Woods Carrie L, Maleta Katy, Ortmann Kimmy
Biology Department University of Puget Sound Tacoma WA USA.
Ecol Evol. 2021 Jun 20;11(14):9631-9641. doi: 10.1002/ece3.7786. eCollection 2021 Jul.
Plant-plant interactions change through succession from facilitative to competitive. At early stages of succession, early-colonizing plants can increase the survival and reproductive output of other plants by ameliorating disturbance and stressful conditions. At later stages of succession, plant interactions are more competitive as plants put more energy toward growth and reproduction. In northern temperate rainforests, gap dynamics result in tree falls that facilitate tree regeneration (nurse logs) and bryophyte succession. How bryophyte-tree seedling interactions vary through log succession remains unclear. We examined the relationships of tree seedlings, bryophyte community composition, bryophyte depth, and percent canopy cover in 166 1.0 m plots on nurse logs and the forest floor in the Hoh rainforest in Washington, USA, to test the hypothesis that bryophyte-tree seedling interactions change from facilitative to competitive as the log decays. Tree seedling density was highest on young logs with early-colonizing bryophyte species (e.g., ) and lowest on decayed logs with , a long-lived moss that reaches depths >20 cm. As a result, bryophyte depth increased with nurse log decay and was negatively associated with tree seedling density. Tree seedling density was 4.6× higher on nurse logs than on the forest floor, which was likely due to competitive exclusion by forest floor plants, such as . Nurse logs had 17 species of bryophytes while the forest floor had six, indicating that nurse logs contribute to maintaining bryophyte diversity. Nurse logs enable both tree seedlings and smaller bryophyte species to avoid competition with forest floor plants, including the dominant bryophyte, . is likely a widespread driver of plant community structure given its dominance in northern temperate forests. Our findings indicate that plant-plant interactions shift with succession on nurse logs from facilitative to competitive and, thus, influence forest community structure and dynamics.
植物与植物之间的相互作用会随着演替从促进作用转变为竞争作用。在演替的早期阶段，早期定居的植物可以通过改善干扰和胁迫条件来提高其他植物的存活率和繁殖产量。在演替的后期阶段，随着植物将更多能量投入到生长和繁殖中，植物间的相互作用更具竞争性。在北方温带雨林中，林窗动态导致树木倒下，这有利于树木更新（保育木）和苔藓植物演替。苔藓植物与树木幼苗之间的相互作用如何随木材演替而变化仍不清楚。我们在美国华盛顿州霍雨林的保育木和森林地面上的166个1.0米的样地中，研究了树木幼苗、苔藓植物群落组成、苔藓植物深度和树冠覆盖率之间的关系，以检验随着木材腐烂，苔藓植物与树木幼苗之间的相互作用从促进作用转变为竞争作用这一假设。在带有早期定居苔藓植物物种（如 ）的年轻木材上，树木幼苗密度最高，而在带有 （一种深度可达20厘米以上的长寿苔藓）的腐烂木材上，树木幼苗密度最低。因此，苔藓植物深度随着保育木的腐烂而增加，并且与树木幼苗密度呈负相关。保育木上的树木幼苗密度比森林地面上高4.6倍，这可能是由于森林地面植物（如 ）的竞争排斥所致。保育木上有17种苔藓植物，而森林地面上有6种，这表明保育木有助于维持苔藓植物的多样性。保育木使树木幼苗和较小的苔藓植物物种都能避免与森林地面植物竞争，包括优势苔藓植物 。鉴于其在北方温带森林中的优势地位， 可能是植物群落结构的一个广泛驱动因素。我们的研究结果表明，在保育木上，植物与植物之间的相互作用随着演替从促进作用转变为竞争作用，从而影响森林群落结构和动态。
