PARENT SESSION
Oral Session #34: Forests: Models of function and structure. Presiding: M. Lechowicz.
Tuesday, August 7, 2001. 1:00 PM to 3:45 PM. Hall of Ideas F.
Understanding old-growth forests using stand-level processes.
Gutsell, Sheri1, Johnson, Edward1, 1
ABSTRACT- Our present understanding of old-growth forests is based primarily on the descriptive characteristics of stands, with little understanding of the processes that give rise to these characteristics. We used age-specific mortality rates, falling rates, and height growth rates to examine four old-growth characteristics: 1) large, dead standing and fallen trees, 2) decreased height growth of canopy trees, 3) canopy gaps, 4) growth of understorey into canopy gaps. Within an old-growth Pinus banksiana - Picea mariana dominated stand, all live and dead (standing and fallen) seedlings, saplings, and trees were sampled. A disk was cut at every metre to the top of each individual for height growth analysis. Dates of recruitment and mortality were determined using dendrochronology. The age-specific mortality rate, reconstructed for the most recent 50-year period, showed that significantly fewer P. banksiana died compared to P. mariana. Dead P. banksiana (14 - 48 cm basal diameter) were generally larger than dead P. mariana (6.4 - 22 cm). Of the dead individuals, 100% of P. banksiana and 33% of P. mariana were fallen. Height growth analysis showed that the height growth of P. banksiana and P. mariana decreased 60 years and 120 years, respectively, after stand initiation. Gap filling in this old-growth stand is unlikely because of the high mortality rates and low growth rates of understorey individuals, and the short fire cycle in the study area.
KEY WORDS: old-growth forest, gap dynamics, age-specific mortality rates, falling rates