Our Team

Arthuros Mangriotis is the Managing Director, Treasurer at Riverstone Earth, where he develops and drives the investment strategy of the firm across all areas.  

He brings over twenty years of fundamental investing experience, developed as a principal at several multibillion-dollar funds.   

Arthuros grew up in Athens and London, studied Classics at the University of Oxford, then earned his MBA at Columbia.   He enjoys cycling, backgammon, and puzzles of all kinds.   

Bret Allen is an Operating Advisor at Riverstone Earth, where he provides strategic insight on ranch operations, land stewardship, and property evaluation. 

He brings over 40 years of experience in the ranching and cattle industry, having led the development of one of the most respected ranching operations in the Northern Rockies over the past 17 years. 

Born and raised on a Montana cattle ranch, Bret studied business and marketing at Western Montana College and Montana State University — and was a member of the rodeo team.

Brooks Tyrrell is a Senior Associate at Riverstone Earth, where he supports the acquisition, development, and management of the firm’s agriculture portfolio, bridging capital allocation with on-the-ground operational performance. 

He brings a background spanning climate finance, regenerative agriculture, and natural capital investment, with work across land development, real estate acquisition, and broader conservation initiatives. He is also Co-Founder of Hermetic, a climate investment platform, and Founder of Hearth Co., a sustainable real estate development company and portfolio in the Greater Yellowstone Ecosystem. 

Brooks is based in Bozeman, Montana, embedded in the ranching and conservation community there. He holds an MA in Ecology from Schumacher College in Devon, England, where he developed a foundation in river restoration and land stewardship, and a BA from the University of Notre Dame. 

Chris Erickson is a Senior Advisor focused on investment opportunities and capital formation at Riverstone Earth. 

Chris has spent over two decades working at the intersection of agriculture and institutional capital. His work has been global in scope, including strategic growth investments for state-owned entities, food security investments on behalf of Middle East sovereign wealth funds, and supporting the expansion of vertically integrated agribusiness companies. 

After college, Chris served in the US Army and remains active in supporting various veterans’ causes across the United States. 

Coby Buck is a Principal at Riverstone Earth with a focus on investments in the agriculture sector.  

Over the last decade, he has worked across the physical commodity markets of agriculture and energy, agricultural technology, and large-scale ranching operations, building platforms in the US and Brazil. 

A graduate of Harvard University, Coby is a member of a fifth-generation ranching family in Colorado.

David Leuschen is Co-Founder of Riverstone Earth, where he brings together decades of energy investing experience with a lifelong connection to ranching, land stewardship, and the American West. A fourth-generation Montanan, David founded Riverstone Earth to invest in agriculture and other nature-based solutions that advance planetary health, improve ranching profitability, and drive superior investment returns. 

David is also Co-Founder of Riverstone Holdings, one of the world’s leading energy and decarbonization investment firms, which has raised more than $45 billion since its founding in 2000. He began his career at Goldman Sachs, where he was a Partner and founder of the firm’s Energy and Power Group. 

Over the past 35 years, David has built Switchback Ranch into one of the leading regenerative ranching operations in the Northern Rockies, spanning 120,000 acres across Montana and Wyoming. The ranch focuses on soil health, regenerative agriculture, carbon sequestration, methane mitigation, superior genetics, and technologies that improve productivity and profitability. 
 

In addition to being on numerous corporate boards, including Pattern Wind, David has served on a number of nonprofit boards focused on conservation, land stewardship, public policy, agriculture, and the American West.  These include Conservation International, The Peterson Institute for International Economics, Montana Land Reliance and the Buffalo Bill Historical Society. In addition to ranching, his primary passions are hunting, fishing, skiing, and flying the high alpine terrain of the ranch with his family – and a few ranch-inspired experiments, including Lazy K Bar Bourbon, which David will happily tell you is America’s #1 bourbon. 

Drew McDonough is a Principal at Riverstone Earth, where he focuses on sourcing, evaluating, and executing investments across the capital structure. 

He brings experience across traditional energy, renewable energy, infrastructure, and real-asset businesses, having previously worked at Riverstone Holdings and Cherokee Investment Partners. 

Drew holds a bachelor's degree in economics from Dartmouth College.

