Drought predisposes piñon–juniper woodlands to insect attacks and mortality

• Published in: The New phytologist Vol. 198; no. 2; pp. 567 - 578
• Main Authors: Gaylord, Monica L., Kolb, Thomas E., Pockman, William T., Plaut, Jennifer A., Yepez, Enrico A., Macalady, Alison K., Pangle, Robert E., McDowell, Nate G.
• Format: Journal Article
• Language: English
• Published: England New Phytologist Trust 01-04-2013; Wiley Subscription Services, Inc
• Subjects: Animals; Annual precipitation; Bark; Bark beetles; Browning; Carbohydrate Metabolism; Carbon Isotopes; climate change; Coleoptera - physiology; Drought; Droughts; Environmental impact; host defense; insect resistance; Insects; juniper; Juniperus - growth & development; Juniperus - parasitology; Juniperus monosperma; Mortality; New Mexico; Pest resistance; Pine needles; Pine trees; Pinus - growth & development; Pinus - parasitology; Pinus edulis; piñon; Plant cover; Plant Leaves - metabolism; Plant structures; Precipitation; resin; Resin canals; Resins; Resins, Plant - metabolism; Resistance mechanisms; Sugars; Tree growth; Tree trunks; Trees; Trees - growth & development; Trees - parasitology; Water availability; Woodlands; USA, New Mexico
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/nph.12174

To test the hypothesis that drought predisposes trees to insect attacks, we quantified the effects of water availability on insect attacks, tree resistance mechanisms, and mortality of mature piñon pine (Pinus edulis) and one-seed juniper (Juniperus monosperma) using an experimental drought study in New Mexico, USA.
The study had four replicated treatments (40 × 40 m plot/replicate): removal of 45% of ambient annual precipitation (H2O−); irrigation to produce 125% of ambient annual precipitation (H2O+); a drought control (C) to quantify the impact of the drought infrastructure; and ambient precipitation (A).
Piñon began dying 1 yr after drought initiation, with higher mortality in the H2O− treatment relative to other treatments. Beetles (bark/twig) were present in 92% of dead trees. Resin duct density and area were more strongly affected by treatments and more strongly associated with piñon mortality than direct measurements of resin flow. For juniper, treatments had no effect on insect resistance or attacks, but needle browning was highest in the H2O− treatment.
Our results provide strong evidence that ≥ 1 yr of severe drought predisposes piñon to insect attacks and increases mortality, whereas 3 yr of the same drought causes partial canopy loss in juniper.