Shaded Saplings Research Articles

Shade and sapling size influence restoration of Araucaria angustifolia

Toward improving reforestation of Brazilian pine (Araucaria angustifolia), two contrasting sapling sizes in either full sun or in the shade of a mixed plantation and the effect of opening the canopy were evaluated for survival, growth, gas exchange, photosynthetic pigments, and leaf anatomy 18 months after being planted. At 23 months after planting, a partial opening was made in the canopy in the mixed plantation, then the saplings were evaluated again after 2 months for the same morphophysiological traits. After 18 months, saplings planted in the full sun had higher survival, growth, pigments, and photosynthesis compared to the shaded saplings. Large saplings had higher survival and growth compared to the small ones. Shaded leaves were thinner and little differentiation of palisade parenchyma and hypodermis. After opening of the canopy, photosynthetically active radiation was 10 times higher, and the saplings quickly grew in height due to increased photosynthesis. Thus, although the species can tolerate shade, growth in the shade is limited. We recommend that for reforestation purposes of Brazilian pine, large saplings should be selected and planted in the open for better development.

High carbon storage in carbon-limited trees.

The concentrations of nonstructural carbohydrates (NSCs) in plant tissues are commonly used as an indicator of total plant carbon (C) supply; but some evidence suggests the possibility for high NSC concentrations during periods of C limitation. Despite this uncertainty, NSC dynamics have not been investigated experimentally under long-term C limitation. We exposed saplings of 10 temperate tree species differing in shade tolerance to 6% of ambient sunlight for 3yr to induce C limitation, and also defoliated one species, Carpinus betulus, in the third season. Growth and NSC concentrations were monitored to determine C allocation. Shade strongly reduced growth, but after an initial two-fold decrease, NSC concentrations of shaded saplings recovered to the level of unshaded saplings by the third season. NSC concentrations were generally more depleted under shade after leaf flush, and following herbivore attacks. Only under shade did artificial defoliation lead to mortality and depleted NSC concentrations in surviving individuals. We conclude that, irrespective of shade tolerance, C storage is maintained under prolonged shading, and thus high NSC concentrations can occur during C limitation. Yet, our results also suggest that decreased NSC concentrations are indicative of C limitation, and that additional leaf loss can lead to lethal C shortage in deep shade.

Architectural differences among shaded saplings of four evergreen broad-leaved tree species in Japan.

Architectural differences among shaded saplings of four evergreen broad-leaved tree species in Japan.

Forest habitat, not leaf phenotype, predicts late‐season folivory of Quercus alba saplings

Summary1. Natural sunlight gradients occur on multiple scales in space and time. However, the direct (via habitat) and indirect effects (via plant quality) of light environment are often confounded, obscuring the relative importance of each in influencing herbivore responses.2. Potted saplings of Quercus alba (white oak, Fagaceae) were grown in either full sun or full shade from budburst to leaf hardening to manipulate leaf phenotype (creating sun or shade leaves), then placed in either sunny light gaps or adjacent shaded forest understorey habitats. This two‐way factorial design isolated the effects of sunlight level during leaf expansion from light environment late in the growing season on leaf phenology, leaf traits associated with host plant quality for herbivores, herbivore density and folivory.3. Sunlight level during leaf expansion and hardening had strong and persistent effects on Q. alba leaf phenology and phenotype. Shade saplings had later budburst (c. 4 days), and fewer but larger leaves, resulting in greater total leaf area compared with sun leaf saplings. Shade leaves had higher water content, specific leaf area and nitrogen content, and lower toughness, carbon content, C/N ratios and concentrations of hydrolysable and condensed tannins than sun leaves.4. Despite the apparent higher quality of shade leaves, forest habitat better predicted damage by folivores than leaf type, suggesting that the direct effects of light environment predominate for herbivory. Potted saplings of both leaf types placed in the shaded understorey suffered almost two times more folivory, on average, than saplings in sunny light gaps, despite more than three times higher mid‐season herbivore density on sun leaf saplings relative to shade leaf saplings.5. Taken together, these results suggest that both leaf phenotype and forest habitat, two factors frequently confounded in nature, have significant but distinct effects on leaf quality and herbivory. These findings have implications for plant–herbivore interactions following disturbances such as treefalls, when shade leaves may be present in sunny habitats, and may help explain patterns of herbivory in understorey plants with early leaf flushing phenology relative to the canopy, when sun leaves are present in the shaded understorey.

