Early spring leaf out enhances growth and survival of saplings in a temperate deciduous forest.
ABSTRACT 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.
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ABSTRACT: Aboveground production in terrestrial plant communities is commonly expressed in amount of carbon, or biomass, per unit surface. Alternatively, expressing production per unit volume allows the comparison of communities by their fundamental capacities in packing carbon. In this work we reanalyzed published data from more than 900 plant communities across nine ecosystems to show that standing dry biomass per unit volume (biomass packing) consistently averages around 1 kg/m(3) and rarely exceeds 5 kg/m(3) across ecosystem types. Furthermore, we examined how empirical relationships between aboveground production and plant species richness are modified when standing biomass is expressed per unit volume rather than surface. We propose that biomass packing emphasizes species coexistence mechanisms and may be an indicator of resource use efficiency in plant communities.03/2015; 3:e849. DOI:10.7717/peerj.849
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ABSTRACT: Species niches are expected to differ between different functional groups and between species with different functional traits. However, it is still unclear how functional traits contribute to niche separation between species coexisting in a community and between sites along environmental gradients.We studied seasonal changes in light partitioning among coexisting species belonging to different functional groups in moorland plant communities at different altitudes. We estimated the lifetime light absorption per unit invested leaf biomass (ΦLleafmass) as a measure of the benefit/cost ratio of light acquisition.Evergreen species absorbed more light in spring, whereas deciduous species absorbed more light in summer. A similar tradeoff was also found between short and tall species within each functional group. As a result, evergreen and shorter species had comparable ΦLleafmass values to those of deciduous and taller species. Evergreen species had higher ΦLleafmass at higher altitudes relative to deciduous species, suggesting that evergreen habit is more advantageous for the lifetime light interception at higher altitudes.Our results demonstrate that phenological tradeoffs for light partitioning can contribute to the coexistence of species with different functional traits. Our results also reveal that the most advantageous traits differ depending on environment.New Phytologist 08/2014; 204(4). DOI:10.1111/nph.12960 · 6.55 Impact Factor
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ABSTRACT: 1. In temperate climates, seedlings and saplings have often been assumed to be more sensitive to late-spring freezes than conspecific adult trees. Yet, no data is available to compare the freezing resistance of juvenile and adult trees at their phenologically most sensitive stage, i.e. during leaf-out.2. Emerging leaves of seedlings, saplings and adult trees were collected in spring 2013 in seven temperate tree species in a mature mixed forest in the foothills of the Swiss Jura Mountains. Freezing resistance of these emerging leaves was assessed using different target temperatures (-13 °C to +4 °C) in 7 computer-controlled freezers. Additionally, we assessed the risk that species encounter freeze damages based on temperature data recorded since 1898.3. The different study species showed contrasting freezing resistance, with the LT50 (median lethal freezing temperature) of emerging leaves ranging from -3.5 ± 0.2 °C (Fraxinus excelsior) to -8.3 ± 0.2 °C (Prunus avium). Within species, juvenile trees (seedlings or saplings) were found to be as sensitive to freezing temperatures as mature trees when the same developmental stage of foliage was compared. Based on phenological observations made during spring 2012, long time–series of temperatures indicate a very low risk of freeze damage at the study site, especially for adult trees.4. Synthesis We conclude that seedlings and saplings are more prone to freeze damage than adult trees because of their earlier flushing rather than due to a higher sensitivity to freezing as such. Our study highlights that the timing of spring phenology has evolved in such a way that it minimizes the risk of freeze damage according to the species-specific LT50. Early flushing species are among the most freezing resistant species during flushing, whereas late flushing species are among the least resistant. We conclude that for the examined species the species-specific freezing resistance during leaf emergence could be extracted from either adult or juvenile trees, as long as it is estimated at a same phenological stage.This article is protected by copyright. All rights reserved.Journal of Ecology 03/2014; 102(4). DOI:10.1111/1365-2745.12251 · 5.69 Impact Factor