Resprouters vs reseeders in South African forest trees; a model based on forest canopy height

1. We expect tree species that regenerate primarily by sprouting to produce fewer seedlings than co-occurring species that regenerate mainly from seedlings, because of the trade-off between allocating resources either to ensuring vegetative reproduction (e.g. protective bark/latent buds) or to sexual reproduction (e.g. seeds).
2. Furthermore, resprouting species, because of their multi-stemmed nature, should be at a relative disadvantage, and therefore relatively infrequent, in tall forests. This is because a resprouting individual allocates resources to a number of basal branches/stems and buds rather than maximizing vertical extension of a single leader, as is the case in a seeder. Also, many tall stems arising from the same multi-stemmed base, as is the case in resprouters, will be relatively poorly supported in comparison to the single stem of a reseeder.
3. To test these two ideas we surveyed a number of plots in a range of South African forests and thicket communities. We noted the numbers of seedlings and resprouts for each species and determined a mean for each site.
4. Short forests and thickets were dominated by multi-stemmed species and there was an almost total absence of seedlings. In contrast, tall forests were dominated by single-stemmed reseeding species and were accompanied by seedlings.     

Resource allocation and storage relative to resprouting ability in wind disturbed coastal forest trees

Many plants persist by resprouting after disturbance. However, the benefits of resprouting (survival) may be traded off against height growth and reproduction. Resources (total non-structural carbohydrates—TNC) that could be allocated to growth or reproduction are stored or mobilised to support resprouting. TNC may either be stored by accumulation where availability exceeds the requirements for growth, or by reserve formation when storage is at the expense of growth. Thus, the mechanism of storage and resource allocation may differ between good (R+) and poor (R?) resprouters in response to nutrient availability and disturbance regime. R+ species typically reserve resources to ensure a rapid resprouting response to disturbance. We test whether R+ and R? species in coastal forest, under chronic wind disturbance, differ in growth rates, biomass allocation, leaf traits, water relations and storage of TNC. Seedlings from three confamilial pairs of R+ and R? tree species were subjected to nitrogen addition, water stress and clipping (simulating herbivory) treatments under greenhouse conditions. R? species had greater height growth rates, larger specific leaf area, lower root mass ratio and lower root TNC than R+ species. These differences between R+ and R? species were maintained irrespective of the levels of nitrogen, water and clipping treatments. R+ species did not increase their TNC concentration under nutrient and water stress, indicating that TNC is stored by reserve formation. R+ species appeared to trade-off growth against storage, while R? species did not. In R+ species, reserve formation is likely a bet-hedging strategy against occasional strong selection events in addition to chronic wind stress. By trading off height growth for better resprouting ability, good resprouters may be able to persist at more frequently disturbed sites (e.g., dune crests and windward slopes), while poor resprouters that have faster height growth can dominate less disturbed sites.     

Resprouting enhances seedling persistence in a subtropical coastal dune forest

In theory, resprouting enables species with low reproductive output (i.e., few seedlings) to persist. The advantage conferred by seedling sprouts on tree species persistence was evaluated in a subtropical coastal dune forest in South Africa. Species with a higher frequency of seedling sprouts demonstrated greater persistence as evidenced by a larger proportion of seedlings >1 year old and a larger seedling bank than species with few seedling sprouts. Resprouted seedlings had a larger basal diameter than true seedlings. Although resprouting resulted in the maintenance of multiple stems in some seedlings, the proportion of multi‐stemmed seedlings was low. Multi‐stemming was not a favoured form of seedling growth except in one species that occupied relatively open sites. Despite the apparent difference among species in resprouting ability, we found that seedling resprouting was not phylogenetically constrained. These results demonstrate that seedling sprouts form an important component of seedling banks in coastal dune forest.     

