Fine Root Growth of Black Spruce Trees and Understory Plants in a Permafrost Forest Along a North-Facing Slope in Interior Alaska

Permafrost forests play an important role in the global carbon budget due to the huge amounts of carbon stored below ground in these ecosystems. Although fine roots are considered to be a major pathway of belowground carbon flux, separate contributions of overstory trees and understory shrubs to fine root dynamics in these forests have not been specifically characterized in relation to permafrost conditions, such as active layer thickness. In this study, we investigated fine root growth and morphology of trees and understory shrubs using ingrowth cores with two types of moss substrates (feather- and Sphagnum mosses) in permafrost black spruce (Picea mariana) stands along a north-facing slope in Interior Alaska, where active layer thickness varied substantially. Aboveground biomass, litterfall production rate, and fine root mass were also examined. Results showed that aboveground biomass, fine root mass, and fine root growth of black spruce trees tended to decrease downslope, whereas those of understory Ericaceae shrubs increased. Belowground allocation (e.g., ratio of fine root growth/leaf litter production) increased downslope in both of black spruce and understory plants. These results suggested that, at a lower slope, belowground resource availability was lower than at upper slope, but higher light availability under open canopy seemed to benefit the growth of the understory shrubs. On the other hand, understory shrubs were more responsive to the moss substrates than black spruce, in which Sphagnum moss substrates increased fine root growth of the shrubs as compared with feather moss substrates, whereas the effect was unclear for black spruce. This is probably due to higher moisture contents in Sphagnum moss substrates, which benefited the growth of small diameter (high specific root length) fine roots of understory shrubs. Hence, the contribution of understory shrubs to fine root growth was greater at lower slope than at upper slope, or in Sphagnum than in feather-moss substrates in our study site. Taken together, our data show that fine roots of Ericaceae shrubs are a key component in belowground carbon flux at permafrost black spruce forests with shallow active layer and/or with Sphagnum dominated forest floor.

Vegetation Height and Diurnal Period Influenced the Landscape-Use Pattern of Small Ruminants in Woodlands around Summer

Despite the huge potential of using woodlands for small ruminant grazing in the southeast US, unmanaged understory shrubs grown beyond animals’ access minimize the utilization of such vegetation. This study aimed to determine the effect of vegetation height and diurnal period on the behavior and distribution patterns of goats and sheep in woodlands around summer. The study was conducted in six woodland plots (0.4 ha each) comprising southern pines and non-pine (non-target) plant species. Non-pine plants in each study plot were assigned to four treatments: cut to 0 m, 0.9 m, or 1.5 m from the ground level or left uncut (control). Cut plant stubs were allowed to regrow to full canopy before stocking animals. Eight Kiko wethers and five Katahdin rams were rotationally stocked in separate plots, and their diurnal (dawn–dusk) behaviors and distribution patterns were monitored when they were in each plot (three plots per animal species) around the summer of 2018. Animal behavior data were analyzed using the general linear model (GLM) procedure with multivariate analysis of variance (MANOVA) in SAS, while animal distribution pattern and weather data were analyzed in SAS using a GLM procedure and the distribution evenness index (DEI) using the Kruskal–Wallis rank-sum test in R. Level of significance was set at 5%. Both animal species visited the control area the least. Wethers browsed predominantly in areas where non-pine plants were cut to 0.9 m from the ground level, and rams grazed mostly in areas where non-pine plants were cut to the ground level, mostly during the post-midday period. Browsing was the dominant feeding behavior of wethers (39% browsing vs. 4% grazing), while rams’ feeding behavior was dominated with grazing (24% grazing vs. 12% browsing). Lying was a predominant diurnal behavior in both wethers (46%) and rams (35%), mostly during the midday period. Wethers had a higher value for DEI than rams during the morning and post-midday periods. This study established that (1) the utilization of woodland understory foliage by small ruminants can be increased by lowering plant height, and (2) both vegetation characteristics and diurnal period are important factors for influencing small ruminants’ behavior while stocked in woodlands around summer.

