Liana Distribution And Abundance In Moist Tropical Forest In Ghana 40 Years Following Silvicultural Interventions

Abstract

Lianas are an important structural aspect of tropical forest ecosystems, but may have negative impacts on tree growth and productivity. We censused lianas in plots that were subjected to three different types of silvicultural intervention in Bobiri forest in Ghana in order to answer two questions: 1) does liana cutting during the initial years of a cutting cycle influence liana densities, basal area and vine loads in tree crowns relative to unlogged forest?; 2) does the duration, intensity and sequence of silvicultural interventions in the initial years of a cutting cycle influence vine loads? Data were gathered from six onehectare plots in each of the three silviculturally-treated stands, with comparative data collected from four one-hectare plots in an unlogged part of the same forest. Lianas were categorised into small (stems =2 - 5 cm DBH) and large sizes (DBH >5 cm) and censused in nested subplots within the one-hectare plots. The extent of liana loading or ‘infestation’ of individual trees ? 20cm DBH was investigated using a 5-point score 0, 1, 2, 3 and 4 within the plots. A total of 697 liana stems were inventoried in both the silviculturally-treated and the unlogged forest. The density of small lianas was relatively higher in the unlogged forest than in treated forest. However, mean densities of large lianas were similar across treatments. For all lianas with DBH = 2 cm, mean densities were lower in the treated forest than in the unlogged forest. Liana loading or ‘infestation’ was dependent on silvicultural treatment consequent to the timing of interventions; while about 9% of stems were completely covered by lianas in forest where climber cutting followed timber harvesting; only about 1% of trees were completely covered by lianas in unlogged forest and forest where liana cutting preceded timber harvesting. Approximately 90% of trees DBH ? 20cm were free of lianas in forest where liana cutting preceded timber harvesting, with ~81% of stems in the same category free of lianas in unlogged forest. However, in forest where liana cutting followed timber harvesting only about 46% of stems were free of lianas. We conclude, from the lower densities of lianas in the silvicultural intervention sites relative to the unlogged sites that even 40 y later the impact of climber cutting was measurable. Although the density of large lianas was not distinct among the silviculturally-treated stands, the interventions promoted greater access to tree crowns by lianas when applied after timber harvesting. Thus the timing of silvicultural interventions in the initial years of a cutting cycle is important since it influences liana load in tree crowns in the long term.

Keywords: Silvicultural systems, Liana load, Tropical Shelterwood System, Post-Exploitation System, Liana inventory