Hannah Peters Siegfried is the General Counsel and People / HR Partner at Riverstone Earth, advancing the ambitious legal, people, and operational goals of the business.  

Hannah brings two decades of leading Legal and People teams inside complex, global organizations across luxury, retail, e-commerce, healthcare tech, and private equity, with an emphasis on steering companies through startup and high-growth stages.  She's advised more boards than she can comfortably count.   

A founder herself, Hannah has been building things, and building them with intention, for a very long time. 

Isabella Arteaga is a Summer Associate at Riverstone Earth, where she supports fund development and investment strategy and due diligence across the platform. 

She brings a background in management consulting and sustainable finance, with experience in McKinsey & Company’s sustainability and private equity practices and in supporting the structuring of sovereign-level nature and climate finance transactions, including debt-for-nature swaps. 

She is currently pursuing a Master of Environmental Management at the Yale School of the Environment and is a fourth-generation pilot — the first woman in her family to fly. 

Jack Erickson is a Summer Analyst at Riverstone Earth, supporting due diligence and underwriting.  

Jack has been immersed in the agriculture and sustainability industry for years, bringing experience from S2G Investments and Boa Safra Ag. At 18, Jack started his first company out of his dorm room. 

Jack grew up in the Boston area before joining the founding class at the University of Austin (UATX), where he is entering his third year studying economics.

Jean Rogers is a Senior Operating Advisor to Riverstone Earth, helping to design innovative structures to drive capital at scale to more sustainable outcomes in energy, agriculture, and oceans.  

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Her stepping stone to Riverstone was Blackstone, where she was global head of ESG. Before getting stoned, she earned a few degrees in environmental engineering and founded the Sustainability Accounting Standards Board (SASB).  

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Her favorite horse named Materiality once came in 6th in the Kentucky Derby.  A lifelong vegetarian, she aims to know each one of David’s 50,000 cattle by name.

Jennifer Young supports executive operations, team coordination, and the firm’s day-to-day organizational effectiveness.

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Jennifer has spent the last few years as David Leuschen’s Executive Assistant and Chief of Staff, supporting him in his roles as Co-Founder of Riverstone Holdings and owner of Switchback Ranch. She brings more than two decades of experience working in the C-suites of financial firms and family offices, where she has helped manage complex operations, staff, estate management, and high-priority initiatives across both business and personal platforms.

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Known for her calm, problem-solving approach, Jennifer helps bridge high-level strategy with daily execution and has a passion for strengthening teams and making organizations run more smoothly. Jennifer divides her time between New York and Montana. She enjoys triathlons, sharpening her culinary skills, and travel adventures with her sons.

Jieh Greeney is a Co-Founder and Chief Operating Officer at Riverstone Earth, where she leads platform build-out, strategy, operations, and value creation.  

Jieh brings decades of experience as a business builder, investor, and advisor across food, farming, wellness, luxury, retail, and hospitality, with an emphasis on creating joy while delivering meaningful human, planetary, and commercial impact. She co-founded McKinsey & Company’s global sustainability and CSR practice, and has led growth and transformation efforts across public and private companies. 

Jieh grew up on a NOFA-certified organic family farm in western Massachusetts before starting her first company in New York City while getting a degree in art and then an MBA at a barely-accredited institution in Boston. 

Bio coming soon.

Kaitlynne Vergona helps drive executive operations, strategic initiatives, and organizational effectiveness across the firm. 

She brings experience supporting senior leadership teams in fast-paced, high-growth environments, with a focus on aligning priorities, managing complex projects, and enabling teams to operate at their highest level. 

Kaitlynne is an IIN-certified Integrative Nutrition Practitioner and advocate for local food systems, with a passion for building healthier, more resilient communities through food and agriculture. 

Kyle Chea is Director of Platform Operations & Investor Relations at Riverstone Earth, where he leads operational coordination with internal and external partners, and keeps investors engaged with exciting, interesting, and critical information about how Riverstone Earth is stewarding their capital across all investment pillars. 

He credits his background in investing, diplomacy, and hospitality development for success in building relationships, translating technical requirements into practical considerations, and articulating value while also having fun.  