Morphological acclimation to understory environments in Abies amabilis, a shade- and snow-tolerant conifer species of the Cascade Mountains, Washington, USA

Light-related plasticity in a variety of crown morphology and within-tree characteristics was examined in sun and shade saplings of Abies amabilis Dougl. ex J. Forbes growing in two late-successional forests with different snow regimes in the Cascade Mountains of Washington, USA. Compared with sun saplings, shade saplings typically had broad flat crowns as a result of acclimation at several scales (needle, shoot, branch, crown and whole sapling). Shoots of shade saplings had a smaller needle mass per unit of stem length than shoots of sun saplings, a feature that enhances light-interception efficiency by reducing among-needle shading. The low annual rate of needle production by shade saplings was associated with a longer needle lifespan and slower needle turnover. Reduced needle production within a shoot was reflected at the branch level, with lateral branches of shade saplings having a smaller needle mass than branches of the same length of sun saplings. Reduced allocation to needles permits greater investment in branches and stems, which is necessary to support the horizontally expanding branch system characteristic of shade saplings. Mean branch age of shade saplings was significantly higher than that of sun saplings. Shade saplings had lower needle mass per unit of trunk biomass or total biomass, reflecting greater investment in the trunk as a support organ. Increased investment in support organs in shade was more evident in the snowier habitat. The observed morphological acclimation makes A. amabilis highly shade and snow-tolerant and thus able to dominate in many late-successional forests in snowy coastal mountain regions.

Early spring leaf out enhances growth and survival of saplings in a temperate deciduous forest

Saplings of many canopy tree species in winter deciduous forests receive the major portion of their light budget for their growing season prior to canopy closure in the spring. This period of high light may be critical for achieving a positive carbon (C) gain, thus contributing strongly to their growth and survival. This study of saplings of Aesculus glabra and Acer saccharum in Trelease Woods, Illinois, USA, tested this hypothesis experimentally by placing tents of shade cloth over saplings during their spring period of high light prior to canopy closure in three consecutive years. Leaf senescence began 16 days (year 0) and 60 days (year 1) earlier for shaded A. glabra saplings than control saplings. No change in senescence occurred for A. saccharum. The annual absolute growth in stem diameter of both species was negligible or negative for shaded saplings, but positive for control saplings. Only 7% of the shaded A. glabra saplings were alive after 2 years, while all control saplings survived for 3 years; only 20% of the shaded A. saccharum saplings survived for 3 years, while 73% of control saplings were alive after the same period. Early spring leaf out is a critical mechanism that allows the long-term persistence of saplings of these species in this winter deciduous forest. Studies and models of C gain, growth, and survival of saplings in deciduous forests may need to take into account their spring phenology because saplings of many species are actually "sun" individuals in the spring prior to their longer period in the summer shade.

Ungulate browsing in winter reduces the growth of Fraxinus and Acer saplings in subsequent unbrowsed years

Browsing by ungulates has become a hotly debated issue in many European mountain forests in the past century. Acer pseudoplatanus L. and Fraxinus excelsior L. are broadleaved tree species that are preferentially browsed by roe deer (Capreolus capreolus) in central Europe. We analyzed growth data from shaded saplings of both tree species to quantify the extent to which height growth after game browsing is reduced in subsequent, unbrowsed years in forest stands. Sixty saplings of F. excelsior and A. pseudoplatanus from forest stands at Albisriederberg (Switzerland) were available to us that had been dissected into pieces that then were split in the middle for counting tree rings and assessing ungulate damage. We fitted the von Bertalanffy growth equation to these height growth data and included a reduction factor for winter browsing. Both tree species showed significantly reduced height growth in unbrowsed years after one to several browsing events in winter, and this effect increased with the number of browsing events. Saplings with a high growth rate showed a higher growth reduction. After winter browsing, height growth of A. pseudoplatanus saplings was less affected in unbrowsed years than that of F. excelsior saplings. We conclude that browsed saplings of these species in forest stands are not able to compensate browsing-induced height loss, but that height differences between browsed and unbrowsed saplings probably increase over time. A comparison between our analysis and the parameters estimated using equations published by Eiberle for predicting age at 130 cm height suggests that our parameter values are rather conservative estimates of the growth reduction effect after winter browsing. Neither F. excelsior nor A. pseudoplatanus show a distinct pattern in browsing-induced growth reduction with respect to soil moisture, nutrient level, and altitude. We thus conclude that our results are likely to be valid for a wide range of forested sites.

