Pollen cone production in jack pine: spatial and temporal patterns subject to natural disturbance by the jack pine budworm

Patterns of jack pine (Pinus banksiana Lambert) pollen cone production are of interest because they may help explain jack pine budworm (Choristoneura pinus pinus Freeman) outbreak patterns. We used generalized linear mixed models to analyze pollen cone production in 180 permanent plots in Ontario, Canada between 1992 and 2008. Pollen cone production increased with stand age, and large trees in sparsely-populated stands produced more pollen cones. Defoliation decreased the propensity of trees to produce pollen cones for at least two years. We also identified important patterns that are not explained by defoliation and stand characteristics. Pollen cone production is spatially synchronized among years, trees in central Ontario produced more pollen cones than trees in northwestern Ontario, and background cone production increased over time in the central region but not in more northwestern plots. Synchronized reproduction is common among tree species, but has not previously been noted for jack pine pollen cones. Increasing cone production in central Ontario may be evidence of changing forest and (or) climatic conditions and deserves further investigation. Our model can be used to quantitatively predict pollen cone production and assess the risk of jack pine budworm defoliation.

The ecological interaction of the mountain pine beetle and jack pine budworm in the boreal forest

As climate change facilitates the range and host expansion of insect species into new ecosystems, the development of newstrategies for managing and preventing biological invasion is receiving considerable interest. In recent years, the range ofthe mountain pine beetle (Dendroctonus ponderosae Hopkins) has expanded from lodgepole pine-dominated forests eastof the Rocky Mountains into lodgepole x jack pine hybrid forest of western Alberta, and may soon invade jack pine forestsof the boreal. Our understanding of factors contributing colonization of jack pine by mountain pine beetle is far fromcomplete and several factors may limit its spread in these forests, including tree resistance and competitors. Among these,the jack pine budworm (Choristoneura pinus pinus Freeman) is one of the most important insect enemies of jack pine andan outbreak defoliator that potentially weakens jack pine trees, which may make them more susceptible to MPB attacks.To develop effective management strategies in the face of the short-run impacts of climate change, we need an in-depthunderstanding of factors influencing establishment and survival of the beetle in jack pine forests.Key words: Choristoneura pinus pinus, Dendroctonus ponderosae, jack pine, range expansion, invasion biology, climatechange in the boreal forest, conifer-mediated interactions, tree induced defences, tripartite interactions