Lonicera Maackii Research Articles

Apparent competition: an impact of exotic shrub invasion on tree regeneration

Invasion of habitats by exotic shrubs is often associated with a decrease in the abundance of native species, particularly trees. This is typically interpreted as evidence for direct resource competition between the invader and native species. However, this may also reflect indirect impacts of the exotic shrubs through harboring high densities of seed predators––known as apparent competition. Here I present data from separate seed predation experiments conducted with two shrub species exotic to North America; Rosa multiflora, an invader of abandoned agricultural land, and Lonicera maackii, an invader of disturbed or secondary forest habitats. Both experiments showed significantly greater risks of seed predation for tree seeds located under shrub canopies when compared to open microhabitats within the same site. These results indicate the potential importance of indirect impacts of exotic species invasions on native biota in addition to the direct impacts that are typically the focus of research.

A dendro-ecological study of forest overstorey productivity following the invasion of the non-indigenous shrub Lonicera maackii

Question: Will a non-indigenous, invasive, understorey shrub, such as Lonicera maackii (Amur honeysuckle) have an impact on the productivity of overstorey trees in hardwood forests? Location: Trees from 12 invaded and four non-invaded sites were sampled in hardwood forests of southwestern Ohio, US. Methods: Changes in radial and basal area tree growth in the ten years prior to L. maackii invasion vs. ten years after invasion were examined using dendrochronological techniques. Intervention analysis was used to detect growth changes 25 years prior to and 25 years following invasion, and estimates of load impacts for L. maackii population and biomass were also calculated. Results: We found that the rate of radial and basal area growth of overstorey trees was reduced significantly in eleven out of twelve invaded sites. Non-invaded sites did not exhibit this consistent pattern of reduced growth. For invaded vs. non-invaded sites, the mean basal area growth was reduced by 15.8%, and the overall rate of basal area growth was reduced by 53.1%. Intervention analysis revealed that the first significant growth reductions were 6.25 ± 1.24 (mean ± SE) years after invasion with the greatest frequency of negative growth changes occurring 20 years after invasion. In invaded stands, 41% of trees experienced negative growth changes. In terms of invasive load estimates per 1000 L. maackii individuals, radial tree growth was reduced by 0.56 mm.a−1, and basal area growth was reduced by 0.74 cm2.a−1, Given these findings, significant economic losses could occur in hardwood forests of Ohio. Conclusions: To our knowledge, this is the first study using dendrochronological techniques to investigate the impact of a non-indigenous, understorey plant on overstorey tree growth. Active management will likely be needed to maintain forest productivity in L. maackii impacted landscapes.

Weather-related patterns of fruit abscission mask patterns of frugivory

Previous studies on frugivory in temperate bird-dispersed plants have concluded that fleshy fruits are removed more rapidly in cold than in warm winters. However, these studies do not distinguish between fruit abscission and frugivory. The implicit assumption that fruit loss reflects frugivory may not be valid; fruit abscission may be important and respond differently to weather. During two winters, we measured fruit loss from an invasive shrub ( Lonicera maackii (Rupr.) Herder) using fruit traps. We examined the effects of temperature and precipitation on fruit retention on shrubs and fruit abscission. In the first year of our study, there was no effect of temperature or precipitation on fruit retention. In the second year, both warmer temperatures and lower precipitation resulted in more fruit retention. In both years, fruit abscission was greater during periods of cold temperatures and high precipitation. These findings suggest that weather-dependent “frugivory” reported for other bird-dispersed plants may actually reflect patterns of abscission.

The relative importance of landscape and community features in the invasion of an exotic shrub in a fragmented landscape

Although invasive plants are recognized as a major ecological problem, little is known of the relative importance of plant community characteristics versus landscape context in determining invasibility of communities. We determined the relative importance of community and landscape features of 30 woodlots in influencing the invasion of Lonicera maackii. We sampled woodlots using the point‐quarter method and calculated canopy openness and basal areas and densities of shrub, sapling and tree species, as well as woody species richness. We used aerial photos and ArcView GIS to calculate landscape parameters from the same woodlots using a buffer distance of 1500 m. We used logistic and linear regression analyses to determine the community and landscape factors that best explain L. maackii presence and density. We also tested whether woodlot invasion by L. maackii begins at woodlot edges.Presence of L. maackii was significantly explained only by distance from the nearest town (logistic regression, p=0.017); woodlots nearer town were more likely to be invaded. Among invaded woodlots, density of L. maackii was positively related to the amount of edge in the landscape (partial R2=0.592) and negatively related to total tree basal area (partial R2=0.134), number of native woody species (partial R2=0.054), and sapling shade tolerance index (partial R2=0.054). Lonicera maackii in woodlot interiors were not younger than those on the perimeters, leading us to reject the edge‐first colonization model of invasion.Our findings reveal that landscape structure is of primary importance and community features of secondary importance in the invasion of L. maackii. This shrub is invading from multiple foci (towns) rather than an advancing front. Connectivity in the landscape (i.e. the number of corridors) did not promote invasion. However, edge habitat was important for invasion, probably due to increased propagule pressure. The community features associated with L. maackii invasion may be indicators of past disturbance.

