lanechaffin 的最愛

Observation made specifically in response to population description in the ICUN page for Quercus havardii. From ICUN:

Multiple literature sources have indicated that Quercus havardii rarely, if ever, reproduces through the agency of acorns (Wiedman 1960). Dhillion et al. (1994) report that "[they] saw not a single case of germination of acorns" . Furthermore, Pettit (1977) states that "it is rare to find a young sand shin-oak plant in the field which had originated from an acorn". Alternatively, Q. havardii reproduces almost exclusively via underground rhizomes (Davis 2013). As this species reproduces clonally, there is difficulty in distinguishing individuals within populations.

Here, I show a photo of 191 acorns collected on 25-26 Aug 2022. The original intent of collection was to boil and eat the acorns. All acorns were collected in about 30-45 minutes in the uncertainty circle indicated along edges of vegetated habitat (road and cleared areas). Acorns were evaluated based on color, shaking, and presence of holes. If discoloration was observed (e.g., black spots or black acorns), acorns were not collected. If movement was felt when acorns were shaken, this signified that the seed had shriveled from the seed coat (bad for germination and eating). Shriveled acorns were not collected. Presence of holes indicated insect larvae had eaten some of the acorns. Acorns with insect larvae can germinate as long as the radical is intact. However, given the original intent was for eating, acorns with insect damage were not collected.

On 26 Aug 2022, a handful were removed, boiled and eaten. After removal, 191 acorns remained. On 28 Aug 2022 and possibly the day before, the acorns started germinating. The acorns were kept in a dark location around room temperature until 29 Aug 2022. On 29 Aug 2022, the acorns were refrigerated to stop germination. The first set of photos were taken on 4 Sep 2022.

4 Sep 2022: 58 showed signs of germination, 2 showed insect holes, and 1 showed signs of discoloring.
4-9 Sep 2022: Data recorded but lost.

9 Sep 2022: 28 showed signs of germination with one of the germinated acorns showing signs of insect damage.
10 Sep 2022: 18 showed signs of germination, 5 exhibited movement when shaken. Noticed data lost 4-9 Sep 2022. Recounted
10 Sep 2022 (totals): total germinated: 132 (108 before 10 Sep [5 bagged separately] + 18 recorded 10 Sep + 3 germinated with holes + 3 given away on 9 Sep). Total germinated with holes: 3. Total discolored without germination: 2. Total with movement when shaken: 6. Total waiting to germinate (not in any of the above categories: 48. Total acorns: 132+3+2+6+48 = 191. Current germination rate 69.1%.
11 Sep 2022: +7 (139) showing signs of germination. +1 (5) showed insect holes. +1 (7) movement when shaken. 72.8% germination rate.
13 Sep 2022: +5 (144) showing signs of germination. 75.4% germination rate. It seems like the smaller acorns germinate later than the larger acorns.
15 Sep 2022: +4 (148) showing signs of germination. 77.5% germination rate.
16 Sep 2022: +2 (150) showing signs of germination. 78.5% germination rate.
18 Sep 2022: +2 (152) showing signs of germination. 79.6% germination rate.
20 Sep 2022: +1 (153) showing signs of germination. 80.1% germination rate.
27 Sep 2022: +2 (155) showing signs of germination. 81.2% germination rate.
27 Sep 2022 (final): All non-germinated acorns opened on this day. +1 (156) showing signs of germination. 81.7% germination rate. 9 discolored/moldy. 8 without signs of germination: 4 with off-center embryo, 1 with fused cotyledons at apex, 3 normal. If all 8 eventually germinated, max germination rate = 85.9%.

Current intent, evaluate germination rate of healthy acorns. If I had thought to do this before, I could have collected all acorns (including discolored and eaten ones) to get an idea of survival rate due to insect predation. Ultimate survival rate is likely extremely low given how little time these acorns have to find a habitable place to germinate (acorns shrivel in days without cloud cover). However, if the acorns happen to drop during a time when it rains enough to allow the radical of a few of the seeds to get into the ground and establish, and if one or two of those plants survive to produce there own acorns once in 100 years or so (maybe even 1,000 years or so), replacement rate is achieved. It's worth noting that plants seem to produce more acorns adjacent to bare habitat. Whether this is a response to resource availability or actual resource investment in locations where seeds will find open habitat to colonize, who knows.