Stem demography and post-fire recruitment of a resprouting serotinous conifer

Abstract. The contribution of resprouts and seedling recruitment to post-fire regeneration of the South African fynbos conifer Widdringtonia nodiflora was compared eight months after wildfires in 1990. Stems on all trees were killed by fire but resprouting success was > 90 % at all but one site. A demographic study of burned skeletons revealed that prior to these fires, nearly all plants were multi-stemmed (4–9 stems/plant) and multi-aged, indicating continuous sprout production between fires. All stems were killed by these 1990 fires and at most sites > 90 % of the stems were burned to ground level. All diameter stems were susceptible to such incineration as, at most sites, there was no difference in average diameter of stems burned to ground level and those left standing. Individual genets usually had all ramets incinerated to ground level or all ramets charred, but intact, suggesting certain micro-sites burned hotter, whereas other sites were somewhat protected. Although not true of the 1990 fires, there was evidence that occasionally Widdring-tonia stems may survive fire. At one site, four of the 16 plants sampled had a burned stem twice as old as the oldest burned stem on the other 12 plants at the site, suggesting some stems had survived the previous fire (ca. 1970) and this conclusion was supported by fire-scars on these four stems that dated to ca. 1970. Based on the highly significant correlation between stem diameter and cone density left standing after the 1990 fires, we calculated that for most sites > 80 % of the initial cone crop was incinerated by fire. This is important because we observed a strong relationship between size of the canopy cone crop surviving fire and post-fire seedling recruitment. Under these conditions we hypothesize that sprouting confers a selective advantage to genets when fires cause heavy losses of seed. The infrequent occurrence of sprouting in the Cupressaceae suggests the hypothesis that resprouting is an apomorphic or derived trait in Widdringtonia. Data from this study suggests resprouting provides a selective advantage under severe fynbos fires, which are not only 'stand-replacing fires,’but also are intense enough to incinerate cone-bearing stems.     

Sprouting capacity of <Emphasis Type="Italic">Persea borbonia</Emphasis> and maritime forest community response to simulated laurel wilt disease

There are numerous examples of how exotic insect pests and pathogens have altered the dominance of native tree species. Changes to the structure of associated communities will depend on whether the affected species survives and if so, the degree to which it is diminished. In the southeastern USA, Persea borbonia, a common tree found in many coastal plain habitats, is the primary host of laurel wilt disease (LWD); infection rates and main-stem mortality are catastrophically high (>90%) in invaded populations. We simulated the effects of LWD prior to its arrival in coastal Mississippi by girdling and then removing the main stems of P. borbonia trees. Over a 2-year period, we monitored P. borbonia persistence via basal resprouts, understory light availability, and community structure. Removal of P. borbonia main stems resulted in a 50% increase in light transmission (measured at 1 m above ground level). All treated individuals produced basal resprouts, the size and number of which were positively related to initial tree girth. Post-treatment increases in basal area were greatest for the sub-canopy species, Ilex vomitoria, and were significantly higher in treatment versus control plots. Woody seedlings and herbaceous plants showed no significant trends in composition and abundance over time or between control and treatment plots. Our results suggest that removal of P. borbonia and subsequent resprouting causes shifts in P. borbonia size class frequencies and sub-canopy species dominance but has negligible impacts on understory plant community dynamics.     

Photosynthetic, hydraulic and biomechanical responses of Juglans californica shoots to wildfire

Leaf gas exchange and stem xylem hydraulic and mechanical properties were studied for unburned adults and resprouting burned Juglans californica (southern California black walnut) trees 1 year after a fire to explore possible trade-offs between mechanical and hydraulic properties of plants. The CO₂ uptake rates and stomatal conductance were 2–3 times greater for resprouting trees than for unburned adults. Both predawn and midday water potentials were more negative for unburned adult trees, indicating that the stems were experiencing greater water stress than the stems of resprouting trees. In addition, the xylem specific conductivity was similar in the two growth forms, even though the stems of resprouting trees were less vulnerable to water-stress-induced embolism than similar diameter, but older, stems of adult trees. The reduced vulnerability may have been due to less cavitation fatigue in stems of resprouts. The modulus of elasticity, modulus of rupture and xylem density were all greater for resprouts, indicating that resprouts have greater mechanical strength than do adult trees. The data suggest that there is no trade-off between stem mechanical strength and shoot hydraulic and photosynthetic efficiency in resprouts, which may have implications for the success of this species in the fire-prone plant communities of southern California.     

