Holocene forest development and maintenance on different substrates in the Klamath Mountains, northern California, USA

Abstract

The influence of substrate on long-term vegetation dynamics has received little attention, and yet nutrient-limited ecosystems have some of the highest levels of endemism in the world. The diverse geology of the Klamath Mountains of northern California (USA) allows examination of the long-term influence of edaphic constraints in subalpine forests through a comparison of vegetation histories between nutrient-limited ultramafic substrates and terrain that is more fertile. Pollen and charcoal records spanning up to 15000 years from ultramafic settings reveal a distinctly different vegetation history compared to other soil types. In non-ultramafic settings, the dominant trees and shrubs shifted in elevation in response to Holocene climate variations resulting in compositional and structural changes, whereas on ultramafic substrates changes were primarily structural, not compositional. Fire activity was similar through most of the Holocene with the exception of declines over the last 4000 years on ultramafic substrates, likely due to the reduction of understory fuels and cooler wetter conditions than in the middle Holocene. These results suggest that the tree and shrub distributions were more responsive to past climate changes on non-ultramafic substrates compared to those on ultramafic substrates. The combination of these dynamics may help explain high levels of plant diversity in the Klamath Mountains and provide insights for managing these complex ecosystems.

Resource colimitation governs plant community responses to altered precipitation

“…Our results demonstrate a mechanism by which low-productivity systems can exhibit greater resistance to climate change and show the predictive power that functional traits have in forecasting species' distributional shifts. Our work thereby links the general theory of resource colimitation (17) and functional trait syndromes (36)(37)(38) to a substantial body of previous evidence from experiments (13,14,30,32), analyses of natural climatic variability (26,33) and geographic variability (63), and even results from paleoecology (31). Our findings illustrate the potential for ecological theory and experiments to improve our predictions of the ecological effects of climate change.…”

“…A variety of evidence is consistent with this prediction (29). For example, effects of experimental warming and drought were lower in an infertile limestone grassland than in a fertile ex-cultivated grassland (13,30); post-Pleistocene vegetation change was less pronounced on infertile peridotite than in forests on fertile granitic substrates (31); and in our study system, both experimental watering (25,32) and ambient variation in annual precipitation (33,34) had less effect on grasslands on serpentine soils than on more productive grasslands on sedimentary soils. If these contrasting plant community responses to climate are attributable to colimitation by water and nutrients, then several important implications follow.…”

Warming-induced upslope advance of subalpine forest is severely limited by geomorphic processes

“…Whereas the study of temperature limitation of physiological pathways in woody vegetation is fundamental, it is insufficient to explain the complex reality of landscape-scale (ecologically relevant) high-elevation tree cover, because it overlooks the fact that climatic limitation can prevail only on a small proportion of the landscape. Together with temperature, trees tend to experience other controlling mechanisms, such as those related to the physical characteristics of the lithosphere on which they grow (14)(15)(16)(17). Although some of our model variables are linked to avalanches or landmass movements, the present study did not directly address disturbance processes [e.g., wildfires, insect outbreaks (23)], which would add even more complexity to the dynamics of subalpine tree-cover change under warmer climate scenarios.…”

“…Changes in high-elevation tree cover will, thus, result from modifications on any of these controlling processes. Although topography and geomorphology have been identified as important in setting the observed heterogeneity of highelevation mountain tree cover (13)(14)(15)(16)(17)(18)(19), the effect of geomorphology on present and future high-elevation tree cover remains unquantified, and site-based studies overwhelmingly treat terrain physiognomy as a uniform neutral background. To address these questions, we conducted a statistical modeling exercise of tree presence at high spatial resolution (10 m) over a ∼100-km 2 area comprising the geologic and geomorphic diversity found in the Front Ranges of the Canadian Rocky Mountains of Alberta ( Fig.…”

Patterns of terrestrial and limnologic development in the northern Greater Yellowstone Ecosystem (USA) during the late-glacial/early-Holocene transition

“…Large-scale climatic variability is clearly the primary driver of postglacial ecosystem change at broad temporal and spatial scales; however, substrate, local topography, and species life-history traits become increasingly important at finer scales (e.g., Brubaker, 1975;Millspaugh et al, 2000;Oswald et al, 2003;Briles et al, 2011). Furthermore, modern studies have highlighted strong linkages between limnologic development and trajectories of soil and vegetation development in newly deglaciated catchments (Engstrom et al, 2000;Engstrom and Fritz, 2006), but few paleoecological sites compare terrestrial and aquatic responses in the past to understand how well these linkages were expressed in the early stages of postglacial landscape development (but see Birks et al, 2000).…”