Leaf and root extracts of the invasive shrub, Lonicera maackii, inhibit seed germination of three herbs with no autotoxic effects

In addition to effects mediated by resource competition, some invasive plants may impact surrounding vegetation by secreting compounds that are directly inhibitory to growth. Lonicera maackii, an invasive Asian shrub of forests and open areas in eastern and midwestern North America, has devastating effects on understory vegetation, some of which persist even after this shrub is removed. In this study, we explored the potential of aqueous extracts of the leaves and roots of this plant to inhibit seed germination of Impatiens capensis, Alliaria petiolata, Arabidopsis thaliana, and L. maackii in Petri dish bioassays. Both L. maackii root and leaf extracts significantly decreased germination in the three herb species. This inhibitory effect generally increased with increasing extract concentration and was more pronounced with application of leaf extract than root extract. However, when the same extracts were applied to seeds of L. maackii itself, germination was delayed in some cases, but was not significantly reduced by the end of the experiment. Germination of L. maackii seeds even reached significantly higher levels in some extract treatments than in no-extract controls. This implies that L. maackii can successfully inhibit the germination of other plants with few autotoxic effects and may even promote the germination of its own seeds.

Forest Restoration in Urbanizing Landscapes: Interactions Between Land Uses and Exotic Shrubs

Abstract Preventing and controlling exotic plants remains a key challenge in any ecological restoration, and most efforts are currently aimed at local scales. We combined local‐ and landscape‐scale approaches to identify factors that were most closely associated with invasion of riparian forests by exotic shrubs (Amur honeysuckle [Lonicera maackii] and Tatarian honeysuckle [L. tatarica]) in Ohio, U.S.A. Twenty sites were selected in mature riparian forests along a rural–urban gradient (<1–47% urban land cover). Within each site, we measured percent cover of Lonicera spp. and native trees and shrubs, percent canopy cover, and facing edge aspect. We then developed 10 a priori models based on local‐ and landscape‐level variables that we hypothesized would influence percent cover of Lonicera spp. within 25 m of the forest edge. To determine which of these models best fit the data, we used an information‐theoretic approach and Akaike's information criterion. Percent cover of Lonicera was best explained by the proportion of urban land cover within 1 km of riparian forests. In particular, percent cover of Lonicera was greater in forests within more urban landscapes than in forests within rural landscapes. Results suggest that surrounding land uses influence invasion by exotic shrubs, and explicit consideration of land uses may improve our ability to predict or limit invasion. Moreover, identifying land uses that increase the risk of invasion may inform restoration efforts.

Restoration of a Forest Understory After the Removal of an Invasive Shrub, Amur Honeysuckle (Lonicera maackii)

Abstract The recruitment of native seedlings is often reduced in areas where the invasive Amur honeysuckle (Lonicera maackii) is abundant. To address this recruitment problem, we evaluated the effectiveness of L. maackii eradication methods and restoration efforts using seedlings of six native tree species planted within eradication and unmanipulated (control) plots. Two eradication methods using glyphosate herbicide were evaluated: cut and paint and stem injection with an EZ‐Ject lance. Lonicera maackii density and biomass as well as microenvironmental characteristics were measured to study their effects on seedling growth and survivorship. Mean biomass of Amur honeysuckle was 361 ± 69 kg/ha, and density was 21,380 ± 3,171 plants/ha. Both eradication treatments were effective in killing L. maackii (≥ 94%). The injection treatment was most effective on large L. maackii individuals (>1.5 cm diameter), was 43% faster to apply than cutting and painting and less fatiguing for the operator, decreased operator exposure to herbicide, and minimized impact to nontarget vegetation. Deer browse tree protectors were used on half of the seedlings, but did not affect survivorship or growth. After 3 years, survival of native seedlings was significantly less where L. maackii was left intact (32 ± 3%) compared with the eradication plots (p < 0.002). Seedling survival was significantly different between cut (51 ± 3%) and injected (45 ± 3%) plots. Species had different final percent survival and rates of mortality. Species survival differed greatly by species (in descending order): Fraxinus pennsylvanica > Quercus muehlenbergii ≥ Prunus serotina≥ Juglans nigra > Cercis canadensis > Cornus florida. Survivorship and growth of native seedlings was affected by a severe first‐year drought and by site location. One site exhibited greater spring soil moisture, pH, percent open canopy, and had greater survivorship relative to the other site (55 ± 2 vs. 30 ± 2%). Overall, both L. maackii eradication methods were successful, but restorationists should be aware of the potential for differential survivorship of native seedlings depending on species identity and microenvironmental conditions.

