Clonal Shrub Research Articles

Combined effects of fire and drought are not sufficient to slow shrub encroachment in tallgrass prairie.

Woody encroachment-the spread of woody vegetation in open ecosystems-is a common threat to grasslands worldwide. Reversing encroachment can be exceedingly difficult once shrubs become established, particularly clonal species that resprout following disturbance. Single stressors are unlikely to reverse woody encroachment, but using multiple stressors in tandem could be successful in slowing or reversing encroachment. We explored whether increasing fire frequency in conjunction with multi-year drought could reduce growth and survival of encroaching shrubs in a tallgrass prairie in northeastern Kansas, USA. Passive rainout shelters (~ 50% rainfall reduction) were constructed over mature clonal shrubs (Cornus drummondii) and co-existing C4 grasses in two fire treatments (1-year and 4-year burn frequency). Leaf- and whole-plant level physiological responses to drought and fire frequency were monitored in shrubs and grasses from 2019 to 2022. Shrub biomass and stem density following fire were unaffected by five years of consecutive drought treatment, regardless of fire frequency. The drought treatment had more negative effects on grass leaf water potential and photosynthetic rates compared to shrubs. Shrub photosynthetic rates were remarkably stable across each growing season. Overall, we found that five consecutive years of moderate drought in combination with fire was not sufficient to reduce biomass production or stem density in an encroaching clonal shrub (C. drummondii). These results suggest that moderate but chronic press-drought events do not sufficiently stress encroaching clonal shrubs to negatively impact their resilience following fire events, even when fire frequency is high.

Save or spend? Diverging water‐use strategies of grasses and encroaching clonal shrubs

Abstract Shrub encroachment is one of the primary threats to mesic grasslands around the world. This dramatic shift in plant cover has the potential to alter ecosystem‐scale water budgets and responses to novel rainfall regimes. Understanding divergent water‐use strategies among encroaching shrubs and the grasses they replace is critical for predicting shifts in ecosystem‐scale water dynamics as a result of shrub encroachment, particularly if drought events become more frequent and/or severe in the future. In this study, we assessed how water‐use traits of a rapidly encroaching clonal shrub (Cornus drummondii) and a dominant C4 grass (Andropogon gerardii) impact responses to changes in water availability in tallgrass prairie. We assessed intra‐annual change in depth of water uptake, turgor loss point and stomatal regulation in each species. Sampling took place at Konza Prairie Biological Station (northeastern KS, USA) during the 2021 and 2022 growing seasons. Cornus drummondii shifted from shallow to deep soil water sources across the 2021 and 2022 growing seasons. This plasticity in depth of water uptake facilitated a ‘wasteful’ water‐use strategy in C. drummondii, where stomatal conductance and transpiration rates continued to increase even when no further gain in photosynthetic rate occurred. A. gerardii photosynthetic rates and stomatal conductance were more variable through time and were more responsive to changes in leaf water potential than C. drummondii. However, intra‐annual adjustment of turgor loss point was more pronounced in C. drummondii (ΔπTLP = −0.48 MPa ± 0.15 SD) than in A. gerardii (ΔπTLP = −0.29 MPa ± 0.19 SD). Synthesis. These results suggest that C. drummondii is highly resilient to changes in water availability in surface soils and will likely remain unaffected by future droughts unless they are severe enough to reduce the availability of deep soil water. Given that clonal shrubs are key invaders of grasslands world‐wide, increased leaf‐level water loss is expected to accelerate ecosystem‐level drying as clonal shrub encroachment proceeds in mesic grasslands.

Shelterwood harvests promote high breeding bird diversity and shrubland species for less than 10 years in hardwood forests

