Mediterranean climate effects. II. Conifer growth phenology across a Sierra Nevada ecotone

Abstract

Growth and xylem water potential of the lower elevation conifers Pinus jeffreyi and Abies concolor and the higher elevation Pinus monticola and Abies magnifica were monitored in their montane Mediterranean habitat of the southernmost Sierra Nevada mountains of California. Measurements were made across the ecotone between the midmontane and upper montane forests and through light and heavy snowfall years.Radial stem growth, averaging ∼1.5 mm/yr, started 2 wk after snow melt, providing that maximum air temperatures had reached 21°C, and ended when predawn water potentials fell rapidly at the onset of the summer drought. Leader growth started on or after a fixed date, providing that minimum air temperatures were above -4°C for Pinus species or +2.5°C for Abies species. The cue for leader growth was inferred to be photoperiodic. Leader growth ended when either a determinate internode length of ∼1 mm was reached or predawn water potentials fell rapidly. Abies magnifica grew more rapidly than the low-elevation species, but had a shorter growth period; its annual leader growth, as a consequence, was only 35 mm/yr vs. 50 mm/yr for the low-elevation species. Needle growth was similarly determinate in the absence of early drought. This growth phenology contributes to determining species distribution across the ecotone.

Growth of Norway spruce (Picea abies L.) saplings in subalpine forests in Switzerland: Does spring climate matter?

“…We surmise that this is due to the fact that we did not focus on tree growth near its upper limit of elevation, but rather tried to capture the conditions of the subalpine zone, where the growing season is considerably longer. Our results also disagree with findings from southern Sweden (Bergh et al, 1999), from lower montane forests in the Sierra Nevada, USA (Royce and Barbour, 2001), and from treeline environments in the Rocky Mountains, USA (Weisberg and Baker, 1995;Hessl and Baker, 1997), where late-lying snow in spring increased sapling growth. This may be due to the different climatic conditions in these typically much drier forests, where spring soil moisture is more critical compared to our mesic sites.…”

“…As in other investigations, the saplings studied here responded positively to lower canopy cover (LAI) because of the higher availability of direct (Imbeck, 1987b;Brang, 1998;Mayer, 1999;Ewers et al, 2001) and possibly also diffuse light (Frehner, 2002;Ruel, 2002;Lajzerowicz et al, 2004). Increased direct light also warms the rooting zone of saplings (Tranquillini, 1979), which stimulates photosynthesis (Day et al, 1989), the uptake of water and nutrients (Mellander et al, 2004), the allocation to root growth (Brang, 1996;Kirdyanov et al, 2003), bud burst (Partanen et al, 1998;Royce and Barbour, 2001) and height growth (Coates et al, 1991;Lajzerowicz et al, 2004). However, given that saplings in our study grew best under moderate forest canopy cover, our findings imply that while increased light and soil heating is advantageous to growth (Körner, 1998(Körner, , 1999, saplings also benefit from partial canopy shading that provides protection from extreme daily temperature amplitudes and possible drought (Imbeck, 1987a;Jonasova and Prach, 2004).…”

Soil respiration response to experimental disturbances over 3 years

“…1A and B). Tree physiological processes and microbial decomposition depend on sufficient soil moisture levels during the growing season (Royce and Barbour, 2001). SRR in Sierran old-growth, mixed conifer forests generally peaks shortly after snowmelt (in May, June and/or July) and decreases as moisture becomes limiting .…”

Climate change impacts on forest growth and tree mortality: a data-driven modeling study in the mixed-conifer forest of the Sierra Nevada, California

“…These changes would hasten the onset of drought stress that occurs in the late summer and early fall before the winter rains return. The result would be a shorter growing season due to lack of moisture, which is already recognized as a primary growth constraint on most commercial timber sites in Sierran forests (Royce and Barbour 2001b). Given the relationship between tree growth and summer temperature, it was not surprising that the most severe effects of projected climate change coincided with the most severe increases in temperature.…”