Documenting the chronology of ecosystem health erosion along East African rivers

Abstract

Pristine tropical ecosystems are currently suffering under extreme demographic pressure. This has led to habitat destruction and disturbances, an important precondition for the invasion of exotic species into pristine ecosystems, with detrimental effects on biodiversity. In this study, we analysed the chronology of land cover changes along rivers in south-eastern Kenya using historical aerial photographs and current aerial pictures taken from a drone. We assessed quantity and quality of riparian thickets along these rivers in 1961, 1980 and 2015/ 2016 and analysed effects of fundamental land cover changes on arthropod abundance and diversity. Our data show effects from demographic pressure by the increasing number of human settlements rising by 425% from 1961 to 2015/2016 (i.e. from 36 to 189 settlements). 58.5% of the land surface originally covered by pristine riparian forests was cleared and transformed into agricultural land. After clearance and agricultural usage it frequently became fallow land and was invaded by the exotic shrub species Lantana camara. While the total coverage of riparian vegetation did not change over time, its quality declined dramatically. Currently 36.6% of the cleared pristine riparian forest is covered by L. camara thickets, and only 22.5% of the pristine riparian forest has remained unchanged over time. This modification of the vegetation structure impacts biodiversity. The abundances of three guilds of arthropods significantly differed between pristine and L. camara-dominated riparian vegetation, with herbivorous arthropods and ants being more abundant in pristine than in L. camara-dominated vegetation. Our data show that habitat destruction and disturbance is the prerequisite for subsequent invasion by exotic plant species, having a strong effect on species composition and diversity at higher trophic levels.

Seasonality and landscape characteristics impact species community structure and temporal dynamics of East African butterflies

“…Furthermore, the riparian vegetation, where it still exists, has largely been replaced by invasive exotic plant species (e.g. Lantana camara ) 12 . The landscape of our second study site along Kainaini River represents a still largely intact riparian forest with adjoining dry savannahs.…”

“…These rivers are naturally bordered by dense riparian vegetation, home of a unique flora and fauna with many specialised and endemic species 11 . The substantial increase of settlements and hence human activities (in particular subsistence agriculture) along these rivers and in general across the dryland areas has caused severe degradation of both the riparian forests 12 , 13 and the dry savannahs 14 . The resilience of both ecosystems is rather limited, and many questions about the effects of human and natural impacts on these ecosystems and the species living therein remain unresolved.…”

Movement ecology of Afrotropical birds: Functional traits provide complementary insights to species identity

“…To minimize the effect of seasonal variation, all our fieldwork was conducted at the end of the respective dry seasons. Our study area is characterized by fast human population growth (KNBS Kenyan Bureau of Statistics, ) and subsequent destruction and degradation of pristine riparian habitats (Habel, Teucher, Ulrich & Schmitt, ). Today, the landscape consists of a mosaic of riparian thickets, agricultural land, small settlements, and the riverbed of Nzeeu river.…”

Use of unmanned aircraft systems (UAS) and multispectral imagery for quantifying agricultural areas damaged by wild pigs

“…5-10 cm) and temporal resolutions (e.g. daily or even hourly revisit times), thus they can assist with precision agriculture (Candiago et al, 2015;Christiansen et al, 2017;Hunt and Daughtry, 2018), rangeland monitoring (Laliberte et al, 2010;Laliberte et al, 2011;Sankey et al, 2018), forest mapping (Wallace et al, 2012;Getzin et al, 2014;Birdal et al, 2017), ecosystem monitoring (Habel et al, 2018), invasive species mapping (Samiappan et al, 2017), and detecting and monitoring pest infestations (Lehmann et al, 2015;Puig et al, 2015). Data collected by UAS have also been used recently to estimate damage to agricultural crops by wild pigs (Michez et al, 2016;Rutten et al, 2018;Samiappan et al, 2018).…”