We compared forest structure and breeding bird communities between shelterwood harvests (SW; n = 15) and mature upland hardwood forests (M; n = 16) over 17 years (Y). Both were relatively static throughout the study period in M. In contrast, heavy canopy reduction and increased light after timber harvests in SW initiated rapid increases in small tree stem densities and shrub cover driven primarily by blackberry (Rubus spp.) - a clonal shrub that “pioneers” recently disturbed, high-light environments. This open-canopy forest structure with low, dense vegetation was short-lived; young trees reached canopy closure within 10 years, with concomitant reductions in blackberry cover and stem density. Total abundance, species richness, and diversity of breeding birds was greater in SW than M, especially the first several years post-harvest; in Y6 these metrics were more than twice as high in SW as in M. Higher abundance, richness, and diversity in SW was driven by an influx of shrubland associates (indigo buntings (Passerina cyanea), chestnut-sided warblers (Setophaga pensylvanica), Eastern towhees (Pipilo erythrophthalmus)) and positive or neutral responses by most other species; only ovenbirds (Seiurus aurocapilla) were more abundant in M. Abundances of shrubland bird species in particular tracked temporal changes in SW forest structure but each differed slightly in their patterns of increase, peak (with 15–26 times more in SW than M), and decline. By Y10 breeding bird communities in SW resembled those in M, although total abundance, species richness, and diversity remained slightly higher in SW throughout the study period. Total abundance, species richness, diversity, and abundance of shrubland bird species were positively- and ovenbird was negatively correlated with blackberry cover, indicating that it is a suitable stand-alone predictor of post-disturbance young forest and changes in breeding bird communities as forests mature. Our results show that young hardwood forests provide habitat for shrubland bird species and promote high breeding bird diversity for <10 years.

Climate Overrides the Influence of Microsite Conditions on Radial Growth of the Tall Multi-Stemmed Shrub Alnus alnobetula at Treeline.

Green alder (Alnus alnobetula), a tall multi-stemmed deciduous shrub, is widespread at high elevations in the Central European Alps. Its growth form frequently leads to asymmetric radial growth and anomalous growth ring patterns, making development of representative ring-width series a challenge. In order to assess the variability among radii of one shoot, among shoots belonging to one stock and among stocks, 60 stem discs were sampled at treeline on Mt. Patscherkofel (Tyrol, Austria). Annual increments were measured along 188 radii and analyzed in terms of their variability by applying dendrochronological techniques. Results revealed a high agreement in ring-width variation among radii of one shoot, among shoots of one stock and largely among stocks from different sites, confirming the pronounced limitation of radial stem growth by climate forcing at the alpine treeline. In contrast to this, a high variability in both absolute growth rates and long-term growth trends was found, which we attribute to different microsite conditions and disturbances. These factors also override climate control of radial growth under growth-limiting environmental conditions. Based on our findings we provide recommendations for the number of samples needed to carry out inter- and intra-annual studies of radial growth in this multi-stemmed clonal shrub.

Evidence for scale-dependent root-antation feedback and its role in halting the spread of a pantropical shrub into an endemic sedge.

Vegetation pattern formation is a widespread phenomenon in resource-limited environments, but the driving mechanisms are largely unconfirmed empirically. Combining results of field studies and mathematical modeling, empirical evidence for a generic pattern-formation mechanism is demonstrated with the clonal shrub Guilandina bonduc L. (hereafter Guilandina) on the Brazilian island of Trindade. The mechanism is associated with water conduction by laterally spread roots and root augmentation as the shoot grows-a crucial element in the positive feedback loop that drives spatial patterning. Assuming precipitation-dependent root-shoot relations, the model accounts for the major vegetation landscapes on Trindade Island, substantiating lateral root augmentation as the driving mechanism of Guilandina patterning. Guilandina expands into surrounding communities dominated by the Trindade endemic, Cyperus atlanticus Hemsl. (hereafter Cyperus). It appears to do so by decreasing the water potential in soils below Cyperus through its dense lateral roots, leaving behind a patchy Guilandina-only landscape. We use this system to highlight a novel form of invasion, likely to apply to many other systems where the invasive species is pattern-forming. Depending on the level of water stress, the invasion can take two distinct forms: (i) a complete invasion at low stress that culminates in a patchy Guilandina-only landscape through a spot-replication process, and (ii) an incomplete invasion at high stress that begins but does not spread, forming isolated Guilandina spots of fixed size, surrounded by bare-soil halos, in an otherwise uniform Cyperus grassland. Thus, drier climates may act selectively on pattern-forming invasive species, imposing incomplete invasion and reducing the negative effects on native species.

