Effects of simulated herbivory and intraspecific competition on the compensatory ability of birches

• Published in: Ecology (Durham) 1993-06, Vol.74 (4), p.1136-1142
• Main Authors: Hjalten, J. (Northern Arizona University, Flagstaff, AZ), Danell, K, Ericson, L
• Format: Article
• Language: English
• Subjects: ADAPTACION; ADAPTATION; AGRONOMIC CHARACTERS; ALTURA; Animal and plant ecology; Animal, plant and microbial ecology; Apical dominance; BETULA PUBESCENS; Biological and medical sciences; BIOLOGICAL COMPETITION; BIOMASA; BIOMASS; BIOMASSE; Browsing; CARACTERE AGRONOMIQUE; CARACTERISTICAS AGRONOMICAS; COMPETENCIA BIOLOGICA; COMPETITION BIOLOGIQUE; CRECIMIENTO; CROISSANCE; DEFOLIACION; DEFOLIATION; Demecology; Density; ECOLOGIA VEGETAL; Ecological competition; Ecology; Flowers & plants; Fundamental and applied biological sciences. Psychology; Growing seasons; GROWTH; Hardwood trees; HAUTEUR; HEIGHT; Herbivores; PHYTOECOLOGIE; PLANT COMPETITION; PLANT ECOLOGY; Plant growth; PLANT INTERACTION; Plants; Plants and fungi; RESPONSES; STAND DENSITY; SUECIA; SUEDE; SWEDEN
• ISSN: 0012-9658; 1939-9170
• DOI: 10.2307/1940483

To improve our knowledge regarding plant responses to herbivory we subjected juvenile birches (Betula pubescens) to different types of simulated herbivory, i.e., removal of the top (1 cm) of the main stem or defoliaiton (including removal of main stem top), and to different levels of intraspecific competition (i.e., three stand densities). Treatments were also repeated during the following year. Birch responses to these treatments were measured as changes in plant height and dry mass. Defoliated plants showed reduced growth irrespective of the level of intraspecific competition. Topped plants in the low-density plots showed enhanced growth, i.e., over-compensation, whereas topped plants growth in the high- and medium-density plots were unaffected by the treatments. Our results indicate that we should expect a continuum of plant responses to herbivory. Thus, there is little value in asking whether herbivory has a positive or negative effect on plant growth. Instead, emphasis should be placed on identifying conditions under which we would expect different responses. Further, we suggest that overcompensation should not generally be considered as an adaptive response that has evolved as a consequence of natural selection due to herbivory, but rather as an indirect consequence of selection for competitive ability. Because apical dominance (assumed to be an adaptation to competition) restricts growth, the growth rate will increase if apical dominance is removed.