Arthropods are not declining but are responsive to disturbance in the Luquillo Experimental Forest, Puerto Rico

A number of recent studies have documented long-term declines in abundances of important arthropod groups, primarily in Europe and North America. These declines are generally attributed to habitat loss, but a recent study [B.C. Lister, A. Garcia, Proc. Natl. Acad. Sci. USA 115, E10397–E10406 (2018)] from the Luquillo Experimental Forest (LEF) in Puerto Rico attributed declines to global warming. We analyze arthropod data from the LEF to evaluate long-term trends within the context of hurricane-induced disturbance, secondary succession, and temporal variation in temperature. Our analyses demonstrate that responses to hurricane-induced disturbance and ensuing succession were the primary factors that affected total canopy arthropod abundances on host trees, as well as walkingstick abundance on understory shrubs. Ambient and understory temperatures played secondary roles for particular arthropod species, but populations were just as likely to increase as they were to decrease in abundance with increasing temperature. The LEF is a hurricane-mediated system, with major hurricanes effecting changes in temperature that are larger than those induced thus far by global climate change. To persist, arthropods in the LEF must contend with the considerable variation in abiotic conditions associated with repeated, large-scale, and increasingly frequent pulse disturbances. Consequently, they are likely to be well-adapted to the effects of climate change, at least over the short term. Total abundance of canopy arthropods after Hurricane Maria has risen to levels comparable to the peak after Hurricane Hugo. Although the abundances of some taxa have declined over the 29-y period, others have increased, reflecting species turnover in response to disturbance and secondary succession.

Fosamine ammonium impacts on the targeted invasive shrub Rhamnus cathartica and non-target herbs

Fosamine ammonium (Krenite®) is a foliar herbicide that primarily targets woody plant species; however, formal evaluations of its efficacy and potential for non-target impacts are scarce in the literature. The few tests of fosamine ammonium that exist focus primarily on its use in open environments, and the value of fosamine ammonium in controlling invasive understory shrubs is unclear. Here, we test the impact of fosamine ammonium on invasive common buckthorn (Rhamnus cathartica L.) and co-occurring herbaceous plants across six forest sites in Minnesota, USA. Rhamnus cathartica treated with fosamine ammonium had a 95% mortality rate, indicating high efficacy of fosamine ammonium for use against R. cathartica. Non-target impacts varied between forbs and graminoids such that forb cover was reduced by up to 85%, depending on site, whereas graminoid cover was sparse and impacts of fosamine ammonium on graminoids were unclear. These results indicate that while fosamine ammonium can provide effective control of R. cathartica and other understory shrubs, there is potential for significant non-target impacts following its use. We therefore suggest that land managers carefully consider the timing, rate, and application method of fosamine ammonium to achieve desired target and non-target impacts.

Shrub traits of forest and shrubland reveal different growth strategies

<p>Shrub plants play important roles in both forest and shrubland ecosystems. Analyzing the differences of functional traits of shrubs grown in understory of forest communities and in various shrublands can explore the adaptation strategies of shrubs in different habitats. Nine functional traits of leaf and twig collected from 20 dominant shrub species in 24 plots distributed in three habitats: forest shrub layer, secondary shrubland and primary shrubland, in Beishan Mountain of Jinhua, Zhejiang Province, eastern China, were measured. The overall differences, inter- and intra-specific variations and the differences in various life forms of shrub traits in three different habitats were statistically analyzed. Results show that: 1) There are differences of nine plant traits for shrubs grown in three different habitats. The understory shrubs have larger leaf area (LA) and specific leaf area (SLA), smaller leaf dry matter content (LDMC), leaf tissue density (LTD) and twig tissue density (TTD), while shrubs in secondary shrubland have larger leaf thickness (LT) and LTD, smaller SLA and twig dry matter content (TDMC) compared with shrubs from the primary shrubland. 2) The intraspecific variation coefficients of SLA, twig diameter (TD), TTD, and TDMC in understory shrubs are the largest, while the interspecific variation coefficients of SLA, LDMC, TDMC, and TTD in ​​secondary shrubland are the smallest. 3) Among different life forms, the understory evergreen shrubs have significant higher LT, LTD, and LDMC than deciduous shrubs, while deciduous shrubs have significant higher SLA than evergreen shrubs. The differences of LT and SLA between evergreen and deciduous shrubs of primary shrubland are the same as those of understory shrubs, but the differences of LTD and LDMC between evergreen and deciduous shrubs have the opposite trend. 4) The main source affecting shrub traits is species, along with an explanation ratio from 38.01% to 78.92%. The second source is habitat. In short, compared to shrubs from shrublands, understory shrubs in forest communities form a series of trait combinations that are larger LA and SLA, smaller LTD, TTD, and LDMC to adapt to the understory environment with less light and stronger competition. Secondary shrubland, compared to the primary shrubland, has a series of shrub trait combinations that are larger LT, LTD and TD, smaller LA, SLA, TDMC and twig bark thickness (TBT) to store more nutrients.</p>

