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. 2019 Feb 18;10:132.
doi: 10.3389/fpls.2019.00132. eCollection 2019.

Long-Term Studies Reveal Differential Responses to Climate Change for Trees Under Soil- Or Herbivore-Related Stress

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Free PMC article

Long-Term Studies Reveal Differential Responses to Climate Change for Trees Under Soil- Or Herbivore-Related Stress

Amy V Whipple et al. Front Plant Sci. .
Free PMC article

Abstract

Worldwide, trees are confronting increased temperature and aridity, exacerbating susceptibility to herbivory. Long-term studies comparing patterns of plant performance through drought can help identify variation among and within populations in vulnerability to climate change and herbivory. We use long-term monitoring data to examine our overarching hypothesis that the negative impacts of poor soil and herbivore susceptibility would be compounded by severe drought. We studied pinyon pine, Pinus edulis, a widespread southwestern tree species that has suffered extensive climate-change related mortality. We analyzed data on mortality, growth, male reproduction, and herbivory collected for 14-32 years in three areas with distinct soil-types. We used standardized precipitation-evapotranspiration index (SPEI) as a climate proxy that summarizes the impacts of drought due to precipitation and temperature variation on semi-arid forests. Several key findings emerged: (1) Plant performance measurements did not support our hypothesis that trees growing in stressful, coarse-textured soils would suffer more than trees growing in finer-textured soils. Stem growth at the area with coarse, young cinder soils (area one) responded only weakly to drought, while stem growth on more developed soils with sedimentary (area two) and volcanic (area three) substrates, was strongly negatively affected by drought. Male reproduction declined less with drought at area one and more at areas two and three. Overall mortality was 30% on coarse cinder soils (area one) and averaged 55% on finer soil types (areas two and three). (2) Although moth herbivore susceptible trees were hypothesized to suffer more with drought than moth resistant trees, the opposite occurred. Annual stem growth was negatively affected by drought for moth resistant trees, but much less strongly for moth susceptible trees. (3) In contrast to our hypothesis, moths declined with drought. Overall, chronically water-stressed and herbivore-susceptible trees had smaller declines in performance relative to less-stressed trees during drought years. These long-term findings support the idea that stressed trees might be more resistant to drought since they may have adapted or acclimated to resist drought-related mortality.

Keywords: climate change; drought; growth; herbivory; long-term; reproduction; tree.

Figures

FIGURE 1
FIGURE 1
Data for the cross soil-type/area comparisons testing H1. (A) Standardized precipitation-evapotranspiration index, SPEI from the DRI website for the 12 months preceding the completion of annual stem growth (Abatzoglou et al., 2017) for which negative numbers indicate greater drought stress. SPEI for the strobili count analysis is different from the one used for stem measures as it is based on the 12 months prior to pollen production in May. Area one is the stressful, coarse soil site. (B) Annual stem length growth mean ± SE for the three areas. The coefficients provided are the slopes of the stem growth relationship to SPEI from the mixed model ARMA analysis in Table 3A and the p-values are tests of significant difference between the area one slope versus areas two and three. (C) Number of male strobili clusters mean ± SE for the three areas. The coefficients provided are the slopes of the male strobili count relationship to SPEI from the repeated measures Poisson link function analysis in Table 3B and the p-values are tests of significant difference between the area one slope versus areas two and three.
FIGURE 2
FIGURE 2
For the cross soil-type/area comparison (H1) these data are the cumulative mortality from 2002 to 2007 across the three areas. Significant differences as indicated by different letters above the bars come from the binomial mixed model in Table 4.
FIGURE 3
FIGURE 3
Data for the moth resistant and susceptible tree comparisons (H2). (A) Standardized precipitation-evapotranspiration index, SPEI from the DRI website for the 12 months preceding the completion of annual stem growth (Abatzoglou et al., 2017) for which negative numbers indicate greater drought stress. SPEI for the strobili count analysis is different from the one used for stem measures as it is based on the 12 months prior to pollen production in May. (B) Annual stem growth mean ± SE for resistant and susceptible trees. The coefficients provided are the slopes of the stem growth relationship to SPEI from the mixed model analysis in Table 5A and the p-value is the test of significant difference between slopes for moth resistant versus moth susceptible trees. (C) Number of male strobili clusters mean ± SE for the resistant and susceptible trees. The coefficients provides are the slopes of the male strobili count relationship with SPEI from the mixed-model analysis in Table 5B and the p-value is the test of significant difference between slopes for moth resistant versus moth susceptible trees.
FIGURE 4
FIGURE 4
The decline in moth killed stem counts on large susceptible trees through time in comparison to resistant trees. There is a significant positive relationship between moth attack and the climate proxy, SPEI, for susceptible trees (Table 6).

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