Gaps in a gappy forest: plant resources, longleaf pine regeneration, and understory response to tree removal in longleaf pine savannas

McGuire, John; Mitchell, Robert J.; Moser, E. Barry; Pecot, Stephen D.; Gjerstad, Dean H.; Hedman, Craig W.

doi:10.1139/cjfr-31-5-765

Cited by 72 publications

(141 citation statements)

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“…forest in Wyoming. McGuire et al (2001) found steep declines in pine fine root length at distances from gap edge as small as 9 m during the first year after gaps were created in a P. palustris forest. Interestingly, our threshold for pine root mass to drop to near zero (65% gap fraction) corresponds well with a threshold level of light in canopy gaps where planted P. palustris seedlings began to show substantial response to light increases (Palik et al 1997).…”

Section: Within-ecosystem Scale: Gapsmentioning

confidence: 90%

“…1): (1) control (no disturbance); (2) single trees harvested (1.5-2.7 m 2 ha -1 removed depending on block) to create a well-dispersed residual stand; (3) trees harvested leaving small~30-m-diameter gaps (2.4-3.9 m 2 ha -1 removed); and (4) trees harvested leaving larger~50-mdiameter gaps (2.8-3.4 m 2 ha -1 removed). The small and large gap treatments produce openings that have been shown to significantly alter light, soil resources and establishment of P. palustris seedlings (Grace and Platt 1995;Palik et al 1997;McGuire et al, 2001). In late fall 1997, stands were harvested by machine, limbs were severed, and stems were carefully removed to minimize disturbance to the soil and understory vegetation.…”

Section: Overstory Treatment Plotsmentioning

confidence: 99%

“…A better understanding of this competitive interaction may be gained if effects of roots on resources and responses of roots to resource levels can be measured (Goldberg 1990). Furthermore, responses should be calculated per unit of surface or length, because pine roots tend to be much thicker than non-pine roots (McGuire et al 2001). The fact that roots of P. palustris can only form ectomycorrhizae, whereas non-pine roots can produce a wide variety of mycorrhizal forms, further complicates comparisons of competitive effects or responses.…”

Section: Within-ecosystem Scale: Biotic Factorsmentioning

confidence: 99%

“…Disturbances kill roots, but some plants may be more affected than others, which results in a shift in the balance between competing root systems. If enough roots are lost, belowground gaps are formed with reduced resource uptake and altered soil conditions that may influence subsequent root growth (McGuire et al, 2001).…”

Section: Introductionmentioning

confidence: 99%

“…In forests, belowground gaps are relatively short-lived and their influences on root responses depend on gap size (Silver and Vogt 1993;Wilczynski and Pickett 1993;Parsons et al 1994a;Jones et al 1996;Schroeer et al 1999;McGuire et al 2001). The ephemeral nature of gaps is related to the overlap of root systems which allows surviving trees to quickly colonize space liberated by the disturbance, and minimizes increases in resource availability within gaps (Parsons et al 1994b).…”

Section: Introductionmentioning

confidence: 99%

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Controls of fine root dynamics across a gradient of gap sizes in a pine woodland

et al. 2003

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Controls of fine dynamics were investigated in a Pinus palustris Mill. (longleaf pine) woodland subjected to two understory vegetation treatments (control versus removed) and four overstory treatments (no gap control, and canopy gaps of three sizes with constant total gap area per stand). Fine root (<2 mm diameter) dynamics were measured over 11 months using ingrowth cores (all treatments) and minirhizotrons (understory removed in no gap control and large gap treatments only). At the fine (microsite) spatial scale, pine and non-pine root mass production responded negatively to each other (P=0.033). Each life form was significantly (P< or =0.028) related to nearby overstory density, and pine root production compensated for reductions in non-pine roots if understory vegetation was removed. Soil moisture and NO(3) mineralization rate were negatively related to pine root mass production (ingrowth cores; P<0.001 and P=0.052) and positively related to pine root length production, mortality and turnover (minirhizotrons; P from <0.001 to 0.078). Temperature variance was negatively related to pine root lifespan P<0.001) and positively related to pine root turnover (P=0.003). At the ecosystem scale, pattern of overstory disturbance (gap size and number) had no significant effect on non-pine, pine, or total root production. However, the presence of gaps (versus the no-gap control) increased non-pine root mass production (ANOVA, P=0.055) in natural understory conditions, and reduced pine root mass production (P=0.035) where the understory was removed. Ecosystem-wide pine root length production, mortality and turnover were positively related to weekly soil temperature (P< or =0.02). In natural systems, fine root dynamics are highly variable and strongly affected by biotic factors. Roots quickly close belowground gaps because one life form (pine or non-pine) compensates for the absence of the other. When understory vegetation is removed, however, pine roots respond to the local abiotic environment, particularly moisture and NO(3).

