|Hochstrasser, Tamara - NEW MEXICO STATE UNIV|
Submitted to: Journal of Vegetation Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 22, 2004
Publication Date: October 1, 2004
Citation: Hochstrasser, T., Peters, D.C. 2004. Subdominant species distribution in microsites around two lifeforms at a desert grassland-shrubland transition zone. Journal of Vegetation Science. 15(5):615-622. Interpretive Summary: Our objective was to compare the abundance of subdominant plants in microsites around individual grasses and shrubs at a grassland-shrubland ecotone. We expected that species richness would be lower around shrubs than around grasses, leading to lower species richness of shrublands compared to grasslands. However, our results showed that subdominant species abundance was higher around shrubs than grasses. There were also greater differences in species abundance and composition when comparing microsites around grasses than microsites around shrubs. These results show that factors in addition to dominant species, such as disturbance, need to be accounted for when considering landscape scale biodiversity.
Technical Abstract: In many vegetation types, plant species diversity is dependent on the abundance of subdominant plants in microsites around dominant plants. Our objective was to compare subdominant abundance in microsites around dominant grasses and shrubs in the same landscape context. We investigated the distribution of subdominant plants in three microsites (canopy, canopy edge and interspace) around individual shrubs (creosotebush, Larrea tridentata) and grasses (black grama, Bouteloua eriopoda) at a grassland-shrubland transition zone that has been encroached by shrubs within the past 50-100 years. Subdominant plants were sampled using plots of variable size according to microsite type and dominant plant size. Contrary to our expectations, subdominant species abundance was higher in microsites around creosote shrubs than in microsites around black grama. Furthermore, differences in species abundance and composition were higher among microsites around grasses than among microsites around shrubs. The distribution of subdominants was mostly explained by their phenological characteristics, which indicates the importance of temporal variation in resources to their persistence. This detailed study of coexistence patterns around dominants revealed ecological contrasts between two dominant lifeforms, but other factors (such as disturbances) have to be taken into consideration to evaluate landscape-scale diversity.