The relationships between relative growth rate, meristematic potential and compensatory growth of semiarid-land shrubs

Abstract

Inherent relative growth rate has been suggested as a major determinant of plant species' capacity to regrow and compensate for tissues lost to herbivores. We investigated: 1) the relationship between compensatory growth capacity and relative growth rate (RGR) in six semiarid-land shrubs following removal in winter or spring of 90% of the previous year's growth, 2) the influence of loss of buds on production of new growth and 3) the relationship between meristematic potential and the capacity to produce new growth in four of the six semiarid-land shrub species. Four-year-old plants growing under field conditions were used in the study. The species with the highest inherent growth rate, sagebrush [Artemisia tridentata ssp. vaseyana (Rydb.) Beetle], died following the severe clipping treatments. The other five species exactly compensated for lost tissues. Inherent growth rates and compensatory growth capacity of the shrubs were not correlated. Loss of 90% of the buds on the previous year's growth did not limit production of new growth. Instead, shrubs that lost buds produced more new growth biomass than the controls. The shrub species had significantly different meristematic potential. Curlleaf mountain mahogany (Cercocarpus ledifolius Nutt.) and serviceberry (Amelanchier alnifolia Nutt.) had the greatest and least number of buds and long shoots per plant, respectively. The number of long shoots produced following bud removal was positively correlated with new growth biomass, while the percentage of long shoots produced at the basal position on twigs was negatively correlated with new growth biomass. Our results suggest that inherent growth rate is not likely to influence production of new growth following browsing when resources for growth are not limiting. In contrast, the ability of a shrub to initiate long shoot growth is likely to influence production of new growth even when resources for growth are abundant.

Herbivory and plant competition reduce mountain beech seedling growth and establishment in New Zealand

“…None of the apparent changes in competitive ability in mountain beech varied with simulated herbivory, which was also found by Wandera et al (1992) for shrubs. Thus, no evidence from our study suggests that the tolerance of mountain beech seedlings to herbivory varies with resource availability.…”

“…Other studies demonstrate that seedlings better tolerate herbivory in lower productivity environments (e.g. Hilbert et al 1981;McNaughton and Chapin 1985;Van Auken and Bush 1989;Schmid et al 1990;Bonser and Reader 1995), or that resource availability is not important for seedling recovery (Wandera et al 1992). The ability of plants to tolerate herbivory can also vary with plant species or functional group (Hicks and Reader 1995).…”

Trade-off between plant growth and defense? A comparison of sagebrush populations

“…The EV population, for instance, combined slow inherent growth with an aboveaverage response to browsing. Comparisons between different species of aridland shrubs have also failed to find correlations between inherent growth rate and browsing tolerance (Wandera et al 1992;Bilbrough and Richards 1993).…”

Leaf compensatory growth as a tolerance strategy to resist herbivory in Pancratium sickenbergeri

“…The net effect of single or repeated grazing events on the cumulative growth of plants may be zero, negative, or positive, depending on the availability of leaf area, meristems, stored nutrients, and soil resources, and on the frequency and intensity of defoliation (Kulman 1971;Lee and Bazzaz 1980;Marquis 1984;Crawley 1985;Noy-Meir 1993). The ability to tolerate damage and then regrow requires a combination of normal growth processes, specialized structures, and physiological traits (Belsky 1986;Wandera et al 1992). These structures and traits (such as thorns, tannins, and growth responses) have many functions, but they may have evolved, at least in part, in response to recurrent damage by herbivory.…”