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Section: Within-ecosystem Scale: Gapsmentioning

confidence: 90%

Section: Overstory Treatment Plotsmentioning

confidence: 99%

Section: Within-ecosystem Scale: Biotic Factorsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Controls of fine root dynamics across a gradient of gap sizes in a pine woodland

et al. 2003

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Methods to test the interactive effects of drought and plant invasion on ecosystem structure and function using complementary common garden and field experiments

Alba

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Fahey

et al. 2017

Ecology and Evolution

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Abiotic global change drivers affect ecosystem structure and function, but how they interact with biotic factors such as invasive plants is understudied. Such interactions may be additive, synergistic, or offsetting, and difficult to predict. We present methods to test the individual and interactive effects of drought and plant invasion on native ecosystems. We coupled a factorial common garden experiment containing resident communities exposed to drought (imposed with rainout shelters) and invasion with a field experiment where the invader was removed from sites spanning a natural soil moisture gradient. We detail treatments and their effects on abiotic conditions, including soil moisture, light, temperature, and humidity, which shape community and ecosystem responses. Ambient precipitation during the garden experiment exceeded historic norms despite severe drought in prior years. Soil moisture was 48% lower in drought than ambient plots, but the invader largely offset drought effects. Additionally, temperature and light were lower and humidity higher in invaded plots. Field sites spanned up to a 10-fold range in soil moisture and up to a 2.5-fold range in light availability.Invaded and resident vegetation did not differentially mediate soil moisture, unlike in the garden experiment. Herbicide effectively removed invaded and resident vegetation, with removal having site-specific effects on soil moisture and light availability. However, light was generally higher in invader-removal than control plots, whereas resident removal had less effect on light, similar to the garden experiment. Invasion mitigated a constellation of abiotic conditions associated with drought stress in the garden experiment. In the field, where other factors co-varied, these patterns did not emerge. Still, neither experiment suggested that drought and invasion will have synergistic negative effects on ecosystems, although invasion can limit light availability. Coupling factorial garden experiments with field experiments across environmental gradients will be effective for predicting how multiple stressors interact in natural systems.

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The path back: oaks (Quercusspp.) facilitate longleaf pine (Pinus palustris) seedling establishment in xeric sites

et al. 2016

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Mitchell. 2016. The path back: oaks (Quercus spp.) facilitate longleaf pine (Pinus palustris) seedling establishment in xeric sites. Ecosphere 7(6):e01361. 10.1002/ecs2.1361Abstract. Understanding plant-plant facilitation is critical for predicting how plant community function will respond to changing disturbance and climate. In longleaf pine (Pinus palustris Mill.) ecosystems of the southeastern United States, understanding processes that affect pine reproduction is imperative for conservation efforts that aim to maintain ecosystem resilience across its wide geographic range and edaphic gradients. Variation in wildland fire and plant-plant interactions may be overlooked in "coarse filter" restoration management, where actions are often prescribed over a variety of ecological conditions with an assumed outcome. For example, hardwood reduction techniques are commonly deemed necessary for ecological restoration of longleaf pine ecosystems, as hardwoods are presumed competitors with longleaf pine seedlings. Natural regeneration dynamics are difficult to test experimentally given the infrequent and irregular mast seed events of the longleaf pine. Using a long-term, large-scale restoration experiment and a long-term monitoring data site at Eglin Air Force Base, Florida (USA), this study explores the influence of native fire-intolerant oaks on longleaf regeneration. We test for historical observations of hardwood facilitation against the null hypothesis of competitive exclusion. Our results provide evidence of hardwood facilitation on newly germinated longleaf pine seedlings (<2 yr old) after two mast seeding events (1996, 2011). Using regression-tree and Kaplan-Meier survival analyses, we found that deciduous oak midstory density was the most significant variable associated with longleaf pine seedling survival rates in the first 2 yr after germination. We found that as few as 43 oak midstory stems ha −1 were sufficient to facilitate seedling survival, but as many as 1400 stems ha −1 maintained facilitation without competitive exclusion of seedlings. We found that 1.5-yr-old pine seedlings were more moisture stressed under more open canopy conditions when compared to those immediately adjacent to a midstory oak canopy. Recognition that deciduous oaks are important facilitators of longleaf seedling establishment on xeric sites represents a significant departure from conventional wisdom and current management practices that has largely focused on competitive exclusion. This points to a critical role of a deciduous oak midstory of moderate densities for long-term ecosystem resilience in xeric longleaf pine ecosystems in light of climate uncertainty.

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Gaps in a gappy forest: plant resources, longleaf pine regeneration, and understory response to tree removal in longleaf pine savannas

Cited by 72 publications

References 0 publications

Controls of fine root dynamics across a gradient of gap sizes in a pine woodland

Controls of fine root dynamics across a gradient of gap sizes in a pine woodland

Methods to test the interactive effects of drought and plant invasion on ecosystem structure and function using complementary common garden and field experiments

The path back: oaks (Quercusspp.) facilitate longleaf pine (Pinus palustris) seedling establishment in xeric sites

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