New patterns of establishment and growth of Picea , Abies and Betula tree species in subalpine forest gaps of Jiuzhaigou National Nature Reserve, Sichuan, southwestern China in a changing environment

Abstract:Litterfall is the primary source of carbon and nutrients that determine soil fertility in forest ecosystems. Most current studies have focused on foliar litter, but the seasonal dynamics and allometric scaling relationships among different litter components (e.g., foliar litter, woody litter, reproductive litter, and epiphytic litter) are poorly understood. Here, we investigated the litter production of various litter components in a sub-alpine spruce-fir forest on the eastern Tibetan Plateau based on one year of observations (from August 2015 to July 2016). Our results showed that total litter production (L T ) was 2380 kg·ha −1 ·year −1 (3% of the aboveground forest biomass), of which 73.6% was foliar litter (L F ), 15.6% was woody litter (L W ), 3.0% was reproductive litter (L R ), 1.3% was epiphytic litter (L E ), and 6.5% was miscellaneous material (L M ). The total litterfall was bimodal (with peaks occurring in April and October) and was dominated by tree species (85.4% of L T , whereas shrubs accounted for 6.8% of L T ). The litter production of evergreen species (68.4% of L T ) was higher than that of deciduous species (23.8% of L T ). Isometric relationships were observed between litter components and the total litter (i.e., L F ∝L T 0.99≈1 and L R ∝L T 0.98≈1 ), and allometric relationships were also found (i.e., L W ∝L T 1.40>1 and L M ∝L T 0.82<1 ). However, because some components did not exhibit obvious seasonal dynamics (i.e., L E ), some relationships could not be expressed using allometricand L E versus L M ). Thus, the different litter components showed different seasonal dynamics, and the total litter dynamics were primarily determined by the variation in foliar litter. In addition, the allometric relationships of the forest litterfall varied with the litter components, functional types (evergreen versus deciduous) and vertical structures (tree versus shrub). This study provides basic data and a new insight for future plant litter studies.

Section: Annual Litter Productionsupporting

confidence: 88%

Seasonal Dynamics of Litterfall in a Sub-Alpine Spruce-Fir Forest on the Eastern Tibetan Plateau: Allometric Scaling Relationships Based on One Year of Observations

Yang

Tan

et al. 2017

“…The local administration is hence greatly concerned with the succession trend and the rate at which the broadleaved species (e.g., B. albosinensis) are replaced by the conifers (e.g., Pinus tabuliaeformis Carr.) [2]. In recent years, the local administration Table 1.…”

Section: Introductionmentioning

confidence: 99%

Responses of Sap Flow of Deciduous and Conifer Trees to Soil Drying in a Subalpine Forest

Yan

Wang

Zhang

et al. 2018

Co-occurring species may adopt different water-use strategies to adapt to limited soil water. In Jiuzhaigou Valley, a continuous decline in soil water after an initial recharge from the thawing of snow and frozen soil in early spring was observed, but its effects on the sap flow dynamics of co-occurring species are not well understood. To clarify the species-specific water-use strategy, variations in sap flow and environmental conditions were investigated for two co-occurring species (Betula albosinensis Burk. and Pinus tabuliaeformis Carr.) in a mixed forest during a transition from the wet to dry period in 2014. Sap flow was measured using Granier-type thermal dissipation probes, and the soil-water content was measured using time-domain reflectometry probes for a successive period. Our study showed that B. albosinensis maintained relatively high transpiration until late into the season regardless of soil moisture, while the transpiration of P. tabuliformis showed a continuous decrease in response to seasonal soil drying. Sap flow for both species exhibited a marked hysteresis in response to meteorological factors and it was conditioned by the soil-water status, especially in the afternoon. We found that P. tabuliformis was sensitive to soil-water conditions, while for B. albosinensis, the sap flow was not very sensitive to changes in soil-water conditions. These results indicate that B. albosinensis could manage the water consumption conservatively under both dry and wet conditions. These results may have implications for evaluating the species-specific water-use strategy and carrying out proper reforestation practices.

“…In the subalpine region of southwestern China, widespread coniferous forests have provided an important economic resource (i.e., ecological tourism) and have acted as important ecological refuges along the upper reaches of the Min River [23]. Simultaneously, coniferous forests have also experienced different degrees of disturbance from natural events [22,23].…”

Section: Introductionmentioning

confidence: 99%

“…is one of the dominant tree species observed along the elevation gradient (2800-3800 masl) of subalpine mature coniferous forests in southwestern China. Regeneration is restricted by many factors (e.g., temperature and soil) in forests [22,23]. Therefore, Abies faxoniana saplings and small trees are typically rare in mature subalpine coniferous forests [22,25], and comprehensive research is needed to understand in detail the mechanisms of affecting their natural regeneration.…”

Section: Introductionmentioning

confidence: 99%

“…Moreover, although many studies have evaluated the effects of elevation or forest gaps on plant regeneration [16,23,28], the methodology is still a considerable limitation for exploring the internal mechanisms in current forest gap studies. For example, the influence of abiotic factors on regeneration is simultaneously induced by elevation and forest gaps.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

How Forest Gap and Elevation Shaped Abies faxoniana Rehd. et Wils. Regeneration in a Subalpine Coniferous Forest, Southwestern China

Chen

Liu

2018

Abstract:Focusing on the underlying ecological mechanisms of dominant species regeneration in forest gaps at a landscape scale can provide detailed understanding for gap-based forest management. The individual effects of forest gaps or elevation on the regeneration of Abies faxoniana Rehd. et Wils. are well known, although elucidating how gap characteristics and elevation concurrently influence regeneration remains an important challenge. In this paper, we present an explorative study using structural equation models (SEMs) to assess the direct and indirect effects of forest gaps and elevation on Abies faxoniana Rehd. et Wils. regeneration. Four of the predicted SEMs showed the following results: (1) Temperature, photosynthetic photon flux density (PPFD), soil total carbon, gap openness, shrub layer cover, herb layer cover, and moss layer thickness in forest gaps were associated with Abies faxoniana regeneration along an elevation gradient in subalpine coniferous forest. (2) Elevation had a generally negative and indirect effect on Abies faxoniana regeneration. Forest gaps positively affected regeneration when compared with non-gap plots and gap size was positively related to small tree regeneration density and the ratio of height to diameter at breast height (HD ratio) of the tallest Abies faxoniana small trees but was negatively related to Abies faxoniana sapling regeneration density. (3) In forest gaps, the Abies faxoniana sapling density and HD ratio of the tallest Abies faxoniana small trees were mainly indirectly influenced by elevation, and Abies faxoniana small tree regeneration density was directly associated with the dominance of the sapling regeneration density. In summary, Abies faxoniana regeneration was negatively and largely affected by elevation (total effect), although forest gaps enhanced Abies faxoniana regeneration by multiple pathways (direct and indirect effects).