Competitive effects of the invasive shrub, Lonicera maackii (Rupr.) Herder (Caprifoliaceae), on the growth and survival of native tree seedlings

Invasive plants are often associated with reduced cover of native plants, but rarely has competition between invasives and natives been assessed experimentally. The shrub Lonicera maackii, native to northeastern Asia, has invaded forests and old fields in numerous parts of eastern North America, and is associated with reduced tree seedling density in Ohio forests. A field experiment was conducted to test the effects of established L. maackii on the survival and growth of transplanted native tree species. The experiment examined above-ground competition (by removing L. maackii shoots) and below-ground competition (by trenching around transplanted seedlings). The effects of above-ground competition with L. maackii were generally more important than below-ground competition, though both were detected. Shoot treatment was the key determinant for the survival of all species except P. serotina, whereas trenching only enhanced survival for A. saccharum caged and P. serotina, and only in the shoot removal treatment. For the surviving seedlings, L. maackii shoot removal increased growth of A. saccharum seedlings protected with cages, but actually reduced the growth of unprotected Q. rubra and A. saccharum seedlings, indicating that L. maackii shoots confer some protection from deer browsing. Significant interactions between root and shoot treatment on Q. rubra growth parameters, specifically greatest growth in the shoot present & trenched treatment, is attributed to protection from deer browsing combined with release from below-ground competition. Despite this protective function of L. maackii shoots, the overall effect of this invasive shrub is increased mortality of native tree seedlings, suggesting it impacts the natural regeneration of secondary forests.

Diminished Plant Richness and Abundance Below Lonicera maackii, an Invasive Shrub

Abstract The Asian shrub Lonicera maackii (Amur honeysuckle) is now common in many secondary forests in southwestern Ohio and adjacent states. We found lower species richness and abundance in plots (0.5 m2) placed below crowns of L. maackii than in plots placed away: all species (53% lower richness and 63% lower cover), tree seedlings with canopy potential (−41% richness and −68% density) and seed + bud bank (−34% richness and −33% density). Moreover, most individual taxa had lower abundance below L. maackii: 86% of herbs, 100% of trees and 56% of seed + bud bank taxa. In addition, richness of all species and richness and density of tree seedlings decreased in forests with longer residence time of L. maackii.

Effects of the Exotic Invasive Shrub Lonicera maackii on the Survival and Fecundity of Three Species of Native Annuals

Abstract Negative effects on native plant populations are often attributed to invasions by exotic plants, but experimental evidence is lacking to support many of these claims. Lonicera maackii, an exotic shrub with long leaf phenology, has become naturalized throughout the eastern United States. This study investigated the effects of L. maackii on demography of Galium aparine, Impatiens pallida and Pilea pumila, native annual herbs in differing phenological categories. These interactions were examined in two Ohio forest stands. One stand has a history of logging, burning and grazing and a higher L. maackii density, whereas the other stand has little anthropogenic disturbance and a lower L. maackii density. Three types of experimental plots were established: L. maackii removal, L. maackii present and, at the less disturbed stand, L. maackii absent. Seedlings of the annuals were transplanted and monitored for 1 y for survival to reproductive age and fecundity. In the more disturbed stand, survival of Galium...

Effects of Exotic Lonicera and Rhamnus on Songbird Nest Predation

Abstract: Habitat fragmentation and disturbance exacerbate the invasion of exotic plant species that, in turn, may attract nesting songbirds by providing a branch structure suitable for nest sites. We document that American Robin (Turdus migratorius) nests in two exotic plants, Lonicera maackii and Rhamnus cathartica, experienced higher predation than nests built in comparable native shrubs (Crataegus, Viburnum) and native tree species. This was due to a combination of lower nest height, the absence of sharp thorns on the exotic species, and perhaps a branch architecture that facilitated predator movement among the exotic species. In a more subtle interaction, nesting Wood Thrushes (Hylocichla mustelina) experienced apparent competition with robins for nest sites in Lonicera, and this interaction was further aggravated by an increased selectivity for Lonicera by nesting robins, possibly due to their early leaf flush and expansion. By documenting increased nest predation in songbirds nesting in exotic shrubs, our results suggest that restoring native plant communities may benefit the surrounding avian community.

