Ecological Dynamics Of Helichrysum (Asteraceae) Shrubs Cover And Their Effect On Orchids In Kitulo National Park, Tanzania
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Date
2025-08
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NM-AIST
Abstract
Grassland ecosystems are undergoing major ecological transformations due to anthropogenic disturbances. In protected areas such as Kitulo National Park (KNP) in Tanzania, the spread of dwarf Helichrysum shrubs has potential impact on native herbaceous plant species like orchids. While Helichrysum species are known to thrive in degraded, low-nutrient soils, there is limited empirical evidence on the mechanisms driving their spread and the ecological consequences of their encroachment in tropical montane grasslands. This study aimed to assess the drivers of Helichrysum expansion and their ecological interaction with orchids. Fieldwork was conducted across multiple zones within KNP, categorized based on their historical land use as ‘grazed crop’, ‘grazed’, and ‘wild’. A total of 222 quadrats were established to assess the abundance and diversity of Helichrysum and orchid species. Soil samples were analyzed to determine nutrient composition, and controlled experiments were conducted to evaluate Helichrysum regeneration under different fire treatments (unburned, early burned, late burned) and disturbance regimes (cutting stems, uprooting). Additionally, germination trials were carried out in the laboratory to test the effect of fire-simulated temperatures on Helichrysum splendidum seed germination. The orchid species' responses were evaluated in terms of relative interaction intensity (RII), physiological vigor, and flowering metrics under varying Helichrysum cover levels. Results revealed that Helichrysum splendidum was the most dominant shrub species, with significantly higher abundance in historically disturbed zones; the 73% and 46% more in ‘grazed crop’ and ‘grazed’ areas, respectively, than in the ‘wild’ zone. Orchid richness and abundance significantly declined with increasing Helichrysum cover. Fire played a dual role while complete burning induced vigorous Helichrysum resprouting, early burns significantly suppressed seedling recruitment and reduced seed bank density. Temperature treatments confirmed that seeds exposed to 80°C and 110°C had significantly lower germination than unheated and those heated at 50°C (p < 0.001), suggesting fire-inhibits germination of Helichrysum seed. This study concludes that the spread of Helichrysum shrubs in Kitulo National Park is largely driven by legacy effects of past land use and soil nutrient depletion. High shrub cover negatively affects orchid diversity and species richness. Management strategies that include burning early in the season and physically removing shrubs can reduce the spread of Helichrysum and support the protection of native orchid species and the variety of plants in montane grasslands.
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