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, 7 (1), 6370

Forest Productivity Mitigates Human Disturbance Effects on Late-Seral Prey Exposed to Apparent Competitors and Predators

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Forest Productivity Mitigates Human Disturbance Effects on Late-Seral Prey Exposed to Apparent Competitors and Predators

Daniel Fortin et al. Sci Rep.

Abstract

Primary production can determine the outcome of management actions on ecosystem properties, thereby defining sustainable management. Yet human agencies commonly overlook spatio-temporal variations in productivity by recommending fixed resource extraction thresholds. We studied the influence of forest productivity on habitat disturbance levels that boreal caribou - a threatened, late-seral ungulate under top-down control - should be able to withstand. Based on 10 years of boreal caribou monitoring, we found that adult survival and recruitment to populations decreased with landscape disturbance, but increased with forest productivity. This benefit of productivity reflected the net outcome of an increase in resources for apparent competitors and predators of caribou, and a more rapid return to the safety of mature conifer forests. We estimated 3-fold differences in forest harvesting levels that caribou populations could withstand due to variations in forest productivity. The adjustment of ecosystem provisioning services to local forest productivity should provide strong conservation and socio-economic advantages.

Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Figure 1
Figure 1
(a) Stand height, (b) total canopy cover, and (c) canopy cover comprised of deciduous vegetation, as a function of their age for five categories of proportions of potentially productive stands (forest productivity) in eastern Canadian boreal forest. The lines are estimated from the models that are presented in Supplementary Tables S1 and S2, and, accordingly, the influence of productivity on all three stand attributes varies significantly with age.
Figure 2
Figure 2
Variation in weighted estimates of (a) female survival and (b) calf/female ratio (the recruitment index) as a function of total disturbance within six ranges of boreal caribou in eastern Canadian boreal forest. Lines are predicted trends and symbols are the actual values, with the size reflecting the number of observed females during each year of survey (range: 6–22 females for survival; range: 50–252 females for recruitment index).
Figure 3
Figure 3
Combination of total disturbance (fire and logging) and the proportion of potentially productive stands (the forest productivity index) for which the annual rate of change in the female population (λ f) is equal to 1 (solid line), with the lower limit yielding λ f ≥ 1 at least 95% of the time. The population tends to increase (λ f > 1) below the line and decline (λ f < 1) above it. Symbols represent the combination for individual populations, with respect to the observed combination of disturbance during their last year of monitoring.
Figure 4
Figure 4
Changes in forest stand characteristics during the first 80 years of secondary succession in eastern Canadian boreal forest, together with a potential scenario of changes in trophic interactions that is consistent with the higher growth of caribou populations observed in more productive boreal forests. Change in animal size reflects how the abundance of a given species varies over time, whereas arrow size is proportional to trophic interaction strength. The illustration indicates that in 25-year-old stands, moose have access to more deciduous vegetation in high than low productivity forests, which results in higher moose density in landscape largely comprised of these stands, and subsequently in higher grey wolf density. Likewise, black bears have access to more grasses, forbs and berries in 25-year-old stands found in more productive landscapes, thereby leading to high predation rates on calves and, therefore, to relatively low recruitment in productive forests that are largely comprised of these early-seral stands. Ultimately, the faster succession towards relatively safe forests that are largely comprised closed-canopy conifer stands would be largely responsible for the relatively high growth of boreal caribou population in high- than low-productive forests.
Figure 5
Figure 5
Location of six populations of boreal caribou that were monitored in eastern Canadian boreal forest. The figure was created in the R statistical environment.

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