Stem demography and post fire recruitment of Podocarpus drouynianus: a resprouting non-serotinous conifer

Podocarpus drouynianus is unusual in the Podocarpaceae and conifers in general in being a strongly resprouting species which thrives in a fire-prone environment. The species is a dioecious, multi-stemmed shrub endemic to the eucalypt forests of the south-west of Western Australia. Stems are killed by fire but it is able to regenerate its foliage from a lignotuber. The total bud bank seems to be released by burning and death of the shoots, while pruning without fire releases only a proportion of available buds. Growth rate of resprouts is initially rapid, with stems reaching 25% of their mature length in the first year after fire. However, growth of juvenile plants is very slow. Fire promotes cone production on the new stems about one year after fire. The large seed is recalcitrant but timing of germination coincides with the wettest time of the year in the area where the species grows. Pyrogenic coning avoids loss of seed due to severe fires and is a form of mast reproduction that benefits this species by increasing pollen transfer and producing a mass seed crop to attract the primary vertebrate disperser – the emu. The strong resprouting ability ensures the species is resilient to frequent disturbance and to severe predation of the seed crop. Vertebrate dispersal tends to concentrate seed lots, making them vulnerable to predation if they are deposited in open areas. However, being dispersed by a large vertebrate will ensure long-distance dispersal, often to areas beyond that which was subject to fire. These would include vegetated areas, where the large seeds could lodge in safe sites and produce seedlings that are able to survive under the shade of established plants. © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 149 , 433–449.     

Tissue water relations of three chaparral shrub species after wildfire

Summary We compared the tissue water relations among resprouts and seedlings of three chaparral species during the first summer drought after wildfire. Two of the species, Rhus laurina and Ceanothus spinosus recover after fire by a combination of resprouting and seedling establishment (facultative resprouters), whereas a third species, Ceanothus megacarpus recovers by seedling establishment alone (obligate seeder). Our objectives were to document any differences in tissue water characteristics that might arise between resprouts and seedlings and to test the hypothesis that seedlings of obligate seeders develop more drought tolerant characteristics of their tissues than seedlings of facultative resprouters. We found that resprouts had much higher predawn values of water potential, osmotic potential, and turgor potentials than seedlings. Predawn turgor potentials of resprouts were 1.5 MPa through July and August when turgor potentials for seedlings remained near 0 MPa. During summer months, midday water potentials were 2 to 3 MPa higher for resprouts than seedlings and midday conductances of resprouts were two to five fold greater than those of seedlings. Even though resprouts did not experience severe water stress like seedlings, their tissue water characteristics, as determined by pressure-volume curve analyses, were similar by the peak of the drought in August. Further-more, the tissue water characteristics of seedlings from the obligate seeder, C. megacarpus, were similar to those of facultative resprouters — R. laurina, and C. spinosus. We attribute the observed differences in plant water status between resprouts and seedlings to differences in rooting depths and access to soil moisture reserves during summer drought. We conclude that the higher growth rates, photosynthetic performance, and survivorship of postfire resprouts are primarily a result of higher water availability to resprouting tissues during summer months. It appears that the greater seedling survivorship during summer drought observed for the obligate seeder, C. megacarpus, is not associated with more favorable tissue water characteristics.     

Long-term post-fire resprouting dynamics and reproduction of woody species in a Brazilian savanna

Resprouting is an efficient life history strategy by which woody savanna species can recover their aboveground biomass after fire. However, resprouting dynamics after fire and the time it takes to start producing flowers and fruits are still poorly understood, especially for the Brazilian savanna (Cerrado biome), where fire is an important driver of vegetation structure and ecosystem functioning. We investigated the resprouting dynamics and production of flowers and fruits of 26 woody species (20 tree and 6 shrub species for a total of 485 individuals) that were burned and the production of flowers and fruits for a subset of 12 species (139 individuals) in an unburned area in a Brazilian savanna. We classified the species’ resprouting strategies as hypogeal (at the soil level, with main stem death), epigeal (on the main stem or crown), and hypogeal + epigeal. We used generalized linear mixed-effect models to identify the post-fire recovery patterns for five years. Individuals with basal resprouts (hypogeal and hypogeal + epigeal resprouting) produced an average of 6 basal resprouts, but only 33% of resprouts survived after five years. Individuals in burned areas produced fewer flowers and fruits than individuals in unburned areas. At least a subset of individuals in all the resprouting strategies started to produce flowers and fruits in the first-year post-fire. About 68% of the species with hypogeal resprouts produced flowers and fruits in the first-year post-fire, but the intensity of flowering and fruiting was lower compared to individuals with other resprouting strategies over time. Although woody species have invested in post-fire growth and sexual reproduction in all resprouting strategies, the long time needed to recover these processes can make these species more vulnerable to frequent fires.     

