and becoming established on thick forest floors (Bazzaz 1996). In addition, the root plates or mounds constitute microsites with higher light availability or reduced competition. For example, Nakashizuka (1989) showed for an old-growth mixed temperate forest with a bamboo understorey that the mounds created through tree fall were more important for tree regeneration particularly for species with small seeds than the gaps created at the same time. Often, mounds are characterised by favourable conditions for root growth, which result from the forest floor mixing with mineral soil, increased soil temperature and favourable soil moisture regimes, especially when the surrounding soils are not free-draining (Clinton and Baker 2000). Mounds may also be sites of increased soil faunal activity (Troedsson and Lyford 1973). At the same time, pits represe nt microsites that accumulate forest floor material and are often moister than their surroundings (Beatty and Stone 1986; 10 Rooting Patterns of Old Growth Forests 219 Liechty et al. 1997). Mound disturbance is also very important in boreal or alpine forests, in which nutrients become locked up in the forest floor; the mixing of forest floor with mineral soil remobilises these nutrients. For Picea sitchensis-Tsuga heterophylla forests in south-east Alaska, Bormann et al. (1995) calculated that windthrow and associated soil mixing is required every 200 to 400 years to maintain soil fertility (see Chap. 9 by Wardle, this volume). Although the creation of pit-and-mound micro-topog raphy has some important ecosystem functions and clearly contributes to soil heterogeneity, particularly in old forests, there is no information on its effect on rooting patterns, and little information on its effect on soil biodiversity. However, pits and mounds as well as coarse woody debris (CWD) appear to be important structures in maintaining the diversity of vascular plants in old-growth forests, especially where these have to compete with an understorey of shade-tolerant tree seedlings (Miller et al. 2002). Whether the maintenance of aboveground plant species diversity, through specific associations with belowground micro-flora and fauna, provides positive feedback to belowground biodiversity is uncertain. The diversity of mycorrhizal fungi does not follow patterns of plant diversity (Allen et al. 1995). If mounds are a preferred substrate for tree growth, and hence colonisation by roots, this may also create positive feedback leading to spatial variation in the accumulation of organic matter. 10.5 Old-Growth Structures Harbouring Roots It has been recognised that so-called ‘‘residual structural elements’’ play an impor- tant role in the conservation of biodiversity in managed forests (Franklin et al. 1997). The term describes structures such as standing dead trees (snags), logs on the ground, residual live trees, and undisturbed vegetation patches, which can be found following natural disturbance events in old forests, but which are usually removed or are much reduced when forests are harvested regularly. Franklin et al. (1997) created the term ‘‘life-boating’’ for the retention of these structures in managed forest ecosystems to illustrate the function of these structures as refuges for different taxonomic groups during the re-organisation and aggradation phase of ecosystem development. Interestingly, this concept has been applied so far only to aboveground structures. Therefore, we might ask whether old-growth forests also have belowground structural elements that provide important habitat or are impor- tant for ecosystem functions following disturbance. Obvious candidates for such residual structures are root channels. Are there more, deeper root channels in old- growth forests, and what are their functions? Root channels can be create d by soil cracks or by old, decaying roots. Such channels constitute preferential flow paths for seepage water, act as dispersion pathways for microorganisms and invertebrates, and facilitate root movement through the soil and possibly the deep rooting of young trees. Based on measure- ments of soil microbial biomass and activity, Bundt et al. (2001a) have suggested 220 J. Bauhus [...]... more strongly in nutrient-enriched soil patches than species with larger mean root diameters In the context of this chapter, we need to ask whether belowground functional diversity associated with different fine root systems might increase with forest developmental phase, and whether it might differ in old- growth forests from that found in other successional stages Some old- growth forests are characterised... seasonally water-logged conditions, it is easy to picture how stratification might develop, but whether this phenomenon becomes more or less accentuated with stand age has not been investigated However, 10 Rooting Patterns of Old Growth Forests 225 increasing nutrient limitations owing to the accumulation of forest floor material might lead to more pronounced stratification in old- growth forests 10. 7 Conclusions... soil chemical, biological and hydrological properties and processes in old- growth forests (see also Chap 11 by Gleixner et al., this volume) While not strictly regarded as contributing to belowground structural diversity, structural features of the forest floor such as CWD, which is often more prominent in old- growth than in younger forests (Chap 8 by Harmon, this volume), also may contribute to the spatial... (e.g Dell et al 1983; Nepstad et al 1994), there is no indication that fine roots extend to greater depth in old- growth forests This is also unlikely, since the maximum vertical extent of root systems will probably be related to the transpirational demand of the vegetation, which is not higher in old- growth stands (e.g Vertessy et al 1996) A number of studies have described stratification of root systems... 10. 3 Reduction in conifer fine root biomass and mycorrhizal root tips in different micro sites in a 50 m gap as compared to Douglas fir old growth (Vogt et al 1995) et al 2003), and Graham et al (1994) showed that continual provision of CWD is important for a high level of ectomycorrhizal infections in conifer roots in forest ecosystem soils in the Rocky Mountains Large amounts of CWD in old- growth forests, ... tree fall gap dynamics of old growth nothofagus forests in Tierra del Fuego, Argentina J Veg Sci 4:642 654 Reich PB, Tjoelker MG, Walters MB, Vanderklein DW, Buschena C (1998) Close association of RGR, leaf and root morphology, seed mass and shade tolerance in seedlings of nine boreal tree species grown in high and low light Funct Ecol 12:327 338 10 Rooting Patterns of Old Growth Forests 229 Ritter E,... about the longevity of such channels We can imagine that root channels may be more abundant in old- growth forests, since these forests contain more structural roots, which provide channels upon their death and decay However, the rate of formation of root channels can also be high, if not higher, in selection forests, where single trees or groups of trees are harvested at regular intervals and their stumps... distribution in the long term (see also Lusk 1995) There may be other particularly important microsites for fine root growth in old- growth forests, such as the skirts around the base of trees created by litterfall, especially bark shedding; however, no information is available on this subject 10. 6 Influence of Stand Age on Diversity of Functional Root Types, Mycorrhizae, and the Vertical Patterning of Root.. .10 Rooting Patterns of Old Growth Forests 221 that root channels can be continual hot-spots of soil activity Preferential flow paths appear to be particularly stable in uncultivated or old forest soils (Beven and Germann 1982) They facilitate the transport of immobile nutrients such as phosphorus,... complementarity of specific traits is not known In most situations, the development of forests towards old- growth conditions represents a strong environmental filter selecting for shade tolerant species that can regenerate in the understorey or in gaps However, shade tolerance often has been linked to low relative growth rates, low specific root length and low root length ratios (root length per unit . was shown that fine root growth, mortality and decomposition in 4-year -old stands was as high, if not higher, than in 1 0-, 2 9-, or 8 0- to 10 0- year -old stands of an oak-hickory forest.Wheredataonfinerootbiomassfrom the. Chapter 10 Rooting Patterns of Old- Growth Forests: is Aboveground Structural and Functional Diversity Mirrored Belowground? Jurgen Bauhus 10. 1 Introduction When we think of old- growth forests, . influences for long periods of time. 10. 4 Pit-and-Mound Topography in Old- Growth Forest In addi tion to root gaps, small scale gap-phase disturbance in old- growth forests may also lead to heterogeneity