Tropical forest tree mortality, recruitment and turnover rates: calculation, interpretation and comparison when census intervals vary

Abstract

Summary1 Mathematical proofs show that rate estimates, for example of mortality and recruitment, will decrease with increasing census interval when obtained from censuses of non-homogeneous populations. This census interval effect could be confounding or perhaps even driving conclusions from comparative studies involving such rate estimates. 2 We quantify this artefact for tropical forest trees, develop correction methods and re-assess some previously published conclusions about forest dynamics. 3 Mortality rates of > 50 species at each of seven sites in Africa, Latin America, Asia and Australia were used as subpopulations to simulate stand-level mortality rates in a heterogeneous population when census intervals varied: all sites showed decreasing stand mortality rates with increasing census interval length. 4 Stand-level mortality rates from 14 multicensus long-term forest plots from Africa, Latin America, Asia and Australia also showed that, on average, mortality rates decreased with increasing census interval length. 5 Mortality, recruitment or turnover rates with differing census interval lengths can be compared using the mean rate of decline from the 14 long-term plots to standardize estimates to a common census length using λ corr = λ × t 0.08 , where λ is the rate and t is time between censuses in years. This simple general correction should reduce the bias associated with census interval variation, where it is unavoidable. 6 Re-analysis of published results shows that the pan-tropical increase in stem turnover rates over the late 20th century cannot be attributed to combining data with differing census intervals. In addition, after correction, Old World tropical forests do not have significantly lower turnover rates than New World sites, as previously reported. Our pan-tropical best estimate adjusted stem turnover rate is 1.81 ± 0.16% a − 1 (mean ± 95% CI, n = 65). 7 As differing census intervals affect comparisons of mortality, recruitment and turnover rates, and can lead to erroneous conclusions, standardized field methods, the calculation of local correction factors at sites where adequate data are available, or the use of our general standardizing formula to take account of sample intervals, are to be recommended.

Dynamics of the woody vegetation of two areas of Cerrado sensu stricto located on different substrates

“…In order to correct the bias related to the variation in the interval between censuses, we applied a correction factor (Lewis et al 2004), based on the formula λ corr = λ × t 0.08 , where: λ is the rate and t is the interval in years. We also calculated the number of individuals of each diameter class that persisted, died, were recruited and either immigrated or emigrated (Lieberman et al 1985), as proposed by Spiegel (1976).…”

Changing Ecology of Tropical Forests: Evidence and Drivers

“…Results have been contentious since the first studies suggested that tropical forests were not in long-term equilibrium (Phillips & Gentry 1994, Phillips et al 1998, with criticisms focusing on perceived methodological problems (Clark 2002) and statistical ambiguities (Sheil 1995). Although many of the potential statistical and methodological flaws have since been investigated and resolved Chave et al 2008;Lewis et al 2004cLewis et al , 2009Phillips et al 2002aPhillips et al , 2009, the "changing ecology of tropical forests" hypothesis is still hotly debated (Muller-Landau 2009, Wright 2005. This debate arises, in part, because of inherent limitations in the use of forest plots to detect and understand widespread changes in the functioning of tropical forests, particularly the limited number and length of time such plots have been monitored, and constraints on understanding the drivers of trends given the limited monitoring of the tropical environment.…”

Dinâmica da comunidade arbórea em uma floresta estacional semidecidual sob queimadas recorrentes

“…Muitos estudos abordam a dinâmica das florestas tropicais (Lang & Knight 1983;Lieberman et al 1985;Denslow 1987;Swaine et al 1990;Korning & Balslev 1994;Sheil & May 1996;Laurance et al 1998;Holl 1999;DeWalt et al 2003; Lewis et al 2004;Saiter et al 2011). Especificamente no Brasil, florestas semidecíduas, têm sido estudadas com relativa frequência (Oliveira-Filho et al 1997; Nascimento et al 1999;Chagas et al 2001;Guilherme et al 2004;Appolinário et al 2005;Oliveira-Filho et al 2007;Paiva et al 2007;Higuchi et al 2008;Silva & Araujo 2009).…”