He is from Nassau, Bahamas and prefers being barefoot or on the water. He graduated from Vassar College with an AB in History and Chinese, and an MBA from Duke University where he was the lead singer of Supply and DeBand, the #1 business school band in North Carolina. An avid rower, he is the founder of the Nassau Rowing Club, the first rowing club in The Bahamas and the largest in the Caribbean. 

Lauren Singer is a Principal at Riverstone Earth, where she focuses on methane, agriculture, climate strategy, and platform development across the firm’s natural capital and decarbonization work. 

She brings more than 15 years of experience as a founder, operator, investor, and sustainability strategist, with work spanning consumer behavior, packaging, carbon, methane, climate finance, supplier engagement, and end-of-life systems. She previously co-founded Overview Capital, an early-stage climate investment platform focused on methane and short-lived climate pollutants. 

Lauren studied environmental science and policy at NYU and sustainability management at Columbia Climate School. She has given a TED Talk viewed more than 4.6 million times, fit all her trash from 1 year in a mason jar, and is still trying to convince everyone that methane is the most underrated climate lever on earth. 

Matt Jansen is a Senior Operating Advisor, Downstream for Riverstone Earth, where he focuses on value dislocation, food security, and value creation.   

Matt is a lifelong Ag professional. He grew up in Ag, is educated in Ag, and has spent over 35 years working in Ag where he has led several, large multi-national corporations across the globe.  He most recently served as COO of North America for Darling Ingredients, and prior was SMD for Stepstone Group, CEO of Saudia Arabia Livestock Investment Co, CEO of COFCO International, and SVP/President of ADM Global Oilseeds.  

Matt has an Agriculture Economics degree from the University of Arkansas - Go Hogs! He speaks Portuguese, makes wine, and recently was named FIFA World Cup Ambassador for Dallas.    

Rob Inches is a Senior Advisor focused on innovation, thought leadership, investment opportunities, and capital formation at Riverstone Earth. 

Rob has nearly four decades of direct investment experience at Goldman Sachs and his own firms.  His current firm, Transition Point Advisors helps investors capitalize on lateral thinking, deep domain expertise, and multi-variate growth drivers of transformational change.  A recognized thought leader, Rob has published eight papers advancing new concepts for effective deployment of capital.  His most recent paper, Asset Allocation Revisited, focuses on real anti-fragile assets, such as farm, ranch land, water, and timber as effective diversifying assets in a period of profound change.   

Rob received his BA from Harvard and his MBA from Wharton.  He enjoys skiing, cycling, golf and back country adventures with his family.  He also serves on the Corporate Board of Woods Hole Oceanographic Institution.

Robert Tichio is Senior Advisor, Investments at Riverstone Earth, where he brings deep experience across private equity, capital markets, and energy investing to help shape the firm’s investment strategy and execution.  

Robert is CEO and Managing Partner of Fortescue Capital, a New York-based green energy investment platform launched by Fortescue to support large-scale energy transition and industrial decarbonization projects. Prior to Fortescue, Robert spent 18  years at Riverstone Holdings, where he was a Partner and Managing Director focused on investments across energy, power, infrastructure, and decarbonization. He previously worked in Goldman Sachs’ Principal Investment Area and began his career in J.P. Morgan’s Mergers & Acquisitions group. 

Robert graduated Phi Beta Kappa from Dartmouth College and earned an MBA with Distinction from Harvard Business School. He has served on a number of public and private company boards across energy, infrastructure, and decarbonization – and, as an award-winning Broadway producer, is the rare investor whose portfolio includes both industrial decarbonization and Tony-winning theater. 

Sohum Khatoria is a Summer Analyst at Riverstone Earth.

He brings experience in climate risk modeling and agricultural finance, with published research recognized by the World Food Prize Global Youth Institute.  

He is a rising sophomore at Columbia College studying Mathematics and Sustainable Development. 

Tommy Mellott is a Summer Analyst at Riverstone Earth, where he focuses on capital formation, workflow automation, and fostering a positive and energetic environment. 

Tommy brings six years of experience in leading elite organizations — competing for two D1 national championships as a captain in college before competing in the NFL. Concurrently, he partnered with an economic consulting firm specializing in agriculture risk management innovation to improve forecasting for insurance producers. 

Tommy grew up in Montana before running an IP based NIL business and graduating Summa Cum Laude in Financial Engineering at Montana State University.