Structural characteristics of Abies mariesii saplings in a snowy subalpine parkland in central Japan

Structural characteristics of Abies mariesii M.T. Mast. saplings growing in sun and shade in a snowy subalpine parkland in central Japan were assessed to infer how saplings acclimate to suppression by larger individuals in a conifer clump and to extremely snowy conditions. Sun and shade saplings produced structurally different current-year shoots, and allocated biomass to needles and stem differently. Compared with sun saplings, shoots of shade saplings had lower needle mass per unit shoot size, which indicates less dense needle packing and more effective use of the limited available light by avoiding mutual shading among needles. Biomass allocation within lateral branches also differed between sun and shade saplings. Compared with sun saplings, needle mass was a smaller proportion of total branch mass in shade saplings although shade saplings retained needles for longer, thereby compensating, in part, for their lower annual production of needles. Thus shade saplings incur a high mechanical cost to support their low-light acclimated, conspicuously flattened crowns in this snowy habitat. Suppressed saplings are an important component of the persistent conifer clumps in snowy subalpine parklands. The observed structural characteristics of A. mariesii saplings, which ensure high shade- and snow-tolerance, contribute to the dominance of the species in snowy subalpine regions in Honshu, Japan.

Functional relationships between crown morphology and within-crown characteristics of understory saplings of three codominant conifers in a subalpine forest in central Japan.

Light-related plasticity of crown morphology and within-crown characteristics were investigated in understory sun and shade saplings of three codominant subalpine conifers, Abies mariesii M.T. Mast., Abies veitchii Lindl. and Picea jezoensis var. hondoensis (Mayr) Rehd. Compared with those of sun saplings, current-year shoots of shade saplings allocated less biomass to needles, resulting in less dense needle packing and hence less mutual needle shading. The proportion of lateral branch biomass in foliage was either similar in sun and shade saplings or greater in shade saplings, depending on the species, suggesting that, over the lifetime of a branch, greater needle longevity in shade compensates for reduced biomass investment in needles of current-year shoots of shade saplings. Saplings with slower-growing branches tended to have greater needle life spans, suggesting that plasticity of branch growth rate and plasticity of needle life span are interdependent. Both Abies species showed greater light-related plasticity of needle life span and branch growth than P. jezoensis. The greater shade tolerance of the Abies species derives from their broad flattened crowns with slow-growing branches. This type of crown development incurs substantial support costs, but the long needle life span of shade saplings of the Abies species compensates, at least in part, for their low annual investment in foliage, especially in the case of A. mariesii, which has a longer needle life span and slower-growing and stouter branches than A. veitchii. Compared with the Abies species, P. jezoensis had a less plastic crown morphology, and less variability of needle life span and branch growth in response to light, resulting in lower shade tolerance. However, compared with the flattened crown of Abies shade saplings, the conical crown of P. jezoensis saplings imposes a smaller support cost, making this species better adapted to rapid height growth than to survival in shade.

Allocation of above‐ground growth is related to light in temperate deciduous saplings

Summary Allocational shifts in response to light may be an important factor in allowing plants to survive in shade, while increasing their extension rates and competitive ability in sun. To investigate this response, the allocation of above‐ground growth between leaves, branches and stems was studied in saplings of Acer pensylvanicum L. and Castenea dentata (Marsh.) Borkh. in the Appalachian mountains of western Virginia, USA. Measurements of current leaf biomass, current and past year leaf numbers and the growth ring widths of branches and stem were used to estimate biomass partitioning for saplings growing in locations ranging from forest understorey to large openings. Both species showed higher leaf area per unit leaf biomass (SLA) and higher allocation of above‐ground growth to leaves in shade than in sun. There were no differences between species in the slopes of the relationships of allocation and SLA vs estimated irradiance, but SLA was significantly greater in A. pensylvanicum than in C. dentata at a given light level. Hence, somewhat lower production per unit leaf area is required to maintain the canopy in A. pensylvanicum, consistent with foresters’ ratings of greater shade tolerance for this species. Greater foliar allocation in shade than sun has also been observed in broad‐leaved evergreen saplings, but generally not in seedlings. This difference is probably related to differences in size and age between seedlings and saplings. Young seedlings typically show exponential growth with no immediate foliar losses, while shaded saplings lie closer to the steady state where new leaves replace old ones with little additional stem growth. Thus trees shift their allocation patterns in an acclimatory fashion, depending on their size and light environment, with the costs of replacing senesced leaves becoming of consequence as juveniles age.

