Species Richness and Stand Stability in Conifer Forests of the Sierra Nevada

Abstract

Theoretical and empirical studies have long suggested that stability and complexity are intimately related, but evidence from long-lived systems at large scales is lacking. Stability can either be driven by complex species interactions, or it can be driven by the presence/absence and abundance of a species best able to perform a specific ecosystem function. We use 64 years of stand productivity measures in forest systems composed of four dominant conifer tree species to contrast the effect of species richness and abundance on three stability measures. To perform this contrast, we measured the annual growth increments of > 900 trees in mixed and pure forest stands to test three hypotheses: increased species richness will (1) decrease stand variance, (2) increase stand resistance to drought events, and (3) increase stand resilience to drought events. In each case, the alternate hypothesis was that species richness had no effect, but that species composition and abundance within a stand drove variance, resistance, and resilience. In pure stands, the four species demonstrated significant differences in productivity, and in their resistance and resilience to drought events. The two pine species were the most drought resistant and resilient, whereas mountain hemlock was the least resistant and resilient, and red fir was intermediate. For community measures we found a moderately significant (P = 0.08) increase in the community coefficient of variation and a significant (P = 0.03) increase in resilience with increased species richness, but no significant relationship between species richness and community resistance, though the variance in community resistance to drought decreased with species richness. Community resistance to drought was significantly (P = 0.001) correlated to the relative abundance of lodgepole pine, the most resistant species. We propose that resistance is driven by competition for a single limiting resource, with negative diversity effects. In contrast resilience measures the capacity of communities to partition resources in the absence of a single limiting resource, demonstrating positive diversity effects.

Overyielding of temperate deciduous tree mixtures is maintained under throughfall reduction

“…For trees, drought effects have been studied extensively on individual tree species, and has shown that drought decreases growth and increases the sensitivity to insect attacks and diseases, thus increasing the likelihood of tree death (Mattson and Haack 1987). How tree species grown in a mixture react to drought is less clear (DeClerck et al 2006;del Rio et al 2014;Pretzsch et al 2014;Zapater et al 2013).…”

δ13C signature of tree rings and radial increment of Fagus sylvatica trees as dependent on tree neighborhood and climate

“…One important issue in the biodiversity-ecosystem functioning debate is the dependence of ecosystem stability on diversity (Odum 1953;Loreau et al 2002;DeClerck et al 2006). Frequently discussed stability parameters of ecosystems are the resistance to, and the resilience after, disturbances such as drought events or herbivore attack.…”

“…It is generally accepted that mixed forests show greater resilience with regard to herbivore attack than monospecific stands (Jactel et al 2005;Pretzsch 2005). However, the relationship between tree species diversity and the resistance to, or the resilience after, drought events in forests is not clear yet (Larsen 1995;DeClerck et al 2006). This question is of high relevance to forestry because natural forests are widely being replaced by monospecific plantations in temperate and in tropical regions while the consequences for ecosystem functioning and stability are poorly known.…”

Phylogenetic Relationships and Genetic Diversity in Collected Resources of Carthamus tinctorius by Random Amplified Polymorphic DNA Markers

“…Plants are 30 to 150 cm tall with globular flower heads (capitula) and commonly, brilliant yellow, orange or red flowers which bloom in July. Each branch will usually have from one to five flower heads containing 15 to 20 seeds per head [4].…”

“…Safflower was also known as carthamine in the 19th century [4]. It is a minor crop today, with about 600,000 tons being produced commercially in more than sixty countries worldwide.…”