COMPENSATORY GROWTH OF THE AFRICAN DWARF SHRUBINDIGOFERA SPINOSAFOLLOWING SIMULATED HERBIVORY

Abstract

Use of long‐term herbivory studies in understanding the effects of livestock grazing on dwarf shrubs of arid zones of Africa is uncommon. Moreover, research has seldom focused on monitoring a 4–5 yr effect of herbivory at the level of individual plants. This study provided information on field‐based experiments and simplified statistical modeling to test compensatory growth responses of individuals of the African dwarf shrub Indigofera spinosa in northwestern Kenya. From August 1986 to January 1990, we simulated livestock grazing during dry and wet seasons and over the full year, whereby plants were defoliated during both wet and dry seasons. Individuals of I. spinosa (n = 480 plants) were subjected to one of five clipping intensities: unclipped control (0%), light (30%), moderate (50%), severe (70%), and very severe (90%) clipping; and defoliated of regrowth (i.e., new biomass). Our findings showed that rainfall, clipping regimes, and seasons of treatment influenced the compensatory growth response. Rainfall more than residual biomass influenced regrowth, while plants with greater residual biomass produced more regrowth than those with less. Optimum residual biomass was achieved under the 30% clipping level, while least was maintained under the 90% level. We separated compensatory growth response into under‐ and overcompensation. We showed that overcompensation occurred under some conditions but not in others. The shrub displayed relative overcompensation with a compensatory ratio (CR) > 1.0 for three continuous years with light clipping regime during the wet season defoliations (WSD). In two of five years there was overcompensation with the dry season defoliations (DSD), but undercompensation (CR < 1.0) with full‐year defoliations (FYD). On average, under the moderate, severe, and very severe clipping regimes the plants had undercompensation. Patterns of change of cumulative regrowth and its derivative, relative growth rates (RGR), provided different compensatory responses. RGR was more positive at lower cumulative regrowth but gradually declined and became negative when cumulative regrowth was maximum. The exception was in WSD where RGR remained positive for three years. DSD by far achieved greater cumulative regrowth than WSD and FYD. However, compared to the controls, FYD (except under light regime) exactly overcompensated for total “biomass budget” while WSD overcompensated under all clipping regimes except very severe. DSD under the light and moderate regimes overcompensated by +343.6% and by +202.7%, respectively. The study showed that I. spinosa combines tolerance with compensatory growth response to cope with a wide array of herbivory and seasons of use. The shrub may be grazed under light regime during the wet and dry seasons as opposed to the full‐year grazing which is unsustainable.

The effect of climate variations on the dynamics of pasture–livestock interactions under cooperative and noncooperative management

“…6): with occasional deviations from the average level of precipitation. (iii) Finally, we incorporate a positive effect of grazing on plant regrowth (20). We use the following notation: for the grazing animals, Y and y i represent, respectively, the total biomass abundance of grazing animals on the pastures and the biomass abundance (animals) belonging to herder i (i.e., Y ϭ ¥ y i , where the sum is over the fixed number of herders with rights to use the grazing area).…”

“…where K is carrying capacity (which we will assume to be affected by the level of precipitation), and the g-function incorporates the effect of grazing on plant growth (20). The optimal harvest strategy (i.e., the slaughtering of livestock) c t ϭ ␦y t applies with stochastic livestock growth rates, and hence the optimal solution of the harvesting problem will not be affected by whether K is fixed or not.…”

Seedling responses to moderate and severe herbivory: a field‐clipping experiment with a keystone Mediterranean palm

“…To evaluate the effect of ungulate herbivory on C. humilis seedling survival and growth (height and diameter), we simulated herbivory by performing field-clipping experiments (e.g. Oba et al 2000;Archibald et al 2021) in both study sites between February and October 2020. In February, we selected, per faecal badger sample, two to 10 emerged seedlings of similar in size (13.5 AE 0.4 cm height, 3.5 AE 0.1 mm diameter; N = 116).…”

“…Belsky 1986;Aguirrebengoa et al 2021), shrubs (e.g. Oba et al 2000;Christie et al 2014), trees (e.g. Guillet & Bergstr€ om 2006;Sampedro et al 2009), and also palms (e.g.…”

The Correlation between Opuntia stricta Distribution and Soil Chemical Composition in Tsavo East National Park

“…As they infiltrate native ecosystems, they displace indigenous plants upsetting the ecological balance between grasses and shrubs in both natural and agricultural environments (Pimentel, 2002). Consequently, these invasions induce changes in species composition, dominant life forms, nutrient cycling, hydrology and decomposition, altering the overall structure and function of ecosystems (Oba et al, 2000). Their rapid reproduction and dispersal capabilities enable them to out compete native species leading to significant economic losses estimated in the billions of USD (Richardson and Pysek, 2001;Wilcove et al, 1998;Yurkonis et al, 2005).…”