Given the ease with which these germinate, restoration is possible, maybe even easy if you don't mind collecting the acorns during a very short time-frame. However, returning a piece of land to its former habitat type could take generations. Next time I'm in Midland, I should check on the plant that was planted there at least 10 years ago.

The third photo shows roots of acorns collected 6-9 Aug 2022. I do not remember the plant time.

REU23_55
Coords uncorrected

Rhizomatous clones 3-4 feet tall. Unusually large scales on acorn cupules. Berm at the side of the road, with Ambrosia psilostachya, Commelina erecta, and Hoffmannseggia glauca.

This thicket is growing next to the Big Prunus. They are shorter, are in full bloom with many leaves.

1. Sepals margins glandular-toothed (see 6th picture)
2. Pedicels glabrous (See 6th picture)

This observation predates the existing subdivision in this area. IF there was ever any question about the loss of topsoil in the Texas Hill Country, this should provide some obvious evidence.
These images show a couple of cut Ashe juniper shrubs (two of many) on the limestone plateau. The age of the stumps is hard to pin down, but they were apparently cut with a hand axe, thus probably pre-dating the era of chainsaws. That puts the age of the stumps probably back into the 1950s or perhaps some decades older. The stumps and their root systems are still intact and in their original setting. I assume these were living junipers at the time they was cut, with intact root systems. The bases of the stumps are on the order of 10 to 12" diameter and the major roots in the image are about 5" diameter. Last time I checked, junipers don't send their roots out into the open air, so this root system was spreading out in topsoil between the ground surface and the limestone bed on which the shrub germinated. Essentially all that topsoil has now washed away, amounting to at least 5" and probably as much as 6" to 10" of soil, in the intervening decades (not centuries) since the shrubs were cut.
This may be an easily recognized example, but it is by no means uncommon to find such evidence in many areas of the Hill Country. The likelihood is that the ranch on which these junipers grew--and where they were cut--had heavily stocked the pasture with goats and sheep in the early to middle 1900s after the initial woodland had been cleared. The resulting loss of ground cover left the topsoil vulnerable to the occasional very hard Hill Country rains. Soil loss might be slow and nearly imperceptible most seasons, but we occasionally get deluges that could have carried away a lot of the unprotected topsoil in just a handful of weather events.

REU23_32
Hybrid with Q. stellata
Not coord-corrected

Large tree 30-35 feet tall. 2 large trunks both >1 feet wide, bark deeply fissured. Leaves weakly bicolored, adaxial surface of leaves cinerous-glaucous. Growing on steep sloping ground (25-30° angle above horizontal) on the W bank of unamed creek. Substrate gravelly towards the top, more silty-clayey towards the creekbed. Associated species include Ambrosia psilostachya, Sapindus drummondii, Artemisia ludoviciana, Sideroxylon lanuginosum, Physalis spp., and Celtis spp.

With outside influence from perhaps Quercus havardii or some other species?

Hunter Hopkin's favorite tree on Matador Wildlife Management Area.

REU23_23
Not coord-corrected

A little more than a dozen larger trunks (>4 inches across) and many smaller trunks forming a grove between the fenceline and the road. Many suckering shoots coming up in mowed area adjacent to the road, plus a carpet of (possibly rhizomatous) growth under the grove. Lots of young fruit. Ground sunken down from the road, abundant leaf litter up to 2 inches deep in spots, many dead fallen branches. Associated plants include Celtis reticulata, Portulaca pilosa, and Rhus aromatica or Rhus triloba. Growing over sand sheet deposits.

The apparently rhizomatous shoots at the base suggest a Quercus havardii x stellata intermediate, but abaxial surface of leaf is also covered with noticeably large, overlapping, stellate hairs that seem more similar in appearance to that found in Quercus margarettae (Ashe) J. K. Small.. Or at least from the specimens I looked at at the Morton Arboretum.