However, in this study, resprouting and multistemminess were the result of the tree-disturbance interaction and not a property of a plant or species and were not phylogenetically restricted. Because the disturbances are predominantly of low severity, leaning trees were able to regain the vertical orientation of the growing area by turning upward (a process referred to as 'up' in this study) and thus survive without regrowth. The greenhouse experiment was conducted in the Botanic Gardens of the School of Biological and Conservation Sciences under the supervision of Alison Young.
The frequency of shrubs in the forest is low due to the action of the herb Isoglossa woodii (Acanthaceae), which covers 65–95% of the forest understorey (Griffiths et al. 2007). The role of phylogeny, site productivity and disturbance frequency and severity in determining the influence of the persistence niche on species performance was analyzed (Fig. 2). A conceptual framework for the study of the role of resprouting and multistemm in forest structure and dynamics.
We investigate links between multistem fitness and phylogeny and examine spatial patterns in the distribution of multistem individuals relative to environmental gradients within subtropical forest. The number of multistemmed individuals was positively associated with substrate instability, wind disturbance and competition. Our analysis of stem sizes within multistemmed individuals shows that trees at Cape Vidal grow multiple.
We investigate the relationships between sprouting and turning of leaning trees and some of their functional correlates. Four predictions of the hypothesis that sprouting and twisting of the main stem represent alternative plant strategies that promote individual survival were tested. The logit transformation was applied to the probabilities of turning up and of a tree with a dead primary trunk.
There was a significant negative relationship between the probability of turning up and the probability of resprouting (Figure 2a; r2 = 0.40, P = 0.004, n = 19). Sample sizes of tree species in relation to leaning, sprouting, twisting of the trunk and whether or not the primary trunk is dead. Twisting of the trunk was more likely for small deviations from the vertical than for large angles of inclination of a trunk from the vertical.
Parameter estimates for the logistic regression of stem upturning at site and tree factors and variables. Frequency distribution of sprouting and twisting of stems of crooked trees by dune position. Several factors may explain the relationship between the probabilities of leaning, sprouting and upturning of stems.
In our study, upturning of stems was mostly associated with disturbances that caused small deviation angles of the main stem from the vertical.
Seedling sprouts usually have larger and older rootstocks than true seedlings of the same shoot size (Hara, 1987). The longer lifespan of seedling sprouts ensures the persistence of the seedling bank so that seedlings can take advantage of suitable growing conditions when they occur (Hara, 1987). Thus, understanding the composition and structure of seedling banks and the ecological importance of true seedlings versus seedling sprouts provides a better understanding of the regeneration dynamics of forest tree species.
In the coastal dune forests of KwaZulu-Natal studied here, a large proportion of adults of most tree species are multistory and we conclude that multistory is a tree-disturbance interaction trait rather than a species trait (Nzunda, Griffiths & Lawes, 2007a). The pH of the upper layer of the forest ranges from 6.7 to 7.4, and the organic matter content ranges from 4.6 to 6.2 percent of dry soil mass. The seedlings were classified according to the year of germination (i.e. the current year or previous years) and into true seedlings or sprouts.
Most of the remaining species had a density of < 1 seedling per square, except for Teclea gerrardii, M. Further evidence for the effect of germination on seedling persistence was provided by comparing the basal diameter of seedling sprouts and true seedlings. Re-sprouting of seedlings serves to increase seedling survival so that it can capture opportunities for niche regeneration in a forest, whereas re-sprouting (and multi-stemming) of adult trees ensures the persistence of already established individuals (i.e. maintenance of the persistence niche).
Financial support was provided by the National Research Foundation of South Africa (Focus Area: Conservation and Management of Ecosystems and Biodiversity; GUN: 2069339) and the Andrew W. The Mazda Wildlife Fund provided logistical support.
Plants can continue to germinate when only a portion of the aboveground biomass is damaged by disturbances such as hurricanes and volcanic eruptions (Basnet 1993; Bellingham, Tanner & Healey 1994; Boucher et al. We examined biomass and carbohydrate reserve allocation patterns for poor and good resprouters in a coastal dune forest where trees emerge mainly in response to chronic, low-severity disturbances that cause warping and partial uprooting (Nzunda et al. 2007a, b) We also conducted an experiment in which we felled trees and created stumps in two height classes to determine the effect of the remobilization of aboveground resources on the number and biomass of sprouts produced.
Important tree species in descending order include Diospyros natalensis (Ebenaceae), Mimusops caffra (Sapotaceae), Drypetes natalensis (Putranjivaceae), Celtis africana (Celtidaceae) and Ochna natalitia (Ochnaceae) (Nzunda et al. 2007a). TNC was not determined for leaves because leaf levels fluctuate diurnally in response to photosynthetic activity and starch export from leaves (Graham et al. Starch concentration was determined as glucose equivalents in residual ethanol extracts (Rose et al.).