Tree growth and competition in a post-logging Quercus mongolica forest on Mt. Sobaek, South Korea

Secondary woodlands in South Korea cover most mountains from low to middle elevations. While general patterns of forest succession are well understood, little is known about mechanisms of stand recovery after disturbance. We examined the spatio-temporal variations in establishment, growth, size inequality, and mode of competition among trees in a 50-year-old post-logging Quercus mongolica-dominated stand. We further compared the growth and stem allometry of single trees, presumably of seed origin, with multi-stemmed trees resprouting from stumps. Q. mongolica formed the upper canopy 16–22 m tall, 88.3% of total stand basal area, and 36.2% of total stem density, with most trees established during the first post-logging decade (51.2% were resprouts). During the first three decades, the Q. mongolica recruits grew exponentially, and disproportionately more in diameter than few older reserved trees left after the last cutting. This substantially decreased size inequality. The reverse trend was observed from 1994 to 2004: larger trees grow more, indicating an increasing asymmetry of competition for light. Neighborhood analysis revealed that when target trees had more or larger neighbors, their exponential phase of growth was reduced and maximum size was decreased. After the 50 years of stand development, more than 70% of Q. mongolica showed growth decline as a result of competitive stress, and mortality was about 30%, concentrated in smaller size classes. Compared to single stems, resprouts within clones do not seem to compete less asymmetric as might be expected based on studies of clonal herbaceous plants and physiological integration within genets. As Q. mongolica was also negatively affected by competition from woody species currently prevailing in the lower tree stratum (Tilia amurensis, Acer mono, Fraxinus rhynchophylla, Acer pseudosieboldianum), we predict the stand will become increasingly dominated by these more shade-tolerant trees.     

Fitness and evolution of resprouters in relation to fire

There are many ways that plants may recover vegetatively from dieback caused by fires. Compared with fire-killed species, the presence of woody resprouters in fire-prone floras increases with fire frequency, though this is affected by site productivity that may have opposing correlates along different gradients. Population recovery is enhanced by resprouting when fecundity is low and/or seedling recruitment is not guaranteed. There is resource cycling between vegetative growth and storage but no clear trade-off between fecundity and storage, and more attention needs to be given to the role of somatic mutations in reducing fecundity. Seven fitness benefits of post-fire resprouting are noted that centre around the rapid return to adult growth rates and early flowering and seed set without the risks of recruitment failure. The extent of resprouting at the individual, population, and species levels varies greatly but it is under genetic control. Recent studies on the evolution of resprouting in fire-prone systems have shown that types of resprouting (clonality, rootstocks, epicormic bud strands) are derived from surrounding parent lineages lacking these traits and confined to non-fire-prone environments. The oldest lineages with fire-related resprouting date to at least 61 million years ago, indicating that seed plants have had a long evolutionary relationship with fire. Various genetic mechanisms, including beneficial somatic mutations, have been invoked to explain how speciation of resprouters may keep pace with non-sprouters.     

Post-fire regeneration strategies of Californian coastal sage shrubs

Summary Regeneration methods for coastal sage srub vegetation after fire were studied in the coastal Santa Monica Mountains of southern California. Six sites were sampled two years after a large fire of fall, 1978. The intensity of fire varied. Foliar cover and flowering incidence were recorded for individuals regenerating by resprouting or from seed. Resprouting plants contributed most to post-fire recovery, comprising 95% of the relative foliar shrub cover; 84% of resprout and 47% of seedling cover had flowered. An ANOVA of reproductive mode and fire intensity indicates that resprout total cover and individual size are significantly greater than those of seedlings, regardless of fire intensity. Among sites the average foliar cover of resprouts exceeded that of seedlings by factors ranging from 9 to 63. All coastal sage species examined resprout, although the potential vigor of resprouting appears to vary widely within genera (e.g. Encelia, Eriogonum, and Salvia) and even within species. In the second growing season following fire seedling density increased due to seeds shed by resprouted shrubs. Most of the cover on these stands of coastal sage scrub is destined to be either crown-sprouted individuals or their progeny.     

