Shade tolerance

Ecologists often invoke interspecific facilitation to help explain positive biodiversity-ecosystem function relationships in plant communities, but seldom test how it occurs. One mechanism through which one species may facilitate another is by ameliorating abiotic stress. Physiological experiments show that a chronic excess of light can cause stress that depresses carbon assimilation. If shading by a plant’s neighbors reduces light stress enough, it may facilitate that plant’s growth. If light is instead most often a limiting factor for photosynthesis, shading may have an adverse, competitive effect.In a temperate tree diversity experiment, we measured stem growth rates and photosynthetic physiology in broadleaf trees across a gradient of light availability imposed by their neighbors. At the extremes, trees experienced nearly full sun (monoculture), or were shaded by nearby fast-growing conifers (shaded biculture).Most species had slower growth rates with larger neighbors, implying ...

Wood density is a key variable for understanding life history strategies in tropical trees. Differences in wood density and its radial variation were related to the shade-tolerance of six canopy tree species in seasonally dry tropical forest in Thailand. In addition, using tree ring measurements, the influence of tree size, age and annual increment on radial density gradients was analysed. Wood density was determined from tree cores using X-ray densitometry. X-ray films were digitized and images were measured, resulting in a continuous density profile for each sample. Mixed models were then developed to analyse differences in average wood density and in radial gradients in density among the six tree species, as well as the effects of tree age, size and annual increment on radial increases in Melia azedarach. Average wood density generally reflected differences in shade-tolerance, varying by nearly a factor of two. Radial gradients occurred in all species, ranging from an increase of...

We used tree-rings to reconstruct long-term patterns of suppression, release and growth among five sympatric canopy tree species representing the full range of shade tolerance in a seasonal tropical forest in western Thailand. We expected that the frequency and duration of suppression and release events would be positively correlated with shade tolerance. All five species showed evidence of major and moderate growth releases. As expected, Melia azederach, an extreme heliophile, had the fewest releases. However, among the other species the number of major releases was consistent across the range of shade tolerance. The most significant difference among the species was the number of moderate releases recorded. There was a general positive correlation between the number of moderate releases and shade tolerance; however, Chukrasia tabularis, a relatively shade-intolerant species, had an anomalously high number of moderate releases. The study species also showed considerable variation in...

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ABSTRACTSixteen percent of tree stems 10 cm diameter or greater recorded in seven 1 ha plots in Rabongo Forest, Uganda had stem damage attributable to elephants (Loxodonta africana). We propose four strategies that may help tree species persist under these conditions: repellence, resistance, tolerance and avoidance. We sought and found evidence for each strategy. Large, shade‐tolerant Cynometra alexandri dominated basal area (often >50%) and showed severe scarring. Nearly 80 percent of stems were small pioneer species. Scarring frequency and intensity increased with stem size. Stem‐size distributions declined steeply, implying a high mortality to growth rate ratio. Tree species with spiny stems or with known toxic bark defenses were unscarred. Epiphytic figs escaped damage while at small sizes. Mid‐successional tree species were scarce and appeared sensitive to elephants. Savanna species were seldom scarred. Taking stem size‐effects into account by using a per‐stem logistic model...

Shade tolerance, the minimum light requirement for plant survival, is a key trait for understanding community assembly and forest dynamics. However, it is poorly defined for tree species to date. Current methods of measuring shade tolerance vary considerably in their performance. For instance, some measures of shade tolerance are unreliable except under some specific conditions. Therefore, it is necessary to compare the performance of these methods to provide guidance of choosing appropriate shade tolerance measures in future studies. We collected a large dataset of light traits and other life history traits for 137 understory wood species in a subtropical forest and tested the performance of five commonly used shade-tolerance indices. Results showed that all the shade-tolerance measures, except the low-light abundance index, performed poorly in distinguishing and ranking shade tolerance of the tested species. The shade tolerance quantified by the low-light abundance was consistent ...

Summary Understanding the factors that limit species distributions along environmental gradients is a central question of ecology. Here, we evaluate the hypothesis that the traits that result in performance trade‐offs between habitats contribute to the turnover of woody species along a rainfall gradient in the Isthmus of Panama. We studied 24 plant species with contrasting distributions along this rainfall gradient. We measured 18 morphological and physiological traits, and three performance variables in seedlings planted in common garden experiments in two contrasting sites across the Isthmus. We found evidence for a trade‐off suggesting that better survival during the dry season corresponded to a lower growth rate in the forest understorey. This trade‐off correlated well with the distribution of the species along the rainfall gradient and was explained mostly by variation in photosynthetic capacity. While not all species fit into this trade‐off, most dry‐distribution species, whic...

