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

Department of Plant Biology, University of Illinois, Urbana, IL 61801, USA.
Oecologia (Impact Factor: 3.09). 04/2008; 156(2):281-6. DOI: 10.1007/s00442-008-1000-7
Source: PubMed


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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    • "observed (Fig. 11D). This can be due to earlier budburst and leaf growth for sub-canopy tree species (Augspurger, 2008), resulting in close to fully developed leaves by the time of the first measurement. "
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    • "On the other hand, shorter species had a greater light absorption during the spring because of their evergreen habit or because of earlier leaf expansion. This is similar to the phenological avoidance observed in understory plants in deciduous forests; their earlier leaf expansion in spring compared with that of canopy trees contributes to their lifetime carbon gain (Uemura, 1994; Augspurger, 2008; Ida & Kudo, 2008). Interestingly, this tradeoff was observed across each of the evergreen and deciduous species studied here, suggesting that functional differentiation in relation to maximum leaf height and phenology is maintained in each functional group (Fig. 4). "
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