About 75% of the land mass of Papua New Guinea is covered by primary forest which is assumed to have a high biodiversity. Overall there has been little decrease in the area under primary forest although some has resulted from logging activities and expansion of plantation agriculture. Shifting cultivation is the main form of agricultural land-use but due to intensification of the agricultural systems there has been little extension into primary forest areas. There are large areas in the humid lowlands where the tall shrub Piper aduncum L., a native from tropical America (Mexico to Bolivia), has invaded locally forming monospecific stands. Despite its rapid invasion and widespread occurrence very little research has been conducted on this and its effects.