Development and characterization of microsatellite markers for Ardisia japonica (Primulaceae), an evergreen clonal dwarf shrub

ABSTRACT Microsatellite markers were first developed for Ardisia japonica (Primulaceae), an evergreen clonal shrub that commonly grows in the understory of various types of temperate forests in East Asia. Of the 69 primer pairs designed based on genomic sequence data, 13 pairs showed clear microsatellite peaks and allelic polymorphisms with tetraploidy in ramets from two populations. Ramets were successfully assigned to multilocus lineages (genets) using microsatellite markers. The number of alleles per locus ranged from 3 to 8, and the observed heterozygosity ranged from 0.468 to 0.881. These will be useful for the assignment of genets and for investigating the genet-level population genetics and ecology of the understory clonal shrub.

Radial Stem Growth of the Clonal Shrub Alnus alnobetula at Treeline Is Constrained by Summer Temperature and Winter Desiccation and Differs in Carbon Allocation Strategy Compared to Co-Occurring Pinus cembra

Green alder (Alnus alnobetula) is currently the most expanding shrub species in the Alps. Because dense thickets impair tree establishment, understanding how climate affects shrub growth is essential for predictions of treeline dynamics. We evaluated ring width data from &gt;50 A. alnobetula stems sampled at treeline on Mt. Patscherkofel (Central European Alps, Austria) to identify main climatic drivers and influence of climate warming on radial stem growth (RG). We also compared RG of A. alnobetula with RG of the co-occurring treeline conifer Swiss stone pine (Pinus cembra). We addressed our questions through calculation of response functions and evaluation of climate in years showing exceptional growth deviations. Response function analyses and evaluation of growth trends during 1991–2020 revealed that RG of A. alnobetula is significantly and directly related to summer temperatures. Precipitation in January also showed a direct relationship to RG, indicating effects of frost drought on RG. Surprisingly, nitrogen fixing A. alnobetula showed strikingly lower RG compared to P. cembra, and the latter also responded more strongly to the increase in summer temperature in the course of climate warming. We explain these findings by different carbon allocation strategies, i.e., preference of “vertical” stem growth in late successional P. cembra vs. favoring “horizontal” spread in the pioneer shrub A. alnobetula.

What and Why: South Dakota Rangeland Livestock Producers’ Usage of Parasiticides

In many mesic grasslands, such as the central Great Plains in North America, frequent fire is a key regulator of ecological processes. Long periods of infrequent fire facilitate the conversion of herbaceous-dominated grassland to woody-dominated shrubland or woodland. At the Konza Prairie Biological Station in northeast Kansas, one infrequently burned portion of the landscape has undergone transformation from grassland to woodland after nearly 30 yr without fire. In Spring 2017, a prescribed burn was implemented to assess fire effectiveness on woody plant mortality. A postfire census of 3 000+ individual woody plants identified the distribution of species by size (height), topographic position, and slope on the landscape. Mortality and canopy fire damage were calculated for each individual. In lowland locations with near-continuous shrub cover (30.7% of the landscape), woody plants were unaffected by fire. However, in upland and slope locations, where shrubs and trees were sparser, survival probability varied by topographic position and species. In these locations 68% of all woody individuals experienced 90% or greater fire damage to the canopy, with 56% of these individuals exhibiting new canopy regrowth within 2 mo after the fire. The two most abundant woody shrubs, Cornus drummondii and Rhus aromatica, showed high survival at all height classes and landscape positions. The two abundant tree species, Gleditsia triacanthos and Juniperus virginiana, showed increased survival probability with tree height that varied by landscape position. Survival of J. virginiana also varied according to proximity and size of neighboring clonal shrubs, providing a mechanism for persistence of this fire-sensitive tree species even at small height classes. The probability survival curves developed here are useful for managers assessing when to prescribe fire to maximize mortality for J. virginiana and provide insight relevant for broader ecological understanding of woody encroachment within grasslands throughout the world.

Fire and browsing interact to alter intra-clonal stem dynamics of an encroaching shrub in tallgrass prairie.

