Effects of Climate and Stand Age on Annual Tree Dynamics in Tropical Second-Growth Rain Forests

Abstract

We monitored mortality and recruitment annually for six years for all trees Ն5 cm diameter at breast height in four 1-ha plots in second-growth, lowland rain forests in northeastern Costa Rica. Stands initially ranged in age from 12 to 25 years since abandonment of cattle pastures. In younger stands, abundance decreased 10-20% in the small size class (5-9.9 cm dbh), but increased 49-100% in the large size class (Ն25 cm dbh). In the two youngest plots, 45.0% and 27.6% of the common tree species showed annual population increases of 3% or more, whereas 10% showed annual decreases of 4% or more. Annual rates of tree mortality for all size classes and recruitment into the 5-cm size class varied significantly among years, and mortality rates of trees 5-9.9 cm dbh were higher in younger than in older stands. Tree mortality was highest during the 1997-1998 El Niño Southern Oscillation (ENSO) year; on average, 5.6%, 3.5%, and 1.4% of trees died in the small, intermediate, and large size classes, respectively. Mortality rates during the ENSO year were 1.9 times higher for trees Ն10 cm dbh compared to non-ENSO years. Annual mortality rates for trees Ն10 cm dbh decreased significantly with increasing dry-season rainfall, but not with total annual rainfall during the census periods. Tree mortality (particularly for trees Ն25 cm dbh) in these secondary forests was highly sensitive to dryseason rainfall, even during non-ENSO years. Increased tree mortality during ENSO years is likely to accelerate forest dynamics and successional change in wet tropical secondgrowth forests.

Species diversity and successional dynamics in the secondary forest of Obafemi Awolowo University Biological Gardens Ile-Ife, Nigeria

“…This does not agree with the findings of Chazdon et al (2005), who stated that younger forests (less than 15 years since abandonment) are certainly more dynamic in overall stem density and community sizes than older sites. However, Chazdon et al (2007) opined that stem density does not show a predictable pattern with stand age.…”

Community dynamics during early secondary succession in Mexican tropical rain forests

“…To our best knowledge, examples of studies on community-level dynamics and underlying mechanisms in young secondary tropical forests are much less common. Recently Chazdon et al (2005) monitored recruitment, growth and mortality of trees ≥ 5 cm dbh annually for 6 y in four 12-25-y-old sites on abandoned cattle pastures. Earlier Uhl (1987) examined growth, mortality and recruitment over 5 y following slash-andburn agriculture in one plot in the Amazon of Venezuela.…”

Visual assessment of wilting as a measure of leaf water potential and seedling drought survival

“…Recent evidence indicates that, even in moist and wet tropical forests, low water availability plays a prominent role for plant population dynamics, local and regional distribution patterns, community composition and diversity and ecosystem function (Bongers etal. 1999, Bunker & Carson 2005, Chazdon et al 2005, Engelbrecht et al 2007 Furthermore, in agroforestry, a major factor determining the success of stand establishment in tropical reforestation efforts is known to be the careful matching of water availability and the moisture requirements of species (Evans 1996, Gerhardt 1993.…”