Liana Biomass and Leaf Area of a "Tierra Firme" Forest in the Rio Negro Basin, Venezuela

Abstract

In evergreen tropical rain forest, growing on a nutrient-poor Oxisol (lateritic soil) near San Carlos de Rio Negro, Venezuela, the average total above-ground dry weight of lianas was 15.7 t ha-I which was 4.5 percent of the estimated above-ground forest biomass. The average leaf area index of lianas was 1.2 M2 m-2 and constituted 19 percent of total forest leaf area. In comparison to trees, liana stems are small in diameter relative to the sizes of their crowns. This difference in allometry occurs because lianas rely on other plants for support and liana stems generally have large diameter and thus efficient xylem vessels. By maintaining the conducting capacity of their vessels for longer periods of time than do trees, lianas are able to increase further their leaf biomass-stem diameter ratios. Increases in cross sectional areas of liana stems are associated with proportionately larger increases in leaf biomass than comparable increases in cross sectional areas of tree stems. LIANAS ARE WOODY CLIMBING PLANTS that typically rely on other plants for mechanical support. They are often strikingly apparent in tropical forests (Spruce 1908, Richards 1952, Longman and Jenik 1974), but little quantitative information exists on liana abundance. The present study reports liana biomass and leaf area in a tierra firme (never flooded) forest in the Rio Negro Basin near San Carlos de Rio Negro, Venezuela; Jordan and Uhl (1978) gave estimates of tree biomass in the same area. Data from destructively sampled lianas are also used to examine quantitatively the relations between stem diameter, leaf biomass, and total above-ground biomass. STUDY SITE AND METHODS The study site was in the Territorio Amazonas, Venezuela near San Carlos de Rio Negro (1?56'N, 67?03'W) at an elevation of 119 m. This area receives an average of 3500 mm of rainfall per year and average monthly rainfall exceeds 100 mm even during the dry period (January through March; Heuveldop 1977). Sampling was conducted in evergreen forest growing on a nutrient impoverished Oxisol with slopes less than 5?. Charcoal fragments found in most soil samples (Stark and Spratt 1977) suggest a history of human use (i.e., possible clearing and burning), but there was no evidence of recent clearing. Uhl and Murphy (1981) point out that low soil fertility may be responsible for the low tree basal area (28 m2 ha-'), low canopy stature (tallest trees 25-30 m), and high density of stems (232 trees >20 cm dbh per ha). The average above-ground biomass (dry weight) of living trees in the study area was 335 t ha-1 (Jordan and Uhl 1978). Global surveys of forest biomass suggest an average for tropical forests of approximately 450 trha-' (Lieth 1975). Liana abundance and size-class distribution were estimated by species in 20 randomly located 100 m2 circular sample plots. In each plot I measured the dbh (diameter at 1.3 m or above the buttresses) of every tree and liana >2 m tall, determined the species of each liana, and recorded the sizes of the trees upon which the lianas grew. Lianas <2 m tall were identified, counted, and recorded as free standing (upright) or climbing. Only lianas rooted in the plots were enumerated. Many of the underground connections between stems had undoubtedly broken and decomposed. For this reason, an individual for the purposes of this study was considered to be an independently climbing or self-supporting stem. Plants in the Araceae were not included because many species are herbaceous and grow as epiphytes or hemiepiphytes (plants that either start out or end up their lives as epiphytes). Lianas for biomass determinations were selected to represent the range of observed diameters and included only the most common species. Large lianas often pass from canopy tree to canopy tree but, by climbing several times into the canopy and cutting supporting tree branches, it was possible to extract lianas from the tree tops. As a result, lianas harvested for biomass determination are reasonably complete. On the ground all the liana leaves were removed by hand and weighed on hanging scales. I randomly selected and weighed 50 leaves from every harvested liana for subsequent determination of wet-to-dry weight conversion factors; an additional 10 leaves were randomly selected from each liana for determination of area-weight relations. To estimate stem biomass, I cut up and weighed all the stems and branches and selected small (5-10 cm long) sections of representative diameters for weight and density determinations. I Present address: Department of Botany, University of Florida, Gainesville, Florida 32611, U.S.A. BIOTROPICA 15(3): 185-189 1983 185 This content downloaded from 157.55.39.118 on Fri, 22 Apr 2016 06:20:53 UTC All use subject to http://about.jstor.org/terms TABLE 1. Lianas used in biomass regressions.