The expansion of woody species into grasslands has altered community structure and ecosystem function of grasslands worldwide. In tallgrass prairie of the Central Great Plains, USA, decreased fire frequency and intensity have increased the cover and abundance of woody species. In particular, clonal shrub cover has increased at accelerated rates due to vegetative reproduction and resprouting after disturbance. We measured the intra-clonal stem demography and relative growth rates (estimated change in woody biomass) of the shrub Cornus drummondii in response to fire frequency (4 vs 20year burn intervals) and simulated browsing during the 2018 and 2019 growing seasons at Konza Prairie Biological Station (Manhattan, Kansas). Overall, infrequent fire (4year burn interval) increased intra-clonal stem relative growth rates and shrub relative growth rates. Intra-clonal stem relative growth rates were reduced in unbrowsed clones in 2018 due to drought and simulated browsing reduced intra-clonal stem relative growth rates in 2019. Additionally, simulated browsing nearly eliminated flower production within clones but did not affect intra-clonal stem mortality or recruitment within a growing season. Fire in conjunction with simulated browsing reduced estimated relative growth rates for entire shrub clones. Browsed shrubs that experienced prescribed fire in 2017 had reduced intra-clonal stem densities compared to unbrowsed shrubs and stem densities of browsed shrubs did not recover in 2018 or 2019. These results illustrate that infrequent fire alone promotes the expansion of clonal shrubs in tallgrass prairie and multiple interacting disturbances (e.g., fire and browsing) are required to control the spread of clonal shrubs into grasslands.

Is a Prescribed Fire Sufficient to Slow the Spread of Woody Plants in an Infrequently Burned Grassland? A Case Study in Tallgrass Prairie

In many mesic grasslands, such as the central Great Plains in North America, frequent fire is a key regulator of ecological processes. Long periods of infrequent fire facilitate the conversion of herbaceous-dominated grassland to woody-dominated shrubland or woodland. At the Konza Prairie Biological Station in northeast Kansas, one infrequently burned portion of the landscape has undergone transformation from grassland to woodland after nearly 30 yr without fire. In Spring 2017, a prescribed burn was implemented to assess fire effectiveness on woody plant mortality. A postfire census of 3 000+ individual woody plants identified the distribution of species by size (height), topographic position, and slope on the landscape. Mortality and canopy fire damage were calculated for each individual. In lowland locations with near-continuous shrub cover (30.7% of the landscape), woody plants were unaffected by fire. However, in upland and slope locations, where shrubs and trees were sparser, survival probability varied by topographic position and species. In these locations 68% of all woody individuals experienced 90% or greater fire damage to the canopy, with 56% of these individuals exhibiting new canopy regrowth within 2 mo after the fire. The two most abundant woody shrubs, Cornus drummondii and Rhus aromatica, showed high survival at all height classes and landscape positions. The two abundant tree species, Gleditsia triacanthos and Juniperus virginiana, showed increased survival probability with tree height that varied by landscape position. Survival of J. virginiana also varied according to proximity and size of neighboring clonal shrubs, providing a mechanism for persistence of this fire-sensitive tree species even at small height classes. The probability survival curves developed here are useful for managers assessing when to prescribe fire to maximize mortality for J. virginiana and provide insight relevant for broader ecological understanding of woody encroachment within grasslands throughout the world.

Spatio-temporal differences in leaf physiology are associated with fire, not drought, in a clonally integrated shrub.

In highly disturbed environments, clonality facilitates plant survival via resprouting after disturbance, resource sharing among interconnected stems and vegetative reproduction. These traits likely contribute to the encroachment of deep-rooted clonal shrubs in tallgrass prairie. Clonal shrubs have access to deep soil water and are typically thought of as relatively insensitive to environmental variability. However, how leaf physiological traits differ among stems within individual clonal shrubs (hereafter ‘intra-clonal’) in response to extreme environmental variation (i.e. drought or fire) is unclear. Accounting for intra-clonal differences among stems in response to disturbance is needed to more accurately parameterize models that predict the effects of shrub encroachment on ecosystem processes. We assessed intra-clonal leaf-level physiology of the most dominant encroaching shrub in Kansas tallgrass prairie, Cornus drummondii, in response to precipitation and fire. We compared leaf gas exchange rates from the periphery to centre within shrub clones during a wet (2015) and extremely dry (2018) year. We also compared leaf physiology between recently burned shrubs (resprouts) with unburned shrubs in 2018. Resprouts had higher gas exchange rates and leaf nitrogen content than unburned shrubs, suggesting increased rates of carbon gain can contribute to recovery after fire. In areas recently burned, resprouts had higher gas exchange rates in the centre of the shrub than the periphery. In unburned areas, leaf physiology remained constant across the growing season within clonal shrubs (2015 and 2018). Results suggest single measurements within a shrub are likely sufficient to parameterize models to understand the effects of shrub encroachment on ecosystem carbon and water cycles, but model parameterization may require additional complexity in the context of fire.

