6 Major Physiographic Zones of the Lower Rio Grande Valley, Texas (from Hathcock et al. 2014, in press)

South Texas Refuge Complex

STRC MISSION To restore, enhance, and protect the natural diversity of the Lower

Rio Grande Valley of Texas

Two-Pronged Approach

Acquisition -- land/easements • Create corridors* • Conserve unique biota • Very high, immediate priority

Restoration -- mature riparian woodlands • Create corridors* • Augment and enhance habitat blocks • Long-term ecosystem sustainability

STRC Restoration Program

• Facilitate succession • 5,000 ha planted since mid-1980’s • Early sites direct-seeded/low-density

(<600 plants/ha) transplants • Currently 200 ha/year @ 1,000-2,000

plants/ha (50-60 species) • Additional 3,000 ha slated for future

Texas ebony Ebanopsis ebano

Seedlings in “Mini” (6” x 1.5”) Plant Bands

all-thorn goat-bush Castela erecta

Evaluation of Effectiveness Traditional

• Focus on maximum area/numbers of plants • 1st-Year Survivorship (re-plant?) • No long-term data

Current • Increased focus on similarity to natural climax

communities • Poor results observed anecdotally at many

past sites • Possible to evaluate 15 to 25-year-old sites

Study Methods

• Non-Systematic, Qualitative Surveys – 2 distinct association-level mature woodland

communities – noted dominant species within 4 vertical strata

• Belt-Transect Surveys – 9 Sites (3 direct-seed, 5 transplant, 1 control) – counted all individual woody plants within 2 to

3-m belt

Ebenopsis ebano – Ehretia anacua / Condalia hookeri Forest Texas Ebony – Anacua / Brasíl Forest

(from International Vegetation Classification, NatureServe 2012)

Santa Ana National Wildlife Refuge, Alamo

Edge of Ebony-Anacua/Brasĺl Forest, Ranchito Tract

Tamaulipan Coastal Shrubland, saline

Tamaulipan Coastal Shrubland, non-saline

Condalia hookeri (brasíl)

Ziziphus obtusifolia (lotebush) Zanthoxylum fagara (colima)

Guaiacum angustifolium (guayacán) Forestiera angustifolia (elbow-bush)

Ebony-Anacua/Brasíl Forest Structure

• Canopy 7-8 m tall; 80-100% closed • Dense mid-story • Open understory (80% litter/bare ground, 20% forbs/weak shrubs)

Dominant Woody Species • Canopy (3): Ebenopsis ebano, Ehretia anacua, Prosopis

glandulosa • Sub-Canopy (6): Condalia hookeri, Havardia pallens, Amyris

madrensis, Guaiacum angustifolium, Diospyros texana, Acacia farnesiana

• Mid-Story (3): Phaulothamnus spinescens, Ziziphus obtusifolia, Celtis pallida

• Understory (1): Malpighia glabra

Total Woody Species: 30

Tamaulipan Coastal Shrubland

Structure • Canopy: overall sparse (10-50% closed), 4-5 m high • Mid-story: 1-2.5 m; patchy to dense • Understory: 0-1 m, dense

Dominant Woody Species • Canopy (3): Prosopis glandulosa, Yucca treculeana, Ebenopsis

ebano • Mid-Story (5): Forestiera angustifolia, Phaulothamnus spinescens,,

Ziziphus obtusifolia, Celtis pallida, Zanthoxylum fagara (non-saline sites)

Total Woody Species: 25

25-Year-Old Direct-Seed Site, Ranchito Tract

18-Year-Old Direct-Seed Site, Ranchito Tract

Acacia farnesiana (huisache) Leucaena pulverulenta (tepeguaje) Prosopis glandulosa (honey mesquite) Parkinsonia aculeata (retama)

12-Year-Old Transplant Site, Ranchito Tract

Preliminary Results of Belt-Transect Surveys at Ranchito and La Coma Tracts

Site Planting Method

Year(s) Planted

Area Sampled

(ha)

Plant Density (No./ha)

No. Species

Simpson Diversity

Index

Ranchito Transplant 1994-2005 2.4 720 33 0.93

Ranchito Direct Seed

1989, 1996 2.4 883 18 0.71

Ranchito None (Control) 1989 1.0 777 14 0.50

La Coma Transplant 1995 0.2 4,219 27 0.81

Preliminary Results – Species Composition

Site Planting Method n

% Early Succ.

% Late Succ.

No. Late-Succ. Sp.

Dominant Late-Succ. Sp.

Ranchito Transplant 1,698 51.4 40 25 E. ebano (21%) 7 other sp. (60%)

Ranchito Direct Seed 2,140 49.8 50.2 12 E. ebano (95%)

Ranchito None (Control) 752 93.9 6.1 8 ---

La Coma Transplant 926 45.8 54.2 21

H. pallens (40%) Z. fagara (20%) E. anacua (11%)

Discussion

• Transplant sites had higher overall diversity and proportion of late-successional species

• Recruitment highest, with more desirable species, at transplant sites (esp. La Coma)

• Transplant sites and mature sites were fairly similar in species richness and dominants with exceptions…

Discussion (cont.)

Under-Represented Species

– Forestiera angustifolium (elbow-bush) – Phaulothamnus spinescens (snake-eyes) – Diospyros texana (chapote) – Guaiacum angustifolia (guayacán) – Condalia hookeri (brasíl; La Coma only) – Zanthoxylum fagara (colima; Ranchito only) – Amyris madrensis (Sierra Madre torchwood;

Ranchito only)

Aspects Applicable to Other Restoration Projects

• Qualitative Descriptions of Association-Level Dominants/Sub-Dominants (e.g., IVC Descriptions, non-systematic samples)

• Measures of Recruitment/Survivorship • Control Plots (=Evidence of Project Merit)

Acknowledgements

American Forests (Global Re-Leaf Grant)

Florentino Caldera (USFWS) Chris Pérez (USFWS) Rene Ruíz (USFWS)

Mitch Sternberg (USFWS)