Forest successional processes drive changes in abundance not diversity of bee communities within Mississippi production forests

Processes structuring bee community composition in agricultural landscapes are relatively well-documented compared to those in landscapes dominated by other anthropogenic land uses, like production forests of the southern United States.  Southern forests cover 214 million acres of US land with wood production contributing almost $30 billion to the regional economy.  However, production forests have historically been under-sampled due to the perception that they might offer little habitat to support diverse bee communities.  However, these forests are managed in roughly 20 year harvest cycles that provide a moderate level of disturbance, potentially providing opportunities for bee colonization and for studying the effects of forest succession in a simplified and standardized setting.  To study the relationship between bee community composition and forest successional age, we sampled bees across pine plantations representing three age classes in southern Mississippi for 2 years (2012 and 2013).  We surveyed 6 sites, each with 2 transects assigned to 3 age classes based upon age since tree planting.  Trapping and netting yielded >100 species including 2 range expansions and several new state records. Utilizing ordination (non-metric dimensional scaling), we found that transects of the oldest age (12-20 years) class grouped together and were distinct from the other two age classes (0-1 & 3-5 years).  This general pattern remained consistent for bee community composition, abundance, and evenness, but was not observed for species diversity (Chao estimator).  Our results indicate that as forest patch age increases, overall abundance declines significantly, while species diversity remains relatively constant.  Consistent with this relationship, evenness (Pielou’s index) increases significantly with patch age.  Thus, our results suggest that production forest landscapes might prove valuable for examining bee metacommunity dynamics in the context of heterogeneous landscapes with regular and relatively frequent disturbance regimes.  Our results are also consistent with those of similar studies in the southeastern US.  When combined, these suggest that, while traditionally thought to be poor landscapes for bees, managed southern forests and even production pine plantations can support diverse communities of these beneficial insects with levels of species diversity approaching that of natural areas.