Stem orientation is related to growth rate, leaf dimensions, and the deciduous habit in temperate forest saplings

The orientation of the central stem is a key component of tree architecture. Stem orientation was related to extension rate in saplings growing in light conditions ranging from forest understories to large openings in 11 deciduous angiosperms, 1 evergreen angiosperm, and 2 evergreen conifers in the Appalachian Mountains of the southeastern United States. Most of the deciduous species showed pronounced differences between arced, dorsiventrally symmetric forms in slow-growing, shaded saplings and erect, radially symmetric forms in fast growing, sunlit saplings. In contrast, the evergreen species showed little or no shift in stem orientation in relation to growth rate and tended to be more erect in shade than the deciduous species. Evergreen saplings studied at other sites were also more erect in shade than the deciduous species studied here. Within the deciduous species, the degree of arcing in shade declined with increasing leaf size and petiole length. These results, involving two congeneric pairs, suggest that stem orientation is related more to leaf dimensions and leaf habit than to taxonomic classification per se. The positioning of a single cohort of nonoverlapping leaves in shaded deciduous saplings may increase the efficiency of light interception in arced forms, as compared with evergreen saplings, where new leaves must be positioned in relation to older leaf cohorts.Key words: tree architecture, growth rate, stem orientation, morphological plasticity.

Tree architecture in relation to leaf dimensions and tree stature in temperate and tropical rain forests

Summary 1 The architecture and leaf dimensions (petiole length, blade length and blade width) of 403 tree species were studied at six sites ranging from lowland equatorial to temperate Australian rain forest. The branching patterns of understorey saplings and exposed canopy trees were classified as orthotropic (three‐dimensional arrangements of leaves about ascending twigs) or plagiotropic (leaves arranged in planes, usually along the sides of horizontal twigs). 2 Among understorey saplings, orthotropic species had larger leaves and longer petioles than plagiotropic species. Discriminant analysis showed that the two groups could be separated by petiole length and the ratio of blade width to length, with those orthotropic species having short petioles also tending to have narrow blades. 3 The petiole length distinguishing orthotropy from plagiotropy showed a linear decrease with increasing latitude, as small‐leaved short‐petioled orthotropic species were relatively abundant at the temperate Australian sites. 4 The likelihood of a species being plagiotropic was weakly related to its shade tolerance and not related to adult stature or abundance, i.e. understorey leaf display was more closely related to leaf dimensions than to life‐history attributes. This importance of leaf dimensions may reflect their influence on light interception and mechanical support requirements. 5 A smaller fraction of species was plagiotropic in the canopy than in the understorey, particularly in Australia, where many short‐petioled species shifted from plagiotropic to orthotropic on attaining the canopy. 6 This switch from plagiotropy to orthotropy appeared to be associated with excess light levels relative to photosynthetic capacity, slow branch extension rates and low illumination angles. Thus, leaf display is related to leaf dimensions in shaded saplings, but light and physiological factors may have a greater influence on canopy architecture.

Correspondence of environmental tolerances with leaf and branch attributes for six co-occurring species of broadleaf evergreen trees in northern California

For the angiosperm dominants of northern California’s mixed evergreen forests, this study compares the display of photosynthetic tissue within leaves and along branches, and examines the correspondence between these morphological attributes and the known environmental tolerances of these species. Measurements were made on both sun and shade saplings of six species: Arbutusmenziesii (Ericaceae), Chrysolepischrysophylla (Fagaceae), Lithocarpusdensiflorus (Fagaceae), Quercuschrysolepis (Fagaceae), Quercuswislizenii (Fagaceae), and Umbellulariacalifornica (Lauraceae). All species had sclerophyllous leaves with thick epidermal walls, but species differed in leaf specific weight, thickness of mesophyll tissues and in the presence of a hypodermis, crystals, secretory idioblasts, epicuticular deposits, and trichomes. The leaves of Arbutus were 2 – 5 times larger than those of Chrysolepis, Lithocarpus and Umbellularia and 4 – 10 times larger than those of both Quercus species. Together with differences in branch architecture, these leaf traits divide the species into groups corresponding to environmental tolerances. Shade-tolerant Chrysolepis, Lithocarpus, and Umbellularia had longer leaf lifespans and less palisade tissue, leaf area, and crown mass per volume than the intermediate to intolerant Arbutus and Quercus. Having smaller leaves, Quercus branches had more branch mass per leaf area and per palisade volume than other species, whereas Arbutus had less than other species. These differences in display of photosynthetic tissue should contribute to greater growth for Quercus relative to the other species under high light and limited water, for Arbutus under high light and water availability, and for Chrysolepis, Lithocarpus, and Umbellularia under limiting light levels.