Variable Forest Structure and Fire Reconstructed Across Historical Ponderosa Pine and Mixed Conifer Landscapes of the San Juan Mountains, Colorado

Late-1800s land surveys were used to reconstruct historical forest structure and fire over more than 235,000 ha in ponderosa pine and mixed conifer landscapes of the San Juan Mountains, Colorado, to further understand differences among regional mountain ranges and help guide landscape-scale restoration and management. Historically, fire-resistant ponderosa pine forests with low tree density and relatively frequent fire, the most restorable forests, covered only the lower 15%–24% of the study area. The other 76%–85% had dominance by mixed- to high-severity fires. Both ponderosa pine and dry mixed conifer had generally pervasive, often dense understory shrubs, and ~20% of pine and ~50%–75% of mixed conifer forests also had high historical tree density. Intensive fuel reduction and mechanical restoration are infeasible and likely ineffective in the upper part of the pine zones and in mixed conifer, where restoring historical fire and creating fire-adapted communities and infrastructure may be the only viable option. Old-growth forests can be actively restored in the lower 15%–24% of the montane, likely increasing landscape resistance and resilience to fire, but mixed- to high-severity fires did also occur near these areas. This imperfect resistance suggests that fire-adapted human communities and infrastructure are needed throughout the study area.

134 Vegetation characteristics and diurnal periods influenced the landscape-use pattern of goats and sheep in woodlands

Woodlands dominate the landcover in the Southeast and offer great opportunities for expanding small-ruminant grazing. However, unmanaged understory shrubs grown beyond animals’ access minimizes the utilization of such vegetation. Managing the understory shrubs and non-target trees to lower heights may increase animals’ access to woodland vegetation and alter the landscape-use patterns of animals. The study objective was to determine the effect of vegetation height on the behavior and distribution of Kiko wethers and Katahdin rams in woodlands. The study was conducted in six woodland plots (0.4-ha each) containing southern pine and hardwood trees and numerous understory vegetation. The non-pine species were either cut to one of the heights from the ground level (0 m, 0.91 m, 1.52 m) or left uncut (control). Once the cut vegetation grew back and attained the full canopy, Kiko wethers (8, 48–50 months old, 72.8 ± 2.29 kg live weight) and Katahdin rams (5, 29–32 months old, 95.5 ± 4.31 kg live weight) were rotationally stocked in separate plots (3 plots each species), and their diurnal (dawn-dusk) behaviors and distribution patterns monitored when they were in each plot during the summer of 2018. Data were analyzed in Kruskal-Wallis rank sum test in R. Both wethers and rams visited the control treatment the least, rams grazed mostly in areas with short vegetation (0 m), and wethers visited more to areas with higher vegetation (1.52 m) than rams for feeding (P < 0.001), which was predominant during the post-midday period (3:00-dusk) (P < 0.0001). Browsing was the dominant feeding behavior of wethers (39% browsing vs. 4% grazing), while rams’ feeding behavior was dominated with grazing (24% grazing vs. 12% browsing). Lying was the dominant diurnal behavior of both wethers (46%) and rams (35%), and predominant during the midday period (11 a.m.-3:00 p.m.) (P <0.05). Vegetation heights and diurnal period highly influenced animals’ behavior.