Resprouting responses of trees in a fire‐prone tropical savanna following severe tornado damage

Fire and windstorms can cause severe disturbance, but their consequences for trees may differ. Resprouting enables persistence through frequent and severe disturbance. To explore responses to an abnormal disturbance and evolutionary hypotheses about resprouting as an adaptation, we analysed patterns of resprouting in four taxa following a tornado in a tropical savanna (Kakadu National Park, northern Australia) that is frequently burnt but is rarely subject to severe windthrow. Resprouting (i.e. survival) rates varied markedly among taxa and damage types, from 35% in uprooted Acacia spp. (Mimosaceae) to over 90% in eucalypts (Myrtaceae) and Erythrophleum chlorostachys (Caesalpiniaceae) with persistent tertiary branches. Most resprouting was from the epicormic strand‐bank on the stem or branches. Across all taxa, greater architectural damage reduced resprouting rates. Damage was magnified by proximity to the centre of the tornado path, suggesting an additional effect of internal damage. Smaller trees, trees whose trunks were snapped below 2 m, and those closer to the tornado path were more likely to resprout basally or from the roots rather than epicormically, although in Acacia spp. these resprouting modes were positively correlated. We hypothesize that trees of fire‐prone savannas have evolved to grow rapidly out of the flame zone; this was supported by more detailed analyses of Eucalyptus tetrodonta suggesting that resprouts emerging nearer the ground grow faster. Resprouting at ground level may be a bet‐hedging strategy to spread the risk of mortality among multiple stems when elevated sprouting was not possible. We conclude that the adaptation of eucalypts to frequent fire does not jeopardize their survival (by comparison with the more generalist Acacia spp.) following severe windthrow, providing an example of ‘exaptation’ rather than trade‐off in fitness under contrasting stressors.     

When sex is not enough: ecological correlates of resprouting capacity in congeneric tropical forest shrubs

In moist tropical forests resprouting may be an important component of life history, contributing to asexual reproduction through the clonal spread of individuals derived from shoot fragments. However, in contrast to other ecosystems where resprouting is common, the ecological correlates of resprouting capacity in tropical forests remain largely unexplored. In this study we characterized shade tolerance, resprouting capacity and sexual reproductive success of eight co-occurring Piper species from lowland forests of Panama. In field experiments we found that shade-tolerant Piper species had a higher capacity to regenerate from excised or pinned stem fragments than light-demanding species in both gap and understory light conditions. In contrast, shade-tolerant species had lower recruitment probabilities from seeds, as a consequence of lower initial seed viability, and lower seedling emergence rates. All Piper species needed gap conditions for successful seedling establishment. Of 8,000 seeds sown in the understory only 0.2% emerged. In gaps, seed germination of light-demanding species was between 10 and 50%, whereas for shade-tolerant species it was 0.5–9.8%. We propose that the capacity to reproduce asexually from resprouts could be adaptive for shade-tolerant species that are constantly exposed to damage from falling litter in the understory. Resprouting may allow Piper populations to persist and spread despite the high rate of pre-dispersal seed predation and low seed emergence rates. Across Piper species, we detected a trade-off between resprouting capacity and the annual viable seed production per plant but not with annual seed mass produced per plant. This suggests that species differences in sexual reproductive success may not necessarily result from differential resource allocation. Instead we suggest that low sexual reproductive success in the understory may in part reflect reduced genetic diversity in populations undergoing clonal growth, resulting in self-fertilization and in-breeding depression.     

Solutions to fire and shade: resprouting,growing tall and the origin of Eurasian temperate broadleaved forest

