Does Rhododendron maximum L. (Ericaceae) Reduce the Availability of Resources Above and Belowground for Canopy Tree Seedlings?

Nilsen, Erik T.; Clinton, Barton D.; Lei, Thomas T.; Miller, Orson K.; Semones, Shawn W.; Walker, John F.

doi:10.1674/0003-0031(2001)145[0325:drmler]2.0.co;2

Cited by 82 publications

(86 citation statements)

References 23 publications

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“…Our data showed that most tree seedlings will not persist for more than 2-3 years in the shade of the thickets (Lei et al 2002 Seedlings in these brighter F + R locations should persist for longer periods of time. However, the absence of older tree seedlings in these brighter patches under R. maximum thickets implicates other contributing factors, such as below-ground competition and interference with mycorrhizal association Nilsen et al 2001), are further restricting tree seedling survival under the thickets. Given the persistence of R. maximum in the Coweeta forest, it could have an enduring effect on regenerating tree seedlings and, consequently, on the forest landscape of the region.…”

Section: Discussionmentioning

confidence: 98%

“…Therefore, the energetic balance and survival of regenerating tree seedlings depends heavily on the spatial and temporal distribution of PPFD reaching below the R. maximum shrubs and on the LCP of those regenerating seedlings. Although other factors such as allelopathy , mycorrhizal association ) and below ground resources (Nilsen et al 2001;Beier et al 2005) may contribute to seedling mortality under R. maximum, we hypothesize that light limitation is having an overriding effect. To test this hypothesis we made detailed measurements of spatial and temporal light patterns using both hemispherical photographs and quantum sensors in forest sites with and without thickets of R. maximum.…”

Section: Introductionmentioning

confidence: 86%

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Light environment under Rhododendron maximum thickets and estimated carbon gain of regenerating forest tree seedlings

2005

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.Canopy tree recruitment is inhibited by evergreen shrubs in many forests. In the southern Appalachian mountains of the USA, thickets of Rhododendron maximum L. restrict dominant canopy tree seedling survival and persistence. Using R. maximum as a model system, we examined available light under the thickets and the photosynthetic responses of seedlings of canopy tree species. We tested the hypothesis that the additional shading from under R. maximum drives carbon gain in seedlings below the threshold for growth and survival. A reduction in light under the thicket was found where canopy openness (derived from canopy photographs) under R. maximum was half the amount measured in forest without R. maximum. R. maximum also reduced direct radiation by 50% and diffuse radiation by 12-29% compared to forest without the shrub layer. Mean mid-day PPFD (photosynthetically active photon flux density between 1000 and 1400 h) under R. maximum (obtained from quantum sensors) was below 10 pnol m-2 s-I on both clear and overcast days and the amount of sunflecks greater than 10 pmol m-2 s-' PPFD was only O-20 min per day. In contrast, forest without R. maximum received a mean PPFD of 18 -25 p o l m-2 s-' on clear days and a cumulative sunfleck duration of 100-220 min per day in all sky conditions. Consistent with light availability between the sites, daily carbon gain in Quercus rubra L. seedlings was lower in forest with R. maximum compared to forest where the shrub was absent. The presence of the shrub layer also significantly suppressed average mid-day photosynthesis of both Q. rubra and Prunus serotina Ehrt. seedlings on 8 out of 11 measurement dates. However, parameters derived from light response curves between seedlings growing in forest sites with or without a thicket of R. maximum was significantly different only in A,, (maximum photosynthetic rate), indicating a lack of further acclimation to the deeper shade under R. maximum. While the additional shade cast by R. maximum is sufficient to prevent the regeneration of tree seedlings under this shrub, there was sufficient heterogeneity in light under the thicket to imply that deep shade only partially explains the complete inhibition of regenerating canopy trees under R. maximum.

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Section: Discussionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 86%

Light environment under Rhododendron maximum thickets and estimated carbon gain of regenerating forest tree seedlings

2005

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“…Shrub understories decrease seedling density, growth and survival (Beckage et al, 2000;Nilsen et al, 2001;Collier et al, 2002;Lei et al, 2002;Fagan and Peart, 2003;Gorchov and Trisel, 2003;Lambers and Clark, 2003). This effect has been found with invasive shrubs outside their native range, such as Lonicera maackii and Rhamnus frangula, as well as shrubs in their native range such as Rhododendron maximum, Buxus sempervirens and Juniperus communis.…”

Section: Introductionmentioning

confidence: 92%

“…Shrub canopies limit resources required for seedling establishment and survival. Shrubs reduce light levels on the forest floor (Beckage et al, 2000;Nilsen et al, 2001;Lei et al, 2002) and decrease soil moisture and nutrient levels (Putz and Canham, 1992;Nilsen et al, 2001). Litter accumulation (Beckage et al, 2000) and increased seedling predation by small mammals under shrubs (Rousset and Lepart, 2000) also create difficulties for seedling establishment.…”