Forest Colonization and Developmental Growth of the Invasive Shrub Lonicera maackii

Abstract The invasive shrub Lonicera maackii (Rupr.) Herder (Amur honeysuckle) dominates the understory of many deciduous forests in southwestern Ohio and other areas. Extensive sampling of an isolated population of L. maackii was used to elucidate its colonization of a forest woodlot and subsequent growth and development. The current population age structure indicated that colonization likely occurred by a series of small dispersal events. The population remained small for about ten years and then increased dramatically, presumably due to the seed reproduction of the early colonizers. Young prereproductive shrubs are characterized by rapid height growth and high stem recruitment. After shrubs become reproductive at age 5–8, height growth continues but basal stem recruitment is reduced and radial growth increases shrub basal area. Allocation of primary production apparently shifts from stem recruitment and height growth in young shrubs to a balance of height growth, radial expansion and reproduction in ol...

Landscape Structure and Spread of the Exotic Shrub Lonicera maackii (Amur honeysuckle) in Southwestern Ohio Forests

The Asian shrub Lonicera maackii (Rupr.) Herder has been widely used as an ornamental in the eastern United States. First planted in Oxford, Ohio, around 1960, it has since spread into forest patches in the surrounding agricultural landscape. Despite its abundance, and its bird-dispersed fruits, the spread of Lonicera maackii has been unequal in different directions, with local distribution limits much farther N than W of Oxford. Our objective was to determine whether the distribution limits of L. maackii in these two directions were correlated with differences in landscape structure: percentage of forest land and degree of forest connectivity. Aerial surveys were used to determine the current distribution of L. maackii in forest patches in a belt transecting N and W from Oxford. The N transect, which had more extensive spread of L. maackii, had greater forest cover and connectivity. In both transects, L. maackii reached its distribution limit when forest cover dropped to <5% and forest connectivity was 0%. Large expanses of agricultural land apparently act as a barrier to the dispersal of this naturalized shrub.

Invasibility and Effects of Amur Honeysuckle in Southwestern Ohio Forests

The Asian exotic Amur honeysuckle ( Lonicera maackii [Rupr.] Herder) has become the dominant shrub in many forests in southwestern Ohio and in some other locations in the eastern United States. Our research focused on the invasibility of forest communities and relationships of L. maackii to the abundance of tree seedlings and herbs. We surveyed 93 forest stands near Oxford, Ohio (USA) to determine L. maackii cover, time since invasion, tree canopy cover, tree basal area, and a shade tolerance index. Stepwise multiple regression indicated that greater than one‐half of the variation (r 2 = 0.550) in Lonicera cover was correlated to five variables (in descending order of importance): tree canopy cover, distance from Oxford, shade tolerance index, tree basal area, and time since invasion. The results suggest that high light levels and proximity to an abundant seed source increase forest invasibility. Tree seedling density, species richness of seedlings, and herb cover were all inversely related to L. maackii cover. When Lonicera becomes abundant, future structure and composition of forests could be affected and local populations of herbs threatened.

Comparative Responses of Lonicera maackii (Amur Honeysuckle) and Lindera benzoin (Spicebush) to Increased Light

-In shadehouses providing 1%, 25%, and 100% of full sun photosynthetic photon flux density (PPFD), we measured growth, acclimation of net photosynthesis (An), and leafand branch-level plasticity of two deciduous shrubs, a nonindigenous species [Lonicera maackii (Rupr.) Herder] and an indigenous species [Lindera benzoin (L.) Blume]. This comparative research assessed potential plant performance in response to modified disturbance regimens that increase light availaiblity. When forest-grown shrubs were moved to conditions of increased light, Lonicera maackii had maximum stem growth at 100% PPFD, higher An in pre-existing leaves, greater acclimation ability in pre-existing leaves, and greater plasticity of stomatal density and branchlevel allocation. Maximum stem growth of Lindera benzoin occurred at 25% PPFD. The inability of this species to use light above 25% PPFD was likely the result of biochemical limitation to carbon capture although relatively greater allocation of energy to roots may have contributed. As canopy thinning and fragmentation increase light availability in disturbed forests, high-resource invasive species such as L. maackii are likely to assume greater importance with concomitant decreases in importance of low-resource species such as L. benzoin.