Tree species of Eurasian broadleaved forest possess two divergent trait syndromes with contrasting patterns of resource allocation adapted to different selection environments: short-stature basal resprouters that divert resources to a bud bank adapted to frequent and severe disturbances such as fire and herbivory, and tall trees that delay reproduction by investing in rapid height growth to escape shading. Drawing on theory developed in savanna ecosystems, we propose a conceptual framework showing that the possession of contrasting trait syndromes is essential for the persistence of broadleaved trees in an open ecosystem that burns. Consistent with this hypothesis, trees of modern Eurasian broadleaved forest bear a suite of traits that are adaptive to surface and crown-fire regimes. We contend that limited opportunities in grassland restricts recruitment to disturbance-free refugia, and en masse establishment creates a wooded environment where shade limits the growth of light-demanding savanna plants. Rapid height growth, which involves investment in structural support and the switch from a multi-stemmed to a monopodial growth form, is adaptive in this shaded environment. Although clustering reduces surface fuel loads, these establishment nuclei are vulnerable to high-intensity crown fires. The lethal effects of canopy fire are avoided by seasonal leaf shedding, and aerial resprouting enhances rapid post-fire recovery of photosynthetic capacity. While these woody formations satisfy the structural definition of forest, their constituents are clearly derived from savanna. Contrasting trait syndromes thus represent the shift from consumer to resource regulation in savanna ecosystems. Consistent with global trends, the diversification of most contemporary broadleaved taxa coincided with the spread of grasslands, a surge in fire activity and a decline in wooded ecosystems in the late Miocene–Pliocene. Recognition that Eurasian broadleaved forest has savanna origins and persists as an alternative state with adjacent grassy ecosystems has far-reaching management implications in accordance with functional rather than structural criteria. Shade is a severe constraint to the regeneration and growth of both woody and herbaceous growth forms in consumer-regulated ecosystems. However, these ecosystems are highly resilient to disturbance, an essential process that maintains diversity especially among the species-rich herbaceous component that is vulnerable to shading when consumer behaviour is altered.     

Size Dependency of Post-Disturbance Recovery of Multi-Stemmed Resprouting Trees

In frequently burned ecosystems, many plants persist by repeated resprouting from basal or belowground buds. This strategy requires that plants reach a balance between biomass loss and recovery, which depends on the shape of the relationship between pre- and post-fire size. Previous analyses of this relationship, however, have focused on the size of the largest stem, which ignores the importance of the multi-stem growth habit that is common in pyrogenic ecosystems. We hypothesized that the presence of multiple stems causes a substantial shift in the relationship between pre- and post-fire size and in the relationship between pre-fire size and size recovery. We measured the height and basal diameter, then calculated volume and biomass, of all stems of six tree species before and nine months after complete removal of aboveground biomass via coppicing. The number of resprouts was correlated with the original number of stems for four species. For all species, the relationship between pre-coppicing and resprout size fit a positive curvilinear function, and the shape of this curve did not differ for maximum and total stem size. Smaller individuals recovered a larger proportion of their pre-coppicing size than larger individuals, but the shape of the size recovery curves were the same regardless of whether the analysis was performed with all stems or only the largest stem. Our results indicate that measuring only the largest stem of multi-stemmed individuals is sufficient to assess the ability of individuals to recover after complete loss of aboveground biomass and persist under frequent burning.     

Persistence on inselbergs: the role of obligate seeders and resprouters

Aim To investigate if the current theories associated with recruitment strategies are sufficient to explain differences in the proportions of obligate seeders and resprouters on inselbergs and in the matrix. Location The New England Batholith of eastern Australia. Methods The importance of life form and regenerative response of flora species are compared for twenty‐four archipelagos of inselbergs habitat islands and for their adjacent matrix. Forward stepwise multiple linear regression is used to correlate measured and modelled variables with differences in the proportional abundance of obligate seeders on inselbergs at three levels of sampling. Results A total of 216 inselbergs were surveyed and information on 826 vascular plant species was collated. Herbs were the most common life form both on and off inselbergs. There were generally more shrubs on inselbergs than in the matrix. Resprouters were more common everywhere. However, obligate seeders were proportionately more common on inselbergs. The degree of insularity of outcrop floras accounted for 23–37% of the variance in the proportional abundance of obligate seeders at three sampling scales. Main conclusions A model is proposed whereby the mechanisms that influence the abundances of obligate seeders and resprouters are different on inselbergs and in the matrix. Inselberg environments are harsh, arid, have limited safe recruitment sites and below ground resources, but are not light limited. In such habitats, obligate seeders with persistence life‐history traits are favoured. Within the matrix in eastern Australia frequent biomass removal disturbances occur (such as fire) and resprouting is advantageous. High turnover obligate seeders with no persistence life‐history traits can be favoured in the matrix with a reduced disturbance regime and where competition for light still occurs. Some of these matrix obligate seeders occur on inselbergs due to their infrequent disturbance regimes.     