Effects of grazing intensity on sexual and clonal reproduction in a clonal xerophytic shrub

Effects of grazing intensity on sexual and clonal reproduction in a clonal xerophytic shrub

Propagation of Shinnery Oak as a Framework for Restoration

Shinnery oak (Quercus havardii) is a native clonal shrub that contributes to an imperiled biotic community in the southern Great Plains of North America. Nevertheless, there is little information on shinnery oak ecology and this lack of information hinders potential restoration of shinnery oak in areas where it has been eliminated. We provide findings from a study conducted to assess emergence and seedling survival from acorns collected in western Oklahoma in 2016. We observed that cold stratification treatments (i.e., acorns stored at 2°C for 2 weeks) and greater acorn size resulted in higher emergence. Although we found no effect of acorn size on seedling survival, we observed that shade reduced seedling survival (P < 0.005). Our study provides previously unknown information on several fundamental aspects of shinnery oak ecology and offers a baseline for restoration efforts by documenting successful shinnery oak emergence and factors associated with seedling survival.

Impacts of Sand Burial and Wind Erosion on Regeneration and Growth of a Desert Clonal Shrub.

Sand burial and wind erosion caused by sand movement are common phenomena in desert environments, but the effects on clonal shrub have rarely been investigated. Here, we assessed how sand movements affect the population regeneration capacity of juvenile clonal fragments of the shrub Calligonum mongolicum growing in mobile desert sand dunes. We investigated the population status and natural regeneration capacity in three types of mobile dunes (heavy wind erosion, heavy sand burial and moderate sand burial). Clonal propagation of C. mongolicum was markedly different across sites. Moderate sand burial sites had the largest ramet density and bud number per unit length of rhizome, and the overwinter survival rate was significantly higher at sand burial sites than at wind erosion sites, suggesting that C. mongolicum may have well adapted to the moderate sand burial environment. We further examined the effects of clonal integration on clonal regeneration of this species. Physiological, biochemical and morphological characteristics of parent and daughter ramets growing in heterogeneous sandy habitats (sand burial or wind erosion) were measured. The results showed that being connected or severed from the maternal plant critically determined survival of daughter ramets on wind eroded rhizomes. When eroded rhizomes remained connected, the mother ramets had the highest chlorophyll a, b and a + b contents. However, both the mother plant and the daughter ramets undergoing erosion had higher proline and soluble protein levels than sand buried ramets. Meanwhile, the daughter ramets undergoing sand burial had higher photosynthetic rates (Pn), chlorophyll fluorescence parameters (Fm and Fo), and phenotypic traits of assimilating shoots, i.e., node number, length and volume than wind-eroded ramets. However, significant differences with mother plants, whether connected or severed, were very limited. It was concluded that moderate sand burial environments promoted clonal reproduction and growth of C. mongolicum. Additionally, physiological integration with mother raments in favorable conditions can alleviate stress on daughter ramets exposed to wind erosion. This physiological effect may do not occur for sand buried daughter ramets. These survival strategies and phenotypic responses should be carefully considered in shrub and sand dune management in sand fixation plantations of C. mongolicum.

Responses of the Clonal Florida Endemic Shrub Polygonella myriophylla to Fire and Mechanical Disturbance

There is an unsettled debate on the benefits of mechanical disturbance for native species in fire-prone habitats. We compared the demographic effects of fire and mechanical treatments (Gyro-tracing) on Polygonella myriophylla, a prostrate clonal shrub listed as endangered and narrowly endemic to pyrogenic scrub ecosystems in south-central Florida. This species is commonly found in gaps within a matrix dominated by resprouting shrubs, but also occurs under other shrubs and along the shoulders of adjacent road-side habitats. We designed and executed a replicated (that plots per treatment, 1 ha per plot; total 147 initial plants) experiment including plots burned, mechanically chopped, with both treatments and without treatments at the Lake Wales Ridge Wildlife and Environmental Area - Carter Creek in Highlands County, central Florida (2005-2008; treated in summer of 2005). Cumulative mortality of standing P. myriophylla after 3 y was higher in burned plots (> 80%) than in chopped-only and untreated plots (∼ 50 % and ∼ 40 % respectively). Post disturbance growth in canopy area among the surviving plants was consistently higher in mechanically disturbed plots compared to untreated plots and intermediate burned conditions. We found three putative seedlings, accounting for less than 3% of the initial genets, before treatment application, but many seedlings after treatments. Seedling recruitment (∼ 90) post-treatment was higher in disturbed plots, highest when both treatments occurred together, and almost null in untreated plots. Recruitment was highest in the first-year post disturbance (70%), decreasing in subsequent years. Disturbances may improve the persistence of P. myriophylla by increasing recruitment and individual growth, however; fire and mechanical disturbance should be used with caution for this species given many plants died during treatment.

