Gap-scale disturbance processes in secondary hardwood stands on the Cumberland Plateau,Tennessee, USA |
| |
Authors: | Justin L Hart Henri D Grissino-Mayer |
| |
Institution: | (1) Department of Geography, University of North Alabama, Florence, AL 35632, USA;(2) Department of Geography, The University of Tennessee, Knoxville, TN 37996, USA |
| |
Abstract: | Disturbance regimes in many temperate, old growth forests are characterized by gap-scale events. However, prior to a complex
stage of development, canopy gaps may still serve as mechanisms for canopy tree replacement and stand structural changes associated
with older forests. We investigated 40 canopy gaps in secondary hardwood stands on the Cumberland Plateau in Tennessee to
analyze gap-scale disturbance processes in developing forests. Gap origin, age, land fraction, size, shape, orientation, and
gap maker characteristics were documented to investigate gap formation mechanisms and physical gap attributes. We also quantified
density and diversity within gaps, gap closure, and gap-phase replacement to examine the influence of localized disturbances
on forest development. The majority of canopy gaps were single-treefall events caused by uprooted or snapped stems. The fraction
of the forest in canopy gaps was within the range reported from old growth remnants throughout the region. However, gap size
was smaller in the developing stands, indicating that secondary forests contain a higher density of smaller gaps. The majority
of canopy gaps were projected to close by lateral crown expansion rather than height growth of subcanopy individuals. However,
canopy gaps still provided a means for understory trees to recruit to larger size classes. This process may allow overtopped
trees to reach intermediate positions, and eventually the canopy, after future disturbance events. Over half of the trees
located in true gaps with intermediate crown classifications were Acer saccharum, A. rubrum, or Liriodendron
tulipifera. Because the gaps were relatively small and close by lateral branch growth of perimeter trees, the most shade-tolerant A. saccharum has the greatest probability of becoming dominant in the canopy under the current disturbance regime. Half of the gap maker
trees removed from the canopy were Quercus; however, Acer species are the most probable replacement trees. These data indicate that canopy gaps are important drivers of forest change
prior to a complex stage of development. Even in relatively young forests, gaps provide the mechanisms for stands to develop
a complex structure, and may be used to explain patterns of shifting species composition in secondary forests of eastern North
America. |
| |
Keywords: | Canopy gaps Disturbance Forest development Mixed hardwoods Succession Tennessee |
本文献已被 SpringerLink 等数据库收录! |
|