Browsing by Author "Lin, Jie"

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    Testing shade tolerance as a mechanism of dynamics in three forests of Big Thicket National Preserve, southeast Texas
    (2002) Lin, Jie; Harcombe, Paul A.
    I investigated the role of shade tolerance in the dynamics of three forests of Big Thicket National Preserve, southeast Texas. In a mature mesic forest, shade-intolerant species had higher high-light growth and lower low-light growth than tolerant species. Results suggested that there was a tradeoff between high-light growth and low-light growth across species. Moreover, low-light survival and high-light growth were negatively correlated across species. In contrast to northern hardwood forests where survival in low light may be achieved at the expense of growth, my results suggested that shade-tolerant species in this southern mixed forest can grow faster as well as survive better than shade-intolerant species in low light. I conclude that both juvenile growth and survival are important components of shade tolerance and their relationships may be system-specific. In a floodplain forest, growth responses to light were consistent with the expectation that shade-intolerant species grow faster than shade-tolerant species in high light and vice versa. But mortality risks of some shade-tolerant species were unexpectedly high. The increased flooding during one of the study time periods may be responsible for the high mortality risks of shade-tolerant species. The results further supported that the success of shade-tolerant species in this forest may be limited by flooding as previous studies suggested. Compared with the mesic site, common species showed little intraspecific differences in shade tolerance. In a sandy upland pine-oak forest, low-light growth responses of saplings corresponded to shade tolerance expectation. However, shade-intolerant species did not show faster growth than shade-tolerant species in high light possibly because these species are drought-tolerant. The correspondence between increasing stem density and increasing death rates of shade-intolerant xeric dominants suggested that recent increases in canopy shading may be responsible for high death rates of these species. Cross-site comparison showed that shade-tolerant species had better performance at the dry site than at the mesic site. Consistent with the facilitative effect found at dry sites, these species may benefit from the less competition from surrounding vegetation.
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    Testing two measures of shade tolerance in a mesic forest in southeast Texas
    (1999) Lin, Jie; Harcombe, Paul A.
    I used sapling demographic data to investigate the relationship between shade tolerance and parameter estimates of a mortality-growth model and a height-diameter model. The study site is at Wier Woods, a mesic forest in southeast Texas. The results show that species order for probability of mortality at zero growth corresponds closely to the standard shade tolerance classification: the probability of mortality at zero growth decreases as shade tolerance rank increases. Also, the probability of mortality decreases rapidly as growth increases for shade-intolerant species, while showing little variation for shade-tolerant species. Therefore, this study provides strong support for the assertion that the mortality-growth relationship is a key life-history characteristic that determines shade tolerance. The results of a linear regression of height against DBH show that shade-intolerant species have steeper slopes than shade-tolerant species. This implies that a trade-off of photosynthate allocation between height growth and diameter growth may be an additional mechanism that influences shade tolerance.