Effects of soil properties and clonal growth on the apparent sex ratio of the flowering stems of the dioecious clonal shrub Aucuba japonica var. borealis growing in an evergreen coniferous secondary forest

In dioecious plants, the frequencies of flowering stems in each sex produced through clonal growth provide important information on the potential for reproductive success in the populations. However, apart from the light environment in their habitat, the factors affecting the flowering of each sex have not been well documented in shrub species that can maintain their populations in shady environments. In this research, we investigated seven soil variables and the flowering of stems of Aucuba japonica var. borealis in patches of this dioecious clonal shrub with different apparent stem sex ratios in an evergreen coniferous secondary forest with a shady forest floor. Of the 53 patches examined, 52 contained stems with flowers. Flowering stem ratios exhibited a positive relationship with available soil phosphate but a marginal negative relationship with exchangeable magnesium, whereas soil water content was associated with a female-biased flowering sex ratio. Stem density tended to be negatively related to flowering stem ratios in patches containing stems with female flowers but not males. While the results demonstrate that abundant amounts of certain nutrients and moisture in soils promote the production of flowers and/or a bias toward femaleness in patches, it is suggested that antagonistic effects of cations in the soil can inhibit the flowering of both sexes. In addition, the trade-off between sexual reproduction and clonal propagation in the females may amplify the variations in flowering in the population.

Sand-burial and wind erosion promote oriented-growth and patchy distribution of a clonal shrub in dune ecosystems

Habitat selection by oriented-growth of plants has been investigated but field evidence for such growth is scarce, impeding efforts at sand stabilization and dune ecosystem restoration. Further, how clonal shrubs adapt to dune environments is unknown. In this study, we test the hypotheses that oriented-growth and patchiness are adaptive strategies of clonal shrubs to dune environments, while wind erosion and sand burial are the driving factors. We sampled 250 rhizomatous fragments to assess oriented-growth of Calligonum arborescens, and investigated the distribution (east, southeast, south, southwest, west, northwest, north and northeast) of C. arborescens in four different habitats of active dunes: inter-dune areas, windward slope, leeward slope, and the top of dune. We found that most of the fragments of C. arborescens grew in the northeastern and southwestern directions. Ramet number and biomass, and rhizome length and biomass in these two directions were significantly higher than those found in other directions. Interestingly, these directions were perpendicular to the direction of prevailing winds. Distribution of C. arborescens differed among habitats. Total number of individuals was significantly higher in inter-dune areas and on windward slopes than on top and leeward slopes of dunes; more clonal ramets were produced on top of dunes than elsewhere, and only 16.7% were found on leeward slopes. Both sand-burial and wind erosion affected the growth and regeneration of C. arborescens. Ramet number and biomass production decreased with increasing depth of burial and severity of erosion, but increased in moderate erosion treatments. We conclude that fragments of C. arborescens exhibited oriented-growth; most of the rhizomes grew in the direction perpendicular to the prevailing wind direction. Most of C. arborescens were found in inter-dune lands and on windward slopes. C. arborescens was well established in active dune fields through both vegetative propagation and sexual reproduction. Sand-burial and wind erosion were the key factors which led to the oriented-growth and patchiness of C. arborescens.