Resprouting Ability of Six Atlantic Shrub Species

Resprouting from subterranean structures is a principal method of vegetative regeneration that many shrub species show after a disturbance. This study, therefore, aims to determine the resprouting capacity and intensity of six dominant species in an Atlantic shrubland area located in the NW of the Iberian Peninsula and compare their resprouting and germinating strategies. Resprouting intensity is measured using three variables: individual probability of resprouting, number of resprouts and length of these sprouts in three plant-age classes. The intensity for each species was calculated using a simple index (IRI) that included the three measured variables. All studied species, excepting Erica umbellata, could resprout. According to the IRI values, there are three groups of species: strong resprouters (Ulex europaeus, Ulex minor and Pterospartum tridentatum), weak resprouters (Ulex micranthus and Genista triacanthos) and non-resprouters (E. umbellata). The germination of strong resprouters is highly stimulated by fire. Frequent disturbances remove the non- and weak resprouter populations and promote the strong resprouter ones.     

Relationship between leaf traits and fire-response strategies in shrub species of a mountainous region of south-eastern Australia

Background and Aims

Resprouting and seed recruitment are important ways in which plants respond to fire. However, the investments a plant makes into ensuring the success of post-fire resprouting or seedling recruitment can result in trade-offs that are manifested in a range of co-occurring morphological, life history and physiological traits. Relationships between fire-response strategies and other traits have been widely examined in fire-prone Mediterranean-type climates. In this paper, we aim to determine whether shrubs growing in a non-Mediterranean climate region exhibit relationships between their fire-response strategy and leaf traits.

Methods

Field surveys were used to classify species into fire-response types. We then compared specific leaf area, leaf dry-matter content, leaf width, leaf nitrogen and carbon to nitrogen ratios between (a) obligate seeders and all other resprouters, and (b) obligate seeders, facultative resprouters and obligate resprouters.

Key Results

Leaf traits only varied between fire-response types when we considered facultative resprouters as a separate group to obligate resprouters, as observed after a large landscape-scale fire. We found no differences between obligate seeders and obligate resprouters, nor between obligate seeders and resprouters considered as one group.

Conclusions

The results suggest that facultative resprouters may require a strategy of rapid resource acquisition and fast growth in order to compete with species that either resprout, or recruit from seed. However, the overall lack of difference between obligate seeders and obligate resprouters suggests that environmental factors are exerting similar effects on species'' ecological strategies, irrespective of the constraints and trade-offs that may be associated with obligate seeding and obligate resprouting. These results highlight the limits to trait co-occurrences across different ecosystems and the difficulty in identifying global-scale relationships amongst traits.     

Structure and Dynamics of Populations of Japanese Barberry (Berberis Thunbergii DC.) in Deciduous Forests of New Jersey

Japanese barberry, Berberis thunbergii DC., has become a prominent exotic species in deciduous forests throughout the eastern and midwestern US. Populations range from small plants occurring at low densities to dense, impenetrable thickets of plants with up to 40 stems/individual. A study was undertaken at Morristown National Historical Park in New Jersey to document plant densities, plant size, recruitment through vegetative processes of new shoot initiation and clonal spread and recruitment from seedling establishment, and mortality of stems and plants. Nearly 2000 shoots on 370 plants were individually marked and followed for two growing seasons, and over 1000 seedlings were also individually marked and followed. Populations vary much more in total shoots/area than they do in plant individuals/area, or in mean plant size (shoots/plant), as even the sparse populations have a few large individuals. Shoot mortality is less than new shoot initiation, but most plants do not change in size or change by small numbers of stems. However, the number of new shoots per plant increases as plant size increases. Once plants have three stems, they suffer little or no mortality. Seedling establishment is proportional to the density of shoots, so that as plants grow in size, local recruitment from seed increases. Large numbers of seedlings, and a survival rate of 10%, combine to make seedling recruitment a major component of population increase. The combination of multiple forms of vegetative and seed-based population growth, and the very low rates of plant mortality due to the multi-stemmed growth form explains the ability of this invasive species to rapidly produce dense, persistent populations.