Page 15 - LandscapeSA Issue 106

fEATURE

MANAgINg RISKS TO BIODIVERSITY

USINg INSEcTS AND PATHOgENS

BY cANDIcE LYONS AND ALANA DEN BREEYEN

The Western Cape is home to one of the world’s biodiversity hotspots, the fynbos biome.
The species richness within this biome rivals that found within species-rich rainforests
in South America. Like several other biomes within South Africa, the fynbos biome

faces multiple threats from various sources, including habitat encroachment, frequent
and hot fire events resulting from climate change, drought and invasive species.

lobally, invasive species cause invasive is tied very closely to human Controlling invasive plant species
significant ecosystem impacts. movement. In South Africa, the species The three methods used to control invasive
GAmongst the main issues that have become most invasive have only plant species include manual clearing,
surrounding the spread and abundance done so post-1652. With the expansion chemical spraying or biological control
of invasive species is their impact on local of trade routes and the advent of air using insects and pathogens. Of these three
biodiversity. This includes their impact on travel, pathways for invasive species grew methods, the most economically viable
indigenous vegetation and communities exponentially. Invasive species were either (long-term), and the most environmentally
and habitat structure, which has introduced purposefully, such as those non-damaging, is biological control, which
cascading consequences on ecosystem introduced for the forestry sector, those uses insects and pathogens to control the
function. The term “ecosystem function” introduced for dune stabilisation and spread or density of invasive plants. The
refers to the ability of a natural system to ornamental purposes, or were introduced history of biological control in South Africa
provide goods and services to humans, accidentally. spans more than a century with successes
either directly or indirectly. Invasive and failures over this time. Two successful
species tend to increase fuel loads, According to the National Environment biocontrol stories include controlling
which in turn leads to more extreme and Management and Biodiversity Act prickly pear cacti and Port Jackson willow
catastrophic fire events. 2014, invasive species within South in South Africa.
Africa are listed whatever the route of
So how do species become introduction and subsequent invasion. Before the release of a moth and cochineal
invasive? Scientific methods categorise invasive insect in the 1930s, mission prickly pear
Invasive species establish and thrive in species within South Africa according grew in extremely dense, impenetrable
areas where they otherwise would not to their level of ‘invasiveness’. The most stands. Farmers would often lose livestock
naturally occur, primarily due to their problematic weeds requiring immediate due to the inability of livestock to escape
ability to outcompete native species. eradication or control are listed as cactus-infested areas. Today, mission prickly
Invasive plants have a faster growth Category 1 invaders. Familiar problematic pear is no longer considered as significant a
rate, produce more seeds or alter the and common Category 1 invasive weed as it was pre-1933.
system to such an extent that it becomes species include several wattle species,
uninhabitable by native vegetation. The silky hakea, bugweed, pines and several In 1987, a gall-forming rust fungus was
rate at which invasive species become cactus species. released to manage the density and

Azolla filiculoides is a red water fern considered a good success story in terms of biological control.
PHOTOS BY DR. ANDREW MccONNAcHIE.

Azolla filiculoides in Ficksburg (before) Azolla filiculoides in Fickburg (after three months)

Landscape SA • Issue 106 2021 13