Abiotic constraints on the establishment of<i>Quercus</i>seedlings in grassland

Danner, Brett T.; Knapp, Alan K.

doi:10.1046/j.1365-2486.2003.00574.x

Cited by 17 publications

(19 citation statements)

References 46 publications

(61 reference statements)

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“…Given that oak seedling survival was strongly positively associated with water in this and other studies (Davis et al 1999;Danner and Knapp 2003), we expected that the reduced seedling survival in the non-indigenous grasses under dry and normal conditions would have been associated with depressed soil water levels. However, as the results showed, soil water levels were the same in the non-indigenous and native grasses subplots (Figure 1).…”

Section: Discussionmentioning

confidence: 64%

“…Another possible explanation for the survival differences could be that, because the native plants intercepted more light in the dry subplots, they reduced water stress on the seedlings, i.e., by producing a nurse plant effect (Bertness and Callaway 1994;Holmgren et al 1997;Danner and Knapp 2003). Seedling survival was slightly higher in native grass subplots when seedlings experienced only shoot competition from the grasses (81% in the non-indigenous grass subplots vs. 95% in the native grass subplots).…”

Section: Discussionmentioning

confidence: 99%

“…A study of oak encroachment in Kansas native grasslands found that although drought may negatively affect oak establishment, the oak seedlings are likely capable of tolerating the projected drier climate in the future, and thus forest expansion into the grasslands is likely to continue (Danner and Knapp 2003). While the same may hold true in grassland openings in native savannas and woodlands in Minnesota, a different scenario seems more likely in old fields located on coarse-grained soils.…”

Section: Discussionmentioning

confidence: 99%

“…In contrast, oaks regularly establish in the grassland openings of adjacent native savannas and woodlands (Peterson and Reich 2001) and in native grasslands further south (Danner and Knapp 2003). The old fields and native environments differ in their dominant grass species, with the native savannas and grasslands dominated by native warm-season grasses and the old fields normally dominated by introduced European cool season grasses.…”

Section: Introductionmentioning

confidence: 99%

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Non-indigenous grasses impede woody succession

et al. 2005

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With the proliferation of old fields and the decline of native grasslands in North America, non-indigenous grasses, which tend to colonize and dominate North American old fields, have become progressively more abundant. These new grasses can differ from native grasses in a number of ways, including root and shoot morphology (e.g., density of root mat, height of shoots), growth phenology (e.g., cool season vs. warm season growth), and plant-soil-water relations due to differences in photosynthetic physiology (C 3 vs. C 4 ). Woody plants have been slow to colonize some old fields in the prairie-forest border area of North America and it is hypothesized that non-indigenous grasses may be contributing to the poor establishment success of woody plants in this region, possibly through more intense competition for resources. To test this hypothesis, a multi-factorial field experiment was conducted in which water, nitrogen, and grass functional group (non-indigenous C 3 and native C 4 species) were manipulated in a study of survival of oak seedlings. The grass type variously affected some of the different growth measurements, however, the effects of grass type on seedling growth were small compared to the effects on seedling survival. The results showed that when grown under dry conditions, seedlings growing in non-indigenous grasses experienced up to a 50% reduction in survival compared to those growing in native grasses under the same conditions. Analyses of root and shoot competition showed that the cause for the reduced survival in the non-indigenous grasses was due primarily to underground processes. The findings confirmed our initial hypothesis that nonindigenous grasses are likely contributing to the poor establishment success of woody plants in these old fields. However, the explanation for the reduced oak seedling survival in non-indigenous grasses does not appear to be due to reduced resource availability since soil water levels did not differ between nonindigenous and native grass plots and other resource levels measured (light, NO 3 , and NH 4 ) were higher in non-indigenous grass plots under dry conditions. An alternative explanation is that the non-indigenous grasses modify the soil environment in ways that, under dry conditions, are deleterious to emerging oak seedlings. Since current climate projections for the upper Midwest are for hotter and drier summers, the results suggest that the resistance of these old fields to oak encroachment will likely increase in the future.

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Section: Discussionmentioning

confidence: 64%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Non-indigenous grasses impede woody succession

et al. 2005

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“…Empirical evidence of the response of plant functional groups to climatic conditions characteristic of drought is therefore important for evaluating predictions of future change. However, such evidence is mostly limited to historical records (15,16), which lack the full range of past drought variability (3), and to short-term experimental manipulations (17,18), which lack a sufficient temporal dimension for understanding future vegetational response.…”

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confidence: 99%

Response of C ₃ and C ₄ plants to middle-Holocene climatic variation near the prairie–forest ecotone of Minnesota

Nelson

Tian

et al. 2003

Proc. Natl. Acad. Sci. U.S.A.

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Paleorecords of the middle Holocene (MH) from the North American mid-continent can offer insights into ecological responses to pervasive drought that may accompany future climatic warming. We analyzed MH sediments from West Olaf Lake (WOL) and Steel Lake (SL) in Minnesota to examine the effects of warm͞dry climatic conditions on prairie-woodland ecosystems. Mineral composition and carbonate ␦ 18 O were used to determine climatic variations, whereas pollen assemblages, charcoal ␦ 13 C, and charcoal accumulation rates were used to reconstruct vegetation composition, C3 and C4 plant abundance, and fire. The ratio of aragonite͞calcite at WOL and ␦ 18 O at SL suggest that pronounced droughts occurred during the MH but that drought severity decreased with time. From charcoal ␦ 13 C data we estimated that the MH abundance of C4 plants averaged 50% at WOL and 43% at SL. At WOL C4 abundance was negatively correlated with aragonite͞calcite, suggesting that severe moisture deficits suppressed C4 plants in favor of weedy C3 plants (e.g., Ambrosia). As climate ameliorated C4 abundance increased (from Ϸ33 to 66%) at the expense of weedy species, enhancing fuel availability and fire occurrence. In contrast, farther east at SL where climate was cooler and wetter, C 4 abundance showed no correlation with ␦ 18 O-inferred aridity. Woody C 3 plants (e.g., Quercus) were more abundant, biomass flammability was lower, and fires were less important at SL than at WOL. Our results suggest that C 4 plants are adapted to warm͞dry climatic conditions, but not to extreme droughts, and that the fire regime is controlled by biomass-climate interactions. P ervasive drought, expected to be associated with climatic change in continental interiors, will have profound ecological, economic, and societal repercussions (1-4). Drought conditions are likely to alter ecosystem function by changing the relative abundance of plant functional groups (e.g., C 3 vs. C 4 ) in natural systems (5-7). For example, episodic droughts that occurred throughout the 20th century in the midwestern United States killed woody C 3 genera, such as Quercus (8-10), and favored better adapted C 3 and C 4 herbaceous species (9). General circulation models coupled with dynamic crop-growth models project that, in agricultural systems, such climatic conditions could significantly reduce both C 3 (e.g., wheat, Triticum aestivum L.) and C 4 (e.g., corn, Zea mays L.) cereal crop yields (11,12), resulting in billions of dollars of economic loss (13,14). Empirical evidence of the response of plant functional groups to climatic conditions characteristic of drought is therefore important for evaluating predictions of future change. However, such evidence is mostly limited to historical records (15, 16), which lack the full range of past drought variability (3), and to short-term experimental manipulations (17, 18), which lack a sufficient temporal dimension for understanding future vegetational response.During the middle Holocene (MH), Ϸ8.0-4.0 thousand years (ka) B.P. (19), the midweste...

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