Bermudagrass turfs are widely used in subtropical to tropical regions and in transition zones for golf courses, landscape areas, and athletic
ields. Lack of adequate cold tolerance in these grasses causes early winter dormancy and an aesthetically unpleasing surface. This study
investigated the efect of sequential Trinexapac-ethyl (TE) applications during the growing season on fall color retention, spring green-
up, and physiological responses related to cold hardiness in bermudagrass cultivars. Trinexapac-ethyl (untreated, 6.0, 12.0, and 18.0 mg
a.i. m-2
) was applied monthly throughout the bermudagrass growing season. According to the results, TE applications enhanced spring
green-up and possessed color retention for 20 and 12 days longer in the irst and second years of the study, respectively. Higher proline
and total carbohydrate contents were observed in the crown of TE-treated as compared to untreated turfs. Hybrid cultivars exhibited
higher spring green-up, rhizome survival, proline content, total carbohydrates, and longer color retention than seeded cultivars. The
higher proline content of the crown was positively associated with enhanced color retention, rhizome survival, and spring green-up.
Finally, these results conirmed that accumulated osmolytes in the crown (resulting from growing-season TE application) minimized
the dormancy period in winter via improvement of fall color retention and spring green-up.

Shadetolerance and regeneration of some heavily exploited timber species(Uvariopsis congensis, Antiaris toxicaria, Funtumia africana,Prunus africana and Aningeria altissima)were studied in two adjacent sites in Kakamega tropical rain forest. The twosites have been subjected to different logging intensities. Within one of thesites, relatively intact areas were compared with adjoining more disturbedones.Seedling presence or absence in mature forest phase, sapling proportions in

Niche differentiation is a major hypothesized determinant of species distributions, but its practical importance is heavily debated and its underlying mechanisms are poorly understood. Trait‐based approaches have been used to infer niche differentiation and predict species distributions. For understanding underlying mechanisms, individual traits should be scaled up to whole‐plant performance, which has rarely been done.We measured seven key traits that are important for carbon and water balance for 37 tropical tree species. We used a process‐based plant physiological model to simulate the carbon budget of saplings along gradients of light and water availability, and quantified the performance of the species in terms of their light compensation points (a proxy for shade tolerance), water compensation points (proxy for drought tolerance), and maximum carbon gain rates (proxy for potential growth rate). We linked species performances to their observed distributions (the realized niches...

The intermediate disturbance hypothesis (IDH) predicts local species diversity to be maximal at an intermediate level of disturbance. Developed to explain species maintenance and diversity patterns in species‐rich ecosystems such as tropical forests, tests of IDH in tropical forest remain scarce, small‐scale and contentious. We use an unprecedented large‐scale dataset (2504 one‐hectare plots and 331 567 trees) to examine whether IDH explains tree diversity variation within wet, moist and dry tropical forests, and we analyse the underlying mechanism by determining responses within functional species groups. We find that disturbance explains more variation in diversity of dry than wet tropical forests. Pioneer species numbers increase with disturbance, shade‐tolerant species decrease and intermediate species are indifferent. While diversity indeed peaks at intermediate disturbance levels little variation is explained outside dry forests, and disturbance is less important for species r...

We evaluated the immediate effects of group selection harvesting on the establishment of yellow birch (Betula alleghaniensis Britt.) and black cherry (Prunus serotina Ehrh.) seedlings in maple-dominated hardwood stands of Algonquin Provincial Park, Ontario. Group selection gaps were compared to single-tree selection cutting and uncut reference stands pre-harvest and one growing season post-harvest using a before-after-control-impact (BACI) design. The percent cover of yellow birch seedlings increased significantly more in gaps than in single-tree selection and reference plots. Black cherry seedling cover increased significantly more in gaps than in reference plots, but increased at a similar rate in gaps and single-tree selection plots. Increased soil exposure and closer seed trees resulted in increased yellow birch recruitment when harvesting occurred in the late-summer-fall. These factors had little influence on yellow birch recruitment when harvesting occurred in the winter. The ...

Climate change is predicted to result in warmer and drier Neotropical forests relative to current conditions. Negative density‐dependent feedbacks, mediated by natural enemies, are key to maintaining the high diversity of tree species found in the tropics, yet we have little understanding of how projected changes in climate are likely to affect these critical controls. Over 3 years, we evaluated the effects of a natural drought and in situ experimental warming on density‐dependent feedbacks on seedling demography in a wet tropical forest in Puerto Rico. In the +4°C warming treatment, we found that seedling survival increased with increasing density of the same species (conspecific). These positive density‐dependent feedbacks were not associated with a decrease in aboveground natural enemy pressure. If positive density‐dependent feedbacks are not transient, the diversity of tropical wet forests, which may rely on negative density dependence to drive diversity, could decline in a futu...

Susanto D, Hayatudin, Setiawan A, Purnomo H, Ruhiyat D, Amirta R. 2017. Characterizing nutrient status and growth of Macaranga gigantea in tropical rainforest gaps after selective logging in East Kalimantan, Indonesia. Biodiversitas 18: 996-1003. Selective logging caused the formation of forest gaps, which stimulate the growth of the pioneer tree species. This study aims to determine the characteristic of soil nutrients status and plant growth of Macaranga gigantea in the tropical rainforest gaps after selective logging in East Kalimantan, Indonesia. We established research plots 50mx50m in natural forest production, 1 until 10 years after selective logging. The measured data of each plot is the number of trees of M. gigantea, its stem diameter, and its height, and also the soil and leaf nutrient concentration. The results showed that the soil has a pH (H2O) of 5.3 ± 0.27, cation exchange capacity of 10.6 ± 2.98 meq. 100 g-1, base saturation of 27.7 ± 10.44%, while the concentration...