Adaptive introductions: How multiple experiments and comparisons to wild populations provide insights into requirements for long-term introduction success of an endangered shrub

Recovery of an imperiled plant species may require augmentation of existing populations or creation of new ones. Hundreds of such projects have been conducted over the last few decades, but there is a bias in the literature favoring successes over failures. In this paper, we evaluate a series of introductions that experimentally manipulated microhabitat and fire in an adaptive introduction framework. Between 2002 and 2012, we (and our collaborators) carried out ten introductions and augmentations of Florida ziziphus Pseudoziziphus (Condalia, Ziziphus) celata, a clonal shrub limited to very small populations and narrowly endemic to pyrogenic central Florida sandhills. Six of the introductions were designed as experiments to test hypotheses about how demographic performance was affected by microhabitat, fire, and propagule type. Introduced transplants had high survival (<90% annually), inconsistent growth, and little transition to reproduction, while introduced seeds had low germination and survival. Transplants were more efficient than seeds as translocation propagules. Shaded (vs. open) sites supported generally higher transplant and seedling survival and seed germination percentages, but growth responses varied among experiments. Supplemental irrigation increased transplant survival and seed germination, but otherwise seedling and plant survival and growth were not significantly affected. Contrary to expectations based on wild populations, introduced propagules have not been more successful in unshaded sites, suggesting that Florida ziziphus has broader microhabitat preferences than hypothesized. Compared to wild plants, introduced plants had similar survival and responses to fire, slower growth, and more delayed flowering. Introduced plants had no clonal spread. While no introduced population has demonstrated a capacity for long-term viability, one augmented population has flowered and produced viable fruits. Given that Florida ziziphus genets are long-lived, low levels of sexual reproduction may be adequate for the establishment of viable populations. Thus, after many translocations over more than a decade, it is premature to characterize any single translocation as a success or a failure, underscoring the need for a long view of translocation success.

The genetic consequences of long term habitat fragmentation on a self-incompatible clonal plant, Linnaea borealis L.

Self-incompatible species with restricted seed and pollen flow are considered the most vulnerable to the deleterious genetic effects of habitat fragmentation. Immediate effects of fragmentation are expected to be loss of allelic diversity and differentiation of fragments by genetic drift. Later, loss of S allele diversity may lead to restricted mate availability, increased relatedness of genotypes within patches, accelerated loss of genetic diversity and eventual loss of capacity for seed production. We studied the self-incompatible clonal shrub Linnaea borealis within the Cairngorms National Park, Scotland, whose pinewood habitat has been fragmented for an extensive period, possibly millennia. Exhaustive sampling revealed 123 patches (median length 15m), 91% of which were further than the maximum pollen flow distance from their nearest neighbours (30m). Using ten microsatellite markers, only 21% of the patches produced more than one multilocus genotype. Individual genotypes extended from 1 to 74m. Bayesian clustering of the 179 multilocus genotypes revealed six clusters. One cluster occupied a geographically distinct area where seed production still occurs and showed significant genetic differentiation from (Fst=0.164, P<0.01) and significantly lower allelic richness (AR=4.0 vs AR=7.0 P<0.01) than the remainder of the sample set. Spatial genetic structure in the total sample set indicated significant relatedness of clones within the first 1.5km. Overall, L. borealis in Scotland seems to be experiencing extreme genetic effects of chronic population fragmentation with only 16% of patches having the capacity for seed production. Genetic rescue is being undertaken by transplanting unrelated clones from >1.5km distance into extant monoclonal patches.

Sex-different response in growth traits to resource heterogeneity explains male-biased sex ratio

In dioecious plants, differences in growth traits between sexes in a response to micro-environmental heterogeneity may affect sex ratio bias and spatial distributions. Here, we examined sex ratios, stem growth traits and spatial distribution patterns in the dioecious clonal shrub Aucuba japonica var. borealis, in stands with varying light intensities. We found that male stems were significantly more decumbent (lower height/length ratio) but female stems were upright (higher height/length ratio). Moreover, we found sex-different response in stem density (no. of stems per unit area) along a light intensity gradient; in males the stem density increased with increases in canopy openness, but not in females. The higher sensitivity of males in increasing stem density to light intensity correlated with male-biased sex ratio; fine-scale sex ratio was strongly male-biased as canopy openness increased. There were also differences between sexes in spatial distributions of stems. Spatial segregation of sexes and male patches occupying larger areas than female patches might result from vigorous growth of males under well-lit environments. In summary, females and males showed different growth responses to environmental variation, and this seemed to be one of possible causes for the sex-differential spatial distributions and locally biased sex ratios.