The effects of seed ingestion by livestock, dung fertilization, trampling, grass competition and fire on seedling establishment of two woody plant species.

Julius Tjelele,Luthando Dziba,David Ward,Wei Wang

doi:10.1371/journal.pone.0117788

Abstract

The increasing rate of woody plant encroachment in grasslands or savannas remains a challenge to livestock farmers. The causes and control measures of woody plant encroachment are of common interest, especially where it negatively affects the objectives of an agricultural enterprise. The objectives of this study were to determine the effects of gut passage (goats, cattle), dung (nutrients), fire, grass competition and trampling on establishment of A. nilotica and D. cinerea seedlings. Germination trials were subjected to the following treatments: 1) seed passage through the gut of cattle and goats and unpassed/ untreated seeds (i.e. not ingested), 2) dung and control (no dung), 3) grass and control (mowed grass), 4) fire and control (no fire), 5) trampling and control (no trampling). The interaction of animal species, grass and fire had an effect on seedling recruitment (P < 0.0052). Seeds retrieved from goats and planted with no grass and with fire (6.81% ± 0.33) had a significant effect on seedling recruitment than seeds retrieved from goats and planted with grass and no fire (2.98% ± 0.33). Significantly more D. cinerea and A. nilotica seeds germinated following seed ingestion by goats (3.59% ± 0.16) than cattle (1.93% ± 0.09) and control or untreated seeds (1.69% ± 0.11). Less dense grass cover, which resulted in reduced grass competition with tree seedlings for light, space and water, and improved seed scarification due to gut passage were vital for emergence and recruitment of Acacia seedlings. These results will contribute considerably to the understanding of the recruitment phase of woody plant encroachment.

Highlights

An increase in woody vegetation density [1, 2] known as woody plant encroachment, has been widely reported in southern Africa [3, 4]
To better understand the mechanisms involved, we studied the effects of gut passage, dung, grass competition, fire and trampling on seedling emergence, seedling establishment and recruitment of Dichrostachys cinerea and Acacia nilotica seeds
Seedling emergence was significantly greater for the treatment combination of seed treatment, mowed grass (Gc), and fire (F) (8.68% ± 0.36) than passage through the gut of goats, grass competition, and fire (4.47% ± 0.24)

Summary

Introduction

An increase in woody vegetation density [1, 2] known as woody plant encroachment, has been widely reported in southern Africa [3, 4]. The increasing rate of woody plant encroachment in grasslands and savannas is a challenge to livestock farmers [5, 6]. Seed Ingestion on Seedling Recruitment density suppresses the productivity of herbaceous plant species [1] and eventually reduces rangeland carrying capacity [1, 7]. The reduction in carrying capacity is of great concern because African savannas have a rapidly growing human population [1]. There is considerable interest in understanding woody plant encroachment [1] in order to improve livestock production

Objectives

Methods

Results

Conclusion