Response of Understory Species to Gap Formation and Soil Disturbance m Lonicera maackii Thickets

AbstractWe studied the utility of gap formation and soil disturbance as methods to enhance establishment of plant species in the understory of a northern Kentucky forest where Lonicera maackii (Amur honeysuckle) produced dense thickets. In May 1994, gaps (5 m diameter) were cut in the shrub thicket. In adjacent areas, the shrub canopy remained intact. Subplots were established where soil was either turned with a spade to a depth of 15 cm or not disturbed. We monitored plant establishment for three growing seasons (1994, 1995, and 1996). Shrub removal increased light availability to about 10% of full sun. Gap formation had a significant (p &lt; 0.05) and positive influence on total plant density (exclusive of L. maackii), and soil disturbance did not (p &gt; 0.05). After three growing seasons, the most important species were L. maackii, Alliaria petiolata, Parthenocissus quinquefolia, Vitis vulpina, and Acer negundo. Of these species, only V. vulpina showed significantly (p &lt; 0.05) higher densities in gaps. Other less important species such as Phytolacca americana, Campsis radicans, and Eupatorium rugosum occurred almost exclusively in gaps. Of the 44 taxa observed in this study, most were generalist species that also occur in early successional habitats. Long‐term dominance of the understory by L. maackii has likely modified system attributes with corresponding effects on community development. Shrub removal provides a window of establishment for various plant species, but successful restoration may require further management species availability and to control new invaders.

Organic Matter Budgets for Streams: A Synthesis

Organic Matter Budgets for Streams: A Synthesis

Amur Honeysuckle, Its Fall From Grace

Amur Honeysuckle, Its Fall From Grace

DISTRIBUTION OF THE NON-NATIVE SHRUB LONICERA MAACKII IN KRAMER WOODS, OHIO

This study examined the distribution of Lonicera maackii (Amur honey-suckle) in a 5.2-ha old-regrowth deciduous forest in southwestern Ohio, and focused on its associations with: (1) forest-edge and internal-forest conditions; and (2) composition and structure of the native flora. Fine-scale vegetation patterns were measured in 60 nested plots and mapped with a geographic information system. L. maackii accounted for 24% of the relative importance of understory trees and shrubs based on its density (3361/ha), frequency (95%), and basal area (1.89m2/ha). Within-patch densities correlated significantly with edge attributes, but stem-basal areas were best explained by a covariate model that coupled edge conditions with internal topographic settings. Detrended correspondence analysis identified spatial patterns of community diversity in the understory native flora, and honeysuckle abundances were highest in small discontinuous community patches. Species richness and densities of native shrubs (Lindera benzoin and Viburnum prunifolium) and Acer saccharum saplings were lower when honeysuckle abundances were >3000/ha and/or basal areas were >4 m2/ha. These findings identified the importance of forest-edge and internal-forest conditions on spatial patterns of invasion by L. maackii and support management plans that target locations within a forest patch and forest-patch locations of highest potential impact. [Key words: conservation, eastern deciduous forest, exotic plants, forest ecology, landscape ecology.]

Foliar Nutrient Dynamics and Resorption in Naturalized Lonicera maackii (Caprifoliaceae) Populations in Ohio, USA

Foliar phosphorus (P) and nitrogen (N) concentrations and nutrient resorption in the forest understory shrub Lonicera maackii (Rupr.) Maxim (Caprifoliaceae) were measured along contiguous topographic gradients in two southwestern Ohio forests during 1992-1994. Mean summer foliar P varied significantly among topographic positions (but not sites or years), with uplands having greatest P concentrations and bottomlands exhibiting the lowest. Unlike for P, the mean summer foliar N concentrations varied little among sites, topographic positions, and years. Mean absolute and proportional P resorption ranged from 0.48 mg/dM2 (33.7%) in slope positions to 0.80 mg/dM2 (53.1%) in bottomland positions. Repeated-measures analysis of variance (RMANOVA) for P resorption indicated significant topographic and year effects, a site X year and a site X year X topographic interaction. Mean absolute and proportional foliar N resorption ranged from 6.82 mg/dM2 (30.7%) in bottomlands to 8.41 mg/dM2 (37.3%) in slope positions. RMANOVA indicated a significant topographic effect for both absolute and proportional N resorption and a significant year effect for absolute N resorption. These significant year effects for P and N stemmed from lowest resorption of nutrients in 1993. The results for P resorption support the hypothesis that foliar resorption is greater in forested sites with lower P fertility. However, resorption rates for N did not support the hypothesis clearly, as slopes with intermediate N availability had greater N resorption rates than did N-rich bottomlands.