Joint control of plant ecological strategy by climate, regeneration mode, and ontogeny in Northeastern Chinese forests

Research on how plant ecological strategies (competitive, stress-tolerant,
or ruderal) vary within species may improve our understanding of plant and
community responses to climate warming and also successional changes. With
increasing temperature, the importance of ruderal (R) and stress-tolerance
(S) components is hypothesized to decrease, while the strength of the
competitive (C) component should increase. Offshoots and younger plants
are predicted to have greater R and smaller S components. Leaf area, leaf
dry matter content, and specific leaf area were measured for 1,344 forest
plants belonging to 134 species in Northeastern China, and C, R, and S
scores calculated for each. Linear mixed effect models were used to assess
how these indicators differed among study sites (n = 2), regeneration
types, ontogenetic stages, and plant life forms. The two study sites have
an average annual temperature difference of 0.675°C, simulating a
temperature increase of 0.630°C due to climate warming. Higher
temperatures reduce low-temperature stress and frost damage, which may
explain the observed decrease in R and S scores; at the same time, plant
competitive ability increased, as manifested by higher C scores. This
effect was most pronounced for herbs, but nearly negligible as compared to
the effect of regeneration type for trees and of ontogeny for woody
species. Resprouting trees and younger woody plants had higher R scores
and lower S scores, a sign of adaptation to high disturbance. A small
increase in mean annual temperature led to shifts in CSR strategy
components for herbaceous species, without altering the vegetation type or
community composition. Offshoots and younger plants had higher R and lower
S scores, shedding light on similar changes in the ecological strategies
of tree communities during secondary succession, such as the transition of
Quercus mongolica coppices to forest, and age-related changes in Populus
davidiana-Betula platyphylla forests.