However, the good reproducers in this study differ from reproducers in fire-prone habitats because they maintain higher concentrations of TNC in their stems than in their roots (Bell et al. 1996). In our study, good breeders had greater root:shoot ratios, root and stem TNC concentration, and number and dry mass of shoots produced from stems than poor breeders. Trees in our study area continue to reproduce in response to other disturbances, and depending on the severity of the disturbance, are clearly capable of using either or both below- and above-ground resources to reproduce.
This study highlights the adaptive advantage of germination through remobilization of aboveground resources and the importance of niche persistence (Bond & Midgley 2001) in this habitat.
These differences between poor and good respirators were maintained independent of the levels of nitrogen, water and rock treatment. Mean ± SE of relative growth rate for pairs of poor and good re-sprouts within families with and without nitrogen supplementation. Mean ± SE of root mass ratios for pairs of poor and good resprouts within families with and without nitrogen addition (see Figure 1 for family and seedling categories).
Thus, the TNC storage capacity of the studied species was based on the formation of reserves and not on accumulation. The greater allocation to root biomass and root storage of TNC for good resprouting plants than for poor resprouting plants in this study is similar to experimental results from fire-exposed environments (Knox & Clarke 2005; Schwilk & Ackerly 2005). The low severity of disturbances favors poor growers (Nzunda et al. 2007b), while the chronic nature of disturbances favors good growers (Nzunda et al. 2007a), resulting in coexistence.
Carbohydrate reserve formation is achieved at the expense of growth, so good sprouters have a lower growth rate than poor sprouters (Chapin et al. Because they have lower SLA than poor sprouters, good sprouters were more sclerophyllous than poor sprouters. Higher sclerophilia in good sprouters than poor sprouters resprouters in coastal dune forests is favored by drying coastal winds.
In contrast, in forests, good regrowth ability is associated with shallow roots (Sakai et al. 1997) and therefore a lower SLA for good regrowth prevents excessive water loss.
The forest has a high incidence of sprouting resulting in multistemming (Nzunda et al. 2007a). Diameter size-class distribution of main stems was evaluated using a size distribution index (SDI) which is the skewness coefficient of the diameter at breast height (dbh) distribution around the center of the dbh range (Nanami et al. 2004). Average size class distribution of top 20 tree species (according to importance value index rating of Nzunda et al. 2007a).
Higher allocation of resources to root biomass and storage due to good regenerating than poor regenerating (Nzunda et al. 2008b) results in lower seed investments due to good regenerating than poor regenerating (Bond & Midgley 2003). Larger seeds from poor resprouters may have a greater chance of emergence deeper in the soil and greater seedling survival in the first year than smaller seeds from good resprouters (Brown et al. 2003). Recruitment of new individuals from seedlings is limited for good sowers because they occupy dune tops and seaward slopes exposed to sea breezes and prefer resprouting rather than reseeding (Nzunda et al. 2007a, b).
In response to tilting, good reproducers mostly sprout and lose the primary stem, while poor reproducers mainly regain the vertical orientation of the primary stem and thus avoid reproduction (Nzunda et al. 2007b). Because of their lower growth rate, good breeders tend to be restricted to sites with more disturbance than those occupied by poor breeders at Cape Vidal as well as elsewhere (Kruger et al. 1997; Nanami et al. 2004). , because in less disturbed places good resprouters are over-populated quickly by poor resprouters.
Thus, good resrouters at Cape Vidal were most common on dune crests and seaward slopes exposed to strong offshore winds (Nzunda et al. 2007a).
At Cape Vidal, good resprouters stored more resources below and above ground than poor resprouters. At Cape Vidal, good resprouters had lower growth rates and produced fewer seeds with lower individual seed mass than poor resprouters. As a result, good resprouters had lower seedling abundance and limited seedling recruitment to young and adult trees.
However, as elsewhere, the lower recruitment of new specimens by good re-sprouts at Cape Vidal was compensated by greater persistence due to the production of more shoots than poor re-sprouts (Kruger et al. Thus, good re-sprouts at Cape Vidal were most common on dune ridges and slopes facing the sea that have been exposed to strong sea winds Less investment in seeds by good growers results in less production of seedlings and new specimens from seedlings.
Therefore, good sprouts were most common on dune ridges and seaward slopes exposed to sea winds. Because of the cost of resprouting in terms of storage allocation found in this study (Nzunda et al. 2008a), poor resprouting in chronically disturbed environments may also mature earlier than good resprouting. Good re-sprouts are more likely to be lean than poor ones (Sakai et al. 1997; Nzunda et al. 2007).
In addition to higher seedling growth rates for poor reproducers than good reproducers (Chapter 6), reproductive ability has also been associated with lower seedling survival (Bond & Midgley 2003).