The Architecture and Allometry of Mangrove Saplings

1. The architecture and allometry of eight populations of mangrove tree saplings of seven species (1.5-3 m in height) were studied at Sungei Merbok, Kedah, Peninsular Malaysia. Three populations (Bruguiera cylindrica, Bruguiera parvilfora and Rhizophora apiculata) were growing in shaded conditions, the other five (Avicennia alba, Rhizophora apiculata, Rhizophora mucronata, Sonneratia alba and Xylocarpus granatum) were in the open. 2. Comparisons were made between the population specific allometric regressions for dimension pairs of the form ln γ=b 1 ln x+b 0 . The bifurcation ratio (R b ) for the-branching system of each sapling was calculated. 3. In the majority of the allometric regressions the populations differed significantly in b 0 but not b 1 , though some significant slope differences were found, particularly for regressions involving root dry weight. 4. The allometric analysis showed that for saplings of the same height, those growing in the shade had lower shoot dry weight and lower dry weight and area of leaves than the open-grown ones. The shaded saplings also exhibited a greater accumulation of foliage at the top of the plant. 5. Xylocarpus granatum was notable for a low investment in leaves, which was probably explained by recent flushing, and in roots, which may reflect the limited development of pneumatophores in this species. The shaded Bruguiera populations showed a relatively high root investment probably because of their abundant pneumatophore development. 6. When compared to published results of allometric analyses for shaded saplings from lowland tropical rain forest and warm temperate rain forest it was found that the shaded mangroves were consistently more similar to the unshaded mangroves than to the rainforest saplings. This may be because the shaded mangroves were growing under higher average irradiances than those from the rain forests. It is argued, however, that mangrove species are inherently more likely to show an architecture better suited to high irradiance conditions than the majority of broad-leaved evergreen rain-forest trees

Influence of light level on the growth and morphology of saplings in a panamanian forest

Leaf spacing and aboveground growth were monitored in saplings of ten species in a range of light environments in a Panamanian lowland humid forest. One‐ to 2‐m‐tall individuals of the chosen species had intermediate to large leaves on stems with few or no branches. Saplings in high light environments grew faster in height and produced more biomass per unit leaf area than shaded saplings for all species. These growth responses involved morphological plasticity with greater extension per unit biomass increment increasing the height growth rate of gap‐grown saplings and greater biomass allocation to leaves decreasing the whole plant light compensation point in shade. The relative performance of the species also varied across the light gradient and was related to differences in leaf lifespan and specific leaf mass. Light‐demanding species grew as rapidly in shade as shade‐tolerant species, but the shorter leaf lifespan of the former necessitates higher production rates to maintain a given leaf area, largely excluding light‐demanders from shaded understory locations. Height growth rate was positively correlated with leaf spacing for each species, and differences between species in the height growth rate‐internode length relationship were related to interspecific differences in specific leaf mass. Thus, sapling growth histories may be inferred from their morphologies.

INFLUENCE OF NEIGHBORS ON TREE FORM: EFFECTS OF LATERAL SHADE AND PREVENTION OF SWAY ON THE ALLOMETRY OF LIQUIDAMBAR STYRACIFLUA (SWEET GUM)

Liquidambar styraciflua (sweet gum) saplings were open grown (control), guy‐wired to prevent wind‐induced sway (constrained), or guy‐wired within open‐topped shade cloth cylinders to simulate shading by neighboring trees (shaded). Mechanical stability was assessed after 2 years of growth by field measurement of whole‐tree flexibility and with the critical buckling height predictions of five allometrical models. Data from this experiment are supplemented with measurements of sweet gum trees growing in a 9‐year‐old pine plantation; individuals crowded but not overtopped by pines are compared with similar‐aged trees growing in openings within the plantation.Changes in aboveground architecture were stimulated by both prevention of sway and lateral shade but the effect of the latter was most pronounced; shaded saplings approached or exceeded their calculated critical height and buckled under their own weight when the shade cloth cylinders were removed. Rates of aboveground biomass acquisition, total leaf area, wood density, and wood elastic moduli did not differ among the three treatments; changes in stem allometry accounted for most of the observed differences in tree stability. Sweet gum trees growing in a pine plantation responded similarly to neighbors; crowded trees had larger height: diameter ratios and more closely approached their calculated critical heights than did trees growing in the open. Sweet gum saplings growing in dense stands of similar‐sized plants may surmount their neighbors by allocating relatively more wood to height growth than to girth increment.