Section: Introductionmentioning

confidence: 99%

“…This effect has been found with invasive shrubs outside their native range, such as Lonicera maackii and Rhamnus frangula, as well as shrubs in their native range such as Rhododendron maximum, Buxus sempervirens and Juniperus communis. In the Southern Appalachians, where the effect of a R. maximum understory has been extensively studied, seedling densities for at least six canopy tree species were decreased under that species: Acer pennsylvanicum, Acer rubrum, Fraxinus americana, Quercus rubra, Tsuga canadensis, and Prunus serotina (Beckage et al, 2000, Nilsen et al, 2001Lei et al, 2002;Lambers and Clark, 2003). An understory of L. maackii decreased both the number of species and seedling density (Collier et al, 2002), while removing the shoots of L. maackii increased the survival of four native tree species that were transplanted into plots with the shrub (Gorchov and Trisel, 2003).…”

Section: Introductionmentioning

confidence: 99%

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Tree Seedling Establishment Under the Native Shrub, Asimina triloba

Baumer¹,

Runkle²

2010

Castanea

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Species that form forest understory layers affect canopy tree seedling establishment worldwide. In the Eastern United States, shrub understories like Rhododendrom maximum, a native evergreen species, and Lonicera maackii, an exotic, invasive species, diminish tree seedling survival. I compared the density and survival of canopy tree seedlings under and outside patches of the native shrub, Asimina triloba (L.) Dunal (Annonaceae) (pawpaw). I also conducted a manipulative experiment to determine whether above ground or below ground competition was more important in seedling growth and survival. Above ground competition was manipulated by tying back the leaves of the pawpaw and below ground competition was manipulated by trenching the perimeter of the study plots. Tree seedling density was approximately three times greater outside pawpaw patches than under pawpaw over the range of sites. Seedlings under pawpaw were both younger and shorter than those outside of pawpaw. Survival varied by species. Acer saccharum seedlings were about one and a half times more likely to survive outside pawpaw than under pawpaw. Prunus serotina seedlings were about three times more likely to survive outside pawpaw than under pawpaw. In contrast, pawpaw did not affect the survival of Fraxinus spp. seedlings. Differing survival rates may reflect characteristics related to the species shade tolerance. Light (measured by canopy densiometer) was greater outside pawpaw than under pawpaw. No significant differences in moisture levels were detected; however, at three of the four sites, moisture iv was greater under pawpaw than outside of pawpaw. The combination of above ground and below ground factors was more important in the survival and growth (measured by biomass) of planted A. saccharum seedlings under pawpaw than either above ground or below ground factors alone. Given that conditions such as elevated deer herbivory and tree diseases may provide opportunities for pawpaw to expand, continued attention to the pawpaw understory is warranted.v

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Increased tree water use with the development of a dense understory layer in a North American hardwood forest

Rasoanaivo,

Mekontchou,

Rochon

et al. 2024

Ecohydrology

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The formation of a single species, recalcitrant understory vegetation layer can limit tree regeneration and, in the long term, modify the composition of forests. Few studies have investigated how recalcitrant vegetation influences competition for water resources although the formation of a dense understory is likely to modify the forest water balance. In eastern North American hardwood forests, the development of a dense understory layer of American beech (Fagus grandifolia) has been observed in stands dominated by sugar maple (Acer saccharum), a phenomenon that shares many characteristics associated with recalcitrant vegetation. Given that water availability is generally negatively correlated with stand density, we hypothesized that the formation of a dense understory beech layer increased competition for water resources, thus leading to reduced water use by sugar maple trees in beech‐dominated stands. Using thermal dissipation sensors, we measured sap flux density (Fd) of two sugar maple trees at three beech‐dominated sites and three control sites. During the growing season, Fd of sugar maple trees was significantly larger at beech‐dominated sites compared to control sites, indicating a greater rate of water use by sugar maples in stands with a dense understory beech layer. We provide two hypotheses to explain our results at the tree scale: (i) reduced cover by forest floor vegetation could limit transpiration by this layer, thus allowing increased water availability to supply transpiration by overstory trees, or (ii) increased tree transpiration rate could be a mechanism to satisfy nutrient requirements in beech‐dominated stands often associated with lower soil fertility.

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Does Rhododendron maximum L. (Ericaceae) Reduce the Availability of Resources Above and Belowground for Canopy Tree Seedlings?

Cited by 82 publications

References 23 publications

Light environment under Rhododendron maximum thickets and estimated carbon gain of regenerating forest tree seedlings

Light environment under Rhododendron maximum thickets and estimated carbon gain of regenerating forest tree seedlings

Tree Seedling Establishment Under the Native Shrub, Asimina triloba

Increased tree water use with the development of a dense understory layer in a North American hardwood forest

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